Translocation (Extended Only)
BiologyΒ· 8.4Β· 15 min read
1. Definition and Basics of Translocationβ β ββββ± 3 min
Translocation
The active movement of sucrose and amino acids from sources to sinks in the phloem tissue of flowering plants.
Example:
Sucrose produced in mature leaves during photosynthesis is moved to growing root tips for energy via translocation.
Translocation is an energy-dependent process, meaning it requires energy released from respiration in plant cells to move dissolved assimilates. Unlike xylem transport, which only moves upwards from roots to shoots, translocation can occur in both upward and downward directions depending on the plantβs immediate needs.
State the name of the tissue responsible for translocation, and the two main substances transported via this process.
- 1
First, recall that translocation is a unique function of phloem tissue, not xylem tissue.
- 2
The two main dissolved substances transported via translocation are sucrose (the stable storage sugar produced by photosynthesis) and amino acids (the building blocks of proteins).
- 3
Final answer: Phloem tissue transports sucrose and amino acids.
Exam tip:
Always specify phloem when answering translocation questions; writing 'vascular tissue' or 'xylem' will lose marks in extended papers.
2. Sources and Sinksβ β β βββ± 4 min
Source and Sink
A source is a plant part that produces or releases assimilates into the phloem, while a sink is a plant part that uses or stores these assimilates.
Example:
During the growing season, mature leaves (source) send sucrose to developing tomato fruits (sink) to support growth.
Common sources include mature photosynthesising leaves, germinating seeds breaking down stored food, and storage organs (like tubers or bulbs) releasing stored starch at the start of the growing season. Common sinks include growing roots, shoots, developing flowers, fruits, and storage organs building up starch reserves for winter.
A daffodil bulb grows new leaves in early spring, using stored food from the bulb. State the source and sink for translocation in this daffodil in early spring, explaining your answer.
- 1
First, identify the part releasing stored assimilates: the underground bulb is breaking down stored starch to supply energy for new growth, so this is the source.
- 2
Next, identify the part using assimilates: the new growing leaves are using the sucrose from the bulb to grow, so these are the sink.
- 3
Final answer: Source = daffodil bulb, as it releases stored starch as sucrose for transport. Sink = new growing leaves, as they use the sucrose for growth.
Exam tip:
Remember that storage organs can be sources or sinks depending on the time of year: they are sinks when storing food in summer, and sources when breaking down stored food to support new growth in spring.
3. Comparing Translocation and Transpirationβ β β βββ± 4 min
Exam questions frequently ask you to compare translocation and transpiration, so it is critical to memorise their key differences to avoid mixing them up and losing marks.
Feature | Translocation | Transpiration |
|---|---|---|
Tissue used | Phloem | Xylem |
Substances transported | Sucrose, amino acids | Water, mineral ions |
Direction of transport | Both upward and downward | Upward only |
Process type | Active (requires energy from respiration) | Passive (driven by evaporation) |
Purpose | Transport organic nutrients to where they are needed | Supply water for photosynthesis, cool the plant, maintain cell turgor |
A student writes the following statement: 'Transpiration moves sucrose from leaves to fruits in the phloem'. Identify two errors in the studentβs statement, and correct them.
- 1
First error: The process named is incorrect. The movement of sucrose in phloem is translocation, not transpiration.
- 2
Second error: Transpiration occurs in xylem, not phloem, and transports water and mineral ions, not sucrose.
- 3
Corrected statement: 'Translocation moves sucrose from leaves to fruits in the phloem'.
Exam tip:
If asked to compare the two processes, use a clear table structure in your answer to make it easy for the examiner to award marks for each difference.
4. Extended Response Exam Practiceβ β β β ββ± 4 min
Extended Paper 4 questions often ask for 3-4 mark explanations of translocation, so you need to structure your answers to include all required marking points to score full credit.
Explain the process of translocation in flowering plants. (3 marks)
- 1
Mark point 1: State that translocation is the movement of sucrose and amino acids in phloem tissue.
- 2
Mark point 2: Explain that movement is from sources (parts that make or release assimilates) to sinks (parts that use or store assimilates).
- 3
Mark point 3: Note that translocation is an active process that requires energy released from respiration to occur.
Exam tip:
Always mention that translocation requires energy from respiration for 3+ mark questions; this is a frequently missed marking point that costs many students full marks.
5. Common Pitfalls
Wrong move:
Stating that translocation occurs in xylem tissue.
Why:
Xylem is only responsible for transpiration of water and mineral ions; only phloem carries out translocation.
Correct move:
Explicitly name phloem as the tissue responsible for translocation in all answers.
Wrong move:
Claiming translocation only moves upwards in the plant.
Why:
Unlike xylem transport, phloem can move assimilates both up to growing shoots and down to roots or storage organs.
Correct move:
State that translocation occurs in both upward and downward directions.
Wrong move:
Confusing source and sink roles for storage organs year-round.
Why:
Storage organs are sinks when storing food in summer, but sources when breaking down stored food for new growth in spring.
Correct move:
Always link the role of a storage organ to the time of year or growth stage of the plant.
Wrong move:
Forgetting to mention translocation is an active process in extended answers.
Why:
This is a required marking point for all 3+ mark translocation questions.
Correct move:
Add that translocation requires energy from respiration to earn full marks.
Wrong move:
Stating that glucose is transported during translocation.
Why:
Glucose is too reactive to be transported around the plant, so it is converted to stable sucrose first.
Correct move:
Always name sucrose as the main sugar transported in translocation.
6. Quick Reference Cheatsheet
Key Term | Core Exam Fact |
|---|---|
Translocation | Active movement of sucrose + amino acids in phloem, both directions |
Source | Produces/releases assimilates (e.g. mature leaves, germinating seeds) |
Sink | Uses/stores assimilates (e.g. roots, fruits, growing shoots) |
Translocation vs Transpiration | Phloem, active, both directions vs Xylem, passive, up only |
7. Frequently Asked
Is translocation tested in Core IGCSE Biology papers?
No, this topic is exclusively tested in Extended papers (Papers 2 and 4) and never appears in Core papers (Papers 1 and 3) for CIE IGCSE Biology 0610.
What is the main difference between xylem and phloem transport?
Xylem transports water and mineral ions upwards only via passive transpiration, while phloem transports sucrose and amino acids in both directions via active translocation.
Going deeper
What's Next
Now that you have mastered translocation for CIE IGCSE Biology 0610 Extended, you are ready to apply this knowledge to exam-style questions and other related topics. Translocation is frequently tested alongside plant tissue structure and transpiration, so make sure you can clearly distinguish between all three processes for both multiple choice and extended response questions. It is also common for questions to link translocation to photosynthesis, as the sucrose transported during translocation is a product of photosynthesis in mature leaves. Practicing past paper extended response questions will help you remember all required marking points and avoid common errors that lose marks.