Two Fusions Happen Inside One Ovule and Both Are Needed
Follow the pollen tube from the stigma to the embryo sac, work out why one fusion gives a diploid embryo and the other a triploid endosperm, and see what the ovary and the ovule become.
Why does a flowering plant fertilise twice instead of once?
In almost every animal, fertilisation is one event. One sperm fuses with one egg, a zygote forms, and the story begins.
In a flowering plant two fusions happen, in the same ovule, at almost the same moment. Two male gametes arrive together in the pollen tube, and each has a different target.
One fuses with the egg cell and makes the embryo — the future plant. That is the fertilisation you would expect.
The other fuses with two other nuclei in the same sac and makes the endosperm — the food store that will feed the embryo until it can feed itself.
So the plant makes the baby and the baby's packed lunch in the same operation, and both fusions are necessary. An embryo with no endosperm has nothing to live on; an endosperm with no embryo feeds nothing.
That pairing is unique to flowering plants, and it is the reason the whole event is called double fertilisation.
The arithmetic is worth watching too, because it comes out unusual. The embryo ends up diploid, as an embryo should. The endosperm ends up triploid — three sets of chromosomes — and that odd number is the fingerprint of the second fusion.
This page covers the third part of the ICSE Class 9 Biology chapter on flowering plants: the events between pollination and fertilisation, double fertilisation and triple fusion with their products, and the fruit and the seed with the significance of each.
In a flowering plant two fusions happen, in the same ovule, at almost the same moment. Two male gametes arrive together in the pollen tube, and each has a different target.
One fuses with the egg cell and makes the embryo — the future plant. That is the fertilisation you would expect.
The other fuses with two other nuclei in the same sac and makes the endosperm — the food store that will feed the embryo until it can feed itself.
So the plant makes the baby and the baby's packed lunch in the same operation, and both fusions are necessary. An embryo with no endosperm has nothing to live on; an endosperm with no embryo feeds nothing.
That pairing is unique to flowering plants, and it is the reason the whole event is called double fertilisation.
The arithmetic is worth watching too, because it comes out unusual. The embryo ends up diploid, as an embryo should. The endosperm ends up triploid — three sets of chromosomes — and that odd number is the fingerprint of the second fusion.
This page covers the third part of the ICSE Class 9 Biology chapter on flowering plants: the events between pollination and fertilisation, double fertilisation and triple fusion with their products, and the fruit and the seed with the significance of each.
What happens between the pollen landing and the gametes meeting?
The pollen grain germinates on the stigma and grows a tube all the way down the style into the ovule, carrying the two male gametes to the embryo sac.
Pollination ended when the grain landed. Everything in this section happens afterwards, and it can take from a few hours to several days.
The sequence, step by step.
- A pollen grain lands on the stigma. It must be of the same species and compatible with that flower, or nothing further happens
- The sticky surface of the stigma holds the grain, and the grain absorbs water and nutrients from it
- The grain germinates. Its outer wall, the exine, is tough and does not stretch, so the inner wall, the intine, grows out through a thin germ pore as a slender pollen tube
- The tube grows down through the style, digesting a path with enzymes as it goes, and it is guided chemically towards the ovary
- Inside the tube travel the two male gametes, formed by the division of the generative nucleus, with the tube nucleus ahead of them
- The tube enters the ovule, usually through the micropyle, and pushes on to the embryo sac
- The tip of the tube bursts, releasing the two male gametes into the embryo sac
Two details of that sequence carry marks.
The exine does not stretch — so the tube must emerge through a germ pore, a thin place deliberately left in the tough outer wall. A pollen grain without a germ pore could not germinate at all, and that is why the pores are counted and described when a pollen grain is examined.
And the tube is guided, not wandering. It grows towards the ovary because of chemical signals from the ovule, which is why a pollen tube does not grow sideways out of the style or in circles.
Notice what the pollen grain actually is, because it explains the whole design. It is not a gamete. It is a tiny package that contains the gametes and can survive being dried, blown about and carried on an insect's leg — and then grow a tube to deliver its contents to the right place.
