GRADE 9 Lesson
SUMMARY OF PROPERTIES OF SERIES AND PARALLEL CIRCUITS
FUSES AND CIRCUIT BREAKERS
Our
houses are wired in parallel. This means
that every time another appliance is switched on, the current
flowing in the circuit increases. As
current increases, so does the heat
generated. The circuit breaker and the fuse are two ways to protect the house
from heat overload. They prevent fires. They contain a mechanism that opens the
circuit when the current drawn is too high.
1. A FUSE
The
metal conductor in a fuse has a low melting point. When the heat rises, the metal melts, breaking the circuit. They are still
used in stoves. They have to be replaced each time they break the circuit.
2. A CIRCUIT BREAKER
Simply put, the
circuit breaker is a strip consisting of two metals joined together (a bimetallic strip). Each expands at a different
rate as temperatures rise. The metal that expands more than the other causes
the strip to bend toward the less expansive metal. This causes the strip to
bend away from its contact point, and the circuit is broken.
SOURCES
OF ELECTRICITY
98%
of
1.
HYDRO-ELECTRIC PLANTS (63%)
Water
is stored in large dams. The enormous water pressures generated at the bottom
of the dam are tunnelled down the Penstock to a turbine. It turns the turbine,
which converts the kinetic energy to electrical energy.
PROS: Clean form of generation.
CONS: Large tracts of land,
including valuable ecosystems, have to be flooded.
2. BURNING FOSSIL FUELS = THERMOELECTRIC GENERATION (21%)
Coal,
oil and natural gas are derived from organisms that died and decayed many years
ago. We dig them up and burn them. They are burnt in furnaces. The heat rising
up converts water to steam. The steam flows through pipes that turn a turbine,
which converts kinetic energy to electrical energy.
SEE
PAGE 396 OF THE TEXTBOOK.
PROS: Great for the economies of
CONS:
Open pit mining rips up the land. Burning fossil fuels generates sulphur
dioxide, that creates acid rain, and carbon dioxide which is a greenhouse gas
that adds to global warming.
3.
THERMONUCLEAR ELECTRICAL GENERATION (15%)
REFER TO THE
CANDU REACTOR PAGE 397 OF THE TEXTBOOK (Canadian Deuterium
Uranium Reactor)
Uranium
in the form of small bundles are placed in a number of
fuel rods. These rods are placed in the reactor core. The uranium is bombarded
by neutrons, which causes the uranium to split, and in so doing, release
massive amounts of energy. This is called nuclear fission. In the process more
neutrons are released which will go onto bombard other bundles in what becomes
a chain reaction. The reaction is controlled by control rods that absorb
neutrons, and so the amount of fission is regulated by how far these rods are
pushed into the reactor core. The energy heats up water which turns a turbine
which generates electricity.
PROS: very clean
CONS: The fission byproducts (wastes) are very radioactive and need to be
handled and stored very carefully. Any radioactivity that escapes is damaging
to all life.
ELECTRICITY
All electricity
involves electrons. There are two branches of electricity:
1.
Static Electricity:
the electric charges are not moving. The electrons build up in one place. This charge
builds up on insulators, because they don’t allow electrons to move. The build
up of static charge can be removed by discharging the object, or grounding the object, which will return
the object to neutral.
2.
Current Electricity:
the electric charges are moving in a conductor. A conductor allows electrons to
move through it.
STATIC ELECTRICITY
There are three
ways to create Static Electricity:
1.
by friction.
2.
by induction.
3.
by contact or conduction.
1. FRICTION: When two insulators are rubbed against each
other (friction), electrons move from the one object to the other. The object
that lost the electrons will be positively charged, and the object that gained
the electrons will be negatively charged. These charges then stay in one place
on the insulators.
But
which object will gain electrons and which will lose electrons? It depends on the object. Some substances
like to give up electrons more than others. Objects are placed in what is
called the electrostatic series. The
further down the substance is on the series, the more it will take electrons
(see handout).
2.INDUCTION: A static charge can also be induced. This occurs
when a charged object is brought close to but not touching another object. A
positively charged object will pull electrons toward it on the neutral atoms,
making them polarised. A negatively charged object will repel electrons away
from it on the neutral atoms, making them polarised. The neutral object is now
attracted to the charged object. The charge induced will be opposite to that of
the charged object. If the charged object is moved away, the electrons will
move back to where they were. The neutral object is still neutral overall.
Later you will see a situation where the newly charged object can be grounded.
In this situation, it does develop an overall charge.
3. CONTACT/CONDUCTION: Finally, an object can be charged
by allowing a charged object to touch it. In this case the object will acquire
the same charge as the charged object.
THREE LAWS OF CHARGES
1.
Like
charges repel
2.
Unlike
charges attract
3.
All
neutral objects are attracted to any charged objects.
CHARGING BALLOONS BY FRICTION
AND THEN INDUCING
CHARGES IN NEUTRAL OBJECTS.
The
attraction of the object depends on many factors. Here are some:
i.
