Correct Answer: A

Rationale: Parkinson's disease is primarily caused by the loss of dopamine-producing neurons in the brain. Dopamine is a neurotransmitter that plays a crucial role in coordinating movement. The reduction of dopamine levels leads to the characteristic motor symptoms of Parkinson's disease, such as tremors, rigidity, and bradykinesia. Choice B, acetylcholine, is involved in functions like muscle contraction and autonomic nervous system regulation but is not primarily affected in Parkinson's disease. Serotonin (Choice C) is involved in mood regulation and sleep, not the main neurotransmitter affected in Parkinson's disease. Glutamate (Choice D) is the major excitatory neurotransmitter in the central nervous system and is not primarily implicated in Parkinson's disease pathophysiology.

Correct Answer: A

Rationale: The correct answer is the right atrium. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava. It then pumps this deoxygenated blood to the lungs via the pulmonary artery for oxygenation. The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle. The right ventricle receives oxygen-poor blood from the right atrium and pumps it to the lungs. The left ventricle receives oxygenated blood from the left atrium and pumps it to the rest of the body.

Correct Answer: A

Rationale: When a muscle shortens and generates force, it is contracting. Contraction is the process by which muscle fibers develop tension and exert a pulling force on the bones they are attached to, resulting in movement. Relaxation refers to the phase when a muscle returns to its original length, allowing for rest or preparation for the next contraction. Extension, on the other hand, is the movement that increases the angle between body parts, moving them further apart. Atrophy is unrelated to muscle contraction and refers to the wasting away or decrease in size of muscle tissue due to disuse or disease. Therefore, the correct answer is 'Contraction.'

Correct Answer: A

Rationale: The unit of force in the SI system is the Newton (N). It is defined as the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared. In the SI system, force is measured in Newtons, not in kilograms, meters, or seconds. Choice B, Kilogram (kg), is incorrect because kilograms are units of mass, not force. Choice C, Meter (m), is incorrect because meters are units of length, not force. Choice D, Second (s), is incorrect because seconds are units of time, not force.

Correct Answer: B

Rationale: Endocrine glands release hormones directly into the bloodstream without the use of ducts. This allows the hormones to be distributed throughout the body to target organs or tissues. Exocrine glands, on the contrary, release their secretions through ducts to the external environment or onto a surface, such as sweat glands. Apocrine and merocrine glands are both types of exocrine glands that release their secretions through different mechanisms. Apocrine glands release their secretions along with portions of the cell itself, while merocrine glands release their secretions through exocytosis without loss of cellular material.