What advantage does the activity of osteoblasts and osteoclasts impart to vertebrates, even after growth has finished?
A) As old bones are dissolved, new bones can be formed.
B) The cells enable bone to lengthen and shorten as needed.
C) Bone growth never finishes; it continues at a slow pace throughout life.
D) The cells allow bone to get stronger as physical demands are placed on it.
D
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The hemoglobin molecule ____
a. transports oxygen from the lungs to the cells of the body b. prevents sickle cell anemia when present in high enough concentrations in the blood c. is involved in amino acid metabolism d. acts as a cell surface receptor e. is controlled by a single gene
Which one of the following nonhormonal chemical messengers is important in local control of blood flow and blood clotting?
A) prostaglandins B) nerve growth factor C) tumor angiogenesis growth factor D) histamine E) epidermal growth factor
An unknown element is found to contain 45 protons and an atomic mass of 64, what is its atomic number?
A. It cannot be determined. B. 19 C. 45 D. 64
0.2 mls of a 10-4 dilution of a virus preparation yields 90 plaques. What is the number of PFU per ml in the undiluted virus preparation?
A. 4.5 × 107 B. 9.0 × 108 C. 4.5 × 106 D. 9.0 × 105