The shape of the lesson
By the end of the lesson, learners can
- Why cells need ATP: Spend ATP on active transport, then on movement, then on an anabolic reaction, and watch the ATP and ADP + Pi counters.
- Fuels and their RQ: Pick carbohydrate, lipid, protein and anaerobic in turn.
- Measuring RQ with a respirometer: Choose germinating peas, press Run for 10 minutes and record how far the liquid moves in both tubes.
- Energy for: active transport, movement, anabolic reactions.
- ATP: small amounts, one step, soluble, quickly remade, universal.
- RQ = CO2 produced ÷ O2 taken in: 1.0 carbohydrate, 0.7 lipid, 0.9 protein.
- Respirometer: KOH tube = O2 uptake; water tube = O2 − CO2.
One picture every idea returns to
Living organisms need energy for active transport, movement and anabolic reactions such as DNA replication and protein synthesis. Respiration transfers energy from substrates to ATP, the universal energy currency: its hydrolysis to ADP and phosphate releases energy in small, usable amounts, in one step, wherever it is needed. ATP is made by substrate-linked phosphorylation and by chemiosmosis in the membranes of mitochondria and chloroplasts. Lipids release about twice as much energy per gram as carbohydrates or proteins because they contain more hydrogen. The respiratory quotient (RQ) is the number of molecules of CO2 produced divided by the number of molecules of O2 taken in: about 1.0 for carbohydrate, 0.7 for lipid and 0.9 for protein, and it can be measured with a respirometer.
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, One small molecule pays for everything.. Pumping ions, contracting muscle and copying DNA all need energy, and every cell pays for them in the same currency. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Why cells need ATP | Spend ATP on active transport, then on movement, then on an anabolic reaction, and watch the ATP and ADP + Pi counters. Project tab 1 of the lab (Energy and respiration lab, ATP) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Fuels and their RQ | Pick carbohydrate, lipid, protein and anaerobic in turn. Project tab 2 of the lab (Energy and respiration lab, substrates and RQ) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Measuring RQ with a respirometer | Choose germinating peas, press Run for 10 minutes and record how far the liquid moves in both tubes. Project tab 3 of the lab (Energy and respiration lab, respirometer) and let a student drive it while the class predicts. | Frayer Model |
| 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, 19 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 Measuring RQ with a respirometer, 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.
Frayer Model
Pairs fill a four-box grid for the key term: definition, characteristics, examples and non-examples. The non-examples box is where the misconceptions surface, so give it the most time.
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 |
|---|---|
| Energy is not "stored in the bond" and released by breaking it. | Breaking any bond needs energy. Energy is released by the whole hydrolysis reaction, because the products (ADP and phosphate) are more stable than ATP and water. Write "hydrolysis of ATP releases energy". |
| RQ is CO 2 divided by O 2, never the other way up. | A quick check: lipids must come out below 1, because they need extra oxygen to oxidise all that hydrogen to water. |
| A gauze platform keeps the organisms off the KOH, which is corrosive. | And in tube B a liquid that does not move does not mean no respiration: it means the volume of CO 2 given out equals the volume of O 2 taken in (RQ = 1). |
Energy, ATP and respiratory quotients: worksheet
6 questions, 19 marks. Written in the style of the papers; no past paper question is reproduced.
Outline why living organisms need energy. Give one example of each use.
Describe the features of ATP that make it suitable as the universal energy currency.
Explain why lipids have a higher energy value per gram than carbohydrates when used as respiratory substrates.
Tripalmitin is respired according to the equation 2C51H98O6 + 145O2 → 102CO2 + 98H2O. Calculate the RQ and state what it indicates.
A respirometer contained germinating seeds. With potassium hydroxide in the tube, the liquid moved 24 mm in 10 minutes. With water instead, it moved 6 mm in the same direction. The capillary bore has a radius of 0.5 mm. Calculate the volume of oxygen taken in and the RQ, and suggest the substrate.
Suggest how the reliability and validity of a respirometer experiment with blowfly larvae could be improved.
Answer key and marking notes
- Active transport: moving ions or molecules against a concentration gradient, for example the sodium-potassium pump.
- Movement: for example muscle contraction, or cilia and flagella beating.
- Anabolic reactions: building large molecules from small ones, for example protein synthesis or DNA replication.
- Hydrolysis of ATP releases energy in small, manageable amounts (about 30.5 kJ mol−1), so little is wasted.
- Hydrolysis is a single-step reaction catalysed by one enzyme, so energy is released quickly when needed.
- ATP is small and soluble, so it moves easily within a cell, but cannot leave the cell.
- ATP is quickly regenerated from ADP and phosphate, and the same molecule is used in all organisms.
- Lipids (fatty acids) contain a greater proportion of hydrogen atoms per gram than carbohydrates.
- Most ATP is made in oxidative phosphorylation, which depends on hydrogen carried by reduced NAD and reduced FAD.
- More hydrogen gives more reduced coenzymes, more protons pumped and so more ATP per gram (and more oxygen is needed).
- RQ = 102 ÷ 145 = 0.70.
- This is the typical RQ of a lipid, so lipid is the respiratory substrate.
- O2 uptake = πr2h = 3.14 × 0.52 × 24 = 18.8 mm3 in 10 minutes.
- CO2 produced corresponds to 24 − 6 = 18 mm of movement.
- RQ = 18 ÷ 24 = 0.75.
- This is close to 0.7, so the seeds are mainly respiring lipid (perhaps with some carbohydrate).
- Place the respirometer in a thermostatically controlled water bath and allow time to equilibrate before taking readings.