So the pollen grain solves a problem that an animal never has to face. An animal's gametes meet in a moist environment and can swim. A plant is fixed in one place, its gametes cannot travel by themselves, and the journey may be through dry air over a long distance. The answer is to send the gametes inside a waterproof carrier and grow a private tunnel at the far end, and that is what the exine and the pollen tube between them accomplish.
Pollination ended when the grain landed. Everything in this section happens afterwards, and it can take from a few hours to several days.
The sequence, step by step.
- A pollen grain lands on the stigma. It must be of the same species and compatible with that flower, or nothing further happens
- The sticky surface of the stigma holds the grain, and the grain absorbs water and nutrients from it
- The grain germinates. Its outer wall, the exine, is tough and does not stretch, so the inner wall, the intine, grows out through a thin germ pore as a slender pollen tube
- The tube grows down through the style, digesting a path with enzymes as it goes, and it is guided chemically towards the ovary
- Inside the tube travel the two male gametes, formed by the division of the generative nucleus, with the tube nucleus ahead of them
- The tube enters the ovule, usually through the micropyle, and pushes on to the embryo sac
- The tip of the tube bursts, releasing the two male gametes into the embryo sac
Two details of that sequence carry marks.
The exine does not stretch — so the tube must emerge through a germ pore, a thin place deliberately left in the tough outer wall. A pollen grain without a germ pore could not germinate at all, and that is why the pores are counted and described when a pollen grain is examined.
And the tube is guided, not wandering. It grows towards the ovary because of chemical signals from the ovule, which is why a pollen tube does not grow sideways out of the style or in circles.
Notice what the pollen grain actually is, because it explains the whole design. It is not a gamete. It is a tiny package that contains the gametes and can survive being dried, blown about and carried on an insect's leg — and then grow a tube to deliver its contents to the right place.
So the pollen grain solves a problem that an animal never has to face. An animal's gametes meet in a moist environment and can swim. A plant is fixed in one place, its gametes cannot travel by themselves, and the journey may be through dry air over a long distance. The answer is to send the gametes inside a waterproof carrier and grow a private tunnel at the far end, and that is what the exine and the pollen tube between them accomplish.
What are double fertilisation and triple fusion, and what does each produce?
Two separate fusions occur in the embryo sac: one male gamete fuses with the egg cell, and the other fuses with the secondary nucleus.
What is waiting inside the embryo sac.
- The egg cell, or ovum, which is haploid — one set of chromosomes, written
- Two polar nuclei, each haploid, which fuse together to form the secondary nucleus. Being two haploid nuclei joined, the secondary nucleus is diploid, written
The first fusion — syngamy. One male gamete fuses with the egg cell :
The product is the zygote, which is diploid. This is true fertilisation, and the zygote develops into the embryo — the young plant with its radicle, plumule and cotyledons.
The second fusion — triple fusion. The other male gamete fuses with the secondary nucleus :
The product is the primary endosperm nucleus, which is triploid. It develops into the endosperm, the nourishing tissue that feeds the growing embryo.
Why each name means what it says.
- It is called triple fusion because three haploid nuclei take part — one male gamete and the two polar nuclei. Three nuclei, one product
- The whole event is called double fertilisation because two fusions occur in the same embryo sac, using the two male gametes that arrived in one pollen tube
Do the arithmetic and the two names explain themselves. The zygote is and the endosperm nucleus is . A triploid tissue cannot arise from a single fusion of two haploid nuclei — the only way to reach is for three haploid sets to come together, which is precisely what triple fusion does. So the ploidy is the proof, and a question asking why the endosperm is triploid is answered by that sum.
What every part becomes after fertilisation.
- Zygote becomes the embryo
- Primary endosperm nucleus becomes the endosperm
- The ovule becomes the seed
- The ovary becomes the fruit
- The integuments of the ovule become the seed coat, its two layers being the testa and the tegmen
- The calyx, corolla, stamens, style and stigma have done their work and usually wither and fall off
That last line is worth noticing. The petals that made the flower beautiful, the anthers that made the pollen and the stigma that caught it are all discarded once the pollen has been delivered. A flower is temporary machinery, and what survives it is the fruit and the seed. A question listing the fates of the floral parts expects the withering as well as the transformations.
