What are the chemical messengers that control growth, differentiation, and metabolism of specific target cells called?

Correct Answer: A

Rationale: Hormones are signaling molecules produced by glands in multicellular organisms. They travel through the bloodstream to specific target cells where they regulate various physiological processes, including growth, differentiation, and metabolism. Neurons (choice B) are nerve cells that transmit nerve impulses and are not responsible for controlling growth, differentiation, or metabolism. Glands (choice C) produce and release hormones but are not the chemical messengers themselves. Second messengers (choice D) are molecules involved in intracellular signal transduction, not the primary chemical messengers controlling growth, differentiation, and metabolism. Therefore, hormones (choice A) are the correct answer as they match the description provided in the question.

Correct Answer: B

Rationale: The correct answer is B: Sensory neuron. A sensory neuron is responsible for carrying impulses from sensory receptors to the spinal cord. These neurons transmit information about external stimuli from the periphery to the central nervous system for processing and response. Choice A, Motor neuron, is incorrect as motor neurons carry signals from the central nervous system to muscles and glands, enabling movement and secretion. Choice C, Interneuron, is incorrect as interneurons act as connectors between sensory and motor neurons, primarily facilitating communication between the two. Choice D, Bipolar neuron, is incorrect as bipolar neurons are specialized sensory neurons found in some sensory organs like the retina of the eye and the olfactory epithelium.

Correct Answer: D

Rationale: The upper respiratory tract includes structures such as the nose, nasal cavity, pharynx, and larynx. These structures are responsible for filtering, warming, and humidifying the air. The lower respiratory tract comprises the trachea, bronchi, bronchioles, alveolar ducts, and alveoli. Bronchioles, alveolar ducts, and alveoli are all part of the lower respiratory system, involved in gas exchange. Therefore, the correct answer is 'None of the above' as none of the listed options are part of the upper respiratory tract.

Correct Answer: C

Rationale: The alveoli are the primary site for gas exchange in the respiratory system. These tiny air sacs in the lungs are where oxygen is taken up into the bloodstream and carbon dioxide is released from the bloodstream into the lungs to be exhaled. The trachea (Choice A) is the windpipe that carries air to and from the lungs but is not directly involved in gas exchange. Bronchioles (Choice B) are smaller airway branches that lead to the alveoli but do not participate in gas exchange themselves. The larynx (Choice D) plays a role in producing sound and protecting the airway but is not primarily responsible for gas exchange.