Question

Fig. represents aprocess in plants. The set up was placed in bright sunlight. Answer the following questions:

1. 1. Name the physiological process depicted in the figure.
   2. Why was oil added to the water?
2. When placed in bright sunlight for four hours, what do you observe with regard to the initial and final weight of the plant? Give a suitable reason for your answer.
3. What happens to the level of water when this setup is placed in:
   1. Humid conditions?
   2. Windy conditions?
4. Mention any three adaptations found in plants to overcome the process mentioned in (a).
5. Explain the term ‘Guttation’.

Answer 1

1. 1. Transpiration
   2. Oil was added to the water to prevent its evaporative loss.
2. Upon exposure to bright sunlight for four hours, the final weight will be less than the initial weight because some water will be lost from the aerial parts of the plant by transpiration.
3. 1. When this setup is placed in humid conditions, there is no change in the level of water.
   2. When this setup is placed in humid conditions, the level of water drops.

4. The three adaptations found in plants to overcome transpiration are:

   • Sunken stomata: The stomata may be sunken or covered by hairs (eg. Nerium)
   • Narrow leaves: The leaves may become narrower to reduce surface area.
   • Fewer stomata: The number of stomata may be reduced.
5. Plants growing in a moist, warm soil and under humid conditions possess specialised structures called hydathodes on tips and margins of leaves. Water escapes in liquid form at night and accumulates in drops at the hydathodes. This process is known as guttation. 
   Guttation usually occurs at night when transpiration has stopped, and the rate of absorption is high. Under these conditions, root pressure is highest, forcing water upward through the xylem elements and eventually exuding as drops from hydathodes near the leaf margins.
   Guttation can also occur during daytime if plants are situated in damp and warm soils or in humid conditions, hence increasing root pressure.
   Guttation is commonly observed around the tips and margins of leaves in grasses, wheat, rye, barley, nasturtium, Colocasia, and tomato during the early morning following a humid and warm night.