Which term best describes a resource that governs the rate of a biological process?

• A. Limiting factor.
• B. Niche.
• C. Ecosystem.
• D. Symbiosis.

Answer: (A)

The main idea here is a limiting factor—the resource or condition that determines how fast a biological process can occur. When one resource is in short supply, it slows down the process, and the rate can only rise again once that resource becomes more available. For example, light, nutrients, water, or optimal temperature can limit photosynthesis or growth; if light is scarce, plants can’t photosynthesize quickly no matter how good other conditions are. If the limiting resource is increased, the rate can improve until another factor becomes limiting. The other terms describe different concepts: a niche is an organism’s role in its environment, an ecosystem is the whole system of living and nonliving parts, and symbiosis is a close interaction between species. So the resource that governs the rate of a biological process is the limiting factor.