Chapter 5 - The Cell

5-1 What is a Cell?

     cells   -make up all living thing
               -small, individual units
               -usually cannot be seen with the naked eye
 

Development of the Cell Theory

-350 years ago idea of cells unknown

-mid 1600's

        - Leeuwenhoek:
                > microscope makes "seeing"
                    cells possible

- Hooke > calls the "little rooms" he sees
    in a slice of cork cells -1830's- Schleiden
                >observes plant cells
                >states all plants were made up
                    of similar units, or cells
                >used the term "protoplasm"

            -Schwann

                >proposed that animals were
                    made up of cells

   -Brown
      >discovered the nucleus and
          coined the term

   -Virchow
      >stated "all cells arise from
           preexisting cells"


-1860's- Schultze

                > defined protoplasm as "the
                    physical basis of life"
 
 
 


-THE CELL THEORY states:

    > all living things are made up of one or more cells

> cells are the basic units of structure and function   > all cells come only from other living cells by the
        process of cell division
 
 
 

Exceptions to the CELL THEORY:
1-viruses-have genetic material,

reproduce inside of cells, but are
not cells themselves 2-some cells parts-such as mitochondria and
    chloroplasts-have DNA and can duplicate
3-the first cells must have arisen from noncellular structures
 
  The Two Basic Cell Types

prokaryotic cells
        - membranes do not separate different areas
            of the cell

- make up the smallest single-celled organisms          - example: bacteria

eukaryotic cells
         - have membrane-bound structures

         - example of an important such structure
            is the nucleus

          - present in all living things, except bacteria
 

Both types:
         - have cell membrane to keep
                cell environment constant
         - carry out same life processes
 
 

prokaryotic - means "without nucleus"
eukaryotic - means "true nucleus"
 

5-2 Cell Structure

CELL PARTS--
cell walls; cell membrane; cytoplasm

ORGANELLES--specialized internal structures
nucleus; endoplasmic reticulum; ribosomes; Golgi bodies; lysosomes; mitochondria; microtubules;
microfilaments; centrioles; cilia; flagella; vacuoles; plastids

[Figure 5-5, p. 83 Tiger Book]

[OH #7-Organelles]

cell walls

-rigid, gives cells their shape

-lies just outside the cell membrane

-present in all plant cells

-not in animal cells

[OH #8-Plant and Animal Cells/pg.83 Fig. 5-5]
 

cell membrane

-another name is plasma membrane

-controls movement of materials into and
    out of the cell

-maintains homeostasis
 

cell membrane structure

-two layers-lipids

-made of lipids, proteins, and carbohydrates

-different proteins for different functions

- e.g. transport proteins

receptor proteins
enzymes
binding proteins


permeability of the cell membrane

selectively permeable

- some substances can pass through freely
- some only at certain times

- others not at all

- fluid-mosaic model-double lipid

layer in which proteins float [OH#6 Fluid Mosaic/Fig. 5-6, p84] nucleus

- control center for metabolism and reproduction

- largest organelle

- contains the hereditary material
        (genetic information):
                -contains one or more nucleoli, which are
                    made up of DNA, RNA, and protein
                -chromosomes are found here

cytoplasm
- watery material between the cell membrane and
    the nucleus

- where many chemical reactions of metabolism occur

entoplasmic reticulum
-fluid-filled canals

-used to transport materials within the cell

-divides cells into compartments

-rough texture contains ribosomes

-smooth texture, no ribosomes
 

ribosomes

-sites of protein synthesis
 
 

Golgi bodies (or Golgi complex)

-stacks of flattened membrane sacs

-serves as a "packaging" mechanism for
        secretions synthesized  in the cell

lysosomes

-specialized vacuole

-aids process of nutrition

-contains hydrolytic enzymes used in
        intracellular digestion

-may help recycle aging or defective cells
 

mitochondria

- small, round or slipper-shaped

- releases energy

- performs chemical respiration

- "powerhouse of the cell"

- synthesizes ATP
 

centrioles

-cylindrical, located near the nucleus

-primarily in animal cells

-involved in cell division/reproduction
 

vacuoles

-fluid-filled

-contains water, enzymes, or other

substances, such as food
 

chloroplasts

-pigment-containing structure

-found primarily in plant and algae cells

-photosynthesis occurs here

-primary pigment is chlorophyll

-maintaining a relatively constant internal cell
    environment is essential for life

-several processes need to occur in the cell in order
    to maintain this homeostasis


 

5-3 Maintaining a Constant Cell Environment
 

TRANSPORT

passive -no cellular energy is used

            -e.g. diffusion, osomisis

active   -requires energy

            -"pumps" material from low concentration to
                    higher concentration

-e.g. phagocytosis, pinocytosis
DIFFUSION

-form of passive transport

-material goes from higher concentration
            to a lower concentration
 

OSMOSIS

-the diffusion of water into or out of the cell

-from a region of high water concentration
        to a lower water concentration
 

PHAGOCYTOSIS
-large, solid/undissolved particles become enclosed in
    a vacuole and are digested
-requires cellular energy

PINOCYTOSIS
-large, liquid/dissolved particles become enclosed in
    a vacuole and are digested
-requires cellular energy

 

5-4 Organization of Cells and Living Things
 

> human body is made up of millions of cells

> in many-celled organisms, cells have

        to work together
 

> five main levels of organization:
 
Level Organization Some Examples
1
 cells muscle; skin
2
 tissues smooth; skeletal;

cardiac
3
 organs heart; liver; lungs
4
 organ systems circulatory; skeletal; respiratory
5
 organism  humans; animals

 

END of Chapter 5 NOTES