Q.The brown colour of Phaeophyceae is chiefly due to the accessory pigment:

Chlamydomonas is a small, ovoid, biflagellate green alga; its key labelled parts are the cell wall, two flagella, cup-shaped chloroplast with pyrenoid, nucleus, eyespot, and contractile vacuoles.

A hand-drawn figure can't be rendered in this text format, so here is the structure described part by part exactly as it would be labelled in a diagram, moving from outside to inside:

1. Cell wall: a rigid, smooth wall (made of glycoprotein, not cellulose) surrounding the cell, giving it its characteristic ovoid/pear shape.
2. Flagella (2): two whip-like, equal-length flagella project from the anterior (narrower) end of the cell, used for swimming; this is why Chlamydomonas is described as biflagellate.
3. Eyespot (stigma): a small, reddish-orange, light-sensitive spot located near the base of the flagella, at the anterior end, embedded in the chloroplast; it helps the cell detect light direction for phototaxis (swimming towards light).
4. Contractile vacuoles (2): two small, pulsating vacuoles located close to the base of the flagella at the anterior end; they regulate water balance by periodically expelling excess water from the cell.
5. Chloroplast: a single, large, cup-shaped (or bell-shaped) chloroplast occupies most of the cell, with its open end towards the anterior; it contains chlorophyll and carries out photosynthesis.
6. Pyrenoid: a dense proteinaceous body embedded within the chloroplast (usually at its base), associated with starch synthesis and storage.
7. Nucleus: a single, centrally located nucleus lies within the cup of the chloroplast, controlling the cell's activities.
8. Cytoplasm: fills the space between the chloroplast and the cell membrane, containing the usual cell organelles.

Together, a labelled diagram would show, from the anterior tip inward: the two flagella emerging through the cell wall, the eyespot and the two contractile vacuoles just behind them, the cup-shaped chloroplast with its pyrenoid filling the body of the cell, and the nucleus nestled inside the chloroplast's cup.