Connect starch storage and cellulose walls to glucose
Distinguish two uses of photosynthetic carbohydrate.
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 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 smaller molecule builds both named carbohydrates?
What you will learn
- Distinguish two uses of photosynthetic carbohydrate.
- Use the stated evidence to explain the method and its limits.
Store an energy source
Plants can convert photosynthetic glucose into starch for storage. Starch provides an energy store because its building blocks can later be made available for respiration. Describing starch as an energy store does not mean starch itself performs respiration.
Starch is insoluble, so storage does not add the same concentration of dissolved particles as leaving all the glucose dissolved. This supports storage without treating starch as a transport sugar in the phloem.
Build a different large carbohydrate
Glucose can also be used to make cellulose for cell walls. Cellulose has a structural role: it helps walls support cells and resist excessive expansion. Starch and cellulose have different arrangements of glucose building blocks and different functions.
A photosynthesising leaf can direct carbohydrate into several uses. Finding cellulose in a wall does not show that the wall is a starch store, and finding starch does not mean all the carbohydrate remains unused forever.
Sources for this lesson
Pause and explain
Which use fits cellulose?
Worked example
A plant allocates some new glucose to a tuber store and some to new cell walls. Name the large carbohydrates involved.
Show the worked solution
- Identify storage as starch.
- Identify the wall material as cellulose.
- Keep function separate from shared glucose building blocks.
Answer Starch provides the energy store; cellulose builds the cell walls.
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.
Name the photosynthetic-carbohydrate form used as an energy store.
Give me a hint
Think of the iodine starch test.
Compare my reasoning
- Identify starch.
- State its storage role.
Starch is used as an energy store.
Look for these in your work
- Name starch.
- State energy storage.
Explain why glucose can support both storage and the building of new cell walls.
Give me a hint
The plant can convert glucose into different large molecules.
Compare my reasoning
- Glucose can build starch.
- Glucose can also build cellulose.
- Different structures give different roles.
Glucose building blocks can form starch for storage or cellulose for cell walls.
Look for these in your work
- Include both molecules and functions.
- Avoid treating them as identical.
A student finds starch in a leaf and concludes that the leaf makes no cellulose. Evaluate the conclusion.
Give me a hint
Detection of one substance does not exclude another.
Compare my reasoning
- The starch test detects starch.
- The leaf can use glucose in more than one pathway.
- Cell walls can contain cellulose at the same time.
The conclusion is unsupported; starch storage and cellulose wall construction can coexist.
Look for these in your work
- Limit the inference to the starch test.
- Name the other possible use.
Common mistakes
- Do not exchange the roles of starch and cellulose.
- Phloem transport is associated with sucrose, not starch granules.
What can you explain now?
Which use fits cellulose?
Compare with the explanation
Building cell walls.
Its role here is structural.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain how one glucose source can support storage and structural growth.
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.