Question

The following question is a source-based/case-based question that follows. Read the case carefully and answer the questions that follow.

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.

1. Name and define the process by which green plants prepare food.  (1)
2. Write chemical equation involved in the above process.  (1)
3. 1. State in proper sequence the events that occur in synthesis of food by desert plants.  (2)
      OR
   2. Explain giving reasons what happens to the rate at which the green plants will prepare food:  (2)
      1. during cloudy weather, and
      2. when stomata get blocked due to dust.

Answer 1

i. Photosynthesis: In this process, sunlight, water, and carbon dioxide are used by green plants to make food (usually glucose) and oxygen.

ii. Chemical Equation for Photosynthesis:

\[\ce{6CO2 + 6H2O + light energy -> C6H12O6 + 6O2}\]

iii. a. Sequence of Events in Food Synthesis by Desert Plants (CAM Photosynthesis):

1. Nighttime: CO₂ Uptake:
   • At night, the stomata open to let as little water out as possible.
   • When CO₂ comes into contact with the leaf, the enzyme PEP carboxylase changes it into oxaloacetic acid. This acid is then changed into malate and kept in vacuoles.
2. Daytime: CO₂ Release and Sugar Formation:
   • The stomata close during the day to save water.
   • The stored malate is decarboxylated, which lets CO₂ out from inside it.
   • The CO₂ that is released goes into the Calvin cycle, which uses light energy to make carbs. 

OR

b. Effect on the Rate of Food Preparation:

1. During Cloudy Weather: 
   • Reduced Light Intensity: When there is less light, there is less energy to power the light-dependent reactions of photosynthesis. This slows down the process of making food generally.
2. When Stomata Are Blocked by Dust:
   • Restricted CO₂ Uptake: The stomata can get clogged with dust, which stops CO₂ from getting into the leaf. The rate of photosynthesis (and food production) slows down when there is less CO₂ for the Calvin cycle.