Assuming that the energy transfer efficiency between trophic levels is 10%, how much grain would be required to produce 70 kg of human biomass if the grain is eaten by cows and the cows are eaten by humans?

Options

A. 210 kg
B. 700 kg
C. 2,100 kg
D. 7,000 kg

Answer

To solve the problem of how much grain is required to produce 70 kg of human biomass, given that the energy transfer efficiency between trophic levels is 10%, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Trophic Levels**:
- In this scenario, there are two trophic levels:
- First trophic level: Grain (food source)
- Second trophic level: Cows (primary consumers)
- Third trophic level: Humans (secondary consumers)

2. **Energy Transfer Efficiency**:
- The energy transfer efficiency between trophic levels is given as 10%. This means that only 10% of the energy (or biomass) from one level is passed on to the next level.

3. **Calculate the Biomass Needed at Each Level**:
- We need to find out how much biomass is needed at the cow level to produce 70 kg of human biomass.
- Since only 10% of the biomass from cows is converted into human biomass, we can set up the equation:
\[ \text{Biomass needed from cows} = \frac{\text{Human biomass}}{\text{Efficiency}} = \frac{70 \text{ kg}}{0.10} = 700 \text{ kg} \]

4. **Calculate the Grain Required for Cows**:
- Now, we need to find out how much grain is required to produce 700 kg of cow biomass.
- Again, using the same efficiency:
\[ \text{Grain needed} = \frac{\text{Biomass needed from cows}}{\text{Efficiency}} = \frac{700 \text{ kg}}{0.10} = 7000 \text{ kg} \]

5. **Final Answer**:
- Therefore, the total amount of grain required to produce 70 kg of human biomass is **7000 kg**.

### Summary of Steps:
- Calculate the biomass needed at the cow level using the efficiency.
- Calculate the grain needed to produce that cow biomass using the same efficiency.