The shape of the lesson
By the end of the lesson, learners can
- Three turns, one triose phosphate: Click each stage chip in turn: carbon fixation, reduction, regeneration and products.
- What the cycle makes: Click products in the simulator.
- Fixation: rubisco, CO2 + RuBP (5C) → 2 GP (3C).
- Reduction: GP → TP using ATP and reduced NADP.
- Regeneration: TP → RuBP using ATP.
- Light off: GP up, RuBP down. CO2 off: GP down, RuBP up.
One picture every idea returns to
The Calvin cycle (light-independent stage) takes place in the stroma and uses the ATP and reduced NADP from the light-dependent stage to make complex organic molecules. It has three main stages. Fixation: the enzyme rubisco combines carbon dioxide with ribulose bisphosphate (RuBP, 5C), giving two molecules of glycerate 3-phosphate (GP, 3C). Reduction: GP is reduced to triose phosphate (TP, 3C) in reactions using reduced NADP and ATP. Regeneration: most of the TP is used to regenerate RuBP, in reactions that use ATP. The remaining TP is used to make carbohydrates, lipids and amino acids, and some GP is used to make amino acids.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Fix, reduce, regenerate.. In the stroma, carbon dioxide is captured by a five-carbon acceptor and built up into sugars. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Three turns, one triose phosphate | Click each stage chip in turn: carbon fixation, reduction, regeneration and products. Project tab 5 of the lab (Photosynthesis lab, the Calvin cycle) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: What the cycle makes | Click products in the simulator. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 17 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in What the cycle makes, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Rubisco fixes carbon dioxide; it does not use ATP. | ATP and reduced NADP are used in the reduction of GP to TP, and ATP again in regenerating RuBP. Also: RuBP is 5C, GP and TP are both 3C. |
| In data questions about switching the light off, the first change is in the reduction step: GP rises because it is still being made from RuBP but can no longer be reduced, and RuBP falls because it is not regenerated. | Return to What the cycle makes: ask a pair to state the correct version and show it on the lab before moving on. |
The Calvin cycle: worksheet
6 questions, 17 marks. Written in the style of the papers; no past paper question is reproduced.
Outline the three main stages of the Calvin cycle.
Explain how the light-independent stage depends on the light-dependent stage.
A suspension of algae was given radioactive carbon dioxide in bright light. After 5 minutes the light was switched off. The concentration of GP rose to about double its value, while RuBP fell to near zero. Explain these results.
Calculate the number of turns of the Calvin cycle, and the number of ATP molecules, needed to produce one molecule of glucose.
State how the intermediates GP and TP from the Calvin cycle are used by the plant.
Rubisco makes up a large proportion of the protein in a leaf. Suggest why a plant needs such a large amount of this enzyme.
Answer key and marking notes
- Fixation: rubisco catalyses the combination of carbon dioxide with RuBP (5C) to give two molecules of GP (3C).
- Reduction: GP is reduced to triose phosphate (TP) using reduced NADP and ATP.
- Regeneration: RuBP is regenerated from TP in reactions that use ATP.
- The light-dependent stage supplies ATP and reduced NADP to the stroma.
- Reduced NADP provides hydrogen / electrons and ATP provides energy to reduce GP to TP.
- ATP is also needed to regenerate RuBP; without light these run out, and the Calvin cycle stops within seconds or minutes.
- In the dark, the light-dependent stage stops, so no ATP or reduced NADP are produced.
- GP can no longer be reduced to TP, but GP is still formed from RuBP and CO2 by rubisco, so GP accumulates.
- RuBP is still used in fixation but cannot be regenerated (needs TP and ATP), so its concentration falls.
- Fixation therefore stops once the RuBP is used up.
- Each turn fixes one CO2; glucose has 6 carbons, so 6 turns are needed (giving 2 TP, which make one hexose).
- Each turn uses 3 ATP (2 for reduction, 1 for regeneration), so 6 × 3 = 18 ATP (and 12 reduced NADP).
- GP is used to make some amino acids.
- TP is used to make carbohydrates, for example glucose, sucrose, starch and cellulose.
- TP is also used to make lipids (glycerol and fatty acids) and amino acids.
- Rubisco has a very slow rate of reaction / fixes only a few CO2 molecules per second.
