Which of the following ions binds to the troponin complex, initiating muscle contraction?
Potassium.
Calcium.
Phosphorus.
Sodium.
The Correct Answer is B
Calcium ions play a crucial role in initiating muscle contraction.
When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.
Some of this calcium attaches to troponin, which causes it to change shape. This shape change exposes binding sites for myosin on the actin filaments.
Myosin’s binding to actin causes cross-bridge formation, and muscle contraction begins.
The other ions mentioned in the question do not have this specific role in muscle contraction.
Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.
Phosphorus ions are important for energy metabolism but do not bind to the troponin complex.
Sodium ions are important for generating action potentials but do not bind to the troponin complex.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
The polarity of water molecules explains its solvent abilities for certain substances.
Water is a polar molecule because it has a partial positive charge on one end and a partial negative charge on the other end due to the unequal sharing of electrons between the oxygen and hydrogen atoms.
This polarity allows water to dissolve other polar substances and ionic compounds.
Choice A. Kinetic energy of liquid water molecules is not the correct answer because kinetic energy refers to the energy of motion and does not directly explain water’s solvent abilities.
Choice B. High specific heat is not the correct answer because specific heat refers to the amount of heat required to raise the temperature of a substance and does not directly explain water’s solvent abilities.
Choice C. High surface tension is not the correct answer because surface tension refers to the cohesive forces between liquid molecules and does not directly explain water’s solvent abilities.
Correct Answer is C
Explanation
The pH scale is a logarithmic scale that measures the acidity or alkalinity of a solution.
A solution with a pH of 7 is neutral, while a solution with a pH less than 7 is acidic and a solution with a pH greater than 7 is alkaline.
Because the pH scale is logarithmic, each whole number change in pH represents a tenfold change in acidity or alkalinity.
Therefore, a substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.
Choice A. A substance with a pH of 3 is two times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline and also incorrectly states the magnitude of the difference in acidity or alkalinity.
Choice B. A substance with a pH of 3 is two times more acidic than a substance with a pH of 4 is not correct because it correctly states that the substance with a lower pH is more acidic but incorrectly states the magnitude of the difference in acidity.
Choice D. A substance with a pH of 3 is 10 times more alkaline than a substance with a pH of 4 is not correct because it incorrectly states that the substance with a lower pH is more alkaline.
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