And notice that double fertilisation is a feature of flowering plants alone. No other group of plants does it. That is why it is worth a name of its own, and why it appears in the definition of the group.
What is waiting inside the embryo sac.
- The egg cell, or ovum, which is haploid — one set of chromosomes, written
- Two polar nuclei, each haploid, which fuse together to form the secondary nucleus. Being two haploid nuclei joined, the secondary nucleus is diploid, written
The first fusion — syngamy. One male gamete fuses with the egg cell :
The product is the zygote, which is diploid. This is true fertilisation, and the zygote develops into the embryo — the young plant with its radicle, plumule and cotyledons.
The second fusion — triple fusion. The other male gamete fuses with the secondary nucleus :
The product is the primary endosperm nucleus, which is triploid. It develops into the endosperm, the nourishing tissue that feeds the growing embryo.
Why each name means what it says.
- It is called triple fusion because three haploid nuclei take part — one male gamete and the two polar nuclei. Three nuclei, one product
- The whole event is called double fertilisation because two fusions occur in the same embryo sac, using the two male gametes that arrived in one pollen tube
Do the arithmetic and the two names explain themselves. The zygote is and the endosperm nucleus is . A triploid tissue cannot arise from a single fusion of two haploid nuclei — the only way to reach is for three haploid sets to come together, which is precisely what triple fusion does. So the ploidy is the proof, and a question asking why the endosperm is triploid is answered by that sum.
What every part becomes after fertilisation.
- Zygote becomes the embryo
- Primary endosperm nucleus becomes the endosperm
- The ovule becomes the seed
- The ovary becomes the fruit
- The integuments of the ovule become the seed coat, its two layers being the testa and the tegmen
- The calyx, corolla, stamens, style and stigma have done their work and usually wither and fall off
That last line is worth noticing. The petals that made the flower beautiful, the anthers that made the pollen and the stigma that caught it are all discarded once the pollen has been delivered. A flower is temporary machinery, and what survives it is the fruit and the seed. A question listing the fates of the floral parts expects the withering as well as the transformations.
And notice that double fertilisation is a feature of flowering plants alone. No other group of plants does it. That is why it is worth a name of its own, and why it appears in the definition of the group.
What are a fruit and a seed, and why does a plant need both?
A fruit is the ripened ovary of a flower, and a seed is the ripened ovule inside it.
The fruit.
- It develops from the ovary after fertilisation, and it contains the seeds
- A true fruit develops from the ovary alone. Examples: mango, tomato, grape
- A false fruit has other floral parts contributing to the edible portion — usually the thalamus. Examples: apple, pear, cashew
- A parthenocarpic fruit develops without fertilisation, and therefore has no seeds. Examples: banana, some varieties of grape
The seed.
- It develops from the ovule, and contains three things: the embryo, a store of food, and a protective seed coat
- The embryo consists of the radicle which becomes the root, the plumule which becomes the shoot, and one or two cotyledons
- The food is stored either in the cotyledons or in the endosperm
- The seed coat comes from the integuments of the ovule — the tough outer testa and the thin inner tegmen
Significance of the fruit.
- It protects the developing seeds from damage, from drying out and from being eaten before they are ready
- It helps in the dispersal of the seeds. A fleshy edible fruit is eaten and the seeds are carried away and dropped elsewhere; a winged fruit is carried on the wind; a hooked fruit catches on an animal's coat
- It stores food which nourishes the developing seed, and which in a fleshy fruit is the reward that attracts the dispersal agent
Significance of the seed.
