Distinguish xylem and phloem in leaf vascular bundles
Link water supply, support and sugar transport with 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 raw material does xylem supply to photosynthetic leaf tissue?
What you will learn
- Link water supply, support and sugar transport with photosynthesis.
- Use the stated evidence to explain the method and its limits.
Supply and support
A vascular bundle or vein contains xylem and phloem. Xylem supplies water and mineral ions and also supports the plant. Water is a photosynthetic raw material, while minerals include nitrate and magnesium with their stated biosynthetic roles.
In the supplied typical cross-section, xylem is shown toward the upper side of the bundle and phloem toward the lower side. Use the actual specimen and source key for image identification: position and cell arrangement matter, and an ambiguous coloured patch alone does not establish a tissue identity.
Transport carbohydrate away
Phloem carries sucrose and other organic nutrients between sources and destinations. In this leaf model it can distribute products of photosynthesis to growing or storage tissues; it is not the main water-supply route replacing xylem.
A vein is not a pore for unrestricted air entry. Distinguish the cellular transport bundle from intercellular air spaces and stomata. The transport functions support synthesis and allocation, while detailed vessel structure and translocation are developed in the later plant-transport sequence.
Sources for this lesson
Pause and explain
Which tissue distributes sucrose from photosynthesising tissue?
Worked example
Assign the two supplied roles: water and minerals arriving at a leaf, and sucrose moving to a growing root.
Show the worked solution
- Water and mineral supply: xylem.
- Sucrose transport: phloem.
- Both tissues are in the vascular bundle.
Answer Xylem supplies water and minerals; phloem transports sucrose to other tissues.
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 two transport tissues in a leaf vascular bundle.
Give me a hint
Use the water/mineral and organic-nutrient tissues.
Compare my reasoning
- Identify xylem.
- Identify phloem.
Xylem and phloem.
Look for these in your work
- Both names.
- Do not substitute mesophyll layers.
Explain one way each tissue supports the photosynthetic leaf’s function.
Give me a hint
Distinguish incoming raw material and carbohydrate distribution.
Compare my reasoning
- Xylem supplies water and mineral ions.
- Phloem distributes sucrose made from photosynthetic carbohydrate.
Xylem supplies water and minerals; phloem moves organic nutrients to destinations.
Look for these in your work
- Correct two functions.
- Link them to the leaf.
An unfamiliar stained cross-section has a central cell cluster. A student assigns every red cell to xylem only from colour. Evaluate.
Give me a hint
Stain colour is not a universal tissue code.
Compare my reasoning
- Check orientation and cell arrangement.
- Use the source key and resolved structures.
- Do not label ambiguous individual cells solely from red colour.
Colour alone is insufficient; identify the vascular region and use structural evidence or a reliable key for xylem and phloem.
Look for these in your work
- Reject a universal colour rule.
- Specify stronger identification evidence.
Common mistakes
- Do not exchange the named transport roles.
- A vein is tissue, not simply an air gap.
What can you explain now?
Which tissue distributes sucrose from photosynthesising tissue?
Compare with the explanation
Phloem.
That is its stated organic-nutrient transport role.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain how a vein supports supply and distribution without confusing it with gas spaces.
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.