Pollination and Fertilization Quiz

Pollination and Fertilization

• Pollination is the transfer of pollen grains from the anther to the stigma. A pollinator, such as an insect or wind, carries the pollen.

• Types of Pollination:

  • Autogamy: Pollen from the same flower falls on the stigma.
  • Geitonogamy: Pollen from one flower falls on the stigma of a different flower on the same plant.
  • Allogamy (Cross-pollination): Pollen from one flower falls on the stigma of another flower on a different plant of the same species.

Self-Pollination

• Pollen from the anther to the stigma of the same flower or another flower of the same plant.

• General qualities of a plant are consistent across its flowers.

• Cleistogamy: Some flowers do not open; pollen is transferred without exposing the flower to external factors. Happens in some legumes.

• Advantages:

  • Guaranteed pollination as stamen and carpels mature together.
  • Preserves parental characteristics indefinitely.
  • No pollen grain wastage.
  • Flowers don't need to be large or showy.
  • Scent and nectar aren't necessary.
  • Economical for the plant.

• Disadvantages:

  • Weakening of a variety or species, poor quality of seeds, less vigorous offspring.
  • Weaker or defective plant characteristics are not eliminated making it impossible to breed improved varieties

Cross-Pollination

• Pollen transfer between flowers of different plants but of the same species.

• Advantages

  • Healthier offspring.
  • Abundant and viable seeds.
  • Production of new varieties (e.g., cross-pollinating different varieties of the same species).

• Disadvantages

  • Pollination is not always certain.
  • Wastage of pollen (as a large quantity is needed).
  • Uneconomical for the plant (as large and colorful flowers and nectar production).

Conditions Favoring Cross-Pollination

• Unisexuality: Male and female flowers grow on separate plants (e.g., palms) or on the same plant (e.g., cucumbers).
• Dichogamy: Timing of maturation difference between male and female structures (e.g., protandry – anthers mature before stigma).
• Self-sterility: Pollen from one plant will not fertilize the stigma of the same plant.
• Herkogamy: Physical barriers between anther and stigma making self-pollination difficult (e.g., different heights of stigma and anther).
• Heterostyly: Different heights of anthers and stigmas in some flowers hindering self-pollination (e.g., primrose).

Agents of Cross-Pollination

• Abiotic agents (non-living):

  • Wind (Anemophily): Flowers are small, lack bright colors, often dull green, minimal scent or nectar. The pollen is light, dry and smooth, the stigma is feathery to capture wind-blown pollen (e.g., grasses, trees).
  • Water (Hydrophily): Plants produce a large number of pollen grains that are buoyant in water (e.g., Vallisneria).

• Biotic agents (living):

  • Insects (Entomophily): Flowers are large, brightly colored, and scent and nectar to attract insects (e.g., lilies, roses, fruit trees).
  • Birds (Ornithophily): Flowers are large with bright colors and a strong or sweet scent, and nectar from the flower (e.g., hummingbirds, honeysuckle).
  • Bats (Chiropterophily): Flowers produce nectar in the evening, and bloom at that time (e.g., Anthocephalous, Bauhinia).
  • Artificial Pollination: Humans manually transfer pollen (e.g., for creating different plant varieties).
  • Elephants (Elephophily): These pollinating agents are rather large (e.g., Rafflesia).

Fertilization

• Fusion of male and female gametes (nuclei).

• Pollen grain (male gamete) fertilizes the ovule (female gamete)

• Zygote forms

• Zygote → Embryo → New baby plant.

• Double Fertilization:

  • One sperm nucleus fuses with the egg nucleus to form the zygote (first cell of sporophyte).
  • Another sperm nucleus fuses with two polar nuclei to form the endosperm, the food source for the developing embryo.

Fate of Floral Parts After Fertilization

• Sepals, petals, and stamens usually wither and fall off.
• Ovary wall becomes the fruit.
• Ovule becomes the seed.
• Integuments become the seed coat.
• Fertilized egg becomes the embryo.