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The blood cells likely placed in a "hypotonic solution".
<u>Option: A</u>
<u>Explanation:</u>
When human blood cells are immersed in a solution with a low concentration of solute than is present in cells, osmosis allows water to pass through the cells, allowing the cells to get swollen; such a fluid is hypotonic to the cells. But when held in a solution with a greater concentration of solute, osmosis allows water to pass out of the cell, the cell is smaller and crenated in form; then a solution is hypertonic to the cells.
Healthcare facilities preserve human blood cells in a plasma solution that has the proper salt and protein ratios. Such solution is formulated to be mildly hypertonic to the red cells, thus maintaining the integrity of the cells and avoiding hemolysis.
Because these smaller cells can access and pass through the membranes of the other cell membranes and permeable coverings easily and voluntarily unlike larger cells. It is also for efficient for these smaller and miniscule cells to penetrate and travel, delivering and transporting goods and materials such as nutrients, oxygen and waste throughout the body without consuming enough energy and conserving lesser space.
For simple reasons, they are faster, more efficient and consumes little space, and most especially depletes lesser energy.
Trait is an obvious, observable, and measurable trait; it is the expression of genes in an observable way. An example of a phenotypic trait is a specific hair color
Respiratory system and Circulatory system :P