Percentage gain and loss of massSpec 1.17
In short
Percentage change in mass lets you compare potato cylinders that started with different masses. It is calculated as (final mass − initial mass) ÷ initial mass × 100. A positive answer is a percentage gain and a negative answer is a percentage loss. For example, a cylinder that goes from 3.00 g to 2.55 g has a change of −15%.
Different cylinders may start with slightly different masses, so you compare them using the percentage change in mass.
A positive answer is a percentage gain. A negative answer is a percentage loss.
Percentage change in mass
A potato cylinder has a mass of 3.00 g. After 30 minutes in a salt solution its mass is 2.55 g. Calculate the percentage change in mass.
- change in mass = 2.55 − 3.00 = −0.45 g
- −0.45 ÷ 3.00 = −0.15
- −0.15 × 100 = −15%
Answer: −15% (a loss of 15%)
Divide by the initial mass, not the final mass. Keep the minus sign if the mass decreased.
Quick check
Define diffusion.
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The net movement of particles from a region of higher concentration to a region of lower concentration.
Define osmosis.
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The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
What does active transport need that diffusion does not?
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Energy from respiration.
A potato cylinder gains mass in a solution. What does this tell you about the solution?
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It is more dilute than the cell contents.
Write the equation for percentage change in mass.
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(final mass − initial mass) ÷ initial mass × 100.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026