Which of the following events occurs initially when Escherichia coli cells are in a gradient of a chemorepellent?
A. Flagella rotate clockwise
B. CheY is phorphorylated
C. CheA autophosphorylates
D. Cells tumble
Answer: C
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What information is provided by the fossil record that cannot be provided by examining living organisms?
A. All of the answer options are correct. B. a record of extinct species C. absolute dates for when different taxa diverged D. records of environmental conditions E. timing of mass extinctions
In an antibody- mediated immune response,
what causes effector helper T cells to release cyokines?
a. binding to antigen presenting dendritic cells b. binding to a bacterial complement c. binding to a naive helper T cell d. binding to a B cell e. engulfing a bacterium
RNA silencing involves
A) miRNAs. B) siRNAs. C) double-stranded RNA. D) a protein called Dicer. E) All of these
The ________ valves prevent blood from flowing back into the heart once it has left the ventricles
Fill in the blank(s) with correct word