reproduction in plants

• what are the parts of a flower ?

  • flower stalk
  • receptable
  • sepals
  • petals
  • stamens
  • carpels
• petals are modified leaves that

  • brightly coloured to attract insects for pollination
  • provide a platform for insects to land
  • have lines that guide insects to the base of the petals to obtain nectar
• sepal are modified leaves which enclose and protect the other parts of the flower in the bud stage
• flower stalk attaches the flower to the stem
• receptable is the swollen end of the flower stalk
• the stamen consists of an anther and a filament
• filament hold the anther in a suitable position to disperse the pollen
• anther produces pollen grains and splits to release them when they are mature
• pollen grains contain male gametes which are produced by meiosis and are haploid
• carpel consists of an ovary, a style and stigma
• stigma is a swollen structure at the end of the style and receives the pollen grains. when it matures, it secretes a sugary fluid to stimulates the pollen grain to germinate
• the style connects the stigma to the ovary, holding the stigma in a suitable position to trap pollen grains
• ovary contains one or more ovules, where the inside contains the female gamete called ovum, which is produced by meiosis
• pollination is the transfer of pollen grains from the anther to the stigma
• self pollination is the transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant
• features favour self- pollination

  • bisexual flowers with anthers and stigmas maturing at the same time
  • stigma situated directly below anthers
• in certain plants with bisexual flowers, their flowers never open, so only self pollination can occur
• (+) of self pollination

  • only 1 parent required
  • Offspring more likely to inherit beneficial qualities from the parent plant
  • Does not need to depend on external factors such as insects or wind for pollination
  • Higher probability that pollination will occur as anthers are close to stigma, as compared to cross- pollination
  • Less pollen and energy are wasted in self- pollination as compared to cross- pollination
• (-) of self pollination

  • less genetic variation in the offspring as compared to cross pollination, so species is less well adapted to changes in the environment
  • continued self pollination may lead to offspring becoming weaker, smaller and less resistant to disease
• cross pollination is the transfer of pollen grains from the anther of one plant to the stigma of a flower from another plant of the same species
• features that favour cross pollination

  • Some plants, e.g. papaya, bear either male or female flowers, making it unable to undergo self pollination
  • In many plants with bisexual flowers, the anthers and the stigmas may mature at different times.
  • The stigmas of plants with bisexual flowers may be situated some distance away from the anthers so that self-pollination is unlikely
• (+) advantages of cross pollination ?

  • The offspring produced may have inherited beneficial qualities from both parents.
  • Greater genetic variation in the offspring produced as compared to self-pollination, increasing the chance of the species surviving changes in the environment because any change in the environment is less likely to destroy all the varieties in a species.
  • More viable seeds are produced which can survive longer before germination
• (-) of cross pollination

  • Two plants are required.
  • It depends on external factors such as insects or wind for pollination.
  • Since the pollen grains have to be transferred from the anther of one plant to the stigma of another plant, there is a lower probability that pollination will occur, as compared to self-pollination.
  • More energy and pollen are wasted as compared to self-pollination.
• Clitoria flower is bisexual but specially adapted for pollination by insects
• How is the clitoria flower's sepals adapted ?

  It has 5 green sepals
• How is the clitoria flower's petals adapted?

  • It has 5 brightly coloured petals of different sizes and shapes
  • The large, deep blue petal has nectar guides on it to guide insects to where nectar is located
• how is the clitoria flower's stamen adapted ?

  • The flower has stamens with long filaments.
  • Nectar, secreted by the flower, collects at the bottom of the stamen trough. Thus, the nectar can be reached only by an insect with a long tubular mouth or proboscis, for example, a bee or a butterfly.
• how is the clitoria flower's carpel adapted ?

  • The stigma is small and compact. It is located at the end of the style.
  • The style is a long, curved, hairy structure.
  • The ovary is long and narrow with a single row of ovules.
• process of insect pollination of clitoria

  1. An insect like a bee lands on the petal
  2. The insect follows the nectar guide into the flower.
  3. It forces its way and moves in to collect the nectar.
  4. As it moves in, the stigma and anthers brush against the hairy back of the insect, causing pollen grains from the anther stick to the hairy back of the insect
  5. Simultaneously, pollen grains from another flower on the insect's back are transferred to the sticky stigma.
• pollination of Ischaemum muticum

  • The stamens have long filaments and protruding anthers.
  • When the filaments sway in the wind, the dust-like pollen is shaken free and dispersed by the wind.
  • The stigmas are large, extended and feathery. Thus, they provide a large surface area to receive any pollen that is floating around in the wind.
• how are petal different in insect-pollinated flower than is wind-pollinated flower ?

  insect-pollinated flowers are usually large with brightly coloured petals to attract insects while wind-pollinated flowers are usually small and dull-coloured, without petals.
• how are nectar different in insect-pollinated flower than is wind-pollinated flower ?

  Nectar is present in insect-pollinated flower while nectar is absent in wind-pollinated flower
• how scent different in insect-pollinated flower than is wind-pollinated flower ?

  insect-pollinated flowers are fragrant or sweet- smelling while wind-pollinated flowers are odourless.
• how stigmas different in insect-pollinated flower than is wind-pollinated flower ?

  insect-pollinated flower stigmas are usually small, compact and do not protrude out of the flower but wind-pollinated flower stigmas are large, feathery and usually protrude out of the flower to provide a large surface area to trap pollen.
• how stamens different in insect-pollinated flower than is wind-pollinated flower ?

  insect-pollinated flower stamens are not pendulous and usually do not protrude out of the flower but wind-pollinated flower stamens have long pendulous filaments and protruding anthers, making pollen grains are easily shaken out.
• how are pollen grains different in insect-pollinated flower than is wind-pollinated flower ?

  Pollen is fairly abundant in insect-pollinated flowers while pollen is more abundant in wind-pollinated flowers

  Pollen grains in insect-pollinated flowers are usually larger with rough surfaces so that they can readily cling onto the body of insects while pollen grains in wind-pollinated flowers have smooth surfaces and are tiny and light so that they are easily blown about by the wind.
• how are nectar guides different in insect-pollinated flower than is wind-pollinated flower ?

  In insect-pollinated flowers, nectar guides are present to guide insects towards the nectar while in wind-pollinated flowers, nectar guides are absent
• Post-fertilisation Changes

  • The ovary becomes the fruit
  • The ovule becomes the seed
  • The zygote becomes the embryo. The embryo consists of the embryonic shoot, the embryonic root and the cotyledons
  • The petals, the style and stigma, and the anthers wither and drop off.

  
• fertilisation process


  1. The pollen grain germinates after it comes into contact with the stigma, in response to the sugary fluid secreted by the mature stigma.
  2. A pollen tube grows out from each pollen grain. The male gamete enters the pollen tube.
  3. As the pollen tube grows, it secretes enzymes to digest the surrounding tissue of the stigma and style. Thus, the pollen tube grows down the style into the ovary.

  
• fertilisation process after enzyme is secreted by pollen tube


  1. The pollen tube enters the ovule through an opening in the ovule wall called the micropyle.
  2. Within the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the male gamete.
  3. The nucleus of the male gamete fuses with the nucleus of the ovum to form the zygote. This is fertilisation.
  4. After fertilisation, the ovary develops into the fruit and the ovule develops into the seed.