Forms the outer layer of an embryo.

mesoderm

ectoderm

endoderm

none of the above

During sunny hours, a large amount of build up between the hours of 1: 00-5: 00 pm. a. ozone b. mercury c. lead d. sulfuric acid

Which of the following is a way that minerals are used? a. industry construction technology d. all of the above

All but one describes an effect of aging on the digestive system. a) decreased acid secretion b) decreased elasticity of stomach c) capacity to resist damage decreases d) food remains in stomach for less time