- It contains the embryo, the next generation of the plant, together with the food to start it growing before it can make its own
- It protects the embryo through unfavourable conditions in a dormant state, so that the species survives a drought, a cold season or a fire, and germinates when conditions improve
- It is the unit of dispersal, spreading the species to new ground and away from competition with the parent
- It carries the hereditary characters to the next generation, and a seed formed by cross-pollination carries the variation that the previous part of this chapter explained
Now the point that ties the two together. The seed carries the life and the fruit carries the logistics. Everything a seed does is about the next generation surviving; everything a fruit does is about getting that seed away from the parent and keeping it safe on the way.
Which is why dispersal matters so much more than it first appears. A seed falling straight down lands in the shade of its own parent, competing with a much larger plant for the same light, water and minerals — and it will usually lose. The fruit exists to prevent exactly that, and a mango that is sweet enough to be carried a kilometre away and dropped is a mango tree solving its offspring's competition problem.
And parthenocarpy is the neat exception that tests the definitions. A banana is a genuine fruit — it developed from an ovary — but it has no seeds, because no fertilisation occurred. So a fruit does not prove that fertilisation happened, and a question asking whether a seedless fruit is a fruit at all is answered by the definition: it is the ripened ovary, seeds or no seeds.
The fruit.
- It develops from the ovary after fertilisation, and it contains the seeds
- A true fruit develops from the ovary alone. Examples: mango, tomato, grape
- A false fruit has other floral parts contributing to the edible portion — usually the thalamus. Examples: apple, pear, cashew
- A parthenocarpic fruit develops without fertilisation, and therefore has no seeds. Examples: banana, some varieties of grape
The seed.
- It develops from the ovule, and contains three things: the embryo, a store of food, and a protective seed coat
- The embryo consists of the radicle which becomes the root, the plumule which becomes the shoot, and one or two cotyledons
- The food is stored either in the cotyledons or in the endosperm
- The seed coat comes from the integuments of the ovule — the tough outer testa and the thin inner tegmen
Significance of the fruit.
- It protects the developing seeds from damage, from drying out and from being eaten before they are ready
- It helps in the dispersal of the seeds. A fleshy edible fruit is eaten and the seeds are carried away and dropped elsewhere; a winged fruit is carried on the wind; a hooked fruit catches on an animal's coat
- It stores food which nourishes the developing seed, and which in a fleshy fruit is the reward that attracts the dispersal agent
Significance of the seed.
- It contains the embryo, the next generation of the plant, together with the food to start it growing before it can make its own
- It protects the embryo through unfavourable conditions in a dormant state, so that the species survives a drought, a cold season or a fire, and germinates when conditions improve
- It is the unit of dispersal, spreading the species to new ground and away from competition with the parent
- It carries the hereditary characters to the next generation, and a seed formed by cross-pollination carries the variation that the previous part of this chapter explained
Now the point that ties the two together. The seed carries the life and the fruit carries the logistics. Everything a seed does is about the next generation surviving; everything a fruit does is about getting that seed away from the parent and keeping it safe on the way.
Which is why dispersal matters so much more than it first appears. A seed falling straight down lands in the shade of its own parent, competing with a much larger plant for the same light, water and minerals — and it will usually lose. The fruit exists to prevent exactly that, and a mango that is sweet enough to be carried a kilometre away and dropped is a mango tree solving its offspring's competition problem.
And parthenocarpy is the neat exception that tests the definitions. A banana is a genuine fruit — it developed from an ovary — but it has no seeds, because no fertilisation occurred. So a fruit does not prove that fertilisation happened, and a question asking whether a seedless fruit is a fruit at all is answered by the definition: it is the ripened ovary, seeds or no seeds.
Exam tip
Exam tip: do the ploidy arithmetic and list every fate
Pollination ends when the grain lands; fertilisation begins when the tube bursts. Keep the two words on their own stages.
Give the germination sequence in order: lands on a compatible stigma, absorbs water and nutrients, the intine grows out through a germ pore, the tube grows down the style, enters through the micropyle, and bursts in the embryo sac.
Say the exine does not stretch — that is why the tube emerges through a germ pore.
The tube carries TWO male gametes, with the tube nucleus ahead.
Syngamy: male gamete + egg cell = zygote , which becomes the embryo.
