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 need to understand the different types of productivity in an ecosystem. Here’s a step-by-step breakdown:

### Step 1: Understand the Concept of Productivity
- **Productivity** refers to the rate at which biomass is produced in an ecosystem. It is crucial to differentiate between different types of productivity: Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).

**Hint:** Remember that productivity is about biomass production, and there are different types based on how much is available for consumption.

### Step 2: Define Gross Primary Productivity (GPP)
- **Gross Primary Productivity (GPP)** is the total amount of organic matter produced by photosynthesis in a given area over a specific time period. It includes all the biomass produced by producers (like plants) before any is used for their own respiration.

**Hint:** GPP is the total biomass produced, but not all of it is available to other organisms.

### Step 3: Define Net Primary Productivity (NPP)
- **Net Primary Productivity (NPP)** is the amount of biomass that remains after the producers have used some of the GPP for their own metabolic processes (respiration). NPP is essentially the total biomass available for consumption by heterotrophs (organisms that cannot produce their own food).

**Hint:** NPP is what is left for heterotrophs after producers have taken what they need.

### Step 4: Identify the Role of Heterotrophs
- **Heterotrophs** are organisms that rely on consuming other organisms for their energy and nutrients. They cannot produce their own food and depend on the biomass produced by autotrophs (like plants).

**Hint:** Think of heterotrophs as consumers in the ecosystem that rely on the biomass produced by plants.

### Step 5: Analyze the Options
- The question asks for the total dry weight accessible to heterotrophs.
- **Option 1: Gross Primary Productivity** - Incorrect, as this includes biomass used by producers.
- **Option 2: Net Primary Productivity** - Correct, as this represents the biomass available for heterotrophs.
- **Option 3: Secondary Productivity** - Incorrect, as it refers to the biomass produced by heterotrophs.
- **Option 4: Tertiary Productivity** - Incorrect, as this term is not standard in ecological productivity discussions.

**Hint:** Focus on what is available for consumption by heterotrophs when evaluating the options.

### Conclusion
The total dry weight accessible to heterotrophs in an ecosystem is represented by **Net Primary Productivity (NPP)**.

**Final Answer:** Option 2: Net Primary Productivity (NPP)