Which of the following describes a characteristic of the plasma membrane?
The plasma membrane is composed of a bilayer of protein molecules.
The plasma membrane is selectively permeable.
The plasma membrane does not participate in cellular activities
The plasma membrane receptors are specialized lipids.
The Correct Answer is B
a. The plasma membrane is composed of a bilayer of protein molecules: This is incorrect. The plasma membrane is primarily composed of a bilayer of phospholipids, with proteins interspersed within this bilayer.
b. The plasma membrane is selectively permeable: This is correct. The plasma membrane regulates the entry and exit of substances, allowing certain molecules to pass while restricting others.
c. The plasma membrane does not participate in cellular activities: This is incorrect. The plasma membrane is actively involved in various cellular activities, including signaling, transport, and maintaining homeostasis.
d. The plasma membrane receptors are specialized lipids: This is incorrect. Receptors on the plasma membrane are typically proteins, not lipids, which are involved in signal transduction and cellular communication.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
a. Acetylcholine: This is the primary neurotransmitter at neuromuscular junctions. It binds to receptors on muscle cells (specifically nicotinic acetylcholine receptors) and triggers an action potential, leading to muscle contraction.
b. Calcium: While calcium ions are essential for muscle contraction, they are not neurotransmitters. Instead, they play a role in the release of acetylcholine from the nerve terminal and in the contraction process within muscle cells.
c. Adenosine triphosphate (ATP): ATP is the primary energy carrier in cells but is not a neurotransmitter. It is crucial for muscle contraction, as it provides the energy for various steps in the contraction cycle.
d. Sodium: Sodium ions are involved in generating action potentials and depolarizing muscle cells, but they are not neurotransmitters.
Correct Answer is B
Explanation
a. Mouth: The mouth is primarily responsible for the mechanical breakdown of food and the beginning of starch digestion via salivary amylase, but it is not a major site of nutrient absorption.
b. Small intestine: The small intestine is the primary site for nutrient absorption. The majority of carbohydrates, proteins, fats, vitamins, and minerals are absorbed here through its extensive surface area provided by villi and microvilli.
c. Large intestine: The large intestine primarily absorbs water and electrolytes. It is not a major site for nutrient absorption.
d. Stomach: The stomach is mainly involved in the mechanical and chemical breakdown of food, particularly proteins, but only a small amount of nutrients (e.g., alcohol, some drugs) are absorbed here.
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