- A large quantity is needed to fix carbon dioxide fast enough to keep up with the supply of ATP and reduced NADP from the light-dependent stage.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is the product of the reaction catalysed by rubisco?
- Atwo molecules of glycerate 3-phosphate (GP)
- Bone molecule of triose phosphate (TP)
- Cone molecule of ribulose bisphosphate (RuBP)
- Done molecule of glucose
Which molecules are used in the reduction of GP to triose phosphate?
- AATP and reduced NADP
- BATP only
- Creduced NADP and oxygen
- Dcarbon dioxide and ATP
Which molecule acts as the carbon dioxide acceptor in the Calvin cycle?
- Aribulose bisphosphate (RuBP)
- Bglycerate 3-phosphate (GP)
- Ctriose phosphate (TP)
- Dreduced NADP
Which molecules can a plant make from glycerate 3-phosphate (GP), as well as from triose phosphate?
- Asome amino acids
- Bcellulose
- Cstarch
- Dfatty acids
For every 6 molecules of carbon dioxide fixed in the Calvin cycle, how many molecules of triose phosphate are made, and how many leave the cycle?
- A12 made, 2 leave
- B6 made, 1 leaves
- C12 made, 10 leave
- D6 made, 5 leave
The graph shows the concentrations of GP and RuBP in an alga before and after the light was switched off. Which row identifies X and Y?
- AX is GP and Y is RuBP
- BX is RuBP and Y is GP
- CX is TP and Y is GP
- DX is RuBP and Y is TP
In Calvin's experiments, algae were given radioactive carbon dioxide and killed after a few seconds. Which compound was the first to become radioactive?
- Aglycerate 3-phosphate
- Btriose phosphate
- Cribulose bisphosphate
- Dglucose
A plant is deficient in nitrate ions. Which product of the Calvin cycle would the plant be least able to make?
- Aamino acids
- Bsucrose
- Cstarch
- Dtriglycerides
Quiz key
Rubisco combines carbon dioxide with RuBP (5C); the unstable 6C intermediate splits at once into two molecules of GP (3C). TP is formed later, when GP is reduced. RuBP is the substrate of rubisco, not its product. Glucose is made from TP outside the cycle, not by rubisco.
Reduced NADP provides the hydrogen (electrons) to reduce GP, and ATP provides energy. ATP alone cannot reduce GP. Oxygen is not used in the Calvin cycle. Carbon dioxide is used in the fixation step, not in reduction.
RuBP (5C) accepts carbon dioxide in the reaction catalysed by rubisco. GP is the 3C product of that reaction. TP is formed by reducing GP and is used to regenerate RuBP. Reduced NADP is a reducing agent, not a carbon acceptor.
GP is used to make some amino acids. Cellulose and starch are carbohydrates made from TP (via hexoses). Fatty acids are lipids made from TP. Only amino acids can be made from both intermediates.
6 CO2 + 6 RuBP gives 12 GP, reduced to 12 TP. Ten TP (30 C) regenerate 6 RuBP (30 C), so 2 TP (6 C, the carbon fixed) leave, enough for one hexose. 6 made and 1 leaves is the figure for 3 CO2. 10 leaving and 5 leaving reverse the proportions: most TP must stay in the cycle.
Without ATP and reduced NADP, GP cannot be reduced, but rubisco still makes GP from RuBP and carbon dioxide, so GP (X) rises. RuBP is still used but cannot be regenerated, so RuBP (Y) falls. Reversing them predicts the change for cutting off carbon dioxide, not light. TP falls in the dark, so it cannot be the rising curve X; and the option with RuBP as X fails because RuBP falls, it does not rise.
Fixation of the labelled carbon dioxide by rubisco gives GP first, so it is labelled within seconds. TP is labelled next, after GP has been reduced. RuBP becomes labelled only after several turns, when labelled TP has been used to regenerate it. Glucose is labelled later still, as it is made from TP.
Amino acids contain nitrogen in their amine group, so although their carbon skeletons come from GP and TP, they cannot be made without a nitrogen source such as nitrate. Sucrose and starch are carbohydrates containing only C, H and O. Triglycerides (lipids) also contain only C, H and O, and are made from TP.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.