1. Complete the following table (Carefully study the carbon, oxygen, and nitrogen cycles).
| Bio-geochemical cycles | Biotic Processes | Abiotic Processes |
| 1. Carbon cycle | Photosynthesis, respiration, decomposition | Combustion, volcanic activity, diffusion in oceans |
| 2. Oxygen cycle | Respiration, photosynthesis | Oxidation, ozone formation, weathering of rocks |
| 3. Nitrogen cycle | Nitrogen fixation, nitrification, denitrification, decomposition | Lightning, volcanic eruptions, leaching in soil |
2. Correct and rewrite the following statements and justify your corrections.
a. Incorrect: Carnivores occupy the second trophic level in the food chain.
Correct: Carnivores occupy the third trophic level in the food chain.
Justification: The first level is for producers (plants), the second for herbivores, and the third for carnivores.
b. Incorrect: The flow of nutrients in an ecosystem is considered to be a ‘one-way’ transport.
Correct: The flow of nutrients in an ecosystem is cyclic.
Justification: Nutrients like carbon, oxygen, and nitrogen are continuously recycled through biotic and abiotic components.
c. Incorrect: Plants in an ecosystem are called primary consumers.
Correct: Plants in an ecosystem are called producers.
Justification: Plants prepare their own food using sunlight through photosynthesis; hence, they are producers.
3. Give reasons.
a. Energy flow through an ecosystem is ‘one-way’.
Answer: Energy flows in one direction—from the sun to producers and then to consumers and decomposers. It cannot be recycled because energy is lost as heat at each trophic level.
b. Equilibrium is necessary in various bio-geochemical cycles.
Answer: Equilibrium ensures that elements like carbon, nitrogen, and oxygen are available in balanced amounts for living organisms. Disturbance in these cycles can cause pollution and affect life processes.
c. Flow of nutrients through an ecosystem is cyclic.
Answer: Nutrients are reused through processes such as photosynthesis, respiration, and decomposition. These cycles ensure that nutrients return to the environment for use by plants again.
4. Explain the following cycles in your own words with suitable diagrams.
a. Carbon Cycle
The carbon cycle shows how carbon moves between the atmosphere, living organisms, and the earth. Plants absorb carbon dioxide during photosynthesis and convert it into food. Animals eat plants and release carbon dioxide back into the air through respiration. Decomposition and burning of fuels also release carbon dioxide. Thus, carbon keeps circulating in nature.
b. Nitrogen Cycle
The nitrogen cycle explains how nitrogen moves between the atmosphere, soil, and living organisms. Nitrogen from the air is converted into compounds by bacteria during nitrogen fixation. Plants absorb these compounds, and animals get nitrogen by eating plants. When organisms die, decomposers return nitrogen to the soil and air, completing the cycle.
c. Oxygen Cycle
The oxygen cycle maintains the balance of oxygen in nature. Plants release oxygen during photosynthesis, which is used by animals and humans during respiration. Through breathing and decay, oxygen is returned to the environment as carbon dioxide, which plants again use for photosynthesis.
5. What would you do to help maintain the equilibrium in the various bio-geochemical cycles? Explain in brief.
To maintain balance in natural cycles, I would:
- Plant more trees to increase oxygen and absorb carbon dioxide.
- Avoid burning fossil fuels unnecessarily to reduce pollution.
- Reduce the use of chemical fertilizers that harm soil nitrogen balance.
- Encourage recycling of organic waste to enrich the soil naturally.
- Spread awareness about protecting the environment and natural resources.
6. Explain in detail the inter-relationship between the food chain and food web.
A food chain shows the direct transfer of energy from one organism to another, like plant → herbivore → carnivore.
A food web is a network of several interconnected food chains in an ecosystem.
They are related because many food chains combine to form a food web. This interconnection helps maintain balance in nature, ensuring that energy and nutrients are distributed properly among organisms.
7. State the different types of bio-geochemical cycles and explain the importance of those cycles.
Types of bio-geochemical cycles:
- Carbon cycle
- Oxygen cycle
- Nitrogen cycle
- Water cycle
- Phosphorus cycle
Importance:
- They recycle essential elements required for life.
- Maintain balance between biotic and abiotic components.
- Support plant growth and sustain life processes.
- Prevent accumulation or shortage of elements in nature.
8. Explain the following with suitable examples.
a. What type of changes occur in the amount of energy during its transfer from plants to apex consumers?
As energy moves from one trophic level to another, it decreases. Plants capture solar energy, and only about 10% of this energy is passed to the next level. By the time it reaches apex consumers, very little energy remains.
b. What are the differences between flow of matter and of energy in an ecosystem?
- Energy Flow: It is one-way; energy moves from the sun to producers and consumers and is lost as heat.
- Matter Flow: It is cyclic; nutrients like carbon and nitrogen are reused through natural cycles.