What term describes the functional unit of a skeletal muscle responsible for muscle contraction?

Correct Answer: B

Rationale: The correct answer is B, 'Sarcomere.' The sarcomere is indeed the functional unit of a skeletal muscle responsible for muscle contraction. It is composed of actin and myosin filaments that interact to generate muscle contraction. Choice A, 'Myofibril,' is incorrect as myofibrils are composed of sarcomeres, not the functional units themselves. Choice C, 'Tendon,' is incorrect as tendons connect muscles to bones and do not directly participate in muscle contraction. Choice D, 'Myoglobin,' is incorrect as myoglobin is a protein that stores oxygen in muscle cells and is not directly involved in muscle contraction.

Correct Answer: B

Rationale: The dendrites are the part of the neuron that receives signals from other neurons and conducts them toward the cell body. They play a crucial role in gathering incoming signals and transmitting them to the cell body for processing. The axon, on the other hand, is responsible for carrying signals away from the cell body. The synapse is the point of connection between two neurons facilitating communication, while the myelin sheath is a protective layer surrounding the axon that aids in accelerating signal transmission.

Correct Answer: C

Rationale: Thyroxine, also known as T4, is a hormone produced by the thyroid gland that plays a crucial role in regulating the body's metabolism, growth, and development. It helps control the rate at which the body uses energy, affects protein synthesis, and influences the body's sensitivity to other hormones. Calcitonin (A) is another hormone produced by the thyroid gland, but its primary function is to regulate calcium levels in the blood. Parathyroid hormone (PTH) (B) is produced by the parathyroid glands and is involved in regulating calcium and phosphorus levels in the body. Insulin (D) is a hormone produced by the pancreas that helps regulate blood sugar levels.

Correct Answer: C

Rationale: Atrial systole is the phase of the cardiac cycle during which the atria contract, pushing blood into the ventricles. This occurs after the atria have been filled during atrial diastole. Ventricular systole refers to the phase when the ventricles contract to push blood out of the heart, not when the atria contract. Ventricular diastole is the phase when the ventricles relax and fill with blood, not when the atria contract. Therefore, the correct answer is atrial systole as it specifically describes the atrial contraction phase.

Correct Answer: B

Rationale: The correct answer is B: Alveoli. The alveoli are the small air sacs in the lungs where gas exchange occurs. Oxygen from the air we breathe passes into the bloodstream through the alveoli, while carbon dioxide from the bloodstream passes out of the body through the alveoli. Choice A, Bronchi, are the main airways in the lungs and not the site of gas exchange. Choice C, Trachea, refers to the windpipe, which is a different structure than the alveoli. Choice D, Bronchioles, are smaller airways branching off from the bronchi and are not where gas exchange primarily occurs.