Photosynthesis

• Organs of a plant

  • Root
  • Stem
  • Leaf
  • Flower
• Word equation for photosynthesis

  1. Carbon dioxide + water

  2. Glucose + oxygen
• Symbol equation for photosynthesis

  CH2O + 6O2
• Factors affecting the rate of photosynthesis


  • Light intensity
  • Carbon dioxide concentration
  • Temperature
  • Amount of chlorophyll
• Limiting factor


  Anything that is in short supply that prevents photosynthesis happening at its maximum rate
• Why the rate of photosynthesis is affected by temperature


  The process of photosynthesis is controlled by enzymes
• Parts of a plant that can be eaten

  • Roots (e.g. potato, carrot)
  • Stem (e.g. celery, rhubarb)
  • Leaf (e.g. lettuce, cabbage)
  • Flower (e.g. broccoli, cauliflower)
  • Seeds (e.g. hazelnuts, pumpkin)
  • Fruits (e.g. apple, pear)
• Plants produce oxygen that living things need to breathe
• Plants start every food chain (as producers) and are therefore an essential food source for humans and other animals
• Photosynthesis


  A process in which green plants use sunlight to make their own food
• Chloroplast


  Where photosynthesis takes place in a plant cell
• Photosynthesis


  Carbon dioxide + water → glucose + oxygen
• Temperature increases

  Rate of photosynthesis increases
• Testing a leaf for starch

  Heat leaf in boiling water

  2. Heat leaf in boiling ethanol

  3. Wash and spread on white tile

  4. Add iodine solution
• Role of starch in plants

  As an energy store, or it can be converted to glucose and used for respiration, making fruits, cell walls and proteins
• Root hair


  • Large surface area to increase the rate of absorption
  • Contains lots of mitochondria, which release energy from glucose during respiration in order to provide energy
• Water transport in plants

  1. Xylem transports water and minerals from the roots to the leaves

  2. Phloem transports glucose and amino acids from the leaves to the rest of the plant
• Minerals plants need


  • Nitrates
  • Phosphate
  • Potassium
  • Magnesium
• How plants absorb minerals

  Through the roots
• Phosphorus deficiency in plants

  Makes young leaves look purple and roots grow poorly
• Magnesium deficiency in plants

  Makes leaves look yellow
• Plant hormones


  • Auxin
  • Gibberellins
  • Ethylene
• Function of plant hormones

  To promote growth in plants
• Tropism


  A plant response to a stimulus eg. phototropism-a shoot grows towards light
• Function of auxin

  Auxins control the growth of plants by promoting cell division and causing elongation in plant cells (the cells get longer)
• Importance of plant hormones in agriculture

  • Can be used as weed killers
  • To promote plants to grow taller
  • To control the ripening of fruit
• Most photosynthesis happens in the leaves
• Why the palisade layer is at the top of a leaf

  Palisade cells need to absorb sunlight as they contain many chloroplasts for photosynthesis
• Why leaves have a large surface area

  • To absorb as much light as possible
• Why leaves have veins

  To transport water and glucose around a plant
• Why leaves have a waxy surface

  To reduce water loss
• Why leaves are thin

  To allow gases to diffuse in and out easily
• What do guard cells do

  Open and close the stomata
• Gases that go in and out of the stomata

  • In-Carbon Dioxide
  • Out-Water Vapour, Oxygen
• Why stomata are only found on the bottom of a leaf

  To prevent water loss from the leaf