Reproduction in Plants
Reproduction in Plants
Sexual Reproduction
Most multicellular organisms reproduce sexually.
Involves the union of male and female sex cells (gametes) to form a unique individual.
Male gametes are called sperm.
Female gametes are called eggs.
Formation of gametes occurs in specialized reproductive organs by meiosis.
Gametes and Zygote Formation
Gametes are haploid (n), containing one of each chromosome.
When the two gametes fuse at fertilization, they form a zygote.
The zygote is diploid (2n).
It undergoes mitosis to form a large number of cells that develop into the new individual.
Reproduction in Flowering Plants
Flowers serve as the reproductive structures in plants that produce gametes and allow fertilization.
Result of fertilization is the formation of a seed.
Male Reproductive Organs
Male reproductive organs are the stamens.
Each stamen typically has a long stalk called the filament.
At the end of the filament is the anther, which produces the pollen grain (male gametophyte).
Pollen grain contains sperm cells.
Female Reproductive Organs
The female reproductive organ is the pistil.
Contains an ovary, the central swelling at the base.
The ovary produces the female gamete (eggs or ovules) and encloses the seeds as they form.
The style is a slender stalk connecting the ovary to the stigma.
The stigma at the top of the style is where pollen is deposited.
Other Flower Structures
Flowers have additional structures that assist in fertilization:
Sepals: Enclose and protect other flower parts during the bud stage, usually small and green.
Petals: Arranged in a circle around reproductive organs to attract pollinators.
Common Flower Parts
Anther: Produces pollen grain.
Stamen: Male reproductive part, consists of filament and anther.
Stigma: Receives pollen.
Style: Connects stigma and ovary.
Pistil: Female reproductive part consisting of ovary and style.
Petal: Attracts pollinators.
Sepal: Protects the flower in bud stage.
Ovary: Contains ovules (eggs).
Pollination and Fertilisation
Fertilisation is carried out by insects, wind, birds, bats, other animals, or water.
Pollination occurs when a pollen grain lands on a stigma.
A cell in the pollen grain produces a pollen tube that penetrates the stigma's surface.
Fertilization Process
The pollen tube carries two sperm cells down through the style to the ovary.
Fertilization occurs in the ovule when the egg fuses with one of the sperm cells.
Although most flowers are bisexual, they often prevent self-pollination by maturing pollen and ovary at different times.
Methods of Pollination
Pollination by Insects
Flowers pollinated by insects are often brightly colored, open during the day, and have a strong aroma.
Typically tubular-shaped and may have a nectar guide (not visible to humans) guiding insects.
Bees are significant pollinators for many plants.
Role of Bees in Pollination
Bees collect energy-rich pollen or nectar for survival.
Pollen sticks to their fuzzy hair, transferring to other flowers as bees visit.
Apiarists can assist in pollination by moving hives to areas with blooming native plants.
Cross-Pollination Process
Pollen from stamens sticks to a bee as it visits a flower for food.
Bee travels to another plant of the same type, transferring pollen.
Pollen on the bee sticks to the pistil of a flower on the other plant.
Pollination by Bats
In tropical and desert regions, bats pollinate flowers that bloom at night.
Flowers are large, white or pale-colored, with strong scents and ample nectar.
Bats become covered in pollen while seeking nectar, transferring it to the next flower.
Pollination by Birds
Small birds, like hummingbirds, are known to pollinate orchids and wildflowers.
These flowers are sturdy, brightly colored, and allow birds to feed without entanglement.
Pollen is deposited on the bird's head and neck.
Pollination by Wind
Many conifers and grasses are pollinated by wind.
Wind-pollinated flowers are usually small and green, producing large amounts of pollen with no nectar or scent.
Their stigmas are exposed and feathery.
Pollination by Water
Some aquatic plants, like Australian sea grass, are pollinated by water.
Pollen floats on water and deposits inside flowers upon contact.
Seeds and Fruits
After fertilisation, the ovule develops into a seed, protected by a tough outer coat.
As seeds develop, the ovary forms a fruit to protect seeds and aid in dispersal.
Germination and Development
Seed embryos remain dormant until suitable conditions arise.
Germination begins as seeds sprout and grow out of their coats.
Factors influencing germination include water, oxygen, temperature, and light.