# 5.7: Questions

## Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

1. Crystallization is usually fatal to cells because:

 Yes No a Crystals can puncture cell walls Yes No b The formation of crystals changes the ionic ratios in the cytosol Yes No c Crystallization speeds up the cell reactions Yes No d Ice formation causes water to be drawn into the cell by osmosis causing the cell to swell and burst Yes No e Nucleation of the crystals requires large amounts of energy

a. Yes

b. Yes

C. No

D.Yes

e. No

2. Ice formation in cells can be limited by:
 Yes No a The presence of antifreeze proteins Yes No b The dispersion of water in the cellular structure, which limits heterogeneous nucleation Yes No c The formation of starch from sugar Yes No d The introduction of Ice Nucleating Agents (INAs) into the cells Yes No e The freezing of extracellular water

a. Yes

b. Yes

C. No

D.No

e. Yes

3. Crystallization of minerals in the cells can be limited by:

 Yes No a The presence of anti-freeze proteins Yes No b The hydrolysis of starch to sugar Yes No c The preferential formation of a glass Yes No d The increased activity of the Golgi Apparatus

a. No

b. Yes

C. Yes

D.No

In some alpine plants, extracellular ice formation occurs at around –2°C. What is the critical radius for ice nucleation at this temperature?

In these plants, the extracellular ice forms on ice nucleating agents. If an ice nucleating agent is a circular disc and is a perfect template for ice, what size must it be for nucleation to occur at –2°C?

(For the ice-water interface, the interfacial energy γ = 0.028 J m-2; the latent heat of freezing of ice is ΔHv = -3.34 x 108 J m-3.)

hint: The critical radius for nucleation is r*, where r* = -2γ /ΔGv, and γ is the solid-liquid interfacial energy and ΔGv is the free energy of freezing per unit volume. For further details see the section on nucleation and crystallization.

$r^{*}=-\frac{2 \gamma}{\Delta G_{v}}=-\frac{2 \gamma}{\Delta S_{v} \Delta T}=-\frac{2 \gamma T_{m}}{\Delta H_{v} \Delta T}$