The diagram of an apparatus given below demonstrates a particular process in plants. Study the same and answer the questions that follow: The diagram of an apparatus given below demonstrates a particular process in plants. Study the same and answer the questions that follow:
State two limitations of using this apparatus.
Topic: Limitations of the potometer
Answer
- It is difficult to INTRODUCE THE AIR BUBBLE and to keep the apparatus airtight; an air bubble entering the xylem would block the water column altogether.
- The CUT TWIG may not remain fully alive for long, and a cut shoot is not a whole plant — its natural root system has been removed.
(Also acceptable: it measures water UPTAKE, not transpiration, and the two are not identical.)
Two limitations, one mark.
THE FUNDAMENTAL ONE, worth giving if you can only give one: a potometer measures ABSORPTION and we use it as a substitute for TRANSPIRATION. The two are close but NOT equal, because a small fraction of the water taken up is used in photosynthesis and retained in the tissues rather than transpired.
Questions on apparatus usually reward the candidate who knows what the instrument ACTUALLY measures as opposed to what it is used for.
Other limitations: the shoot may die during a long experiment, and it is difficult to reset the bubble accurately for repeat readings.