Questions & Answers

A cell will swell up if _________
A. The concentration of water molecules in the cell is higher than the concentration of water molecules in the surrounding medium.
B. The concentration of water molecules in the surrounding medium is higher than water molecules concentration in the cell.
C. The concentration of water molecules is the same in the cell and in the surrounding medium.
D. Concentration of water molecules does not matter.

Answer
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Hint: Water molecules always tend to move from a region of higher concentration to lower concentration. 

Complete answer:
If we keep the cell in a solution where the surrounding concentration of water is more than that of the cell inside the water will move from higher concentration to the lower concentration that is from outside to inside so the cell will absorb the water. Hence, the imbibition of the cell and the cell swells up. 
This is only possible when the solution is hypertonic inside the cell and hypotonic outside the cell, that is the solute is in higher concentration inside the cell and lower outside the cell. When the particular concentration of water molecules present in the surrounding medium is higher than the present water molecule concentration within its cell, the cell tends to swell up. This swelling is due to the  higher concentration of water outside the cell and when it tends to get inside the result is swelling of that particular cell.
Hypotonic solutions help diabetic patients by rehydrating the cell when the patient goes through ketoacidosis in which the intracellular space gets dehydrated so we introduce a hypotonic solution to them. 
When we place animal cell in hypotonic solution that is cell without having cell wall so the cell could get enough uptake of water which may result in the rupture of the cell but if the plant cell are kept instead they will resist bursting due to the presence of cell wall and shows turgor pressure phenomena. 

Hence the correct answer is option (B).

Note: So when the osmotic pressure forces the water to diffuse into the cell the cell gets turgid and seems to be bloated.
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