BIOL1030 Chap.9 Flowers, Pollination and Seeds
Flowers, Pollination and Seeds
Flowers, Pollination and Seeds covers Lecture 7 of the plant unit: how a plant rooted in place reproduces. It defines the sporophyte, the pollen grain and the embryo sac, and explains why flowering plant gametophytes are unusually small and dependent. Flower parts and their jobs lead into pollination by wind and animals, with rewards, heat-producing titan arums, deceptive orchids and coevolution as examples.
The chapter separates pollination from fertilisation, explains double fertilisation and its diploid zygote and triploid endosperm, and follows the ovule and ovary into seed and fruit. Self-pollination and outcrossing, dispersal and germination types, sexual and asexual reproduction, and the heat sensitivity of reproduction close the topic.
What this chapter covers
- 01
Flower parts and what each one does
- 02
Sporophyte, gametophyte and gamete in flowering plants
- 03
Rewards, heat, scent and deception in pollination
- 04
Pollination versus fertilisation
- 05
Double fertilisation: zygote and endosperm
- 06
Seeds, fruits, dispersal and germination
- 07
Outcrossing, asexual reproduction and heat stress
Worked example · free
Count the chromosomes through double fertilisation
- 1Gametes are haploid, so each sperm and the egg carry n = 7 chromosomes.
- 1The central cell holds two haploid nuclei, so it carries 2 x 7 = 14 chromosomes in total.
- 1Sperm plus egg gives the zygote 7 + 7 = 14 chromosomes, the diploid state of the sporophyte.
- 1The second sperm plus the central cell gives endosperm 7 + 14 = 21 chromosomes, which is triploid.
Key terms
- Sporophyte
- The diploid, spore-producing generation, which in flowering plants is the visible plant.
- Embryo sac
- The female gametophyte of a flowering plant, a few cells inside the ovule that produce the egg.
- Double fertilisation
- The two fusions in angiosperms, sperm with egg and sperm with the central cell, producing zygote and endosperm.
- Endosperm
- The triploid tissue formed from the central cell that nourishes the developing embryo.
- Hypogeal germination
- Germination in which the cotyledons stay below the soil surface.
Flowers, Pollination and Seeds FAQ
Is pollination the same as fertilisation?
No. Pollination is the transfer of pollen from anther to stigma. The pollen must then germinate and grow a tube down the style into the ovule, and only then do sperm fuse with the egg and central cell. A flower can therefore be pollinated and still fail to set seed.
Why is double fertilisation considered a key innovation?
It is unique to flowering plants and creates two products at once: the diploid zygote that becomes the embryo and the triploid endosperm that feeds it. Together with flowers, fruits and seeds it is credited with the evolutionary success of the angiosperms.
Why do so many plants avoid fertilising themselves?
Selfing guarantees some seed but reduces genetic diversity and can expose harmful mutations through inbreeding. Cross-pollination maintains variation, so natural selection often favours outcrossing and many species carry mechanisms that reduce the chance of self-fertilisation. Asexual spread avoids the problem only by producing clones.
Why is plant reproduction especially vulnerable to heat?
Of all the stages in a plant's life, pollination, fertilisation and seed set are among the easiest for heat to damage. High temperatures reduce pollen viability and slow pollen-tube growth, lowering seed set, and a warming climate raises the risk of this damage during flowering for crops and wild species.
What is the difference between epigeal and hypogeal germination?
In epigeal germination the seed leaves, or cotyledons, are carried above the soil as the seedling emerges. In hypogeal germination the cotyledons stay below ground while the shoot grows up past them. Either way, germination establishes the next sporophyte generation from the embryo the seed protected.
Exam move
Start by drawing the flowering plant life cycle with every structure labelled as sporophyte, gametophyte or gamete, and add ploidy to each. Then rehearse the sequence from pollen landing to seed and fruit as numbered steps, marking where pollination ends and fertilisation begins, because many questions hinge on that boundary.
Make a compact table of pollinator attraction strategies with one example each, and another comparing sexual and asexual reproduction. Close by explaining aloud why heat during flowering can cut yields even when bees are busy. Then check each answer against the double fertilisation diagram.
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