In an isotonic solution, the concentration of solutes is equal inside and outside the cell, which means there is no net movement of water across the plasma membrane.
If no energy is used (i.e., there is no active transport), molecules will move across the plasma membrane based on their concentration gradients through passive transport. In this case:
- Water (H₂O): Because we are in an isotonic environment, the water molecules will not have a net movement into or out of the cell.
- Carbon dioxide (CO₂): If there is a higher concentration of CO₂ inside the cell compared to the outside, CO₂ will move out of the cell. Conversely, if CO₂ is at a higher concentration outside, it will move into the cell.
- Oxygen (O₂): Similarly, if there is a higher concentration of O2 inside, it will leave the cell, and if it is higher outside, O₂ will move into the cell.
Based on the options provided, the most accurate statement would depend on the existing concentrations of CO₂ and O₂, but in an isotonic situation specifically regarding water:
- Some H₂O will not enter the cell nor leave it (because of isotonic conditions).
- The same logic applies to the case of gases (O₂ and CO₂), which can freely diffuse depending on their gradients.
If you need to choose from the given options regarding the net movement, "Some CO₂ will leave the cell" or "Some O₂ will enter the cell" might be correct depending on the respective concentrations. However, without specific concentrations of gases provided, a general response regarding water would be that there would be no net movement of water.
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