Year 9 plant growth

• Photosynthesis


  1. Energy and chlorophyll are needed

  2. Energy is transferred by light (usually from the Sun)

  3. Energy becomes stored in glucose
• Photosynthesis


  A series of chemical reactions that can be summarised using a word equation
• Getting water


  1. Water is taken out of the soil by the roots

  2. Roots are adapted to absorb water from a large volume of soil

  3. Root hair cells have a large surface area to help absorb water quickly

  4. Water flows up xylem vessels to the leaf
• Water is needed because mineral salts are dissolved in it, which keep plants healthy
• Water stops plants wilting by filling up their cells, and it can keep their leaves cool
• Getting carbon dioxide


  1. Air, containing carbon dioxide, diffuses into leaves through small holes called stomata

  2. Leaves are thin so carbon dioxide does not need to go far before reaching the cells that need it
• Increasing the amount of carbon dioxide around a plant can often speed up photosynthesis
• Aerobic respiration


  1. Plant cells release the energy stored in glucose

  2. Glucose + oxygen -> carbon dioxide + water
• All living cells need energy and so all living cells respire
• Aerobic respiration happens all the time, but photosynthesis can only happen when there is light
• Uses of glucose


  • Respiration to release energy
  • Making other substances that act as stores of energy (e.g. starch)
  • Making new materials for growth (e.g. cellulose, lipids, proteins)
• To make proteins, mineral salts called nitrates are needed
• New substances made by a plant are carried around the plant in phloem vessels
• Modern farming methods that can cause environmental problems

  • Clearing land of hedges
  • Using pesticides (e.g. herbicides, insecticides)
  • Using fertilizers
• Reasons for modern farming methods

  • To create more land for crops and make it easier for machinery to move around
  • To kill pests that compete with or harm the crops
  • Fertilizers contain mineral salts that help plants grow and increase yield
• Problems caused by modern farming methods

  • Destroys habitats, can cause soil erosion
  • Pesticides can kill useful organisms as well as pests, damaging food webs
  • Fertilizers can wash into streams and rivers, causing pollution
• Planting huge areas of a single variety reduces biodiversity
• Leaves


  • They are wide to have a large surface area to trap as much light as possible
  • They are arranged so that they do not shade one another
• Palisade cells


  • They are found near the upper surface of leaves
  • They are packed with chloroplasts
  • Chloroplasts contain chlorophyll, a green chemical that absorbs energy transferred by light and uses it to power photosynthesis
• Increasing the amount of light can often speed up photosynthesis
• Breeding varieties


  1. Farmers and plant breeders select a plant with certain characteristics

  2. The offspring that have the best of these characteristics are then bred from again (selective breeding)

  3. Two different varieties are bred together to try to produce offspring with characteristics from both varieties (cross-breeding)