Biology
What are tropic movements? Briefly explain various types of tropic movements in plants.
Answer
Growth movements occurring in response to unidirectional external stimuli in a plant part are known as tropic movement or tropism.
Different types of tropic movements in plants are:
- Phototropism — Movement of plant parts towards or away from light is termed phototropism. The plants grown in light illuminating them from all directions grow more or less upwards. Shoots of most plants grow towards the source of light, it is termed positive phototropism. Roots grow away from light and hence are negatively phototropic.
- Geotropism — Movement of plant organs in response to gravity is termed geotropism. Roots are positively geotropic because they grow in the direction of gravity. The shoot grows upwards, means against gravity, and hence is negatively geotropic.
- Chemotropism — Chemotropism is the phenomenon of growth of plant organs in response to chemicals. When plant organs grow away from the chemical response, it is called negative chemotropism. When plant parts grow towards the chemical response, it is called positive chemotropism. The pollen tube grows towards the sugary substance secreted by the stigma of the flower.
- Hydrotropism — Movement of plant organs in response to water is termed hydrotropism. Roots grow towards the source of moisture and hence are positively hydrotropic.
- Thigmotropism — The growth movement of plant parts in response to touch stimulus is called thigmotropism. Plants such as sweet peas and vines have tendrils which coil around other plants in response to one sided contact or touch. Stimulus is perceived by tendril tips and then it is transmitted to basal parts. Weak-stemmed plants use twining stems and tendrils to climb on other plants/objects which provide them support. Hence, twining stems and tendrils are positively thigmotropic.
Related Questions
The diagram given alongside shows a type of tropism. Study the same and answer the questions that follow:
(a) Name and define the type of tropism shown in the diagram.
(b) Label the guidelines (1) to (4).
(c) Name two effective stimulants that help in the growth of part (2).
(d) Name two groups of plants where part (2) grows towards gametophyte with the help of the stimulants mentioned in (c).
Study the diagrams given below and answer the following questions.
(a) Name the structures shown as X and Y in the figures (A) and (B), respectively.
(b) Write the functions performed by the structures X and Y.
(c) Name the phenomenon depicted and define it.
(d) How do the structures X and Y differ from each other?
(e) Give examples of the plants which show the said phenomenon.
Given below are the figures showing some kinds of tropic movements in plants. Study the same and answer the following questions:
(a) Which one of these figures is correct? Give reason in support of your answer.
(b) Name the kind of movements shown by the root system and the shoot system. Define each.
(c) What are the two stimuli which affect root system and shoot system positively ? Name them.
(d) Which of the following stimuli affect the growth of root strongly?
- Gravity
- Water
(e) Draw a neat and labelled diagram of the longitudinal section of a pistil showing chemotropism in an angiospermic plant.
The figure given below depicts a kind of tropic movement in plants. Study the same and answer the following questions.
(a) What kind of a movement is shown in figure. Define it.
(b) How does this movement differ from geotropism?
(c) Name the stimulus responsible for thigmotropism. Give one example of a plant showing thigmotropism.
(d) Name one stimulus which gives a positive response for the roots but negative response for the shoot.
(e) Draw a neat and labelled diagram of the part of plant showing leaf tendril. Name the plant.