Cells

Cell membrane

A cell membrane is made of fats.

What does it do ?
• Holds cell content together.
• Partially permeable
• Controls chemicals entering and leaving the cell.
• The proper name for a cell membrane is plasma membrane.

Diffusion gaseous exchange.
• All cells need to take in oxygen, and excrete carbon dioxide.
• It is easy for these small molecules to fit through the tiny pores of the cell membrane.
• This is called diffusion.
• The overall movement of substances diffusing across the membrane is from of region of their high concentration to a region of their low concentration.
• We say the movement is down the concentration gradient.

Osmosis
• osmosis is a special kind of diffusion for water only.
• Needed as a solvent for chemical reactions.
• Needed to transport dissolve chemicals onto and out of the cell and across the cytoplasm.

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