Plasma cells are derived from
A) macrophages.
B) B cells.
C) T cells.
D) dendritic cells.
E) neutrophils.
B
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Which substance can easily cross the human blood brain barrier in a healthy individual?
a. viral proteins b. bacterial DNA c. human white blood cells d. cortisol e. albumin
Activation energy is not required for nonspontaneous reactions
Indicate whether the statement is true or false.
In catabolite repression systems of some Gram-positive bacteria, such as Bacillus subtilis, transcription of catabolic operons is regulated by CcpaA (catabolite control protein A) rather than cAMP. Propose a hypothesis to explain the preferential use of glucose in the presence of a second sugar such as sucrose by Bacillus subtilis.
A. CcpaA acts as an inducer of sucrose operon genes in Bacillus subtilis when glucose, but not lactose, is present. B. CcpaA acts as a repressor of sucrose operon genes in Bacillus subtilis when both sugars are present. C. CcpaA acts as an inducer of sucrose operon genes in Bacillus subtilis when both sugars are present. D. CcpaA acts as a repressor of sucrose operon genes in Bacillus subtilis when lactose, but not glucose, is present.
In 1858, a German scientist named Rudolph Virchow stated that spontaneous generation of living things from nonliving matter was impossible. This statement contributed to the development of the cell theory. In effect, what was Virchow saying?
A) Cells exist in a wide variety of shapes and sizes. B) All cells come from existing cells. C) The cell is the basic unit of all organisms. D) Cells are alive.