GCSE Biology Unit 2 AQA

Revision card for things you need to know for B2

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  • Created by: asdfghjkl
  • Created on: 13-12-12 19:48


Human cells contain:

  • nucleus- contains gentic material
  • cytoplasm- contains enzymes, control chemical reactions
  • cell membrane- hold cell together and controls what goes in and out
  • mitochondria- when most of the reactions for respiration take place
  • ribosomes- where proteins are made in the cell

Plant cells contain:

  • ridgid cell wall- made of cellulose, support and strengthens cell
  • permanent vacuole- contains sap, weak solution of sugar and salts
  • chloroplasts- where photosynthesis occurs, contains chlorophyll

Yeast is a single celled organism- it has a nucleus, cytoplasm and a cell membrane surrounded by a cell wall. Bacterial cells have no nucleus- it has a cell membrane, cytoplasm surrounded by a cell wall, the genetic material floats in the cytoplasm

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Diffusion- the spreading out of particles from an area of HIGH CONCENTRATION to an area of LOW CONCENTRATION

diffusion happens in both solutions and gases because the particles in these substances are free to move around freely.

The bigger the difference in concentration the fater the diffusion rate.

Dissolved substances can move in and out of cells by diffusion but only very small molecules can diffuse through cell mebranes though eg oxygen, glucose, amino acids and water

Big molecules like starch and proteins cant fit through the membrane, particles move from where there's a high concentration to where there is a low concentration

The particles move about randomly

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Specialised Cells 1

1) Palisade leaf cells- adapted for photsynthesis

  • acked with chloroplasts, more packed at top of the cells so they are nearer the light
  • tall shape- large surface area for absorbing CO2 from the air in the leaf
  • thin shape- meaning more can be packed in at the top of the leaf

2) Guard cells - adapted to allow gas exchange and control water loss

  • kidney shape which opens and closes the stomata (pores) in a leaf
  • when plant has a lot of water- guard cells fill up and become turgid, makes the stomata open so gases can be exchanged for photosynthesis
  • when plant has little water- guard cells lose watter and become flaccid making the stomata close, helps stop too much water vapour escaping
  • thin outer walls and thickened inner walls making the opening and closing work
  • sensitive to light- close at night to water water without losing on photosynthesis
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Specialised Cells 2

3) Red bood cells- adapted to carry oxygen

  • concave shape- big surface area for absorbing oxygen, helps them to pass smoothly rhough capillaries
  • packed with haemoglobin
  • no nuclues- more room for haemoglobin

4) Sperm and egg cells- specialised for reproduction

  • egg cell- carry the female DNA and to nourish the developing embryo, contains food reserves
  • sperm- fuses with egg, egg's membrane chanes its structure to stop more sprem getting in, makes sure offspring ends up with the right amount of DNA
  • sperm function- to get male DNA to the female DNA, long tail and streamlined head to help it swim to the egg, lots of mitochondria to provide the energy needed, carries enzymes to digest through the egg cell membrane
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Cell Organisation

cells--> tissues--> organ--> organ systems--> organism

tissue: a group of similar cells that work together to carry out a particular function, e.g.muscular tissue, glandular tissue, epithelial tissue. it can include more than one type of cell

organs: a group of different tissues that work together to perfom a certain function e.g. the stomach is made up of muscular tissue, glandular tissue and epidthelial tissue

organ systems: a group of organs working together to perform a particular function e.g. the digestive system  breaks down food and is made up of organs such as glands, stomach, small intestine, liver

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Plant Structure and Photosynthesis

plant cells are organised into tissues and organs too

e.g. mesophyll tissue-where photosynthesis in a plant occurs, xylem and phloem- transports things like water, mineral ions and sucrose, epidermal tissue- over the whole plant

carbon dioxide + water ------sunlight-----> glucose + oxygen

photosynthesis produces glucose using sunlight

  • happens inside chloroplasts
  • chloroplasts contain chlorophyll- which aborbs sunlight and uses is energy to covert CO2 and water into glucose and oxygen (as a by product)
  • happens in leaves of all green plants
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The Rate of Photosynthesis

affected by light intensity, CO2 concentration and the temperature.

