Biology summary and key concepts

Biology Summary

A population of grasshoppers in the Kansas prairie has two color phenotypes, green and brown. Typically, the prairie receives adequate water to maintain healthy, green grass. Assume a population of birds that eats grasshoppers moves into the prairie. How will that affect natural selection of the grasshoppers? How might this change in a drought year?

In this instance the grasshoppers which are most suitably adapted to current conditions will be far more likely to survive. In normal conditions, when the prairie is adequately hydrated to keep grasses healthy and green, those grasshoppers with green coloration will be naturally camouflaged and will escape predation by newly arriving birds. Conversely, the brown grasshoppers will stand out against the green backdrop and will easily be picked off by voracious birds, leaving mostly green insects to repopulate the prairie as the population of brown grasshoppers is depleted. In drought conditions, however, the situation would reverse itself, as the dried and dying grasses would soon turn brown. This shift in the natural environment around the grasshoppers would leave the green specimens exposed to predation, while those with brown coloration would escape relatively unscathed.

Suppose someone presented data from their research that showed the DNA of a newly discovered species was composed of: 30% guanine, 30% adenine; 20% thymine, 20% cytosine. Based on what you know about DNA structure, explain why these data do not make sense.

It has been firmly established that guanine always bonds to cytosine and this bond must occur in equal proportions. Having 30% guanine with only 20% cytosine would be genetically impossible. The correct formulation with a guanine level at 30% would be 30% cytosine, with the remaining 40% split equally between adenine (20%) and thymine (20%).

You are asked to determine if two species have a common evolutionary ancestor. Describe the methods or processes that you would use to determine if they have a common ancestor. Discuss why similar structures in the two species (such as wings or claws) may not necessarily indicate evolution from a common ancestor.

I would begin my classification by identifying any and all anatomical features shared by both species which appear to hold the same function. By searching for homologies such as similar bone structure one can begin deducing whether or not the two species have evolved from a common ancestor. Caution is advised in this approach, however, due to the frequent occurrence of homoplasies, or similarities which have occurred along independent evolutionary lines. An example of the misleading nature of homoplasies can be found in the case of butterflies and birds. While both species share the common adaptation of winged flight, with the wings of both creatures even sharing a similar external appearance, the internal structure of each wing is wholly incongruent. This incongruence is highly indicative that both species evolved from independent ancestors, which is why a more thorough investigation must be undertaken.

When a rabbit eats the lettuce in your garden, all of the energy in the lettuce is used by the rabbit. Is this statement true or false? Defend your answer.

This statement is false because the theory of trophic dynamics holds that the energy of a producer is transferred to its consumer at a rate between 10 and 20%. Every organism transfers energy and converts it to biomass at varying levels of efficiency, meaning the lettuce will have already utilized much of its existing energy for the sake of growth before it is consumed by the rabbit.