True or false? the circulatory system of humans is composed of two loops: the systemic circulation, in which blood flows between the heart and lungs, and the pulmonary circulation, in which blood flows between the heart and the rest of the body.

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

Select the correct answer from each drop-down menu. in an experiment, dr. travis examined the effects of calcium intake on osteoporosis, a condition that causes an increased risk of bone fractures. the amount of calcium is variable. the risk of bone fractures .

Explain how the number of similarities between the embryos from early stage to late stage is used as evidence of a common ancestry