Severe combined immunodeficiency
occurs when
a. T cells are improperly formed.
b. B cells are improperly formed.
c. an individual has no adaptive immunity.
d. all of the above occur.
Answer: D
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Horozontal rows of parenchymal cells that tranport materials horizontally are called?
A. rays B. tracheids C. vessel elements D. fibers E. sieve tubes
The process that converts one molecule of nitrogen to ammonia using 16 molecules of ATP is called ____
a. ammonia-oxidation b. ammonification c. nitrogen fixation d. nitrification e. denitrification
Typically, the gate of an ion channel remains closed until a(n) ____ binds to the receptor
a. ligand b. enzyme c. G protein d. target cell e. first messenger
Figure 4.16
What is a main function of the structure in the accompanying figure labeled B?
A. It controls cell shape. B. It separates DNA during cell division. C. It helps nerve cells lengthen. D. It is found in hair. E. It helps regulate DNA replication.