SAT - Biology Subject Human Anatomy and Physiology Questions and Answers — Questions and Answers
Question 1: Which of the following describes the primary role of calcium ions (Ca2+) in the contraction of a skeletal muscle fiber?
- To bind to the myosin heads, activating them for the power stroke.
- To generate the action potential that propagates along the sarcolemma.
- To bind to troponin, which causes tropomyosin to shift and expose the myosin-binding sites on actin. (Correct answer)
- To provide the energy for the detachment of the myosin head from the actin filament.
Correct answer: To bind to troponin, which causes tropomyosin to shift and expose the myosin-binding sites on actin.
In skeletal muscle contraction, an action potential triggers the release of Ca2+ from the sarcoplasmic reticulum. These calcium ions then bind to troponin, a protein complex on the actin filament. This binding causes a conformational change that moves the tropomyosin protein, uncovering the sites on actin where myosin heads can bind, thus initiating the cross-bridge cycle and muscle contraction.
Question 2: A patient is found to have a consistently high level of blood calcium (hypercalcemia). A defect in which of the following glands or hormones would most likely contribute to this condition through a failure of negative feedback?
- Overproduction of calcitonin by the thyroid gland.
- Underproduction of parathyroid hormone (PTH) by the parathyroid glands.
- Overproduction of insulin by the pancreas.
- Overproduction of parathyroid hormone (PTH) by the parathyroid glands. (Correct answer)
Correct answer: Overproduction of parathyroid hormone (PTH) by the parathyroid glands.
Parathyroid hormone (PTH) is responsible for raising blood calcium levels by stimulating its release from bones, increasing its reabsorption in the kidneys, and promoting the activation of Vitamin D to enhance intestinal absorption. In a normal negative feedback loop, high blood calcium would suppress PTH secretion. An overproduction of PTH would override this feedback, leading to chronically high blood calcium levels (hypercalcemia).
Question 3: Which of the following correctly traces the path of deoxygenated blood as it enters the heart and is pumped toward the lungs?
- Left Atrium → Left Ventricle → Aorta
- Superior Vena Cava → Right Atrium → Right Ventricle → Pulmonary Artery (Correct answer)
- Pulmonary Vein → Left Atrium → Left Ventricle → Pulmonary Artery
- Right Ventricle → Right Atrium → Superior Vena Cava → Lungs
Correct answer: Superior Vena Cava → Right Atrium → Right Ventricle → Pulmonary Artery
Deoxygenated blood from the systemic circuit returns to the heart via the superior and inferior vena cavae, entering the right atrium. From there, it passes through the tricuspid valve into the right ventricle. The right ventricle then contracts, pumping the deoxygenated blood through the pulmonary valve into the pulmonary artery, which carries it to the lungs for oxygenation.
Question 4: The primary function of the Loop of Henle within the nephron of the kidney is to:
- filter large proteins and blood cells out of the blood plasma.
- secrete waste products like urea and ammonia into the filtrate.
- create a salt concentration gradient in the renal medulla. (Correct answer)
- reabsorb all glucose and amino acids from the filtrate.
Correct answer: create a salt concentration gradient in the renal medulla.
The Loop of Henle establishes a hypertonic (high salt) concentration gradient in the interstitial fluid of the renal medulla. This gradient is critical for the final step of urine concentration, as it allows the collecting ducts to reabsorb water from the filtrate under the influence of antidiuretic hormone (ADH), thereby conserving water for the body.
Question 5: During the transmission of a nerve impulse, the rapid depolarization of the neuron's membrane is primarily caused by which event?
- The influx of potassium ions (K+).
- The efflux of sodium ions (Na+).
- The influx of sodium ions (Na+). (Correct answer)
- The efflux of chloride ions (Cl-).
Correct answer: The influx of sodium ions (Na+).
When a neuron reaches its threshold potential, voltage-gated sodium channels open rapidly. This allows a massive influx of positively charged sodium ions (Na+) to rush into the cell, down their electrochemical gradient. This rapid influx of positive charge causes the membrane potential to shoot up from negative to positive, an event known as depolarization, which is the rising phase of the action potential.
Question 6: In the human respiratory system, the exchange of oxygen and carbon dioxide between the air and the blood occurs across the walls of the alveoli and capillaries. By which physical process does this gas exchange primarily occur?
- Active Transport
- Osmosis
- Facilitated Diffusion
- Simple Diffusion (Correct answer)
Correct answer: Simple Diffusion
Gas exchange in the lungs occurs via simple diffusion. Oxygen moves from the alveoli (where its partial pressure is high) into the blood of the pulmonary capillaries (where its partial pressure is low). Simultaneously, carbon dioxide moves from the blood (high partial pressure) into the alveoli (low partial pressure). This movement does not require energy or carrier proteins; it is driven solely by the difference in partial pressures of the gases.
SAT - Biology Subject Human Anatomy and Physiology Questions and Answers
Which of the following describes the primary role of calcium ions (Ca2+) in the contraction of a skeletal muscle fiber?