Earth Science: Plants and Fungi – Pollination, Fertilization, Fruit, and Seed Dispersal
Seed-bearing plants produce seeds for reproduction. These consist of a plant embryo and nutritious tissue enclosed in a protective seed coat.
During pollination, male pollen is transferred from pollen sacs onto the stigma of a female flower. Gymnosperms such as spruce trees usually have flowers of separate sexes, so they are either female or male. Together they make up a cone; their pollen is dispersed by the wind.
Angiosperms typically have hermaphrodite flowers. They contain female reproductive organs, carpels, as well as male organs, stamen. Pollination mechanisms are not limited to relatively random wind or water dispersal; there are many other, sometimes highly specialized mechanisms.
Pollen is most often carried by insects or other small animals which receive a “treat” in the form of nutritious pollen or sweet nectar from the female flower. Many plant species attract certain animal species, such as birds and bats, using color or scent. Flowers are also constructed to fit their corresponding pollinator. Some common types are composite, bell-shaped, and funnel-lipped flowers.
Fruits and seeds
In angiosperms, pollen sticks to the stigma of the female flower and grows a pollen tube. Then the male gamete travels through the tube into the female ovary. This is where the actual fertilization takes place by the union of the ovule and gamete. Male and female genomes combine and a fruit develops within the first few weeks following fertilization.
The flower disintegrates and the ovary increases in size and becomes fleshy. A seed begins to grow from the endosperm nucleus. An embryo plant is waiting inside the seed to create the next generation. The seeds are enclosed by the fruit until they reach maturity. The fruit is formed for optimal dispersal of the seeds.
The fruits of the greater bur- dock are sticky and carry hooks to attach to animals themselves, which will then disperse the seeds. Maple and dandelion seeds are equipped with feathers, wings, or parachutes for wind dispersal.
POLLINATION BY MAMMALS
Not only insects, but mammals can also help plants disperse pollen. The Australian honey possum has specialized in eating the nectar and pollen of banksia flowers by licking it off with its very long, bristly tongue. A large amount of pollen attaches to its fur while the animal is climbing the large and rigid flowers.
The pollen is wiped off again, when the possum visits another plant. Many tropical plants are pollinated by mammals such as bats or flying foxes Some of these plants include the baobab and wild banana trees.
BASICS
CROSS-POLLINATION increases genetic diversity and chances for better environ- mental adaptation Most plants have anatomical or bio- chemical mechanisms that prevent self-pollination.
Unlike gymnosperms. the ovules of angio- sperms are enclosed in a protected chamber of the ovary.