Lesson 3 Essay
1- Compare and contrast directional selection and disruptive selection, and provide an example of each.
Directional selection occurs when one extreme of a trait is favored and the distribution curve shifts in that direction. An example of this is the human struggle with malaria. The mosquito Anopheles transmits the disease. A new drug for the disease and a insecticide for the mosquito was created. But over the years they became resistant to it and multiplied, shifting the distribution curve toward the resistant type of parasite. Disruptive selection is where any two extremes of a trait are favored over any intermediate phenotype. For example, British land snails are found in low vegetation areas. The thrushes …show more content…
4- Providing examples, explain how sexual reproduction in plants has evolved to become less dependent on water.
The nonvascular plants and even a few vascular plants like ferns reproduce by having the sperm swim through the external environment. This swimming requires a water film in the external environment, and also requires that the ovum be in a structure close enough to the ground that the sperm can swim to it. Gymnosperms and angiosperms make pollen. Sperm are confined within a pollen grain. So no swimming is required. Wind and animal pollination/dispersal has helped plants a lot. If a plant lives in the water and let a bunch of its gametes loose, they