Triple fusion: male gamete + secondary nucleus = primary endosperm nucleus , which becomes the endosperm.
Write the arithmetic out — and . It proves the endosperm is triploid and earns the mark on its own.
"Triple fusion" is named for the THREE haploid nuclei — one male gamete and the two polar nuclei. "Double fertilisation" is named for the TWO fusions in one embryo sac.
List every fate: zygote to embryo; primary endosperm nucleus to endosperm; ovule to seed; ovary to fruit; integuments to seed coat (testa and tegmen); and the calyx, corolla, stamens, style and stigma wither and fall.
True fruit from the ovary alone (mango); false fruit with the thalamus contributing (apple); parthenocarpic fruit with NO fertilisation and no seeds (banana).
Seed = embryo (radicle, plumule, cotyledons) + stored food + seed coat.
And for significance, give the fruit protection and dispersal and the seed the embryo, its food, dormancy and heredity — each as a separate point.
Give the germination sequence in order: lands on a compatible stigma, absorbs water and nutrients, the intine grows out through a germ pore, the tube grows down the style, enters through the micropyle, and bursts in the embryo sac.
Say the exine does not stretch — that is why the tube emerges through a germ pore.
The tube carries TWO male gametes, with the tube nucleus ahead.
Syngamy: male gamete + egg cell = zygote , which becomes the embryo.
Triple fusion: male gamete + secondary nucleus = primary endosperm nucleus , which becomes the endosperm.
Write the arithmetic out — and . It proves the endosperm is triploid and earns the mark on its own.
"Triple fusion" is named for the THREE haploid nuclei — one male gamete and the two polar nuclei. "Double fertilisation" is named for the TWO fusions in one embryo sac.
List every fate: zygote to embryo; primary endosperm nucleus to endosperm; ovule to seed; ovary to fruit; integuments to seed coat (testa and tegmen); and the calyx, corolla, stamens, style and stigma wither and fall.
True fruit from the ovary alone (mango); false fruit with the thalamus contributing (apple); parthenocarpic fruit with NO fertilisation and no seeds (banana).
Seed = embryo (radicle, plumule, cotyledons) + stored food + seed coat.
And for significance, give the fruit protection and dispersal and the seed the embryo, its food, dormancy and heredity — each as a separate point.
Did you know
Why a seed that falls straight down is a seed in trouble
A large tree drops a great many seeds, and most of them land directly beneath it. Almost none of those will ever become a tree.
It is easy to assume the problem is crowding — too many seedlings in one place. That is part of it, but the bigger problem is the parent.
A seedling under a mature tree is competing for light with something a hundred times its size, whose canopy is already intercepting almost all of it. It is competing for water and minerals with a root system that has had decades to spread through that same patch of soil. The contest is not close.
So a plant that could only drop its seeds at its own feet would be producing offspring that mostly die in its own shade. And this is the problem the fruit exists to solve.
Every kind of fruit is a different answer to it. A fleshy sweet fruit is a bribe — an animal eats it, walks or flies some distance, and deposits the seeds elsewhere, often with a helping of manure. A winged or plumed fruit is a glider, spinning away on the wind. A hooked or bristly fruit is a stowaway, catching in fur and travelling until the animal grooms it out. A coconut is a boat, floating on seawater until it reaches a beach.
None of those has anything to do with fertilisation, which was over long before the fruit began to form. The fruit is pure logistics.
And it explains an everyday puzzle: why is a mango sweet? Not for our benefit, and not for the seed's nutrition — the seed has its own food store inside. The sweetness is the fee paid to whatever carries the seed away, and a fruit sweet enough to be worth carrying a kilometre is a tree buying its offspring a patch of unshaded ground.
Which makes the fruit the part of a plant that thinks about where its children will live — and the reason an orchard has to be planted by somebody, because left alone the seeds would never have got far enough apart.
It is easy to assume the problem is crowding — too many seedlings in one place. That is part of it, but the bigger problem is the parent.
