TERMINOLOGY OF THE PLANT UNIT:

 

1. VASCULAR VS NON-VASCULAR PLANTS

    NON-VASCULAR PLANTS:

Ø     Lack vascular tissue (xylem and phloem)  

Ø     need to live in moist places because this brings moisture to every part of the plant without needing or using a transport system.

Ø     Diffusion is enough to take the water and dissolved substances to all parts of the plant.

Ø     This reliance on diffusion for transport limits their size.

Ø     Very simple plants that lack true roots, stems and leaves.

Ø     Moss, liverwort and hornwort.

    VASCULAR PLANTS:

Ø     Have vascular tissue to transport water and dissolved nutrients to every part of the plant, enabling it to grow tall and in places that are drier.

Ø     Have true roots, stems and leaves.

Ø     The early forms are ferns, horsetail and then came gymnosperms and angiosperms.

 

2. GYMNOSPERM VS ANGIOSPERM

GYMNOSPERM:

Ø     have naked seeds or seeds without a seed coat. The seed is a sexually reproduced structure with a diploid zygote that developed into an embryo surrounded by nourishment. The seed is the result of the fertilization of an egg by sperm (pollen).

Ø     Male cones produce pollen. Pollination occurs. The seed develops in the female cone. The seeds are dispersed by the wind and germinate if they find favourable conditions.

ANGIOSPERM:

Ø     seed covered by a testa, and the ovary of the flower that often develops into a fruit.

Ø     Flowers contain male and female parts that produce sperm (pollen) and ova. Pollination occurs. The seed develops in the ovary and is dispersed by various means to germinate if it finds favourable conditions.

Ø     Divided into monocotyledons and dicotyledons: see table page 523 of textbook.

 

4. STRUCTURE OF XYLEM AND PHLOEM:

These vascular elements are found in roots, stems and leaves, and are arranged differently in each.

XYLEM:

Ø     Carry water from root to leaf, where it is used and transpired (lost through pores called stomata).

Ø     Long hollow tubes of nonliving cell walls.

Ø     Two kinds: tracheids and vessel elements.

Ø     They die as they mature.

Ø     Gymnosperms only have tracheids and angiosperms have both.

Ø     Water passes through pits in the adjacent end walls.

Ø     Xylem also provides support and strength to stems.

Ø     Refer p135 course pack

PHLOEM:

Ø     Translocates of sugars in a solution down from the leaves or up from the roots.

Ø     Phloem is made up of a companion cell and sieve tube element with sieve tube plates between the elements.

Ø     The cells are alive and translocation is an active process.

Ø     Plant hormones are also carried in the phloem.

Ø     Refer p135 course pack.

 

5. TROPISMS AND NASTIC MOVEMENTS:

A tropism is a directional growth response to an unequal stimulation from the environment. It controls the growth of the plant by affecting the production of plant hormones. The plant grows toward (positive tropism) or away from the stimulus (negative tropism) and this is achieved by affecting the number and size of cells in different parts of the plant. The three tropisms are

Ø     phototropism (response to light),

Ø     gravitropism (response to gravity)

Ø     thigmotropism (response to touch shown by vining plants that grow toward an object touching them so they can coil around the object).

Nastic movements are responses to stimuli that are not directional. The plant does not grow in a particular direction. Instead, it may alter the turgor pressure in cells in a way that moves the plant temporarily away from a stimulus.  

 

SEEDS AND EMBRYOS

 

NOTES:

1.     A seed is a dormant (alive but not growing) package containing an embryo produced through sexual reproduction and food for that embryo to grow during the germination process.

2.     A testa is a tough, waterproof covering around an angiosperm seed. It protects the embryo, decreasing its exposure to oxygen and water.

3.      The micropyle is a channel for water and oxygen to the embryo. It conditions are right, the seed will swell, break the testa in the case of a dicot seed, and the embryo will begin to metabolise the stored nutrients of the cotyledons and endosperm (monocot) to grow toward light and water. It is important not to flood a seed with water as the required oxygen will not enter the micropyle and the embryo will die.

4.     The endosperm is the tissue around the monocot embryo and is made of starch, a food source for the embryo.

5.     The cotyledons are “seed leaves” that store lipid and protein as a food source. The cotyledons will go green on contact with sunlight, and provides food (stored and by photosynthesis) until the first true foliage leaves can photosynthesise.

6.     The radicle is the lowest part of the embryo below the hypocotyl and becomes the root. It grows down in response to gravity.

7.     The epicotyl is the part of the embryo above the cotyledons and is the first meristem (rapidly growing tissue) of the shoot.

8.     The hypocotyl is the tissue below the cotyledons and becomes the lower stem.

9.     The plumule is the leaves at the tip of the epicotyl. In the monocot seed the plumule is protected by the coleoptile, a protective sheath.

 

 

 

REQUIREMENTS FOR GERMINATION AND THE EFFECTS OF ENVIRONMENTAL FACTORS ON SEED GERMINATION

 

DESIGN YOUR OWN LAB

 

MATERIALS

Petri dishes

Paper toweling

Radish seeds

Light, water, temp regulation (heat, fridge), salt and any other environmental chemicals

 

PURPOSE

Design an experiment that analyses the effect of certain environmental conditions on the germination of radish seeds.

 

Write a hypothesis, a procedure, set up the experiment, collect data, write up the results, discuss the results and write a conclusion.

 

 

 

SEEDS AND EMBRYOS

 

PURPOSE

To examine the structure of representative angiosperm seeds and compare a monocotyledon with a dicotyledon seed.

 

·        A) Define the terms cotyledon, testa, micropyle, endosperm, radicle, coleoptile, plumule, epicotyl, hypocotyl.

·        B) What mature plant structures do the epicotyl, plumule, the hypocotyls and radicle become?

 

PROCEDURE

 

A. DICOTYLEDON SEED

1. Obtain a soaked dicot seed.

2. Examine it. Note that it is covered with a coat called the testa.

3. Note the concave side has a flattened area called the hilum. It is the point where the

    seed was attached to the ovary.

4. Look for a tiny pore below the hilum, called the micropyle. Water is taken up here for

    germination. However, flooding the seed with water will prevent enough oxygen from

    getting to the seed through this pore and result in rotting.

5. Draw and label the external structure of the dicot seed.

 

·        D) What is the purpose of the seed coat?

·        E)  Why is the seed soaked in water before dissecting?

 

6. Gently separate the two cotyledons to expose the embryo between.

7. Examine the embryo. Locate the true foliage leaves attached to the epicotyl. The

     hypocotyl is attached to the cotyledons and the radicle extends down from the

     hypocotyl.

8. Draw and label the opened seed and embryo.

 

·        F) Explain why this is a dicotyledon seed.

 

B. MONOCOTYLEDON SEED

1. Obtain a soaked corn kernel or seed.

2. Observe the wide and narrow ends, and locate the scarred area where the seed was

    attached to the cob.

3. Cut the seed open lengthwise.

4. Identify the epicotyl (plumule), hypocotyl, and radicle.

5. Add a drop of iodine to the cut side.

 

·        G) Which part of the seed turned black?

·        H) What is iodine a test for?

 

6. Draw the exposed surface and label it.

 

 

MOVEMENT OF WATER IN XYLEM

 

Water is taken up by the root epidermis and root hairs by osmosis; it enters the xylem in the root; diffuses from the stem to all parts of the plant; enters the numerous veins in the leaf, and about 99% of it is lost by transpiration through pores called stomata in the leaf.

 

There are theories about how this happens:

1. ROOT PRESSURE

·       There is a higher concentration of water in the soil, which causes it to enter the root via osmosis.

·       This creates a pressure that pushes the water up the stem

·       Minerals can move by active transport into the roots, adding to the osmotic gradient for water.

·       Root pressure is not a major factor in water transport.

 

2. CAPILLARY ACTION

·       This is the observed ability of water to cling to the sides of a narrow tube due to adhesive forces between water and tube (opposite polarities create attractive forces). This accounts for some of the water movement against gravity.

 

3. COHESION -TENSION THEORY

·       Water is a polar molecule in which the slightly positive H atom of one molecule and the slightly negative O of another molecule are attracted to each other (the hydrogen bond). This is the cohesive force that allows us to pour water.

·       A continual column of water is thus created in the xylem that can withstand pressures up to 20 000kPa (tensile steel).

·       As a water molecule escapes from a stoma so another molecule is pulled into the root to replace it – there are no air locks or breaks in this cohesive and high-tension column.

 

 

THE TRANSPORT IN PHLOEM:

TRANSLOCATION OF NUTRIENTS UP AND DOWN THE PLANT

 

  THE PRESSURE-FLOW OR MASS-FLOW THEORY

 

·       In the upper part of the plant, near the leaves, sucrose is actively pumped into the phloem.

·       As a result of the high sugars here, water moves by osmosis into the phloem from the xylem nearby.

·       This then moves as a mass or bulk movement down the stems: the water entering the phloem  creates a water pressure pushing the nutrients along.

·       In the roots, sucrose is actively pumped out of the phloem for storage as starch.

·       Osmosis causes water now to move out of the phloem, and back into the xylem.

·       In the spring, in plants like the maple, this stored starch in the roots is broken down to sucrose and is pumped into the phloem. The mass movement is the same, but will happen up to the stems in order to provide sugars for new bud and leaf growth.

 

 

 

 

FERMENTATION

 

A substrate (usually glucose) is broken down by glycolysis alone. Therefore no oxygen is used for releasing the substrate’s energy (anaerobic respiration).

Glycolysis ends with the production of end products like lactic acid, acetic acid, alcohol, carbon dioxide and hydrogen gas.

 

a.Examples of Lactic acid production.

·         anaerobic respiration in animals e.g humans will produce lactic acid during high intensity exercise. Aerobic respiration is shut down in this kind of exercise because insufficient amounts of oxygen can get to the exercising muscle.

·         anaerobic bacteria. For example, Lactobacillus acidophilus found in yoghurt, and the many bacteria used to make cheeses, break down lactose to glucose and galactose, which enters glycolysis, and lactic acid is the end product produced.

 

b. Examples of Alcohol (ethanol) production

• yeasts used to make wine from grapes, and alcohols/beers from various grains will convert sugars to alcohol.

 

c. Examples of Carbon dioxide production

• bread yeast (Saccharomyces cerevisiae) produces carbon dioxide and alcohol from sugar. The carbon dioxide makes the bread rise.

 

Just by the way:

• sourdough bread: uses yeast and lactobacilli
• soda bread: the CO₂ comes from sodium bicarbonate (NaHCO₃)
• Putrefaction differs from fermentation in breaking down proteins, not carbohydrates.

 

 

 

PHOTOSYNTHESIS

 

//is an energy acquiring pathway occurring in autotrophic plants. It consists of two parts:

 

·         The light dependent pathway or reaction: traps the sunlight’s energy and converts it to chemical energy ATP and NADPH.

 

·         The light independent pathway or reaction: takes the chemical energy and uses it to make glucose.

 

Do plants respire?

 

PHOTOPHOSPHORYLATION

//The phosphorylation of ATP from ADP in the light dependent pathway of photosynthesis.

 

 

A. THE LIGHT DEPENDENT PATHWAY

• Occurs in the grana i.e. the piles of thylakoids in the chloroplast.
• Uses photosystems embedded in the thylakoid membranes. A photosystem is a protein and chlorophyll cluster (mostly chlorophyll a is used).
• In Non-cyclic photosynthesis, the only form we will deal with, the sun hits Photosystem II and this excites electrons.
• The electrons enter an electron transport chain in which some of the energy is taken out of the electrons. This energy will be used to make ATP.
• The same electrons are then accepted by the second photosystem, called photosystem I.
• For the second time the electrons are excited by sunlight, and enter a second electron transport chain, in which some of the energy is again released from the electrons. This will be used to make more ATP.
• The electrons, still containing the sun’s energy, are finally accepted by NADP and this, together with H ions, forms NADPH. The sun’s energy is trapped in the electron of the H atom.

