At what temperature is viable pollen grain germplasm cryopreserved in liquid nitrogen in pollen banks for long-term agricultural crop breeding programs?
Answer and explanation
Correct answer: C. -196°C
- Step 1: Cryopreservation is an ex-situ conservation technique where biological tissues (pollen, embryos, gametes) are stored at ultra-low temperatures.
- Step 2: Storage is carried out in liquid nitrogen at its boiling point of (77 Kelvin).
- Step 3: At this temperature, all intracellular biochemical reactions and enzymatic decay are suspended, preserving pollen viability intact for decades.
Answer
-196°C
Why not the others: '-20°C' is the temperature of standard commercial domestic freezers used for short-term food storage; '-80°C' is standard ultra-low mechanical freezer temperature used for laboratory reagents; '0°C' is the freezing point of water and does not arrest metabolic aging in pollen.
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