Four Main Processes

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

·  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.

·  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

·  Equilibrium: the point at which a roughly equal amount of particles are entering and leaving the cell at the same rate (speed)

·  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.