What is a limiting factor?

• A. A resource that restricts the rate of a process.
• B. A factor that always increases population growth.
• C. A tool used to measure growth.
• D. A type of energy produced by cells.

Answer: (A)

A limiting factor is a resource or condition that restricts the rate at which a process occurs. In biology, the speed of growth, metabolism, or a population’s increase depends on having enough of essential resources such as food, water, space, or a suitable environment. When one of those resources is scarce, it slows down or limits the process—even if all other factors are adequate. For example, in a pond, if nutrients or oxygen become scarce, the population cannot keep increasing rapidly, no matter how favorable other conditions are. The correct choice captures this idea: a resource that restricts the rate of a process. The other options describe something different: a factor that always increases growth, a measuring tool, or a type of cellular energy, none of which define limiting factors.