Sexual Reproduction in Flowering Plants
Class 12 · Biology
4 ideas in Class 12 Biology, explained in plain words, with games and quizzes to practise.
Anther, Pollen and Ovule
Part of: Before Fertilisation
The anther holds four pollen sacs wrapped in four wall layers, the innermost tapetum feeding young pollen. Mother cells divide by meiosis into tetrads that mature into two- or three-celled pollen with a tough sporopollenin coat. The ovule shelters one embryo sac: egg apparatus at the micropyle end, antipodals at the chalaza end, and a central cell with two polar nuclei.
Why it matters. These structures stage every later event, and wall-layer and ploidy questions recur in exams.
Formulas
- One anther holds four microsporangia
- Four wall layers with tapetum innermost
- Embryo sac is 7-celled and 8-nucleate
Key words
- Tapetum
- : The innermost anther wall feeding young pollen.
- Microsporogenesis
- : Meiotic formation of microspores from mother cells.
- Sporopollenin
- : The ultra-tough exine material resisting decay.
- Germ pore
- : An exine gap sprouting the pollen tube.
- Embryo sac
- : The 7-celled, 8-nucleate female gametophyte.
- Filiform apparatus
- : Synergid thickenings guiding the pollen tube.
Try it in two minutes
- Count the four sacs and four wall layers on a sketch.
- Trace one mother cell into a tetrad.
- Place the seven cells of the embryo sac on a diagram.
Try at home. Explain why pollen survives as fossils but intine does not.
Pollination and Outbreeding
Part of: Before Fertilisation
Autogamy moves pollen within one flower, geitonogamy between flowers of one plant, xenogamy between plants. Wind, water and animals carry grains; plants discourage selfing with timing, spacing, self-incompatibility and separate male and female flowers. Breeders use emasculation and bagging to control crosses.
Why it matters. Mating-pattern logic underlies hybrid breeding and most application questions in this chapter.
Key words
- Autogamy
- : Pollination within the same flower.
- Geitonogamy
- : Pollination across flowers of one plant.
- Xenogamy
- : Pollination between different plants.
- Cleistogamy
- : Selfing in buds that never open.
- Self-incompatibility
- : A genetic block stopping self-pollen.
- Emasculation
- : Removing anthers before crossing.
- Bagging
- : Covering flowers against stray pollen.
Try it in two minutes
- Sort the three pollination types by donor and receiver.
- Match each agent to one flower adaptation.
- List four outbreeding devices in one line each.
Try at home. Decide whether a garden creeper with unopened buds selfing sets seed by cleistogamy or by insect visits.
Double Fertilisation
Part of: Fertilisation
One male gamete fuses with the egg (syngamy) to form a diploid zygote; the other fuses with two polar nuclei (triple fusion) to form a triploid endosperm nucleus. The pollen tube enters through the micropyle into a synergid guided by the filiform apparatus. Endosperm tissue forms first to feed the young embryo.
Why it matters. Double fertilisation is unique to flowering plants and its products anchor many exam questions.
Formulas
- Syngamy: gamete + egg gives diploid zygote
- Triple fusion: gamete + 2 polar nuclei gives triploid PEN
Key words
- Syngamy
- : Fusion of one gamete with the egg.
- Triple fusion
- : Fusion of one gamete with two polar nuclei.
- Zygote
- : The diploid first cell of the embryo.
- Primary endosperm nucleus
- : The triploid nucleus starting endosperm.
- Micropyle
- : The ovule pore admitting the tube.
Try it in two minutes
- Write the two fusion equations.
- Track the tube from stigma to synergid.
- Order endosperm first, embryo after.
Try at home. Explain why the zygote waits while endosperm builds.
Seeds, Fruits and Apomixis
Part of: After Fertilisation
The zygote grows through proembryo, globular and heart stages into a dicot embryo with two cotyledons or a monocot with one scutellum. Seeds keeping endosperm are albuminous; those consuming it are not. Ovaries become true fruits and thalamus-aided ones are false; seedless fruits form by parthenocarpy. Apomixis makes seeds without fertilisation and polyembryony packs many embryos in one seed.
Why it matters. Seed and fruit classes plus hybrid-seed uses of apomixis are favourite reasoning questions.
Key words
- Albuminous seed
- : A seed keeping endosperm at maturity.
- Perisperm
- : Persistent nucellus in some seeds.
- Pericarp
- : The fruit wall from the ovary.
- False fruit
- : A fruit aided by the thalamus.
- Parthenocarpy
- : Seedless fruit without fertilisation.
- Apomixis
- : Seed formation skipping fertilisation.
- Polyembryony
- : Many embryos in one seed.
- Scutellum
- : The single grass cotyledon.
Try it in two minutes
- Split seeds by endosperm kept or eaten.
- Split fruits by ovary only or ovary plus thalamus.
- Contrast parthenocarpy, apomixis and polyembryony.
Try at home. Sort kitchen seeds into albuminous and non-albuminous piles and justify each.
What your child will practise
- Anther, Pollen and Ovule: Desert Puzzle (Clue Puzzle)
- Anther, Pollen and Ovule: Desert Quick Fire (Quick Fire)
- Double Fertilisation: Space Puzzle (Clue Puzzle)
- Pollination and Outbreeding: Ocean Quick Fire (Quick Fire)
- Seeds, Fruits and Apomixis: Jungle Quest (Flip and Match)
- Quiz: Anther, Pollen and Ovule (8 questions)
- Quiz: Double Fertilisation (8 questions)
- Quiz: Pollination and Outbreeding (8 questions)
- Quiz: Seeds, Fruits and Apomixis (8 questions)