 

• Photolysis: the sunlight is also used to split water into:
1. H ions which will be used to for making ATP
2. Electrons which replace the excited electrons lost from the chlorophyll
3. Oxygen which is respired

 

• The H ions are pumped by the energy released from the electron transport chains to one side of the thylakoid membranes. This creates an electrochemical gradient that allows the H ions to run through H-ATPase pumps and thus generate ATP (chemiosmosis).

 

At the end of this pathway, NADPH and ATP have been formed and will be passed into the stroma of the chloroplasts for the second pathway.

 

b. THE LIGHT INDEPENDENT PATHWAY:

• Occurs in the stroma of the chloroplast
• The pathway is called the Calvin cycle and involves three phases:
•  

1. Phase one: Carbon Fixation:

• Ribulose biphosphate (RuBp) (5-C) bonds to CO₂ to form an unstable 6-C intermediate (CO2 is fixed) .
• This splits into two 3-C molecules: 3-phosphoglycerate (PGA).
• This process happens three times over, sothat:

3CO₂ + 3RuBp à 6 PGA

 

2. Phase 2: Reduction Reaction

• Add ATP energy:

                The 6PGA + 6ATP à 6 molecules of     

                                   1,3 biphosphoglycerate

 

• Add NADPH:

              6 molecules of 1,3 biphosphoglycerate + 6NADPH à

                                          6glyceraldehyde -3-phosphate (G3P)

 

3. Phase 3: RuBp regeneration

• 5 G3P are rearranged to form 3RuBp, using 3ATP
• One G3P is left over
• The three phases are repeated to make another G3P
• The two G3P molecules will bond to form glucose

       (two 3C à 6C compound)

 

Overall process: 12H₂O + 6CO₂ + SUNLIGHT à 6O₂ + C₆H₁₂O₆ + 6H₂O

 

 

 

 

DEFINITIONS FOR CELLULAR TRANSPORT

 

1. SOLUTION: a mixture of chemicals dissolved in a liquid.

 

2. SOLVENT: that part of the solution into which the chemicals/substances are dissolved. It is usually present in the larger amount. In biology the solvent is usually water (the universal solvent) in which case biological solutions are usually called aqueous solutions.

 

3. SOLUTE: that part of the solution that is dissolved into the liquid.

 

4. SELECTIVELY PERMEABLE MEMBRANE: cell membranes allow some molecules to pass freely through it, but controls the movement of other molecules. Gases and non-polar, non-ionised substances (fat-soluble substances) pass through easily, but ions and electrolytes, and large water-soluble substances are controlled.

 

5. DIFFUSION: is the passive movement of substances down their concentration gradient i.e. from an area of high to an area of low concentration of that substance. Movement occurs until the gradient is lost. No energy is used to push substances. Diffusion is a slow process of transport and would be inadequate to transport substances over large distances. This is what limits cell size.

 

6. OSMOSIS: is the movement of water by simple diffusion across a selectively permeable membrane from an area of high water concentration to an area of low water concentration. The movement is controlled by the amount of solute present on either side of the membrane.

 

 

 

THE CELL MEMBRANE

 

• Very thin (about 8nm across)
• Also called the plasma membrane/ the double lipoprotein layer/bilayer
• It is made up of phospholipids and protein
• The phospholipids consists of  2 fatty acid chains, glycerol, phosphoric acid and a nitrogen containing compound like choline or inositol. If the compound is choline the phospholipids is called lecithin.
• The lipid is “water hating” or hydrophobic, whilst the rest of the phospholipid molecule is “water loving” or hydrophilic. Because of this, the membrane forms a bilayer to ensure that only a hydrophilic molecule faces the inside and the outside of the cell to keep the membrane in solution. The hydrophobic parts are tucked in the middle like the ham in a sandwich.
• The proteins are varied: they form pores, receptors and carriers. Each protein is very specific for the substrate it will work with.
• The membrane is called a “fluid mosaic” because the protein is studded in amongst the phospholipids like mosaic tiles, and because the phospholipids can slide sideways and are quite fluid.
• If the fatty acids are mainly saturated (no double bonds between the carbons), the cell membrane will be quite rigid. To maintain fluidity, the cell pushes cholesterol out of the spaces between the fatty acids to make the membrane more fluid. This is one of the reasons a diet high in saturated fat increases cholesterol levels in the blood. If there are many unsaturated fatty acids making up the membrane, because they have bends in them, making them stick out sideways rather than flat, the membrane becomes more fluid. The membrane takes in cholesterol to make it less fluid, and this drops blood cholesterol levels. Hence a diet high in unsaturated fats (oils especially omega 3 and 6) will bring down blood cholesterol levels.
• The main function of the membrane is to control what enters and leaves the cell, and to respond to messages to metabolise or cease metabolism. Hormones of different types are constantly binding to receptor proteins on the membrane and giving the message to alter permeability or metabolism. When cells touch each other, they also slow down cell their division.
• Small hydrophobic molecules (fat soluble molecules) can go straight across the membrane through the lipid portion. This includes oxygen, carbon dioxide, nitrogen and molecules like benzene and some drugs.
• Small, uncharged polar molecules (hydrophilic) can also diffuse straight through. Examples are water, glycerol, and alcohol.
• Large uncharged polar molecules need carrier transport proteins to get across. This includes amino acids, glucose and nucleotides. Insulin also has to make the membrane permeable to the first two.
• Ions need to pass through protein pores. These are specific and electrochemical gradient dependent. There are pores specifically for hydrogen, sodium, bicarb, potassium, calcium, chlorine and magnesium ions. These ions will diffuse from areas of high to areas of low concentration.
• The membrane is also able to pump ions against concentration gradients using protein carriers and energy.

 

Movement across the membrane can occur in a number of ways:

1. Simple diffusion of substances
2. Osmosis of water
3. Carrier transport using carrier protein: passive or active
4. Mass or bulk movement of substance: exo~ & endocytosis.

 

 

PROTEINS IN THE CELL MEMBRANE

 

1. RECEPTOR PROTEIN:
• Binds to hormones that carry messages to the cell
• The receptors is specialized or substrate specific
• The binding of the two changes the activity of the cell. This could result in changes in permeability of the membrane by opening up ion channels; activation of enzymes for certain metabolic functions; the formation of secondary messengers inside the cell to change metabolic activities; or increased metabolism could result.
• Sometimes drugs can bind to these receptors, blocking a specific signal from getting through.

 

 

2. CARRIER TRANSPORT PROTEIN:
• The carrier binds to its substance and carries it across.
• Substrate specific
• Saturable
• Passive carrier mediated transport relies on a concentration gradient to decide the direction of the substance’s movement. No energy is required (= passive)
• Active carrier mediated transport will move the substance against the concentration gradient. It does this by having a greater affinity for the substance on the side where the concentration is lower. Energy in the form of ATP is needed for this movement and these proteins are called pumps.

 

3. CHANNEL OR PORE PROTEINS:
• Create pores to control ion movement
• Substrate specific
• Movement depends on electrochemical gradients.

 

 

4. RECOGNITION PROTEINS:
• Are the fingerprint of the cell. They are specific proteins called antigens which allow for recognition and prevent the immune system from recognizing them as foreign and destroying them. They include the blood groups (A, AB, B and O) and the HLA markers. When a tissue with different markers are transplanted into the body, the immune system will recognize these proteins as foreign and the tissue will be rejected. Therefore tissue typing and immunosuppressive corticosteroids are important in transplants.

 

 

THE HUMAN KARYOTYPE

 

The karyotype is a photograph of the chromosomes in the nucleus of a somatic cell. Blood or skin cells are grown in a glass container. A special solution stops cell division in meiotic metaphase where they are clear to see. The chromosomes are separated, stained and photographed. Enlarged images are cut out and arranged in pairs according to size, shape and appearance. Special staining reveals the unique banding patterns of each chromosome.

 

ERRORS IN REPLICATION: MUTATION

 

Mistakes can occur during meiosis e.g a failure to separate: nondisjunction – trisomy or triploidy results. Embryos with too many or too few autosomes rarely survive (miscarriage). Down Syndrome is trisomy 21. It is a group of disorders that occur together. There is mild to moderate mental impairment and a large, thick tongue, short and stocky build. They are more susceptible to infections and often have abnormalities in vital organs. 40% have heart defects. Greater chance of developing senility. The condition is often associated with the age of the mother.

 

Chromosomes can also mutate by a portion undergoing an inversion: chromosomal inversion, deletion, duplication and translocation.

In deletion, a part of the chromosome is lost. Viruses, irradiationand chemicals can cause parts of the chromosome to break off. The loss is actual genes. If part of chromosome 5 is lost, a child is mentally handicapped, has an abnormal larynx that makes the child cry like a cat (called cri-du-chat)

In duplication, a gene sequence is repeated one or more times within one or several chromosomes. Too many repeats affect the functioning of the gene. In Fragile X syndrome a duplication occurs in chromosome X (700 repeats of the same sequence).

In Inversion, a gene segment becomes free and then reinserts in the reverse order.

In translocation, part of one chromosome changes places with another part of the same chromosome or with part of another nonhomologous chromosome. If part of chromosome 14 exchanges with part of chromosome 8, cancer can occur.

 

Mistakes can occur during DNA replication. There are different types: base pair substitution occurs when one base pair is replaced by another; and a frameshift mutation which occurs when one or more base pairs are added or deleted. The number of these that are passed on is small because there are special enzymes that “proofread” the new strand of DNA.

Mutations can cause cells to lose control of the cell division rate and grow abnormally. This leads to cancer. 

External influences can cause mutation, like radiation and exposure to chemicals like Agent Orange or mustard gas. UV light causes the hydrogen bonds to break in base pairs on DNA, and these then fuse to 2 adjacent bases. This results in abnormal replication and cell division.

 

 

 

MEIOSIS

 

INTERPHASE

• The cell continues normal activity.
• DNA replicates: Each of the 46 chromosome consists of 2 sister chromatids joined by a centromere.
• The nucleus is present and the chromosomes form a mass of DNA called chromatin.

 

MEIOSIS ONE

 

Prophase One

• The sister chromatids joined by their centromere become visible
• The nuclear membrane and nucleolus disappear.
• The centrioles separate to opposite poles and spindle fibre forms
• The homologous pairs come together to form tetrads
• The inner chromatids of the homologous pairs cross over and exchange genes. This is called chiasmata. This means that all four of the sister chromatids in a tetrad  have different and unique genetic information

 

Metaphase one

• The tetrads attach to the spindle at the equator.

 

Anaphase one

• The homologous chromosomes separate from each other and move to opposite poles.

 

Telophase one

• The nuclei reform at opposite poles. Each nucleus is haploid i.e. has only half the number of chromosomes. Each nucleus will have one of each of the 23 chromosomes, as apposed to a homologous pair of each of the 23 chromosomes.
• Reduction division has ended

 

Cytokinesis separates the cell into two hapoid cells

 

 

MEIOSIS TWO:

Both of the above two cells will go through this:

 

Prophase Two

• The nuclei disappear and spindle forms. The 23 chromosomes become visible as sister chromatids joined at the centomere

 

Metaphase Two

• The 23 chromosomes (sister chromatids joined at the centromere) line up at the equator.

 

Anaphase Two

• The sister chromatids  separate, and each (now called a chromosome) travels to the opposite pole.

 

Telophase Two

• The haploid nuclei reform at each pole.

 

Cytokinesis

• The cell divides into two haploid cells. As there are two cells from meiosis one dividing into two cells now in meiosis two, at the end of meiosis there will be four haploid cells. Each cell is unique genetically.
• In the ovary, three of the four cells die, and only one remains as an ovum.
• In the testis, all four cells will become sperm.