A seedling under a mature tree is competing for light with something a hundred times its size, whose canopy is already intercepting almost all of it. It is competing for water and minerals with a root system that has had decades to spread through that same patch of soil. The contest is not close.
So a plant that could only drop its seeds at its own feet would be producing offspring that mostly die in its own shade. And this is the problem the fruit exists to solve.
Every kind of fruit is a different answer to it. A fleshy sweet fruit is a bribe — an animal eats it, walks or flies some distance, and deposits the seeds elsewhere, often with a helping of manure. A winged or plumed fruit is a glider, spinning away on the wind. A hooked or bristly fruit is a stowaway, catching in fur and travelling until the animal grooms it out. A coconut is a boat, floating on seawater until it reaches a beach.
None of those has anything to do with fertilisation, which was over long before the fruit began to form. The fruit is pure logistics.
And it explains an everyday puzzle: why is a mango sweet? Not for our benefit, and not for the seed's nutrition — the seed has its own food store inside. The sweetness is the fee paid to whatever carries the seed away, and a fruit sweet enough to be worth carrying a kilometre is a tree buying its offspring a patch of unshaded ground.
Which makes the fruit the part of a plant that thinks about where its children will live — and the reason an orchard has to be planted by somebody, because left alone the seeds would never have got far enough apart.
Exam relevance
Why does NEET keep returning to double fertilisation?
Because the ploidy of the embryo sac is one of the most reliably examined calculations in plant reproduction, and double fertilisation is where it is settled.
This is the foundation for Class 12 Biology Sexual Reproduction in Flowering Plants, examined in NEET. Class 12 keeps every term here and supplies the detail: the seven-celled, eight-nucleate embryo sac with its egg apparatus of one egg cell and two synergids, three antipodal cells, and the two polar nuclei that make the central cell. The pollen tube is shown entering through a synergid guided by chemicals from the filiform apparatus, and the two gametes are released there.
Ploidy questions are a standing NEET item. You are given a part of the seed or the ovule and asked for its number of chromosome sets. The whole set follows from the two sums on this page: the embryo is , the endosperm , the seed coat and the nucellus because they are maternal tissue, and the egg, synergids and antipodals . Getting the endosperm right is the key, and the arithmetic is what secures it.
The routes of entry are named and asked. Class 12 gives porogamy through the micropyle, chalazogamy through the chalaza and mesogamy through the integuments. The micropyle route described here is porogamy, the commonest, and the others appear as recall items.
The endosperm becomes a topic of its own. Class 12 distinguishes free nuclear, cellular and helobial endosperm development, and separates endospermic seeds where the endosperm persists from non-endospermic seeds where it is absorbed into the cotyledons — which is exactly the monocot-against-dicot difference the next part of this chapter takes up. Coconut water as free nuclear endosperm is a favourite example.
Apomixis and polyembryony are examined alongside parthenocarpy. Class 12 covers seed formation without fertilisation, and the citrus fruit with more than one embryo. The parthenocarpic banana mentioned here is the applied version, and its use in producing seedless fruit commercially is examinable.
Fruit and seed classification continues in morphology. Class 11 Morphology of Flowering Plants covers true and false fruits and the fruit types, and the significance of the seed given here — dormancy, dispersal, heredity — carries into Class 12 Strategies for Enhancement in Food Production, where seed banks and germplasm conservation depend on the embryo surviving dormant for long periods.
The economic angle is examined. Class 12 notes that the endosperm of wheat, rice and maize is what human agriculture actually harvests — the food we eat from a cereal grain is triploid endosperm tissue, which follows directly from the triple fusion on this page.
What the questions look like. For board work, expect describe the events from pollination to fertilisation, explain double fertilisation and triple fusion with their products, define fruit and seed, and state the significance of each. Ploidy must be shown where asked. For NEET, expect ploidy of a named structure, the embryo-sac diagram, routes of pollen tube entry, endosperm types and apomixis.
How board and competitive emphasis differ. A board paper rewards the named sequence and the two fusions with their products. A competitive paper assumes both and asks for the chromosome number of a stated tissue, or which cell the pollen tube enters through.
