HS-LS1-5: Modeling How Photosynthesis Stores Light Energy
In plain English: HS-LS1-5 is the NGSS high school performance expectation that asks students to use a model to show how photosynthesis transforms light energy into stored chemical energy. Students trace matter (carbon dioxide and water in, glucose and oxygen out) and energy (light in, chemical energy stored in sugar) with diagrams, the balanced equation and conceptual models. It is usually taught in Biology.
Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.
Clarification Statement: Emphasis is on illustrating inputs and outputs of matter and the transfer and transformation of energy in photosynthesis by plants and other photosynthesizing organisms. Examples of models could include diagrams, chemical equations, and conceptual models.
Assessment Boundary: Assessment does not include specific biochemical steps.
Next Generation Science Standards · Disciplinary Core Idea: From Molecules to Organisms: Structures and Processes · Official standard
Students build and use models that show how photosynthesis transforms light energy into stored chemical energy. They track two things separately: matter (6 CO₂ and 6 H₂O are rearranged into one C₆H₁₂O₆ and 6 O₂, with every atom conserved) and energy (light absorbed by chlorophyll becomes chemical energy in the glucose and oxygen, and the rest leaves as thermal energy). Students use three kinds of models: a labeled system diagram, the balanced chemical equation and a conceptual model they critique and revise. They also analyze invented data from classroom-style investigations as evidence for the model.
The official Clarification Statement reads: "Emphasis is on illustrating inputs and outputs of matter and the transfer and transformation of energy in photosynthesis by plants and other photosynthesizing organisms. Examples of models could include diagrams, chemical equations, and conceptual models." The Assessment Boundary reads: "Assessment does not include specific biochemical steps." So this lesson treats the chloroplast as a system with inputs and outputs. The light-dependent reactions, the Calvin cycle, ATP and electron carriers are beyond this standard and do not appear in any activity, homework or quiz item.
Learning Objectives
By the end of this lesson, students will be able to:
Use a system diagram to show the matter inputs (carbon dioxide, water) and outputs (glucose, oxygen) of photosynthesis and the energy input (light) and outputs (stored chemical energy, thermal energy)
Use the balanced equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ to show that atoms and mass are conserved
Calculate how much light energy a photosynthesizing organism stores as chemical energy, using 2,870 kJ per mole of glucose
Analyze data from photosynthesis investigations and explain the results with a model
Critique a conceptual model of photosynthesis and revise it so matter and energy are tracked correctly
Prior Knowledge Required
Students should already be comfortable with:
Photosynthesis in the cycling of matter and flow of energy into and out of organisms MS-LS1-6
Atoms are conserved in chemical reactions, so mass is conserved MS-PS1-5
Cell parts and their functions, including chloroplasts MS-LS1-2
Reading a chemical formula such as C₆H₁₂O₆ and counting the atoms of each element
Energy is conserved: it changes form but is not created or destroyed
Show a photo of a large field pumpkin next to a pumpkin seed. Students write alone for two minutes, then share with a partner.
Warm-Up Prompt
"A pumpkin seed with a mass of about 0.3 grams grows into a plant that makes a 9-kilogram pumpkin in one summer. Where did the matter in the pumpkin come from? Where did the energy stored in it come from?"
Record answers in two columns on the board, "matter" and "energy," without correcting them yet. Many students name soil, fertilizer or water as the source of the mass, and some say the Sun's light "turned into" the pumpkin. Keep both ideas visible: by the end of the lesson students should be able to explain, with a model, where the atoms in the pumpkin came from and why light is energy, not matter.
Direct Instruction20 minutes
Part 1: The system model. Project Diagram 1. Define the system as a chloroplast inside a leaf cell and draw the boundary. Ask students to sort every arrow into matter or energy. Stress three points:
Matter in: carbon dioxide enters leaves from the air through stomata; water travels up from the roots. Algae and cyanobacteria take both from the water around them.
Energy in: chlorophyll absorbs light, mostly blue and red wavelengths, and reflects much of the green light, which is why leaves look green. Light is energy, not matter: it adds no atoms.
Out: the atoms leave as glucose and oxygen. Part of the absorbed light energy is now stored as chemical energy in the glucose-oxygen system; the rest leaves as thermal energy. Energy changes form but the total is conserved.
