AP Biology

Cells transport substances across their membrane. Choose THREE of the following four types of cellular
Osmosis Active transport Facilitated diffusion Endo/exocytosis
For each of the three transport types you choose,
a. Describe the transport process and explain how the organization of cell membranes functions in the movement of specific molecules across the membrane; and
b. explain the significance of each type of transport to a specific cell ( you may use different cell types as examples)

This is one of my AP practice homeworks, and i don't know how to do this one.Please help.

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  1. Sorry can't help you. I need help on this subject too.

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  2. Osmosis:
    A) Is the movement of water from higher concentration to lower concentration. Water molecules are small enough to diffuse through the semi-permeable cell membrane, and so it requires no energy from the cell.
    B) Osmosis is used in every cell of your body to bring water in and get it out. If placed in a pure water (hypotonic solution) cells would burst because water would continually come in. (Red blood cells must maintain their turgor pressure/shape by having the right amount of water)

    Active Transport:
    A) Is transport of substances in and out of cells that requires energy from the cell because it goes against the concentration gradient. Proteins on the membrane help in active transport
    B) The sodium-potassium pump is the classic example, and is in every cell. The membrane has proteins in it onto which 3 Na ions attach from inside, and 2 K ions from outside. Using the cells energy the protein changes shape and throws the Na out and brings the K in.

    Facilitated Diffusion:
    A) Not all molecules are small enough or have the right charge (polar) to go through the membrane. Proteins on the cell membrane help in transporting larger substances in and out. But unlike the active transport, no energy is used because the diffusion still occur down the concentration gradient.
    B) Helps carry glucose into cells for them to use it as energy.

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