Which of the following statements about skeletal muscle contraction is false?
(a) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane.
(b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.
(c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament.
(d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.
Choice (b) is false. Muscle contraction is triggered by an efflux of Ca2+ from the sarcoplasmic reticulum into the cytosol.
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Consider the food chain of grass ? grasshopper ? mouse ? snake ? hawk. About how much of the chemical energy fixed by photosynthesis of the grass (100 percent) is available to the hawk?
A) 0.01% B) 0.1% C) 1% D) 10% E) 60%
The molecule shown above is the purine ____
a. thymine b. adenine c. uracil d. guanine e. cytosine
Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation. Surprisingly, this stops mitosis. Specifically, Taxol must affect _____
A) the structure of the mitotic spindle B) anaphase C) formation of the centrioles D) chromatid assembly
Which of the following statements is TRUE?
A) Oxygen is a product of cellular respiration; carbon dioxide is a product of photosynthesis. B) Lactic acid is a product of aerobic respiration; ethyl alcohol is a product of fermentation. C) Oxidation is the loss of electrons; reduction is the gain of electrons. D) Glucose is a product of aerobic respiration; lactic acid is a product of anaerobic respiration.