Part 2: The equation as a model. Write 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ and work through the examples below. Tell students the value you use: about 2,870 kJ of chemical energy is stored for every mole of glucose made (a standard textbook value). Remind them that a chemical equation hides the many steps inside the chloroplast; for this standard the equation summarizes inputs and outputs only.
Chemical equation model: counting atoms
Show that 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ is balanced by counting each element on both sides.
Result: Carbon: 6 = 6. Hydrogen: 6 × 2 = 12 and 12. Oxygen: 6 × 2 + 6 × 1 = 18 and 6 + 6 × 2 = 18. Every atom is conserved.
Chemical equation model: tracking mass
Using C = 12.01, H = 1.008 and O = 16.00 g/mol, compare the mass of the reactants and products for one mole of glucose made.
Result: Reactants: 6(44.01) + 6(18.016) = 264.06 + 108.096 = 372.156 g. Products: 180.156 + 6(32.00) = 372.156 g. Mass is conserved.
Energy accounting: stored chemical energy
A garden row of bean plants makes 0.25 mol of glucose in one sunny day. Using 2,870 kJ per mole, how much light energy did it store as chemical energy?
Result: 0.25 mol × 2,870 kJ/mol = 717.5 kJ stored in the glucose and oxygen
Energy accounting: how much light is stored
An algae culture absorbs 40,000 kJ of light energy in a day and makes 0.35 mol of glucose (invented data). What percent of the absorbed light energy was stored?
Result: 0.35 × 2,870 = 1,004.5 kJ stored; 1,004.5 ÷ 40,000 ≈ 2.5%. The other 38,995.5 kJ leaves mostly as thermal energy.
Conceptual model: separating matter and energy
A student writes "light + water → sugar." Revise the model so it tracks matter and energy correctly.
Result: Matter: CO₂ + H₂O → C₆H₁₂O₆ + O₂ (carbon comes from CO₂, not from light). Energy: light energy → chemical energy + thermal energy.
Use Diagram 2 with the fourth example so students see how thin the stored slice is. Close the part by returning to the warm-up columns: which ideas does the model support, and which does it rule out?
Guided Practice15 minutes
Show the invented data below from a common demonstration: a sprig of elodea (waterweed) in a test tube of water with a little baking soda, lit by an LED lamp, with the water temperature checked by thermometer before each trial. Pairs answer the questions, then the class discusses.
Oxygen bubbles from an elodea sprig in 5 minutes at four lamp distances (invented data)
Lamp distance
Trial 1
Trial 2
Trial 3
Mean
10 cm
42
45
39
42
20 cm
30
28
32
30
30 cm
17
19
18
18
40 cm
9
11
10
10
Lamp off, tube covered
0
1
0
0.3
Describe the pattern. (The mean count falls at every step as the lamp moves from 10 cm to 40 cm: 42, 30, 18, 10.)
Which arrow in Diagram 1 do the bubbles represent, and which arrow does the lamp distance change? (The bubbles are mostly oxygen, a matter output; the distance changes the light energy input.)
What does the covered tube show? (With almost no light input, almost no oxygen is released, so light is required.)
Why check the temperature before each trial? (So that a change in warmth is not the reason the rate changed.)
Listen for students who say the plant "makes more energy" when it is closer to the lamp. Redirect: the plant absorbs more light energy and stores more of it as chemical energy; it does not create energy.
Independent Practice10-15 minutes
Students draw their own system model for a different organism: a saguaro cactus, whose green stem carries out photosynthesis. The model must show the system boundary, two matter inputs, two matter outputs, the energy input and both energy outputs, with matter and energy arrows drawn differently. Then they answer: on one day the cactus makes 0.1 mol of glucose. How much light energy did it store as chemical energy? (0.1 × 2,870 = 287 kJ.) How many moles of carbon dioxide did it take in? (0.6 mol.) Collect the models to check for the errors listed in the assessment guidance.
Closure5 minutes
Exit ticket: (1) Name the two matter inputs and the one energy input of photosynthesis. (2) A plant makes 3 glucose molecules. How many water molecules does it use? (18.) (3) Draw one arrow for matter and one for energy that cross the boundary of a leaf, and label each.