A conductor allows easy movement of
electrons through it. It will not easily be induced. It will easily pick up the balloon’s charge if it touches it, and
conduct it away.
ii.
An insulator on the other hand does not
allow easy movement of electrons through it. They can be induced and will be
attracted to the balloon.
Some insulators are
better than others for inducing a charge. However, once the charge is induced,
it will stay in one place, and so the object will stay attracted to the
balloon.
FABRIC SOFTENER
The
fabric softener leaves the drier sheet and enters the fabric of the clothes in
the drier. The softener is hydrophilic which means it likes to hold onto water.
So it keeps a little bit of water in the fabric of the clothes. This makes the
clothes soft and prevents them from sticking from static in the drier and when
you wear them after drying. This is because that tiny amount of extra moisture
in the clothes makes them conductors not insulators. And conductors cannot
build up a static charge.
PREGNANCY
AND THE DEVELOPMENT OF THE BABY
FIRST
TRIMESTER
Weeks
1-12
SECOND
TRIMESTER
Weeks
13-24
THIRD
TRIMESTER
Weeks
25-38
RISKS TO
PREGNANCY
Teen pregnancy, cigarettes, alcohol and substance
abuse, radiation, pollutants, medications, mother’s age over 35yrs, poverty, infections
like German Measles (Rubella), poor nutrition,
caffeine, artificial sweeteners, diabetes and eclampsia.
EFFECTS OF
PREGNANCY ON THE MOTHER
MENSTRUAL
CYCLE
DEFINITION: The menstrual cycle is a 28 day cycle which prepares the female body for a possible pregnancy.
NOTE:
MENSTRUATION is not the same
as the menstrual cycle. Menstruation is the shedding of the endometrium
(lining of the uterus) when a pregnancy does not occur.
NOTE: MENARCHE is the first menstruation i.e. the start of the fertile period
MENOPAUSE is the last menstruation i.e. the end of the fertile period
1.
THE FOLLICULAR PHASE: DAY 1 TO 14
· Stimulates the development of a follicle in the ovary
· Stimulates the ovary to secrete estrogen
2. OVULATION : DAY 14
The pituitary gland secretes Luteinising Hormone (LH) in a sudden surge (The “LH Surge”). This surge causes the follicle to release its developed ovum.
3. LUTEAL PHASE: DAY 14 TO 28
MEIOSIS
INTERPHASE
MEIOSIS ONE
Prophase One
Metaphase one
Anaphase one
Telophase one
Cytokinesis separates
the cell into two hapoid cells
MEIOSIS TWO:
Both of the above
two cells will go through this:
Prophase Two
Metaphase Two
Anaphase Two
Telophase Two
Cytokinesis
DNA
Each chromosome has one large DNA molecule in it, wound up around proteins. If the DNA in a chromosome were completely stretched out, it would be about 1.8 m long. So it has to be very wound up to be inside a nucleus we can only see with a microscope.
DNA consists of two strands joined together by bonds between their bases.
Each strand is made up
of nucleotides. A nucleotide consists
of a phosphate joined to a sugar which is in turn joined to a nitrogen-base
molecule. The nucleotides are joined together by bonds between the sugar of one
nucleotide and the phosphate of the next nucleotide.
There are four nitrogen-base molecules: adenine, guanine, thymine and cytosine. Adenine and thymine always join together. Thymine and cytosine always join together. It is the joining of these bases which unites the two strands. The strands are then twisted into a double helix.
During Interphase the
DNA replicates. To do this, the bonds between the bases break, and the two
strands come apart. Complementary bases (i.e. the one that is correct for the
exposed bases of the two strands) come into the gap, and join with the exposed
bases. Two identical strands result. We say the DNA has made an exact copy of
itself. These two identical chromosomes are called sister chromatids
joined by a centromere.
Humans have 23 types of chromosomes: called chromosome # 1, # 2 etc. Each of these chromosomes codes for different information. For example chromosome number 23 is a sex chromosome that determines whether you are male or female.
We have a pair of each
of these 23 chromosomes, because your mother provides you with a set from 1-23
and so does your father. So we 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.
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.
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.
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
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.
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.
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:
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.
·
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.
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.
MICROSCOPES
·
Light
passes from the observed object to the eye.
·
SIMPLE
MICROSCOPE: one lens
·
COMPOUND
MICROSCOPE: two lenses: objective and ocular lens. Can magnify up to 1000
times. Preparation of the slides kills the cells. Many cell organelles are
difficult to see. Stains are used to make structures easier to see
·
PHASE
CONTRAST MICROSCOPES: enable us to view living material without killing or
staining the preparation. It magnifies to 1500 times.
B.
ELECTRON MICROSCOPES:
·
Electrons
pass through the object.
·
Magnifies up to 100 000 times. The preparation
kills the cells.
·
It was
developed by Max Knoll and Ernst Ruska in
·
The
electrons bounce off the surface of the object. A three-dimensional
picture is obtained.
Scanning Electron
Microscope (SEM) debuted in 1942 with the first commercial instruments around 1965.
Its late development was due to the electronics involved in
"scanning" the beam of electrons across the sample