Biology AQA Unit 2

Biology AQA Unit 2 all topics

  • Created by: lrmm
  • Created on: 20-05-10 21:34


  • Most animal cells contain a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
  • Plant cells contain all the structures seen in animal cells as well as a cell wall and chloroplasts and a permanent vacuole filled with sap.
  • Enzymes control the chemical reactions inside cells.
  • Cells may be specialised to carry out a particular function. E.g fat cells, cone cells
  • Diffusion is net movement of particles from an area where they are at a high concentration to an area where they are at a lower concentration.
  • Osmosis if the diffusion/movement of water from a high concentration to a low water concentration through a partially permeable membrane.
1 of 7


  • carbon dioxide+water+(light energy)=glucose+oxygen
  • During p/s light energy is absorbed by chlorophyll in chloroplasts. used to convert carbon dioxide and water into glucose. Oxygen released as by-product.
  • Leaves are well adapted to allow maximum p/s to take place.
  • Limiting factors=light, temp, carbon dioxide levels.
  • We can artificially change the environment in which we grow plants. we can use this to observe the effect of different factors on the rate of p/s.
  • Plant cells use some of the glucose the make in p/s for respiration.
  • Some of the soluble glucose produced during p/s is converted into insoluble starch for storage.
  • Plant roots absorb mineral salts including nitrate for healthy growth and magnesium for greenness.
  • If mineral ions are deficient plant develops symptoms because it cannot grow properly.
2 of 7

Pyramids of Biomass

  • Radiation from the sun is the main source of energy for all living things. The Sun's energy is captured and used by plants during p/s.
  • The mass of living material at each stage of a food chain is less then the previous stage. The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
  • The amount of biomass and energy gets less and less as some material lost in waste, some used up in respiration for movement and maintaining body temp.
  • The efficiency of food production can be improved by reducin the number of stages in our food chains. It would be most efficient if we just ate plants.
  • If you stop animals moving and keep them warm, they lose a lot less energy.
3 of 7

Decay and Carbon

  • Living organisms remove materials from the environment as they grow. they return them when they die through the action of decompose rs.
  • Dead materials decay because they are broken down(digested) by microorganisms
  • De composers work quickly in warm moist conditions and good oxygen supply
  • The decay process releases substances which pants need to grow.
  • In a stable community the processes remove materials and are balanced by the processes which return materials.
  • The constant cycling of carbon in nature is known as the carbon cycle.
  • Carbon dioxide is removed from the atmosphere by p/s and returned through respiration and combustion.
  • The energy originally captured by green plants is eventually transferred back into plants, into decompose rs or as heart into environment.
4 of 7


  • Catalysts increase the rate of chemical reactions. Enzymes are biological catalysts.
  • Enzymes are protein molecules made up of long chains of amino acids. the chains are folded to from active site where the substrate binds with the enzyme.
  • Enzyme activity is affected by temp and PH
  • High temp and wrong PH can affect shape of active site and stop it working.
  • Enzymes catalyse processes such as respiration, p.s and protein synthesis.
  • Aerobic respiration - glucose+oxygen=carbon dioxide+water +energy
  • Enzymes catalyse the breakdown of large food molecules into smaller molecules during digestion.
  • Digestive enzymes are produced inside cells but they work outside cells in gut.
  • Enzymes in the ribosomes catalyse the build up of proteins from amino acids.
  • The enzymes of the stomach work best in acid conditions.
  • The enzymes made in pancrea and S.I work best in alkaline conditions.
  • Bile produced by the liver neutralises acid and emulsifies fats.
  • Biological detergents may contains proteases and lipase's.
  • Proteases, carbohydrates and isomerase are used in food industry.
5 of 7


  • The internal conditions of your body have to be controlled to maintain a constant internal environment
  • Poisonous waste products are made all the time and need to be removed.
  • Carbon dioxide is produced during respiration and leaves body via lungs
  • Urea is produced by your liver as excess amino acids are broken down and removed by kidneys in urine.
  • Body temp must be mainted at level enzymes work best. monitored and conrollted my thermoregulatory centre in your brain.
  • Body respons to coold you down or warm you up if core body temp falls.
  • Blood glucose concentration is monitored and controlled by pancreas
  • Insulin and glycogen are hormones involved in controlling blood sugar concentration. Insulin converts glucose to glycogen; glycogen- glycogen-glucose
  • In diabetes the blood glucose may rise to fatally high levels because pancreas does not secrete enough insulin. can be treated by infections before meals.
6 of 7

Cell division and growth

  • Body cells divide by mitosis to produce identical cells for growth, repair and replacement.
  • Most types of animal cells differentiate at an early stage of development. Many plant cells can differentiate throughout their life.
  • Embryonic stem cells and adult stem cells can be made to differentiate into many different types of cells.
  • Cells in reproductive organs divide to form gametes
  • Body cells have two sets of chromosomes and gametes have only one
  • Gametes are formed by meiosis
  • Sexual reproduction gives rise to variety because genetic information from two parents is combined.
  • Gregor Mendel was first person to suggest separately inherited factors (genes)
  • Chromosomes are made up of large molecules of DNA. A gene is a small section of DNA which codes for a particular combination of amino acids which made a specific protein.
  • In humans, ** femal XY mal. some features controlled by single gene. Genes have different forms called alleles, dominant/recessive.
  • Huntington's disease is caused by dominant cystic fibrosis caused by recessive
7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »