B2 Revision notes

Revision notes for the 2nd module of GCSE AQA biology

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  • Created on: 25-04-10 10:30
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Specialised Cells
Animal cells ­ Nucleus - contains genetic material that controls the activities of cell
Cytoplasm ­ gel like substance ­ contains enzymes that control chemical reactions
Cell membrane ­ holds cell together and controls what goes in and out
Mitochondria ­ in cytoplasm ­ reactions for respiration ­ energy ­ cells need to work
Ribosome's ­ where the proteins are made in the cell
Plant cell ­ all the bits of animal ­ few extra
Rigid cell wall made of cellulose
Permanent vacuole ­ contains cell sap, weak solution of sugar & salt
Chloroplasts ­ where photosynthesis occurs, which makes food for the plant, contains green
substance called chlorophyll
Palisade leaf cells are adapted for photosynthesis ­ more are crammed into top of cell to get
near to light
Tall shape means a lot of surface area exposed for absorbing CO2
Thin shape means you can pack a lot into the top of the leaf
Palisade layer ­ where most photosynthesis happens
Guard cells are adapted to open and close the pores in a leaf
So gases can be exchanged for photosynthesis
Closes when shortage of water ­ stops too much water vapour escaping
Red blood cells adapted to carry oxygen
Concave shape gives big surface area to carry oxygen, also so it passes smoothly
Packed with haemoglobin
No nucleus ­ to make more room for haemoglobin
Blood is counted as a tissue
Egg cell carries female DNA and nourishes developing embryo ­ huge food reserves
When fertilised eggs membrane instantly changes to stop more sperm getting in
Lot of mitochondria in sperm to give it energy
Sperm carries enzymes to digest through the egg cell membrane

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Diffusion is the passive movement of particles from an area of high concentration to an area
of low concentration
Membrane of cell holds cell together but also lets stuff in and out
Osmosis is the movement of water molecules across a partially permeable membrane from a
region of high water concentration to a region of low water concentration
Special case of diffusion
Photosynthesis happens inside chloroplasts
Chloroplasts contain chlorophyll which absorbs sunlight and uses its…read more

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Pyramid of Biomass
Energy is passed on along the pyramid, lost in Respiration, excretion.…read more

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Enzymes are catalysts produced by living things but it has to be at the right
A catalyst is a substance which increases the speed of a reaction, without being
changed or used up in the reaction.…read more

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Uses of Enzymes
Used to change foods
Proteins in baby foods are pre digested so they're easier for baby to digest
Carbohydrate digesting enzymes (carbodrases) can be used to turn starch syrup into
sugar syrup
Glucose syrup fructose syrup ­ good for slimming foods
Enzymes very useful in industry ­ Speed up reactions without the need for high
temperatures and pressures.
ADVANTAGES ­ they are specific, low temperature, low energy, low cost. Work for a
long time, biodegradable ­ less pollution.…read more

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Homeostasis is the maintenance of a constant internal environment.
6 things need to be controlled
BODY TEMPERATURE ­ too hot ­ hairs lay flat, sweat produced more blood closer to
surface to quicken heat loss.…read more

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That determines what cell it will be ­ red blood, skin
Everyone's DNA is different ­ except identical twins
Cell division - MITOSIS
Mitosis makes new cells for growth and repair
MITOSIS is when a cell reproduces itself by splitting to form two identical offspring
Body cells have 2 copies of each chromosome ­ one from `mother' one from `father'. So
humans have 2 copies of chromosome 1,2,3,4,5.... etc.
23 pairs of chromosomes from human cell, 23rd pair are different.…read more

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Mitosis and meiosis are two ways that cells reproduce.
By mitosis a cell splits to create two identical copies of the original cell.…read more

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Most cells are specialised for the job they do
Differentiation is the process by which a cell changes to become specialised for its job
Stem cells are undifferentiated and can cure many diseases as they can change and replace
faulty cells in the body
Adults have stem cells, but only found in certain places ­ bone marrow.…read more

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Cystic Fibrosis is caused by a recessive allele, so if the diagram above were a human, ff
would have it
Embryos can be screened for genetic disorders, but there is a big debate!
PRO ­ it will stop people suffereing, there are laws to stop it going too far,during IVF most
embryos are destroyed anyway, treating disorder costs loads of money
AGAINST ­ people could eventually pick desirable embryo's e.g.…read more


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