Volvox and Chlamydomonas are similar because they

The correct answer is both (a) and (b).

To understand why this is correct, let us analyze the characteristics of both organisms step-by-step:

1. Classification (Chlorophyta):
Both Volvox and Chlamydomonas belong to the phylum Chlorophyta, commonly known as green algae. They share fundamental biological traits, such as containing chlorophyll a and b, possessing cell walls made of cellulose, and storing food reserves in the form of starch.

2. Motility:
Both organisms are motile, meaning they have the ability to move actively using specialized structures:
- Chlamydomonas is a unicellular organism that possesses two flagella at its anterior end, which it beats in a whip-like fashion to swim through water.
- Volvox is a colonial organism. Each colony is a hollow sphere containing thousands of individual cells that resemble Chlamydomonas. Each of these surface cells has flagella, and their coordinated beating allows the entire sphere to roll and steer through the aquatic environment.

Since both organisms belong to Chlorophyta (a) and both are motile (b), the correct choice is both (a) and (b).