Step 1: Understanding the Concept:
When living animal cells, such as red blood cells (RBCs), are immersed in an external salt solution, water molecules move across the semi-permeable cell membrane via osmosis. Osmosis is the spontaneous net movement of solvent molecules from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic) until an equilibrium is established.
Step 2: Detailed Explanation:
1. Human red blood cells naturally contain an internal solute environment that has an osmotic concentration equivalent to a 0.9% (w/v) sodium chloride (NaCl) solution.
2. In this question, the blood cells are placed into a 1% (w/v) NaCl solution.
3. Comparing these concentrations, a 1% NaCl solution is more concentrated than the inside of the cell ($1%>0.9%$). This means the external environment is a hypertonic solution.
4. Due to the osmotic gradient, water molecules will exit the cell interior (where the water chemical potential is higher) and flow into the surrounding salt solution to try to dilute it.
5. As water continuously leaves the cytoplasm, the red blood cells lose their internal turgor pressure and undergo structural collapse, a process known as crenation or shrinking.
Therefore, placing the cells in a 1% NaCl solution causes them to shrink. This matches option (B).
Step 3: Final Answer:
The blood cells will shrink.