Reproduction in plants

Sexual vs asexual reproduction

Sexual reproduction:

produces gametes

fertilisation takes place

genetic variation in offspring

Survival value:

Sexual: changing environment

Asexual: stable environment

Asexual reproduction in plants

Can use runners, bulbs and tubers to produce more plants

Cuttings

A piece of a plant's stem, with a few leaves attached, is cut from a healthy plant

Placed in damp soil/compost where it will grow roots and develop into a new plant

Sexual reproduction in plants

Plants produce specialised haploid gametes in their flowers

Male gametes contained with pollen grains

Female gametes are egg cells, KA ova

Pollination

Transferring male gametes to female gametes

Normally carried out by wind or insects

Pollination –> fertilisation
–> zygote develops into a seed
–> seed becomes enclosed in a fruit

Production of gametes and pollination

Pollen grains: produced in the anthers of the stamens

Ova: produced in ovules in the ovaries

Pollination: pollen is transferred from the anthers to the stigma

Occurs within the same flower => KA self-pollination

Pollen transferred to different flower => KA cross-pollination

Both can be wind/insect

Insect- vs wind-pollinated flowers

Insect | wind

Positions of stamens:

Enclosed within flower
=> insect must make contact

exposed
=> wind can easily blow pollen away

Position of stigma

enclosed within flower
=> insect must make contact

Exposed
=> catch pollen blowing in the wind

Type of stigma

Sticky
=> pollen grains attach from insects

Feathery
=> catch pollen blowing in the wind

Size of petals:

Large
=> attract insects

Small

Colour of petals:

Brightly coloured
=> attract insects

Not brightly coloured, usually green

Nectaries:

Present
=> produce nectar as a reward for insects

Absent

Pollen grains:

larger, sticky grains / grains with hooks
=> stick to insects' bodies

Smaller, smooth, inflated grains
=> carry in the wind

Fertilisation

Nucleus of the pollen grain must fuse the the nucleus of the ovum

Pollen grain forms a pollen tube
–> grows down through the tissue of the style and into the ovary
–> curves around to enter the opening in an ovule
–> tip of tube dissolves, allowing pollen grain nucleus to move out of the tube and into the ovule
–> fertilises ovum nucleus

Seed and fruit formation

Once fertilisation takes place changes take place in the ovule and ovary
=> ovule becomes a seed, ovary becomes a fruit

  1. zygote develops into an embryonic plant with radicle (small root) and plumule (shoot)
  1. other contents of the ovule develop into a food store for the young plant when the seed germinates
  1. the ovule wall becomes the seed coat, KA testa
  1. the ovary wall becomes the fruit coat – can take many forms depending on the type of fruit

Germination

Seed contains a plant embryo, consisting:

radicle

plumule

one or two cotyledons (seed leaves)

Food store is used up, providing nutrients to allow radicle and plumule to grow

Also a food store in cotyledons or another part

Radical grows down into the soil
–> absorbs water and mineral ions

Plumule grows upwards towards the light
–> starts photosynthesis

Germination ends once the seedling can photosynthesise

Cotyledons

Dicots – plants with 2 cotyledons
eg. peas, beans
–> food stored in cotyledons as protein and starch

Monocots – have one cotyledon
eg. orchids, irises
–> have separate food store of starch

Conditions needed for germination

Warm temperatures
=> enzymes can act efficiently

Water
=> chemical reactions in solution

Oxygen
=> respiration

Germination is the growth of a new plant from a seed

Seeds dispersed from parent plant contain 10% water
=> restricts metabolism so it can remain alive but dormant for a long time

PRACTICAL: investigate the conditions needed for germination

Set up four test tubes with seeds in/on a medium

Tube A: wet cotton wool, 20°C

Tube B: seeds on dry cotton wool, 20°C
=> absence of water

Tube C: boiled water with a thin surface layer of oil, 20°C
=> absence of oxygen

Tube D: wet cotton wool, in a fridge at 4°C
=> absence of heat

Results

Tube A will germinate

Tubes B and C will not germinate

Tube D may germinate, but very slowly