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Cell BiologyWorked Example

Worked Example: Percentage Change in Mass (Osmosis Practical)

Part of Cell Transport · GCSE GCSE Biology revision

This worked example covers Worked Example: Percentage Change in Mass (Osmosis Practical) within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 14 of 19 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.

Topic position

Section 14 of 19

Practice

23 questions

Recall

20 flashcards

🧮 Worked Example: Percentage Change in Mass (Osmosis Practical)

In the required osmosis practical, you cut potato chips, weigh them, put them in different salt solutions, then weigh them again. You calculate the percentage change in mass to compare results fairly (since chips may not all start at the same mass).

Formula

Percentage change in mass = (Final mass − Initial mass) ÷ Initial mass × 100

Worked Example

Given: A potato chip has an initial mass of 2.5 g. After being placed in distilled water for 24 hours, its final mass is 2.8 g.

  1. Change in mass = 2.8 − 2.5 = +0.3 g
  2. Percentage change = 0.3 ÷ 2.5 × 100 = +12%
  3. The positive sign shows the chip gained mass — water entered by osmosis (distilled water is hypotonic relative to the potato cells).

A Second Example (Mass Lost)

Given: A potato chip has an initial mass of 3.0 g. After 24 hours in 1.0% salt solution, its final mass is 2.7 g.

  1. Change in mass = 2.7 − 3.0 = −0.3 g
  2. Percentage change = −0.3 ÷ 3.0 × 100 = −10%
  3. The negative sign shows the chip lost mass — water left the cells by osmosis (salt solution is hypertonic relative to the potato cells).

Why Use Percentage Change, Not Just Change?

If one chip started at 2.0 g and another started at 4.0 g, a raw change of 0.3 g means very different things for each. Percentage change standardises the result, allowing fair comparison between chips of different starting masses.

Quick Check: A potato chip has an initial mass of 4.0 g. After 24 hours in 0.8% salt solution its final mass is 3.6 g. Calculate the percentage change in mass and explain what happened to the potato cells.

Keep building this topic

Read this section alongside the surrounding pages in Cell Transport. That gives you the full topic sequence instead of a single isolated revision point.

Surface Area to Volume RatioCommon Misconceptions About Cell TransportThe Cell's Transport SystemCell Transport — Tap to Explore the 3 Mechanisms

Practice Questions for Cell Transport

Which statement best describes diffusion?

  • A. The movement of particles from a region of low concentration to high concentration
  • B. The net movement of particles from a region of high concentration to low concentration
  • C. The movement of water molecules through a partially permeable membrane
  • D. The movement of particles using energy from respiration
1 markfoundation

Explain how osmosis causes a plant cell to become plasmolysed when placed in a concentrated sugar solution.

3 marksstandard

Quick Recall Flashcards

Define diffusion
The movement of particles from an area of high concentration to an area of low concentration down a concentration gradient. No energy is required (passive process).
Define osmosis
The movement of water molecules from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration) through a semi-permeable membrane.

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Surface Area to Volume Ratio

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Common Misconceptions About Cell Transport