Plant nutrition

• Photosynthesis process 


  1. Energy from sunlight is absorbed by chlorophyll

  2. Green plants use this energy to make the carbohydrate glucose from the materials carbon dioxide and water

  3. Oxygen is made and released as a waste product
• Photosynthesis


  The process by which plants manufacture carbohydrates from raw materials using energy from light
• Products of photosynthesis


  • Glucose used as a source of energy in respiration
  • Starch for storage
  • Lipids for an energy source in seeds
  • Cellulose to make cell walls
  • Amino acids (used to make proteins) when combined with nitrates and other mineral ions absorbed by roots
• Glucose produced in photosynthesis won't affect osmosis in cells
• Glucose produced in photosynthesis is converted into sucrose for transport around the plant
• Glucose produced in photosynthesis is used in respiration to release energy for the cell
• Glucose produced in photosynthesis is converted into fats and oils for energy storage in seeds
• Photosynthesis equation


  Carbon dioxide + Water -> Glucose + Oxygen
• The reactants (carbon dioxide and water) are taken up by the roots and transported through the xylem to the leaves
• The balanced chemical equation for photosynthesis is 6CO2 + 6H2O -> C6H12O6 + 6O2
• Limiting factors for photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration
• Water is not considered a limiting factor for photosynthesis as the amount needed is relatively small compared to the amount transpired from a plant
• The number of chloroplasts or the amount of chlorophyll in the chloroplasts can also affect the rate of photosynthesis
• Temperature


  The temperature of the environment affects how much kinetic energy all particles have, so temperature affects the speed at which carbon dioxide and water move through a plant
• Lower temperature


  Less kinetic energy particles have, resulting in fewer successful collisions occurring over a period of time
• Increasing temperature


  Increases the kinetic energy of particles, increasing the likelihood of collisions between reactants and enzymes which results in the formation of products
• Higher temperatures


  Enzymes that control the processes of photosynthesis can be denatured (where the active site changes shape and is no longer complementary to its substrate), reducing the overall rate of photosynthesis
• Effect of temperature on the rate of photosynthesis

  1. Increasing rate as number of collisions between substrates and enzymes increases

  2. Optimum temperature

  3. Enzymes begin to denaturate, rate decreases
• Light intensity


  • The intensity of the light available to the plant will affect the amount of energy that it has to carry out photosynthesis
  • The more light a plant receives, the faster the rate of photosynthesis
  • This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
• Effect of light intensity on rate of photosynthesis

  1. At lower light intensities, the increase in the rate is linear

  2. At this point, some other factor becomes limiting

  3. The graph levels off

  4. The rate becomes constant
• Carbon dioxide concentration


  • Carbon dioxide is one of the raw materials required for photosynthesis
  • The more carbon dioxide that is present, the faster the reaction can occur
  • This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
• Effect of carbon dioxide concentration on rate of photosynthesis

  1. At lower concentrations, the increase in rate is linear

  2. At this point, some other factor becomes limiting

  3. The graph levels off

  4. The rate becomes constant
• Chlorophyll


  • The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis
  • The more chloroplasts a plant has, the faster the rate of photosynthesis
  • The amount of chlorophyll can be affected by: diseases (such as tobacco mosaic virus), lack of nutrients (such as magnesium), loss of leaves (fewer leaves means fewer chloroplasts)
• Leaf Structures


  • Wax cuticle
  • Upper epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Lower epidermis
  • Guard cell
  • Stomata
  • Vascular bundle
  • Xylem
  • Phloem
• Wax cuticle


  Protective layer on top of the leaf, prevents water from evaporating
• Upper epidermis


  Thin and transparent to allow light to enter
• Palisade mesophyll


  Column shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis
• Spongy mesophyll


  Contains internal air spaces that increases the surface area to volume ratio for the diffusion of gases (mainly carbon dioxide)
• Lower epidermis


  Contains guard cells and stomata
• Guard cell


  Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in, oxygen to diffuse out
• Stomata


  Where gas exchange takes place: opens during the day, closes during the night, evaporation of water also takes place from here. In most plants, found in much greater concentration on the underside of the leaf to reduce water loss
• Vascular bundle


  Contains xylem and phloem to transport substances to and from the leaf
• Xylem


  Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata
• Phloem


  Transports sucrose and amino acids around the plant
• Leaf features

  • Large surface area
  • Thin
  • Chlorophyll
  • Network of veins
  • Stomata
  • Thin, transparent epidermis
  • Thin wax cuticle
  • Palisade cell layer at top
  • Spongy layer
• Large surface area (leaf)


  Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis
• Thin


  Allows carbon dioxide to diffuse to palisade mesophyll cells quickly
• Chlorophyll


  Absorbs light energy so that photosynthesis can take place
• Network of veins


  Allows the transport of water to the cells of the leaf and carbohydrates from the leaf for photosynthesis (water for photosynthesis, carbohydrates as a product of photosynthesis)
• Stomata


  Allows carbon dioxide to diffuse into the leaf and oxygen to diffuse out