AQA Biology, B2 - Cells

This is the notes I made for GCSE Biology Unit 2 Topic 1, Cells.

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  • Created by: S.W
  • Created on: 21-03-11 12:37
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Biology Revision
B2.1 ­ Cells
Key Words
Light microscopes ­ an instrument used to magnify specimens using lenses and light
Electron microscopes ­ an instrument used to magnify specimens using a beam of electrons
Specialised ­ adapted for a particular function
Tissue ­ a group of specialised cells all carrying out the same function
Organ ­ a group of different tissues working together to carry out a particular function
Organ system ­a group of organs working together to carry out a particular function
Partially permeable ­ allowing only certain substances to pass through
Solvent ­ a liquid in which some solids will dissolve
Solute ­ the solid which dissolves in a solvent to form a solution
Osmosis ­ the net movement of water from an area of high concentration (of water) to an area of
low concentration (of water) along a concentration gradient
Active transport ­ the movement of substances against a concentration gradient and/or across a cell
membrane, using energy
Function of the Cells
1. Cell membrane
Controls what can enter or leave the cell
2. Nucleus
Contains the DNA which determines the characteristics of the cell
3. Cytoplasm
Site of chemical reactions in the cell, controlled by enzymes
4. Mitochondria
Site of aerobic respiration
5. Ribosome
Site of protein synthesis
6. Cell wall
Supports the cell (strengthens it, keep the cell in shape)
7. Chloroplast
Contains chlorophyll, Site of photosynthesis
8. Vacuole

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Diffusion is the net movement of molecules move from an area of high concentration to an
area of low concentration. They are said to move down a concentration gradient. Diffusion only
happens in gas and solid.
Diffusion is a passive process which means that no energy is needed but if there are more heat
energy diffusion happens quicker because the molecules move faster.
Molecules diffuse until they are evenly spaced apart and dynamic equilibrium is reached. Molecules
never stop moving.…read more

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Dilute solution have a high concentration of water molecules.
Concentrated solution has a low concentration of water molecules.
Osmosis in plant cell
If the plant cell is in a concentrated solution...
The vacuole loses water by osmosis therefore it loses pressure. The cytoplasm has
pulled away from the cell wall, the cell is plasmolysed. The plant tissue droops and wilts.
If the plant cell is in a solution of same concentration as the vacuole...
No changes occur.…read more


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