You. you have just come back from a three-month-long expedition in the amazon rain forest. as you take off the hat you wore throughout the trip, you notice some unusual particles. always curious, you put one of these particles in a drop of water on a microscope slide and take a look through your microscope. having seen some cells under the microscope before, you recognize that these particles appear to be made of cells. recalling what you have learned about cells, you marvel at the ability of these tiny things to support their life functions. you then remember that they could not easily get much bigger without drastic changes. explain why cells are so small, considering the relationship between surface area and volume for objects of different sizes but similar shapes.

Over the past 60 years, many amphibian species have experienced significant population declines and some species have become extinct. scientists suspected that local human activities such as the destruction of wetlands, regional pollution, and deforestation were the main reasons for these losses. however, research over the past 20 years reveals significant amphibian population declines in protected areas of the world, such as nature preserves and parks. these global declines suggest widespread problems including increased ultraviolet radiation, acid rain, and disease. in switzerland, for example, 14 of the 20 native amphibian species are threatened with extinction. chytridiomycosis is a fungal disease first identified in 1998 as a cause of massive amphibian deaths. in some severely impacted populations, a few individuals have survived, perhaps because of some natural resistance. if these resistant individuals continue to survive and prosper, new resistant populations might emerge. this would be an example of the founder effect artificial selection genetic drift natural selection sexual selection

The function of the excretory system is to control homeostasis and

Compare the shapes of the bones of the human skull with the shapes of the bones of the human leg. how do the shapes differ? why are the shapes important?