Describe the difference between arteries and veins in terms of their function.

The structures that insects use for gas exchange are called [drop].

The sounds of the heart beating that you may hear are directly caused by:

There are four chambers of the heart, the 2 atria pump blood into the ventricles and the 2 ventricles pump blood out of the heart.

45). Males are XY. 

47). Two people with the same genotype for a condition such as asthma have different phenotypes. This results from what type of inheritance pattern?

16). Sex hormones are produced by gonads. 

48). An abnormal number of one or more chromosomes (either extra or missing copies) is called _____.

42). Males produce higher levels of estrogen. 

43). In a fetus, sex hormones shape development of sexual anatomy.