Correct Answer: A

Rationale: The diaphragm is the primary muscle responsible for breathing. It is a large, dome-shaped muscle located at the base of the chest cavity. When it contracts, it flattens, increasing the volume of the chest cavity and causing inhalation. When it relaxes, it returns to its dome shape, decreasing the volume of the chest cavity and causing exhalation. The intercostal muscles, located between the ribs, assist the diaphragm in breathing by expanding and contracting the chest cavity. The rectus abdominis and pectoralis major are not directly involved in the process of breathing.

Correct Answer: B

Rationale: The correct answer is B. The thymus is not a principal organ of the nervous system; it is part of the immune system. The brain, spinal cord, and ganglia are principal organs of the nervous system. The brain is responsible for processing information, the spinal cord helps transmit signals between the brain and the rest of the body, and ganglia are clusters of nerve cells that support the nervous system's functions. Therefore, the thymus is the correct answer as it is not directly involved in nervous system functions.

Correct Answer: B

Rationale: The correct answer is B: Ribosome. Ribosomes, the cellular structures located in the cytoplasm or on the endoplasmic reticulum, are responsible for protein synthesis in the cell. They are the sites where mRNA is translated into proteins, making them essential for the synthesis of proteins in all living cells. The other choices, such as the nucleus (choice A), endoplasmic reticulum (choice C), and Golgi apparatus (choice D), are not directly involved in protein synthesis. The nucleus contains DNA and is responsible for housing the genetic material, the endoplasmic reticulum is involved in protein folding and transport, and the Golgi apparatus is responsible for modifying, sorting, and packaging proteins.

Correct Answer: B

Rationale: The correct answer is the Medulla oblongata. This structure, located in the brainstem, plays a crucial role in regulating essential functions such as breathing, heart rate, and blood pressure. It serves as a control center for autonomic functions necessary for maintaining life. The Cerebrum (Choice A) is mainly responsible for higher brain functions such as thinking and voluntary movements, not for regulating basic physiological processes like breathing and heart rate. The Cerebellum (Choice C) is involved in coordination, balance, and muscle control, but not in regulating breathing and heart rate. The Hypothalamus (Choice D) plays a role in regulating body temperature, hunger, and thirst, but it is not primarily responsible for controlling breathing and heart rate.

Correct Answer: B

Rationale: The correct answer is B: Occipital lobe. The occipital lobe, situated at the back of the brain, is specifically responsible for processing visual information received from the eyes. It plays a crucial role in interpreting and making sense of visual stimuli, allowing individuals to perceive and comprehend the world around them. The Temporal lobe (Choice A) is involved in processing auditory information and memory, not visual processing. The Parietal lobe (Choice C) is responsible for processing sensory information from various parts of the body, but not specifically visual information. The Frontal lobe (Choice D) is involved in functions such as decision-making, problem-solving, and voluntary movement, but not processing visual stimuli.