 

 

CHROMOSOMES

You have a pair of each of the 23 chromosomes, because your mother provides you with a set from 1-23 and so does your father. So you have 23 pairs, or 46 chromosomes. These pairs are called HOMOLOGOUS PAIRS. For example, in order to be a female you need an X sex chromosome from your mother and one from your father (XX = female). If you are male, you received an X sex chromosome from your mother, and a Y chromosome from your father (XY = male).

 

When a cell has 46 chromosomes, we say it is diploid. When a cell has only one of each of the 23 chromosomes and therefore only 23 chromosomes, we say it is haploid. All cells in your body (somatic cells) have 46 chromosomes. Only ova (eggs) and sperm are haploid, because they must join together to form a zygote (the first cell of the embryo) with 46 chromosomes. Ova and sperm are called gametes. Gametes are produced in specialized tissue called the gonads – the ovary (ova) or the testis (sperm). The gametes are produced by a reduction division called meiosis. 

 

 

GENETICS

 

1. //Genetics is the branch of biology that deals with the principles of variation and inheritance in animals and plants.
2. Anton van Leewenhoek (1632-1723) examined gametes of humans under his microscope and discovered “animalcules” in semen that he thought were preformed embryos.
3. During 1800’s the ‘blending theory’ suggested that sperm and egg mix, resulting in offspring that are a blend. Sex cells were called gametes.

 

GREGOR MENDEL (1822-1884)

An Austrian monk who used a series of experiments as the basis for his theories of genetic inheritance.

He used an ideal organism, the domestic pea plant, to study genetics. It is ideal because:

1. Binary variation existed in 7 specific and easily observable traits (distinguishing characteristics): plant length (tall/short), colour of seed (yellow/green), colour of flower (white/purple), colour of pod (green/yellow), pod shape (inflated/constricted), seed shape (round/wrinkled) and flower position (axial/terminal). Each trait is on a separate chromosome and so is inherited separately and independently from any other trait (this is in fact an assumption that is not quite true)
2. The characteristics were clear-cut, with no continuum: discontinuous variation

 (e.g. height is continuous, 2 colours are discontinuous)

3. Short life cycle
4. Easy to grow and handle e.g. size
5. Mating could be controlled – the flowers promoted self-pollination (fertilise eggs with pollen of same flower). He could manipulate this.
6. Large # of offspring
7. He could look at one characteristic at a time.

 

·        First, he had to create purebreds:

//organisms descended from ancestors of a distinct type.

He did this through selective breeding: selectively breeding a single trait e.g. tall with tall, over and over from generation to generation, until all offspring are tall. Any progeny that were not tall would be discarded in the next breeding. The plants would eventually be ‘true breeding’.

 

·        Secondly, he experimented on Monohybrid crosses:

1. The purebred plants were called the parent, or P, generation.
2. He crossed a tall with a short. The offspring were the first filial generation, or F₁ generation. They were the ‘hybrid’ plants. Because only one trait is involved, this is called a ‘monohybrid cross’.
3. When he crossed a tall with a short pure breed, the F₁ were all tall. Mendel concluded that tall must be a dominant trait: a characteristic that is always expressed, or always appears, in the offspring if present in one of the parents. He said short was a recessive trait: a characteristic that will only be expressed in the offspring if it is the only trait present. Otherwise it will be latent (present but inactive and therefore not expressed). He found that in each trait, one was dominant the other recessive.
4. Mendel concluded that heredity was not a blending of traits, but rather that a Law of Dominance applies: //when individuals with contrasting traits are crossed, the offspring will only express the dominant trait.

 

SEE HOW TO MAKE A PUNNETT SQUARE TO SHOW THE F₁ GENERATION

PUNNETT SQUARES

A punnett square is a way of organizing all the possible combinations of alleles. It is used to calculate the probability of inheriting a particular trait. All the possible gametes for 1 parent are listed across the top and all the possible gametes for the other parent are listed down the side of the square. Copying the row and column gamete into the squares gives all the possible crosses. The genotype and phenotype possibilities  and the ratios are shown.

THE LAW OF PROBABILITY

This law forms the basis for solving genetic problems. The 2 alleles each parent has represents probability. The probability of getting a particular combination of alleles in a zygote depends on the genetic makeup of the parents. What is actually inherited happens entirely by chance.

 

·        Next, Mendel allowed the F₁ generation to self-pollinate, producing the F₂ generation. He found that 3 out of 4 plants expressed the dominant trait, and 1 out of 4 expressed the recessive trait. This 3:1 ratio is called the Mendelian Ratio.

 

SEE HOW TO MAKE A PUNNETT SQUARE TO SHOW THE F₂ GENERATION:

Using the Punnett squares on an f₁ x f₁ cross:

                      T                                                                                     t

T                         TT	Tt
t                          Tt	tt

 

 

DO PAGE 48 – 49 course pack

 

 From this Mendel realised that:

a.       Each F₁ parent must have 2 hereditary factors.

b.      These factors must separate in the parent. Only one factor from each parent is given to the offspring.

c.       The offspring inherit one factor from each parent. If the dominant factor was inherited from either parent it would be expressed

d.      The recessive factor is only expressed if it is the only factor present.

 

This makes up his First Law of Heredity: The Law of Segregation: //inherited traits are determined by pairs of factors. These factors separate, so there is only one present in the gamete.

 

Today

·        We call these ‘factors’ genes: A DNA sequence coding for a single polypeptide that governs the expression of a particular trait.

·        Genes occur in alternate forms, called alleles: one of a possible number of states of genes, distinguished from other alleles by their (phenotype) actual expression. Mendel was seeing 2 alleles – one dominant and one recessive. These genes occupy specific places on chromosomes called loci.

·        Genes are found on chromosomes: each chromosome is a DNA molecule complexed with proteins to form a thread-like structure containing genetic information. They are seen during division. Chromatin is the resting form.

·        Chromosomes are paired, which means that we get two of each chromosome type. They both have the same gene sequences but the alleles can be different. These are called homologous pairs. We get one from each parent.

·        If the alleles for a gene on the homologous pairs are the same, we say the individual is homozygous for that trait. If the alleles are different, we say the individual is heterozygous for that trait. In this case, the dominant trait will be expressed.

·        The genotype is the genetic constitution of an organism i.e. the full complement of all genetic information they have.

·        The phenotype is the observable expression of the genetic information.

 

SEE SIMPLE DOMINANT/RECESSIVE TRAITS IN HUMANS

 

DO PAGE 50 – 51 COURSE PACK

DO P52 OF COURSE PACK

 

SIMPLE DOMINANT TRAITS IN HUMANS

A simple dominant trait is one for which there are only 2 possible alleles – dominant and recessive. Examples of this are

Dominant: widow’s peak hairline; tongue rolling; straight thumb; (freckles; long eyelashes); unattached earlobes.

 

DETERMINING THE GENOTYPE

This is done by performing a test cross.

This involves crossing an individual of unknown genotype with a known homozygous recessive individual. The offspring will has certain phenotypes that will allow you to determine whether the unknown parent is homozygous or heterozygous. It is also helpful for determining how many alleles govern a single trait.

 

EXAMPLE:

A normal size Alaskan Malamute dog may be homozygous for size or heterozygous. To find out, it is crossed with a dwarf-size dog:

                              d                                                                   d

D                         Dd	Dd
D                         Dd	Dd

Offspring are all dominant . Therefore the dog must have been homozygous

 

                             d                                                                    d

D                          Dd	Dd
d                           dd	dd

Half are dominant, half are recessive. Therefore the dog must have been heterozygous.

 

Two pieces of evidence can be used to determine an autosomal dominant allele: if the allele is expressed in heterozygotes and homozygotes, and secondly, if one parent is heterozygous and the other homozygous recessive for the allele, then 50% of the offspring will have the trait.

 

 

MENDEL’S SECOND EXPERIMENT

A DIHYBRID CROSS

 

Monohybrid crosses investigate one trait at a time. But the next step was to find out how multiple traits are inherited. Did the inheritance of one characteristic influence the inheritance of another trait?

 

Mendel selectively bred pea plants until the offspring always had round, yellow seeds i.e. homozygous dominant for both traits. He bred them with pure strain wrinkle, green seeds. He then performed a DIHYBRID CROSS.  He found the f₁ generation all had round, yellow seeds. The offspring were all heterozygous for the 2 traits and round (R) and yellow (Y) were dominant. This didn’t really tell him if one was influencing the other. So he crossed individuals of the f₁ generation.

 

REFER TO PUNNETT SQUARE FOR THE OUTCOME.

 

The phenotypic outcome was 9:3:3:1. By looking at the genotype it was clear that there was no indication that the inheritance of one trait influenced that of another trait – and therefore the inheritance of one trait was independent of that of another trait:

 

LAW OF INDEPENDENT ASSORTMENT

A ratio of 9:3:3:1 could be explained if the alleles from one trait were inherited independently of another. This led to his second law: the inheritance of alleles for one trait does not affect the inheritance of alleles for another trait. This means that offspring may have new combinations of alleles that are not present in either parent.

 

DETERMINING THE GENOTYPE OF AN INDIVIDUAL FOR 2 TRAITS: THE TEST CROSS

Cross an individual that shows the dominant phenotype for both traits with an individual  that is homozygous recessive for the same two traits.

1. If the individual is homozygous dominant then the offspring will all be heterozygous and display the dominant phenotype.
2. IF the individual is heterozygous dominant then there is a 25% chance that the F₁ generation will show the recessive condition for both traits:

 

P = purple flower

p = white flower

r = wrinkled pea shape

R = round pea shape

 

 Unknown individual                                                homozygous individual: pr

PR	PpRr
Pr	Pprr
pR	ppRr
pr	prpr

 

Outcome: 1 purple flower with round peas; one purple flower with wrinkled peas; one white flower with round peas; one white flower with wrinkled peas

i.e. 1:1:1:1

 

Complete p 141 of textbook numbers 1-9 

COMPLETE COURSE PACK P53, 54, 55

 

BEYOND MENDEL’S LAWS

 

Some traits do not follow Mendel’s laws of inheritance.

 

INCOMPLETE DOMINANCE

In some cases, neither allele is dominant. The traits then blend if they are both present. In incomplete dominance a heterozygote is a mixture. An example is the snapdragon, which is either red or white, but a heterozygous individual will be pink.

When there is incomplete dominance, the letters are both capital e.g for the snapdragon: R and R’, and so a pink will be RR’. In the f₂ generation of two pink f₁ generations there will be 25% red, 50% pink and 25% white: 1:2:1. This is different from the 3:1 of Mendel.

In humans an example of incomplete dominance is voice pitch: low and high occur in men who are homozygous, whilst intermediate pitch occurs in heterozygotes.

 

 

CO-DOMINANCE

Both alleles are dominant, and both are expressed in the heterozygous individual. For example feather colour in chickens is governed by two dominant alleles. Black and white (B) and (W) are homozygous. The heterozygote would be checkered black and white. In co-dominance, the phenotype shows both characteristics, not a mixture as occurs with incomplete dominance.

 

MULTIPLE ALLELES

Many genes have many alleles, not just two. Blood groups in humans is an example. The 3 alleles coding for the glycoproteins on the surface of RBCs are type A (I^A) , type B (I^B) and a recessive third type which is neither A nor B and which we call type 0 (i). I^A and I^B are codominant, and are dominant over i.

 

PHENOTYPE (BLOOD TYPE)	GENOTYPES
A B AB O	IAIA OR IAi IBIB OR IBi IAIB ii

 

Skin colour is another example.

 

In fact it has been found that Mendel was not intirely correct in his law of independent inheritance – that the inheritance of one allele can affect the inheritance of a second allele, or affect how and when a trait is expressed.

