A scientist is developing new packaging materials. She tests two samples: one made from a synthetic polymer called polythene, and one made from a biopolymer called starch. Explain why polythene is a polymer and describe one key difference between synthetic polymers and biopolymers in terms of their origin and their breakdown in the environment.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Polythene is used to make plastic bags and food wrapping. Starch is a natural polymer found in plants such as potatoes and wheat.
Model answer (5 marks)
A polymer is a large molecule made from many small repeating units (monomers) joined together.
Polythene is a polymer because it consists of many ethene monomers joined together to form a long repeating chain structure.
Synthetic polymers are made from crude oil or other non‑renewable petrochemical sources, whereas biopolymers come from living organisms or natural, renewable sources.
Synthetic polymers such as polythene are non‑biodegradable and do not break down in the environment.
Biopolymers such as starch are biodegradable and can be broken down by microorganisms in the environment.
Polythene is a polymer because it consists of many ethene monomers joined together to form a long repeating chain structure.
Synthetic polymers are made from crude oil or other non‑renewable petrochemical sources, whereas biopolymers come from living organisms or natural, renewable sources.
Synthetic polymers such as polythene are non‑biodegradable and do not break down in the environment.
Biopolymers such as starch are biodegradable and can be broken down by microorganisms in the environment.
Examiner tips
- Use the exact definition of a polymer – large molecule of repeating units. Show the structure of polythene (ethene monomers). Mention origin (petrochemical vs natural) and biodegradability. Keep answer concise to fit 5 marks.
Common mistakes
- Saying polythene is a polymer without mentioning ethene monomers. Confusing ‘synthetic’ with ‘natural’ without explaining origin. Forgetting to state that biopolymers are biodegradable.
Mark scheme (5 marks)
- A polymer is a large molecule made from many small repeating units (monomers) joined together
- Polythene is described as a polymer because it consists of many ethene monomers joined together / it has a long repeating chain structure
- Synthetic polymers are made from crude oil / non-renewable petrochemical sources, whereas biopolymers come from living organisms / natural / renewable sources
- Synthetic polymers such as polythene are non-biodegradable / do not break down in the environment
- Biopolymers such as starch are biodegradable / can be broken down by microorganisms in the environment
Key terms in this question
polymer · synthetic polymer · biopolymer
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Polymers and life questions
- Nylon is a synthetic polymer used to make clothing and ropes. Explain why nylon …
- DNA is a naturally occurring polymer found in the nucleus of living cells. Expla…
- Starch is a naturally occurring polymer found in foods such as potatoes and brea…
- Explain why the majority of plastics used in everyday products are difficult to …