Lesson at a Glance | He Tirohanga Whakamua
Ngā Whāinga Ako | Learning Intentions
Students will know
- That enzymes are globular proteins that function as biological catalysts, speeding up metabolic reactions without being consumed.
- How enzymes lower the activation energy () required for a chemical reaction to proceed.
- The difference between the historical Lock-and-Key Model and the modern Induced Fit Model (active site undergoes a subtle shape change upon substrate binding to mold precisely around the substrate).
Students will demonstrate
- By drawing activation energy progress curves with and without enzymes.
- By completing formative Section 5 in their class exercise book or revision folder.
Curriculum alignment
- NZC (2007) · Science · Level 7 · Living World: “Explore the diverse ways in which animals and plants carry out the life processes.”
Do Now | Tīmatanga Whakaaro (10 min)
Activation Energy Prompt:
"Many reactions in cellular respiration would proceed too slowly at body temperature without enzymes. How do cells speed these reactions without heating themselves?"
Unpack: A reaction must overcome an activation-energy barrier (). Enzymes provide an alternative pathway with a lower barrier, allowing reaction steps to proceed rapidly at cell temperatures without the enzyme being consumed.
Activation Energy (15 min)
1. What the barrier is
Activation energy (Ea) is the energy a reaction must be given to get started — the hump that has to be climbed even when the reaction releases energy overall.
2. What an enzyme actually does
It lowers Ea by holding the substrate in a strained, reaction-ready position and stabilising the transition state. It does not push the reaction; it lowers the hurdle.
3. Read the energy diagram
Draw the uncatalysed and catalysed curves on the same axes. The start and end points are identical. Only the height of the peak changes — and that difference is the enzyme's entire effect.
4. The error that costs the marks
Writing that the enzyme "gives the reaction energy" or "makes more product". It changes the RATE, not the yield and not the energy change.
Mahi | Do this: Draw both curves, label Ea on each, and mark the two points that must not move. Then write one sentence that would lose a mark, and rewrite it correctly underneath.
Lock-and-Key vs Induced Fit Model (15 min)
Active site is a rigid, pre-formed 3D shape exactly complementary to the substrate. Substrate fits like a key into a lock.
Active site is flexible. As the substrate approaches, the enzyme undergoes a conformational shape change, molding around the substrate to strain bonds and catalyse the reaction.
📁 Formative Cell Biology Mastery Portfolio — Section 5: Enzyme Action & Energy Models
Complete this formative practice section in your exercise book. This enzyme-action work prepares you for the external standard; it is not a separate NZQA submission. Use the energy-diagram and induced-fit teaching on this page, so no separate portfolio template is required.
Section 5 Requirements:
1. Activation Energy Graph: Plot Reaction Progress vs Energy showing the high peak uncatalyzed vs lowered peak catalysed by an enzyme.
2. Induced Fit Step-by-Step Diagram: Draw 3 stages: 1) Free Enzyme & Substrate → 2) Enzyme-Substrate Complex (Conformational Fit) → 3) Released Products & Unaltered Enzyme.
3. Specificity Rationale: In one paragraph, explain how the active site's three-dimensional shape and induced fit make an enzyme specific to its substrate, and why the enzyme can be reused after products leave.
Exit Verification | Ka Mutu Hoki (5 min)
Exit Check:
"My Section 5 diagram illustrates how the Induced Fit model involves a conformational change in the enzyme active site upon substrate binding."
Teacher Planning & NCEA Alignment
NCEA Level 2 Biology Alignment (4 Credits External):
- Enzyme Function: Demonstrate understanding of biological catalysts, activation energy reduction, and active site specificity.
- Models of Action: Compare Lock-and-Key vs Induced Fit models using tertiary protein structure rationale.
Vocabulary: Enzyme, biological catalyst, activation energy (), substrate, active site, Lock-and-Key, Induced Fit, conformational change.
Paired concept in Guided Media & Evidence: enzyme structure & action →