Differentiation Strategies
For Struggling Students
Give a partly finished system diagram with empty boxes for inputs and outputs and a word bank (carbon dioxide, water, glucose, oxygen, light energy, thermal energy)
Use two colors every time: one for matter arrows and one for energy arrows, so students can see the two stories side by side
Count atoms with physical pieces (Activity 2) before counting them on paper
For Advanced Students
Ask students to compare the percent of absorbed light stored by two invented crops and propose which other inputs could limit the rate on a bright day
Ask why the chemical energy is best described as stored in the glucose-oxygen system rather than "in the bonds of glucose," and connect this to cellular respiration (HS-LS1-7)
Ask students to extend their model to show where the sugar goes next inside the plant (beyond this standard, see HS-LS1-6)
Assessment Guidance
What to Look For
Strong models keep matter and energy separate: arrows for carbon dioxide, water, glucose and oxygen carry atoms, and arrows for light and thermal energy carry energy only. Watch for these errors: light drawn as an ingredient that becomes part of the sugar, soil named as the source of the plant's mass, energy that disappears or is "used up" with no thermal output, and oxygen and carbon dioxide reversed. In calculations, check that students multiply moles by 2,870 kJ/mol and that they state the percent of absorbed light energy that was stored, not the reverse ratio. Do not grade on the names of biochemical steps: the standard does not assess them.
02
Classroom Activities
3 Activities
1
Floating Leaf Disks
35 minSmall groups (3-4)
Students run a classroom-safe investigation in which spinach leaf disks sink and then float as photosynthesis produces oxygen. They use the results as evidence for the matter output and the light energy input in their model.
Safety
Wear safety goggles: the solution can squirt out of a syringe
Use plastic syringes with no needles
Keep lamp cords and plugs away from the cups, and wipe up spills right away
Procedure
Make the solution: about 1/8 teaspoon of baking soda (sodium bicarbonate) in 300 mL of water, plus one drop of dish soap. The bicarbonate supplies dissolved carbon dioxide
Punch 20 disks from spinach leaves with a paper hole punch or a drinking straw, avoiding large veins
Put 10 disks in a syringe, draw in about 5 mL of solution, cover the tip with a finger and pull the plunger to remove air from the leaf. Repeat until the disks sink. Do the same with the other 10 disks
Place each set of 10 disks in a clear cup with 3 cm of solution. Put one cup 15 cm under an LED lamp. Cover the other cup with foil and place it beside the first
Every 2 minutes for 16 minutes, record how many disks float in each cup
If the Lab Does Not Work: Sample Data
Invented results for the lit cup at 0, 4, 8, 12 and 16 minutes: 0, 1, 4, 8 and 10 disks floating out of 10. The foil-covered cup: 0 disks floating at every time.
Discussion Questions
Why do the disks float? Which output of your model fills the air spaces in the leaf?
In the sample data, when were half of the lit disks floating? (Between minute 8, with 4 floating, and minute 12, with 8 floating.)
Which input did the foil remove, and what happened as a result?
Where did the carbon atoms for the sugar come from in this setup?
Modification for Distance Learning
Students analyze the sample data, graph floating disks against time for both cups, and write a claim, evidence and reasoning paragraph that refers to their system model.
2
Rearrange the Atoms
20 minPairs
Pairs use molecular model kits, or colored paper circles, to act out the chemical equation as a physical model: every atom in the reactants is reused in the products, and a light energy card shows where energy enters.
Procedure
Give each pair 6 black carbon pieces, 12 white hydrogen pieces and 18 red oxygen pieces, plus one card labeled "light energy"
Build 6 carbon dioxide molecules and 6 water molecules. Check that no pieces are left over
Place the light energy card next to the reactants, then take the molecules apart and build 1 glucose (6 C, 12 H, 6 O in one cluster) and 6 oxygen molecules
Move the light energy card to sit with the glucose and oxygen, and write one sentence about what the card now stands for (stored chemical energy)
Discussion Questions
Did you need any extra atoms, or have any left over? What does that tell you about mass?
How many pieces of each color would you need to build the reactants for 5 glucose molecules? (30 carbon, 60 hydrogen, 90 oxygen.)
The card is not an atom. Why is it a better way to show light than adding a piece to the glucose?
What does the physical model leave out that a real chloroplast does?
Variation: Paper Circles
Without model kits, pairs cut circles from colored paper and tape them into molecules on a sheet, then peel and re-tape them into the products.
3
Critique and Revise the Model
25 minSmall groups (3-4)
Groups critique three flawed student models of photosynthesis against a checklist, then build one revised model on poster paper that tracks matter and energy correctly.