 

 

REFER LAB ON BLOOD GROUPS

COMPLETE PAGE 64 OF COURSE PACK

WORK THROUGH P58-64 OF COURSE PACK

COMPLETE P65 OF COURSE PACK

Refer the textbook sample problems on blood groups and on the coat colour of rabbits (p145). Complete textbook p146-9 problems.

 

The combined work of Gregor Mendel, Walter Sutton and Theodor Boveri formed the basis of  the Chromosome Theory of Inheritance, which states that genes are located on chromosomes and chromosomes provide the basis for the segregation and independent assortment of genes.

 

 THE X AND Y CHROMOSOMES

 

The Y has 1% of the genes found on the X . Thought to have arisen through an inversion mutation.

Chromosomes are not always important in determining sex. Reptile sex is determined by temperature – 23 to 27 celcius = male; any cooler or warmer it will be female. The temperature affects genes which can turn an embryo into a male or female.

 

Some traits that are passed on are  carried on the sex chromosome. This is called Sex-Linked Inheritance. A gene on the X chromosome is called X-linked, and one on the Y chromosome is called Y-linked. Most known sex-linked traits are X-linked.

Examples of X-linked traits in humans are colour blindness and haemophilia. For a women to be colour-blind, she must inherit 2 recessive alleles. The genotype is written as X or Y with the allele in superscript. For example, red or white eyes in Drosophila is X-linked. So a white-eyed male would be X^rY and a homozygous red eyed female would be X^RX^R. When doing punnett squares on sex linked inheritance, assume the trait is located on the X chromosome unless otherwise stated.

 

In females, one of the X chromosomes is inactivated. This inactivation is random and so different X chromosomes are active in different cells. The inactivated X chromosome is called the Barr body.

 

A tortoiseshell cat is an example of random X chromosome inactivation. This pattern only occurs in female cats. Each has a random distribution of orange and black patches. The gene for both these colours is on the X chromosome. A tortoiseshell is heterozygous for coat colour, so the colour that is expressed in a patch depends on which X is inactivated in those cells.

 

POLYGENIC INHERITANCE

 

Many traits are controlled by more than one gene. The proteins that are synthesised in response to these genes work together to form a range of variation, or continuous variation. Continuous variation is variation among individuals in a population in which there is a gradient of phenotypes for one trait. In humans, height and skin colour are examples.

In corn, the range in ear length is continuous: A and B make the ear long; a and b make the ear short, and combinations make for different lengths:

 

AB                                Ab                                aB                                ab

AB  AABB         longest	AABb long	AaBB long	AaBb medium
Ab    AABb          long	Aabb medium	AaBb medium	Aabb short
aB     AaBB          long	AaBb medium	AaBB medium	AaBb short
ab     AaBb          medium	Aabb short	AaBb short	Aabb shortest

The longest and shortest are the most rare.

 

MODIFIER GENES

 

These are genes that modify the expression of a trait. For example there are only 2 eye colour genes – with or without melanin (brown or blue). Modifiers are thought to bring about the variation.

 

CONSTRUCTING A PEDIGREE

 

      Male

      Female        Colour represents recessive and dominant for a single trait. 

Generations are indicated by roman numerals.

 

NB: The study of inheritance is restricted to the recessive and dominant nature of a particular trait. Half a square or circle coloured indicates a carrier (heterozygous). In humans usually only the phenotype is known and so the genotype has to be guessed.

 

COMPLETE P 148 OF TEXTBOOK NUMBER 8

 

CLONING

 

Cloning is the production of identical copies of molecules, genes, cells or whole organisms. The copy is made vegetatively, not sexually.

To create Dolly, and egg cell was taken from one adult female sheep and the nucleus was removed. A nucleus from a mammary gland cell of an adult female was added. The egg cell was implanted into the uterus of a surrogate mother. This work was done by Ian Wilmut in 1997.

Cloning is used in agriculture to produce copies of high-quality crops. In medicine is used in medicine to produce identical strains of bacteria.

Genes are often cloned. Multiple copies of DNA is produced by inserting sections of DNA bacterial DNA using viral transduction. When the bacteria replicates, the DNA is also replicated/cloned. Insulin is manufactured in this way. The cloning vector is usually a virus or a plasmid (extrachromosomal DNA found in bacteria)

 

PATHOLOGIES ASSOCIATED WITH AUTOSOMAL INHERITANCE

 

1. AUTOSOMAL RECESSIVE INHERITANCE DISEASE

There are many disorders.

Tay-Sachs: the brain and spinal chord begins to deteriorate at about 8 months. By 1yr the baby is blind, mentally handicapped, and have extreme lower motor neuron muscle atrophy. The condition is due to a lack of an enzyme in the lysosomes of the brain cells, so that certain sphingolipids are not are not broken down. The lipid builds up, destroying brain cells. Carriers have half the level of enzyme, and this can be tested as a way to identify carriers. The incidence is high among  Central and Eastern Europe Ashkenazic jews.

Phenylketonuria (PKU): The enzyme to convert phenylalanine to tyrosine is absent or defective, and the products of abnormal breakdown of this amino acid damage the developing nervous system, leading to mental handicap. Babies appear normal and deteriorate as the amino acid builds. The only way to treat this is to avoid phenylalanine. Every baby is tested at birth.

Albinism is due to a lack of an enzyme to produce melanin, or the melanin lacks the ability to enter pigment cells.

 

2. CO-DOMINANT INHERITANCE DISEASE

Sickle cell anaemia is a defect in the haemoglobin. It consists of the haeme fraction and 4 polypeptide chains – two alpha and 2 beta. In this anaemia, one amino acid glutamic acid at a point on the beta chain is replaced by valine, resulting in abnormal sickle haemoglobin. The allele Hb^S indicates abnormal haemoglobin and the allele Hb^A indicates normal Hb. The abnormal Hb can pick up O₂ but when it gives up the oxygen, the Hb changes shape and clumps with other Hb molecules in the RBC. The RBC becomes stiff and deformed, and crescent-shaped, causing life-threatening thrombi. There is constant pain and often premature death.

                        Hb^A                                                        Hb^S

HbA                  HbAHbA	HbAHbS
HbS                   HbSHbA	HbSHbS

Heterozygotes have the sickle cell trait, whilst homozygotes with the trait have sickle cell disease.

In some African regions almost half the population is heterozygous, because it confers an advantage against malaria. This is an example of the heterozygous advantage. They produce enough normal RBCs to meet their O₂ needs, and enough sickle cells to reduce their susceptibility to infection.

 

3. AUTOSOMAL DOMINANT INHERITANCE DISEASE

Quite rare. Some are caused by rare mutations, whilst others only arise when after affected individuals pass the age of being able to have children. The usual situation is:

 

                    A                                                           a

a              Aa	aa
a           Aa	aa

 

 50% are affected.

 

Progeria causes rapid aging. It does not run in families.

Huntington Disease results in rapid brain deterioration over about 15 years. Symptoms appear at about age 35, and begin with irritability, mild memory loss, and then involuntary arm and leg movements. Loss of co-ordination and ability to speak plus memory, eventually leading to death in the 40’s or 50’s.

 

4. INCOMPLETE DOMINANCE DISEASE

Familial Hypercholesterolaemia: a heterozygote has some symptoms. 50% of the LDL receptors on cells are defective and cannot bind to blood LDL, resulting in twice the normal blood LDL. Homozygous recessives don’t produce any receptors and have 6 times the normal LDL, causing heart attacks as early as 2 years.

 

5. X-LINKED RECESSIVE INHERITANCE DISEASE

Haemophilia A is carried by the female with one allele on the X chromosome, and they have almost normal clotting time. If a female has 2 alleles she can have the condition. Boys inherit the condition only from their mothers, since they only get their X chromosome from their mothers.

This condition affected the Romanov family and some members of Queen Victoria’s family.

Colour blindness: to perceive colour there are 3 separate alleles, each coding for red, green and blue pigments or opsins respectively. Opsins are protein molecules found in cones in the retinal. Each cone carries one type of pigment. The allele for blue is found on an autosome, but red and green are found on the X chromosome. If the  allele for green is normal but the red is defective  he cannot distinguish between red and green. If the red allele is normal but the green is defective again he cannot distinguish between the two.

If the father is colourblind, then both girls will be carriers. The males will be normal.

If the mother is a carrier, then the there is a 50% chance that the boy will be colourblind and a 50% chance that the girl will be a carrier.

XO = Turners syndrome. Short, low IQ, sterile, webbed neck

XXY = male. Tall. Low IQ. Sterile.

XYY = male. Tall. Klinefelders syndrome

 

 

BIOTECHNOLOGY   Biotechnology//manipulation of biological organisms to obtain desired products or effects.   Genetic engineering//altering the sequence of DNA molecules. In 1976 Herbert Boyer and Stanley Cohen co-founded Genentech, the first biotech company to go public on the stock exchange.   Genetically modified organisms: genetic manipulation of organisms, that involves the transfer of genes from one species to another, to create transgenic organisms.   METHODS OF GENE TRANSFER:   1.We can cut up DNA using restriction endonucleases and place sections into plasmids for transfer. The cut piece of DNA can then be placed in another organism using ligase enzymes.   Restriction endonucleases or enzymes// Bacterial enzymes that cleave DNA into fragments by recognizing specific recognition sites.We isolate them and use them to cut up DNA. In bacteria they are used like a crude immune system – it scans the bacterial DNA for viral fragments of a bacteriophage virus. About 2500 have been isolated and are specific for about 200 different target sites. Over 200 are available for use in labs.   DNA Ligases recreate the bonds to reform the DNA. Ligases join complementary sticky ends produced by the same restriction enzyme.   An example is found on p34 of the course pack: human DNA is spliced using the enzyme, which also cuts the plasmid of a bacteria. The piece then is fit into the plasmid. The plasmid is now a recombinant DNA //combination of the original plasmid and foreign DNA. The plasmid can be replicated by the bacteria, and the foreign gene will be cloned//exact copies of the original fragment made when the cell divides. The bacteria can now make human insulin.   PLASMIDS: //small circular pieces of DNA that can exit or enter the bacterial cell. Each has several thousand base pairs.They carry genes for resistance to toxic heavy metals (Hg, Cd, Pb), to break down herbicides, industrial chemicals, petrol.   A plasmid  responsible for crown gall (a plant disease that causes large tumours in plants) called the Ti plasmid (tumour inducing) is used to carry genes into plant cells. The plasmid infects broad-leaved crops like tomato, tobacco, soya. The tumour causing genes are removed and the space  is filled with the DNA for transfer. The Ti plasmid is then shot into the plant cells using a gene gun.   2. Viruses can be used as vectors that carry DNA to a host cell. A virus will inject DNA into a host cell and hence deliver DNA.   The delivery vehicle for the gene must have several characteristics: it must be safe, it must efficiently deliver the gene to a high percentage of cells and it must be targeted specifically to the appropriate cells. Turning a virus into a delivery vehicle requires altering the virus to prevent it from causing disease. This involves making replication-defective viruses that have been engineered so they can’t reproduce in the body once delivered. The genes required for viral reproduction have been removed. While this prevents the virus from spreading in the patient, and limits the amount of inflammation caused in the body, it makes the virus less efficient at getting into cells and delivering the therapeutic gene. Thus, very high doses of virus vector are required to treat a patient, which are harder to produce and can lead to safety issues. 3. The plasmid/ liposome conjugate (VICL). Plasmids are closed circles of DNA that are very stable and will reproduce in bacteria, yeast, and human cells. The therapeutic gene is encoded in the plasmid DNA with regulatory elements that can control its expression levels. The plasmid is mixed with fatty-acid molecules, the same as surround our cells. The fatty-acids create a shell around the DNA called a liposome. Because liposomes are made of the same molecules as the outside of our cells, they can mix and fuse with cells when they touch, spilling their contents into the cell.   Unfortunately, they are not very efficient and there is no integration of the plasmid DNA. Therefore, the gene is not stable and the procedure must be repeated every few months. The main advantages are that plasmid/liposome complexes are really easy to manufacture, cause no immune response, and can carry large genes. Additionally, the insertion of proteins into the outside of the liposome may allow them to bind to only certain cell types, making it possible to target them to diseased cells and no others.

