Chapter 2

Cells

Comparing Cells

•      Cells differ in size and shape depending on their function

–    Ex:  nerve cell needs to communicate between places, so it is a long cell

–    Ex:  a muscle cell can contract and change it’s shape

•      Two cell types:

•      Prokaryotic – lack membrane-bound internal structures

•      Eukayrotic – contain membrane-bound internal structures

Cell Organization

Cell wall

–    Tough, rigid outer coverings that protect the cell and give it shape

–    Made of cellulose

–    Only in plants, algae, fungi and most bacteria

–    “frame of a house”

•      Cell Membrane

–    A protective layer around all cells

–    Inside the cell wall, if it is present

–    Allows food and gasses into the cell and waste products out of the cell

–    “the bouncer”

Cell Structures

•      Cytoplasm

–    A gelatin-like substance inside the cell membrane

–    Medium for things to move about in the cell

•      Cytoskeleton

–    Scaffolding-like structure in cytoplasm which helps cell keep its shape

•      Organelles

–    Membrane bound structures inside eukaryotic cells that helps the cell perform life processes

Cell Structures

•      Nucleus

–   Organelle that directs all cell activities

–   Contains instructions for everything a cell does (within the DNA)

–   “foreperson”

Cell Structures

•      Chloroplasts

–   Organelles in plants and a few bacteria that help the organism make food

–   Photosynthesis occurs here

•      Mitochondria

–   Organelles in all eukaryotes that release the energy from food and turn it into something the organism can use

–   “powerhouse”

Cell Structures

•      Ribosomes

–    Organelles that make proteins

–    Produced in the nucleus

•      Endoplasmic Reticulum (ER)

–    Series of folded membranes from the nucleus to the cell membrane

–    Moves materials around in a cell

•      Two types of ER

–    Rough – ribosomes are attached

–    Smooth – no ribosomes attached

•    Material movement and lipid processing

Cell Structures

•      Golgi Bodies

–    Sort proteins and other cellular substances and package them into membrane-bound structures called vesicles

–    “post office”

•      Vacuoles

–    Organelles that serve as temporary storage for materials

•    Can be water, waste products, food, etc.

–    Vacuoles make up most of the volume of plant cells

Cell Structures

•      Lysosomes

–   Organelles that contain digestive chemicals that help break down food molecules, cell wastes, and worn-out cell parts

–   “recycler”

 

From Cell to Organism

•      Cell

•      Tissues

–   Groups of similar cells working together on one job

•    Ex: muscle tissue, nervous tissue

•      Organ

–   Different types of tissues working together

•    Ex:  muscle, brain

From Cell to Organism

•      Organ System

–   A group of organs working together on a particular function

•    Ex:  muscular system, nervous system

•      Organism

–   All of organ systems working together to create a particular organism

 

Early Microscopes

•      CD-ROM

•      Dutch reading glass maker put two lenses at ends of a tube (1500s)

–   Larger image

•      Antonie van Leeuwenhoek (Dutch fabric merchant)

–   First simple microscope (p. 50 in book)

–   Could magnify up to 270 times

Modern Microscopes

•      Use lenses to bend light

•      A simple microscope has one lens while a compound microscope (what we have here) has mulitple lenses

–    Ex:  one lens at 10x – 10 times bigger

•    Two lenses at 10x – 100 times bigger

•      Stereomicroscopes have two eyepieces, which create a three-dimensional image

The Light Microscope

Electron Microscopes

•      Use a magnetic field inside a vacuum to bend electronic beams

–   Scanning Electron Microscope (SEM) bounce electrons off the sample to create a 3-D image

–   Transmission Electron Microscope (TEM) send electrons through a sample to see internally

•      Either way, electons then end up on a screen to produce an image (kind of like older TVs)

Cell Theory

•      1665, Robert Hooke looked at cork under a microscope

–   Made of little boxes he named cells

•      1830s, Matthias Schleiden studied plant parts

–   Concluded all plants are made of cells

Cell Theory

•      Theodor Schwann looked at animal cells

–   Concluded all animals are made up of cells

•      Rudolf Virchow

–   Said that cells come from other cells that already exist

Cell Theory

•      All organisms are made up of one or more cells

•      The cell is the basic unit of organization in organisms

•      All cells come from pre-existing cells

Cell Processes

•      Passive Transport – the movement of substances through a cell membrane without the use of energy

–    Diffusion (movement of substance from high to low concentration)

–    Osmosis (diffusion of water across a selectively permeable membrane to equal out concentrations - equal ratios)

•      Active Transport – the movement of substances through the cell membrane using energy

•      Endocytosis & Exocytosis – vesicles transport large materials into (endocytosis) and out of (exocytosis) the cell

Cell Processes

•      Photosynthesis

–    The process plants and other organisms use to convert sunlight energy into chemical energy or sugars to be used as food

•      Respiration

–    The process in which chemical reactions break down food molecules into simpler substances and release stored energy

•      Fermentation

–    Cells that do not have enough oxygen for respiration use this process to release some of the stored energy in glucose molecules

Cell Processes

•      Cell Division – process where one cell splits into two cells

•      Mitosis – process in which the nucleus divides to form two identical nuclei

–    Four stages: Prophase, Metaphase, Anaphase, Telophase

–    Happens during growth of organism or during asexual reproduction

•      Meiosis – process in which the nucleus divides to form cells with half the genetic material of the original

–    Eight Stages: Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

–    Happens when an organism produces gametes (sex cells) for sexual reproduction