The Three Models
Model A: "Sunlight + carbon dioxide + water → glucose." An arrow shows sunlight becoming part of the glucose molecule, and oxygen is missing
Model B: "Oxygen + water + light → glucose + carbon dioxide." The gases are reversed
Model C: All the matter arrows are correct, but the light energy arrow ends at the chloroplast with the note "energy used up," and nothing leaves as thermal energy or stored energy
Checklist
Is there a clear system boundary?
Are there two matter inputs and two matter outputs, all correct?
Is energy drawn with a different kind of arrow from matter?
Does all the incoming energy go somewhere (stored chemical energy or thermal energy)?
Do the atoms balance?
Discussion Questions
Which checklist item does each model fail?
What would you ask the author of Model A to explain about where the carbon atoms come from?
How would Model C change if you added an energy output?
Modification for Distance Learning
Share the three models on one slide deck. Each group annotates one model with comments, then builds its revised model on a shared slide for a class gallery.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A System Model of Photosynthesis
Solid arrows carry matter and dashed arrows carry energy. Carbon dioxide and water enter the chloroplast and leave as glucose and oxygen, with every atom conserved. Light energy enters; part of it leaves the system stored as chemical energy in the glucose and oxygen, and the rest leaves as thermal energy.
Diagram 2: Energy Accounting for an Algae Culture
The bar is drawn to scale for the invented data in the fourth worked example. Only a small part of the absorbed light energy is stored as chemical energy; the rest is released, mostly as thermal energy. The total is still 40,000 kJ: energy changes form but is conserved.
04
Homework Assignment
~30 min
HS-LS1-5 Homework: Modeling Photosynthesis
Directions: Show all calculations with units. Use 2,870 kJ of stored chemical energy per mole of glucose. In every model, draw matter arrows and energy arrows differently and label each one. All data sets are invented for practice.
Part 1: The Equation as a Model (Problems 1-2)
A kelp cell makes 4 glucose molecules. Using the balanced equation, how many carbon dioxide molecules and water molecules does it use, and how many oxygen molecules does it release? Count the carbon, hydrogen and oxygen atoms on each side to show they balance.
Over two weeks, a sunflower makes 0.500 mol of glucose. Using the molar masses CO₂ = 44.01, H₂O = 18.016, C₆H₁₂O₆ = 180.156 and O₂ = 32.00 g/mol, find the mass of carbon dioxide and water it used and the mass of glucose and oxygen it made. Show that the total mass of the reactants equals the total mass of the products.
Part 2: Energy in the Model (Problems 3-4)
A small plot of potato plants absorbs 115,000 kJ of light energy over one week and makes 0.8 mol of glucose (invented data). (a) Using 2,870 kJ/mol, how much energy did it store as chemical energy? (b) What percent of the absorbed light energy is that? (c) How much absorbed energy was not stored, and in what form did most of it leave?
Draw a system model for photosynthesis in a single-celled alga floating in a lake on a summer day. Show the system boundary, two matter inputs, two matter outputs, the energy input and two energy outputs, using different arrows for matter and energy. Then use your model to predict what happens to the sugar stored in the alga if ice and snow cover the lake and block the light for several weeks, and explain why.
Part 3: Evidence from Data (Problems 5-6)
A bean plant is sealed in a clear chamber with a carbon dioxide sensor (invented data). With the lamp on, CO₂ falls from 400 ppm to 310 ppm in 60 minutes. With the lamp off, CO₂ rises from 400 ppm to 430 ppm in 60 minutes. (a) Find the rate of change in ppm per minute for each condition. (b) Explain both results with your photosynthesis model and the fact that the plant carries out cellular respiration all the time. (c) If respiration continues at the same rate with the lamp on, estimate the rate at which photosynthesis alone removes CO₂.
