Biology · Lesson 15

Reproduction in plants: flowers, pollination, fruits, seeds, germination

JAMBWAECNECO

What the syllabus asks

JAMB: Reproduction in plants: floral parts, pollination, fertilisation, fruits, seeds and their dispersal, germination

WAEC: Reproduction in flowering plants: structure of a flower, types of flowers, pollination (self and cross, agents, adaptations), fertilisation, development of fruits and seeds, classification of fruits, dispersal of fruits and seeds, structure of seeds, germination (epigeal and hypogeal) and conditions for germination; asexual (vegetative) reproduction

NECO: Reproduction in flowering plants: structure of a flower, types of flowers, pollination (self and cross, agents, adaptations), fertilisation, development of fruits and seeds, classification of fruits, dispersal of fruits and seeds, structure of seeds, germination (epigeal and hypogeal) and conditions for germination; asexual (vegetative) reproduction

What you will learn

Identify the parts of a flower and state their functions.
Distinguish between types of flowers and kinds of placentation.
Explain self- and cross-pollination and the adaptations of insect- and wind-pollinated flowers.
Describe fertilisation and the formation of fruits and seeds.
Classify fruits and describe their dispersal.
Describe seed structure, germination types and conditions for germination.
Describe common methods of vegetative propagation.

Key points

A flower has sepals, petals, stamens (anther + filament) and carpels (stigma + style + ovary).
Flowers may be complete or incomplete, bisexual or unisexual, regular or irregular.
Placentation: marginal (bean), axile (orange), parietal (pawpaw), basal (sunflower).
Pollination moves pollen to stigma; self or cross; agents mainly insects and wind.
Insect flowers: bright, scented, sticky pollen; wind flowers: dull, feathery stigma, light abundant pollen.
Double fertilisation: male + egg → zygote (2n); male + polar nuclei → endosperm (3n).
Ovary → fruit, ovule → seed; a fruit has two scars, a seed one.
Dispersal by wind, water, animals, explosion reduces competition.
Germination needs water, oxygen and warmth; epigeal (bean) or hypogeal (maize).
Vegetative organs: tubers, corms, bulbs, rhizomes, suckers; artificial: cuttings, grafting, budding, layering.

Start here: The flower and its parts

A flower is not just for beauty. It is a shoot specially changed for sexual reproduction. Pick a flower of the pride of Barbados (flamboyant's cousin) or the common hibiscus and look at it from the outside in. You find four rings, or whorls, attached to the swollen tip of the stalk called the receptacle.

Calyx: the outermost ring of green sepals. They protect the flower when it is a bud.
Corolla: the ring of petals. In insect-pollinated flowers they are bright and scented to attract insects.
Androecium: the male ring of stamens. Each stamen has a stalk called the filament and a head called the anther, which makes pollen grains.
Gynoecium: the female part in the centre, made of one or more carpels. Each carpel has a sticky stigma that receives pollen, a style that holds the stigma up, and an ovary that contains ovules.

The calyx and corolla together are called the perianth. In some flowers, such as the lily, sepals and petals look the same and are called tepals. Many flowers have nectaries at the base of the petals that make sweet nectar for insects.

Male part: stamen = anther + filament. Female part: carpel = stigma + style + ovary.

Worked example 15.1

A flower has 5 sepals, 5 petals, 10 stamens and 1 carpel. Each anther makes 2,400 pollen grains. How many pollen grains does the flower make?

Pollen comes only from anthers, one per stamen, so there are 10 anthers.
Total = 10 × 2,400 = 24,000 grains.

24,000 pollen grains

⚠️ Common mistake: calling the whole carpel the "ovary". The ovary is only the swollen base of the carpel.

Try it yourself. Which part of the flower receives pollen?

Show solution

The stigma.

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Practice questions

1. In flowering plants, the ovary develops into the

fruit
seed
testa
pericarp only

Show answer

A: fruit
Ovary → fruit; ovule → seed; integuments → testa.

2. A seed in which the food is stored in the cotyledons, such as the bean, is

endospermic
monocotyledonous
hypogeal
exalbuminous (non-endospermic)

Show answer

D: exalbuminous (non-endospermic)
Bean stores food in its cotyledons, so it lacks endosperm.

3. Which agent of pollination is associated with flowers that have feathery stigmas and light pollen?

Birds
Water
Wind
Insects

Show answer

C: Wind
Wind-pollinated flowers (e.g. grasses, maize) have light pollen and feathery stigmas.

4. The male part of a flower is the

sepal
stamen
carpel
petal

Show answer

B: stamen
Anther and filament.

5. Pollen is produced in the

anther
stigma
ovary
style

Show answer

A: anther
The top of the stamen.

Key words

Stamen: Male part of a flower: anther and filament.
Carpel (pistil): Female part: stigma, style and ovary.
Gynoecium: All the carpels of a flower.
Androecium: All the stamens of a flower.
Perianth: Calyx and corolla together.
Pollination: Transfer of pollen grains from anther to stigma.
Fertilisation: Fusion of a male gamete with a female gamete.
Double fertilisation: One male nucleus fuses with the egg, another with the polar nuclei to form endosperm.
Hermaphrodite (bisexual) flower: A flower with both stamens and carpels.
Placentation: Arrangement of ovules inside the ovary.
Pericarp: The fruit wall, formed from the ovary wall.
Cotyledon: Seed leaf, often storing food.

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