HS-LS1-7: Modeling Cellular Respiration as Bonds Breaking and Forming
In plain English: HS-LS1-7 is the NGSS high school performance expectation that asks students to use a model to show that cellular respiration is a chemical process: bonds in food molecules and oxygen break, new bonds form in carbon dioxide and water, and the result is a net transfer of energy. The focus is on inputs and outputs, not the steps. It is usually taught in Biology.
Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in a net transfer of energy.
Clarification Statement: Emphasis is on the conceptual understanding of the inputs and outputs of the process of cellular respiration.
Assessment Boundary: Assessment should not include identification of the steps or specific processes involved in cellular respiration.
Next Generation Science Standards · Disciplinary Core Idea: From Molecules to Organisms: Structures and Processes · Official standard
Students build and use models of cellular respiration at two levels. At the level of matter, glucose and oxygen go in and carbon dioxide and water come out, with every atom accounted for: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O. At the level of energy, the bonds in glucose and oxygen are broken, which takes energy in, and new bonds form in carbon dioxide and water, which releases more energy than was taken in. The difference is the net energy transferred, part of it to molecules the cell uses for work and the rest as thermal energy. Students test the model against gas data from germinating seeds and from people exercising, and they critique flawed models.
The official Clarification Statement reads: "Emphasis is on the conceptual understanding of the inputs and outputs of the process of cellular respiration." The Assessment Boundary reads: "Assessment should not include identification of the steps or specific processes involved in cellular respiration." So glycolysis, the Krebs cycle and the electron transport chain are beyond this standard and do not appear in any activity, homework or quiz item. ATP is named only as the molecule that carries energy to cell work. Every bond energy on the page is a standard average value. For the energy released, this page uses about 2,870 kJ per mole of glucose, the same value as the HS-LS1-5 photosynthesis lesson, so the two pages agree. Some books give about 2,800 kJ per mole, the heat measured when glucose burns in a calorimeter; either is fine if students state the value they use.
Learning Objectives
By the end of this lesson, students will be able to:
Use a model to show that the atoms in glucose and oxygen are rearranged into carbon dioxide and water, with every atom and all of the mass conserved
Use bond energies to show that forming the bonds of the products releases more energy than breaking the bonds of the reactants takes in, giving a net release of energy
Analyze gas data from living things and explain it with the inputs and outputs of respiration
Explain where the released energy goes: part to cell work and part to thermal energy
Critique and revise models of respiration that break conservation of matter or of energy
Prior Knowledge Required
Students should already be comfortable with:
Food is rearranged into new molecules that support growth or release energy MS-LS1-7
Atoms are conserved in chemical reactions MS-PS1-5
Photosynthesis makes glucose and releases oxygen HS-LS1-5
Reading chemical formulas and coefficients, and using rounded molar masses (C 12, H 1, O 16 g/mol)
Rates from a table or graph (change divided by time)
Have students breathe normally onto a cold window or a mirror, or show a photo of breath fog on a cold day. Then pose the question.
Warm-Up Prompt
"You ate a sandwich yesterday. Some of its atoms are now leaving your body with every breath. Which atoms, and in what molecules? Where did the energy of the sandwich go? Draw a model with arrows for matter and a different kind of arrow for energy."
Share a few models. Many students say food is turned into energy, or leave carbon dioxide out of their model. Keep the drawings: students revise them at the end.
Direct Instruction15-20 minutes
Inputs and outputs. Cells in plants, animals, fungi and many microbes carry out cellular respiration all the time. The inputs are food molecules such as glucose and oxygen; the outputs are carbon dioxide and water, and energy is transferred. In cells with a nucleus, most of this happens in the mitochondria. The overall model is C6H12O6 + 6 O2 → 6 CO2 + 6 H2O. The many steps in between are beyond this standard.
Bonds and energy. Breaking a chemical bond always takes energy in, and forming a bond always releases energy. Respiration breaks the bonds in glucose and oxygen and forms the bonds in carbon dioxide and water. Because the product bonds are stronger overall, more energy is released when they form than was needed to break the reactant bonds. Part of the net energy is captured in ATP, which carries it to cell work such as muscle contraction, and the rest becomes thermal energy. Use Diagram 1 for the system and Diagram 2 for the energy accounting.
