Photosynthesis

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