Flower Structure & Pollination Method (Cambridge O Level Biology)

• Flowers are the reproductive organ of the plant
• They usually contain both male and female reproductive parts
  • The male reproductive parts are called the stamen
    • Each stamen consists of an anther and a filament
  • The female reproductive parts are called the carpel
    • Each carpel consists of a stigma, style, ovary and ovules
• Plants produce pollen which contains a nucleus inside that is the male gamete
• Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another)
• This means plants have to have mechanisms in place to transfer pollen from the anther to the stigma
• This process is known as pollination and there are two main mechanisms by which it occurs: transferred by insects (or other animals like birds) or transferred by wind
• The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function

 

Parts of the flower table

Structure	Description
Sepal	Protects unopened flower
Petals	Brightly coloured in insect-pollinated flowers to attract insects
Anther	Produces and releases the male sex cell (pollen grain)
Filaments	Provides support to the anther
Stigma	Sticky top of the female part of the flower which collects pollen grains
Style	A stalk that connects the stigma and ovary
Ovary	Produces the female sex cell (ovum)
Ovule	Contains the female sex cells (found inside the ovary)

 

General flower structure diagram

Structure of a flower

Features of an insect-pollinated flower table 

Feature	Insect-pollinated flower
Petals	Large and brightly coloured to attract insects
Scent and Nectar	Present - entices insects to visit the flower and push past stamen to get to nectar
Number of Pollen Grains	Moderate - insects transfer pollen grains efficiently with a high chance of successful pollination
Pollen Grains	Larger, sticky and / or spiky to attach to insects and be carried away
Anthers	Inside flower, stiff and firmly attached to brush against insects
Stigma	Inside flower, sticky so pollen grains stick to it when an insect brushes past

Features of a wind-pollinated flower table 

Feature	Wind-pollinated flower
Petals	Small and dull, often green or brown in colour
Scent and Nectar	Absent - no need to waste energy producing these as no need to attract insects
Number of Pollen Grains	Large amounts - most pollen grains are not transferred to another flower so the more produced, the better the chance of some successful pollination occurring
Pollen Grains	Smooth, small and light so they are easily blown by the wind
Anthers	Outside flower, swinging loose on long filaments to release pollen grains easily
Stigma	Outside flower, feathery to catch drifting pollen grains

• The pollen produced by insect and wind-pollinated flowers is also different:

  • Insect-pollinated flowers produce smaller amounts of larger, heavier pollen grains that often contain spikes or hooks on the outside so they are better able to stick to insects
  • Wind-pollinated flowers produce large amounts of small, lightweight pollen grains that are usually smooth