Chapter 2 - Reproduction in flowering plants

• Flowers are the reproductive organs of flowering plants.
• DIFFERENT PARTS OF THE FLOWER (1) Male parts

  The stamen is the male reproductive part of a flower it consists of the anther and the filament.

  1. The anther is made up of pollen sacs, containing pollen grans.
  2. Pollen grains contain sperm (male reproductive cells), which can fertilize eggs. A fertilized egg develops into a seed that may lead to the formation of a young plant.
  3. The filament is a thin stalk that holds the anther up.
• DIFFERENT PARTS OF THE FLOWER (1) Female parts

  The carpel is the female reproductive part of the flower. The term pistil is used to refer to a carpel, or several carpels fused together. The carpel consists of the ovary, style, and stigma.

  1. The stigma receives the pollen grains.
  2. The style connects the stigma to the ovary.
  3. The ovary may contain one or more ovules.
  4. Each ovule contains an egg (ovum), the female reproductive cell.

  
• Not all flowers have both male and female parts. In some flowering plants, the male and female parts are found of the same flower, while others are found on separate flowers.

  Dioecious - Male and female parts are found on the same flower.

  Monoecious - Male and female parts are found on separate flowers.
• The male and female reproductive cells are known as gametes. Reproduction that involves the fusion of a male gamete and a female gamete is called sexual reproduction.

  Sexual reproduction in flowering plants involves the processes of pollination, fertilization, seed formation, and seed dispersal. After seeds are dispersed, they will germinate if conditions are right.
• The transfer of pollen from the anther to the stigma is called pollination. Pollen can easily be carried by wind or animals from the anther to the stigma of the same or another flower.
• COMPARING FLOWERS POLLINATED BY WIND AND ANIMALS

  Wind-pollinated flowers:

  • Petals: Small, dull-coloured, or absent
  • Scent: unscented
  • Nectar: absent
  • Stigma: Large or feathery, protrude out of the flowers
  • Stamens: Long, hang loosely out of the flowers.
  • Pollen grains: Numerous, tiny and light.

  Animal-pollinated flowers:

  • Petals: Showy, brightly coloured
  • Scent: Pleasant scent
  • Nectar: Present
  • Stigma: Small, do not protrude out of the flowers
  • Stamens: Do not hang loosely or protrude out of the flowers
  • Pollen grains: Sticky or spiky
• Insects such as bees, butterflies, moths, and wasps are important pollinators. Birds, bats, and humans also help pollinate flowers.
• WHAT HAPPENS AFTER POLLINATION?

  1. The pollen grains contains two cells -- a tube cell and a generative cell.
  2. The tube cell starts growing downwards to form the pollen tube.
  3. The generative cell divides to form 2 sperm nuclei. They travel through the tube to reach the ovule.
  4. One of the sperm nuclei fuses with the egg nucleus in the ovule to form a zygote (fertilized egg).
  5. The other sperm nucleus fuses with the central nucleus which will form the endosperm (food store for the seed).
• HOW ARE SEEDS FORMED?

  After fertilization, the petals and other parts that help in pollination wither and fall off. Seed formation begins.

  1. The zygote develops into an embryo that will eventually develop into a young plant.
  2. The endosperm starts to form, it stores and provides the food for the embryo.
  3. Each ovule develops into a seed, which carries the embryo and endosperm.

  The ovary develops into a fruit, which carries and protects the seeds. The seeds are released when fruit is ripe.
• Seeds can be dispersed by wind, water, animals, and explosions.
• SEEDS DISPERSED BY WIND

  Seeds that are dispersed by wind are usually small and light. The fruits may be fluffy or have a wing-like or parachute-like structures. They enable them to float, spin or glide in the air to be carried by the wind over long distances.
• SEEDS DISPERSED BY WATER

  The fruits or seeds dispersed by water are usually able to float on water.
• SEEDS DISPERSED BY ANIMALS

  The animals and humans help disperse the seeds as they move around. Some fruits are sweet and juicy. Animals eat them and disperse the seeds by throwing them away after eating the fruits. Sometimes, they swallow the seeds with the fruits. Some of these seeds are dispersed when they pass out with the animal droppings.
• SEEDS DISPERSED BY EXPLOSIONS

  When ripe, some fruits can split open with an explosive force. This can fling the seeds far away to disperse them.