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The maintenance functions of all living organisms must go on even when they are not doing anything particular. Even when we are just sitting in a class or even asleep, this maintenance job has to go on. These maintenance processes require energy to prevent damage and break-down of cells and tissues, which is obtained by the individual organism from the food prepared by the autotrophs, called producers.

(a) Name and define the process by which green plants prepare food.

(b) Write chemical equation involved in the above process.

(c) State in proper sequence the events that occur in synthesis of food by desert plants.

OR

(c) Explain giving reasons what happens to the rate at which the green plants will prepare food

  1. during cloudy weather, and
  2. when stomata get blocked due to dust.

Photosynthesis

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Answer

(a) Photosynthesis is the process by which green plants use carbon dioxide and water, in the presence of sunlight and chlorophyll, to make food (glucose) and release oxygen.

(b) The chemical equation for photosynthesis is:

6CO2+12H2O→ChlorophyllSunlightC6H12O6+6H2O+6O26\text {CO}2 + 12\text H2 \text O \xrightarrow [\text {Chlorophyll}]{\text {Sunlight}} \text C6 \text H{12} \text O6 + 6\text H2 \text O + 6\text O_2

(c) In desert plants (like cacti), photosynthesis occurs in a slightly modified way :

  • Stomata open at night to take in carbon dioxide (to prevent water loss).
  • The absorbed CO2 is stored as an intermediate compound.
  • During the day, when sunlight is available, this stored CO2 is used for photosynthesis while stomata remain closed.

OR

  1. During cloudy weather : The rate of photosynthesis decreases because less sunlight reaches the plants, reducing the energy available for the process.
  2. When stomata get blocked due to dust : The entry of CO2 into leaves is reduced, slowing down photosynthesis since CO2 is one of the main raw materials.

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