MS-LS2-3: Modeling How Matter Cycles and Energy Flows in Ecosystems
In plain English: MS-LS2-3 is the NGSS middle school performance expectation that asks students to develop a model of how matter cycles and energy flows among the living and nonliving parts of an ecosystem. Matter is used again and again and is never used up, while energy enters as sunlight and leaves as heat. It is usually taught in middle school life science.
Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.
Clarification Statement: Emphasis is on describing the conservation of matter and flow of energy into and out of various ecosystems, and on defining the boundaries of the system.
Assessment Boundary: Assessment does not include the use of chemical reactions to describe the processes.
Next Generation Science Standards · Disciplinary Core Idea: Ecosystems: Interactions, Energy, and Dynamics · Official standard
Students develop and revise models that show how matter and energy move through an ecosystem. Matter is anything that has mass and takes up space, such as water, air, soil and the bodies of living things. Energy is what makes things move, grow and warm up; in ecosystems it arrives mostly as sunlight. Students sort the living parts of an ecosystem (plants, animals, fungi, bacteria) from the nonliving parts (sunlight, air, water, soil, rock), and they draw arrows that follow matter and energy between them. The key pattern is that matter cycles: the same matter is used again and again, passing from air, water and soil into living things and back. Energy flows: it enters as sunlight, passes along food chains and leaves as heat, so it must keep coming in.
The NGSS Clarification Statement says: "Emphasis is on describing the conservation of matter and flow of energy into and out of various ecosystems, and on defining the boundaries of the system." The Assessment Boundary says: "Assessment does not include the use of chemical reactions to describe the processes." So this page describes processes in words and arrows, with no chemical equations. Students model a pond, a forest floor, a garden, a stream and other ecosystems, and they practice drawing a system boundary, the line that separates what is inside the system from what is outside, so they can see what crosses it. All data sets are invented for teaching and labeled as invented.
Learning Objectives
By the end of this lesson, students will be able to:
Sort the parts of an ecosystem into living and nonliving parts, and place them in a model
Develop a model with arrows that shows matter cycling among living and nonliving parts, including the role of decomposers
Show in a model that energy enters an ecosystem as sunlight, passes along food chains and leaves as heat
Define a system boundary and use simple numbers to show that matter is conserved as it crosses the boundary or stays inside it
Find and fix errors in another student's model of an ecosystem
Prior Knowledge Required
Students should already be comfortable with:
How matter moves among plants, animals, decomposers and the environment 5-LS2-1
That the energy in animals' food was once energy from the sun 5-PS3-1
That plants get the materials they need for growth chiefly from air and water 5-LS1-1
Adding, subtracting and finding fractions of whole numbers
Hold up a fallen leaf from the schoolyard. Tell students that a forest drops a thick layer of leaves every fall, yet the forest floor is not buried meters deep after a hundred years.
Warm-Up Prompt
"Where do all the fallen leaves go? Draw a quick sketch that shows what happens to the matter in this leaf over the next year. Then add the sun to your sketch. Does the sun's energy end up in the same place as the leaf's matter?"
Collect two or three sketches. Many students say the leaves "disappear" or "turn into dirt". Ask what "disappear" would mean for matter, and point out that the lesson will test whether matter can really disappear.
Direct Instruction15-20 minutes
Two rules for every ecosystem model. A model is a drawing or object that shows how the parts of a system are connected. Diagram 1 is a model of a pond. Each box is a part of the ecosystem, and each arrow shows something moving from one part to another.
Matter cycles. Plants and algae (simple water plants) take in matter from the air and water. Animals get matter by eating plants or other animals. Decomposers, such as bacteria, fungi and some worms and insects, break down dead organisms and wastes and return the matter to the soil, water and air, where plants can take it in again. Matter is conserved: it is never created or destroyed, only moved and rearranged, so the arrows for matter form loops.
Energy flows. Energy enters as sunlight, which plants and algae capture to make food. Food carries energy to the animals that eat it. At every step, living things use energy to move, grow and stay alive, and most of it leaves as heat. Heat cannot be used by plants to make food, so energy does not loop back. It must keep coming in from the sun.
System boundary. Before you draw arrows, decide where the system ends. Then you can see which matter and energy cross the boundary and which stay inside.
Use Diagram 1 with the guided practice and Diagram 2 with the second example.
Defining the system boundary (a garden bed)
Invented data for a 2 m × 1 m school garden bed over one season. Inside the boundary: soil, plants, earthworms, insects and decomposers. Crossing the boundary: sunlight in and heat out; rainwater in; 5 kg of raked leaves spread on top as mulch; 12 kg of vegetables picked and taken home.
Result: Matter out in the harvest: 12 kg. Matter in as mulch: 5 kg. The harvest carries 12 - 5 = 7 kg more plant matter out than the mulch brings in, including nutrients from the soil. Model: unless matter is brought back in, for example as more leaves or plant scraps, the soil in the bed slowly runs low on nutrients.
Matter cycles through decomposers (Diagram 2)
Invented monthly measurements of dead leaves on the ground in one forest plot, in grams per m². October: 520; November, after more leaves fall: 560; then down to 160 in August.
