SPI Biology · Reproduction

Reproduction in Flowering Plants

A flower is the plant's reproductive part: pollen from the stamen reaches the stigma, a pollen tube carries the male gamete to the ovule, and the gametes fuse.

All Reproduction notes

Why this matters

Three questions in the bank, two EASY and one MODERATE: a pair of bisexual flowers, what fertilisation means, and why one pollen grain on a stigma did not grow a tube. Learn the parts of a flower, then the order: pollination first, fertilisation after.

Concept 1 of 2: Parts of a flower, bisexual and unisexual flowers

The male part of a flower is the stamen, which makes pollen. The female part is the pistil (carpel), which holds the ovules. A flower with both is bisexual; a flower with only one of them is unisexual.

Definition

Stamen (male): an anther on a filament. The anther makes pollen grains.
Pistil or carpel (female): stigma (sticky top), style (tube), ovary (holds the ovules).
Bisexual flower: has both stamens and pistil. Examples: hibiscus, mustard, rose, pea.
Unisexual flower: has only stamens or only a pistil. Examples: papaya, watermelon, cucumber, maize.
After fertilisation the ovary becomes the fruit and the ovules become seeds.

Flower	Stamens and pistil	Type
Hibiscus	Both	Bisexual
Mustard	Both	Bisexual
Papaya	Only one, on separate plants	Unisexual
Watermelon	Only one in each flower	Unisexual Papaya and watermelon are the unisexual examples to remember.

Practice this conceptself-check · 4 quick reps

The same idea in a practice question:

Practice questionEasy

Example 1 · Reproduction · Reproduction in Flowering Plants

Select a pair of bisexual flowers from the following:

Taking every flower as bisexual

Many flowers have both parts, but papaya and watermelon do not. Check each flower in a pair: one unisexual flower makes the pair wrong.

Concept 2 of 2: Pollination and fertilisation

Pollination is delivery: pollen is carried to a stigma. Fertilisation is the meeting itself: a male gamete fuses with the female gamete inside the ovule. In between, the pollen grain must grow a tube down the style, and it grows only on a stigma of its own kind of plant.

Definition

Pollination: transfer of pollen from an anther to a stigma, by insects, wind, water or birds.
Self-pollination: the same flower or plant. Cross-pollination: another plant of the same kind.
On a compatible stigma (same species), the pollen grain grows a pollen tube down the style to the ovule. Pollen of another species does not grow.
Fertilisation: the fusion of the nuclei of the male and female gametes. It forms the zygote.
Making gametes is a different step, done before all of this.

Step	What happens	Where
Pollination	Pollen carried to the stigma	Anther to stigma
Pollen tube	Grows from the pollen grain to the ovule	Down the style
Fertilisation	Male and female gamete nuclei fuse into a zygote	Inside the ovule Transfer is pollination; fusion is fertilisation.

Practice this conceptself-check · 4 quick reps

The same idea in a practice question:

Practice questionEasy

Example 2 · Reproduction · Reproduction in Flowering Plants

Fertilisation is the process of

Calling the transfer of a gamete fertilisation

Carrying the male gamete to the female one is only the step before. Fertilisation is the fusion of their nuclei.

Blaming the way pollen arrived

Once a pollen grain is resting on the stigma, it does not matter whether wind or an insect brought it. What decides if it grows a tube is whether it comes from a compatible plant.

Drill 1 more on pollination and fertilisation

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Parts of a flower, bisexual and unisexual flowers4 rows

Flower	Stamens and pistil	Type
Hibiscus	Both	Bisexual
Mustard	Both	Bisexual
Papaya	Only one, on separate plants	Unisexual
Watermelon	Only one in each flower	Unisexual Papaya and watermelon are the unisexual examples to remember.

Pollination and fertilisation3 rows

Step	What happens	Where
Pollination	Pollen carried to the stigma	Anther to stigma
Pollen tube	Grows from the pollen grain to the ovule	Down the style
Fertilisation	Male and female gamete nuclei fuse into a zygote	Inside the ovule Transfer is pollination; fusion is fertilisation.

Watch out for (3)

Taking every flower as bisexual
→ Parts of a flower, bisexual and unisexual flowers
Calling the transfer of a gamete fertilisation
→ Pollination and fertilisation
Blaming the way pollen arrived
→ Pollination and fertilisation

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