Which element is used in jewelry due to its malleability and resistance to tarnish?

Correct Answer: C

Rationale: Gold is the correct answer. Gold is a popular choice for jewelry due to its exceptional malleability, allowing it to be easily shaped into intricate designs. Moreover, gold is resistant to tarnish, ensuring the jewelry retains its beauty over time. Iron is not commonly used in jewelry due to its susceptibility to rusting. Copper is also not as popular in jewelry making as gold due to its tendency to tarnish and cause skin discoloration. While silver is used in jewelry, it is more prone to tarnish compared to gold, making it less ideal for long-lasting pieces.

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: A

Rationale: The axon is the part of the neuron responsible for transmitting signals away from the cell body and toward other neurons or muscles. It is a long, slender projection covered by the myelin sheath, which speeds up signal transmission. Dendrites, on the other hand, receive signals from other neurons and transmit them toward the cell body. The synapse is the junction between two neurons where communication occurs, but it is not responsible for transmitting signals away from the cell body.

Correct Answer: C

Rationale: The correct answer is C, the peripheral nervous system. The peripheral nervous system is responsible for transmitting signals from the sensory organs to the central nervous system. It consists of nerves that connect the central nervous system to the rest of the body, including sensory nerves that carry information from the sensory organs to the brain and spinal cord. Choices A, B, and D are incorrect. The autonomic nervous system is responsible for involuntary functions like heart rate and digestion, the somatic nervous system controls voluntary movements, and the central nervous system consists of the brain and spinal cord.

Correct Answer: A

Rationale: Calcitonin, produced by the thyroid gland, is responsible for regulating calcium levels in the blood. It works by decreasing blood calcium levels through two main mechanisms: promoting calcium uptake by bones and decreasing calcium reabsorption in the kidneys. Parathyroid hormone (PTH), on the other hand, increases blood calcium levels by promoting calcium release from bones and increasing calcium absorption in the intestines. Thyroxine, another thyroid hormone, primarily regulates metabolism and has no direct influence on calcium levels. Insulin, produced by the pancreas, is involved in regulating blood sugar levels and is not related to calcium homeostasis.