How material moves in and out of the cell ?
PASSIVE TRANSPORT (does not require energy)
a. Diffusion - Diffusion is the movement of molecules, other than water, from an area of high concentration to an area of low concentration. No ATP energy is used. eg. Perfume filling a whole room. -Molecules move like this naturally, so no chemical or cellular energy is needed.
How does the size of molecules, temperature and concentration gradient affect diffusion?
- Size of the molecules, temperature, and the size of the concentration gradient affects the speed of diffusion. Large molecules diffuse slower that small ones, the greater the concentration difference the faster the rate of diffusion and increased temperature speeds up diffusion. The reason diffusion takes place faster is because of the increased number of collisions of the particles. When you heat up something the particles vibrate faster, collide more often and spread out faster. When the concentration is high, there is a greater number of particles in the solution. With a greater number of particles, there is a greater chance of collision and thus spreading out. Large molecules need more energy to begin moving and thus diffuse slower.-Lipid-soluble molecules can diffuse through the membrane easily. Oxygen and carbon dioxide pass through easily. Water passes through easily even though it is lipid insoluble. (see protein lined pores)
b. Osmosis - Flow of water from a high concentration to a low concentration across a selectively permeable membrane. Ex. Water moving from the large intestine into the blood.
c. Facilitated transport - is also the movement of molecules from a high concentration to a low concentration. Lipid insoluble substances such as glucose and amino acids are taken across by "carrier proteins". These carrier proteins are embedded in the plasma membrane and will pick up, carry and regulate the rate that specific molecules move into the cell. No chemical energy is required in this process .eg. amino acids, glucose and other breakdown products of food are absorbed by the small intestine.d. Active Transport - It is the movement of molecules across a living membrane from an area of low concentration to an area of high concentration with the aid of a carrier protein and using energy or ATP.
The diagram below represents the sodium/potassium pump a kind of active transport.
ACTIVE TRANSPORT (requires energy)
§ Two kinds of active transport:
1. Endocytosis - Surrounding a substance with the cell membrane and the subsequent formation of a vesicle to bring these substances into the cell. Energy is used.
There are two kinds of Endocytosis:
a. Phagocytosis - involves the ingestion of large food particles or cellular debris
b. Pinocytosis - involves the ingestion of fluids or dissolved particles.
2. Exocytosis - is the opposite of endocytosis. Materials are surrounded by a vesicle in the cytoplasm of the cell and released from the cell as the vesicle merges with the plasma membrane. Materials such as waste, useless cellular debris, or useful hormones for other cells are released in this manner. Energy is used.
http://www.abbysenior.com/biology/transport_across_membranes.htm
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