The single trap that costs the most marks. Saying the endosperm is diploid. It is triploid, because three haploid sets combine — one male gamete plus the two polar nuclei — and no single fusion of two haploid nuclei could reach . The defence is to write the two sums side by side before answering any ploidy question: for the embryo and for the endosperm. Once those two lines are on the page, every other ploidy in the seed can be read off them.
This is the foundation for Class 12 Biology Sexual Reproduction in Flowering Plants, examined in NEET. Class 12 keeps every term here and supplies the detail: the seven-celled, eight-nucleate embryo sac with its egg apparatus of one egg cell and two synergids, three antipodal cells, and the two polar nuclei that make the central cell. The pollen tube is shown entering through a synergid guided by chemicals from the filiform apparatus, and the two gametes are released there.
Ploidy questions are a standing NEET item. You are given a part of the seed or the ovule and asked for its number of chromosome sets. The whole set follows from the two sums on this page: the embryo is , the endosperm , the seed coat and the nucellus because they are maternal tissue, and the egg, synergids and antipodals . Getting the endosperm right is the key, and the arithmetic is what secures it.
The routes of entry are named and asked. Class 12 gives porogamy through the micropyle, chalazogamy through the chalaza and mesogamy through the integuments. The micropyle route described here is porogamy, the commonest, and the others appear as recall items.
The endosperm becomes a topic of its own. Class 12 distinguishes free nuclear, cellular and helobial endosperm development, and separates endospermic seeds where the endosperm persists from non-endospermic seeds where it is absorbed into the cotyledons — which is exactly the monocot-against-dicot difference the next part of this chapter takes up. Coconut water as free nuclear endosperm is a favourite example.
Apomixis and polyembryony are examined alongside parthenocarpy. Class 12 covers seed formation without fertilisation, and the citrus fruit with more than one embryo. The parthenocarpic banana mentioned here is the applied version, and its use in producing seedless fruit commercially is examinable.
Fruit and seed classification continues in morphology. Class 11 Morphology of Flowering Plants covers true and false fruits and the fruit types, and the significance of the seed given here — dormancy, dispersal, heredity — carries into Class 12 Strategies for Enhancement in Food Production, where seed banks and germplasm conservation depend on the embryo surviving dormant for long periods.
The economic angle is examined. Class 12 notes that the endosperm of wheat, rice and maize is what human agriculture actually harvests — the food we eat from a cereal grain is triploid endosperm tissue, which follows directly from the triple fusion on this page.
What the questions look like. For board work, expect describe the events from pollination to fertilisation, explain double fertilisation and triple fusion with their products, define fruit and seed, and state the significance of each. Ploidy must be shown where asked. For NEET, expect ploidy of a named structure, the embryo-sac diagram, routes of pollen tube entry, endosperm types and apomixis.
How board and competitive emphasis differ. A board paper rewards the named sequence and the two fusions with their products. A competitive paper assumes both and asks for the chromosome number of a stated tissue, or which cell the pollen tube enters through.
The single trap that costs the most marks. Saying the endosperm is diploid. It is triploid, because three haploid sets combine — one male gamete plus the two polar nuclei — and no single fusion of two haploid nuclei could reach . The defence is to write the two sums side by side before answering any ploidy question: for the embryo and for the endosperm. Once those two lines are on the page, every other ploidy in the seed can be read off them.
Key takeaways
Fertilisation, the fruit and the seed: quick revision
- Pollination ends when the pollen lands; fertilisation begins when the pollen tube bursts.
- Sequence: the grain lands on a compatible stigma of the same species, is held by the sticky surface, absorbs water and nutrients, and germinates.
- The exine does not stretch, so the intine grows out through a germ pore as the pollen tube.
- The tube grows down the style, digesting a path and chemically guided, carrying the two male gametes with the tube nucleus ahead.
- It enters the ovule through the micropyle, reaches the embryo sac, and bursts, releasing both gametes.
- The pollen grain is not a gamete — it is a waterproof carrier for the gametes, which is how a fixed plant delivers them across dry air.
