biology unit 2 gcse revision notes higher tier

biology unit 2 gcse revision notes higher tier

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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
Cells are the smallest unit of life.
All living things are made of cells.
Most human cells, like most other animal cells, have the following parts:
o nucleus
o cytoplasm
o cell membrane
o mitochondria
o ribosomes
Plant and algal cells also have:
o cell wall
o chloroplasts
o permanent vacuole
What do these structures do?
Nucleus ­ controls the activities of the cell.
Cytoplasm ­ where most of the chemical reactions take place.
Cell membrane controls the passage of substances in and out of the cell.
Mitochondria where most energy is released in respiration.
Ribosomes where protein synthesis occurs.
Cell wall ­ made of cellulose and strengthens plant cells.
Chloroplasts absorb light energy to make food in plant cells.
Permanent vacuole filled with cell sap in plant cells.
Yeast
Yeast is a singlecelled organism.
The cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall.
Bacteria
Bacterium is a singlecelled organism.
A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall.
The genes are not in a distinct nucleus.
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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 ions.
Solvent = liquid in which the particles are dissolved eg water.
Solute and solvent molecules move around randomly.
Solutes can move into and out of cells by diffusion.…read more

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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 the environment.…read more

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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.…read more

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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 cellulose, which strengthens the cell wall
to produce proteins:
o To produce proteins, plants also use nitrate ions that are absorbed from the
soil.
B2.…read more

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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 will reduce the rate of growth of plants.
Collection of quantitative data
Sampling:
To study the distribution of a species you need to find out:
o The size of the area being studied.…read more

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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.
iii) Lay down a tape or string to mark out transect.
iv) Sample the organisms along the line.
v) Perform further parallel transects to ensure results are reliable.…read more

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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 in a list.
In the case of the slugs this would be 9 slugs per brick
B2.5 Proteins
Summary
Proteins have many functions, both inside and outside the cells of living organisms.…read more

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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 and sequence all of the reactions that occur inside and
outside cells in all living organisms.
Enzymes structure and function
Enzymes are biological catalysts.
Catalysts increase the rate of chemical reactions.…read more

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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 come into contact with
food molecules.
They catalyse the breakdown of large molecules into smaller molecules.
Digestion is the process where food is broken down into substances the body can
absorb.…read more

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