Reproduction in Lower Plants

Reproduction in Lower Plants

We will study the different types of reproduction in two lower plants, one Unicellular

• Algae (Chlamydomonas) and the other multicellular filamentous algae (Spirogyra), Chlamydomonas (A Unicellular Alga)

(i) It is a haploid unicellular alga found in fresh water ponds:

(ii) The plant body is pear-shaped with two flagella attached at the narrow end.

(iii) On one side of the cell an eye spot is present.

(iv) A large cup-shaped chloroplast is present.

(v) Towards the centre, a definite nucleus is present.

(vi) Chloroplast contains a single pyrenoid.

Reproduction

A. Asexual with the help of zoospores

• Chlamydomonas loses flagella and becomes non-motile.
• Its protoplasm (cytoplasm and nucleus) divides mitotically and forms 4-8 zoospores.
• The parent cell wall is ruptured and zoospores are released.
• Each zoospore develops a cell wall and grows into an adult cell.
• The parent cell does not exist any more.

B. Sexual Reproduction

• The cell become non-motile by losing its flagella.
• The protoplasm divides mitotically into 2,4,8,16,32 daughter cells.
• Each daughter cell develops flagella and is released in water by the rupture of mother cell wall. It acts as a gamete.
• The gamete is morphologically identical in structure but all identical (Isogamous).
• Gametes released from two different mother cells fuse together.

The contents of the gametes fuse and form a zygote (diploid). This is the only diploid stage in the life cycle of Chlamydomonas.