Chlorophyta-2  

Chlorophyceae

This is the Largest Class.

Cup-shaped Chloroplasts are Common.

An Eyespot (Stigma) is frequently present. This is used to detect light.

Chloroplast shapes can vary considerably, however.

Individual Chloroplasts may be interconnected.

Pyrenoids are present. These appear to be areas where starch is produced. Pyrenoids also contain a high concentration of RUBISCO. They are consequently thought to be adapted for Carbon fixation at low CO2 levels.

There are at least Three Distinct Groups in the Chlorophyceae

A] Volvocine = Motile

B] Trichocine = NON-Motile & Filamentous

C]  Chlorococcine = NON-Motile & NON-Filamentous

Volvocine Group

All members are flagellated.

Chlamydomonas represents a "basal" organism from which the group may have evolved.

A series of Colonial forms exists.

Each cell resembles Chlamydomonas.

The cells may be embedded in a gelatinous matrix.

Cells are interconnected by cytoplasmic strands.

The number of cells produced by different species is constant.

The ratio of reproductive to vegetative cells is also constant for a particular species.

Volvox represents the pinnacle of this group. It has a low ratio of reproductive to vegetative cells. However, all of the cells in Gonium, become reproductive.

The trend is towards an increase in the number of cells as well as a trend towards cell specialization with most cells specialized for Photosynthesis.