The definition given below describes: " The mass of living at a particular time "

Options

A. Gross primary productivity
B. Standing state
C. Net primary productivity
D. Standing crop

Answer

To solve the question, "The mass of living matter at a particular time," we need to analyze the definitions of the given options:

1. **Gross Primary Productivity (GPP)**: This refers to the total amount of organic matter produced by photosynthesis in an ecosystem. It measures the rate of production but does not specifically refer to the mass of living matter at a particular time. Therefore, this option is incorrect.

2. **Standing State**: This term typically refers to the amount of nutrients (like carbon, nitrogen, phosphorus, etc.) present in the soil at a given time. It does not describe the mass of living organisms, so this option is also incorrect.

3. **Net Primary Production (NPP)**: This is calculated by subtracting the respiration losses from the gross primary production. While it relates to productivity, it does not specifically indicate the mass of living matter at a specific time. Thus, this option is incorrect as well.

4. **Standing Crop**: This term specifically refers to the mass of living material (biomass) present at a particular time in an ecosystem. It is measured at a specific moment and includes all living organisms at a given trophic level. Therefore, this option correctly matches the definition provided in the question.

Based on the analysis, the correct answer is **Standing Crop**.

### Step-by-Step Solution:
1. **Identify the Definition**: The question provides a definition that describes the mass of living matter at a particular time.
2. **Evaluate Each Option**:
- **Gross Primary Productivity**: Incorrect, as it measures production rate, not mass at a time.
- **Standing State**: Incorrect, as it refers to nutrient amounts in soil, not living matter.
- **Net Primary Production**: Incorrect, as it relates to productivity after respiration losses, not mass.
- **Standing Crop**: Correct, as it defines the mass of living material at a specific time.
3. **Select the Correct Answer**: The correct answer is **Standing Crop**.