Compare concentration differences

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or browser document; an ordinary calculator is optional.
• Rule: Concentration difference equals higher millimoles per liter minus lower millimoles per liter. Formula: a-b. Variable key: a = higher concentration (mmol/L), b = lower concentration (mmol/L)
• Distinct worked inputs and result: A distinct comparison has 9 and 3 mmol/L: difference 9-3=6 mmol/L.
• Assessment case 1: Supplied case 1: higher concentration (mmol/L)=12; lower concentration (mmol/L)=4, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?
• Assessment case 2: Supplied case 2: higher concentration (mmol/L)=15; lower concentration (mmol/L)=6, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?
• Assessment case 3: Supplied case 3: higher concentration (mmol/L)=20; lower concentration (mmol/L)=8, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?
• Assessment case 4: Supplied case 4: higher concentration (mmol/L)=18; lower concentration (mmol/L)=5, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?
• Assessment case 5: Supplied case 5: higher concentration (mmol/L)=25; lower concentration (mmol/L)=10, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?
• Assessment case 6: Supplied case 6: higher concentration (mmol/L)=30; lower concentration (mmol/L)=12, using the explicitly named quantities. Concentration difference equals higher millimoles per liter minus lower millimoles per liter. What result follows?

Learn the idea

A concentration gradient is a spatial difference, not a guarantee that every particle moves one way. Net diffusion can coexist with individual random motion in both directions.

Concentration difference equals higher millimoles per liter minus lower millimoles per liter. The formula in the supplied model is a-b. Variable key: a = higher concentration (mmol/L), b = lower concentration (mmol/L). Use the same concentration unit. Net movement differs from each individual path.

A distinct comparison has 9 and 3 mmol/L: difference 9-3=6 mmol/L. Gradient direction depends on the measured substance. Track the quantity and unit before calculating. Explain the meaning of a positive, negative or fractional result when relevant. A numerical answer supports the stated model calculation; broader claims require the additional measurements and assumptions described here.

1. Name the measured quantities and their units before substituting values.
2. Write the stated rule and use the variable key to match each symbol to its explicitly named quantity.
3. Calculate each supplied case separately, keeping intermediate arithmetic and the result unit.
4. Explain the result in context and identify the assumption that would invalidate direct use of the rule.

Check your reasoning

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Take it further

Changed-input task: use the same stated model with higher concentration (mmol/L)=13; lower concentration (mmol/L)=4. Expected result: 9 mmol/L. Explain what changes and keep this assumption: Gradient direction depends on the measured substance.

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