At DuPont, researchers have used both yeast and bacteria as hosts to grow the raw material, which they have spun into fibres. Robert Dorsch, DuPont’s director of biochemical development, says the globules of protein, comparable with marbles in an egg, are harvested and processed. ‘We break open the bacteria, separate out the globules of protein and use them as the raw starting material. With yeast, the gene system can be designed so that the material excretes the protein outside the yeast for better access,’ he says.
‘The bacteria and the yeast produce the same protein, equivalent to that which the spider uses in the drag lines of the web. The spider mixes the protein into a water- based solution and then spins it into a solid fibre in one go. Since we are not as clever as the spider and we are not using such sophisticated organisms, we substituted man- made approaches and dissolved the protein in chemical solvents, which are then spun to push the material through small holes to form the solid fibre.’
Researchers at DuPont say they envisage many possible uses for a new biosilk material. They say that earthquake-resistant suspension bridges hung from cables of synthetic spider silk fibres may become a reality. Stronger ropes, safer seat belts, shoe soles that do not wear out so quickly and tough new clothing are among the other applications. Biochemists such as Lewis see the potential range of uses of biosilk as almost limitless. ‘It is very strong and retains elasticity; there are no man-made materials that can mimic both these properties. It is also a biological material with all the advantages that has over petrochemicals,’ he says.
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Question Focus: Identifying one host organism used to grow the raw material
Correct Answer: yeast
Why this is correct: The diagram shows two starting organisms. The passage clearly says DuPont researchers used yeast as one host to grow the raw material. That is why yeast fits this position on the diagram.
Passage Reference: At DuPont, researchers have used both yeast and bacteria as hosts to grow the raw material
Common Mistake: Some students think only bacteria is correct because the passage explains bacteria in more detail later. This is a partial truth trap. Both organisms are used.
Paraphrasing: Passage: 'used both yeast and bacteria as hosts' = Diagram: 'starting organism'
Tips: When a diagram shows two parallel items, check if the passage lists them together.
Key Vocabulary:
- hosts = organisms used to grow something
- raw material = basic substance
Question Focus: Identifying the second host organism
Correct Answer: bacteria
Passage Reference: At DuPont, researchers have used both yeast and bacteria as hosts to grow the raw material
Why this is correct: The passage states that bacteria is also used as a host. On the diagram, this label refers to the second organism involved in the same stage.
Common Mistake: Students sometimes repeat yeast for both gaps. This is a context shift trap because the diagram shows two different inputs.
Paraphrasing: Passage: 'used both yeast and bacteria' = Diagram: 'second host organism'
Tips: Do not repeat the same word unless the diagram clearly shows repetition.
Key Vocabulary:
- bacteria = microscopic organisms
- host = living container
Question Focus: Identifying what the globules are made of
Correct Answer: protein
Passage Reference: the globules of protein, comparable with marbles in an egg, are harvested and processed. 'We break open the bacteria, separate out the globules of protein and use them as the raw starting material.
Why this is correct: The diagram labels the globules. The passage directly says they are globules of protein, so the answer must be protein.
Common Mistake: Students may write material or fibres, but those come later in the process. This is a wrong section trap.
Paraphrasing: Passage: 'globules of protein' = Diagram: 'globules made of ___'
Tips: If the passage gives an exact noun, copy it exactly. Do not paraphrase.
Key Vocabulary:
- globules = small round particles
- protein = biological substance
Question Focus: Identifying what the protein is dissolved in
Correct Answer: chemical solvents
Why this is correct: The diagram shows a processing stage. The passage explains that researchers dissolved the protein in chemical solvents, which matches this step exactly.
Common Mistake: Students sometimes write water-based solution, which refers to the spider, not DuPont. This is a context shift trap.
Paraphrasing: Passage: 'dissolved the protein in chemical solvents' = Diagram: 'protein dissolved in ___'
Tips: Always check who is doing the action. Spider and researchers use different methods.
Key Vocabulary:
- dissolved = mixed into liquid
- solvents = liquids that dissolve substances
Question Focus: Identifying how fibres are formed
Correct Answer: holes
Passage Reference: which are then spun to push the material through small holes to form the solid fibre
Why this is correct: The diagram shows the final shaping stage. The passage says the material is pushed through small holes, so holes or small holes is correct.
Common Mistake: Some students write fibres, but fibres are the result, not the method. This is a causation trap.
Paraphrasing: Passage: 'pushed through small holes' = Diagram: 'material passes through ___'
Tips: Look for prepositions like 'through'. They strongly limit the grammar of the answer.
Key Vocabulary:
- spun = shaped by forcing through
- fibre = thin strong thread
General Tips:
- Diagram completion questions follow the order of the passage. Use the previous answer to find the next one.
- Always copy the exact word from the passage. Synonyms are not accepted.
- Check grammar clues like prepositions and plural forms before writing your answer.
- If humans and animals are both mentioned, be careful not to mix their processes.
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