Plant Responses

• Plants, like animals, increase their chances of survival by responding to changes in their environment. They can sense light abd grow towards it and sense gravity so shoots grow in the right direction.
• Plants are more likely to respond to herbivory - being eten by animals. Plants have chemical defenses that they can use against herbivory. For example, they can produce toxic chemicals in response to being eaten.
• Alkaloids - These are chemicals with bitter tastes, noxious smells or poisonnour characteristics that deter or kill herbivores. Such as nicotine being highly poisonous to many insects.
• Tannins - These taste bitter, and in some herbivours they can bind to proteins in the gut making them hard to digest. Both of these deter animals from eating them.
• Pheromeones are signalling chemicals that produce a response in other organisms.
• Some plants release alarm pheromones into the air in response in response to herbivore grazing. This can cause nearby plants that select these chemicals to start making chemical defenses such as tannins.
• When corn plants are being eaten by caterpillars, they can produce pheromones which attract parasitic wasps. These wasps then lay their eggs in the caterpillars, which eventually kills them.
• If a single leaflet of the plant mimosa pudica is touched, a signal spreads through the while leaf, causing it to quickly fold up. This may help knock of any small insects feeding on the plant or scare larger predators.
• Plants are more likely to survive if they respond to abiotic stress - anything harmful that's natural but non-living like a drought. Some plants respond to extreme cold by producing their own form of antifreeze.
• A tropism is the response of a plant to a directional stimulus.
• Plants respond to stimuli by regulating their growth.
• A positive tropism is a growth towards the stimulus.
• A negative tropism is a growth away from the stimulus
• Phototropism is the growth of a plant in response to light

  • Shoots are positively phototropic
  • Roots are negatively phototropic
• Geotropism is the growth of a plant in response to gravity.

  • Shoots are negatively geotropic
  • Roots are positively geotropic
• Hydrotropism - Plant growth in response to water. Roots are positively hydrotropic.
• Thermotropism - Plant growth in response to temperature.
• Thigmotropism - Plant growth in response to contact with an object.
• Plants respond to some stimuli using growth hormones - chemicals that speed up or slow down plant growth.
• Growth hormones are produced in the growing regions of the plant and they move where they're needed in the other parts of the plant.
• A growth hormones called gibberellin stimulates seed germination, stem elongation, side shoot formation and flowering.