Food chain is a series of population which starts with producers. It is concerned with:

Options

A. energy flow and transfer of nutrients
B. biotic components only
C. biotic and decomposers
D. both (a) and (b)

Answer

To answer the question regarding what the food chain is concerned with, we can break down the concept step by step.

### Step-by-Step Solution:

1. **Understanding the Food Chain**:
- A food chain is a linear sequence of organisms where nutrients and energy are transferred from one organism to another. It starts with producers, which are typically plants that convert solar energy into chemical energy through photosynthesis.

2. **Identifying the Components**:
- In a food chain, there are various components:
- **Producers**: These are the first trophic level and include plants and phytoplankton.
- **Consumers**: These are organisms that consume producers (primary consumers) and other consumers (secondary and tertiary consumers).
- **Decomposers**: These organisms break down dead matter and recycle nutrients back into the ecosystem.

3. **Energy Flow**:
- The food chain illustrates how energy flows from producers to various levels of consumers. Each step in the food chain represents a transfer of energy, which diminishes at each trophic level due to energy loss as heat.

4. **Nutrient Transfer**:
- Along with energy, nutrients are also transferred through the food chain. Decomposers play a crucial role in breaking down dead organic matter, returning essential nutrients to the soil, which can then be absorbed by plants.

5. **Biotic Components**:
- The food chain consists of biotic components (living organisms) such as producers, consumers, and decomposers. These components are essential for the functioning of ecosystems.

6. **Evaluating the Options**:
- Given the options:
- A: Energy flow and transfer of nutrients
- B: Biotic components only
- C: Biotic and decomposers
- D: Both A and B
- The correct answer is **D: Both A and B**. This is because the food chain is concerned with energy flow, nutrient transfer, and includes biotic components.

### Final Answer:
The food chain is concerned with energy flow, transfer of nutrients, and biotic components. Therefore, the correct option is D: both A and B.