- Use a control tube with glass beads of the same volume as the larvae to correct for changes in temperature or atmospheric pressure.
- Use the same mass of larvae of the same age, repeat at least three times and calculate a mean.
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.
Which process is an anabolic reaction that needs energy from ATP?
- Ajoining amino acids together to form a polypeptide at a ribosome
- Bhydrolysis of starch to maltose by amylase in the gut
- Cdiffusion of oxygen from an alveolus into a red blood cell
- Dosmosis of water from the soil into a root hair cell
Which list shows the components of one molecule of ATP?
- Aadenine, ribose and three phosphate groups
- Badenine, deoxyribose and three phosphate groups
- Cadenine, ribose and two phosphate groups
- Dadenine, glucose and three phosphate groups
Cells use ATP, not glucose, as the immediate source of energy for their reactions. Which statement explains why?
- AATP is hydrolysed in a single step, releasing a small amount of energy where it is needed, while releasing energy from glucose takes many steps
- Ba molecule of ATP contains more energy than a molecule of glucose
- Cglucose cannot dissolve in the cytoplasm, so it cannot reach the reactions
- Dglucose can only be broken down outside the cell, by digestive enzymes
In one hour a small mammal took in 40 cm3 of O2 and gave out 36 cm3 of CO2. What is its RQ, and what does it suggest?
- A0.90, suggesting that protein is being respired
- B1.11, suggesting that some respiration is anaerobic
- C0.90, suggesting that lipid is being respired
- D0.70, suggesting that lipid is being respired
What is meant by substrate-linked phosphorylation?
- Athe direct transfer of a phosphate group from a substrate molecule to ADP, forming ATP
- Bthe synthesis of ATP using energy from protons diffusing through ATP synthase
- Cthe hydrolysis of ATP to ADP to release energy for a reaction
- Dthe addition of phosphate to glucose using ATP at the start of glycolysis
Three organisms were placed in respirometers. The table shows the distance the coloured liquid moved. Which organism is respiring mainly lipid?
- AX
- BY
- CZ
- Dnone of them, because the liquid in tube B moved less than in tube A for every organism
In a respirometer containing 5.0 g of germinating seeds and potassium hydroxide, the liquid moved 35 mm in 10 minutes along a capillary of radius 0.5 mm. What is the rate of oxygen uptake?
- A0.55 mm3 g−1 min−1
- B2.20 mm3 g−1 min−1
- C0.18 mm3 g−1 min−1
- D5.50 mm3 g−1 min−1
Yeast in a sealed respirometer gave an RQ of 1.6. Which conclusion is best supported?
- Asome of the yeast's respiration is anaerobic, releasing CO2 without taking in O2
- Bthe yeast is respiring lipid, which releases more CO2 per O2
- Cthe yeast is respiring protein, which gives an RQ above 1
- Dthe potassium hydroxide has absorbed some of the oxygen
Quiz key
Protein synthesis links amino acids by peptide bonds, building a large molecule from small ones; each amino acid is activated using ATP, so it is an anabolic, energy-requiring reaction. Digesting starch is the opposite, a catabolic hydrolysis that does not need ATP. Diffusion and osmosis are passive processes driven by concentration or water potential gradients, so they need no energy from ATP.
ATP (adenosine triphosphate) is adenine plus the pentose sugar ribose (together adenosine) plus three phosphate groups. Deoxyribose is the sugar in DNA nucleotides, not in ATP. Two phosphate groups describes ADP, the product of hydrolysis. Glucose is a hexose and is not part of any nucleotide.
Hydrolysis of ATP is one reaction catalysed by one enzyme, releasing about 30.5 kJ mol−1, a convenient amount, instantly. Releasing the energy in glucose needs the many steps of respiration. A glucose molecule actually holds far more energy than one ATP, which is why respiration of one glucose makes many ATP. Glucose is soluble and is respired inside cells, so the last two options are false.
RQ = 36 ÷ 40 = 0.90, the typical value for protein (or a mixture of carbohydrate and lipid). 1.11 comes from dividing O2 by CO2, the wrong way up. Lipid gives an RQ of about 0.7, so 0.90 does not point to lipid alone, and 0.70 is not what these volumes give.
In substrate-linked phosphorylation a phosphate group is moved straight from an intermediate (in glycolysis or the Krebs cycle) to ADP. ATP made using a proton gradient is chemiosmosis, the other route. Hydrolysis of ATP uses ATP, it does not make it. Phosphorylating glucose at the start of glycolysis is a phosphorylation of a substrate using ATP, the reverse direction.
RQ = (A − B) ÷ A. X: (30.0 − 9.0) ÷ 30.0 = 0.70, the value for lipid. Y: 20.0 ÷ 20.0 = 1.0, carbohydrate; the liquid in B does not move because CO2 released equals O2 taken in. Z: 22.5 ÷ 25.0 = 0.90, protein. B moving less than A is expected whenever the RQ is 1 or less, so it does not rule out lipid.
Volume = 3.14 × 0.52 × 35 = 27.5 mm3; divided by 10 min and by 5.0 g gives 0.55 mm3 g−1 min−1. 2.20 uses 1 mm (the diameter) as the radius. 0.18 leaves out π. 5.50 divides by the mass but not by the time, so it is the uptake per gram per 10 minutes.
Aerobic respiration of carbohydrate gives 1.0 at most. An RQ above 1 means extra CO2 is released with no O2 used: ethanol fermentation releases CO2 and takes in no O2. Lipid gives about 0.7 and protein about 0.9, both below 1. KOH absorbs CO2, not O2, and in any case an RQ is found by comparing a tube with KOH with one without it.
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.