Plant reproduction

• Asexual reproduction

  • 1 parent
  • Cell division: mitosis
  • Gametes: none produced
  • Offspring: genetically identical
• Sexual reproduction

  • 2 parents
  • Cell division: meiosis
  • Gametes... zygote produced
  • Offspring: genetically different (variation occurs)
• Gametes

  Haploid cells capable of fusion
• Asexual reproduction

  The production of organisms from one parent only (no seeds involved) (plant reproduction)
• Sexual reproduction

  Production of a new individual from the fusion of gametes from both parents
• Female part of a plant

  Carpel
• Male part of a plant

  Stamen
• Carpel composed of

  1. Stigma
  2. Style
  3. Ovary
• Stamen composed of

  1. Anther
  2. Filament
• Sepal function

  Protect flower when it's a bud
• Petals

  • Animal pollinated: large, brightly coloured and scented to attract insects
  • Wind pollinated: small, green or absent
• Anther

  Produces pollen grains by meiosis
• Filament

  Supports the anther and supplies it with food and water using vascular bundles
• Stigma

  Where the pollen lands
• Style

  Where the pollen tube grows towards the ovary
• Ovary

  Contains ovules. Meiosis occurs in the ovule to produce an embryo sac.

  After fertilisation the ovule becomes the seed and the ovary becomes the fruit (tangariiiiine, avocado-h)
• Receptacle

  Supports the plant
• Into to male gamete formation

  • An anther consists of 4 chambers called pollen sacs
  • Each pollen sac is enclosed by a protective epidermis and fibrous layer.
  • The tapetum is a nutrient-rich layer of cells found just inside the fibrous layer
• Male gamete formation

  • Inside each pollen sac are diploid microspore/pollen mother cells
  • These divide by meiosis (genetically different) to produce a cluster of 4 haploid cells called a tetrad
  • Each tetrad soon breaks up to form 4 separate haploid pollen grains/microscopes
  • Each pollen grain divides by mitosis in the pollen sac to form 2 haploid nuclei
  • These nuclei are called the tube and generative nucleus
  • The tube nucleus forms the pollen tube, and then the tube nucleus degenerates
  • The generative nucleus divides by mitosis to form the 2 male gametes in the pollen sac or pollen tube
• Tube nucleus

  Grows pollen tube for fertilisation and then degenerates
• Generative nucleus

  Divides by mitosis to produce 2 male gametes (haploid)
• Structure of male pollen grain

  1. Exine: thick and strong outer wall which has a specific pattern depending on the type of plant
  2. Intine: thin, inner coat
• • Pollen grains are not gametes (do not fuse with cells)
  • Pollen grains form the male sperm nuclei which are gametes
  • When the pollen grains have matured, the walls of the anther become dry and shrivel
  • This causes the anther walls to split (dehiscing), burst and explode pollen grains
• Each ovule is surrounded by

  • Nucellus: supplies nutrients for growth
  • 2 layers called integuments for protection
  • Small pores in the integuments called micropyle for fertilisation and germination where a pollen tube can enter
  • Megaspore mother cell/embryo sac mother cell (diploid) is 1 cell low down in the embryo sac ?
• Development of the embryo sac/megaspore

  • Each ovule is made up of diploid cells (2n)
  • Only one cell in the ovule - the megaspore mother cell - in the ovule divides by meiosis to form 4 haploid cells
  • 3 of them degenerate Remaining cell is the embryo sac/megaspore because it is large
  • The haploid nucleus of the embryo sac divides by mitosis 3 times to form 8 haploid nuclei. These nuclei swell using the food from the nucellus
  • Out of 8 nuclei, 5 degenerate
  • The 3 remaining nuclei form the female gametes
  • 2 form the polar nuclei
  • 1 forms a thin cell wall and becomes the egg cell
• Pollination

  Transfer of pollen from anther to stigma of a flower from the same species
• Fertilisation

  The fusion of two haploid gametes (male and female)(23 chromosomes) to form a diploid zygote
• Species

  Group of organisms that can interbreed and produce fertile offspring
• Germination

  The regrowth of the embryo/seed into a new plant after a period of dormancy, if the environmental conditions are suitable
• Dormancy

  A resting phase of reduced metabolic activity where the seeds undergo no growth
• Dispersal

  The transfer of fruit or seed as far away as possible from the parent plant
• Self pollination = self fertilisation

  1. Transfer of pollen from an anther to stigma on the same flower
  2. Form of interbreeding and seeds may be less vigorous
• Cross pollination = cross fertilisation

  • Transfer of pollen from anther to stigma on a different plant but must be the same species
  • More variation and more vigorous
• Types of pollination

  1. Wind
  2. Animal
• Wind pollination

  Petals

  • Small and green
  • No scent or nectar (don't have to attract insects)

  Pollen:

  • huge amounts to compensate for lost pollen by the wind
  • Small and light -easily carried by the wind

  Anthers

  • Large
  • Outside petals -pollen can easily be removed by the wind

  Stigmas

  • Large and feathery
  • Outside petals -pollen can easily be caught
• Animal pollination Petals

  • Large, coloured, scent and nectar
  • These attract insects

  Pollen:

  • Small amounts -transfer not as risky
  • Spiked or sticky to attach to insect's body

  Anthers

  • Small
  • Inside petals -pollen rubs off insects body as it feeds on nectar

  Stigmas

  • Small and rounded
  • Inside petals -pollen rubs off insects body as it feeds on nectar
• Hay fever

  Cause: allergic reaction to pollen

  Symptoms: sneezing/blocked nose/watery and itchy eyes
• Flowering plants have double fertilisation

  1. Male gamete (sperm nucleus) fuses with egg = zygote → seed
  2. Male gamete (sperm nucleus) fuses with 2 polar nuclei = endosperm (triploid) (acts as a food store)