Question

1. Describe what will occur in each of the following situations, include what the cell will look like, and state which way the water moves (into cell, out of cell, both in and out, or neither):
   1. An animal cell is placed in a solution that is 10 times more concentrated than an isotonic solution (is this solution hypotonic, isotonic, or hypertonic compared to inside the cell?).
   2. An animal cell is placed in a solution that is 10 times more dilute than an isotonic solution (is this solution hypotonic, isotonic, or hypertonic compared to inside the cell?).
   3. A plant cell is placed in a solution that is 10 times more concentrated than an isotonic solution (is this solution hypotonic, isotonic, or hypertonic compared to inside the cell?).
   4. A plant cell is placed in a solution that is 10 times more dilute than an isotonic solution (is this solution hypotonic, isotonic, or hypertonic compared to inside the cell?).
2. Do calcium ions (Ca²⁺) move across a cell membrane by simple diffusion? Why or why not? Is ATP required to move calcium ions across a cell membrane by diffusion? Why or why not?

Answer 1

Answer a: Here net inflow of water will takes place as the cell is in hypotonic condition

Explanation: If cell is placed in a concentrated solution it means the number of solute is more then the number of solvent molecule. So by the mechanism of osmosis we know that the solvent molecules always tends to move from its higher concentration towards its lower concentration through semipermeable membrane. So as here the solute concentration is high insde the cell so finally water molecule will move inside the cell from outside resulting in the cell expension and sometime busting of cell due to high water pressure inside the cell.

Answer b: Here net outflow of water molecule will takes place as the cell is in hypertonic condition.

Explanation: By the above explanation of osmosis the water molecule will move from its higher to its lower concentration area so according to the question as the concentration of solute is more outside then inside the cell (hypertonc condition) so the water molecule will move out of cell for maintaining the balance in the concentration. Due to this outflow of water cell will shrink or will going to reduce in size.

Answer c: Same answer and explanation as described in answer a

Answer d: Same answer and explanation as described in answer b

No calcium ions can not diffuse across the membrane by simple diffusion process because diffusion is the process of passive transport mechanism ( no need of ATP). For the diffusion of ions across the membrane there should be requirement of some channel proteins so it is a type of active transport mechanism. Yes ATP is needed for the process as it is active transport mechanism. By the definition of diffusion we know that during the process of diffusion the movement of partical takes place from its higher concentration towards its lower concentration. This process do not require utilization of energy. As here calcium ion transported on the base of cell requirement which is against the concentration gradient so it will need the expenditure of energy so we can say that it is active transport mechanism.