Define translocation from source to sink
Describe phloem movement of sucrose and amino acids between releasing and using organs.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall xylem/phloem cargo and plant nutrient uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which tissue carries sucrose?
What you will learn
- Define translocation with tissue and cargo
- Identify source and sink by their current roles
A route for organic nutrients
Translocation is movement of sucrose and amino acids in phloem from sources to sinks. A source releases these substances for transport; a sink takes them up for use or storage. The terms describe current roles rather than a permanently assigned organ type.
A mature photosynthetic leaf may release sucrose, while a growing root or fruit uses or stores the arriving material. Source means releasing into the transport pathway; it does not mean that a plant makes every organic nutrient only in one organ.
Use all parts of the definition
A strong account names cargo, tissue and direction relative to source/sink. “Food moves down” is weaker because it neither identifies sucrose/amino acids nor explains upward transport to a shoot.
Transpiration is water-vapour loss from leaves and the associated replacement stream uses xylem. Translocation is phloem movement of organic nutrients. Similar names should not lead to swapped tissues or substances.
Pause and explain
What makes an organ a sink in this account?
Worked example
A mature leaf exports sucrose to a growing fruit. Name the process, tissue, source and sink.
Show the worked solution
- Sucrose movement in phloem is translocation.
- The releasing leaf is the source; the growing/using fruit is the sink.
Answer Translocation in phloem; source: leaf; sink: growing fruit.
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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.
Define translocation using sucrose, amino acids, phloem, source and sink.
Give me a hint
Include materials, tissue and role-based direction.
Compare my reasoning
- Name sucrose and amino acids as cargo.
- State phloem movement from releasing sources to using/storing sinks.
Movement of sucrose and amino acids in phloem from sources to sinks.
Look for these in your work
- Name both cargo types and phloem
- Give source-to-sink movement
A leaf releases sucrose; a growing bud uses it. Identify source and sink with reasons.
Give me a hint
Use what each part does now.
Compare my reasoning
- The leaf releases transported sucrose, so it is the source.
- The bud uses arriving sucrose, so it is the sink.
Source: releasing leaf. Sink: using/growing bud.
Look for these in your work
- Identify both roles
- Justify each using release/use
Correct “translocation is transpiration through phloem”.
Give me a hint
Separate the material and process definitions.
Compare my reasoning
- Transpiration is leaf water-vapour loss.
- Translocation is phloem movement of sucrose/amino acids from source to sink.
They are distinct: transpiration loses water vapour; translocation moves organic nutrients through phloem.
Look for these in your work
- State both definitions
- Keep cargo and tissue correct
Common mistakes
- Defining translocation as water-vapour loss.
- Calling every root a source regardless of what it is doing.
What can you explain now?
What makes an organ a sink in this account?
Compare with the explanation
It uses or stores arriving organic nutrients
Its current receiving role defines the sink.
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Make it stick
Define source and sink without naming a permanently fixed organ.
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.