cell membrane and cell transport mechanisms

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cell membrane and cell transport mechanisms

Post by mommyof4 » Wed Nov 16, 2005 5:26 pm

The structure of a cell membrane is described as a fluid mosaic.Explain this in terms of the cell membrane structure?

Why is it important for cells to control the movement of the substances across their cell membranes?

Why does a cell placed in a hypertonic solution tend to shrink?

Why does a cell placed in hyptonic sloution tend to expand?

Why do cells need to maintain a high surface area to volume ratio?

Why are cell membranes described as semi-permeable?

Describe the following transport mechanisms. Include the energy requirements of each and examples of materials transported.

A: Osmosis
B: Diffusion
C: Active transport

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Post by MrMistery » Wed Nov 16, 2005 7:06 pm

Here's a crazy thought. Read the textbook.
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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cell membrane and cell transport mechanism.

Post by lara » Thu Nov 17, 2005 10:44 am

Molecules and ions can be moved against their concentration gradient, but this process, called ACTIVE TRANSPORT, requires the expenditure of energy (usually from ATP).

DIFFUSION refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. Consider two containers of gas A and B separated by a partition. The molecules of both gases are in constant motion and make numerous collisions with the partition. If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules. In time a uniform mixture of A and B molecules will be produced in the container.
The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.This is a passive method as no energy is spent.
OSMOSIS: the movement of water molecules from an area of high concentration to an area of low concentration.
HYPERTONIC Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
HYPOTONIC Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
CONTROL- refer effect of osmosis
the membrane is very specific about the molecules that enter the cell.so,partially or semi-permeable.
the membrane is flexible.it can shrink,form vesicles that pinches off and is constantly under repair.
for examples:
active transport-Na K pump
diffusion-oxygen moves into the tissues( where its conc. is low) from blood(comin' from lungs).the conc.of oxygen is high in the blood.

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