Sexual Reproduction in Plants (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

• Flowers are the reproductive organs of plants
• They can contain both male and female reproductive parts
• The male parts of flowers produce pollen grains; these contain a nucleus that functions as the male gamete
  • Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another)
• The female parts of flowers contain ovules that contain the female gamete
• During pollination pollen is transferred from the male to the female parts of the flower; this can occur due:
  • Insect pollination
  • Wind pollination

 General flower structure diagram

Flowers are the reproductive organs of plants

Flower structures and functions table

Extended Tier Only

• The anthers and stigma of wind-pollinated flowers are arranged differently to those in an insect-pollinated flower
  • The anthers hang outside the flower on long filaments so that wind can catch the pollen
  • The stigmas extend outside the flower and are often feathery to allow them to catch wind-borne pollen easily

Pollination and fertilisation

• Pollination can be defined as:

The transfer of pollen grains from an anther to a stigma

• Fertilisation occurs after pollination when a pollen nucleus fuses with an ovule nucleus
• The process of fertilisation in flowers involves:
  • The pollen grows a pollen tube down the style
  • The nucleus inside the pollen grain moves down the tube towards the ovule
• After fertilisation a zygote has been formed which will develop into a seed

Fertilisation in a flowering plant involves fusion of a pollen nucleus with a nucleus inside an ovule

Adaptations of flowers

• The features of insect and wind pollination flowers means that they are adapted to be pollinated by different mechanisms:

Adaptations of insect-pollinated flowers table

Adaptations of wind-pollinated flowers table

• Germination is the start of growth in the seed
• Three factors are required for successful germination:
  • Water - allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur
  • Oxygen - so that energy can be released for germination
  • Temperature - germination improves as temperature rises (up to a maximum) as the reactions which take place are controlled by enzymes
• As carbon dioxide is not necessary for germination but also does not inhibit it, it makes no difference whether it is present or not

Investigating Germination

• Set up 4 boiling tubes each containing 10 cress seeds on cotton wool
• Set each test tube as shown in diagram below
• Leave tubes in the set environment for a period of time:
  • A, B (control) and C incubated at 20°C;
  • D placed in a fridge at 4°C
• Compare results and see which tube has the greatest number of germinated seeds

Conditions required for germination

 Conditions required for germination - results: