Back to choose another topic Tropisms, nasties, taxes and other responses to the environment. If the movement is towards the stimulus , then it is said to be positive tropism, but if the movement is away from the stimulus , then it is said to be a negative tropism. Small algae such as Euglena and Chlamydomonas can exhibit movements of the whole organism and such movements are called taxes . Plants can also respond to environmental stimuli without moving, as is the case with the photo periodic response, flowering and vernalisation . A plant hormone is a chemical which is made by one part of the plant , but then travels to another part where it has some effect .
Auxins affect plant growth .
Auxin is made by the growing tips , or meristem, of shoots and roots . The stimulus for its production in the shoot is uneven light distribution . In the root , slight variation in the force of gravity and also light seem to be the stimuli . The auxin diffuses to the area of elongation just behind the tip . Here newly formed cells are developing their vacuoles and becoming bigger .