Correct Answer: C

Rationale: The scrotum is the structure that surrounds and protects the testes. It plays a vital role in maintaining an optimal temperature for sperm production by adjusting the distance of the testes from the body to regulate the effects of external temperature changes. This mechanism helps to safeguard the viability and quality of sperm by ensuring they develop at the right temperature. The epididymis (Choice A) is a coiled tube where sperm mature and are stored, not the structure surrounding the testes. The vas deferens (Choice B) is a duct that carries sperm from the testes to the urethra, not the protective structure around the testes. The prostate gland (Choice D) is part of the male reproductive system, responsible for secreting fluids that nourish and protect sperm, but it is not the structure that surrounds and protects the testes for sperm production.

Correct Answer: D

Rationale: The T wave on an ECG corresponds to ventricular repolarization. Following ventricular depolarization, which is represented by the QRS complex, the ventricles undergo repolarization during the T wave. This phase signifies the recovery of ventricular muscle cells as they prepare for the subsequent depolarization cycle. Choices A, B, and C are incorrect because the T wave specifically reflects the repolarization of the ventricles, not the atria or their respective depolarization or repolarization phases.

Correct Answer: D

Rationale: Sarcomeres are the fundamental contractile units of skeletal muscles and are responsible for muscle contraction. They consist of actin and myosin filaments that slide past each other during muscle contraction. Neurons are responsible for transmitting signals to and from muscles but are not directly involved in muscle contraction. Myofibrils are composed of sarcomeres and are the structures within muscle cells where muscle contractions take place. Tendons are connective tissues that attach muscles to bones and are not directly involved in muscle contraction.

Correct Answer: A

Rationale: A) This statement is true. Prions are infectious agents composed entirely of protein, lacking nucleic acids such as DNA or RNA. They are known for causing neurodegenerative diseases in animals and humans. B) This statement is false. Prions are not easily destroyed by common disinfectants due to their unique structure and resistance to conventional sterilization methods. C) This statement is false. Prions are not a type of antibiotic. They are a distinct class of infectious agents. D) This statement is false. Prions are not live organisms but rather misfolded proteins that can induce abnormal folding in normal proteins, leading to disease.

Correct Answer: A

Rationale: When a wave passes from one medium to another with the same speed, its frequency remains unchanged. Frequency is a characteristic of the source of the wave and does not depend on the medium through which the wave is traveling. Wavelength and speed of the wave can change when passing from one medium to another, but frequency remains constant. This is because the frequency of a wave is determined by the source that produces it, and as long as the speed remains constant, the frequency will not be altered. Amplitude, on the other hand, can change based on factors like energy loss or gain, but it is not a property that remains constant when a wave moves between different mediums with the same speed. Speed, although important for the wave's propagation, is not the property that remains unchanged when the wave transitions between mediums with the same speed. Therefore, the correct answer is frequency.