1. Light: Plants use light for photosynthesis, the process by which they convert light energy into chemical energy. They also use light to regulate their growth and development. For example, plants will grow towards a light source (phototropism).

2. Gravity: Plants respond to gravity by growing roots downwards and shoots upwards (gravitropism). This ensures that roots anchor the plant firmly in the ground and that shoots are able to access sunlight.

3. Touch: Some plants respond to touch by changing their growth patterns. For example, a vine will grow around a support structure if it encounters it (thigmotropism). Others, like the Venus flytrap, use touch to trigger a rapid closing of their trap to capture insects.