Worksheet Solutions: Photosynthesis and Respiration | Biology Class 7 ICSE PDF Download

Part A: Multiple Choice Questions (MCQs)

Q1. Photosynthesis takes place in which cell organelle?
a) Mitochondria
b) Chloroplast
c) Nucleus
d) Ribosome

Answer: b) Chloroplast
Explanation: Chloroplasts contain chlorophyll that absorbs sunlight and carries out photosynthesis.

Q2. Which gas is released during photosynthesis?
a) Carbon dioxide
b) Oxygen
c) Nitrogen
d) Hydrogen

Answer: b) Oxygen
Explanation: Water molecules split during photosynthesis, releasing oxygen into the atmosphere.

Q3. Which factor is not essential for photosynthesis?
a) Carbon dioxide
b) Light
c) Oxygen
d) Chlorophyll

Answer: c) Oxygen
Explanation: Oxygen is a product of photosynthesis, not a requirement. The process needs CO₂, light, water, and chlorophyll.

Q4. In respiration, glucose is broken down to release:
a) Heat only
b) Energy as ATP
c) Vitamins
d) Proteins

Answer: b) Energy as ATP
Explanation: Respiration breaks down glucose into simpler molecules and releases energy stored in ATP for plant activities.

Q5. Which type of respiration produces less energy?
a) Aerobic
b) Anaerobic
c) Both produce equal energy
d) None of the above

Answer: b) Anaerobic
Explanation: Anaerobic respiration occurs without oxygen and yields less energy compared to aerobic respiration.

Part B: Short Answer Questions

Q6. What is autotrophic nutrition? Give an example.
Answer: Autotrophic nutrition is the process by which organisms (like green plants) prepare their own food using sunlight, carbon dioxide, and water through photosynthesis. Example: A mango tree makes its own glucose.

Q7. Why are leaves called the “food factories” of plants?
Answer: Leaves contain chloroplasts with chlorophyll to absorb sunlight. They have stomata for gas exchange and veins to transport water and minerals. This makes them the main site for photosynthesis, earning them the name “food factories.”

Q8. State two differences between aerobic and anaerobic respiration.
Answer:

• Aerobic respiration requires oxygen and gives more energy (ATP), while anaerobic respiration occurs without oxygen and produces less energy.

• Aerobic respiration completely breaks down glucose into CO₂ and water, whereas anaerobic respiration partially breaks glucose into alcohol/ethanol (in plants) and CO₂.

Q9. What role do stomata play in photosynthesis?
Answer: Stomata are small openings on the leaf surface that allow carbon dioxide to enter the plant and oxygen to leave. Guard cells control their opening and closing, ensuring proper gas exchange during photosynthesis.

Q10. Why is photosynthesis important for all living beings?
Answer: Photosynthesis provides food (glucose) for plants and indirectly for animals. It also releases oxygen into the atmosphere, which is essential for respiration in all living organisms.

Part C: Long Answer Questions (with Stepwise Solutions)

Q11. Describe the process of photosynthesis step by step.
Answer:

1. Raw materials: Plants take water from the soil (via roots), carbon dioxide from the air (via stomata), and sunlight.

2. Role of chlorophyll: Chlorophyll in chloroplasts absorbs sunlight energy.

3. Splitting of water: Sunlight energy splits water into hydrogen and oxygen. Oxygen is released into the air.

4. Formation of glucose: Hydrogen combines with carbon dioxide to form glucose (C₆H₁₂O₆).

5. Transport: The glucose is converted into starch for storage or transported by phloem to other plant parts.
   Conclusion: Thus, photosynthesis makes food and releases oxygen—both essential for life on Earth.

Q12. Explain respiration in plants. How is it different from photosynthesis?
Answer:

1. Definition: Respiration is the process by which plants break down glucose using oxygen to release energy.

2. Process:

   • Oxygen is taken in through stomata.

   • Glucose (from photosynthesis) is oxidized to release energy stored as ATP.

   • Carbon dioxide and water are released as by-products.

3. Equation: Glucose + Oxygen → Carbon dioxide + Water + Energy.

4. Difference from Photosynthesis:

   • Photosynthesis makes glucose and oxygen using sunlight.

   • Respiration breaks down glucose to release energy.

   • Photosynthesis occurs in daylight only; respiration occurs day and night.
     Conclusion: Both processes are linked—photosynthesis stores energy, respiration releases it.

Q13. What factors affect photosynthesis? Explain their importance.
Answer:

The rate of photosynthesis depends on several factors. If any one of them is limited, photosynthesis slows down.

Stepwise explanation:

1. Carbon dioxide (CO₂):
   – Plants need CO₂ from the air for making glucose.
   – If CO₂ is low, photosynthesis slows down even if light and water are sufficient.

2. Light:
   – Sunlight provides energy for photosynthesis.
   – More light increases the rate, but too much strong light damages chlorophyll and reduces photosynthesis.

3. Temperature:
   – Enzymes in plant cells work best at a moderate temperature.
   – Very low temperature slows photosynthesis.
   – Very high temperature (above 40°C) destroys enzymes and stops the process.