4. OTHER:

·         Electroporation: expose the cells to rapid pulses at high-voltage current. This allows DNA to enter a cell.

DNA guns – high velocity tungsten microprojections

 

History Of the Discovery of the DNA Molecule

 

• Friedrich Miescher a Swiss chemist first investigated the chemistry of DNA using pus in 1869.
• In the 1920’s it was clear that chromosomes carried our genetic traits. But was it the protein or the DNA that was the genetic material?
• In 1929, Frederick Griffith was able to show that a pathogenic bacteria, even when dead, can send some ‘transforming principle’ to non-pathogenic bacteria to make them pathogenic: Bacterial transformation. He didn’t know what was transferred.
• Joachim Hammerling a Danish biologist conducted experiments in the 1930’s on Acetabularia, a unicellular green alga to identify that hereditary information was inside the nucleus. This work did not identify whether it was protein or DNA that carried the hereditary info.
• In 1944 Oswald Avery repeated Griffith’s experiments with purified DNA and protein. He found it was the DNA not the protein responsible for transformation.
• In 1952 Alfred Hershey and Martha Chase used bacteriophages  to identify whether it was the protein or the DNA that carried the info. The protein capsule of one viral batch was tagged with a sulphur isotope and the phosphorus of the DNA of a second batch of virus with a phosphorus isotope. The phages were allowed to infect and multiply in a bacteria. They were then centrifuged and the supernatant with the actual bacteria was examined. Only the bacteria infected by the ³²P isotope containing virus showed radioactivity. This showed that only the DNA of the virus entered the bacterial cell and was responsible for the replication, not the protein capsules.
• Erwin Chargaff (1947) developed Chargaff’s rule: in DNA the amount of A=T and G=C. This suggested they were paired.
• The DNA structure was investigated by Linus Pauling in California, Rosalind Franklin and Maurice Wilkins in London and James Watson and Francis Crick at Cambridge University. Franklin (mainly) and Wilkins used X-ray diffraction analysis in which a molecule is bombarded with X-rays which are deflected by the molecule producing lighter and darker bands on a photographic film. The 3-D structure is deciphered using math. It showed the helix is about 2nm in diameter and makes a complete turn every 3.4nm. (1nm = 10^-9m/10^-6mm). The helix turns in a clockwise direction. James Watson, Francis Crick and Wilkins got the Nobel Prize in 1962 – Franklin had died in 1958 at the age of 37 from cancer, and the committee doesn’t award prizes to deceased scientists.
• The Human Genome Project started in 1990 and was deciphered in 2001 by Craig Venter at Celera Genomics, a private company. Eric Lander at Whitehead Centre in Massechusetts did a publicly funded mapping. Only about 42 000 protein-encoding genes are present. The rest (95%) are called introns and include VNTRs i.e. variable number tandem repeats and pseudogenes. The ends of chromosomes are called telomeres and are made up of VNTR’s. They prevent the chromosome from fraying. The length is associated with the longevity of the organism – they shorten as its lifetime proceeds. VNTRs are also found at centromeres.

 

THE LIVER

 

 

LIVER FUNCTION

          The liver receives two litres of blood a minute, from both the general circulation (hepatic artery), and the gut (hepatic portal vein).

a.     Immune system filter: It has kupffer cells which remove bacteria, debris and antigen-antibody complexes

b.     Major metaboliser: sorts through the blood, storing or inter converting nutrients as required. It is able to convert glucose to glycogen, glycogen to glucose, amino acids to glucose, amino acid to amino acid, fat or glucose or amino acids to energy, glucose to fat and fat to phospholipid. It can convert beta carotene to vitamin A, and it stores nutrients like glycogen, vitamins B12, A, and D, and iron. It converts vitamin B6 to its active form, pyridoxyl-5-phosphate (5 p173).

c.     Controls blood glucose. It responds to pancreatic insulin and glucagon on an ongoing basis, and either stores glucose as glycogen when the glucose in the blood is too high, or it converts it back into glucose when the blood glucose is too low.

d.     The liver makes 95% of the plasma proteins. Albumen, fibrinogen and prothrombin, essential for clotting.

e.     The liver makes very low density lipoproteins (VLDLs) from chylomicrons absorbed from the gut.

f.       The liver makes 1g of cholesterol daily

g.     The liver makes a litre of bile a day.

h.     The liver metabolises many hormones. It conjugates estrogen, testosterone, adrenaline, thyroid hormone and others, and excretes them in the bile for elimination via the stool.

i.       detoxification of both internal and external harmful substances. It has a detoxification system composed of many enzymes which takes care of heavy metals, coffee, alcohol, nicotine, drugs, pesticides, herbicides, industrial chemicals, hydrocarbons, plant toxins, preservatives, flavourants, microbes, microbial metabolites, hormones and additives.

 

NORMAL BILIRUBIN METABOLISM

          The liver conjugates bilirubin. Conjugated bilirubin can be excreted by the kidneys. However, most conjugated bilirubin is secreted as part of the bile into the gut. Here microbes convert it into urobilinogen. Some urobilinogen is reabsorbed into the blood, and is recycled back to the liver. 5% of urobilinogen is excreted in the urine, giving it its yellow colour. The urobilinogen in the gut is oxidised to stercobilin, giving the stool its brown colour.

         

JAUNDICE

          Jaundice refers to the yellow tint given to body tissues, especially the sclera of the eye, by increased circulating bilirubin. Normal bilirubin levels in the plasma are 0.5 mg%. If these levels go over 1.5 mg%, the skin starts to yellow. Other symptoms and signs are: pruritis (itching) due to circulating bile salts; steatorrhoea (fat in the stool); high cholesterol levels; xanthomas (small fatty lumps deposited in the skin); osteomalacia due to insufficient vitamin D (active vitamin D is made by the liver); and hepatomegaly (an enlarged liver).

 

a. Haemolytic jaundice:   Increased erythrocyte (RBC) haemolysis (breakdown) causes haemoglobin to start diffusing into the tissues. Here macrophages slowly convert it to free bilirubin, which causes jaundice. The liver is normal and can therefore conjugate bilirubin, but this reaches saturation levels. In addition, urobilin excretion by the kidneys is at a maximum and so the urine is very dark. Stercobilin will be present in the stool because the liver is creating and secreting conjugated bilirubin normally. So the presenting picture is jaundice, a dark urine and a normal stool.

 

b. Obstructive jaundice: The cause can be intra-hepatic or extra-hepatic. Intra hepatic causes are viral hepatitis, damage by drugs or alcohol, or cirrhosis. Extra-hepatic causes are gallstones or pancreatic cancer that obstructs the flow of bile out into the small intestine.

          In obstructive jaundice the free bilirubin levels are normal, because there is no excess haemolysis and the liver is conjugating. But the conjugated bilirubin cannot be cleared by secretion via the bile into the gut, either because the bile or hepatic ducts are obstructed, or the liver cells are damaged and hence the pathway to bile secretion is congested. So conjugated bilirubin is reabsorbed into the blood in larger amounts. Conjugated bilirubin can be excreted in the urine, and can be seen as an intense yellow foam on the urine once it is shaken. The stool has minimal stercobilin and is therefore clay-coloured. The presenting picture is jaundice, a yellow foam on urine and a light stool.

HEPATITIS

          Hepatitis can be caused by a virus (hepatitis A, B and C); a bacterium (e.g. TB, syphilis); a fungus; protozoa (e.g. amoeba, malaria); a fluke; or by drugs and alcohol. Hepatitis causes obstructive jaundice. Cirrhosis is a late and irreversible stage of chronic hepatitis.

·         Hepatitis A (infectious hepatitis) is caused by a picornavirus. It is spread by faecal-oral contact or blood. Water and food borne epidemics are common.

·         Hepatitis B (serum hepatitis) is spread by transfusion or by contaminated blood. There is a prodrome of flu-like symptoms, followed by an icteric phase of jaundice. The liver is enlarged and tender. It can go on to chronic hepatitis, usually ending in hepatocellular failure and cirrhosis

·         Hepatitis C (previously called non-A, non-B) is less common, but occurs in 10% of people receiving transfusions. It is called serum hepatitis. Its mortality rate is higher than in the other forms. About 40% can also progress to a chronic condition.

          In hepatitis there is diffuse liver cell destruction, and demonstrable dysfunction. The bile canaliculi (passages) are often obstructed, so that the outflow of bile is impeded and there is cholestasis (bile stasis), with jaundice, as discussed above.

 

Ÿ        The patient is jaundiced, has nausea, vomiting, intolerance of fatty food, an enlarged tender liver, and a fever. The urine is dark and stool light.

 

CIRRHOSIS

          The liver architecture is no longer normal, so that blood flow and bile flow are distorted and often blocked, leading to obstructive jaundice and portal hypertension (pressures in the portal vein draining the intestines go above the normal 8 mmHg). Death usually results from hepatocellular failure.

          Cirrhosis is most often acquired, and is secondary to: alcohol abuse: chemical damage; hepatitis B or C infections; congenital syphilis; and biliary obstruction.

 

GALLBLADDER

GALLSTONES:is due to an imbalance in the composition of bile. Cholesterol is high and lecithin (needed to solubilise it) and bile salts are both low. Stones develop, especially where there is stasis in the gallbladder, and low water intake, which is the vital solvent of bile. These result in abdominal discomfort, bloating, belching, and intolerance to many foods, especially fatty foods.

          If the stone is released from the gallbladder, and becomes stuck in the common bile duct, pain occurs, and bile backs up affecting: the gallbladder (possibly resulting in inflammation); the liver (causing cholestatic jaundice); and possibly the pancreas depending on where the stone is lodged.

          85% of gallstones are made predominantly of cholesterol and some calcium.

 

Ÿ        EFFECTS OF GALLBLADDER REMOVAL

i.        There is no bile reservoir to handle fatty food

ii.       There is some loss of water and minerals, because the gallbladder concentrates bile.

iii.      Colonic cancer in the ascending colon has been associated with gallbladder removal. This is due to the continual dribbling of bile into the gut, where microbes convert it into toxic substances. Eating lots of fibre would help to bind some of this bile

 

 

THE PANCREAS

 

 

PANCREATITIS

          Acute pancreatitis presents with severe pain in the upper abdomin radiating to the back. Fine haemorrhagic spots appear in the flanks and around the umbilicus. The pain is made worse by movement. There is nausea and vomiting, upper abdominal distension, gas, fever, sweating, increased blood pressure and muscle aches. It can go on to massive bleeding and shock.

 

CAUSES

1.       Inflammation in the pancreas can occur secondary to problems elsewhere in the system e.g. cystic fibrosis, systemic lupus erythematosis, or a viral infection.

2.       Acute pancreatic inflammation can follow common bile duct obstruction. The pancreatic duct (the duct of wirsung) and the common bile duct share a common entrance into the duodenum (the ampulla of vater). So blockage in the biliary system often affects the drainage through the pancreatic duct, resulting in backing up of pancreatic digestive juices. This can inflame the pancreas, and the digestive enzymes can even begin autodigestion of the pancreas. The biliary obstruction can be due to a bile stone or due to alcoholic inflammation of the duct.

3.       Pancreatic inflammation can be secondary to alcohol ingestion.

4.       Drugs can cause pancreatitis e.g. diuretics, tetracycline, acetaminophen, cortisol and the pill.

                   Inflammation and some autodigestive damage can result. In most cases, though, the condition is self-limiting. In a few cases, a complication like an abscess occurs, and in a tiny percentage, shock and death results.

