Correct Answer: C

Rationale: The correct answer is C: 'To regulate body functions through hormones.' The endocrine system is responsible for producing and secreting hormones that help regulate various body functions such as growth, metabolism, reproduction, and mood. It does not primarily function to fight infection (A), transport oxygen (B), or break down food (D). While the immune system fights infection, the respiratory system transports oxygen, and the digestive system breaks down food, the main role of the endocrine system is to maintain homeostasis by coordinating and controlling bodily functions through the release of hormones.

Correct Answer: A

Rationale: In a transverse wave, the particles of the medium move perpendicular to the direction of wave travel. This means that the particles move up and down or side to side as the wave passes through the medium. This motion creates crests and troughs in the wave, leading to the characteristic oscillation observed in transverse waves. Choice B is incorrect because in transverse waves, the particle movement is not parallel to the direction of wave travel. Choice C is incorrect as the particles do not move in a circular motion in a transverse wave. Choice D is incorrect as the particles do not move opposite to the direction of wave travel; they move perpendicular to it.

Correct Answer: A

Rationale: Penicillins are a group of antibiotics that target the bacterial cell wall by inhibiting the synthesis of peptidoglycan, a vital component of the cell wall. This inhibition weakens the cell wall, leading to bacterial cell lysis and death. Penicillins are particularly effective against Gram-positive bacteria due to their mechanism of action. Tetracyclines (B) inhibit protein synthesis, Macrolides (C) interfere with bacterial ribosomes, and Fluoroquinolones (D) target bacterial DNA gyrase and topoisomerase IV. Unlike Penicillins, these antibiotics do not directly target the cell wall of bacteria.

Correct Answer: B

Rationale: The correct answer is B, 'Synapse.' The synapse is the specific term that refers to the point of contact between a motor neuron and a muscle fiber, where communication occurs to initiate muscle contraction. At the synapse, neurotransmitters are released by the motor neuron, triggering the muscle fiber to contract. Choice A, 'Sarcomere,' is incorrect as a sarcomere is the basic unit of muscle contraction, not the point of contact between a motor neuron and a muscle fiber. Choice C, 'Tendon,' is incorrect as tendons are fibrous connective tissues that connect muscle to bone, not involved in neuronal communication. Choice D, 'Myofibril,' is incorrect as a myofibril is a structure within muscle fibers where muscle contractions occur, not the specific point of contact for communication between a motor neuron and a muscle fiber.

Correct Answer: B

Rationale: The correct answer is B, Ammonia (NH₃). Ammonia is commonly found in household products and is used in cleaning agents due to its alkaline properties. Sodium chloride (NaCl) is a common salt and not a base. Vinegar is acetic acid, which is acidic in nature. Lemon juice contains citric acid, making it acidic as well. Therefore, ammonia is the only base among the choices provided.