Pollen and Reproduction
The life cycle of a plant may seem unsophisticated, but the process is actually quite complex. Many people equate pollen to allergy miseries or the familiar sight of a bee heavy with pollen sacs as it flies from flower to flower. Pollen plays a crucial role in the reproductive cycle and begins in the anthers, or male portions of flowering plants. But many plants produce pollen: grasses, weeds, trees, or any plant that generates seeds. Pollen is the equivalent of sperm in the human reproductive cycle and contains chromosomes which, when shared with chromosomes in the eggs of the female part of the plant, pass all necessary genetic information to a new embryonic plant.
Flowering and Non-Flowering Plants
Whether the seed-bearing plant is an angiosperm (flowering plants) or a gymnosperm (trees, grasses and plants with wind-borne pollen), it needs help from animals or wind to help spread the pollen formed within its male parts to reach the eggs in female plant parts.
Using a process called meiosis, mature plants are able to divide genetic material in half in order to create sperm and eggs. The sperm becomes the pollen which is protected by a waxy, multi-walled system that surrounds the sperm and prevents it from drying out due to a lack of water and damage from sunlight. An elaborate system of strengthening rods comprises parts of the wall surrounding the sperm. This keeps the pollen shell from collapsing in on itself.
Pollen Grains and Fertilization
When animal pollinators or the wind itself transports pollen from one plant to another, the DNA-wielding pollen grain is deposited near female plant parts of a similar plant. If the female stigma of an angiosperm, or cone in a gymnosperm, is primed to accept the pollen grain, a pollen tube forms to transfer sperm to the egg and fertilization can then take place.
Pollen grains that are carried by pollinators such as bees, wasps and flies need to be sticky, hence the "pollen pants" frequently seen on the back legs of bees. In gymnosperms, the wind-borne pollen is encased in a pollen sac that bursts, sending enough grains of pollen through the air to land on like plants and begin the fertilization process.