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AQA GCSE Biology ­ Unit 2 summary notes




B2.1 Cells and Cell Structures

Summary
All living things are made up of cells. The structures of different types of cells are related
to their functions. To get into or out of cells, dissolved substances have to cross the cell
membranes.

Cells…

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AQA GCSE Biology ­ Unit 2 summary notes






Cells may be specialised to carry out a particular function.

Examples:


Movement into and out of cells

To get into or out of cells, dissolved substances have to cross the cell membranes.
Solutes = particles in solution eg glucose, sodium ions, chloride…

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AQA GCSE Biology ­ Unit 2 summary notes




muscular tissue, to churn the contents
glandular tissue, to produce digestive juices
epithelial tissue, to cover the outside and the inside of the stomach.

The digestive system is one example of a system in which humans and other mammals
exchange substances with…

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AQA GCSE Biology ­ Unit 2 summary notes




light energy
carbon dioxide + water glucose + oxygen

Where does photosynthesis happen?
Leaves are the main site of photosynthesis.
Photosynthesis mainly in occurs in the mesophyll cells.
These cells contain lots of chloroplasts.
Chloroplasts contain chlorophyll.

A palisade mesophyll cell:



Factors…

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AQA GCSE Biology ­ Unit 2 summary notes




The glucose produced in photosynthesis may be converted into insoluble starch for
storage
Plant cells use some of the glucose produced during photosynthesis for respiration.
Some glucose in plants and algae is used:
to produce fat or oil for storage
to produce…

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AQA GCSE Biology ­ Unit 2 summary notes




o It can also become limited in water, so aquatic organisms struggle to respire
and survive.
availability of carbon dioxide:
o Carbon dioxide is essential for photosynthesis.
o This can become limited in an environment where there are many plants.
o This…

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AQA GCSE Biology ­ Unit 2 summary notes




Or, if a particular factor leads to zonation
Eg the effect of the tide and coverage by water on a rocky seashore.

Method
i) Choose the start and end positions of the transect.
ii) Determine the direction and length of the transect.…

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AQA GCSE Biology ­ Unit 2 summary notes





Arrange the data in order: 3,5,6,6,8,9,9,9

The median is the middle number, or the mean of the middle two numbers.

The median number of slugs per brick = 6 + 8 = 7 slugs per brick
2

Mode:
The most common value…

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AQA GCSE Biology ­ Unit 2 summary notes




o They have a specific shape that attaches to antigens.
o Antigens are chemicals that pathogens carry or release.
o The antibody prevents the pathogens from damaging our own cells.

Catalysts:
o Proteins act as biological catalysts called enzymes.
o These control…

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AQA GCSE Biology ­ Unit 2 summary notes




Some enzymes work outside the body cells.
These are called extracellular enzymes.
The digestive enzymes are produced by specialised cells in glands and in the lining of
the gut.
The enzymes then pass out of the cells into the gut where they…

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