Pollination and fertilisation
Joanna George-Johnson, Contributor

Mr. Omar Stennett, design arts teacher at Hopewell High School, in Hanover, demonstrates how to make patterns out of cartridge paper squares, recently. - Photo by Claudine Housen

Pollination: Intercourse for plants

For fertilisation to occur in plants pollination needs to take place first.

• Pollination is the transfer of pollen to the stigma of a flower.
  
  
• There are two types of pollination - self and cross-pollination.
  
  
• Self-pollination: This is when the pollen from a flower is transferred to the stigma of the same flower or a stigma on a flower of the same plant.
  
  
• Cross-pollination: This is when the pollen from one plant is transferred to the stigma on a flower of a different plant.
  
  
• N.B. Please note that pollination is only valid if the pollen transfer is between the same species of plants.

There are different agents of pollination: they are wind, water and animal pollination.

Flowers of different species of plants are adapted for the type of pollination that will occur.

Animal pollinators include bees and humming birds.

Adaptations for insect/ animal pollination

• Flowers have special food resources, such as edible floral parts like petals and nectaries to provide sugar.
  
  
• Attractive petals: Some insects mistake the flower for their sexual partner.
  
  
• Numerous pistils clustered in one location.
  
  
• Numerous stamens clustered in one location.
  
  
• Pollen formed at the site where receptive ovules are developed during each visit by an animal, can both pick up and deliver pollen.

Adaptations for wind pollination

• Effective in areas where plants are leafless during flowering.
  
  
• Effective in open areas

- Meadows, fields, grasslands.

Flower design:

- No petals
- No nectaries
- Often unisexual flowers
- Much pollen on projecting stamens
- Feathery or sticky stigmas on projecting styles

Water Pollination

• Effective for aquatic plants
• Pollen carried by water currents.
• A rare type of pollination.
• Effective for few plant groups.

Flower design:

- Pollen floats
- Pollen is often filamentous or broad
- Pollen tolerates excess water
- Pollen is produced at water level for efficient transfer
- Stigmas elevated to water level for efficient reception of pollen
- Flowers are often unisexual.

Fertilisation

Review of process:

- Pollen germination
- Pollen germinates only on the stigma of same species.
- Pollen takes in water to initiate germination.
- Pollen tube grows down style, directed by tube-cell nucleus.
- Cell nucleus divides to form two sperm nuclei.
- Sperm nuclei migrate down pollen tube.

Pollen tube fuses with female gamete.

- Fuses near egg cell
- Nuclear fusion
- One sperm fuses with egg-cell nucleus to form the zygote.
- one sperm fuses with two polar nuclei

Self-fertilisation versus cross-fertilisation

This is dependent on the type of pollination that occurred.

Questions

1) Distinguish between the features of a typical wind- pollinated flower and an insect-pollinated flower.

2) Give the name of (i) the male part of the flower and the parts that make it up and (ii) the female part of the flower and the parts that make it up.

Joanna George-Johnson teaches at Ardenne High School.
Email: Masterbio@gmail.com.