Plants are autotrophic(auto- self * trophic- feeding)
Photosynthesis (photo-light * synthesis- build up)

  • Photosynthesis is the manufacturing of organic compounds primarily carbohydrates (eg glucose) by green plants from carbon dioxide and water using sunlight
  • it occurs in the green plants

Word Equation

  • carbon dioxide + water ⇨ glucose + oxygen
  • glucose is used during respiration and can be stored as starch(insoluble)
  • oxygen is used during respiration

 

Factors affecting the rate of photosynthesis

  • temperature
  • carbon dioxide
  • light
  • water
  • surface area of leaves
  • chloroplast

 

Limiting factors

process controlled by many factors have its rate determined by a factor 
which is in shortest supply
  • light intensity
  • carbon dioxide concentration
  • temperature

 

The internal structure of a Dicotyledonous leaf

cotyledon is a food storing leaf

MICROSCOPIC CROSS SECTION THROUGH A DICOT LEAF

 

Parts and Functions

  • Cuticle
    • forms a hard surface on top of the leaf to prevent water loss
  • Upper epidermis
    • forms a single layer of cells (forms the upper part of the leaf).
  • Palisade mesophyll
    • cells have plenty of chloroplasts- where most photosynthesis takes place.
  • Spongy mesophyll
    • cells in this zone are not closely packed together to allow easy movement of gases.
  • Stomata
    • these are openings mostly found on the lower part of the leaf on land plants that allow gaseous exchange. These are bound in the lower epidermis
  • Guard cells
    • they control the opening and closure of the stomata.
  • Loer epidermis
    • forms the lower part of the leaf
  • Vascular bundle
    • it is made up of xylem vessels and phloem tubes
  • Xylem vessels
    • transport water and dissolved minerals
  • Phloem tubes
    • transport the manufactured food
  • Chloroplasts
    • the green pigments inn a leaf that give leaves their color

 

How structure of a leaf is adapted to its functions

  • Cuticle
    • waxy
    • transparent
    • water impermeable so prevent water loss
    • allows light to pass through
  • Upper epidermis
    • transparent
    • no intercellular spaces
    • it prevents the water loss
  • Palisade mesophyll
    • just below the upper epidermis
    • cell longitudinally placed
    • closely packed chloroplasts to absorbs much sunlight as possible during photosynthesis
    • large vacuole pushes the chloroplasts toward the outer region so they can absorb more light
  • Spongy mesophyll
    • it has intercellular spaces
    • the walls are moist
    • help in gaseous exchange i.e diffusion of gases
  • Guard cells
    • they regulate the opening and closure of stomata
    • help in gaseous exchange
    • prevent excessive water loss
  • Vascular bundles
    • transport of water & dissolved minerals and food

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