Use the photosynthesis word equation
Place reactants, products and required conditions correctly.
Section B6.1 · Photosynthesis
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-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.
Before you begin
- Recall chloroplasts, enzymes and the difference between photosynthesis and respiration.
- Use the stated observations, quantities and controls; diagrams are schematic.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which substance belongs on the reactant side?
What you will learn
- Place reactants, products and required conditions correctly.
- Use the stated evidence to explain the method and its limits.
Read the arrow
The required word equation is carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. Substances before the arrow are reactants; those after it are products in this summary of carbohydrate synthesis.
Light and chlorophyll are conditions for the process and should be written above or near the arrow. They are not additional material reactants consumed in the same way as carbon dioxide and water.
Use the equation carefully
The word equation is a simplified overall account. It does not mean every glucose molecule remains free glucose in the leaf; the plant can use or convert the carbohydrate after synthesis. It also does not describe the rate or how much oxygen escapes from a respiring plant.
Do not reverse the equation and still call it photosynthesis. Carbon dioxide is taken up and oxygen is produced by the photosynthetic process; the net gas exchange of the whole plant also depends on respiration.
Sources for this lesson
Pause and explain
Where should light and chlorophyll be placed?
Worked example
Complete: ___ + water → glucose + ___, with light and chlorophyll near the arrow.
Show the worked solution
- Choose carbon dioxide as the other raw material.
- Choose oxygen as the other product.
- Keep light and chlorophyll as conditions.
Answer Carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll.
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 required photosynthesis word equation, including the two conditions.
Give me a hint
Put the raw materials first.
Compare my reasoning
- Carbon dioxide + water go before the arrow.
- Glucose + oxygen go after it.
- Include light and chlorophyll near the arrow.
Carbon dioxide + water → glucose + oxygen, with light and chlorophyll.
Look for these in your work
- Correct direction and four substances.
- Include both conditions.
Correct: glucose + oxygen → carbon dioxide + water, labelled “photosynthesis”.
Give me a hint
The raw-material and product sides have been swapped.
Compare my reasoning
- Reverse the material arrangement.
- Add the conditions light and chlorophyll.
For photosynthesis: carbon dioxide + water → glucose + oxygen, with light and chlorophyll.
Look for these in your work
- Keep photosynthesis direction.
- Do not rename the inputs as products.
A plant gives no net oxygen release in a dim-light experiment. Does that observation alone invalidate the photosynthesis word equation?
Give me a hint
Distinguish the process from net whole-plant exchange.
Compare my reasoning
- Photosynthesis may produce oxygen.
- Respiration can use oxygen.
- Net release can be zero when the two effects balance.
No; net gas exchange includes respiration and cannot alone show that photosynthetic oxygen production is absent.
Look for these in your work
- Use the net-exchange distinction.
- Avoid claiming respiration stops in light.
Common mistakes
- Do not list chlorophyll as the carbohydrate product.
- The word equation does not measure a reaction rate.
What can you explain now?
Where should light and chlorophyll be placed?
Compare with the explanation
Near the arrow as required conditions.
They support the process without being listed as the material products.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Write the equation from memory and explain each side.
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.