Topic: Sexual Reproduction of Bryophyta

INTRODUCTION
What is Bryophyta?
A phylum under kingdom Plantae.
Our focus is on Marchantia, a bryophyte.
Features of phylum Bryophyta:
– No roots (but have root-like structure–rhizoid that absorbs water)
– No vascular tissue
– Has gemma cup for asexual reproduction
– Has simple photosynthetic tissue–thallus
– Gametophyte generation is dominant
What is ‘alternation of generation’?
2 phases: gametophyte (n) & sporophyte (2n).
Gametophyte (n) -> mitosis -> gametes (n).
Male gamete (n) + female gamete (n) -> fertilisation -> sporophyte (2n)
Sporophyte (2n) -> meiosis -> spores (n)
Spores (n) -> develop -> gametophyte (n)
Why sporophyte is dependent on gametophyte?
Sporophyte is non-photosynthetic.
It has to depend on gametophyte that is photosynthetic for nutrients.
Important: Most bryophytes are monoecious, except Marchantia (dioecious).
What does monoecious mean?
The male and female structures are found on the same plant.
SEXUAL REPRODUCTION OF MARCHANTIA
Identify the gametophyte and sporophyte.
Gametophyte: spores, thallus, gametes
Sporophyte: zygote, embryo
Describe the life cycle of Marchantia.
1. Young gametophyte n (which develops from spores) develops into male or female thallus.
2. Antheridiophores are borne on the male gametophyte.
Each antheridiophore consists of antheridia, which produces male gametes (antherozoid).
3. Archegoniophore are borne on the female gametophyte.
Each archegoniophore consists of archegonia, which produces female gametes (egg cells).
4. Fertilisation happens in the presence of a film of water.
Rain drops fall and antherozoid is released.
5. The antherozoid swims towards the archegonium, then fuses with ovum to form zygote (2n).
6. The 2n zygote – develop -> embryo – develop -> young sporophyte.
7. The young sporophyte remains attached to gametophyte(thallus) and is dependent upon it.
8. Young sporophyte – develop -> mature sporophyte (2n)
9. Spore mother cells in the mature sporophyte – meiosis -> spores (n)
10. Spores are dispersed by the coiling & uncoiling of elaters, in response to humidity changes.
10. Spore germinates – develop -> gametophyte (n)
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