Sexual Reproduction in Plants

Flower diagram

Diagram of a flower.

Sepals: Leaf like structures that protect the flower when it is a bud.
Petals: Brightly colored and scented to attract insects to feed on nectar. Many have a nectary at the base that produce sugary nectar.
Stamens: Male sex organs. Each one is made up of two parts:
- the anther, pollen grain production
- the filament, a stalk that holds the anther.
Carpels: Female sex organs. Made up of:
- a stigma, where pollen grains attach during pollination
- a style, to connect the stigma to ovary, pollen tube grows down the style
- an ovary, swollen base that contains the ovules, usually becomes the fruit after fertilization
- an ovule, found in the ovary, containing female gametes (egg cells), after fertilization the ovules become seeds.

Diagram of a wind-pollinated flower.

In wind-pollinated flowers, the anthers are different from those in insect-pollinated flowers:
- They are positioned like a pendulum, they are attached to long, thin filaments that hang outside the flower.
- The function of this is to allow the anthers to swing freely in the air, easily releasing light, smooth pollen grains into the air.
The stigmas are made to catch pollen grains in the air.
- They are feathery or branched in appearance.
- They hang outside the flower.
- The feathery structure allows a large surface area to catch wind-borne pollen grains.

In terms of quantity, they are mass produced since most are lost in the air.
They are very light in weight so they can be easily carried by the wind.
They are smooth to prevent clumping together and to drift easily.
They might have air sacs to stay in the wind longer.

Diagram of an insect-pollinated flower.

In terms of quantity, they are produced in smaller amounts for efficient transport.
They are relatively heavy and larger.
They are sticky and spiky to hook onto insect bodies.
There are no special features for aerodynamics.

Feature	Wind-pollinated	Insect-pollinated
Quantity	Produced in massive amounts because most are lost in wind	Produced in small amounts for efficient transport
Weight and Size	Light and small to be carried by the wind	Heavy and large
Texture	Smooth to prevent clumping and to be drifted easier	Sticky or spiky to attach to insect bodies
Aerodynamics	Air sacs to float in the wind longer	No features.

Pollination is the transfer of pollen grains from an anther to a stigma.
Self-pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant.
Cross-pollination is the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.

Genetic variation:
- Since self-pollination is the transfer of pollen grains of the same flower, this leads to very low genetic variation in the offspring since they are very similar to the parent.
- Since cross-pollination is the transfer of pollen grains to a flower on a different plant of the same species, this leads to high genetic variation in the offspring because it combines two different genetic material from two individuals.
Capacity to respond to environmental change:
- Self-pollinated flowers result in not being able to adapt easily to changes in the environment due to the lack of genetic variation .
- Cross-pollinated flowers provides the “raw material” for natural selection. If there is an afvantageous trait in a plant that allows them to survive or adapt to a change in the environment, this trait can be passed on to offspring.
Reliance on pollinators:
- For self-pollinated flowers, there is little to no reliance on external pollinators (e.g. bees, wind), which is an advantage in habitats where pollinators are scarce or where plants are wildly scattered. This ensures there is still seed production even in isolation.
- For cross-pollinated flowers, there is a high reliance on pollinators or wind. If the specific pollinator for a species declines (e.g. caused by habitat loss or pesticides), the plant population may fail to reproduce, leading to a decline in numbers.