In which of the following sexual reproduction is of oogamous type and accompanied by complex post-fertilization developments ?

Options

A. Ulothrix
B. Spirogyrs
C. Polysiphonia
D. Ectocarpus

Answer

To solve the question regarding which organism exhibits oogamous sexual reproduction accompanied by complex post-fertilization developments, we can follow these steps:

### Step 1: Understand Oogamous Reproduction
Oogamous reproduction involves two types of gametes: a large, non-motile female gamete (egg) and a smaller, motile male gamete (sperm). This type of reproduction is characteristic of many higher plants and some algae.

**Hint:** Remember that in oogamous reproduction, the female gamete is larger and non-motile, while the male gamete is smaller and motile.

### Step 2: Analyze the Options
We need to evaluate the given options to identify which organism exhibits oogamous reproduction.

1. **Ulothrix**: This is a green filamentous alga that reproduces sexually through biflagellate gametes, meaning both gametes have flagella and are motile. Thus, it does not exhibit oogamous reproduction.

**Hint:** Look for the presence of motility in both gametes to determine if it is not oogamous.

2. **Spirogyra**: This alga reproduces through conjugation, which does not involve the formation of distinct male and female gametes. Therefore, it is not oogamous.

**Hint:** Conjugation is a form of sexual reproduction that does not fit the definition of oogamy.

3. **Polysiphonia**: This is a dioecious red alga, meaning it has separate male and female plants. The male gametes are produced in male plants and female gametes in female plants. This organism exhibits oogamous reproduction.

**Hint:** Dioecious plants often have distinct male and female gametes, which may indicate oogamous reproduction.

4. **Ectocarpus**: This is another alga that does not exhibit oogamous reproduction, as it typically has isogamous gametes.

**Hint:** Check if the organism has distinct male and female gametes to confirm if it is oogamous.

### Step 3: Conclusion
Based on the analysis, the only organism that fits the criteria of exhibiting oogamous reproduction and complex post-fertilization developments is **Polysiphonia**.

**Final Answer:** Polysiphonia is the correct answer.