Question

From the examples of alternation of generations in plants, identify:
(i) Plant species where mitosis is seen in haploid cells.
(ii) Stages at which mitosis is seen in haploid cells in them

Answer 1

Part 1:Introduction to alternation of generation.
Alternation of the life cycle between diploid and haploid phases or the sporophytic and gametophytic stages in plants is known as alternation of generation.

Part 2: Types of alternation of generation in plants.
$\begin{array}{ccc}\text{Type of life cycle}& \text{Description}& \text{Examples}\\ \text{Haplontic}& \text{Haploid gametophytes}& \text{Algae}\\ & \text{are dominant and}& \\ & \text{free-living. Diploid}& \\ & \text{stage is represented by}& \\ & \text{the short-lived zygote}& \\ \text{Haplo-diplontic}& \text{Sporophytes and}& \text{Bryophytes}\\ & \text{gametophytes are}& \text{Pteridophytes}\\ & \text{multicellular and an}& \\ & \text{intermediate condition}& \\ & \text{exists.}& \\ \text{Diplontic}& \text{Diploid sporophyte is}& \text{Gymnosperms}\\ & \text{dominant and}& \text{Angiosperms}\\ & \text{independant and the}& \\ & \text{haploid stage is}& \\ & \text{represented by the}& \\ & \text{short-lived}& \\ & \text{gametophyte.}& \end{array}$

Part 3: Plant species where mitosis is seen in haploid cells.
Almost all types of plants undergo mitosis in the haploid cells, few of them
are mentioned below:-
● Algae (e.g., Chlamydomonas sp., Spirogyra sp. etc.)
● Bryophytes (e.g., Marchantia sp., Funaria sp., etc.)
● Pteridophytes (e.g., Selaginella sp., Equisetum sp., etc.)
● Gymnosperms (e.g., Cycas sp., Pinus sp., etc.)
● Angiosperms (e.g., Mangifera sp., Triticum sp., etc.)

Part 1: Mitosis in haplontic life cycle.
The main plant body of the bryophyte and some algae is haploid gametophyte. It produces gametes by mitosis.

Part 2: Mitosis in haplo-diplontic life cycle.
Bryophytes and pteridophytes have multicellular gametophytes. Hence, the haploid spore formed in the sporophyte undergoes mitosis to give rise to the gametophyte (protonema stage in mosses develops directly from a spore).
The sex organs in bryophytes are multicellular and haploid. They produce haploid male gametes, antherozoids and female gametes, eggs, by mitotic division.
Development of haploid gametophyte from haploid spore in pteridophyte needs mitosis in haploid cells.

Part 3: Mitosis in diplontic life cycle.
Diplontic plants such as gymnosperms and angiosperms undergo mitosis in the haploid gametophyte formed due to meiosis of gamete mother cell. In gymnosperms, the megaspore (haploid) develops into multicellular gametophyte by mitosis.
Specifically, in case of angiosperms, haploid microspore undergoes mitosis to form male gametes while the haploid megaspore undergoes mitosis to form seven-celled eight-nucleate embryo sac.