Question

Chlamydomonas and spirogyra are both photosynthetic but one of them is a protist and the other is a plant. Justify this statement.

Answer 1

Protista is complex and multicellularity versus unicellularity have nothing to do with this classification (at least not anymore, taxonomy is based on evolution and not anatomy). There's even argument over whether or not it is a true kingdom. Regardless, algae are included within it.

Chlamydomonas appears to be a green algae, which are also sometimes classified as a plant. This is because what we typically think of as plants evolved from the green algae, whereas other algae taxa such as diatoms, red algae, and brown algae are evolutionarily distinct. It really depends on where the line is drawn for where green algae wind up.

Protista in itself is now considered as an artificial clade. Although Chlamydomonas is a unicellular algae, it has many distinct physiology and morphology.

1. Photoactive modulation

2. Reserved food material

3. Mode of nutrition

4. Anatomy

When cladistics with these characters were performed, it has segregated with algae, in particular with members of volvocales. So this is providing a dillema to the taxonomist like Anthoceros in bryophytes.