Explanation:
An ecosystem is a complex system where living organisms interact with each other and with the environment. In order for an ecosystem to be self-sustaining and viable, it needs to have a continuous flow of energy and nutrients. This can be achieved through various food chains, but the most important one is the producer-decomposer food chain.

Producer- Decoposer food chain:
- Producers, such as plants and algae, are capable of creating their own energy through photosynthesis. They convert sunlight, water, and carbon dioxide into glucose, which is used as energy for their growth and survival.
- Decomposers, such as bacteria and fungi, break down dead organic matter into simpler compounds and release nutrients back into the environment. These nutrients are then used by plants to grow and thrive.

Importance of producer-decomposer food chain:
1. Energy flow: Producers are the primary source of energy in an ecosystem. They convert solar energy into chemical energy, which is then transferred to consumers through the food chain. Decomposers play a crucial role in recycling energy by breaking down dead organisms and releasing energy stored in their tissues.
2. Nutrient cycling: Decomposers break down complex organic matter, such as dead plants and animals, into simpler compounds. These compounds are then used by producers to synthesize new organic matter. Without decomposers, nutrients would remain locked in dead organisms and unavailable to other organisms in the ecosystem.
3. Waste decomposition: Decomposers also play a vital role in breaking down and decomposing waste materials produced by living organisms. This helps to maintain a clean and healthy environment within the ecosystem.
4. Balance and stability: The producer-decomposer food chain helps to maintain a balance and stability within the ecosystem. It regulates population sizes, prevents the accumulation of dead organic matter, and ensures a continuous supply of energy and nutrients for all organisms.

Conclusion:
In conclusion, the producer-decomposer food chain is essential for keeping an ecosystem self-sustaining and viable. It provides energy flow, nutrient cycling, waste decomposition, and overall balance and stability. Without this food chain, the ecosystem would not be able to function efficiently and support a diverse range of organisms.

Producer-Decomposer Food Chain

A producer-decomposer food chain is a type of food chain that consists of producers and decomposers. Producers, such as plants, use sunlight to produce energy through photosynthesis. Decomposers, such as bacteria and fungi, break down dead organic matter and recycle nutrients back into the ecosystem. This type of food chain plays a crucial role in maintaining the self-sustainability and viability of an ecosystem.

Importance of Producers
- Producers are the foundation of the food chain as they convert sunlight into energy through photosynthesis. This energy is then transferred to other organisms in the ecosystem.
- Producers provide food and habitat for consumers, which are organisms that consume other organisms for energy.
- They play a vital role in the carbon cycle by absorbing carbon dioxide from the atmosphere and releasing oxygen, contributing to the overall balance of gases in the ecosystem.
- Producers also help in soil stabilization, prevent erosion, and contribute to the water cycle by absorbing water through their roots and releasing it through transpiration.

Role of Decomposers
- Decomposers break down dead organic matter, such as dead plants and animals, into simpler compounds and nutrients.
- They release these nutrients back into the soil, making them available for the producers to take up through their roots.
- Decomposers play a crucial role in the nutrient cycling within an ecosystem, ensuring that essential elements, such as nitrogen and phosphorus, are continuously recycled.
- They help to decompose waste materials and prevent the accumulation of organic matter, which could lead to the release of harmful substances.

Interconnectedness and Balance
- The producer-decomposer food chain highlights the interconnectedness and balance within an ecosystem.
- Producers rely on decomposers to recycle nutrients, which are essential for their growth and survival.
- Decomposers rely on producers to provide them with a constant supply of organic matter to decompose.
- This mutual dependence ensures the self-sustainability and viability of the ecosystem.
- Without decomposers, nutrients would become locked in dead organic matter, and without producers, there would be no organic matter for decomposers to break down.

Conclusion
In conclusion, a producer-decomposer food chain is essential for maintaining the self-sustainability and viability of an ecosystem. Producers convert sunlight into energy and provide food and habitat for consumers. Decomposers break down dead organic matter, recycle nutrients, and prevent the accumulation of waste. The mutual dependence between producers and decomposers ensures the balance and interconnectedness of the ecosystem, making option A the correct answer.