Beans increase or decrease the turgidity of PULVINI cells to change the orientat

Question

Beans increase or decrease the turgidity of PULVINI cells to change the orientation of
leaves. In order to raise the leaf blades to a horizontal position (as in the right side of the
picture) pulvini cells at the junction between petiole and blade import sugar and
potassium ions to increase their ?p from .45 Mpa to .95 Mpa. The pulvini cells are at
equilibrium both before (leaf held more vertically) and after (leaf held horizontally)
moving with an interstitial fluid that is not under pressure and has an unchanging osmotic
potential of -1.3 Mpa. [Please SHOW YOUR WORK]
What is the osmotic potential of the pulvini cell when the leaf blade is horizontal?

Explanation / Answer

Osmotic potential is similar to the osmotic pressure but opposite in charge.

The osmotic pressure deals with the pressure applied on the object. In the given leaf the osmotic pressure is exerted by the potassium ions. The pressure is increased from the 0.45 Mpa to 0.95 Mpa.

So, the total pressure exerted is 0.45 + 0.95 = 1.30 pa

Osmotic pressure is 1.3 Mpa, the osmotic potential will be -1.3 Mpa.

The osmotic potential when the leaf is horizontal, is the difference in the pressure applied.

Therefore, 0.95 - 0.45 = 0.50 Mpa

Osmotic potential is -0.5 Mpa

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