Primary 5 Science - Life Cycle of a flowering plan Page 1 of 6

Upper Block Science

Life Cycle of a Flowering Plant (I)

1. Why do plants reproduce

Plants reproduce their own kind so that they would not become extinct.

2. Parts of a Flower

Male Part

� The male part consists of anther and filament.

� The male part of the flower is also known as stamen.

� Anther contains pollen sacs which produce and release pollen grains.

� Filament supports the anther and holds it in a prominent position.

� Main function of the pollen grains is to fertilize the egg.

Female Part

� The female part consists of style, stigma, ovary and ovules.

� The female part of the flower is also known as pistil.

� Stigma is the platform for receiving pollen grains.

� Style connects the stigma to the ovary.

� Ovary contains undeveloped seeds known as ovules.

� Ovules contain female sex cells otherwise known as eggs.

Anther

Filament

Stigma

Style

Ovary

Ovule

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3. Types of flower

(i) Bisexual flower

• Plants that have both stamen and pistil in the same flower.

• Examples: Lily, Lady’s finger, String bean, Tomato, Hibiscus, Morning glory

(ii) Unisexual flower

• Plants that have stamen or pistil in different flowers.

���� Male and female flowers are found on the same plant.

���� Plant has either all male or all female flowers.

• Examples: Hazel tree, Papaya, Holly tree, Cucumber and Maize plant.

4. Life Cycle of a Flowering Plant

(i) Pollination (ii) Fertilization (iii) Dispersal (iv) Germination

Pollination

Fertilization

Dispersal

Germination

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5. Pollination

• It is the transfer of pollen grains from the anther to the stigma of a flower.

• When a plant’s pollen grains mature and is ready for pollination, the anthers

open by splitting down the middle.

• The 2 sides then curl back to expose and release the pollen grains.

• There are 2 types of pollination: Self pollination and Cross pollination

• Self pollination

� Transfer of pollen grains from the anther of a flower to the stigma of the

same flower (see path labeled as A)

� Transfer of pollen grains from the anther of a flower to the stigma of another

flower of the same plant (see path labeled as B)

• Cross pollination

� Transfer of pollen grains from the anther of a flower to the stigma of another

flower on a different plant. (see path labeled as C)

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6. Advantages of self pollination

•••• Offsprings are identical to the parent plant and retain all of its unique traits.

7. Advantages of cross pollination

• Young plants possess characteristics of both parent plants and are usually

healthier.

• New varieties may be produced which increases the possibility of survival.

8. Agents of pollination

• Agents of pollination refer to those who help to carry out the process of pollination

• Examples are wind and animals.

9. Pollination by wind

• Plants that use wind as pollinator include grasses, trees, rice, wheat, corn and

sugarcane.

• Pollen grains of these plants are small, light and can be easily blown from anthers

and carried by the wind.

• These plants normally have small, dull-coloured and unsecented flowers.

• Wind pollinated flowers produce incredibly large amount of pollen grains as it is

unsure where the wind will carry them.

• Anthers usually dangle outside the flowers to catch wind in order to transport the

pollen grains.

• Stigma are often large and feathery to gain a better chance of sweeping up the

pollen grains in the wind.

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10. Pollination by animals

• When an insect lands on the flowers, pollen grains with hooks / spikes will attach

themselves to the insect’s body or legs.

• When the insect visits another flower, the pollen grains get brushed off and

landed on the stigma of the flower.

• Insects visit flowers to eat the following

� To eat the nectar stored at the base of the petals.

� To eat the pollen grains which are nutritious.

• Colourful petals being brightly coloured or strongly scented attract the insects to

the pollen grains / nectar.

• Special makings / patterns on flower petals (honey guides) leads insects to its

nectar.

• Flowers produce their sweetest and strongest scents when the pollen grains are

ready for pollination.

11. Fertilization

• It occurs when the male gametes (cells) fuse with the female gametes.

• On reaching the stigma, the pollen grains will absorb water and germinate to

produce pollen tubes.

• The growth of pollen tubes is stimulated by a sugary solution secreted by the

stigma.

• The pollen tubes penetrate the stigma and grow through the style and the walls of

the ovary.

• Male gametes are inside the pollen tubes

• Inside each ovule is a female gamete (egg cell).

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12. Formation of Fruits and Seeds

• After fertilization, petals start to wither and eventually fall off.

• Ovary begins to swell to form fruit wall and develop to become a fruit.

• Ovules develop into seeds.

Pollen grains

Pollen tubes

Male gametes

Ovule (female gamate)

Ovary

Style

Stigma