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Key Area 1.2

Revision for Key area 1.2 Transport across membranes

Name two components of the cell membrane Proteins and phospholipids
Describe the permeability of the cell membrane Selectively permeable
What is meant by selectively permeable? It lets some substances pass through rapidly and some substances pass through more slowly, but prevents other substances passing through it at all.
Define diffusion Diffusion is the net movement of molecules from an area where they are at a higher concentration to areas where they are at a lower concentration.
Does diffusion require energy? No
Define osmosis The net movement of water from a region of high water concentration to a region of low water concentration through a selectively permeable membrane.
Does osmosis require energy? No
What happens to an animal cell when placed in a high water concentration? Water moves into the cell by osmosis until the cells swell and burst
What happens to an animal cell when placed in a low water concentration? Water moves out of the cell by osmosis and the cell shrinks
What happens to a plant cell when placed in a high water concentration? Plant cells placed in a solution with a high water concentration compared to their contents (eg pure water) will gain water by osmosis and swell up until their cytoplasm and cell membrane are pushing against their cell wall. They are said to be turgid.
What happens to a plant cell when placed in a low water concentration? Plant cells placed in a solution with a low water concentration compared to their contents (concentrated sugar solution) will lose water by osmosis. Their cell membranes will peel away from their cell walls and they are said to be plasmolysed.
Define active transport Movement of molecules and ions from an area of low concentration to an area of high concentration (against a concentration gradient) which requires energy.
Created by: MissBryce
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