The circulatory system requires the interactions of another body system to regulate and deliver blood. Which of the following actions in another body system contributes to the job of delivering blood? a. protection from pathogens
b. filtering of fluids
c. contractions of muscle tissue
d. secretions of glands

The table shows dates and appearance of index fossils. which rock layers can be dated most precisely? a) a layer containing both a fossil 4 and a fossil 3 b) a layer containing both a fossil 2 and a fossil 3 c) a layer containing both a fossil 1 and a fossil 4 d) a layer containing both a fossil 1 and a fossil 2

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important

Up until 1938, paleontologists accepted the idea that coelacanths (an ancient fish) went extinct at the time that they last appear in the fossil record, about 80 million years ago. but in 1938, a live coelacanth was discovered off the coast of south africa that was compared to the fossil record and found to be the same species what goal of science does this discovery represent