Isogamy is found in Spirogyra in which both gametes are non-motile. In Chlamydomonas, all three conditions, isogamy anisogamy and oogamy are found. Both motile and non-motile gametes are found. In Volvox and Fucus, oogamy is present, where non-motile egg fuses with motile sperm.
So, option 'A' is correct.

Spirogyra is a filamentous green alga that exhibits isogamous reproduction. Isogamy is a type of sexual reproduction in which the gametes are morphologically similar or identical. In Spirogyra, both the male and female gametes are non-flagellated.

Explanation:

Isogamy:
- Isogamy is a form of sexual reproduction where the gametes are similar or identical in size and shape.
- In isogamous organisms, the fusion of two gametes is essential for sexual reproduction.

Spirogyra:
- Spirogyra is a filamentous green alga that belongs to the division Chlorophyta.
- It is commonly found in freshwater habitats like ponds, ditches, and streams.
- Spirogyra exhibits vegetative reproduction by fragmentation and asexual reproduction by the formation of aplanospores.
- Sexual reproduction in Spirogyra occurs through a process called conjugation.

Conjugation in Spirogyra:
- Conjugation is a form of sexual reproduction in Spirogyra, where two filaments come in close contact and exchange genetic material.
- During conjugation, the cells of two adjacent filaments align parallel to each other and form conjugation tubes.
- The contents of one cell, called the donor cell, pass through the conjugation tube and enter the receiving cell.
- The transferred contents include the cytoplasm, nucleus, and chloroplasts, but not the entire cell.
- This process allows for genetic recombination and the formation of new variations.

Isogamous Condition in Spirogyra:
- In Spirogyra, the gametes involved in conjugation are isogamous, meaning they are morphologically similar.
- Both the male and female gametes of Spirogyra are non-flagellated.
- The gametes are produced by the differentiation of certain cells within the filament.
- The male gametes are small and cylindrical, while the female gametes are larger and ovoid.
- The male gametes are released from the donor filament and move towards the receiving filament through the conjugation tube.
- Once inside the receiving filament, the male gametes fuse with the female gametes, resulting in the formation of zygotes.

Therefore, the isogamous condition with non-flagellated gametes is found in Spirogyra (option A).