Pollination in Plants (Edexcel IGCSE Biology: Double Science)

• Flowers are the reproductive organs of plants
• They usually contain both male and female reproductive parts
• 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 (male part of the flower) to the stigma (female part of the flower)
• This process is known as pollination and there are two main mechanisms by which it occurs:
  • Pollination where the pollen is transferred by insects (or sometimes other animals like birds or bats)
  • Pollination where the pollen is transferred by the wind

• The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function

The general structure of a typical flower

Parts of the Flower Table

Insect-pollinated flowers

• For the flowers of many plant species, the pollinating agents are insects (e.g. bees)
• Insects often visit these flowers to collect nectar (a sugary substance produced by insect-pollinated flowers and the base of their petals, which provides the insects with energy)
• As an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect's body
• When the insect visits another flower, it may brush against the stigma of this second flower and in the process, may deposit some of the pollen from the first flower, resulting in pollination
• The structures of an insect-pollinated flower ensure that the flower is well-adapted for pollination by insects

Features of an Insect-pollinated Flower Table

Wind-pollinated flowers

• For wind-pollinated flowers, the process of pollination is more random than it is for insect-pollinated flowers
• When ripe, the anthers open and shed their pollen into the open air
• The pollen is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination
• The structures of a wind-pollinated flower ensure that the flower is well-adapted for pollination by the wind

Features of a Wind-pollinated Flower Table

Cross-pollination and self-pollination

• In insect or wind-pollinated plants, pollination can either occur via cross-pollination or self-pollination
• Cross-pollination occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
• This is the way most plants carry out pollination as it increases the genetic variation in the offspring
• Occasionally, the pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant - this is known as self-pollination
• Self-pollination reduces the genetic variation in the offspring as all the gametes come from the same parent (and are therefore genetically identical)
• Lack of variation in the offspring is a disadvantage if environmental conditions change, as it is less likely that any offspring will have adaptations that suit the new conditions well