Final answer:
Cryoprotectants help in cryopreservation by preventing osmotic stress during freezing, not to decrease blood pH or avoid exchange of materials as stated in option d.
Step-by-step explanation:
Cryoprotectants are substances used in cryopreservation and freezing-point depression to protect biological material from freezing damage. The main application of cryoprotectants is to preserve cells, tissues, and organs at very low temperatures. They work by inhibiting ice crystal formation and maintaining a proper osmotic balance, which is crucial for cell survival during the freezing process. Cryoprotectants, such as glycerol and dimethyl sulfoxide (DMSO), prevent osmotic imbalances by ensuring that the osmotic pressure inside and outside of cells remains equal. This environment helps maintain cell integrity by preventing the cell from shrinking or bursting due to external or internal pressure imbalances.
Conversely, isotonic solutions help avoid osmotic imbalances by maintaining a constant osmotic pressure that matches the cells' natural environment. These solutions are not used to minimize osmotic imbalances but rather to maintain the existing balance to avoid the exchange of materials between the blood and its surroundings. Therefore, the use of cryoprotectants, contrary to option d, does not decrease the pH of the blood nor avoid the exchange of materials; instead, their primary function is to prevent osmotic stress during the freezing process.