Given below is an experimental setup to demonstrate a particular tropic movement in germinating seeds (seeds fixed to a perforated trough of moist sawdust). Study the diagram and answer the questions that follow: Given below is an experimental setup to demonstrate a particular tropic movement in germinating seeds (seeds fixed to a perforated trough of moist sawdust). Study the diagram and answer the questions that follow:
What is meant by ‘Positive’ and ‘Negative’ tropic movements in plants?
Topic: Positive and negative tropism
Answer
A POSITIVE tropic movement is growth TOWARDS the stimulus. A NEGATIVE tropic movement is growth AWAY FROM the stimulus.
The definition is simple, so secure the mark with an EXAMPLE of each — and the best example is the same organ responding oppositely to two stimuli.
THE POINT WORTH MAKING: the SAME plant shows both, and even the same stimulus produces opposite responses in different organs. Gravity draws the root down (positive) and drives the shoot up (negative).
That is why "positive" and "negative" are not judgements about good or bad but simply statements of DIRECTION relative to the stimulus.
Example: a shoot is POSITIVELY phototropic (grows towards light) and NEGATIVELY geotropic (grows away from gravity); a root is the reverse of both.