PHOTOSYNTHESIS

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PHOTOSYNTHESIS
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IMPORTANCE OF PHOTOSYNTHESIS

• Uses energy from sunlight to convert CO2 to
  sugars
• Supplies usable chemical energy for life on Earth
• CO2 H2O C6H12O6 O2

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THE LEAF

• The leaf is a food supply factory
• Adapted to maximize light absorption and CO2
  diffusion
• see page 159

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PARTS OF THE LEAF

• Upper Lower Epidermis
• a single layer of cells covering the upper and
  lower leaf
• Cuticle
• a waxy secretion that forms a water repellent
  covering

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• Mesophyll
• middle layer of cells
• cells loaded with chloroplasts
• Palisade layer single layer just below upper
  epidermis
• Spongy Layer contains air spaces which act as
  CO2 and H2O reservoirs

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• Stomates
• minute pores in epidermis
• gases move in and out of the leaf through
  stomates
• a pair of guard cells controls the opening and
  closing
• when guard cells swell with water, the stomates
  open
• stomates close when guard cells lose water

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CHLOROPLAST

• See page 161
• Outer membrane regulates movement of materials
  into and out of the chloroplast

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• Internal Membrane System
• Thylakoids
• flattened disc
• increase surface area
• contains light absorbing pigments

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• Grana
• stacked thylakoids
• allows maximum absorption of sunlight

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• Stroma
• pale, semifluid substance

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PLANT PIGMENTS

• Chlorophyll
• green pigment
• present in two forms - a and b
• chlorophyll absorbs light
• Accessory Pigments
• carotene - orange
• xanthophyll - yellow

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RATE OF PHOTOSYNTHESIS

• Light Intensity
• increases photosynthesis
• until saturation point
• Temperature
• increases photosynthesis
• until enzymes become denatured

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• O2 and CO2 Concentration
• increase CO2, increase rate
• increase O2, decrease rate