If a radio labelled carbon $C^{14}$ in is supplied to patato plants while it's carrying out photosynthesis in the presence of light, the $\mathrm{C}^{14} \mathrm{O}_2$ will be fixed and form radioactive products of photosynthesis, i.e., glucose $\mathrm{C}_6^{14} \mathrm{H}_{12} \mathrm{O}_6$.
This radioacative glucose is converted to sucrose which would again be radioactive due to transfer of $C^{14}$ from previous sugar molecule. These sucrose molecules then move into pholem and transported to other parts of plant.
Autoradiography technique detects the radioactive carbon (present in sugars) and traces the components and movement in the plant, i.e., through sieve tube channels of phloem from leaves (sources) to different parts (sink).
Attraction of water molecules to polar surfaces describes the adhesive properties of water. Besides, the cohesive properties include the attraction between water molecules. These two cohesive and adhesive properties contributes and help in the upward movement of water by providing.
| (i) High tensile strength | Capability to resist a pulling force, i.e., gravitational force. |
|---|---|
| (ii) High capilarity | Ability to rise in thin tubes or columns, i.e., of tracheids and vessels. |
The intermolecular hydrogen bonding in water ensures that more water molecules are attraction to each other in liquid state than in the gaseous state. This contributes to surface tension which in turn accounts for high capillarity in the xylem column.
Comment on the experimental setup.
(a) What does the setup demonstrate?
(b) What will happen to the level of water if a blower is placed close to setup?
(c) Will the mercury level fluctuate (go up/down) if phenyl mercuric acetate is sprayed on leaves?
(a) Transpirational pull is demonstrated by this set up.
(b) Constant air blowing will increase the rate of transpiration so, level of water will go down.
(c) The mercury level will go down, if phenyl mercuric acetate is sprayed on leaves.