limiting factor - when rate becomes constant pondweed experiment!


light intensity- increase, constant

CO2 concentration- increase, constant

temperature- increase optimum temp decrease

Greenhouse can artificially create the ideal conditions for framing

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How Plants Use Glucose

1) For respiration

  • this releases their enrgy which enables them to convert the rest of the glucose into various other substances which they can use to build new cells and grow
  • gather minerals from the soil

2) Making cell walls

  • converted to cellulose from making strong cell walls, especially in a rapidly growing plant

3) Making proteins

  • glucose is combined with nitrate ions (absorbed from the soil) to make amino acids which are then made into proteins

4) Stored in seeds

  • turned into lipids (fats and oils) for storing in seeds
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How Plants Use Glucose 2

5) stored as starch

  • turned into starch and stored in roots, stems and leaves ready to use when photosynthesis isnt happening eg winter
  • starch is insoluable- better for storing that glucose
  • new plants can be grown- eg potatoes and parsnips
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Distribution of Organisms

Organisms live in different places

  • habitat is a place where an organism lives
  • the distribution of an organism is where an organism is found
  • where an organism is found is affected by environmental factures such as: temperature, availbility of water, availability of oxygen and CO2, availability of nutrients and the amount of light
  • you can stude the distribution of an organism by:
  • 1) measure two quadrats of two sample areas and compare
  • 2) study how the distribution changes across an area (quadrats on a transect)

Use quadrats to study the distribution of small organisms

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Distribution of Organisms 2

When collecting environmental data, you need to think about

1) reliablilty

  • are results repeatable and reproducible?
  • to make sure your results are reliable you need to take a large sample size and use random samples

2) Validity

  • the results must be reliable
  • control all variables
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Enzymes are catalysts produced by living things there act as biological catalysts.

A catalyst is a substance which increase the speed of a reaction without being changed or used up in the reaction

Enzymes are all proteins and so are made up of chains of amino acids. Proteins also act as structural components of tissues, hormones and antibodies. Enzymes have special shapes so they can catalyse reactions

Enzymes need the right temperature and pH

  • changing the temp = changes rate of enzyme catlysed reaction
  • temp increase, rate increase, too hot enzyme's special shape bonds break =denature
  • if pH is too high or too low, the pH interfers with the bonds holding the enzyme together- changes shape = denature
  • all enzymes have optimum pH- ften pH 7 but not always, eg pepsin is an enzyme use to break down proteins in the stomach. It's well suited to the acidic conditions there.
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Enzymes and Digestion

Digestive enzymes break down big molecules into smaller ones eg STARCH, PROTEINS AND FATS into SUGARS, AMINO ACIDS, GLYCEROL and FATTY ACIDS


amylase made in: salivary glands, pancreas and small intestine


protease made in: stomach, pancreas and small intestine


lipase made in: pancreas, small intestine

Bile is produced in the liver and neutralises stomach acid and emulsifies fat. it is stored in the gall bladder before released into small intestine. Bile is alkaline- enzymes in small intestine work best in alkaline soultions

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Enzymes and Digestion 2

The breakdown of food is catalysed by enzymes... which are produces in glands and in the gut lining. Different enzymes catalyse the breakdown of different food molecules.

salivary glands-produce amylase enzyem in saliva

liver- produce bile- neutralises stomach acic and emulsifies fat

gall bladder- where bile is stred before released into small intestine

large intestine- excess water is absorbed

rectum- faeces are stored before they exit via anus

small intestine- produces prtease, amylase and lipase enzymes to complete digestion, digested food is absorbed into blood

pancreas- produces amylase, protease and lipases enzymes- releases into small intestine

stomach- produces protease enzyme and pepsin, produces hydochloric acid to kill bacteria and to give the right pH for the protease enzyme to work.

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Ayman Ilham


good, but please correct any typing mistakes! :)

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