Living organisms use oxygen to __________________.

Correct Answer: C

Rationale: The correct answer is C. Living organisms use oxygen to release energy stored in the molecules of food through a process called cellular respiration. This process involves breaking down glucose molecules in the presence of oxygen to produce energy in the form of ATP. Choice A is incorrect because oxygen does not directly reduce heat production in organisms. Choice B is incorrect because oxygen is involved in accepting electrons rather than donating them in cellular metabolism. Choice D is incorrect because the removal of metabolic wastes is not the primary role of oxygen in living organisms.

Correct Answer: A

Rationale: A blood clot stimulating further clotting is an example of a positive feedback mechanism. In positive feedback, the response enhances or amplifies the original stimulus, leading to an increase in the activity. In this case, the formation of a blood clot triggers more clotting activity, creating a cycle of increasing clot formation. Negative feedback mechanisms, on the other hand, work to maintain homeostasis by counteracting changes. Choices B, C, and D are incorrect as they do not accurately describe the situation of a blood clot stimulating further clotting.

Correct Answer: C

Rationale: The correct answer is C: Water. Water is essential for the human body to survive as it plays a crucial role in various physiological processes like digestion, circulation, and temperature regulation. Nitrogen is abundant in the atmosphere and is not directly obtained from the environment for survival. Waste products are materials that need to be eliminated from the body, not obtained for sustenance. Carbon dioxide is a byproduct of cellular respiration and is expelled from the body through breathing, not obtained as a nutrient.

Correct Answer: B

Rationale: Homeostasis is the body's ability to maintain stable internal conditions despite external changes. To achieve this balance, concentrations of essential substances must remain within specific ranges. Choice A is incorrect because decreasing concentrations would not maintain stability. Choice C is incorrect as increasing concentrations when the body is stressed would disrupt homeostasis. Choice D is incorrect as fluctuating greatly between high and low values would also not support the body's stability. Therefore, the correct answer is B, as it aligns with the concept of homeostasis by emphasizing the need for stability within certain limits.

Correct Answer: C

Rationale: In negative feedback mechanisms, changes away from the normal state stimulate changes in the opposite direction. This is a fundamental concept in biological systems where the response to a stimulus opposes the initial change, helping to maintain homeostasis. Choice A is incorrect because negative feedback does not stimulate changes in the same direction. Choice B is incorrect because negative feedback does not inhibit all body reactions, but rather specific responses. Choice D is incorrect because negative feedback does not stimulate a reduction in all body requirements, but rather adjusts specific functions to restore balance.