Atom balance of the model
Count the atoms on each side of C6H12O6 + 6 O2 → 6 CO2 + 6 H2O.
Result: Carbon 6 = 6. Hydrogen 12 = 12. Oxygen 6 + 12 = 18 on the left and 12 + 6 = 18 on the right. No atom is made or lost; the same atoms are joined in new ways.
Mass balance for one mole
Using rounded molar masses, one mole of glucose is 180 g, O2 is 32 g/mol, CO2 is 44 g/mol and H2O is 18 g/mol.
Result: Inputs: 180 g + 6 × 32 g = 372 g. Outputs: 6 × 44 g + 6 × 18 g = 264 g + 108 g = 372 g. Mass is conserved.
Bond energy model
Average bond energies (kJ/mol): C-C 348, C-H 413, C-O 358, O-H 463, O=O 498, C=O in CO2 799. A glucose molecule has 5 C-C, 7 C-H, 7 C-O and 5 O-H bonds.
Result: Energy in to break bonds: glucose 9,452 kJ plus 6 O=O at 498 kJ, total 12,440 kJ. Energy out when bonds form: 12 C=O and 12 O-H, total 15,144 kJ. Net: 15,144 - 12,440 = 2,704 kJ released, within about 6% of the 2,870 kJ per mole used on this page (average bond energies are estimates).
Gas exchange data from a person
Invented data: during steady exercise fueled mainly by carbohydrate, a runner takes in 2.0 L of O2 per minute and gives off 2.0 L of CO2 per minute.
Result: The ratio is 2.0 ÷ 2.0 = 1.0, which matches the 6 O2 used for every 6 CO2 made (equal gas volumes hold equal numbers of molecules at the same temperature and pressure). Over 30 minutes the runner gives off 60 L of CO2.
Following the mass out of the body
A person respires 90 g of glucose, which is 0.5 mol.
Result: O2 used: 3 mol × 32 = 96 g. CO2 made: 3 mol × 44 = 132 g. Water made: 3 mol × 18 = 54 g. Check: 90 + 96 = 186 g = 132 + 54 g. The mass that enters as glucose and oxygen leaves as the two products.
After the examples, ask: "Where in the bond energy model does the energy come from, if every bond in glucose must be broken?" Students should point to the difference between the two totals, not to the breaking of bonds.
Guided Practice15 minutes
Pairs analyze invented data from a sealed 1 L plastic chamber holding germinating wheat seeds, with sensors for oxygen and carbon dioxide. The table shows the change from the starting values.
Guided practice data: gas changes around germinating wheat seeds (invented)
Time (min)
Drop in O2 (ppm)
Rise in CO2 (ppm)
0
0
0
10
600
590
20
1,200
1,210
30
1,800
1,800
Find the rate of O2 use and of CO2 release over 30 minutes, in ppm per minute.
Find the ratio of CO2 released to O2 used at 10, 20 and 30 minutes. Compare the ratios with the coefficients in the model.
Which inputs and outputs of the model do these data test, and which do they not test?
Write a claim, evidence and reasoning statement: "The seeds are carrying out cellular respiration." Include one number.
Independent Practice10-15 minutes
Each student completes a system model for 36 g of glucose (0.2 mol) respired by muscle cells, using rounded molar masses and about 2,870 kJ released per mole of glucose. They find the mass of O2 used, the masses of CO2 and water made, and the energy released, and they check that mass is conserved.
Then they critique this sentence from a classmate: "The 36 g of glucose was turned into energy, so it is gone." The critique must use their mass totals and say what happened to the energy.
Closure5 minutes
Exit ticket: "Name the two inputs and two outputs of cellular respiration. Then explain in one sentence why respiration releases energy even though every bond in glucose has to be broken." Students return to their warm-up drawing and add the missing arrows for matter and energy.
