Lesson 2 of 12 · 10 min
Algae: body and reproduction
NCERT §3.1
On the first morning the tide is out. Rock pools hold green threads, a slimy film on the stones, and a long brown ribbon of seaweed. Meera's teacher says all three are algae, even though one is thinner than a hair and another is longer than the bus.
The lesson in notes
In short
Algae are simple, thalloid, autotrophic organisms that carry chlorophyll. Most live in water, fresh or marine, but some grow on moist stones, soil and wood, some live with fungi in lichens, and some live on animals such as the sloth bear.
Their size and form vary a lot: colonial Volvox, filamentous Ulothrix and Spirogyra, and marine kelps with very large plant bodies.
Vegetative reproduction is by fragmentation; every fragment grows into a new thallus.
Asexual reproduction is by spores of several kinds. Zoospores are the commonest; they carry flagella, swim, and germinate into new plants.
Sexual reproduction is the fusion of two gametes. When the two are of similar size it is isogamy: the gametes may both be flagellated (Ulothrix) or both lack flagella (Spirogyra).
When two gametes of unlike size fuse it is anisogamy, as in species of Eudorina.
When a large, non-motile female gamete fuses with a smaller, motile male gamete it is oogamy, as in Volvox and Fucus.