Lesson 3 Essay

640 Words Jan 29th, 2016 3 Pages
Lesson 3 Essay Questions:
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
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Most amphibians spend the larval stage in the water and the adult stage on land. This metamorphosis is a distinctive characteristic of amphibians but some don’t practice it. Some are direct developers; the adults don’t return to the water to reproduce so there's not tadpole stage. The great variety of life histories observed among amphibians made them successful colonizers of the land environment. Reptiles are another example of adaptations of land existence. The amniote egg made development on land possible and eliminated the need for water environment during development. This egg provides the embryo with atmospheric oxygen, food, and water; removes nitrogenous wastes; and protects the embryo from drying out from mechanical injury. (Mader & Windelspecht, 2012)
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

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