         

DIABETES MELLITUS

          Roughly translated, diabetes mellitus means lots of sweet urine. Copious amounts of urine are excreted (polyuria), and dehydration results. In diabetes  mellitus, the essential problem is an inability to move blood glucose into the cells of the body, where it can be used or stored as glycogen or fat. Because of this, it reaches high levels in the blood, resulting in a high fasting blood glucose. The large volumes of glucose flowing into the kidney are more than its absorptive ability can handle, and glucose, plus lots of water pulled along with it, are excreted (an osmotic diuresis, with a urine that is sweet). The result is excessive urination, and an accompanying thirst and appetite.

          Pathognomonic for both diabetes I or II is the presence of three symptoms: hyperglycaemia, polyuria and polydipsia (excess thirst).

 

          To understand the difference between type I and type II, some physiology must be covered.

Two vital factors must be present for glucose to enter cells:

1.       The presence of insulin - which is like a key that unlocks the door for glucose to enter.                               

2.       A sensitivity on the part of the cell membranes to respond to insulin, and allow glucose to enter.

                                     

Type One Diabetes: This is called insulin-dependent diabetes (IDD), and starts in childhood. In type I diabetes, factor one (above) is affected: the pancreas is not secreting enough insulin. The cause of this is not certain, but it may be linked to a viral infection or an autoimmune process.      

          Because there is no insulin, glucose cannot enter cells, and accumulates in the blood. Its only outlet is via the urine, and so polyuria, dehydration and polydipsia, already described, results. The cells become starved of their most easily accessible source of energy. The brain is also starved of its major fuel source, blood glucose.

          Other fuels such as fat stores and lean body mass (protein) must be mobilised as sources of energy. This results in weight loss in spite of an increased appetite. The large amounts of fatty acids that are broken down and a byproduct called ketones form. These ketones are excreted in the urine and on the breath, but their high levels in the blood drop the pH to low levels, and affect brain and enzyme function to such an extent that a hyperglycaemic ketotic coma can result. Note that although there is plenty of glucose in the blood, the brain is seriously deprived of glucose, and cannot continue functioning. 

          The excess ketones impairs enzyme functioning. The result is fatigue, which is also brought about by the dehydration, and the inability to use glucose.

          Type I diabetes requires insulin replacement, either as multiple daily injections, or the use of a continuous supply insulin pump. This, together with continual monitoring of blood glucose levels, is used in an attempt to mimic the moment to moment control that the pancreas has over blood glucose levels. It is not easy to get anything like the glucose balance that a normal pancreas achieves.

          Type I diabetics can get two kinds of coma. One is already described: the hyperglycaemic ketotic coma. The other is the result of taking too much insulin, either because of a frank overdose, or because the individual did not eat enough, or did too much exercise, and so the insulin was too much relative to his needs. This is a hypoglycemic hyperinsulinaemic coma. If a diabetic seems to be losing consciousness, and it is not possible to find out which of the two comas he has, the best is to give him glucose (a sweet). This will immediately turn the tide if he is hypoglycemic, and if he is hyperglycaemic, what difference will a little more glucose make? But it also serves to make the diagnosis, and so his needs then become apparent.

         

Type Two Diabetes:        This is called non-insulin dependent diabetes (NIDD) or adult-onset diabetes. In Type II diabetes,  factor  two (above) is affected. The pancreas is not the problem, and is, at first anyway until it begins to collapse, secreting excessive insulin. The problem lies with the resistance that the cells have to insulin, and so great stress is put on the pancreas to push out enough of the messenger (insulin), until the receiver of the message, the cells, listen. It takes years of eating simple sugars, putting on weight and not getting enough exercise to create this disease. As the percentage of fat on the body, and the size of the adipose cells increases, so there is a corresponding decrease in insulin sensitivity. In fact, many people with poor lifestyle habits are either well on their way to this disease, or have it without being aware of it.

          Before the onset of this type of diabetes, there is typically a phase called syndrome X. The essential difference between type II diabetes and syndrome X is the degree of insulin resistance. By the time it has progressed to diabetes, very little glucose can get into the cells, and so instead of getting periods of hyperglycaemia and hypoglycemia in response to meals, as is the case with syndrome X, there is perpetual hyperglycaemia, as the glucose simply has nowhere to go beyond the bloodstream. After a meal, the blood glucose rises to over 200 mg/100ml, and although it does come down (a little goes into cells, and the rest is lost in the urine), it doesn’t come down to fasting levels of 80-90 mg/100 ml. Also, because a little glucose does get into cells, this type of diabetic is less likely to become ketotic or go into a coma.

          Putting Type II diabetics onto insulin injections, will of cause not alleviate the condition.  Instead, this group respond best to healthier food choices, supplements which increase insulin sensitivity, weight loss and exercise. Doctors also prescribe oral hypoglycemic (blood glucose lowering) drugs. These include sulfonylureas like chlorpropamide (diabinese) and tolbutamide (orinase). They work by stimulating an already over stimulated pancreas to pump out more insulin, and they increase insulin sensitivity. The long-term success with these drugs in maintaining blood glucose and hence avoiding complications is estimated at about 30%.

Complications of Diabetes:Diabetes is not a simple disease. If the blood glucose is kept at normal levels, the complications are far less, and we say the disease is well controlled. Hyperglycaemia leads to the complications that plague this disease. The long term effects of high blood glucose are devastating to the body:

1.       Glucose binds to proteins in a process called glycosylation. This changes the structure and the function of the protein:

a)       It binds to low density lipoproteins (LDL) which carry cholesterol around the body. LDLs then cannot bind to their receptors. It is the binding of LDL to its receptor which creates negative feedback inhibition and so cholesterol production is not inhibited and rises high, leading to heart disease.

b)       It binds to the myelin sheath which surrounds nerves and contributes to the degeneration of nervous functioning in the body. This can cause loss of touch and position sense, so that a diabetic can easily hurt himself. It can affect gait, normal digestion and urination. It can contribute to impotence, which depends on the parasympathetic nervous system, or ejaculation which is a sympathetic nervous system function.

2.       Glucose is metabolised by the enzyme aldose reductase to sorbital, which accumulates in cells. When it builds up in the lens of the eye, it contributes to cataract formation. It also accumulates in the nerves, leading to myo-inositol loss, and affecting the speed of nervous transmission.

3.       Glucose is very bioactive and will oxidise to produce large amounts of free radicals. Free radicals damage the linings of blood vessels as well as oxidise the LDLs flowing in the blood, and it is this that so contributes to heart disease.

          The eyes and kidneys are affected by the hypertension, and blindness

           and kidney damage are common complications

4.       Free radicals damage and cause thickening of the basement membranes of small vessels, and this, together with the atherosclerosis, decreases overall blood flow to the periphery, especially to the hands and feet. This slows wound healing.  The sugar is also a good breeding ground for micro-organisms, and so diabetics can develop serious, even gangrenous infections.

                    

Recommendations:          The primary aim in both types of diabetes is to maintain control over blood glucose.  This means never allowing it to ride too high or too low. By doing this, the acute complications from seesawing blood glucose, as well as the long term complications mentioned already, are reduced. The diet should be low in refined sugars and starches, and nutrient dense. Equally important aims are to reduce free radical effects, maintain optimal weight and achieve optimal nutritional status. 

 

 

DIGESTIVE ORGANS AND THEIR EXOCRINE SECRETIONS

 

 

[1] MOUTH

·        Mechanical digestion: changes the way the food looks, not its chemistry

·        Chemical digestion: chemically breaks down the food – catabolism.

                                 Saliva: 99% water, inorganic ions, mucus, amylase and

                                              maltase.

                                              Mildly acid (6-7.5)

                                              Amylase breaks starch down to maltose

                                               Maltase breaks maltose to glucose subunits

                                               Salivary glands: 2 parotids, 2 sublingual, 2

                                               submaxillary

·        Adults have 32 teeth [(2 + 1 + 2 + 3) x 4], children have 20 [(2 + 1 + 2) x 4]

• Tongue papillae have taste buds along their sides for sweet, salty (metals), sour (acid) and bitter (alkaline).

 

ESOPHAGUS: Food moves down by peristalsis, which is the contraction of circular and longitudinal muscle in a rhythmic way that takes the food down to the stomach.

 

[2] STOMACH

·        Mechanical digestion: churning by longitudinal, circular and oblique muscles

·        Chemical digestion: pepsin breaks down proteins to peptide

                                       chains

                                 Lipase (?) breaks down lipids to fatty acid and

                                 monoglycerides

                                 Rennin in babies clots milk – forms curds and whey.

·        Hydrochloric acid: bacteriocydil

                               Denatures protein

                               Releases fat soluble vitamins (A,D,E,K) from food

                               Converts Ca, Fe, Zn to a better ionic form for

                                absorption

                                Converts inactive pepsinogen to active pepsin

·        Mucus: lubricates the bolus of chyme and protects the mucosa/epithelial lining

 

SMALL INTESTINE

Exocrine secretion: Succus Entericus.

This contains:

a)      peptidases: aminopeptidases and dipeptidases that break down peptide chains to amino acids ( note that short peptide fragments and even proteins can also be absorbed)

b)      disaccharidases: break down disaccharides to monosaccharides

·        lactase: breaks down lactose to glucose and galactose

·        Sucrase: breaks down sucrose to glucose and fructose

·        Maltase: breaks down maltose to glucose and glucose

c)      Enteric lipase: breaks down lipids/triglycerides to free fatty acids and monoglycerides

d)      Mucus, water and salt for lubrication

 

PANCREAS

Exocrine secretion:

a.       Proteases: trypsin and chymotrypsin break down interior peptide bonds in polypeptide chains

                      Carboxypeptidase breaks the outer peptide bonds on polypeptide chains

b.      Lipase: breaks down triglycerides to free fatty acids and monoglycerides

c.       Amylase: splits starch/polysaccharides to maltose.

d.      Ribonuclease and deoxyribonuclease splits DNA and RNA nucleotides into free mononucleotides.

 

LIVER

·        Secretes bile,which is made up of :

a.       bilirubin, formed by the breakdown of haemoglobin. A pigment.

b.      bile salts which emulsify fats. Bile salts are made from cholesterol.

c.       Cholesterol, and lecithin to solubilise it

d.      Water, inorganic minerals, bicarbonate (to raise the chyme pH), steroid hormones that are to be excreted, drugs and heavy metals.

·        The function of bile is:

1.      to emulsify fats (micelle formation)

2.      help in the absorption of calcium, cholesterol and fat soluble vitamins

3.      to get rid of wastes. It is the main route of excretion of cholesterol and steroid hormones.

 

BALANCED EATING

 

NOTES:

1.    1 kcal = 4.2kJ

2.    1g of carbohydrate = 4.2kcals (17.2kJ)

3.    1g of fat = 9.3kcals (38.9kJ)

4.   1 oz = 28g

 

A basic mixed diet consists of about 60% carbohydrate, 25% fat and 15% protein.

On a 10 000 kJ a day diet (2380kcals) this would consist of 300g carbohydrate, 60g fat, 75g protein.

 

For example, a sirloin steak of 4 oz  yields 21g of pure protein. So a 12 oz steak (336g) will give you your daily protein intake (this is a large steak). Unfortunately, this will give you about the same number of grams of fat (in excess of your requirements).

 

Another way to do this is to calculate the calories in everything eaten in a day (see c.p. p182). Then ensure that your daily intake shows moderation and variety, and that you choose foods according to:

a.    the 4 basic food groups

b.    the food pyramid

 

THE FOUR BASIC FOOD GROUPS

1. breads and cereals                                      4 or more servings

2. vegetables and fruit                                    4 or more servings

3. milk products                                              2 or more servings

4. meat/beans/nuts group                                2 or more servings

 

 

 

 

 

THE FOOD PYRAMID

1.    6-11 servings of bread, cereal rice, pasta

2.    2-4 servings fruit

3.    3-5 servings vegetables

4.    2-3 servings milk, yoghurt, cheese

5.    2-3 servings meat, poultry, fish, dried beans, eggs and nuts

6.    Use fats, oils and sweets sparingly

 

ONE SERVING IS:

A medium sized fruit or half a cup of fruit; a slice of bread or half a cup of rice, cereal or pasta; a cup of raw vegetables; a cup of milk or yoghurt; 40g of cheese; 85 g of meat, poultry or fish (3 oz - about the size of a deck of cards), 2 eggs.

