Use the yeast anaerobic word equation
Identify alcohol and carbon dioxide as products.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
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
Which cells are specified here?
What you will learn
- Name the yeast products
- Apply the equation to observations
Use the yeast anaerobic word equation
| Feature | Meaning |
|---|---|
| Reactant | Glucose |
| Product one | Alcohol (ethanol) |
| Product two | Carbon dioxide |
| Oxygen | Not a reactant in this pathway |
Name the yeast products
The yeast anaerobic word equation is glucose → alcohol + carbon dioxide. In this example the alcohol is ethanol. The school-level equation omits oxygen from the reactants because oxygen is not used by this pathway. Energy is released, although much less per glucose molecule than in aerobic respiration.
Alcohol and carbon dioxide are different products with different possible observations. Gas bubbles are consistent with gas formation but do not identify the gas by sight. A supplied positive carbon-dioxide test supports gas identity; it does not directly measure the amount of dissolved ethanol or establish the whole oxygen history of a culture.
Apply the equation to observations
Yeast can also use aerobic respiration when conditions allow it. Therefore carbon-dioxide production alone does not prove that every cell was using only the anaerobic pathway. When applying this word equation, use the stated anaerobic conditions or a described controlled investigation, rather than merely assuming anaerobic because bubbles are present.
Keep the reaction separate from muscle anaerobic respiration: muscles have a different specified product model. Write glucose as the reactant and alcohol plus carbon dioxide as the yeast products. Do not add lactic acid from the muscle equation, water from the aerobic equation or oxygen as a required reactant to this particular yeast word equation.
Sources for this lesson
Pause and explain
Which word equation describes the specified yeast pathway?
Worked example
A question specifies anaerobic yeast breakdown of glucose. Name the products.
Show the worked solution
- Use the yeast example, not the muscle example.
- The products are alcohol, specifically ethanol, and carbon dioxide.
Answer Alcohol (ethanol) and carbon dioxide.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
Write the anaerobic yeast word equation.
Give me a hint
Name the glucose reactant and both products.
Compare my reasoning
- Start with glucose.
- Add alcohol and carbon dioxide after the arrow.
Glucose → alcohol + carbon dioxide; the alcohol is ethanol in this model.
Look for these in your work
- Name both products
- Keep oxygen off the reactant side
Can observing CO₂ bubbles alone establish the amount of alcohol formed in a live yeast sample?
Give me a hint
The observation is not a direct alcohol measurement.
Compare my reasoning
- Gas observation concerns carbon dioxide.
- Conditions and a separate or justified proportional measurement are needed for an alcohol amount.
No. CO₂ bubbles alone do not directly measure alcohol amount or prove the culture used only the anaerobic pathway.
Look for these in your work
- Limit the inference
- Separate gas and alcohol measurements
Correct: anaerobic yeast produces lactic acid and needs oxygen as a reactant.
Give me a hint
Use the correct organism-specific equation.
Compare my reasoning
- Yeast forms alcohol and carbon dioxide in this model.
- The pathway does not use oxygen.
Anaerobic yeast forms alcohol (ethanol) and carbon dioxide from glucose without oxygen as a reactant.
Look for these in your work
- Correct the products
- Correct oxygen use
Common mistakes
- Calling every bubble proof of anaerobic conditions.
- Combining yeast and muscle product lists.
What can you explain now?
Which word equation describes the specified yeast pathway?
Compare with the explanation
Glucose → alcohol + carbon dioxide
The alcohol is ethanol here.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Write the yeast equation and qualify a gas-only inference.
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.