CELL PROCESSES
Four main processes:
1. Photosynthesis
2. Cellular Respiration / Fermentation
3. Transportation
4. Cell Division
3) Transportation
Cells require materials (food, water, oxygen, etc) of various sizes and in
varying concentrations. As a result, cells have a number of mechanisms to
transport materials in or out of the cell…across the cell membrane.
Two types:
A) Passive Transport: moves ions or molecules across the cell membrane
with NO expenditure of energy by the cell. Materials move through
protein channels.
B) Active Transport: requires the cell to expend (use) energy, usually in the
form of ATP. Usually moves materials AGAINST the direction of
diffusion.
PASSIVE TRANSPORT
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Passive transport relies on the physical process of diffusion.
Diffusion is the spreading of particles through a liquid or a gas
Diffusion involves the movement of particles from an area of high
concentration to an area of low concentration.
When molecules are evenly spread out in the liquid or gas, a state of
equilibrium has been reached.
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Types of Passive Transport:
- Particles move into/out of the cell by squeezing between the 2
layers of fat cells in the cell membrane. These particles move
from high to low concentration by diffusion.
- Particles moving through the proteins scattered throughout
the cell membrane. This is called Facilitated Diffusion. The
proteins are called Protien Channels. These particles move
from high to low concentration by diffusion.
- Osmosis is when WATER moves into/out of the cell
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Equilibrium: the point at which a roughly equal amount of particles
are entering and leaving the cell at the same rate (speed)
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Influences of the diffusion rate:
- Distance: The greater the distance, the longer the time
required
- Molecules Size: Ions and small organic molecules such as
glucose diffuse more rapidly than do large proteins
- Temperature: The higher the temperature, the faster the rate
of diffusion
ACTIVE TRANSPORT
1) Endocytosis: The movement of large molecules INTO the cell. The cell
membrane surrounds a particle and encloses it in a vesicle. Large protein
molecules and bacteria ENTER the cell this way.
Three types:
A) Pinocytosis: (cell drinking) a type of endocytosis in which
fluids move into the cell
B) Phagocytosis: (cell eating) a type of endocytosis where
cells ingest large objects such as large chunks of dead
organic material. These are sealed off into large vacuoles.
Lysosomes then merge with the vacuole, turning it into a
digestive chamber. The products of the digestion are then
released into the cytosol.
C) Receptor-mediated endocytosis: an endocytotic mechanism
in which specific molecules are ingested into the cell.
Receptors on the plasma membrane of the target tissue
will specifically bind to ligands on the outside of the cell.
An endocytotic process occurs and the ligand is ingested.
Check out these two websites which show the processes of Endocytosis.
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/endocyta.htm
http://personal.tmlp.com/Jimr57/textbook/chapter3/cmf4a.htm
2) Exocytosis: The opposite of endocytosis. The movement of large
molecules OUT of the cell. Large molecules that are manufactured by
the cell are released this way.