Topic: Sexual Reproduction of Spirogyra

INTRODUCTION

What is spirogyra?
is a filamentous algae

Features:
– no stem/root/leaves
– no vascular tissue
– no archegonia

Sexual? Asexual?
Sexual during unfavourable conditions
Asexual during favourable conditions (priority)

How is asexual reproduction?
2n nucleus divides by meiosis to form n nuclei, and only one of the n nuclei will divide to form a new filament.


TAXONOMY
Kingdom: Protoctista
What can you remember about this kingdom?
Simple cellular organisation but with true nucleus (in short, nucleated eukaryotes).
No tissue differentiation.
Can reproduce both sexually (conjugation) or asexually (binary fission).
Name some examples under this kingdom?
Animal-like protists:
Amoeba (rhizopoda) – with pseudopodium (false foot)
Paramecium (ciliophora) – with cilia
Plant-like protists – photoautotrophs/algae:
Euglena (zoomastigna) – with flagellum & eyespot (to detect light)
Spirogyra (chlorophyta) – filamentous
Chlamydomonas (chlorophyta) – unicellular, with red eyespot
Fucus (phaeophyta) – has midrib region
Phylum: Chlorophyta
What can you remember about this phylum?
Photosynthetic.
Cell wall made of cellulose.
Stores food as starch.
SEXUAL REPRODUCTION
Stepwise:
1. 2 filaments come close to each other.
2. Conjugation tubes form between pairs of cell.
3. Protoplasts* from the cells of 1 filament migrate into the cells of another filament through the conjugation tube (from male/donor to female/recipient)
4. 2 protoplasts fuse to form a 2n zygote.
5. The zygote develops a thick protective wall around itself called zygospore. The parent cell walls rot away. The zygospore remains inactive during unfavourable conditions.
6. When the conditions are favourable, the 2n nucleus of zygospore undergoes meiosis–producing 4 n nuclei. Only 1 survives and the other 3 nuclei degenerate.
7. This n nucleus divides mitotically. The zygospore germinates to form a new filament.
*Protoplasts: all cell contents excluding cell wall
These zygospores can withstand harsh conditions, e.g. during cold winter or when the pond dries up.

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