Incomplete double circulation is found in `:-`

Options

A. Reptiles and Birds
B. Amphibia and Reptiles
C. Birds and Mammals
D. Fish an Amphibia

Answer

**Step-by-Step Solution:**

1. **Understanding Circulation Types**:
- There are two main types of circulatory systems: complete double circulation and incomplete double circulation.
- In complete double circulation, blood passes through the heart twice during one complete circuit of the body.

2. **Identifying Heart Structures**:
- Fish have a two-chambered heart (one atrium and one ventricle) and exhibit a single circulation system, which is not considered double circulation.
- Amphibians and reptiles have a three-chambered heart (two atria and one ventricle), which leads to mixing of oxygenated and deoxygenated blood.

3. **Analyzing Amphibians and Reptiles**:
- In amphibians and reptiles, the right atrium receives deoxygenated blood, and the left atrium receives oxygenated blood. However, both types of blood mix in the single ventricle.
- This results in an incomplete double circulation because there is some mixing of blood, which does not allow for fully efficient oxygenation.

4. **Comparing with Other Groups**:
- Birds and mammals have a four-chambered heart (two atria and two ventricles), allowing for complete separation of oxygenated and deoxygenated blood, thus exhibiting complete double circulation.
- Fish do not have double circulation, so they are not included in this category.

5. **Conclusion**:
- Therefore, the organisms that exhibit incomplete double circulation are amphibians and reptiles.

**Final Answer**: Incomplete double circulation is found in amphibians and reptiles.

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