If a plant on a windowsill receives bright light for 12 hours a day but the soil has very little water, what factor most limits the plant's growth?

If a plant on a windowsill receives bright light for 12 hours a day but the soil has very little water, what factor most limits the plant's growth?

• A. Light
• B. Water
• C. Soil color
• D. Temperature

Answer: (B)

Plants grow best when all the essential needs are met, and growth is governed by the factor that’s most scarce relative to the plant’s needs. Here, the plant gets bright light for many hours, so light isn’t the bottleneck. Water, however, is in short supply. Water is needed for photosynthesis and to keep plant cells firm so they can grow properly. When the soil is very dry, the plant can’t pull enough water up from the roots, leaves may wilt, and the stomata may close to reduce water loss. That reduces gas exchange and slows photosynthesis, which limits how much sugar the plant can make and, in turn, how much it can grow. The soil color doesn’t affect growth directly, and temperature isn’t given as a constraint in this scenario, so they aren’t the limiting factor here.

Plants grow best when all the essential needs are met, and growth is governed by the factor that’s most scarce relative to the plant’s needs. Here, the plant gets bright light for many hours, so light isn’t the bottleneck. Water, however, is in short supply. Water is needed for photosynthesis and to keep plant cells firm so they can grow properly. When the soil is very dry, the plant can’t pull enough water up from the roots, leaves may wilt, and the stomata may close to reduce water loss. That reduces gas exchange and slows photosynthesis, which limits how much sugar the plant can make and, in turn, how much it can grow. The soil color doesn’t affect growth directly, and temperature isn’t given as a constraint in this scenario, so they aren’t the limiting factor here.