The ability of organisms to maintain a constant internal environment is known as

Step 1: Analyze the question The question asks for the term describing an organism's ability to keep its internal environment constant (stable temperature, water level, blood sugar, pH, and so on), even when the external environment changes.

Step 2: Explain the concept The word homeostasis comes from "homeo" (similar or steady) and "stasis" (standing or staying). Examples include:

• Thermoregulation: keeping body temperature at about 37°C in humans (sweating when hot, shivering when cold).
• Osmoregulation: controlling water and salt levels, mainly by the kidneys.
• Blood sugar regulation: insulin and glucagon keep glucose levels steady.

Step 3: Check each option

• A. Diuresis: the production of large amounts of urine. It is only one part of water balance, not the whole idea of a constant internal environment.
• B. Plasmolysis: the shrinking of a plant cell's protoplasm away from the cell wall when the cell loses water in a concentrated (hypertonic) solution.
• C. Endosmosis: the movement of water into a cell by osmosis.
• D. Homeostasis: the maintenance of a constant internal environment. This matches the definition exactly.

Step 4: Answer The correct option is D. Homeostasis.

Exam tip: Link the word parts: homeo = same and stasis = steady, so homeostasis means "staying the same". Also remember that plasmolysis and endosmosis both involve water movement in cells, while diuresis relates to urine. Only homeostasis covers the whole idea of balance in the body.