Differentiation Strategies
For Struggling Students
Give an atom tally table with rows for C, H and O and columns for "in" and "out", and have students fill it in from the model kit before using the equation
Provide the bond energy totals and ask students only for the difference and its meaning, before they compute the totals themselves
Use two colors of arrows on every model: one for matter and one for energy, so the two are never mixed up
For Advanced Students
Ask students to explain why the bond energy estimate differs from the measured value, and which assumption in the model causes the gap
Have students compare the inputs and outputs of respiration with those of photosynthesis and explain how the two processes cycle the same atoms
Ask students to design a test of whether germinating seeds respire faster in light or in dark, with a way to separate respiration from photosynthesis
Assessment Guidance
What to Look For
Check that models show both inputs (a food molecule and oxygen) and both outputs (carbon dioxide and water) with atoms conserved. Look for students who say energy is released when bonds break, who say matter turns into energy, or who leave out the thermal energy. In data work, look for rates computed from change over time and for claims that cite a number. Do not ask students to name or order the steps of respiration; the Assessment Boundary rules that out.
02
Classroom Activities
3 Activities
1
Model Kit: Break the Bonds, Form New Ones
20 minPairs
Pairs build one glucose molecule and six oxygen molecules, take every bond apart while keeping a tally of each kind of bond broken, and then build six carbon dioxide and six water molecules while tallying the bonds formed. They use the tallies and a bond energy table to account for the energy.
Materials per Pair
Model kit pieces: 6 carbon, 12 hydrogen and 18 oxygen atoms, with single bonds and flexible bonds for double bonds
Bond energy card: C-C 348, C-H 413, C-O 358, O-H 463, O=O 498, C=O in CO2 799 kJ/mol
Tally sheet with two columns: bonds broken and bonds formed
Procedure
Build glucose from the structure card, and build 6 O2 molecules with a double bond in each.
Take the molecules apart one bond at a time and tally each bond broken by type.
Build 6 CO2 and 6 H2O from the same pieces and tally each bond formed. Every piece must be used.
Multiply each tally by its bond energy and add each column.
Safety: keep small pieces off the floor and out of mouths; return the kit with every piece counted.
Discussion Questions
How many bonds did you break in total, and how many did you form? Does a larger number of bonds mean more energy?
Which column has the larger total, and what does the difference stand for?
Your tallies say nothing about how fast the reaction goes or in what order bonds break. Why is that fine for this model? (The steps are beyond this standard.)
Modification for Distance Learning
Students use a free online molecule builder or a drawing of each molecule with every bond numbered, and submit the tally sheet.
2
Seed Respiration Lab: Is Anything Happening in There?
30 minGroups of 3-4
Groups compare carbon dioxide release from germinating peas, dry peas and plastic beads of the same volume. They use either a CO2 sensor in a clear plastic chamber or bromothymol blue, an indicator that turns from blue to green to yellow as carbon dioxide dissolves in it. This lab avoids the potassium hydroxide respirometer, which uses a corrosive chemical.
Procedure
The day before, soak untreated dried peas from a grocery store in tap water. Do not use garden seed from packets, which may be coated with fungicide.
Sensor option: place 25 g of germinating peas in the chamber with the sensor, close it and record CO2 every 2 minutes for 10 minutes. Repeat with 25 g of dry peas and with plastic beads of equal volume.
Indicator option: put 10 mL of dilute bromothymol blue in each of three capped plastic vials, rest a cotton ball on a mesh above the liquid, and put the seeds or beads on the cotton so they never touch the liquid. Compare colors every 10 minutes against a printed color scale.
Safety: wear goggles; bromothymol blue can irritate eyes and stains skin and clothing, so rinse any splash with water and wipe spills at once; do not eat the peas; students with a legume allergy should wear gloves or take the data role; wash hands after the lab.
Sample Data (invented)
CO2 (ppm) at 0, 2, 4, 6, 8 and 10 minutes. Germinating peas: 450, 530, 610, 690, 770, 850. Dry peas: 450, 452, 454, 455, 457, 460. Plastic beads: 450 at every reading.
Discussion Questions
Find the rate for each chamber in ppm per minute. How many times faster is the germinating pea chamber than the dry pea chamber?
Why are the plastic beads part of the design, and what does their flat line rule out?
The dry peas show a small rise. What does this suggest about dry seeds?
