Plant reproduction

• the stamen is the male reproductive part
• the stamen consists of:

  • the anther: contains pollen grains which produce sperm
  • the filament: the stalk that supports the anther
• the carpel consists of:

  • the stigma
  • the style
  • the ovary: contains the female gametes (eggs) inside ovules
• pollination is the transfer of pollen from an anther to a stigma so that the male gametes can fertilise the female gametes in sexual reproduction.
• cross-pollination is a type of sexual reproduction where pollen is transferred from the anther of one plant to the stigma of another.
• plants that cross-pollinate rely on things like insects or the wind to help them pollinate.
• plant adaptations for pollination by insects:

  • brightly coloured petals to attract insects
  • scented flowers and necteries
  • sticky pollen grains that stick to insects as they go from plant to plant
  • a sticky stigma so that pollen picked up from insects will stick to the stigma
• features of plants that are adapted for wind pollination:

  • small dull petals
  • no nectaries or strong scents
  • lots of pollen grains - which are small and light so that they can easily be carried by the wind
  • long filaments: hang the anthers outside the flower so that a lot of pollen gets blown away
  • stigma: large and feathery to catch pollen as it's carried past by the wind. it often hangs outside the flower
• fertilisation:

  1. a pollen grain lands on the stigma, usually with help from insects or the wind
  2. a pollen tube grows out of the pollen grain and down through the style to the ovary and into the ovule
  3. a nucleus from the male gamete moves down the tube to join with a female gamete in the ovule
  4. fertilisation is when the two nuclei fuse together to make a zygote. this divides by mitosis to form an embryo.
  5. each fertilised female gamete forms a seed. the ovary develops into a fruit around the seed.
• flowering plants can only be fertilised by pollen grains from the same species.
• a seed will often lie dormant until the conditions around it are right for germination.
• seeds need the right conditions to start germinating:

  • water - to activate the enzymes that break down the food reserves in the seed
  • oxygen - for respiration which transfers the energy from food for growth
  • a suitable temperature - for enzymes inside the seed to work
• germination only starts when all conditions are suitable.
• 1. seed takes in water and starts to grow using its store of energy
  2. the first root starts to grow down into the soil
  3. the shoot grows up
  4. extra roots grow and the first green leaves appear
• a developed seed contains an embryo and a store of food reserves, wrapped in a hard seed coat. when a seed starts to germinate it gets glucose for respiration from its own food store. this transfers the energy it needs to grow. once the plant has grown enough to produces green leaves, it can get its own food for energy from photosynthesis.
• label:

  A) anther

  B) filament

  C) stamen

  D) petal

  E) stigma

  F) style

  G) ovule

  H) receptacle

  I) sepal

  J) ovary

  K) carpel

  
• label:

  A) pollen grain

  B) male gamete

  C) pollen tube

  D) male nucleus travelling to ovary

  E) female nucleus

  
• label:

  A) hard seed coat

  B) embryo root

  C) embryo shoot

  D) food store

  
• investigation of conditions needed for germination:

  • four boiling tubes with cotton wool at the bottom of each
  • tube 1: control
  • tube 2: no water
  • tube 3: low temperature
  • tube 4: no oxygen (use boiled water and add a layer of oil to stop the oxygen in the air from dissolving in the water)
• stem - supports the flower in a suitable position for pollination.
• sepals - enclose the flower when in bud, often green.
• petals - often brightly coloured to attract insects, which help in pollination. they may provide a 'landing platform' for insects visiting the flower. some flowers, including wind-pollinated flowers, do no have coloured petals.
• stamen - made up of the anther and filament
• anther - contains the developing pollen grain and opens when pollen is mature. the pollen grains contain male cells.
• filament - supports the anther
• carpel - made up of the stigma, style and ovary
• stigma - receives pollen during pollination
• style - supports the stigma and a pollen tube grows down the style to reach the ovary
• ovary - contains the ovules
• ovule - contain the female egg cells. after fertilisation by the male cell, an ovule develops into a seed.
• nectary and scent - insects feed on nectar (a sugary solution) and are attracted by the scent.
• wind-pollinated flowers have large pollen with smooth surfaces to help it float through the air; produced in large quantities.
• wind-pollinated flowers often have feathery stigmas which hang outside the flower to increase its chance of catching pollen in the air.
• pollination is the way that pollen is transferred from the stamen to the stigma. the pollen is carried by different agents (e.g. insects, wind, water, birds, mammals)
• self-pollination is when pollen lands on the stigma of the same flower.
• cross-pollination promotes genetic diversity in the offspring.
• when a pollen grain lands on the stigma of a flower a pollen tube starts to grow down through the style towards the ovary. digestive enzymes are produced at the top of the pollen tube, enabling it to grow through the tissues in the style to reach the ovary. the pollen tube enters the ovary through a small gap known as the micropyle and thus reaches the ovule. there the male nucleus in the pollen fuses with the female egg cell in the ovule. fertilisation takes place and a zygote is formed.
• after fertilisation, the ovule develops into the seed. the ovule wall becomes the seed coat (testa) and parts of the flower surrounding the ovule develop into the fruit, which contains the seeds.
• fruits provide a mechanisms for dispersal of seeds, away from the parent plant.
• the seed contains the zygote that will develop into a new plant. the zygote divides into cells that then develop into the embryo. when the seed germinates, the embryo grows into the young seedling. surrounding the embryo are structures known as the cotyledons. these contain food reserves that will supply the young seedling with food materials when the seed starts to germinate.