 

HOLISTIC NUTRITIONAL GUIDELINES:

1.    Eat whole, unprocessed, unrefined, fresh, in season, and preferably organic, food. These foods contains fibre and are nutrient dense. Once we started refining food, we introduced “the empty calorie” into our diets (foods that give us energy, but little in the way of vitamins and minerals). Once food is processed, all sorts of preservatives, flavourants and other additives are put into the food. A lot of the nutrients and fibre are extracted. 

2.    Avoid hydrogenated oils or oils damaged by heat.

3.    Get enough essential fatty acids  (omega 3 and omega 6 oils)

4.    Shop around the outside of a supermarket, not the inside, where the shelved goods are – boxed goods are processed and usually contain hydrogenated fats to prolong shelf-life. 

 

 

NUTRIENTS

 

MACRONUTRIENTS

• Required in large amounts
• Measured in g/ kg body mass per day (g/kg body/day)
• Carbohydrates, protein and fats or tryglycerides

 

MICRONUTRIENTS

• Required in small amounts
• Measured in mg or microg/kg body mass/day
• Vitamins and minerals

 

Note

1. Carbohydrates and fats provide us with energy
2. Protein, fats and minerals are important structural components of our body
3. vitamins and minerals enable our enzymes to catalyse biochemical reactions. Vitamins are also antioxidants

 

CARBOHYDRATES

 

//Compound of carbon and water: C_xH_2nO_n

The name usually ends in –ose

 

1. MONOSACCHARIDE (C₆H₁₂O₆):

• The simplest sugar
• Other sugars are broken down to this form by the body during digestion so that they can be absorbed.
• Includes glucose, fructose and galactose

 

2. DISACCHARIDE (C₁₂H₂₂O₁₁):

• Two monosaccharides bonded together
• glucose + glucose = maltose

broken down by maltase

found in sprouting grains

• b. glucose + fructose = sucrose

broken down by sucrase

cane sugar

also found in beets, pineapple and carrots

• c. glucose + galactose = lactose

broken down by lactase

lactose intolerance is due to a lack of lactase enzyme

milk sugar

 

3. POLYSACCHARIDE (C₆H₁₀0₅)_n + n(H₂O) )

• Many simple sugars joined together.
• “Complex carbohydrate”

1. starch: many maltose units bonded together. Made by plants
2. cellulose: many glucose units joined by a bond humans cannot break, and therefore cannot use for energy. Fibre.
3. Glycogen: glucose bonded together and formed by animals to store energy in the muscles for exercise and the liver to replenish blood glucose.

 

 

FATS/LIPIDS/TRIGLYCERIDES

• Cannot dissolve in water
• Consist of carbon, hydrogen and oxygen
• Are made up of 3 fatty acids and one glycerol molecule.
• Saturated fats are the animal fats that are stable and solid at room temperature. Palm and coconut oil are also saturated.
• Unsaturated fats are plant fats that are liquid at room temperature (oils). Fish oil is also unsaturated. Monounsaturated oils like olive oil and peanut oil are quite stable but the polyunsaturated oils like the seed oils and fish oil are very unstable and easily break down when exposed to heat, light and oxygen. They should never therefore be exposed to these three elements, or else they will become toxic free radicals.

The polyunsaturated oils include the essential fatty acids which must be included in the diet to maintain health – these are the omega 6 and omega 3 oils found in nuts, seeds and oily fish.

 

 

 

PROTEINS

• Are made up of amino acids.
• Amino acids are made up of nitrogen, cargon, hydrogen, oxygen, phosphorus and sulphur

(NCHOPS)

• Amino acids are joined into long peptide chains (primary structure). These are over and over to give the secondary, tertiary and quartenary structures.
• The essential amino acids are lysine, isoleucine, leucine, valine, methionine, phenylalanine, tryptophan and threonine. They must be in the diet, they cannot be made in the cells and they are essential to health.
• All proteins are rated for their quality in two ways:

1. complete vs incomplete protein: complete proteins contain all the essential amino acids in the right proportions
2. biological value (B.V) scale: is a measure of the body’s ability to retain and use the nitrogen in the protein per gram of protein eaten.

• Quality proceeds in the following way: animal >legume>cereal>vegetable

 

 

Vegetarians that eat eggs and dairy will get all the essential amino acids and are getting good protein. But Vegans that only eat vegetables will not get complete protein unless they combine grains, legumes, nuts and seeds in such a way as deficiencies of amino acids in one are compensated by another. They still need to eat a lot to get enough good quality protein, and a lot is lost to the reduced digestibility of this diet. They also lack vitamin B12 (only made by microbes and animals) and iron as animal iron is the most absorbable.

 

 

THE FLOW OF A BOLUS OF BLOOD THROUGH THE HEART

 

1. The Superior and Inferior Venae Cavae (pl) carry deoxygenated blood back to the heart.
2. This deoxygenated blood flows through the right atrium to the right ventricle.
3. The Pulmonary artery carries the deoxygenated blood from the right heart to the lungs.
4. The blood picks up oxygen here and gives off carbon dioxide.
5. The Pulmonary veins carry the oxygenated blood back from the lungs to the left side of the heart. There are two pulmonary veins from each lung.
6. The oxygenated blood flows from the left atrium to the left ventricle and then out of the heart via the aorta.
7. the Aorta carries the oxygenated blood to all parts of the body.

 

 

THE HEART/CARDIAC CYCLE

 

 

1. DIASTOLE

The heart is at rest. During this time it fills with blood.

• The right atrium fills with deoxygenated blood from the body
• The left atrium fill with oxygenated blood from the lungs.

The atrioventricular valves are open and the blood flows from the two atria into both ventricles.

 

2. ATRIAL CONTRACTION: ATRIAL SYSTOLE

Any remaining blood is pushed into the ventricles

 

3. ATRIOVENTRICULAR VALVE CLOSURE

The right tricuspid and left mitral valves close. This results in the “LUB”  heart sound.

 

4. THE VENTRICLES CONTRACT: VENTRICULAR SYSTOLE

Because both AV valves are closed and the semilunar valves are also closed, both ventricles are contracting down on blood in a closed space. This results in a great build-up of pressure. When the pressure in these ventricles exceeds the pressure in the arteries leaving the ventricles, the semi-lunar valves are forced open.Blood now leaves the heart. This is called EJECTION.

 

The semilunar valves prevent the backflow of blood into the ventricles by closing. This gives the “DUB” sound of the heart.

 

After ejection, the heart again enters the diastole period.

 

One  cardiac cyle is one heartbeat. There are 60-80 cycles every minute.

 

 

 

TRANSPORT VESSELS – BLOOD VESSELS

 

ARTERIES/ARTERIOLES

Arteries/arterioles are vessels that must handle high pressures and at the same time they must be elastic. They carry the blood pumped out of the heart to the tissues. In cross-section they consist of 3 layers:

1. An outer connective tissue with elastic fibres
2. A thicker middle layer with alternating circular bands of elastic fibres and smooth muscle. A nervous supply to this layer can cause contraction or relaxation of the muscle and alter the diameter of the vessel.
3. An inner layer of a single layer of epithelial cells (endothelium).

 

VEINS/VENULES

These are vessels that must handle large volumes of blood, at low pressure, that is returning to the heart. Blood return is achieved by:

·         Gravity in vessels above the heart (head and neck)

·         Muscles contracting around the vessels

·         One-way valves inside the vessels that prevent any backflow

The same 3 layers that are found in the arteries are also found in veins, but the middle muscular layer is much thinner. There is no nervous supply to the middle layer and so the diameter of veins/venules cannot be altered.

 

CAPILLARIES

Capillaries reach every corner of the body. The wall is a single layer of endothelium, and the average diameter is 8 microns – just enough for blood cells to pass through. Gases, nutrients and wastes cross the endothelium, allowing exchange between the circulation and the cells.

 

LYMPHATIC SYSTEM

• This consists of a network of lymph vessels and glands (lymph nodes) throughout the body.
•  Lymph, a pale yellow fluid flows through the vessels.
•  Lymph begins as an exudate from capillaries, that bathes the cells. Lymph is caught up into the lymph vessels and is eventually returned to the circulation when the large lymphatic ducts drain into the subclavian veins.
• As the lymph passes the many lymph nodes, lymphocytes formed in the nodes pick up and destroy any infectious agents.

·         Thus the lymphatic system is part of the immune system, as well as being a part of the circulatory system that returns plasma fluid to the blood again.

 

 

TRANSPORT SYSTEMS

 

A transport system delivers nutrients and oxygen to the cells and removes waste.

 

A. ORGANISMS WITHOUT SPECIALIZED TRANSPORT SYSTEMS

 

1. UNICELLULAR ORGANISMS

The entire transport process is achieved through diffusion and active transport across the cell membrane.

2. SIMPLE MULTICELLULAR ORGANISMS

• Hydra and jellyfish also lack any organized transport system.
• Materials are exchanged between the fluid in the body cavity and the cells.
• They have no blood, which is a vascular tissue adapted to carry substances.
•  They have no specialized mechanism for pumping fluids to cells.

 

B. ORGANISMS WITH SPECIALIZED TRANSPORT SYSTEMS

Most multi-cellular organisms have blood vessels, blood and a pump specialized to transport substances around the body. This can be divided into open and closed transport systems:

 

 

1. OPEN TRANSPORT SYSTEMS

• Blood bathes the cells directly.
• The blood does not remain contained within blood vessels all the time.
•  The blood sloshes back and forth and so circulation is slow.
• The respiratory and circulatory systems are separate in these animals, so there is no need for quick gas delivery by the transport system.

An example is the grasshopper that has one vessel, the aorta, and a long tubular heart, that carries blood into the body cavity. This cavity is divided into chambers that bring the blood in contact with cells. Material exchange occurs in the sinuses.

 

2. CLOSED TRANSPORT SYSTEMS

• The blood does not leave the circulatory vessels.
• Blood does not bathe cells directly, but is pumped around the body within a network of vessels.
• Blood circulates in one direction.
• The transport system must also carry gases because the respiratory and circulatory systems are not separate.
• These systems vary in efficiency, measured as the rate at which it can transport substances around the body.
• Worms (annelids), fish, amphibians, reptiles, birds and mammals have closed systems. We will analyse their differences later.

 

 

SEXUAL REPRODUCTION

 

Generally, simple animals reproduce asexually. It is quick, simple and uses less energy, but does not allow for variation, which makes the organism less resistant to changes in the environment (less adaptable to evolutionary forces).

 

Sexual reproduction is common among multicellular organisms.

Definition of sexual reproduction: Two parents produce a genetically unique offspring. Genetic information from two cells is combined to form the genetic code of the new organism. In complex animals, this involves two specialized sex cells – a sperm and an ovum that combine to form a zygote. It results in variation and greater resilience to environmental change.

 

TYPES OF SEXUAL REPRODUCTION

 

1. CONJUGATION

Sometimes bacteria produce sexually by conjugation (usually when under stress). Two cells come in contact and exchange small pieces of genetic information through a conjugation tube that forms between them.

 

2. HERMAPHRODITES

An organism that produces both male and female sex cells. They have both male and female sex organs. They can reproduce with any other member of their species. This is a benefit when the organism does not come into contact with its own kind often, so it does not matter whether that other organism is male or female, they can function as both male or female. Examples are sponges and earthworms.

