Knowledge Organiser
This topic summary covers Knowledge Organiser within Enzymes in Digestion for GCSE Biology. Enzyme structure and function, digestive enzymes, factors affecting enzyme activity, lock and key model, and practical investigations It is section 19 of 19 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 19 of 19
Practice
20 questions
Recall
25 flashcards
Knowledge Organiser
Key Terms
- Enzyme — biological catalyst; protein; not used up
- Active site — specific shape; complementary to substrate
- Substrate — molecule that fits the active site
- Denaturation — permanent shape change of active site
- Optimum — conditions giving fastest reaction rate
- Emulsification — bile breaks large fat droplets into smaller ones
Must-Know Facts
- Amylase: starch to maltose; found in mouth (saliva) and pancreas; optimum pH 7
- Pepsin: proteins to smaller polypeptides; found in stomach; optimum pH 1.5
- Trypsin: proteins to smaller polypeptides and amino acids; found in small intestine; optimum pH 8.5
- Lipase: lipids to fatty acids and glycerol; pancreas and small intestine; optimum pH 8
- Bile: produced by liver, stored in gall bladder, released into duodenum; NOT an enzyme
- Bile functions: emulsifies fats (increases surface area for lipase) AND neutralises stomach acid
- High temperature above optimum = denaturation (irreversible)
- Low temperature = fewer collisions, slower rate (reversible)
- Rate of reaction = amount of product formed ÷ time taken
Common Mistakes
- Saying enzymes are "killed" by high temperatures: Enzymes are denatured — the active site permanently changes shape so the substrate no longer fits. "Killed" is never accepted in mark schemes; always use "denatured."
- Saying bile is an enzyme: Bile does not break chemical bonds — it emulsifies fats by breaking large droplets into smaller ones, increasing surface area for lipase. Bile is produced by the liver and is not an enzyme.
- Forgetting low temperature is reversible but high temperature is not: At low temperatures enzymes slow down but retain their shape — warming restores activity. Above the optimum, denaturation is permanent and activity cannot be restored.
- Mixing up enzyme substrates: Amylase breaks down starch; proteases (pepsin, trypsin) break down proteins; lipase breaks down lipids. Each enzyme is specific to its substrate due to the complementary shape of its active site.
- Stating the wrong food test colour change: Benedict's = blue to brick-red (reducing sugars); iodine = orange/yellow to blue-black (starch); biuret = blue to purple (protein); emulsion test = clear ethanol added to water turns cloudy white (lipids). Learn all four tests — the emulsion test is the one students most often forget.
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Practice Questions for Enzymes in Digestion
What are enzymes?
Explain the effect of increasing temperature on enzyme activity.
Quick Recall Flashcards
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