Question

In crops that grow upto a height of about 1 meter, component of water potential that become non-significant for cell growth after cell division is
(A). Solute potential
(B). Pressure potential
(C). Matric potential
(D). Gravitational potential
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (C) and (D) only.
• C. (A), (B) and (C) only.
• D. (B), (C) and (D) only.

Hint:

To remember: Gravitational potential is only significant for tall trees (like conifers and eucalyptus) where heights exceed 10 meters, while matric potential is only significant in dry seeds or extremely dry soils.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Total soil/plant water potential ($\Psi_w$) is the sum of several components:
\[ \Psi_w = \psi_s + \psi_p + \psi_g + \psi_m \] where $\psi_s$ is solute potential, $\psi_p$ is pressure (turgor) potential, $\psi_g$ is gravitational potential, and $\psi_m$ is matric potential.
The significance of each component depends on the plant's height, tissue hydration state, and cell growth phase.

Step 2: Detailed Explanation:
- Solute Potential ($\psi_s$) and Pressure Potential ($\psi_p$): These are the primary driving forces behind cell growth and elongation.
Following cell division, cells expand when water enters the vacuole due to a highly negative solute potential.
This generates a high internal turgor pressure (positive pressure potential) that physically stretches the cell wall.
Thus, $\psi_s$ and $\psi_p$ remain highly significant for cell expansion.
- Gravitational Potential ($\psi_g$): Gravity causes water to move downward unless balanced by an opposing force.
The gravitational head changes by only $0.1 \text{ MPa}$ for every 10 meters of plant height.
For a crop that is only 1 meter tall, the gravitational potential is around $0.01 \text{ MPa}$, which is negligible compared to the large values of solute and turgor potential.
- Matric Potential ($\psi_m$): This is the force with which water is adsorbed onto cell walls and cytoplasmic colloids.
In fully hydrated, growing cells, matric potential is negligible because the vacuoles are filled with liquid water, and matric forces are restricted to the cell walls.
Therefore, both matric potential ($\psi_m$) and gravitational potential ($\psi_g$) are non-significant for cell growth in short crops.

Step 3: Final Answer:
The water potential components that become non-significant are matric potential (C) and gravitational potential (D).