Which input of respiration could you measure next, and what would you predict?
Challenge Variation
Groups repeat the germinating pea trial with the chamber sitting in a tub of cool water and in a tub of warm (not hot) tap water, predict the effect of temperature on the rate, and explain the result with the model.
3
Model Critique Gallery
20 minGroups of 3-4
Four student models of cellular respiration are posted around the room. Each has at least one flaw. Groups rotate every 4 minutes, write a critique on a sticky note that names the flaw and the evidence against it, and then choose one model to redraw correctly.
The Four Models
Model 1: "During respiration the cell makes new energy, which it stores in its mitochondria."
Model 2: "C6H12O6 + O2 → CO2 + H2O + energy"
Model 3: "The carbon dioxide we breathe out is the oxygen we breathe in with a carbon from the air stuck to it."
Model 4: "Respiration only happens when we exercise and need extra energy."
Discussion Questions
Which model breaks conservation of matter? Show it with an atom count.
Which model breaks conservation of energy, and how would you rewrite it?
What evidence from today's lab or data speaks against Model 4?
Where do the carbon atoms in exhaled CO2 really come from, and what evidence in this lesson supports your answer?
Modification for Distance Learning
Post the four models on a shared slide deck and have groups add comments on each slide, then submit one redrawn model.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A System Model of Cellular Respiration
Glucose and oxygen enter the cell; carbon dioxide and water leave. The atom counts match on both sides, so matter is conserved. Energy is not an ingredient: it is transferred because forming the product bonds releases more energy than breaking the reactant bonds takes in. Part of that energy is captured in ATP and the rest becomes thermal energy.
Diagram 2: Bond Energy Accounting for One Mole of Glucose
Drawn to scale from the average bond energies in the third worked example. The red segment is the difference between the energy released when product bonds form and the energy taken in to break reactant bonds. The estimate is close to the 2,870 kJ per mole used on this page; average bond energies are not exact for every molecule.
04
Homework Assignment
~30 min
HS-LS1-7 Homework: Matter and Energy in Cellular Respiration
Directions: Data sets are invented for practice unless a problem says otherwise. Use rounded molar masses (C 12, H 1, O 16 g/mol) and about 2,870 kJ released per mole of glucose. You do not need the steps of respiration. Show your work and name your evidence.
Part 1: Following the Atoms (Problems 1-2)
A student respires 45 g of glucose (0.25 mol). (a) Find the mass of O2 used and the masses of CO2 and water made. (b) Show that mass is conserved. (c) What fraction of the product mass is carbon dioxide, and how does that product leave the body?
Draw a system model of respiration in one muscle cell. Show where each input comes from (which body system delivers it) and where each output goes. Label every arrow as matter or energy, and add atom counts for one glucose molecule. Then explain why a person breathes faster during exercise, using your model.
Part 2: Accounting for Energy (Problems 3-4)
Data only (this is not a classroom lab, because it uses an open flame and peanuts): a 0.50 g piece of peanut is burned under a can holding 50 g of water, and the water warms by 12 °C. Water takes 4.18 J per gram per °C. (a) How much energy did the water gain? (b) How much is that per gram of peanut? (c) A nutrition label value is about 24 kJ per gram. Give two reasons the measurement is lower. (d) Burning and respiration have the same inputs and outputs. How is respiration different in where the energy goes?
A person at rest uses about 0.25 L of O2 per minute, and about 20 kJ of energy is released for each liter of O2 used. (a) How many liters of O2 does the person use in one day? (b) About how much energy is released per day? (c) The person is not moving. Where does this energy go? (d) Use the bond model to explain why oxygen must keep arriving for the energy release to continue.
Part 3: Data and Models (Problems 5-6)
Rates of CO2 release from germinating peas were measured at three temperatures: 10 °C, 12 ppm/min; 20 °C, 25 ppm/min; 30 °C, 48 ppm/min. Dry peas at 30 °C gave 1 ppm/min. (a) Describe the pattern and find how many times faster the rate is at 30 °C than at 10 °C. (b) Explain the pattern using the inputs and outputs of respiration. (c) Why is the dry pea trial useful? (d) Name one variable that must stay the same across the three temperatures.
