AQA Biology (full revision guide)

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Biology
Cells
Animal cells
1. Nucleus ­ contains the genetic material that controls the cell
2. Cytoplasm ­ where chemical reactions happen, contains enzymes
3. Cell membrane ­ holds the cell together and controls what goes in and out
4. Ribosomes ­ where proteins are made
5. Mitochondria ­ where respiration takes place
Plant cells
1. All the animal cell parts + :
2. Rigid cell walls ­ made of cellulose that supports the cell
3. Chloroplasts ­ where photosynthesis occurs, contains chlorophyll
4. Permanent vacuole ­ contains sap
Yeast cell
1. Nucleus
2. Cytoplasm
3. Cell wall
4. Cell membrane
Bacteria Cells
1. Cell membrane
2. Cell wall
3. Cytoplasm
4. NO NUCLEUS ­ genetic material floats around in the cytoplasm
Diffusion
The spreading out of particles from an area of high concentration to low concentration
The bigger the difference in concentration the faster the diffusion
Cell membranes control what goes in and out. They allow very small substances to diffuse through.
Smaller substances that diffuse through: water, glucose, amino acids and oxygen
Larger substances that cannot diffuse through: starch and proteins
Specialised cells
Palisade leaf cells:
1. Packed with chloroplasts to maximise photosynthesis
2. Top of the cell is even more packed
3. The cells are placed at the top of the plant to absorb the most sunlight
4. The long thin shape maximises surface area ­ the long thin sides are too make sure the most CO2 is absorbed
5. They are thin so that a lot can be packed together

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Guard cells
1. They open and close the stomata (pores) in the leaf
2. Kidney shaped
3. When the plant has a lot of water the guard cells go plump (turgid) and the stomata stays open so gas
exchange can happen
4. When the plant has low water the guard cells are flaccid and close the stomata to stop water getting out
5. They are sensitive to light and close at night
Red blood cells
1.…read more

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Digestive system is made up of
1) Glands - salivary glands and pancreas - produce digestive juices
2) stomach and small intestines - absorbs soluble food molecules
3) liver - produces bile
4) small intestine - absorbs soluble food molecules
5) Large intestine - absorbs water from undigested food - so makes faeces
Photosynthesis
Plants are made up of tissues and organs
Leaf
1. Epidermis (skin)
2. Mesophyll ­ where photosynthesis happens
3.…read more

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Too low ­ enzymes work slowly Too hot ­ enzymes get damaged
Graph looks like a loop with a peak at 37°C
Artificial conditions
Farming ­ green house creates warmer temperature
Winter add a heater ­ so that it doesn't get too hot add ventilation
Light always needed ­ farmers add artificial light to maximise the photosynthesis
Paraffin heaters ­ heats the greenhouse but also releases carbon dioxide as a bi-product
Greenhouse keeps out pests and diseases because it is enclosed
Farmer can add fertilisers…read more

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Transects ­ they show how organisms are distributed along a line
o You measure out a line and either you count the number of organisms you are interested in that touch
the line or you can use a quadrat moving along the line
To work out the population size in your area
You take the mean amount of organisms from your study (above) and you multiply it by the
total area of the place
To make your results reliable you must make them repeatable and…read more

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Enzymes and Digestion
Digestive enzymes break down big molecules into smaller ones
o Starch, protein and fats are big molecules - they are too big to pass through the walls of the
digestive system
o Sugars, amino acids, glycerol and fatty acids are smaller molecules ­ they can pass through the
digestive system
o The enzymes break down the big molecules into the smaller ones
Amylase converts starch into sugar
o Amylase is made in the:
Salivary gland
The pancreas
The small intestine
Protease converts…read more

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Respiration is the process of releasing energy from the breakdown of glucose which goes on in every cell in
your body
Aerobic respiration needs plenty of oxygen
o It is respiration using oxygen
o It is the most efficient way to release energy from glucose
o You can have anaerobic respiration ­ respiration without using oxygen but it doesn't release as much
energy
o Aerobic respiration goes on all the time in plants and in animals
o Most reactions in aerobic respiration happens inside mitochondria…read more

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While high levels of carbon dioxide and lactic acid are detected in the blood by the brain, you keep
breathing hard to fix this problem
Uses of enzymes
Enzymes are uses in biological detergents
o Enzymes are the biological ingredients in biological detergents and washing powder
o They're mainly protein-digesting enzymes (protease) and fat digesting enzymes (lipase) ­
because the enzymes break down animal and plant matter ­ they are ideal for removing stains
like food and blood
o Biological detergents are also more effective…read more

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DNA taken from a crime scene ­ is compared with a DNA sample taken from a suspect
o Paternity Testing
To see if a man is the father of a particular child
Cell Division ­ Mitosis
Mitosis makes new cells for growth and repair ­ It is when a cell reproduces itself by splitting to form two
identical offspring
o Body cells have two copies of each chromosome (one from the mother and one from the father)
o In human cells we have 23 pairs…read more

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Stem Cells
Embryonic Stem Cells can turn into any type of cell
o Some cells are undifferentiated ­ they can develop into different types of cell depending on what
instructions they're given ­ these are stem cells
o Stem cells are found in human embryos ­ all the different types of cells found in a human have to
come from those few cells in the embryo
o Adults have stem cells too ­ but they are only found in specific places (e.g.…read more

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