Question

The green algae include both chlorophytes and charophyceans. Please describe that organism’s anatomy, organization and life history. In what ways are its life cycle similar to or different from that slime molds?

Answer 1

Green algae (Chlorophyta)

• Green algae belong to Kingdom Protista and are also termed as Chlorophyta or chlorophytes.
• 90% of the species belonging to Chlorophyta are restricted to fresh water habitats, 10% of the species are marine or humid terrestrial environment.

Anatomy:

• They are mostly single celled organisms (few multi-celled), belonging to kingdom Protista.
• They have eukaryotic cell structure.
• The cell wall usually contains cellulose.
• Cell contains cell organelles, like mitochondria, Golgi complex, endoplasmic reticulum, plastids, etc., as eukaryotic cells similar to plants.
• Usually there is a single nucleus, though coenocytic forms exhibit multiple nuclei.
• They have autotrophic mode of nutrition. Due to the presence of photosynthetic pigments- Chlorophyll a. chlorophyll b and accessory pigments like carotenes and xanthophylls.
• Photosynthetic pigments are present within the lamellae of an organized chloroplast.
• Reserved food is stored as starch, comprising of amylose and amylopectin.

Organization:

• They have varieties of thallus organization and forms:

1. Unicellular or single celled forms-

• Spherical shapes to irregular shapes.
• May be unicellular motile forms- spherical, oblong or pear-shaped, motility with flagella.
• Example Chlamydomonas.
• Non-motile form- without locomotory outgrowths, cells may be covered with various structures like scales, plates, loricate.
• Example Chlorella.

2. Colonial forms-

• Each single celled form may exist in clump.
• No division of labor between colonial cells, each cell are independent in cellular functions.
• May possesses flagella for motility synchronously.
• Example Oocystis.

3. Coenobium form-

• Cells exists in colonies of fixed or specific numbers of cells.
• Cells often embedded in mucilaginous matrix.
• Most cells are vegetative, few are reproductive, but no division of labour.
• Example Volvox.

Life history:

• Life history includes vegetative and reproductive cells.

1. Vegetative propagation:

• Asexual means of reproduction.
• Occurs by cell division ad fragmentation.
• Asexual spores include- akinetes, zoospores, aplanospores.

2. Reproductive propagation:

• Sexual means of reproduction.
• Modes may be isogamous, anisogamous or oogamous.
• Zygote or oospores formed may exhibit a resting phase by secreting a thick wall around them, and germinate in favorable conditions.

Green algae and slime molds:

Similarities:

• Divisions of kingdom Protista.
• Both are eukaryotic.
• Both may have flagella for motility.
• Mostly are unicellular.
• Asexual and sexual reproduction

Differences:

Green algae	Slime molds
Belongs to division Chlorophyta	Belongs to division Amoebozoa
Autotrophic mode of nutrition	Heterotrophic mode of nutrition
They are photosynthetic: photosynthetic pigments in chloroplast present. Example Chlorella	Decomposers- can break down organic compouds example: plasmodium