The total dry weight accessible to heterotrophs in an ecosystem will from the :

Options

A. Gross primary productivity
B. Net primary productivity
C. Secondary productivity
D. Tertiary productivity

Answer

To solve the question regarding the total dry weight accessible to heterotrophs in an ecosystem, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Heterotrophs**:
- Heterotrophs are organisms that cannot produce their own food and rely on consuming other organisms (plants or animals) for energy. Examples include cows, goats, and other animals.

**Hint**: Remember that heterotrophs are dependent on producers for their energy needs.

2. **Identifying Trophic Levels**:
- In an ecosystem, the first trophic level consists of producers (like plants) that convert sunlight into energy through photosynthesis. Heterotrophs occupy the second trophic level.

**Hint**: Trophic levels indicate the position of organisms in a food chain, with producers at the base.

3. **Understanding Primary Productivity**:
- Primary productivity refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. It can be categorized into:
- **Gross Primary Productivity (GPP)**: Total energy captured by producers.
- **Net Primary Productivity (NPP)**: The energy remaining after the producers have used some for their own respiration.

**Hint**: GPP is the total energy, while NPP is what is available after the producers' energy needs are met.

4. **Calculating Net Primary Productivity**:
- The formula for Net Primary Productivity is:
\[ \text{NPP} = \text{GPP} - \text{Respiratory Loss} \]
- NPP represents the energy that is available for consumption by heterotrophs.

**Hint**: Focus on what remains after producers use energy for respiration, as this is what heterotrophs can utilize.

5. **Conclusion**:
- Since heterotrophs rely on the energy produced by autotrophs (producers), the total dry weight accessible to them in an ecosystem is derived from the Net Primary Productivity (NPP).

**Final Answer**: The total dry weight accessible to heterotrophs in an ecosystem will come from **Option B: Net Primary Productivity**.