Organisation in Plants

• A leaf is an organ because there are many tissues inside the leaf that work together to perform photosynthesis.
• Upper epidermis adaptations:

  • Single layer of transparent cells allow light to pass through.
  • Cells secrete a waxy substance that make leaves waterproof.
• Palisade mesophyll is adapted for it's function as there are tightly packed cells with lots of chloroplasts to absorb as much light as possible for photosynthesis.
• Spongy mesophyll is adapted for it's function as there are air spaces to increase surface area and allow gases to diffuse quickly.
• The function of guard cells is to open and close the stomata.
• The function of the xylem is to transport water and mineral ions from the roots to the rest of the plant.
• Adaptations of the xylem:

  • Made of dead cells.
  • No end wall between cells.
  • Walls are strengthened by a chemical called lignin to withstand the pressure of the water.
• The function of the phloem is to transport dissolved sugars from the leaves to the rest of the plant.
• The purpose of translocation is to transport dissolved sugars to the rest of the plant for respiration, growth and storage.
• Transpiration is movement of water from the roots to the leaves through the xylem.
• The purpose of transpiration is to:

  • Provide water to keep cells turgid.
  • Provide water for photosynthesis.
  • Transport mineral ions to leaves.
• The four factors that affect the rate of transpiration are: temperature, light intensity, humidity and wind speed.
• Higher temperature increases the rate of transpiration.
• Higher levels of humidity decreases the rate of transpiration.
• Increased light intensity increases the rate of transpiration because the stomata open wider to let more carbon dioxide into the leaf for photosynthesis.
• The function of the stomata is to allow diffusion of gases into and out of the plant.
• Stomata are most often found on the underside of leaves.
• Having a high amount of stomata on the underside of leaves reduces the amount of water loss through evaporation.