A student claims: "Plants do photosynthesis instead of cellular respiration." A potted plant is sealed in a clear chamber and kept in complete darkness; the CO2 level rises from 400 ppm to 520 ppm in 60 minutes. (a) Find the rate of change. (b) Explain what the data show about the plant. (c) Revise the student's claim. (d) Predict how the CO2 level would change in bright light, and explain.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Matter
Inputs and outputs correct; atom and mass totals balance with correct arithmetic
Inputs and outputs correct with one calculation error
Energy
Explains net release as product bonds releasing more than reactant bonds take in; tracks energy to work and thermal energy
Says energy is released but gives no bond reasoning, or leaves out thermal energy
Data Analysis
Rates and ratios computed with units and used as evidence
Numbers computed but not linked to the claim
Models
Model labeled, separates matter from energy, and is revised when the evidence calls for it
Model incomplete or mixes matter and energy arrows
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Data sets are invented unless a question says otherwise. Use rounded molar masses (C 12, H 1, O 16 g/mol). No question asks for the steps of respiration. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Slices of fresh potato, whose cells are still alive, are sealed in a dark jar of air for an hour. If the potato cells are carrying out cellular respiration, which change in the jar's air should sensors show?
Answer: A
Respiration uses oxygen and releases carbon dioxide, so O2 falls and CO2 rises. Choice B describes photosynthesis, which cannot happen in a dark jar. Choice D ignores that living plant cells respire.
Question 2 of 20 · Multiple Choice
A student lists the products of cellular respiration as "carbon dioxide and energy." Which output of the model is missing?
Answer: B
The model is C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, so water is the missing product; the hydrogen atoms of glucose end up in it. Choices A and C are inputs, not outputs. Choice D is not in the model at all.
Question 3 of 20 · Multiple Choice
Two glucose molecules are respired completely. How many hydrogen atoms end up in the water that is made?
Answer: C
Each glucose has 12 hydrogen atoms, so 2 glucose molecules have 24, and all of them end up in the 12 water molecules made (12 × 2 = 24). Choice A counts the hydrogen in only one glucose. Choice B counts the water molecules from one glucose instead of atoms.
Question 4 of 20 · Multiple Choice
Using rounded molar masses (glucose 180 g/mol, O2 32 g/mol), what mass of oxygen is needed to respire 360 g of glucose?
Answer: B
360 g is 2 mol of glucose, which needs 12 mol of O2: 12 × 32 = 384 g. Choice A is the oxygen for only 1 mol of glucose. Choice D is the mass of CO2 made (12 × 44 g), not the oxygen used.
Question 5 of 20 · Multiple Choice
Which statement about bonds in cellular respiration is correct?
Answer: D
Breaking any bond takes energy in; forming bonds releases energy. The product bonds release more than the reactant bonds take in, so there is a net release. Choice A is a frequent misconception. Choice C contradicts the fact that bond breaking always takes energy in.
Question 6 of 20 · Multiple Choice
In a bond energy model of a reaction, breaking the reactant bonds takes in 5,000 kJ and forming the product bonds releases 6,300 kJ. What is the net result?
Answer: A
Net = 6,300 - 5,000 = 1,300 kJ, and since more is released than taken in, the reaction releases 1,300 kJ overall. Choice B has the sign reversed. Choice C adds the two totals instead of subtracting.
Question 7 of 20 · Multiple Choice
Invented data: in a sealed chamber, germinating beans raise the CO2 level by 300 ppm in 10 minutes. What is the rate of CO2 release?
Answer: C
Rate = 300 ppm ÷ 10 min = 30 ppm/min. Choice B forgets to divide by the time. Choice D multiplies by the time, and choice A divides by 100.
Question 8 of 20 · Multiple Choice
Germinating seeds release carbon dioxide much faster than dry seeds of the same kind. Which explanation fits the respiration model best?
Answer: C
Growing cells use a lot of energy, so they break down stored food with oxygen quickly and release CO2. Choice D breaks conservation of atoms: water has no carbon. Choice A is wrong because dry seeds are alive, respire very slowly and store food.
