Biogeochemical Cycles - Carbon, Nitrogen, Oxygen, Water - UNSOLVED PRACTICE SET
Chapter: Natural Resources | Topic: Biogeochemical Cycles Carbon Nitrogen Oxygen Water
BIOGEOCHEMICAL CYCLES - CARBON, NITROGEN, OXYGEN, WATER - UNSOLVED PRACTICE SET
Topic: Biogeochemical Cycles Carbon Nitrogen Oxygen Water
Multiple Choice Questions
Q1. In the carbon cycle, plants take in carbon dioxide from the atmosphere during:
- Respiration
- Photosynthesis
- Combustion
- Decomposition
Q2. Nitrogen fixation is the process by which:
- Plants directly absorb nitrogen gas from the air
- Atmospheric nitrogen is converted into usable forms like nitrates by bacteria
- Nitrogen is released from the soil into the air
- Animals eat nitrogen-rich food
Q3. Which of the following organisms plays a key role in the nitrogen cycle by converting atmospheric nitrogen into ammonia?
- Fungi
- Rhizobium bacteria living in legume roots
- Viruses
- Fish
Q4. In the oxygen cycle, oxygen is mainly released into the atmosphere by:
- Animals during respiration
- Plants during photosynthesis
- Burning of fossil fuels
- Volcanic eruptions
Q5. Which biogeochemical cycle does NOT have a significant atmospheric component?
- Carbon cycle
- Nitrogen cycle
- Phosphorus cycle
- Water cycle
Short Answer Questions
Q6. Draw the carbon cycle in words (or describe it step by step). Name the main processes by which carbon moves between the atmosphere, living organisms, and the Earth.
Q7. What is nitrogen fixation? Why can't most plants use nitrogen gas directly from the air? Name two types of bacteria that help in nitrogen fixation.
Q8. Explain the oxygen cycle. How do plants and animals play complementary roles in maintaining the balance of oxygen in the atmosphere?
Q9. Why are biogeochemical cycles called "cycles"? What would happen if any one of these cycles stopped working - for example, if all nitrogen-fixing bacteria suddenly disappeared?
Long Answer Questions
Q10. Explain the nitrogen cycle in detail. Describe the processes of nitrogen fixation, ammonification, nitrification, and denitrification. Explain the role of bacteria in each step and why leguminous plants like peas and beans are important for enriching soil nitrogen.
Q11. "Human activities are disturbing the natural balance of biogeochemical cycles." Discuss this statement by explaining: how burning fossil fuels affects the carbon cycle and causes global warming, how deforestation affects the oxygen and water cycles, how excessive use of nitrogen fertilisers affects the nitrogen cycle and causes water pollution, and what steps are needed to restore these balances.
APPLICATION / ANALYSIS
Q12. Case Study - Carbon Footprint Comparison:
A family in Mumbai calculated their monthly carbon emissions:
| Activity | CO₂ Emitted (kg) |
|---|---|
| Using petrol car (500 km) | 100 kg |
| Electricity from coal power (200 units) | 160 kg |
| LPG for cooking (2 cylinders) | 60 kg |
| Total | 320 kg |
A similar family in a village in Kerala:
- Uses bicycle and bus
- Has solar panels for electricity
- Uses biogas for cooking
- Total emissions: 40 kg
Answer the following:
(a) Calculate how many times more carbon the Mumbai family emits compared to the Kerala village family. Show your work.
(b) Which activity contributes the most to the Mumbai family's carbon footprint? What cleaner alternative could they use?
(c) If every family in India reduced their carbon footprint by 50%, how would this help restore balance to the carbon cycle? Explain.
Q13. Real-Life Application - School Composting Project:
Your school starts a composting pit to recycle food waste from the canteen. Over 3 months:
| Month | Food Waste (kg) | Compost Produced (kg) | Nitrogen Content in Compost |
|---|---|---|---|
| 1 | 100 | 20 | Low |
| 2 | 100 | 25 | Medium |
| 3 | 100 | 30 | High |
The science teacher adds dry leaves and soil with decomposers to the pit.
Answer the following:
(a) Why does the amount of compost increase from month 1 to month 3? What role do decomposers play in this?
(b) How does composting food waste help the nitrogen cycle? Explain the connection to soil fertility.
(c) If this compost is used in the school garden instead of chemical fertilisers, what are two environmental benefits?