Leaf disks were tested under red, blue and green filters and with no filter, using the same lamp (invented data). After 15 minutes, the number of disks floating out of 10 was: red 8, blue 7, green 2, no filter 9. (a) Write each result as a percent. (b) Which color gave the lowest rate? (c) Use your model, including what chlorophyll does, to explain the pattern.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
No Credit (0 pts)
Matter Tracking
Correct molecule counts and masses; atoms and mass shown to balance
Correct method with one counting or arithmetic error
Counts or masses missing or incorrect
Energy Tracking
Stored energy and percent correct, with units; unstored energy identified as mostly thermal
Stored energy correct but percent or energy output missing
Energy created, lost or not calculated
System Model
Boundary, all inputs and outputs, matter and energy arrows distinguished
One input or output missing, or arrow types mixed
Model missing or tracks light as matter
Use of Evidence
Rates or percents computed and explained with the model
Calculations correct but explanation incomplete
Data not used
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Work through the questions in order. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again. Use 2,870 kJ per mole of glucose where needed. All data are invented.
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
In a system model of photosynthesis, which two substances are the matter inputs?
Answer: B
Carbon dioxide and water supply every atom in the products. Choice A lists the outputs, a sign the student reversed the model. Choice C lists the energy input and a pigment, not the substances whose atoms end up in the sugar.
Question 2 of 20 · Multiple Choice
Which energy transformation does photosynthesis carry out?
Answer: C
Chlorophyll absorbs light energy and part of it is stored as chemical energy in the glucose and oxygen. Choice A describes the reverse, like a glow stick. Choice D treats light as matter: light carries energy but adds no atoms.
Question 3 of 20 · Multiple Choice
A seagrass leaf cell makes 8 glucose molecules. How many oxygen molecules does it release?
Answer: D
The equation gives 6 O₂ for every glucose, so 8 × 6 = 48 O₂. Choice A uses a 1:1 ratio. Choice C counts oxygen atoms (48 × 2 = 96) instead of molecules.
Question 4 of 20 · Multiple Choice
Using CO₂ = 44.01 g/mol, what mass of carbon dioxide is needed to make 2 mol of glucose?
Answer: A
Each mole of glucose needs 6 mol of CO₂, so 2 mol needs 12 mol: 12 × 44.01 = 528.12 g. Choice B forgets the coefficient 6 (2 × 44.01). Choice C is the CO₂ for only one mole of glucose. Choice D is the mass of 2 mol of glucose itself.
Question 5 of 20 · Multiple Choice
Over one month, a tomato plant makes 1.5 mol of glucose. Using 2,870 kJ/mol, how much light energy did it store as chemical energy?
Answer: B
1.5 mol × 2,870 kJ/mol = 4,305 kJ. Choice A divides by 1.5 instead of multiplying. Choice D also multiplies by 6, as if each CO₂ molecule stored 2,870 kJ.
Question 6 of 20 · Multiple Choice
A duckweed culture absorbs 50,000 kJ of light energy and stores 1,100 kJ as chemical energy (invented data). What percent of the absorbed energy was stored?
Answer: D
1,100 ÷ 50,000 = 0.022, which is 2.2%. Choice A divides the wrong way (50,000 ÷ 1,100 ≈ 45). Choice C forgets to multiply the decimal by 100.
Question 7 of 20 · Multiple Choice
For each glucose molecule made, the reactants contain 18 oxygen atoms. How many of those oxygen atoms leave the system in the oxygen gas that is released?
Answer: C
The products are C₆H₁₂O₆ and 6 O₂. Glucose keeps 6 oxygen atoms, so 18 - 6 = 12 leave as 6 O₂ molecules (6 × 2 = 12). Choice A counts O₂ molecules instead of atoms. Choice B forgets that glucose also contains oxygen.
Question 8 of 20 · Multiple Choice
Invented data for a pond plant: at 10, 25, 50, 75 and 100 percent of full sunlight, it released 2, 5, 9, 10 and 10 mL of oxygen per hour. Which conclusion is best supported?
Answer: A
Oxygen release rises from 2 to 10 mL/h as light increases, then stays at 10 mL/h from 75% to 100%, so another input, such as carbon dioxide supply, now limits the rate. Choice B is wrong because oxygen is still released at 10 mL/h. Choice C fails: from 25% to 50% the rate goes from 5 to 9, not 10.
Question 9 of 20 · Multiple Choice
Four tubes hold bromothymol blue solution, which is yellow-green when carbon dioxide is dissolved and blue when it is removed. Tube 1: elodea, in light. Tube 2: no plant, in light. Tube 3: elodea, in the dark. Tube 4: no plant, in the dark. After 2 hours only tube 1 turns blue. Which tube shows that the color change needs the plant?
