LIFE CYCLES OF PLANTS - Teaching Biology Project

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ALTERNATION OF

GENERATIONS

1.

2.

3.

Alternation of generations : haploid (n) stage that produces gametes followed by diploid

(2n) stage producing spores.

Haploid : gametes; half the number of chromosomes in somatic cell, indicated by n, result of meiosis.

Diploid : somatic cells; double number of chromosomes in gametes, indicated by 2n; result of fertilisation.

1.

Gametophyte : generation producing gametes in gametangium/ gametangia sexual stage.

2.

Sporophyte : generation producing spores in sporangium/ sporangia – asexual stage.

NB: In higher plants the generations alternate in the life cycle of a plant; in lower plants reproduction is either through gametes

(sexual) or spores etc. (asexual).

1.

A haploid gametophyte generation that produces gametes (n) by mitosis ...

the gametes (n) fuse to form zygote (2n), the start of ...

2.

A diploid sporophyte generation that produces spores (n) by meiosis.

1.

2.

Mosses (Bryophyta)

Ferns (Pterophyta/ Pteridophyta)

Seed plants (Spermatophyta)

Gymnospermae (cone-bearing plants producing seeds)

Angiospermae (flowering plants producing seeds)

Exam guidelines require study of mosses and flowering plants to highlight alternation of generations.

Leaf-like structures of moss gametophyte

Sporangium of moss sporophyte

Fern leaf (sporophyte) with sori (groups of sporangia

GYMNOSPERMS

ANGIOSPERMS

Gymnosperms have two types of sporangia – female and male

Female cones at different ages Male cones

Mosses

Ferns, gymnosperms and flowering plants

Gametophyte dominant

Sporophyte dominant

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