Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____
(a) killing cells immediately, exerting their physiological effects by causing cell death.
(b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression.
(c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.
(d) removing cell-surface receptors from the plasma membrane.
Choice (c) is correct. Although some foreign substances will remove cell-surface receptors from the plasma membrane [choice (d)], this is a long-term response and not part of the initial response.
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After the depolarization phase of an action potential, the resting potential is restored by _____
A) the opening of sodium activation gates B) the opening of voltage-gated potassium channels and the closing of sodium channels C) a decrease in the membrane's permeability to potassium and chloride ions D) a brief inhibition of the sodium-potassium pump E) the opening of more voltage-gated sodium channels
The inner membrane system of chloroplasts consists of flattened sacs called ________ that form stacks called ________.
Fill in the blank(s) with the appropriate word(s).
Which of the following statements is true?
a. Although hormones are carried to all parts of the body, they produce effects only in cells with proper receptors. b. Hormones are limited to steroid compounds. c. Hormones are secreted by specialized exocrine glands. d. Most hormones are controlled by positive feedback mechanisms involving the pituitary gland. e. Hormones are supplied to the body in the diet.
All of the following are associated with the streak plate method of isolation EXCEPT:
a) a solid medium in a Petri dish b) colonies growing at and below the surface of the medium c) a sterile inoculating loop or needle d) isolation of CFU's from one another