Based on the trends shown in the data, explain why some rectangular cells include folds or projections in their plasma membranes .

The folds or projections in the plasma membrane works to increase the surface area of the membrane by many-fold. As can be seen by the increase in certain values, there is a greater surface-area-to -volume-ratio which is indicative of the advantage that cellular processes take place more efficiently this way. Hence, it's favorable for the cells to have folds in its membrane, for instance the villi in the small intestine are finger-like projections that helps in efficient absorption of food into the bloodstream.

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