 

3. SEPARATE SEXES

Most complex animals and some plants have separate male and female sexes/sexual parts.

 

• GYMNOSPERMS

Cone producing plants produce male and female cones which produce sperm and ova. Pollination and fertilization produce seeds inside the female cone which are then dispersed and germinate if they find the right conditions

 

• ANGIOSPERMS

Flowering plants have male and female parts in flowers. Pollination and fertilization result in a seed that will be enclosed in a fruit. Dispersal results in germination if the right conditions are found.

 

• EXTERNAL FERTILIZATION IN ANIMALS

Sex cells unite outside the female body. For example, fish and frogs release egg and sperm into the water and fertilization occurs in the water.

 

• INTERNAL FERTILIZATION IN ANIMALS

In most land animals, the sperm are deposited inside the female’s body, and the ova are fertilized internally. After this, either:

a. Oviparous: a fertilized egg is laid e.g. some reptiles, birds

b. Ovo-viviparous: the embryo develops in the mother’s body but is not nourished by her. It feeds on a yolk sac e.g. some lizards and snakes.

c. Viviparous: embryo is attached to the uterine wall by a placenta and receive nourishment and oxygen from the mother. The baby is born alive. This includes all the placental mammals.

 

 

ASEXUAL REPRODUCTION

 

//Genetically identical offspring are produced from a single parent. There is no fertilization of a female egg by a male sperm. Because the offspring is identical to the parent we say it is a clone.

 

There are different types:

 

1. Mitosis in unicellular (one-celled) organisms (called the protista) results in two ‘offspring’.

 

2. Binary Fission is a simple type of cell division that occurs in bacteria because they are prokaryotes and so will not go through a true mitosis. A bacteria will replicate its ring of DNA into two rings. Each ring will go to opposite poles of the cell, and the cell membrane will pinch off in the middle of the cell. Two new cells are made.

 

3. Budding occurs in yeast, a unicellular form of fungus. A copy of the nucleus is made by mitosis. This migrates to the edge of the cell and buds off, taking a little cytoplasm with it. The bud grows to the size of a yeast cell.

 

 

4. Sporulation occurs in fungi like mushroom and moulds, and in some plants like mosses and ferns. The spore is produced by the plant (single parent) and is genetically identical to the parent plant. It is dispersed. When it finds the right conditions it will grow to look identical to the parent.

Note that a spore is not the same as a seed although it germinates like a seed. A seed is the product of sexual reproduction in which an egg is fertilized by a sperm. A spore is the result of asexual reproduction in which one parent makes an identical copy of itself that can be carried by the wind to another place.

 

5. Regeneration is the ability to regrow a tissue, organ or body part. For example if a starfish or a crayfish loses an arm, it can regrow a new one. Humans have a limited ability to do this – we can regrow skin, hair and nails, but not a lost leg.

 

6. Fragmentation is the ability of a fragment to grow into a whole organism. For example planarian flatworms and sponges can be cut into fragments and each fragment will grow into a whole flatworm or sponge.

 

 

7. Vegetative propagation is the growth of new plants from parts of the parent plant. There are a few types:

·         Growth from bulbs (underground stems) e.g. onions, garlic, lily

·         Growth from tubers (modified storage stems) e.g. potato

·         Growth from roots e.g. carrots

·         Growth from cuttings like a stem with a few leaves

·         Growth of a new plant by taking a stem still attached to the parent plant and covering it in soil – a process called layering e.g. strawberries

Growth of a plant from parts of the parent plant rely on a special type of tissue called meristematic tissue. This is rapidly dividing, undifferentiated stem cell tissue that can give rise to any part of a plant by becoming specialized. It is especially found at the tips of roots and stems for rapid growth of these structures.

 

8. Cloning a plant or animal from a single cell. In 1958, Frederick Stewart published his work with carrots. He was able to take a single meristematic cell from a carrot, place it in a culture medium with growth hormone and allow it to grow and specialize until it eventually became an entire carrot plant. This is growing a plant without using seeds. Carrots, ferns, tobacco, lettuce for example respond well to cloning, whilst grass and legumes do not.

 

The first animal cloning was done by Robert Briggs and Thomas King working with frogs. They removed the nucleus from a female egg (or ovum) – a process called enucleation. Then they took the nucleus from a frog embryo and inserted it into the enucleated egg. This egg cell now had the full amount of DNA and did not need to be fertilized. It grew into an adult frog. Mammals have also been cloned – mice, cats, cows and of course “Dolly” the sheep. Here once the enucleated ovum is injected with the nucleus from an embryo or an adult cell, it has to be implanted into the uterus of a “mother” to take it to term.

 

Recently there have been claims that two human babies have been cloned. A frequent problem has been accelerated aging of these cloned animals. Dolly had to be put down at the age of six because she had the lung and joint disease of an old animal.

 

9. Parthenogenesis is the development of a female ovum without fertilization by a sperm. This occurs in plant lice, aphids, daphnia (water fleas), beetles, ants, bees, wasps, and even some lizards (Rock and Whiptail lizards). For example, a queen bee will lay fertilized eggs that give rise to the females workers as well as unfertilized eggs which by a process of parthenogenesis will grow into the male drones. 

 

 

THE SCIENTIFIC METHOD

 

1. The independent variable is the factor in the experiment that is manipulated by the researcher.

 

2. The dependent variable is the factor in the experiment that changes in response to the independent variable. It is the outcome or effect.

 

Remember that

·        both the independent and the dependent variables have to be measurable variables i.e. the variables in an experiment have to be testable.

·        A hypothesis is a testable prediction or educated guess on the outcome of the experiment. It really doesn’t matter if this is the final outcome of the experiment – a rejection of a hypothesis does not mean the experiment has failed. The outcome is valid in its own right – the hypothesis was just a guess.

 

3. The interfering variables are all the factors that could effect the relationship between the independent and dependent variable. Because we are trying to measure the relationship between these latter two variables, it is important to control the interfering variables.

 

• Interfering variables are controlled in two ways:

(i)                  By inclusion and exclusion criteria. These are choices made right at the start as to who/what will be accepted into a study and who/what will not. These choices are based on the interfering variables identified, which then become part of what is excluded from the study.

(ii)                By using study and control groups. A study group is the group that gets the manipulation and the control is the group that does not. The initial sample subset taken from the population is randomly assigned to one or the other group. In this way it is hoped that the two groups will be the same, and that the same interfering variables are present to the same extent in both groups. If this is achieved there should be no measurable differences between the two. The manipulation is then applied only to the study group. If the two groups are compared with each other, it is logical to assume that any measurable differences between them would have to be due to the manipulation and none of the interfering variables. In this way, the interfering variables have been controlled in that they do not affect the outcome.

 

REMEMBER: We are trying to measure the relationship between the independent and dependent variable, and keep any other variables from getting in the way of this.

 

4.There are many inherent weaknesses in study design:

(i)                  We cannot control all variables. Many times we don’t know all these variables. We cannot screen them all out, and if we use control and study groups we can never be sure if they are the same in all respects and that some bias hasn’t crept into the experiment.

(ii)                The more we control the variables, the less like life it becomes. This becomes a problem when we extrapolate our findings back to the entire population. However, the more we control variables, the more confident we are in any association we see between the independent and dependent variable. This is the catch-22 of research.

(iii)               All experimentation is ultimately subjective. It is also influenced by the society and the age within which that work was done.

 

 

DIVERSITY OF LIFE

 

HISTORY OF THE SIX KINGDOMS

1. Aristotle divided life into Plantae and Animalia. He called these kingdoms.
2. In 1866 Ernst Haeckel proposed a third kingdom the Protista for micro-organisms that were not plant or animal.
3. Fungi were originally included in the plant kingdom, but because they are not photosynthetic, they were put into another kingdom.
4. Bacteria wer prokaryotic and were put into a fifth kingdom the eubacteria, prokaryotae or Monera.
5. In the 1990’s a group of bacteria which lived in extreme conditions like hot, acidic, salty places were found to be very different from other bacteria. They had different RNA, their cell membranes had special fats that could withstand high temperatures and their enzymes could also withstand high temperatures. They were reclassified into a sixth kindom called the Archaea.

 

There is also another level of classification above kingdoms, called the Domains: they are the bacteria, archaea and eukarya (protista, fungi, plantae, animalia)

 

TAXONOMY

Taxonomy is the practice of classifying organisms. 300 years ago, Carolus Linneaus (1707 – 1778) came up with a classification system based on simple physical characteristics. We still use this classification, but where and how organisms are placed within the framework of this classification changes continually, as we find out more about them, and we view the process of grouping organisms in different ways. Today we don’t only consider physical characteristics (anatomy and physiology), but also paleontology, phylogeny (evolutionary relationships), ontogeny (embryological development), behaviour, biochemistry and lately DNA and genetic features.

 

The organisms within each kingdom are further grouped and organized from general to specific, using categories called taxa: phylum, class, order, family, genus, species

 (P.C OF GUS). As we move down the taxa, there are fewer and fewer organisms, and they are more and more closely related in evolutionary terms. Organisms within groups are more closely related to each other than organisms outside the group.

 

Each organism has a two-word name. This is called BINOMIAL NOMENCLATURE. The first word is the genus, the second the species.

 

Organisms belonging to a species are able to breed with each other and produce fertile offspring. Variation among species is the result of genetic mutation and sexual reproduction. Sexual reproduction allows for individual phenotypic expression from a large gene pool. This variation meets the prevailing environmental conditions, and those more equipped to produce many and healthy offspring will survive. This process of natural selection leads to evolutionary development that leads to the variety of kingdoms and the variety within kingdoms.

 

We study evolutionary relatedness by looking at

1. anatomical evidence in fossils
2. the early stages of embryonic development
3. similarities and differences in biochemistry e;g how similar is the sequence of the amino acids in the insulin of two species.
4. DNA. For example 93% of human genes match macaque monkeys, and 98% match chimps. We look at mitochondrial DNA especially because this is only inherited from mother to offspring. 

 

HUMAN SPECIES

Sub species                               sapiens

Species                                      sapiens

Genus                                       Homo

Subfamily                                Homininae

Family                                      Hominidae

Superfamily                             Hominoidea

Suborder                                  Anthropoidae

Order                                        Primates

Infraclass                                  Eutheria

Subclass                                    Theria

Class                                          Mammalia

Superclass                                 Gnathostomata

Phylum                                      chordate

Subkingdom                              Metazoa

Kingdom                                   Animalia

 

PHYLOGENY

//The evolutionary history of organisms

 

CLADISTICS

//a classification scheme that is based on phylogeny

 

CLADOGRAM

//a branching diagram that resembles a phylogenetic tree. It shows relatedness in terms of branching off from common ancestors over time.

 

 

GENETIC ASSIGNMENT

 

You are an employee of a City Health Department and are required to create an informational pamphlet or booklet on a genetic condition or disorder. Produce a pamphlet that is appealing, easy to read but comprehensive. The following formation needs to be included:

1. Characteristics, symptoms and signs and treatments – cures if any.
2. Fatal or not – if so by what age?
3. The genetic inheritance pattern – here you need to explain exactly how this disease is inherited, including a punnett square to show the probability of genotypes and phenotypes.
4. Age of onset
5.  Prevalence in certain populations?
6. Genetic screening available?
7. Lifestyle implications.
8. Other pertinent specific information
9. Separate works cited list (minimum of 3 sources)
10.  Embedded references using the numbering system

 

 

Choose one of the following conditions:

Thalassemia

Albinism

Tay-sachs disease

Familial hypercholesterolaemia

Progeria

Haemophilia

Lou Gehrig’s disease/amylotrophic lateral sclerosis

Muscular dystrophy

Down syndrome

Cystic fibrosis

Turner’s syndrome

Klinefelter’s syndrome

Williams syndrome

Cri du chat syndrome

Other – must be approved by the teacher.