Question 9 of 20 · Multiple Choice
A person is respiring only glucose and takes in 2.4 L of O2 per minute. According to the model, about how much CO2 should the person give off per minute?
Answer: A
The model uses 6 O2 for every 6 CO2 made, and equal gas volumes hold equal numbers of molecules, so the CO2 volume equals the O2 volume: 2.4 L. Choice B divides by 6 and choice C multiplies by 6, as if the coefficients applied to only one gas.
Question 10 of 20 · Multiple Choice
A person respires glucose. Where do the carbon atoms of that glucose end up?
Answer: B
In the model, all 6 carbon atoms of glucose end up in the 6 CO2 molecules, which leave through the lungs. Choice A is wrong because water has no carbon. Choice C breaks conservation of matter: atoms are rearranged, not turned into energy.
Question 11 of 20 · Multiple Choice
A student writes: "Respiration destroys the oxygen we breathe in, and that is where the energy comes from." Which is the best critique?
Answer: D
Atoms are conserved: the 12 oxygen atoms of 6 O2 are still there after the reaction, joined into the products. The energy is the net difference in bond energy. Choice A mistakes a drop in O2 gas for atoms being destroyed. Choice C contradicts the model.
Question 12 of 20 · Multiple Choice
Mushrooms are fungi and cannot carry out photosynthesis. Fresh mushrooms are sealed in a clear jar on a sunny windowsill, and the CO2 level in the jar rises. What best explains this?
Answer: C
Living fungal cells respire, so the jar gains CO2 and loses O2. Choice A is ruled out by the question, and photosynthesis would lower CO2, not raise it. Choice B breaks conservation of atoms: oxygen alone cannot become carbon dioxide.
Question 13 of 20 · Multiple Choice
According to the system model, which change would lower the amount of energy released by a muscle cell's respiration each minute?
Answer: D
Oxygen is an input; with less of it arriving, fewer glucose molecules can be respired each minute, so less energy is released. Choices A and B remove or add outputs, which does not limit the inputs.
Question 14 of 20 · Multiple Choice
About 20 kJ of energy is released for each liter of O2 used. A runner uses 2.5 L of O2 per minute for 20 minutes. About how much energy is released?
Answer: B
O2 used: 2.5 × 20 = 50 L, and 50 × 20 = 1,000 kJ. Choice A is the liters of oxygen, not the energy. Choice C multiplies 20 by 20 and leaves out the 2.5 L per minute.
Question 15 of 20 · Short Answer
Using rounded molar masses, a cell respires 27 g of glucose (0.15 mol). Find the masses of O2 used, CO2 made and water made, and show that mass is conserved.
Each mole of glucose uses 6 mol of O2 and makes 6 mol each of CO2 and water, so 0.9 mol of each. O2: 0.9 × 32 = 28.8 g; CO2: 0.9 × 44 = 39.6 g; water: 0.9 × 18 = 16.2 g. Check: 27 + 28.8 = 55.8 g and 39.6 + 16.2 = 55.8 g.
Question 16 of 20 · Short Answer
About 2,870 kJ is released per mole of glucose. How much energy is released when 54 g of glucose (0.3 mol) is respired, and where does it go?
0.3 × 2,870 = 861 kJ. Part is captured in ATP and used for cell work such as muscle contraction and building molecules, and the rest becomes thermal energy, which helps keep the body warm.
Question 17 of 20 · Short Answer
A student's model is "glucose → energy + CO2." List what is missing or wrong, and write the complete model.
Missing: oxygen as an input and water as an output, and the atoms do not balance. Energy is not a substance made from glucose. Complete model: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, with a net transfer of energy because the product bonds release more than the reactant bonds take in.
Question 18 of 20 · Short Answer
At rest, a person uses 0.30 L of O2 per minute and gives off 0.24 L of CO2 per minute. Find the ratio of CO2 made to O2 used. Does it match the glucose model? What might explain the difference?
Ratio = 0.24 ÷ 0.30 = 0.8. The glucose model predicts 6 CO2 for 6 O2, a ratio of 1.0, so the data do not match glucose alone. The person is also respiring another food molecule, such as fat, that uses more O2 for each CO2 made.
