Photosynthesis – An Introduction
Photosynthesis means synthesis of glucose with the help of light. Green plants trap solar energy and convert it into chemical energy. The green plants are called as autotrophs.
- The Raw Materials. Needed for photosynthesis are carbon dioxide and water.
- Chlorophyll. The green pigment acts as a catalyst. The overall reaction to represent photosynthesis is:
6CO2+12H2O → Sunlight, Chlorophyll → C6H12O6 + 6O2 + 6H2O
Photosynthesis is an anabolic process which occurs in two phases: (i) Light reaction and (ii) Dark reaction. Light reaction has two main steps: (i) Photolysis and (ii) Photophosphorylation.
- Photolysis: It is the splitting of water molecules into OH‾ and H+ ion in presence of light.
- Photophosphorylation. Means conversion of ATP form ADP and phosphate in presence of light.
- Dark Reaction. It do not require light. Here hydrogen ions are used to reduce carbon dioxide to form glucose.
- The immediate product of photosynthesis is glucose which is stored in the form of starch.
- The by product of photosynthesis is oxygen which is the life supporting gas.
- Light reactions take place in grana of chloroplast.
- Dark reactions take place in the stoma of chloroplast.
- Adaptations of leaf for photosynthesis includes large surface area, leaf arrangement, rapid transport, numerous stomata, concentration of chloroplasts in the upper layers of leaf etc.
- Factors Affecting Photosynthesis. Light intensity, carbon dioxide concentration, temperature etc. the experiments include starch test to show that chlorophyll, carbon dioxide, light are necessary for photosynthesis. The release of oxygeri by green plants during photosynthesis. The release of oxygeri by green plants during photosynthesis etc.
- Importance of Photosynthesis. (i) To produce food for all the organisms. (ii) Release oxygen which is a life supporting gas.
- The chemical used to test starch.
- The process by which green plants prepare their own food.
- The products of photosynthesis.
- A plant that does not perform photosynthesis.
- A gas released by green plants during photosynthesis.
- The raw materials needed for photosynthesis.
- The site of light reaction.
- The principle site in a green leaf for photosynthesis.
- The reaction by which the water molecules are broken down by means of light.
- The immediate product of photosynthesis.
- The first stable product formed during CO2 fixation.
- The experiment to demonstrate the importance of light for photosynthesis.
- They energy currency of the cell.
- The substance form which oxygen is evolved during photosynthesis.
ANSWERS/HINTS TO IMPORTANT QUESTIONS
- Iodine 2. Photosynthesis 3. Glucose, water and oxygen.
- Mushroom/Fungus 5. Oxygen 6. Carbon dioxide and water
- Grana of chloroplast 8. Chloroplast 9. Photolysis
- Glucose 11. Phosho glyceric acid (PGA)
- Light screen experiment 13. Water
Distinguish between the following pairs:
- Light reaction and Dark reaction.
- Autotrophs and Heterotrophs.
- Stroma and Grana.
- Photosynthesis and Respiration.
- Chloroplast and chlorophyll.
|Sr. No.||Light Reaction||Dark Reaction|
|1.||(i) It takes place in the presence of light.
(ii) It occurs in the grana of chloroplast.
(iii) Its products are ATP and NADP H2.
|(i) It does not require light.
(ii) It occurs in the stroma of chloroplast.
(iii) Its products are organic compounds.
|(i) They can produce their own food.
(ii) They contain chlorophyll.
|(i) They cannot prepare their own food.
(ii) Do not contain chlorophyll.
|3.||Stroma of Chloroplast||Grana of Chloroplast|
|(i) It is the site of dark reaction.
(ii) It is a non-green granular matrix.
|(i) It is the site of light reaction.
(ii) It is green flattened sac-like structure.
|(i) It is an anabolic process.
(ii) It takes place only in chlorophyll bearing cells.
(iii) Oxygen is released.
(iv) It takes place only in presence of light.
|(i) It is catabolic process.
(ii) It takes place in all cells.
(iii) Carbon dioxide is released.
(iv) Light is not needed.
|(i) It is an organelle of the cell.
(ii) It is living.
|(i) It is the green pigment in chloroplast.
(ii) It is non-living.