# Translocation (Extended Only)

> Biology · CIE IGCSE 0610
> Source: https://www.owlsprep.com/study/cie-0610-u6-translocation/

This extended-only guide covers the definition, mechanism, and exam applications of translocation in plants, as required for CIE IGCSE Biology 0610 section 8.4. You will learn to distinguish this process from transpiration and answer common exam questions.

**Prerequisites:** [Structure of plant transport tissues (xylem and phloem)](https://www.owlsprep.com/study/cie-0610-u6-plant-transport-tissues/); [Transpiration process](https://www.owlsprep.com/study/cie-0610-u6-transpiration/)

## Learning objectives

- Define translocation and identify the plant tissue responsible for the process
- Explain the roles of sources and sinks in translocation, and how they change with growth stage
- Distinguish between translocation and transpiration for comparison exam questions
- Construct complete extended-response answers for translocation questions covering all marking points

## Definition and Basics of Translocation

**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 plant’s immediate needs.

**Worked example:** 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.

## Sources and Sinks

**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.

**Worked example:** 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.

## Comparing Translocation and Transpiration

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 |

**Worked example:** A student writes the following statement: 'Transpiration moves sucrose from leaves to fruits in the phloem'. Identify two errors in the student’s 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.

## Extended Response Exam Practice

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.

**Exam command terms**

- **Explain translocation** — You must include the tissue used, substances transported, direction of movement, and note that it is an active process requiring energy from respiration. *(A 3-mark answer includes: 1) Occurs in phloem, 2) Transports sucrose and amino acids from sources to sinks, 3) Requires energy from respiration.)*

- **Compare translocation and transpiration** — You must give at least two clear, linked differences between the two processes, referencing features like tissue, direction, or energy use.

**Worked example:** 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.

## Common pitfalls

- **Wrong:** Stating that translocation occurs in xylem tissue.
  - Why it fails: Xylem is only responsible for transpiration of water and mineral ions; only phloem carries out translocation.
  - Correct: Explicitly name phloem as the tissue responsible for translocation in all answers.
- **Wrong:** Claiming translocation only moves upwards in the plant.
  - Why it fails: Unlike xylem transport, phloem can move assimilates both up to growing shoots and down to roots or storage organs.
  - Correct: State that translocation occurs in both upward and downward directions.
- **Wrong:** Confusing source and sink roles for storage organs year-round.
  - Why it fails: Storage organs are sinks when storing food in summer, but sources when breaking down stored food for new growth in spring.
  - Correct: Always link the role of a storage organ to the time of year or growth stage of the plant.
- **Wrong:** Forgetting to mention translocation is an active process in extended answers.
  - Why it fails: This is a required marking point for all 3+ mark translocation questions.
  - Correct: Add that translocation requires energy from respiration to earn full marks.
- **Wrong:** Stating that glucose is transported during translocation.
  - Why it fails: Glucose is too reactive to be transported around the plant, so it is converted to stable sucrose first.
  - Correct: Always name sucrose as the main sugar transported in translocation.

## 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 |

## 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.

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