Plant reproduction — A/L Biology

What must I remember about Plant reproduction?

• Angiosperms exhibit alternation of generations with a dominant diploid sporophyte (2n) and a reduced microscopic haploid gametophyte (n) dependent on the sporophyte.
• Microsporogenesis occurs in anther pollen sacs (microsporangia): microsporocytes (2n) undergo meiosis to form tetrads of microspores (n), developing into 2-celled pollen grains (tube cell + generative cell).
• Megasporogenesis occurs in ovules within ovary: single megasporocyte (2n) undergoes meiosis yielding four megaspores (n), of which three degenerate; the functional megaspore undergoes three mitotic divisions to produce the 7-celled, 8-nucleate female gametophyte (embryo sac: 3 antipodals, 2 polar nuclei in central cell, 2 synergids, 1 egg cell).
• Double fertilization is unique to angiosperms: one sperm cell (n) fertilizes the egg (n) to form the diploid zygote (2n), while the second sperm cell fuses with the two polar nuclei to form the triploid primary endosperm nucleus (3n).
• Following fertilization, the ovule develops into a seed (integuments become seed coat / testa, zygote becomes embryo, endosperm stores food), and the ovary wall becomes the fruit pericarp.

Test yourself (1 minute)

1. Pollen tube guidance

   Chemical attraction guides pollen tube growth down style through micropyle; synergids secrete chemical attractants.

2. Ploidy levels

   Zygote/embryo is 2n; Endosperm is 3n; Seed coat (testa) is 2n (maternal tissue); Embryo sac cells before fertilization are n.

3. Self-pollination vs Cross-pollination mechanisms

   Dichogamy (protandry/protogyny), dioecy, self-incompatibility, and heterostyly prevent self-pollination and promote genetic diversity.

Practise Plant reproduction questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 4

What should I study first?

What comes next?

Next in the syllabus

Where does Plant reproduction fit in the syllabus?

Year 1 · Term 3