In which set of organisms does external fertilization occur

Options

A. Echinodermata and mosses
B. Hemichordata and ferns
C. Amphibians and algae
D. Reptiles and gymnosperms.

Answer

### Step-by-Step Solution:

1. **Understanding External Fertilization**:
External fertilization is a reproductive process where the fusion of gametes (sperm and egg) occurs outside the female's body. This typically happens in an aquatic environment, where both gametes are released into the water.

2. **Identifying Organisms**:
We need to analyze the options provided to identify which organisms are known for external fertilization:
- **Option A: Echinodermata and Mosses**: Echinoderms (like starfish) do exhibit external fertilization, but mosses reproduce via spores and do not have a fertilization process involving gametes in the same way.
- **Option B: Hemichordata and Ferns**: Hemichordates may have external fertilization, but ferns reproduce via spores and do not have a gamete fusion process like animals.
- **Option C: Amphibians and Algae**: Amphibians (like frogs) typically release eggs and sperm into water, leading to external fertilization. Algae also reproduce through gametes that fuse outside the organism in water.
- **Option D: Reptiles and Gymnosperms**: Most reptiles have internal fertilization, and gymnosperms reproduce via seeds and do not have external fertilization.

3. **Conclusion**:
Based on the analysis, the organisms that exhibit external fertilization are found in **Option C: Amphibians and Algae**.

### Final Answer:
The correct answer is **Option C: Amphibians and Algae**.

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