🌸

Plant Reproduction

Asexual, sexual, flowers, seeds, dispersal

Asexual vs Sexual Reproduction

Asexual (one parent): Mitosis. Offspring genetically identical (clones). Fast. No mating needed.

Sexual (two parents): Meiosis + fusion (gamete fusion). Offspring genetically different. Slow. Requires pollination.

Asexual: strawberry runners, potato tubers. Sexual: most flowering plants.

Flower Structure

Sepals: Green, protective. Cover bud.

Petals: Coloured, attractive to pollinators.

Stamen (male): Anther (produces pollen) + filament (stalk).

Carpel (female): Stigma (sticky tip, receives pollen) + style (tube) + ovary (contains ovules).

Pollination = transfer of pollen from anther to stigma

Pollination — Wind vs Insect

Feature	Wind-Pollinated	Insect-Pollinated
Pollen	Light, dry, small	Sticky, large
Stigma	Feathery (large surface)	Sticky, small
Petals	Small, green, inconspicuous	Large, coloured, showy
Nectar/odour	No	Yes, attracts insects
Examples	Grass, wheat, hazel	Rose, apple, bee orchid

Fertilisation & Seed Development

Pollination: Pollen lands on stigma (sticky tip)

Pollen tube grows: Down style into ovary (takes hours/days)

Male nucleus fuses with female nucleus: In ovule. Forms zygote. Fertilisation = moment of fusion.

Ovule → seed: Integuments → seed coat. Nucellus → endosperm (food storage).

Ovary → fruit: Protects & disperses seeds.

Seed Structure

Testa (seed coat): Protective layer. Impermeable until imbibition.

Cotyledon(s): Seed leaves. Store food. Monocots (1), dicots (2).

Embryo: Radicle (root), plumule (shoot), cotyledons. Starts growing on germination.

Endosperm: additional food storage in some plants

Seed Dispersal Methods

Wind: Light seeds, wings (e.g., sycamore, dandelion). Blown by wind.

Animal: Seeds in fleshy fruit (e.g., apple, berry). Eaten, digested, excreted elsewhere.

Water: Buoyant seeds/fruits (e.g., coconut). Float to new locations.

Explosive: Pod bursts (e.g., bean, pea). Seeds catapulted away.

Dispersal reduces competition with parent plant for light/water/minerals

Germination — Growth from Seed

Conditions needed: Water (imbibition), oxygen (respiration), warmth (enzyme activity)

First: Radicle (root) grows DOWN (geotropism, gravity response)

Then: Plumule (shoot) grows UP (phototropism, light response)

Stored food used: For growth until leaves develop & photosynthesis starts

Once seedling has leaves → photosynthesis → independent growth

Exam Tips

✓ Asexual: mitosis, identical offspring; sexual: meiosis, variation

✓ Wind pollination: light pollen, feathery stigma, small petals

✓ Insect pollination: sticky pollen, large coloured petals, nectar

✓ Pollen tube grows down style; nucleus fuses in ovule

✓ Dispersal methods: wind, animal, water, explosive

✓ Germination needs: water, oxygen, warmth

Key Takeaways

✅ Asexual: one parent, identical (mitosis)

✅ Sexual: two parents, different (meiosis + fusion)

✅ Wind pollination: light pollen, feathery stigma

✅ Insect pollination: sticky pollen, coloured petals, nectar

✅ Pollen tube grows; nucleus fuses in ovule (fertilisation)

✅ Seed dispersal: wind, animal, water, explosive

✅ Germination: needs water, oxygen, warmth

From seed to flower to seed! 🌸✓