Q.Chlamydomonas is microscopic whereas Sargassum is macroscopic, both are algae. Which characters of these plants include them in one group?

Chlamydomonas (microscopic, unicellular) and Sargassum (macroscopic, over 60 metres long) sit at opposite extremes of algal size, yet both are classified together as algae because the group is defined by body organisation, not scale.

Step 1. Thalloid body. Neither plant differentiates its body into true root, stem and leaves — Chlamydomonas is a single motile cell, and Sargassum, though huge, is still an undifferentiated thallus rather than a plant with true organs.

Step 2. Cell wall and pigment-based photosynthesis. Both have a cell wall built from polysaccharides/proteins and carry chlorophyll-based photosynthetic pigments (both, in fact, belong to classes that carry chlorophyll along with class-specific accessory pigments), making both autotrophic.

Step 3. Reproduction and life cycle. Both reproduce vegetatively, asexually and sexually, and both show alternation of generations with a dominant haploid phase, a pattern general to the algae as described in this chapter. …

List the organisational features (thalloid body, pigment-based autotrophy, alternation of generations) that define Thallophyta, and sh …

• Trying to classify by size instead of by body organisation and reproductive pattern. …