Enzymes and Digestion

Learning Objectives (WALT)

• WALT understand the role of enzymes as biological catalysts in digestion.
• WALT identify specific digestive enzymes, their sources, and the substrates they act upon.
• WALT observe and interpret enzyme activity through practical investigation.
• WALT explain how enzymes affect the rate of chemical reactions in the digestive system.

National Curriculum Links (England)

• Key Stage 4 - Biology: Organisation (Years 9-11)
  • Cells, tissues and organs: Understand how enzymes function in digestion (NC Ref: 4.2a and 4.2b).
  • Bioenergetics: Demonstrate knowledge of enzyme specificity and activity (NC Ref: 4.4a).
  • Working scientifically: Planning and conducting a practical experiment to observe enzyme activity (NC Ref: 7.1a, 7.1b, 7.3a).

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Success Criteria

• I can explain what enzymes are and how they act as biological catalysts.
• I can name key digestive enzymes and correctly match them to their substrate and source.
• I can safely conduct and record observations from a practical experiment investigating enzyme activity.
• I can analyse data from enzyme experiments and draw conclusions on enzyme function.

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Lesson Structure (45 minutes)

Starter (5 minutes)

• Engage with Question: “What happens to your food when you eat it? How is it broken down?”
• Brief class brainstorm on existing knowledge of digestion and enzymes.
• Introduce key vocabulary on the whiteboard: enzyme, catalyst, substrate, active site, digestion.

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Main Teaching (15 minutes)

1. Teacher Explanation & Visuals

   • Define enzymes as proteins that speed up biochemical reactions without being consumed.
   • Explain their role as biological catalysts in digestion: breaking down large food molecules into smaller absorbable units.
   • Introduce main digestive enzymes for this age group:
     • Amylase (saliva, pancreas) → starch into maltose.
     • Protease (stomach, pancreas) → proteins into amino acids.
     • Lipase (pancreas) → lipids into fatty acids and glycerol.
   • Use a simple, dyslexia-friendly labelled diagram showing enzyme sources and substrates.

2. Modelling Enzyme Action

   • Use coloured shapes or an animation to demonstrate enzyme-substrate specificity and the ‘lock and key’ model.
   • Discuss how enzymes lower activation energy, increasing reaction rates.

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Practical Activity (20 minutes)

Lab Investigation: Enzyme Activity in Action

• Objective: Observe the effect of amylase on starch breakdown.

• Materials per group: Iodine solution, starch solution, amylase solution (saliva or yeast extract), spotting tiles or test tubes, pipettes, stopwatch.

• Method:

  • Place drops of starch solution into wells.
  • Add amylase solution.
  • At 1-minute intervals, add iodine to test for starch presence (blue-black colour indicates starch).
  • Record time taken for starch to disappear (no colour change).

• Safety and Dyslexia-friendly Instructions:

  • Provide printed, concise instructions with bullet points and clear visuals.
  • Use coloured labels and diagrams for each step.
  • Have a voice-recorded version of the instructions accessible on a classroom tablet for students with reading difficulties.

• Teacher Role:

  • Circulate to scaffold, prompt scientific questioning, and support accurate data recording.
  • Ask extension questions such as “What might happen if the temperature changes?”

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Plenary (5 minutes)

• Discuss results as a class.
• Recap how amylase catalyses starch digestion and relate back to the human digestive system.
• Pose reflective questions:
  • “Why are enzymes essential for digestion?”
  • “What factors might affect enzyme activity in the body?”

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Differentiation Strategies

• For learners needing support:

  • Provide step-by-step instructions with visuals.
  • Use sentence starters for written observations and conclusions.
  • Pair with peers for collaborative learning.

• For advanced learners:

  • Challenge to design a follow-up experiment testing the effect of temperature or pH on enzyme activity.
  • Introduce basic concepts of enzyme denaturation.
  • Ask for predictions and explanations using scientific terminology.

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Assessment & Feedback

• Formative assessment:

  • Observation during practical: ability to follow the method and accurately record data.
  • Questioning during plenary to assess understanding.
  • Short exit quiz: matching enzymes to substrates and sources (verbal or written).

• Feedback:

  • Immediate verbal feedback during practical.
  • Written feedback on quiz or observation notes, highlighting scientific vocabulary use.

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Extension Activities (Homework or Next Lesson)

• Research other enzymes involved in digestion and prepare a poster or digital presentation.
• Investigate enzyme use in industry (e.g., detergents or food processing) and explain how enzyme properties make them useful.

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Resources Required

• Amylase solution (prepared saliva mimic or safe yeast extract).
• Starch solution.
• Iodine solution.
• Spotting tiles or test tubes.
• Pipettes.
• Stopwatch or timers.
• Whiteboard and markers.
• Dyslexia-friendly handouts and visual aids.

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This lesson combines conceptual understanding with hands-on enquiry, allowing learners to experience the dynamic role of biological catalysts, fully aligned with the National Curriculum for England’s scientific knowledge and practical skills development.