An ecosystem is a complex interacting system of

Options

A. populations
B. individuals
C. communities and their soil conditions
D. communities and their physical environment

Answer

**Step-by-Step Solution:**

1. **Understanding the Definition of an Ecosystem:**
- An ecosystem is defined as a complex interacting system that includes living organisms and their physical environment. It consists of various components that interact with each other.

2. **Identifying Key Components:**
- The key components of an ecosystem include populations (groups of the same species), communities (groups of different species), and their physical environment (abiotic factors like soil, water, temperature, etc.).

3. **Analyzing the Options:**
- The question provides several options:
- **A. Populations**
- **B. Individuals**
- **C. Communities and their social conditions**
- **D. Communities and their physical conditions**
- We need to determine which option best describes the complex interactions within an ecosystem.

4. **Evaluating Each Option:**
- **Option A (Populations):** This option is too narrow as it only refers to groups of the same species, not the interactions with the environment.
- **Option B (Individuals):** This is also incorrect because it focuses on single organisms without considering their interactions or environment.
- **Option C (Communities and their social conditions):** This option is limited as it does not encompass the physical aspects of the ecosystem.
- **Option D (Communities and their physical conditions):** This option correctly includes both the communities of organisms and their physical environment, which is essential for understanding an ecosystem.

5. **Conclusion:**
- The correct answer is **D. Communities and their physical conditions**, as it encapsulates the complexity of interactions between living organisms and their environment.