Why don't arteries need valves

Bacterial cells with thick peptidoglycan and numerous teichoic acid cross-linkages are Gram stained. The organisms stain pink. Which one of the following statements explains this discrepancy?

Which two proccesses are involved in mitotic cell division

Which weathering process involves physical forces but not chemical reactions or dissolving of minerals A. Solution B. Abrasion C. Hydration D. Carbonation

What came first: the genetic variation of different beaks or natural selection acting upon them?

Depolarization of a cell membrane occurs because

Suppose you use a microscope to look at a cell from the leaf of a tree. What structure will you see that would not be found in a cell from your fingernail? A. mitochondria B. cilia C. cell wall D. ribosomes

Name the three energy roles that organisms fill in an ecosystem.

Adrenergic postganglionic neurons release the hormones norepinephrine and epinephrine. Adrenergic postganglionic neurons release the hormones norepinephrine and epinephrine. True False

Which of the following are examples of the first specialized tissues?

Which structure of the trachea prevents it from collapsing inward and obstructing the air passageway?