Answer: B
Tube 2 has the same light as tube 1 but no plant, and it does not change, so the plant is needed. Tube 3 is the control for light, not for the plant. Tube 1 is the test tube itself, not a control.
Question 10 of 20 · Multiple Choice
A student's model reads: "sunlight + carbon dioxide → glucose + oxygen." Which revision fixes the matter in this model?
Answer: C
Glucose has 12 hydrogen atoms and CO₂ has none, so water must be an input. Choice B would reverse part of the model. Choice D removes the energy input the standard asks students to show.
Question 11 of 20 · Multiple Choice
The model says glucose and oxygen together hold more chemical energy than carbon dioxide and water. Which observation is the best evidence for that claim?
Answer: D
Burning turns glucose and oxygen back into carbon dioxide and water, and energy comes out, so the glucose-oxygen system must have held more chemical energy. Choice A is evidence about a matter output, not about stored energy. Choice C shows absorbed light becoming thermal energy, not chemical energy.
Question 12 of 20 · Multiple Choice
A student claims only plants can transform light energy into chemical energy. Which observation contradicts the claim?
Answer: A
Euglena is a single-celled protist, not a plant, yet it releases oxygen only when light is supplied, which matches the photosynthesis model. Choice B is a fungus that gets energy from food. Choice D describes yeast breaking down sugar, not storing light energy.
Question 13 of 20 · Multiple Choice
Elodea releases more bubbles when a lamp is moved closer. A student worries the lamp's warmth, not its light, caused the change. Which added test best separates the two?
Answer: C
A dark tube at the same temperature keeps warmth but removes light, so if few bubbles appear, light is the cause. Choice A changes light and warmth together again. Choice D gives more data but does not separate the two variables.
Question 14 of 20 · Multiple Choice
A geranium leaf is partly covered with foil for two days in sunlight. A starch test then shows starch only in the uncovered part. Starch is how many plants store glucose. What does this evidence support?
Answer: B
The only difference between the two parts is light, and sugar was stored only where light entered. Choice A has no basis in the data. Choice C goes beyond the evidence: the test shows missing starch, not missing chlorophyll.
Question 15 of 20 · Short Answer
A rice leaf cell makes 10 glucose molecules. How many carbon dioxide, water and oxygen molecules are involved? Show that each element balances.
60 CO₂ and 60 H₂O are used, and 60 O₂ are released. Carbon: 60 in CO₂ and 10 × 6 = 60 in glucose. Hydrogen: 60 × 2 = 120 in water and 10 × 12 = 120 in glucose. Oxygen: 60 × 2 + 60 = 180 in the reactants and 10 × 6 + 60 × 2 = 180 in the products.
Question 16 of 20 · Short Answer
A small patch of corn plants stored 7,175 kJ of chemical energy in glucose in one hour. Using 2,870 kJ/mol, how many moles of glucose did it make, and how many moles of carbon dioxide did it take in?
7,175 ÷ 2,870 = 2.5 mol of glucose. The equation uses 6 CO₂ per glucose, so it took in 2.5 × 6 = 15 mol of CO₂.
Question 17 of 20 · Short Answer
A sensor in a pond reads 6.2 mg/L of dissolved oxygen at 8 a.m. and 10.4 mg/L at 2 p.m. on a sunny day (invented data). Find the average rate of change and explain the change with your photosynthesis model.
The change is 4.2 mg/L over 6 hours, so 0.7 mg/L per hour. Algae and water plants absorb sunlight and release oxygen as a matter output faster than organisms in the pond use it, so dissolved oxygen rises during the day.
Question 18 of 20 · Short Answer
A student's model reads: "carbon dioxide + water + chlorophyll → glucose + oxygen," and the chlorophyll arrow ends inside the glucose. Identify the error and explain how to fix it.
Chlorophyll is not a reactant: it is the pigment that absorbs light energy, and it is not used up. The atoms already balance without it (6 C, 12 H, 18 O on each side), so adding chlorophyll would put extra atoms on the left. The fix: remove chlorophyll from the reactants, draw it inside the chloroplast as the absorber, and add a separate energy arrow for light entering and chemical and thermal energy leaving.
Question 19 of 20 · Short Answer
A lettuce crop absorbs 12,000 kJ of light energy and stores 180 kJ as chemical energy (invented data). What percent was stored, and what happened to the rest? Does this break the law of conservation of energy?
