Plants cannot move from place to place, so they must respond to changes in their environment to survive. A stimulus is a change in the environment that an organism detects and responds to. Plants detect and respond to many stimuli, including:- light: its direction, intensity, wavelength, and the length of the day and night (the photoperiod);
- gravity: so roots grow down into the soil and shoots grow up;
- water: roots grow towards moisture;
- touch: climbing plants coil around supports;
- temperature: for example, a cold period triggers germination or flowering in some species;
- chemicals, and attack by herbivores or pathogens.Why plants respondResponding helps a plant to:- maximise photosynthesis, by growing its leaves towards light;
- obtain water and mineral ions, by growing roots down into the soil;
- anchor itself and support its shoots;
- flower and set seed at the right time of year, when pollinators are active and conditions suit seed development;
- avoid being eaten, for example by producing toxic or bad-tasting chemicals such as tannins and alkaloids.How plants respondPlants have no nervous system. Instead, they detect stimuli with specialised receptor molecules, such as light-sensitive pigments, and coordinate their responses using chemicals called plant growth regulators (plant hormones). Most plant responses are changes in growth, so they are slower than animal responses, but they let a plant adjust its shape and development to its environment.
- gravity: so roots grow down into the soil and shoots grow up;
- water: roots grow towards moisture;
- touch: climbing plants coil around supports;
- temperature: for example, a cold period triggers germination or flowering in some species;
- chemicals, and attack by herbivores or pathogens.Why plants respondResponding helps a plant to:- maximise photosynthesis, by growing its leaves towards light;
- obtain water and mineral ions, by growing roots down into the soil;
- anchor itself and support its shoots;
- flower and set seed at the right time of year, when pollinators are active and conditions suit seed development;
- avoid being eaten, for example by producing toxic or bad-tasting chemicals such as tannins and alkaloids.How plants respondPlants have no nervous system. Instead, they detect stimuli with specialised receptor molecules, such as light-sensitive pigments, and coordinate their responses using chemicals called plant growth regulators (plant hormones). Most plant responses are changes in growth, so they are slower than animal responses, but they let a plant adjust its shape and development to its environment.