bioenergetics

• meiosis

  result in sex cells (gametes)

  have half of original chromosome cells

  sexual reproduction

  doubles --> splits --> halves
• mitosis

  produces identical cells

  same chromosomes

  same genetic info

  asexual reproduction

  doubles --> splits
• differentiation

  stem cells become specialised cells by mitosis

  in animals cells it happens early

  in plant cells it happens throughout its life - move a cell into a different area and it will re-differentiate
• cloning

  produce identical offspring

  easier to clone a plant

  cloning of animals have to be done at embryo stage

  cloning of plants can be done at any time
• fertilisation

  fusion of sex cells

  body cells twos (pair) sets of chromosomes while sex cells only have one (single)
• bone marrow

  good source of stem cells
• get stem cells from umbilical cord and not foetus
• cell cycle

  active cell division

  interfase -> no cell division taking place, replicating dna, carrying out normal cell activites

  cell gets bigger
• cell cycle slows down after puberty
• tumour formation

  divides rapidly

  mitosis is fast and interface is small
• benign

  grows in one place

  it does not affect other tissues

  grows rapidly and puts pressure on other cells or tissues around it
• malignant (cancer)

  can travel around the body and damage other cells / tissues

  break apart other cells

  tumour might split and go into bloodstream meaning it spreads
• causes of cancer

  • result of mutations
  • genetic info is changing
  • chemicals eg. tar in tobacco
  • carcinogens
  • ionising radiation - eg. UV light, x-rays
  • virus infections
• during photosynthesis


  • light is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and in algae
  • light is used to covert carbon dioxide (from air) and water (from soil) into sugar (glucose)
  • oxygen is released as a by product
• rate of photosynthesis may be limited by

  • low temperature
  • shortage of carbon dioxide
  • shortage of light
• uses of glucose


  • respiration
  • converted into insoluble starch for storage
  • used to produce fat or oil for storage
  • used to produce cellulose, which strengthens the cell wall
  • used to produce proteins
• to produce proteins plants also use nitrate ions that are absorbed from the soil
• in flowering plants:

  • carbon dioxide enters leaves by diffusion through the stomata
  • most of the water and mineral ions are absorbed by roots
• surface area to volume ratio of leaves is increased by the flattened shape and internal air spaces
• stomata obtains carbon dioxide and removes oxygen and controls water loss
• water loss


  • evaporation is more rapid in hot, dry and windy conditions
  • if plants lose water faster than it is replaced by the roots, the stomata can close to prevent wilting
• flowering plants have separate transport systems

  • xylem tissue transports water and mineral ions from the roots to the stem and leaves
  • the movement of water from the roots through the xylem and out of the leaves is called the transpiration stream
  • phloem tissue carries dissolved sugars from the leaves to the rest of the plant including the growing regions and the storage organs - this is called translocations