(a) (i) Why does a kitchen garden called an artificial ecosystem while a forest is considered to be a natural ecosystem? (ii) While designing an artificial ecosystem at home, write any two things to be kept in mind to convert it into a self-sustaining system. Give reason to justify your answer. OR (b) (i) Construct a food chain of four trophic levels comprising the following: Hawk, snake, plants, rat. (ii) 20,000 J of energy was transferred by the producers to the organism of second trophic level. Calculate the amount of energy that will be transferred by organisms of the third trophic level to the organisms of the fourth trophic level.

Option (a)

(i) Difference between Kitchen Garden and Forest:

• Kitchen Garden (Artificial Ecosystem): It is a human-made ecosystem. Humans select the plants, prepare the soil, water them, and actively maintain the system. It lacks natural self-regulation and diversity.
• Forest (Natural Ecosystem): It is a natural, self-sustaining ecosystem that operates and maintains its balance without any human intervention.

(ii) Designing a Self-Sustaining Artificial Ecosystem:

To make an artificial ecosystem (like an aquarium or terrarium) self-sustaining, we must include:

1. Producers (e.g., green plants/aquatic plants): They capture solar energy to perform photosynthesis, producing organic food and releasing oxygen.
2. Decomposers (e.g., bacteria and fungi): They break down dead organic matter and waste products into simple inorganic substances, returning nutrients to the soil/water for reuse by plants.

• Reason: Without producers, consumers will have no food or oxygen. Without decomposers, dead remains and waste will accumulate, and natural replenishment of nutrients will stop, causing the ecosystem to collapse.

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Option (b)

(i) Food Chain Construction:

The food chain consisting of the given organisms across four trophic levels is:

$$\text{Plants (Producers)} \rightarrow \text{Rat (Primary Consumer)} \rightarrow \text{Snake (Secondary Consumer)} \rightarrow \text{Hawk (Tertiary Consumer)}$$

(ii) Energy Calculation:

According to Lindeman's 10% Law of Energy Transfer, only $10\%$ of the energy available at one trophic level is transferred to the next level.

• Energy transferred to the $2^{\text{nd}}$ trophic level (Rat) = $20,000\text{ J}$
• Energy transferred to the $3^{\text{rd}}$ trophic level (Snake) = $10\% \text{ of } 20,000\text{ J} = \frac{10}{100} \times 20,000 = 2,000\text{ J}$
• Energy transferred to the $4^{\text{th}}$ trophic level (Hawk) = $10\% \text{ of } 2,000\text{ J} = \frac{10}{100} \times 2,000 = 200\text{ J}$

Therefore, the amount of energy transferred by the organisms of the third trophic level (Snake) to the fourth trophic level (Hawk) is $200\text{ J}$.