- Inside the embryo sac: the egg cell , and two polar nuclei that fuse into the secondary nucleus .
- Syngamy: male gamete + egg cell = zygote — true fertilisation — which becomes the embryo.
- Triple fusion: male gamete + secondary nucleus = primary endosperm nucleus , which becomes the endosperm.
- "Triple fusion" is named for the three haploid nuclei involved; "double fertilisation" for the two fusions in one embryo sac.
- The endosperm is triploid, and the arithmetic is the proof.
- Double fertilisation occurs only in flowering plants.
- Fates: zygote to embryo; primary endosperm nucleus to endosperm; ovule to seed; ovary to fruit; integuments to seed coat (testa and tegmen); calyx, corolla, stamens, style and stigma wither and fall.
- Fruit = the ripened ovary. True fruit from the ovary alone (mango, tomato); false fruit with the thalamus contributing (apple, pear, cashew); parthenocarpic fruit formed without fertilisation and therefore seedless (banana).
- Seed = the ripened ovule: the embryo (radicle, plumule, cotyledons), stored food, and the seed coat.
- Significance of the fruit: protects the seeds, aids their dispersal, and stores food that nourishes the seed and rewards the dispersal agent.
- Significance of the seed: carries the embryo and its food; survives unfavourable conditions in a dormant state; is the unit of dispersal; and carries the hereditary characters, including the variation from cross-pollination.
- The seed carries the life and the fruit carries the logistics — dispersal matters because a seed landing under its parent competes with a far larger plant and loses.
- A fruit does not prove fertilisation happened — a parthenocarpic fruit is a genuine fruit with no seeds.
Write down and , name what each produces, and then list the six things the flower's parts turn into — if all six come out, this chapter is finished.
- Sequence: the grain lands on a compatible stigma of the same species, is held by the sticky surface, absorbs water and nutrients, and germinates.
- The exine does not stretch, so the intine grows out through a germ pore as the pollen tube.
- The tube grows down the style, digesting a path and chemically guided, carrying the two male gametes with the tube nucleus ahead.
- It enters the ovule through the micropyle, reaches the embryo sac, and bursts, releasing both gametes.
- The pollen grain is not a gamete — it is a waterproof carrier for the gametes, which is how a fixed plant delivers them across dry air.
- Inside the embryo sac: the egg cell , and two polar nuclei that fuse into the secondary nucleus .
- Syngamy: male gamete + egg cell = zygote — true fertilisation — which becomes the embryo.
- Triple fusion: male gamete + secondary nucleus = primary endosperm nucleus , which becomes the endosperm.
- "Triple fusion" is named for the three haploid nuclei involved; "double fertilisation" for the two fusions in one embryo sac.
- The endosperm is triploid, and the arithmetic is the proof.
- Double fertilisation occurs only in flowering plants.
- Fates: zygote to embryo; primary endosperm nucleus to endosperm; ovule to seed; ovary to fruit; integuments to seed coat (testa and tegmen); calyx, corolla, stamens, style and stigma wither and fall.
- Fruit = the ripened ovary. True fruit from the ovary alone (mango, tomato); false fruit with the thalamus contributing (apple, pear, cashew); parthenocarpic fruit formed without fertilisation and therefore seedless (banana).
- Seed = the ripened ovule: the embryo (radicle, plumule, cotyledons), stored food, and the seed coat.
- Significance of the fruit: protects the seeds, aids their dispersal, and stores food that nourishes the seed and rewards the dispersal agent.
- Significance of the seed: carries the embryo and its food; survives unfavourable conditions in a dormant state; is the unit of dispersal; and carries the hereditary characters, including the variation from cross-pollination.
- The seed carries the life and the fruit carries the logistics — dispersal matters because a seed landing under its parent competes with a far larger plant and loses.
- A fruit does not prove fertilisation happened — a parthenocarpic fruit is a genuine fruit with no seeds.
Write down and , name what each produces, and then list the six things the flower's parts turn into — if all six come out, this chapter is finished.