reproduction in flowering plants

• function of reproduction

  replaces organisms that die maintaining the continuity of the species

  allow numbers to increase when conditions are suitable
• asexual reproduction involves only one parent and no gametes
• sexual reproduction involves two parents

  gametes are produced by meiosis

  gametes fuse to form a zygote.

  sexual reproduction allows for variation
• receptacle - base of the flower
• sepals - protects the flower when its a bud
• petals - attract animials with its big and colourful petals
• male parts of flower (stamen)


  anther - where pollen is made and stored

  filament - the stalk that supports the anther
• female part of the plant (carpels)


  stigma - where pollen lands

  style - a pollen tube grows through this

  ovary - where fertilisation occurs, contains ovules
• male gamete formation

  diploid cells inside of anther divide by meiosis producing pollen grains

  pollen grains contain a single haploid nucleus

  haploid nucleus divides by mitosis producing two haploid male gamete nuclei

  when pollen grains are mature the anther splits open & releases the pollen grains
• structure of pollen sac

  consists of 4 chambers

  each sac has a protective epidermis , fibrous layer, tapetum
• female gamete formation (embryo sac development)

  ovule is made of diploid cells

  one cell divides by meiosis forming a single haploid cell (embryo sac)

  haploid nucleus undergoes mitosis 3 times, resulting in 8 haploid nuclei

  5 of these nuclei die leaving 3 nuclei ( the egg, two polar nuclei)
• pollination is the transfer of pollen from the anther to the stigma of a flower from the same species
• self pollination - the pollen is transferred from the anther to a stigma on the same plant
• cross pollination - the pollen is transferred from anther to a stigma on a different plant
• methods of pollination


  wind

  animals
• benefit of animal pollination

  less wasteful
• disadvantage of wind pollination

  wasteful of pollen
• adaptations of flowers to wind pollination

  petals - small, green color

  pollen - large amounts, light

  anthers - large, outside petals

  stigmas - large and feathery
• adaptations of flowers to animal pollination

  petals- large brightly coloured

  pollen - small amounts, heavy

  anthers- small, inside petals

  stigmas - small and sticky inside petal
• fertilisation is the union of the male and female gametes to form a diploid zygote
• fertilisation of plants part 1

  pollen grain lands on a stigma

  pollen tube grows down style towards the ovule (controlled by tube nucleus)

  the tube nucleus disintegrates once it reaches the micropyle

  the two sperm nuclei move down through the pollen tube and enter embryo sac
• fertilisation of plants part 2

  double fertilisation occurs

  one sperm nucleus fuses with the egg nucleus forming a diploid zygote.

  (this will develop into the embryo of the new plant)

  the second nucleus fuses with the two polar nuclei forming a triploid endosperm nucleus
• seed formation


  fertilised ovule becomes the seed

  the integuments dry and become the testa

  the zygote divides repeatedly by mitosis forming the embryo

  some of the embryo cell grow to form monocots or dicots

  the endosperm nucleus divides rapidly by mitosis producing many 3n cells - these absorbs the nucellus

  endosperm acts as a food store
• non-endospermic seeds are seeds that do not contain endosperm e.g. peanut
• endospermic seeds are seeds that do contain endosperm e.g. corn
• monocots store food in the endosperm
• dicots store food in the cotyledons
• fruit formation


  as a seeds develops, ovary becomes the fruit.

  fruit are designed to protect the seed and help with seed dispersal

  fruit formation is stimulated by auxins in the seeds

  wall of the ovary becomes the pericarp
• dispersal - the transfer of a seed or fruit away from the parent plant
• dispersal is necessary to


  avoid competition with sibling seeds

  increase survival chances

  increase numbers of species

  find new areas to grow
• methods of seed dispersal

  wind

  water

  animal
• wind dispersal


  sycamore produce fruits with wings
• water dispersal


  coconuts have air filled fruit which allows it to float
• animal dispersal


  buttercups produce sticky fruits that stick to animal fur

  strawberries - the deeds are excreted in the faeces far from where it was eaten
• dormacy - the resting period when seeds don't grow and have reduced cell activity and metabolism
• dormancy occurs in several ways

  growth inhibitors (abscisic acid

  the testa (seed coat)

  growth regulator
• dormancy in agriculture and horticulture

  seeds need a cold snap to break dormancy

  this happens as cold temps break down growth inhibitors and stimulate growth promoters (auxins)
• ways to stimulate seed growth for horticulture


  soaking in water

  physical damage

  exposing the seed to cold temperatures
• advantages of dormancy


  plant avoid harsh winter conditions

  maximises the growing season

  the embryo has time to develop
• germination - the regrowth of the embryo, after a period of dormancy, if environmental conditions are suitable