Amount of `CO_(2)` fixed annually is about

Options

A. `7xx10^23` ton
B. `7xx10^13` ton
C. `7xx10^10` ton
D. `7xx10^11` ton

Answer

To solve the question regarding the amount of CO2 fixed annually, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbon Fixation**:
- Carbon fixation is the process by which inorganic carbon (CO2) is converted into organic compounds by primary producers, mainly through photosynthesis.

2. **Identify Primary Producers**:
- Primary producers, such as green plants, utilize sunlight, water, and CO2 to produce glucose, which is an organic form of carbon.

3. **Gross Primary Production (GPP)**:
- The total amount of carbon fixed by primary producers is referred to as Gross Primary Production (GPP). This is the total mass of carbon that is converted from CO2 into organic matter.

4. **Annual Carbon Fixation**:
- It is stated that approximately 258 billion tons of CO2 is fixed annually by primary producers.

5. **Respiration Loss**:
- During the process of respiration, about 40% of the fixed carbon is lost. This means that only 60% of the fixed carbon remains in the ecosystem.

6. **Calculating the Fixed Carbon**:
- To find the amount of CO2 that remains after accounting for respiration:
- Calculate 60% of the total carbon fixed:
\[ \text{Fixed Carbon} = 258 \text{ billion tons} \times 0.60 = 154.8 \text{ billion tons} \]

7. **Convert to Kilograms**:
- Since the question asks for the amount in kilograms, we convert billion tons to kilograms:
\[ 1 \text{ billion tons} = 10^{9} \text{ tons} = 10^{12} \text{ kg} \]
- Therefore,
\[ 154.8 \text{ billion tons} = 154.8 \times 10^{12} \text{ kg} = 154.8 \times 10^{12} \text{ kg} \]

8. **Final Result**:
- The amount of CO2 fixed annually is approximately \( 70 \times 10^{13} \text{ kg} \).

### Final Answer:
The amount of CO2 fixed annually is about \( 70 \times 10^{13} \text{ kg} \).

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