Apply yeast equation amount ratios
Use the 1 : 2 : 2 ratio with appropriate measurement limits.
Section 12.3 · Anaerobic respiration
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall cell processes, enzymes and the distinction between gas exchange and breathing.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the glucose : ethanol : CO₂ coefficient ratio?
What you will learn
- Scale the specified equation
- Avoid a gas-volume shortcut
Apply yeast equation amount ratios
| Feature | Meaning |
|---|---|
| 1 glucose | 2 ethanol + 2 CO₂ |
| 5 glucose | 10 ethanol + 10 CO₂ |
| 8 glucose | 16 ethanol + 16 CO₂ |
| Volume limit | Equal amount ≠ equal liquid/gas volume |
Scale the specified equation
For the specified complete yeast reaction, the coefficients give one glucose to two ethanol and two carbon-dioxide molecules. Three glucose molecules therefore correspond to six of each product. These are proportional model counts used to practise the equation; a living sample contains far more molecules and may have other processes occurring.
The equal product molecule counts do not mean equal visible volumes of ethanol liquid and carbon-dioxide gas. Substances in different phases have different volume relationships, and collected gas can be affected by temperature, pressure and dissolution. Do not read a liquid-to-gas volume equality from the chemical coefficients.
Avoid a gas-volume shortcut
A gas measurement can be linked to a chemical amount only through an appropriate measurement model and stated conditions. Bubbles alone are not counted molecules, and a collected volume is not directly an ethanol concentration. If a problem supplies model molecule counts, use them as given instead of importing an unsupported real-world conversion.
The ratio predicts product amounts for the specified complete reaction, but does not establish that all supplied glucose was consumed in a real culture. A conclusion about rate needs elapsed time as well, while a conclusion about exclusive anaerobic activity needs the described pathway conditions. Separate those claims before using the balanced equation.
Pause and explain
Does equal ethanol and CO₂ molecule count imply equal liquid and gas volumes?
Worked example
Five glucose molecules react completely in the model. Find both product counts.
Show the worked solution
- Multiply each coefficient two by five.
- Each product count is ten.
Answer Ten ethanol and ten CO₂ molecules.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Seven glucose molecules react completely in the yeast model. Find ethanol and CO₂.
Give me a hint
Multiply both product coefficients by seven.
Compare my reasoning
- 7 × 2 gives ethanol.
- 7 × 2 gives CO₂.
Fourteen ethanol molecules and fourteen CO₂ molecules.
Look for these in your work
- Use both coefficients
- Name both products
The model forms sixteen CO₂ molecules. Find corresponding glucose and ethanol counts.
Give me a hint
Divide CO₂ by two, then use the product ratio.
Compare my reasoning
- 16 ÷ 2 = 8 glucose.
- 8 × 2 = 16 ethanol.
Eight glucose molecules correspond to sixteen ethanol molecules.
Look for these in your work
- Reverse the ratio
- Retain the equal product count
A student expects 10 cm³ liquid ethanol from 10 cm³ collected CO₂ because both coefficients are two. Correct the inference.
Give me a hint
Chemical amount is not equal liquid and gas volume.
Compare my reasoning
- The substances occupy different phases.
- Volume depends on physical properties and collection conditions.
The coefficients give equal molecule amounts, not equal liquid and gas volumes; no 10 cm³ ethanol conclusion follows.
Look for these in your work
- Reject volume equality
- State what coefficients do establish
Common mistakes
- Equating liquid and gas volumes from coefficients.
- Treating one bubble as one molecule.
What can you explain now?
Does equal ethanol and CO₂ molecule count imply equal liquid and gas volumes?
Compare with the explanation
No; phase and measurement conditions matter
Coefficients give chemical amount ratios.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Apply 1 : 2 : 2 without converting directly between different-phase volumes.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.