2.20 describe the structure of the leaf and explain how it is adapted for photosynthesis

 

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  • Large surface area – exposes a large surface to the sun and helps to ensure that the maximum amount of light is collected
  • Thin – makes it lighter and easy to support. Short internal distance for penetration of light and transport materials
  • Waterproof waxy cuticle – transparent, allowing for light to reach the chloroplasts in the mesophyll cells.  Prevents direct evaporation of water from the leaf cells (transpiration). Surface run off prevents water loss. Cuticle helps to protect the leaf from infection.
  • Mesophyll cells – photosynthetic tissue composed of 2 layers
  • Palisade mesophyll cells – Packed closely under the epidermis, most of the photosynthesis happens here
  • Spongy mesophyll cells – air spaces allow free diffusion (gaseous exchange) between stomata and mesophyll cells.
  • Leaf veins – spread across the leaf, providing moisture for the plant.
  • Vascular bundle contains the xylem and phloem.
  • Xylem – brings up water and ions from the soil to leaf tissues, to be used in the mesophyll cells. Thickened walls of the xylem holds the leaf flat, horizontal for maximum absorbency of light
  • Phloem – stores glucose and sap, transportation goes both ways.
  • Stomata – tiny pores on the underside of leaves that open during the day, allowing for efficient diffusion of CO2, by the leaf’s mesophyll for photosynthesis. Waste CO2 diffuses out of the leaf during the day from the mesophyll, and at night the stomata close and gaseous exchange between the leaf and atmosphere stops. This helps the plant to conserve energy and water.
  • Drip tip – allows the water to run off the waxy cuticle, into the roots for moisture, reducing water loss.
  • Plant cell tugor pressure – helps the plant to stay upright, in the direction of the sun.

 

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