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PHOTOSYNTHESIS

Introduction

Definition

Conditions Necessary for Photosynthesis

Process of Photosynthesis

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Introuduction

  • Photosynthesis is an important activity of green plants .
  • Food is synthesized from carbon dioxide and water in the presense of chlorophyll and sunlight.

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DEFINITION

  • The process by which green plants make their own food (carbohydrate)from carbon dioxide
  • And water using sunlight in the presense of chlorophyll is called Photosynthesis.

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Conditions Necessary For Photosynthesis

  • The conditions necessary for this process are:
  • Sunlight
  • Chlorophyll
  • Carbon Dioxide
  • Water.

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Process of Photosynthesis

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  • Mesophylls cells (both palisade and spongy)

in leaf are the main centres of activity.

▪During day time ,sunlight is absorbed by the chlorophyll of the upper layers of mesophyll ,especially the palisade calls.

▪Carbon dioxide from the atmosphere enters the leaf by diffusion through stomata.

▪Water from the soil is taken up by the roots ,sent up through the stem to the leaves to be distributed in the mesophyll tissues.

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Main Phases Of Photosynthesis

  • Light Dependent Phase (Photochemical Phase)
  • Light independent Phase (Dark) or (Biosynthetic Phase)

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Summary Chemical Reaction

  • 6CO₂+12H₂O→C₆H₁₂O₆+6H₂O+6CO₂↑
  • The glucose molecule C₆H₁₂O₆ is a simplest sugar soluble in water.

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Steps Involved in Light –Dependent Phase

  • In this phase light plays the key role.Series of reactions occur in quick succession after absorption of light.
  • This reaction takes place in Thyalakoids (containing chlorophyll)of the chloroplast.

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Step 1- Activation of chlorophyll� Step 2-Splitting of water molecule

1- With the absorption of photon (or solar energy)chlorophyll gets activated.

2-This absorbed solar energy splits the water molecule into its components.

2H₂O →4H⁺ +4e⁻ +O₂

Hydrogen ,oxygen and electrons are released.

This whole process is known as Photolysis (splitting by light)

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End products of photolysis

  • NADP picks up the H⁺ ions and form NADPH.
  • NADP⁺ +e⁻+H⁺→NADPH
  • The oxygen is given out as molecular oxygen.
  • 2O → 2O₂
  • The electrons are used in converting ADP to ATP by adding one inorganic phosphate group. ADP +Phosphate →ATP
  • This process is called Phosphorylation.

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  • Whole process takes place with the energy from photons ,that is why it can be called as Photophosphorylation.

The whole process can be represented by the diagram in the next slide.

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Formation Of Starch

  • Most green plants convert glucose into starch,several glucose molecules are polymerised to produce one molecule of Starch.
  • nC₆H₁₂O₆→nC₆H₁₀O₅ with the loss of water molecule .

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