Which of the following does NOT influence plant growth?

1. Analyze the question We need the one factor that does NOT influence plant growth. Four options are known environmental or nutritional requirements for plants, and one is not.

2. Explain the concept Plant growth depends on:

• Light: needed for photosynthesis, which makes food. It also affects flowering and stem elongation (phototropism).
• Water: needed for photosynthesis, for turgidity, for transporting minerals and for germination.
• Temperature: controls enzyme activity, so it affects the rate of photosynthesis, respiration and germination.
• Nutrients (mineral salts): nitrogen, phosphorus, potassium, magnesium and others are needed to build proteins, chlorophyll and cell structures.

Vitamins are organic compounds that animals must take in through their diet, because animals cannot make enough of them (for example Vitamin C in humans). Green plants make their own organic compounds, including the vitamins they need, through photosynthesis and metabolism. So vitamins are not an external factor that plants need to be supplied with for growth.

3. Solution

• A. Light: influences growth ✔
• B. Nutrients: influence growth ✔
• C. Temperature: influences growth ✔
• D. Vitamins: not an external requirement for plant growth ✘
• E. Water: influences growth ✔

4. Answer The correct option is D. Vitamins.

5. Exam tip Remember the plant growth factors with "LWTN": Light, Water, Temperature, Nutrients (plus oxygen and suitable pH). Vitamins are the "animal nutrition" word. When you see vitamins in a plant growth question, think of animal diets, not plant needs.