180 ÷ 12,000 = 0.015, so 1.5% was stored. The other 11,820 kJ was not stored; it left the leaves mostly as thermal energy. Energy is still conserved: 180 + 11,820 = 12,000 kJ. Energy only changed form.
Question 20 of 20 · Short Answer
Plan an investigation with floating leaf disks to test whether the amount of dissolved carbon dioxide affects the rate of photosynthesis. Name the independent and dependent variables, two controlled variables, and your prediction based on the model.
Independent variable: the amount of baking soda (the carbon dioxide source), for example 0, 1/16 and 1/8 teaspoon per 300 mL. Dependent variable: the number of disks floating over time, or the time for half to float. Controlled variables: lamp type and distance, number and size of disks, volume of solution, temperature and the plant species. Prediction: disks with no baking soda float very slowly or not at all, and more carbon dioxide gives faster floating up to a point, because carbon dioxide is a matter input of the model. Safety: goggles and syringes without needles.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS1-5 mean?
HS-LS1-5 asks students to use a model to show how photosynthesis transforms light energy into stored chemical energy. "HS" means high school, "LS1" is the life science core idea From Molecules to Organisms, and 5 is its number. Students must show the inputs and outputs of matter (carbon dioxide and water in, glucose and oxygen out) and how energy is transferred and transformed, using diagrams, chemical equations or conceptual models.
Does HS-LS1-5 include the light reactions and the Calvin cycle?
No. The official Assessment Boundary says assessment "does not include specific biochemical steps." Teachers may mention that photosynthesis happens in many steps, but the light-dependent reactions, the Calvin cycle, ATP and electron carriers are beyond this standard. The focus is the chloroplast as a system: what goes in, what comes out and where the energy goes.
Is HS-LS1-5 taught in Biology or Chemistry?
It is usually taught in high school Biology or Life Science. It uses chemistry ideas, such as balancing an equation and conservation of mass (HS-PS1-7), so it works well when the Biology and Chemistry teachers coordinate.
What counts as a "model" for this standard?
The Clarification Statement names three kinds: diagrams, chemical equations and conceptual models. A good lesson uses all three: a labeled system diagram with inputs and outputs, the balanced equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, and a conceptual model students build, critique and revise. Physical models, such as rearranging atom pieces, are also models.
Is the chemical energy stored "in the bonds" of glucose?
That phrase is common but misleading. Breaking any bond takes energy; energy is released only when new bonds form that are more stable. It is more accurate to say the energy is stored in the chemical system of glucose and oxygen, compared with carbon dioxide and water. When cells later combine glucose with oxygen in cellular respiration (HS-LS1-7), that energy is released.
What energy value should we use for glucose?
This lesson uses about 2,870 kJ per mole of glucose, a standard textbook value for the energy stored when glucose is made from carbon dioxide and water. Some books use a value near 2,800 kJ/mol. Either is fine if students state the value they use and apply it consistently.
Which labs work for this standard in a regular classroom?
Three classroom-safe options are the floating leaf disk lab (spinach, baking soda solution, plastic syringes without needles), counting oxygen bubbles from elodea under an LED lamp, and bromothymol blue indicator tubes that change color as a plant removes carbon dioxide. Students should wear goggles, keep lamps away from water and use no open flames.
What mistakes do students make when modeling photosynthesis?
Frequent ones are drawing light as an ingredient that becomes part of the sugar, naming soil as the source of the plant's mass, reversing oxygen and carbon dioxide, and letting energy disappear. Ask students to draw matter and energy with different arrows, and to check that every atom and every unit of energy is accounted for.
Do only plants carry out photosynthesis?
No. The Clarification Statement says "plants and other photosynthesizing organisms." Algae, including seaweeds such as kelp, and cyanobacteria also transform light energy into stored chemical energy. They take carbon dioxide and water from their surroundings instead of through leaves and roots.
What comes after HS-LS1-5?
HS-LS1-6 follows the carbon, hydrogen and oxygen atoms from sugar into amino acids and other large molecules. HS-LS1-7 models cellular respiration, which releases the stored energy. HS-LS2-5 scales the model up to the carbon cycle among the biosphere, atmosphere, hydrosphere and geosphere.
07
Related Standards
6 standards
These standards connect to HS-LS1-5: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS1-6Prerequisite
Explain with evidence the role of photosynthesis in the cycling of matter and flow of energy
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
