OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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How do you calculate the percentage change in the length of cells placed in a sucrose concentration?

(Final length - initial length) / initial length x 100
(Initial length - final length) / initial length x 100
(Final length + initial length) / initial length x 100
(Final length - initial length) x initial length x 100

The correct answer is: (Final length - initial length) / initial length x 100

To calculate the percentage change in the length of cells that have been placed in a sucrose concentration, the correct formula involves determining how much the length of the cells has changed relative to their original (initial) length. The formula (Final length - Initial length) / Initial length x 100 effectively measures the change by subtracting the initial length from the final length, which gives the absolute change in length. This figure is then divided by the initial length to express that change as a fraction of the original measurement. Multiplying by 100 converts the result into a percentage, allowing for a standard way to communicate the extent of the change relative to the starting value. Other options present alternative calculations. However, they either do not correctly represent the concept of percentage change, involve incorrect arithmetic operations, or misplace the final and initial values in such a way that they do not provide an accurate measure of change relative to the initial value.