B2 AQA Revision Notes

Still waiting for my results back but I made these notes for my exam in January and they helped me a lot.

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Biology 2
Cells
Animal and Plant Cells
Animal Cells
o Nucleus ­ contains genetic information for making new cells or organisms ­ controls the activities
of the cell
o Cytoplasm ­ the liquid gel where all of the chemical reactions needed take place
o Cell Membrane ­ controls the passage of substances in and out
o Mitochondria ­ releases energy during respiration ­ found in the cytoplasm
o Ribosomes ­ where protein synthesis takes place ­ all the proteins needed in a cell are made
here
Plant Cells
o Cell Wall strengthens the cell and gives it support
o Chloroplasts ­ found in all the green parts of the plant ­ absorb the light energy to be used in
photosynthesis
o Vacuole ­ a space in the cytoplasm ­ filled with cell sap ­ important to keep the cells rigid to
support the plant
Chemical Reactions in cells
o Each enzyme controls the rate of a specific reaction so they don't get mixed with other reactions
o Found in all parts of the cell ­ particularly the mitochondria
o Enzymes controlling the reactions of...
Respiration ­ found in mitochondria
Photosynthesis ­ found in chloroplasts
Protein synthesis ­ found on the surface of the ribosomes
Specialised Cells
Cells become specialised to carry out one specific job.
Fat Cell
o Storage cell
o Very little cytoplasm ­ leaves more room for the fat
o Very few mitochondria ­ use little energy
o Can expand up to 1000 times its original size
Cone cell
o Found in human eye
o Make it possible to see in colour
o The outer segment is filled with a chemical ­ visual pigment ­ changes chemically in coloured light
­ then has to be changed back which uses up a lot of energy
o Middle segment is packed with mitochondria ­ produces lots of energy
o The last part of the cell has a synapse ­ connects to the optic nerve which carries the impulses to
the brain
Root hair cell
o Found near to the tips of growing roots
o Enables the plants to take in the water that need
o Increases the surface area for water to move into the cell

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A large permanent vacuole ­ affects the movement of the water across the cell
o Root hair cells are positioned close to the xylem tissue ­ allows the water to be carried up to the
rest of the plant
Sperm Cell
o Long tails so they can swim
o Middle section is full of mitochondria
o Acrosome ­ contains digestive enzymes for breaking down the outer layers of the egg
o Large nucleus ­ genetic information can be passed on
How do substances get in…read more

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Uses energy from respiration
How Plants Produce food
Photosynthesis
Carbon dioxide + water (+light energy) glucose + oxygen
Chloroplasts contain chlorophyll
Some of the glucose is used immediately by the cells in the plant ­ stored as starch
Iodine starch test for photosynthesis
Leaves are adapted
o Broad ­ big surface area for light to fall on
o Contains chlorophyll to absorb the light energy
o Air Spaces to allow carbon dioxide to get in and oxygen to get out
o Veins which bring water…read more

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How Plants use glucose
Glucose is converted to starch for storage
Plants use some of the energy to combine sugars with nutrients to create amino acids
o Built up fats and oils to make the food store in the seeds
Amino acids are built into proteins to be used in the cells
Phloem
o Made of living tissue
o Transports sugars to the rest of the plant
o Transported to growing regions
o Transported to storage organs
Xylem
o Carries water and mineral ions from…read more

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Energy Flows
Pyramids of biomass
Biomass is the mass of living material in an animal or a plant
Usually measured in grams as the dry mass of biological material
The biomass at each stage is less than the previous stage
o Not all organisms at one stage are eaten by the stage above
o Some material that is taken in is then passed out as waste
o Some of the biomass that is eaten is used in respiration
The biomass that is passed on through…read more

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Reactions are controlled by enzymes
Most microorganisms grow better in damp conditions
o Moisture makes it easier to dissolve the food and prevents the decomposers from drying out
Some microbes work without oxygen
Decay happens faster with a surplus of oxygen
The Carbon Cycle
The amount of carbon on the Earth is fixed
Some carbon is locked up in fossil fuels and it released when burnt
Photosynthesis
o Plants use the carbon dioxide in the air
o They use it to make carbohydrates which make…read more

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Enzymes
Enzyme Structure
Activation energy ­ the minimum amount of energy a particle must have to react
Lower the temperature to slow reactions
Catalysts are used to speed up the reactions
Enzymes are biological catalysts
Enzymes are involved in
o Building larger molecules from small ones
o Changing one molecule into another
o Breaking down large molecules to smaller ones
Enzymes are large protein molecules ­ long chains of amino acids
The active site is where the reaction occurs ­ anything that changes the active…read more

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Mitochondria ­ the site of respiration
o Folded inner membrane which increases the surface area for the enzymes to work in
o Cells that need a lot of energy have lots of mitochondria
o Cells that don't need a lot of energy don't have lots of mitochondria
Enzymes in digestion
Enzyme What does it break down? Where is it made? Where does the digestion happen?
Carbohydrases Starch into sugars Salivary glands, Small intestine (mostly) and the
(amylase) (glucose) pancreas, small mouth
intestine
Protease Meat into…read more

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Passed into blood stream to the lungs
o Urea
Produced in the liver when excess amino acids are broken down
Passed from liver cells to the blood
Filtered by kidneys
Stored in bladder
o Maintaining body balance
Water and ions lost in sweat and urine
If content is wrong too much water may move in and out of cells
Controlling body temperature
Control relies on the thermoregulatory centre ­ brain
o Receptors sensitive to temperature change
o Monitor the temperature change of the blood
o…read more

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Treatment
Manage diet
Insulin injections
Inheritance
Cell division and growth
Mitosis
o Produces identical daughter cells
o Asexual reproduction
o Chromosomes line up in the middle
o Split
o Exact copies are made of the chromosomes to make them a pair
o Cell membrane forms down the middle
o Specialized cells can divide ­ only to replace damaged or dead cells
Stem cells not differentiated
Once differentiation has occurred it cannot produce different cells
Stem Cells
Can differentiate and form other cells when they are…read more

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