Plant Reproduction: Wind vs. Insect Pollination, Flower Structure & Fertilisation

Welcome to your comprehensive revision notes on reproduction in plants, focusing on wind and insect pollination, flower structure, and the process of fertilisation. Sexual reproduction in plants involves the fusion of male and female gametes, which is preceded by pollination. Let’s explore these important aspects.

Flower Structure (General Overview)

Before we delve into specific types of pollination, let’s briefly recall the main parts of a flower involved in reproduction:

• Sepals: Usually green, leaf-like structures that enclose and protect the developing bud.
• Petals: Often brightly colored to attract pollinators (in insect-pollinated flowers).
• Stamen (Male Reproductive Part): Consists of:
  • Anther: Contains pollen grains (male gametes).
  • Filament: Supports the anther.
• Pistil or Carpel (Female Reproductive Part): Consists of:
  • Stigma: The sticky or feathery tip that receives pollen.
  • Style: The stalk connecting the stigma to the ovary.
  • Ovary: Contains one or more ovules (containing the female gamete or egg cell).

Wind-Pollinated Flowers

Wind pollination, also known as anemophily, is common in plants like grasses, maize, and oak trees. These flowers have specific adaptations to facilitate pollen transfer by wind.

Structure of Wind-Pollinated Flowers:

• Small and Inconspicuous Petals: Petals are usually absent, reduced, or dull in color as there is no need to attract insects.
• Lack of Scent and Nectar: These flowers do not produce nectar or a strong scent since they don’t need to attract insects for a reward.
• Abundant, Lightweight Pollen: They produce a large quantity of small, lightweight pollen grains that can be easily carried by the wind.
• Loosely Attached Anthers: The anthers are often long and hang outside the flower, allowing the wind to easily shake and release the pollen.
• Large, Feathery Stigmas: The stigmas are typically large and feathery or branched to increase the surface area for trapping pollen grains carried by the wind. They are often held outside the flower to catch the windborne pollen.

Pollination in Wind-Pollinated Flowers:

Pollination in wind-pollinated flowers occurs when the wind carries pollen grains from the anthers of one flower to the stigmas of another flower. This process is largely random, and a vast amount of pollen is produced to increase the chances of successful pollination.

Insect-Pollinated Flowers

Insect pollination, also known as entomophily, is common in many flowering plants that rely on insects like bees, butterflies, and flies to transfer pollen.

Structure of Insect-Pollinated Flowers:

• Brightly Colored Petals: Petals are usually large and brightly colored to attract insects visually.
• Presence of Scent: Many insect-pollinated flowers produce a pleasant scent to lure insects.
• Nectar Production: These flowers often have nectaries at the base, producing a sugary liquid (nectar) that serves as a food reward for visiting insects.
• Sticky or Spiny Pollen: Pollen grains are often larger and have a sticky or spiny surface that allows them to easily attach to the bodies of visiting insects.
• Well-Positioned Anthers: The anthers are positioned in a way that pollen will readily brush onto the insect’s body as it feeds on nectar.
• Sticky Stigma: The stigma is often sticky to ensure that pollen grains carried by insects will adhere to it.

Pollination in Insect-Pollinated Flowers:

Pollination in insect-pollinated flowers occurs when insects visit flowers to feed on nectar or pollen. As they move from one flower to another, pollen grains get attached to their bodies (e.g., legs, wings). When the insect visits another flower of the same species, some of this pollen rubs off onto the sticky stigma, thus transferring the male gametes.

Fertilisation in Plants

Fertilisation in flowering plants occurs after successful pollination. Here’s the general process:

1. Pollen Grain Germination: When a pollen grain lands on a compatible stigma, it absorbs moisture and germinates.
2. Pollen Tube Formation: The pollen grain grows a pollen tube, which is a long, slender tube that grows down through the style towards the ovary.
3. Entry into the Ovary: The pollen tube continues to grow until it reaches the ovary and enters the ovule through a small opening called the micropyle.
4. Release of Male Gametes: The pollen tube carries two male gametes (sperm nuclei).
5. Fusion with the Egg Cell: One of the male gametes fuses with the female gamete (egg cell) inside the ovule. This fusion forms a zygote, which will eventually develop into the embryo of a new plant.
6. Double Fertilisation (in Angiosperms): In flowering plants (angiosperms), the other male gamete fuses with the central cell (which usually contains two polar nuclei) within the ovule to form the endosperm. The endosperm is a nutrient-rich tissue that provides food for the developing embryo.

Conclusion:

Reproduction in plants involves pollination, the transfer of pollen, followed by fertilisation, the fusion of gametes. Wind-pollinated flowers have structures adapted for wind dispersal of pollen, while insect-pollinated flowers have features that attract insects to facilitate pollen transfer. Fertilisation, the crucial step that follows, leads to the formation of the zygote and the beginning of a new plant’s life.

Ready to explore the next stage of plant reproduction, such as seed and fruit development? Check out our other notes on this topic!