what will happen to a red blood cell place in a solution of 99.3% water and 0.7% salt?
The water would flow down its concentration gradient into the cell from a area of high concentration of solute (outside the cell) to low concentration of solute (inside the cell) which, if equilibrium is not met soon, will burst the cell
When a red blood cell is placed in a solution, it can undergo a process called osmosis. Osmosis is the movement of water across a semi-permeable membrane, from an area of lower solute concentration to an area of higher solute concentration. In this case, the solution has a concentration of 0.7% salt, while the red blood cell contains a lower concentration of solutes.
Since water can pass through the red blood cell membrane, it will move from the region of higher concentration (inside the red blood cell) to the region of lower concentration (the external solution with salt). As a result, water will leave the red blood cell, causing it to shrink and potentially become distorted in shape. This process is known as crenation.
The extent of crenation depends on the concentration of the external solution. In this case, the relatively low concentration of salt (0.7%) suggests that the red blood cell will likely undergo some level of crenation, but it may not be severe.
It's important to note that red blood cells are normally found in a physiological saline solution, which has a salt concentration that is closer to 0.9%. So, the external solution described in the question (0.7% salt) is slightly less concentrated than the natural environment for red blood cells.