Introduction to Process Diagrams
Process diagrams appear in approximately 10-15% of IELTS Academic Writing Task 1 questions. They require candidates to describe how something is made, how a system works, or how a natural cycle operates. Many test-takers find process questions challenging because they require a different approach from data-based questions—instead of comparing numbers, you must explain a sequence of stages using appropriate language.
This model answer demonstrates how to structure a response for a linear manufacturing process, using sequencing language and the passive voice effectively. The glass bottle recycling process is an ideal IELTS topic because it features clear stages, specific details such as temperatures, and a cyclical element that rewards careful observation.
The Task
You should spend about 20 minutes on this task.
The diagram below shows how glass bottles are recycled.
Summarise the information by selecting and reporting the main features, and make comparisons where relevant.
Write at least 150 words.
Model Answer
The diagram illustrates the process by which glass bottles are recycled and transformed into new products. Overall, this is a cyclical eight-stage process that begins with the collection of used bottles and ends with their distribution to manufacturers, after which the cycle can begin again.
In the initial stages, glass bottles are collected from households and transported to a recycling facility, where they are sorted according to their colour—green, brown, or clear. The sorted glass is then crushed into small fragments known as cullet, which is subsequently cleaned to remove any impurities such as labels or residue.
Following this, the cullet is heated in a furnace at approximately 1500 degrees Celsius until it melts completely. The molten glass is then poured into moulds to form new bottle shapes. Once moulded, the bottles undergo a cooling process and are inspected for quality. Finally, the finished bottles are packaged and distributed to manufacturers, who fill them with products before they return to consumers. This completes the recycling loop, allowing the process to repeat indefinitely.
(170 words)
Why This Answer Scores Well
Task Achievement
- The response fully addresses the task by describing all eight stages of the recycling process in logical order.
- A clear overview identifies the process as cyclical and consisting of eight stages—this demonstrates an understanding of the diagram’s key features.
- Specific details are included where relevant, such as the furnace temperature of 1500°C and the three glass colours, without overwhelming the reader.
- The cyclical nature is acknowledged at both the beginning and end of the response, showing full comprehension of the process.
Coherence and Cohesion
- The response is organised into clear paragraphs: an introduction with overview, followed by two body paragraphs covering the early and later stages respectively.
- Sequencing language guides the reader through the process: “in the initial stages”, “then”, “subsequently”, “following this”, “once”, “finally”.
- Referencing and substitution are used effectively: “the sorted glass”, “the cullet”, “the finished bottles”.
- The paragraph break at the melting stage creates a logical division between the preparation phases and the production phases.
Lexical Resource
- Technical vocabulary is used accurately: “cullet”, “molten glass”, “furnace”, “impurities”, “residue”.
- The task rubric is paraphrased effectively: “recycled” becomes “recycled and transformed into new products”; “glass bottles” becomes “used bottles” and “finished bottles”.
- Process-specific collocations demonstrate precision: “sorted according to”, “heated in a furnace”, “poured into moulds”, “undergo a cooling process”.
- The phrase “recycling loop” provides an elegant way to describe the cyclical nature of the process.
Grammatical Range and Accuracy
- The passive voice is used consistently and appropriately throughout, which is essential for process descriptions: “bottles are collected”, “glass is crushed”, “cullet is heated”.
- Complex sentences with subordinate clauses add sophistication: “The sorted glass is then crushed into small fragments known as cullet, which is subsequently cleaned to remove any impurities.”
- Participle clauses create variety: “Once moulded, the bottles undergo a cooling process.”
- Present simple tense is maintained throughout, which is appropriate for describing a general process.
Vocabulary Glossary
| Word / Phrase | Meaning / Use in Context |
|---|---|
| cullet | Crushed glass fragments ready for recycling. Using technical terms like this demonstrates strong lexical resource. |
| impurities | Unwanted substances that must be removed. Common in process descriptions involving purification or cleaning stages. |
| molten | Liquefied by heat. Used to describe metals, glass, or other materials heated to their melting point. |
| subsequently | After that; next in sequence. A formal alternative to ‘then’ that adds variety to your sequencing language. |
| undergo | To experience or be subjected to a process. Useful for describing stages where transformation occurs: ‘undergo testing’, ‘undergo treatment’. |
| residue | Material remaining after a process, often unwanted. Similar to ‘impurities’ but specifically refers to leftover traces. |
| furnace | An enclosed structure in which materials are heated to very high temperatures. Essential vocabulary for industrial processes. |
| sorted according to | Organised or separated based on specific criteria. More precise than simply ‘sorted by’. |
| fragments | Small pieces broken from a larger whole. More academic than ‘pieces’ or ‘bits’. |
| completes the loop | Finishes a cycle, allowing it to begin again. Useful for describing cyclical processes. |
| transformed into | Changed from one form to another. Stronger than ‘changed to’ or ‘made into’. |
| indefinitely | For an unlimited time; without end. Useful for emphasising that recycling processes can continue repeatedly. |
Vocabulary Quiz
Part 1: Multiple Choice
Choose the correct answer for each question.
1. What is ‘cullet’?
A) A type of glass bottle
B) Crushed glass fragments ready for recycling
C) The machine that melts glass
D) A type of glass colour
2. Which word means ‘liquefied by heat’?
A) Heated
B) Molten
C) Transformed
D) Processed
3. ‘The bottles undergo inspection’ means the bottles:
A) Avoid inspection
B) Are subjected to inspection
C) Fail inspection
D) Skip inspection
4. What is the best synonym for ‘subsequently’ in a process description?
A) Before
B) Meanwhile
C) Following this
D) Instead
5. Which phrase best describes a process that repeats continuously?
A) The process stops here
B) This completes the loop
C) The process ends
D) This is the final stage
Part 2: Fill in the Blanks
Complete each sentence using a word from the box below.
Word Bank: furnace | impurities | residue | fragments | transformed | indefinitely
- The glass is heated in a _____________ at extremely high temperatures until it melts.
- Any _____________ such as dirt or labels must be removed before the glass can be reused.
- The bottles are crushed into small _____________ called cullet.
- Through the recycling process, old bottles are _____________ into new products.
- Because glass can be recycled repeatedly, the process can continue _____________.
Answer Key
Part 1: Multiple Choice
- B) Crushed glass fragments
- B) Molten
- B) Are subjected to inspection
- C) Following this
- B) This completes the loop
Part 2: Fill in the Blanks
- furnace
- impurities
- fragments
- transformed
- indefinitely
Practice This Question Yourself
Now it’s your turn! Write your own response to this process diagram question in 20 minutes, then compare it to the model answer above. Focus on:
- Writing a clear overview that identifies the process as cyclical
- Using the passive voice consistently
- Including a range of sequencing language
- Incorporating vocabulary from the glossary
How to Continue Your IELTS Study
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