On earth all living organisms constitute:

Options

A. Community
B. Biome
C. Association
D. Biosphere

Answer

To solve the question "On earth all living organisms constitute:", we need to analyze the options provided and understand the definitions of each term.

### Step-by-Step Solution:

1. **Understanding the Options:**
- **Community**: This refers to a group of different species living together in a specific area. It emphasizes interactions among various organisms.
- **Biome**: This is a large ecological area on the earth's surface, with flora and fauna adapting to their environment. Examples include deserts, forests, and grasslands.
- **Association**: This term generally refers to a relationship between two or more organisms, often based on mutual benefits or interactions.
- **Biosphere**: This encompasses all regions of the earth that support life, including land (terrestrial), water (aquatic), and the atmosphere. It includes all living organisms and their interactions with the environment.

2. **Identifying the Correct Answer:**
- The question asks for the term that encompasses all living organisms on Earth.
- While a community refers to specific groups of organisms and a biome refers to larger ecological zones, the biosphere is the most inclusive term that covers all living organisms, including plants, animals, and microorganisms.

3. **Conclusion:**
- Therefore, the correct answer is **Biosphere**. It is the part of the Earth where life exists, extending from the deepest roots of trees to the darkest parts of the oceans and the highest mountain tops.

### Final Answer:
**Biosphere**