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Chapter 7 Notes
Cell Structure and Function
I.
Cells and Cell Theory
A.
Cell: the basic unit of
all forms of life
History
1. Robert Hooke
(1665)
- described the empty chambers
of cork as “cells”
B.
2. Matthias Schleiden (1838)
- all plants are made of cells
3. Theodor Schwann (1839)
- all animals are made of cells
4. Rudolph Virchow (1855)
- all cells come from
preexisting cells
** before this, people believed
in spontaneous generation
C.
Cell Theory
1. All living things are composed of 1
or more cells
2. Cells are the basic units of life
3. All cells come from preexisting cells
** exception: viruses?
II. Prokaryotes and Eukaryotes
A.
B.
Prokaryotic cells do not have nuclei
- example: all bacteria
Eukaryotic cells have nuclei and
organelles
- example: plants, animals, fungi
III. Cell Structures
A.
Cytoplasm: everything between the
membrane and nucleus
1. Structure
a. Cytosol: jelly-like mixture
consisting of water, proteins,
carbohydrates, and other
organic compounds
b. Organelles: structures that
work like miniature organs,
carrying out specific
functions in the cell
(suspended in the cytosol)
2. Function
a. Biological reactions take place in
the cytosol
b. Organelles each have specific
jobs within the cell
3. Analogy
- like the body of a person
organelles = organs
cytosol = everything
surrounding organs
IV. Cell Shape and Size
A.
B.
Maintenance of shape
1. In plants: cell wall
2. In animals: cytoskeleton
Cytoskeleton
- consists of 2 types of structures
1. Microtubules: hollow tubes made of
tubulin
a. Cilia: short,
hair-like
projections
b. Flagella: long,
whip-like
projections
C.
2. Microfilaments: NOT hollow – 2
twisted chains of proteins (like a
rope)
Size of Cells
- can vary from 1 micrometer
(bacteria) to 1 meter (nerve cell)
V.
A.
B.
Movement through the
Membrane
The cell membrane is semipermeable
- only certain molecules can get
through
Passive transport: no energy required
1. Diffusion: the movement of
molecules from a region of high
concentration to a region of low
concentration
- continues until equilibrium is reached
(equal concentrations on both sides of
membrane)
-
-
temperature affects diffusion:
higher = faster
size of particles affects diffusion:
smaller = faster
2. Osmosis: the diffusion of water
across a membrane from high water
concentration to low water
concentration
97%
water
100% water
Which way will the
water move?
Which way will the water
move?
97%
water
90% water
95%
water
This solution is hypertonic
- water diffuses
out of the cell
90% water
95%
water
98% water
This solution is hypotonic
- water diffuses
into the cell
95%
water
95% water
This solution is isotonic
- no net change
C.
3. Facilitated diffusion: uses protein
channels to move molecules from
high concentration to low
concentration
Active Transport: energy required
1. Carrier proteins may act as pumps
-example: sodium-potassium pump
a. Cells continually pump
potassium ions into the cell,
and sodium ions out
b.
Important for
muscle
contraction
and nerve
impulse
transmission
Na+
K+
2. Endocytosis: materials move into cell
a.
b.
Pinocytosis: membrane encloses
a fluid droplet and brings it inside the
cell
Phagocytosis: membrane
encloses a large particle and
brings it inside the cell
3. Exocytosis: materials move outside
the cell
- wastes and cell products may leave
the cell this way