Question 19 of 20 · Short Answer
In a model of respiring one mole of a typical fat (totals estimated from average bond energies and rounded), breaking the bonds of the fat and oxygen takes in about 97,000 kJ and forming the bonds of the products releases about 127,000 kJ. A classmate says, "The cell gets 127,000 kJ." Explain the error and find the net energy transfer.
The 127,000 kJ is only the energy released when product bonds form; 97,000 kJ had to be taken in first to break the reactant bonds. The cell gets the net amount: 127,000 - 97,000 = 30,000 kJ released, more than ten times the energy from one mole of glucose. That is why respiration is described as a net transfer of energy.
Question 20 of 20 · Short Answer
The inside of a compost pile full of microbes and food scraps can get warm to the touch, even on a cool day. Use the model of cellular respiration to explain why.
The microbes respire the food molecules in the scraps, using oxygen and releasing carbon dioxide and water. Each time, the product bonds release more energy than the reactant bonds take in, and much of that net energy becomes thermal energy, which builds up inside the pile.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS1-7 mean?
HS-LS1-7 asks students to use a model to show that cellular respiration is a chemical process in which the bonds of food molecules and oxygen break, new bonds form in new compounds, and energy is transferred overall. The emphasis is on inputs and outputs. The code stands for High School, Life Science, core idea 1 (From Molecules to Organisms: Structures and Processes), performance expectation 7.
Do students need to learn glycolysis and the Krebs cycle for HS-LS1-7?
No. The official Assessment Boundary says assessment should not include identification of the steps or specific processes of cellular respiration. Glycolysis, the Krebs cycle and the electron transport chain belong to later courses. The standard asks for a model of what goes in, what comes out and how energy is accounted for.
Is HS-LS1-7 taught in Biology?
Yes, it is usually taught in high school Biology, often right after photosynthesis. It uses chemistry ideas such as balancing atoms and bond energy, so it also connects well with a chemistry course and with HS-PS1-4.
What models work well for HS-LS1-7?
System diagrams with inputs and outputs, balanced equations used as atom inventories, molecular model kits and bond energy bar charts all work. Strong lessons pair a model with data, such as gas measurements from seeds or people, and ask students where the model falls short.
Why do teachers describe respiration in terms of bonds?
Because the standard defines respiration that way: bonds of food and oxygen molecules break and bonds in new compounds form. Thinking in bonds lets students see where the energy comes from without the steps of the process, and it connects biology with the chemistry of HS-PS1-4.
How is cellular respiration different from burning?
Burning glucose and respiring it have the same inputs, outputs and total energy change, but burning releases the energy all at once as heat and light. Cells release it in many small steps at body temperature, so part of it can be captured for cell work. The steps themselves are beyond this standard.
Where in the cell does cellular respiration happen?
In plant, animal and fungal cells, most of it happens in the mitochondria, with an early part in the cytoplasm. Bacteria, which have no mitochondria, carry it out in their cytoplasm and cell membrane. Students need the location only as part of the system model, not the processes at each location.
What is the role of ATP in HS-LS1-7?
ATP is the molecule that carries part of the released energy to the work a cell does, such as muscle contraction or building molecules. Students can name it in a model. How cells make ATP is one of the specific processes that the Assessment Boundary leaves out.
Does HS-LS1-7 include respiration without oxygen?
No. HS-LS1-7 models respiration with oxygen. Processes that release energy without oxygen, such as fermentation in yeast or muscles, are part of HS-LS2-3, which compares aerobic and anaerobic conditions.
How does HS-LS1-7 connect to other standards?
It builds on the middle school idea that food is rearranged into new molecules that release energy (MS-LS1-7) and on conservation of atoms (MS-PS1-5). It sits beside HS-LS1-5 (photosynthesis) and HS-PS1-4 (bond energy in reactions), and it leads to HS-LS2-3 and HS-LS2-5, where respiration becomes part of the flow of energy and the cycling of carbon in ecosystems.
07
Related Standards
6 standards
These standards connect to HS-LS1-7: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS1-7Prerequisite
Model how food is rearranged into new molecules for growth or to release energy
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