All questions of Our Environment for Class 10 Exam

Food Web:
A food web is a complex network of interconnected food chains that shows the feeding relationships between various organisms in an ecosystem. It represents the flow of energy and nutrients from one organism to another within the ecosystem.

Explanation:
When an organism of a higher trophic level feeds on several types of organisms belonging to a number of lower trophic levels of different food chains, it forms a complex feeding relationship known as a food web.

Here is a detailed explanation of why the correct answer is option 'B' (Food web):

1. Trophic Levels:
- Trophic levels are the positions that organisms occupy in a food chain based on their feeding habits.
- Producers, such as plants, occupy the first trophic level as they convert sunlight into food through photosynthesis.
- Primary consumers, such as herbivores, occupy the second trophic level as they feed on producers.
- Secondary consumers, such as carnivores, occupy the third trophic level as they feed on primary consumers.
- Tertiary consumers, such as top predators, occupy the fourth trophic level as they feed on secondary consumers.

2. Organisms of Higher Trophic Level:
- Organisms of a higher trophic level are those that occupy a trophic level above the primary consumers.
- They primarily feed on the organisms from lower trophic levels to obtain energy and nutrients for their survival.
- These organisms are often carnivores or omnivores that can consume multiple types of organisms from different food chains.

3. Feeding on Several Types of Organisms:
- The organisms of higher trophic levels in a food web feed on several types of organisms from different trophic levels.
- For example, a top predator can consume herbivores from one food chain, as well as carnivores from another food chain.
- This feeding behavior allows them to obtain a diverse range of energy sources and nutrients.

4. Interconnected Food Chains:
- A food web consists of multiple interconnected food chains that represent the feeding relationships within an ecosystem.
- Each food chain in the food web represents the transfer of energy and nutrients from one organism to another.
- The organisms of higher trophic levels in the food web play a crucial role in maintaining the balance of energy flow within the ecosystem.

Therefore, the organisms of a higher trophic level that feed on several types of organisms belonging to a number of lower trophic levels of different food chains constitute a food web.

Conversion of O2 to O3
The transformation of oxygen molecules (O2) into ozone (O3) primarily occurs due to the influence of ultraviolet (UV) radiation. Here’s how the process works:
Role of Ultraviolet Radiation
- Ultraviolet radiation from the sun has enough energy to break the bonds in O2 molecules.
- When O2 is exposed to UV light, it can dissociate into two individual oxygen atoms (O).
- These free oxygen atoms are highly reactive and can readily combine with other O2 molecules to form ozone (O3).
The Ozone Formation Process
- The reaction can be summarized as follows:
- O2 + UV radiation → 2O
- O + O2 → O3
- This process is crucial for the formation of the ozone layer in the Earth's stratosphere, which protects living organisms by absorbing harmful UV radiation.
Significance of Ozone
- Ozone (O3) plays a vital role in shielding the Earth from excessive UV radiation, thereby preventing skin cancer and other health issues.
- It also contributes to the stability of the climate by regulating atmospheric temperatures.
Conclusion
- In summary, the conversion of O2 to O3 occurs predominantly due to ultraviolet radiation. This natural process is essential for maintaining the balance of life on Earth by protecting it from the sun's harmful rays.

The energy available at the producer level can be calculated using the 10% rule. According to the 10% rule, only 10% of the energy from one trophic level is transferred to the next trophic level.

So, if the energy at the fourth trophic level is 3 kJ, then the energy available at the third trophic level (which is the consumer level above the producer level) would be 10% of that, which is 0.1 * 3 kJ = 0.3 kJ.

Similarly, the energy available at the second trophic level would be 10% of the energy at the third trophic level, and so on.

Therefore, the energy available at the producer level (the first trophic level) would be 10% of the energy at the second trophic level, which is 0.1 * 0.3 kJ = 0.03 kJ.

The energy transferred to the lion in the food chain cannot be determined without knowing the specific efficiency of energy transfer at each trophic level. Energy transfer efficiency varies in different ecosystems and can range from 10% to 20%. Without this information, we cannot calculate the exact amount of energy transferred to the lion.