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:
What is the importance of the air bubble in the experiment?
Topic: Importance of the air bubble
Answer
The MOVEMENT OF THE AIR BUBBLE along the graduated capillary tube gives the VOLUME OF WATER TAKEN UP by the shoot in a given time — and so measures the rate of transpiration.
The air bubble is the MARKER that makes the water movement visible. Water is transparent and its flow could not otherwise be seen or measured; the bubble travels with it along a graduated scale, so the distance moved in a known time gives the rate.
THE HABIT TO FORM in every experimental question: ask what each part of the apparatus is FOR. Examiners award marks for understanding the design, not merely the result.
Compare the other transpiration experiments in these papers, where the same problem is solved differently: OIL on the water surface and a WEIGHING MACHINE in 2018, a sealed RUBBER SHEET and a BELL JAR in 2019, MERCURY rising in a glass tube in 2020. Each makes an invisible process measurable.