Biology Semester II |
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| Sections: |
Introduction | Section 1 | Section 2 | Section 3 |
| Section Two: |
Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 |
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Biology: Flowering Plant Reproduction: Part Five Pollination The transfer of pollen from the male anther to the female stigma is called pollination. This is accomplished by a variety of methods. Entomophyly is the transfer of pollen by an insect, such as a bee, wasp, fly, or moth. Anemophyly is the transfer of pollen by wind. Many airborne pollens cause allergies. Other pollinators include birds, bats, water, gravity, and humans (recall Gregor Mendel’s experiments). Some plants (such as garden peas) develop floral structures that ensure self-pollination. Other plants have mechanisms to ensure pollination with another flower or individual. Gravity plays a significant role in the pollination of the corn plant. Corn pollen is quite large and has been experimentally shown to travel no more than one meter (3.3 feet) from the male corn flowers, which are located at the top of the corn plant. Gravity causes the large corn pollen grains to drop down to where the female flowers are. Some aquatic plants release their pollen into water where it floats to another plant. Birds and bats are drawn to certain types of flowers and carry out pollination much the same way an insect does. Insect pollination is perhaps the most intensely studied of the various pollination mechanisms. Many plants and the insects that pollinate them have co-evolved. Co-evolution is the process by which different species adapt and respond to changes in each other.
Some flowers, most notably orchids, have taken co-evolution to the extreme. Orchids can be pollinated only by a particular species of insect. Should that insect become extinct, the plant will only be able to self-pollinate. This would greatly reduce the genetic variation within that plant’s population.
Some plants have their flowers structured so that when the female part of the flower matures, it brushes against the male part of the flower and self-pollinates. Plants of the bean and pea family and the sunflower family have this structure. While such a mechanism tends to limit the genetic variation within a species, it does insure that some sexual reproduction takes place. Plants in the sunflower family have a flowering structure, a flowering head, covered with two types of flowers. Ray flowers occur around the perimeter of the head and disk flowers appear toward the center. The ray flowers have their petals fused and attract pollinators. The disk flowers have inconspicuous petals and tend to self-pollinate. These plants, among the most successful of all plant groups, have both self-pollination and out-pollination mechanisms.
Flower structure of a chrysanthemum, dissected, showing the ray and disk flowers arrayed on a flowering head (right image), and fruits that have developed on a different head (left image). Flower color may correspond to the type of pollinator. The thought is that red petals attract birds and butterflies, yellow petals attract bees, and white flowers attract moths. Wind-pollinated flowers, such as oaks and grasses, have features that make it easier for the wind to carry away the pollen. These plants have reduced petals and generally have small, inconspicuous flowers. | ||||||||
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Why would an insect be attracted to a flower?