Result: From November to August: 560 - 160 = 400 g per m² of dead leaves broke down. The matter did not disappear: decomposers released it into the soil and the air, tree roots took nutrients and water from the soil, and the leaves took in matter from the air, so the trees could grow new leaves, which fall again in autumn. The loop is: tree, dead leaves, decomposers, soil and air, tree.
Energy flows one way (a meadow food chain)
Invented model numbers in energy units for one meadow plot in a summer. Grasshoppers eat plants that contain 200 units of energy and store 20 units in their own bodies. Birds eat grasshoppers that contain 15 units and store 2 units.
Result: Grasshoppers: 200 - 20 = 180 units did not stay in their bodies. Most left as heat while the grasshoppers moved and stayed alive, and the rest left in droppings, which decomposers then used. Birds: 15 - 2 = 13 units left the birds. Heat does not return to the plants, so new energy must arrive as sunlight every day.
Conservation of matter in an aquarium
Invented data. Over one month, the fish in a class aquarium eat 50 g of fish food. Weighing shows the fish gained a total of 5 g.
Result: Matter in = matter stored + matter out: 50 g = 5 g + 45 g. The other 45 g left the fish as droppings and as gases breathed out into the water. Snails and decomposers use the droppings, and the plants take in the matter they release. None of the 50 g was destroyed.
Energy from outside the boundary (a shaded forest stream)
Invented data for one shaded forest stream, per m² of stream bottom in one year. Dead leaves that fall in from streamside trees: 450 g. Algae that grow in the stream itself: 50 g. Stream insects feed on both.
Result: Total food: 450 + 50 = 500 g, and 450 ÷ 500 = 90% of it comes from outside the stream's boundary. Model: most of the energy (and matter) that stream animals use enters from the forest. Prediction: if the streamside trees are cut down, the stream insects lose most of their food, unless more sunlight lets much more algae grow.
After each example, ask: "Which arrows in your model would change if the system boundary were drawn larger or smaller?" For the forest stream, a boundary around the whole valley would put the trees inside the system.
Guided Practice10-15 minutes
Pairs use the pond model in Diagram 1 and the table of its parts.
Parts of the pond model in Diagram 1
Part
Living or nonliving
What it does in the model
Sunlight
Nonliving
brings energy into the pond
Air
Nonliving
gives matter to algae and plants; takes in gases that living things breathe out
Water and mud, with nutrients
Nonliving
holds matter that decomposers release and that plants take in
Algae and water plants
Living
capture the energy in sunlight and make food from matter in the air and water
Snails, tiny animals and fish
Living
get matter and energy by eating
Decomposers
Living
break down dead organisms and wastes
Heat to surroundings
Nonliving
energy leaving the pond
Trace the matter in a dead fish back into a living fish. List each box it passes through, in order.
Find the arrows that carry energy out of the pond. Why is there no arrow from the heat box back to the plants?
A heron flies in, eats several fish and flies to another pond. Add the heron to the model. Does matter cross the pond's system boundary? In which direction?
Write one sentence that explains why the matter arrows form loops but the energy arrows do not.
Independent Practice10-15 minutes
Each student critiques and revises a model. Jordan drew a model of a desert and described the arrows in this table.
Jordan's desert model
Arrow
From
To
Jordan's label
1
Sunlight
Desert grasses
energy
2
Air
Desert grasses
matter
3
Desert grasses
Kangaroo rats (eat grass seeds)
matter and energy
4
Kangaroo rats
Rattlesnakes
matter and energy
5
Rattlesnakes
Sunlight
energy goes back to the sun
Students write (1) which arrow is wrong and why, (2) which part of a complete ecosystem is missing from the model, and (3) a revised model with at least seven arrows. A strong revision removes arrow 5, adds heat leaving every living part, and adds decomposers and desert soil, with arrows from the dead grasses, kangaroo rats and rattlesnakes to the decomposers, from the decomposers to the soil and from the soil to the grasses, so the matter arrows form a loop.
Closure5 minutes
Exit ticket: "Draw a boundary around a potted plant on a windowsill. Name one kind of matter and one kind of energy that cross the boundary going in, and one of each going out." (Example: water and air in, sunlight in; water vapor and fallen leaves out, heat out.) Then return to the warm-up sketches and ask students to add decomposers and a heat arrow.
Differentiation Strategies
For Struggling Students
Give a partly finished model with the boxes drawn and only the arrows to add, and color-code matter and energy arrows
Use a sentence frame for each arrow: "___ moves from ___ to ___ when ___."
Have students trace one path with a finger on Diagram 1 before drawing their own model
For Advanced Students
Ask students to model the same pond in winter, when ice covers it, and explain which arrows get weaker
Have students add a second ecosystem to their model, such as a forest next to a stream, and show the arrows that cross between them
Ask students to design a test with the Activity 1 terrariums that would show whether fungi alone, without pill bugs, can break down leaves
Assessment Guidance
What to Look For
Check that every model includes living and nonliving parts, decomposers, and separate kinds of arrows for matter and energy. Matter arrows should form at least one complete loop, and energy should enter as sunlight and leave as heat with no arrow back. When students do a matter budget, look for "in = stored + out". Listen for students who say that matter is "used up" or that energy "goes back to the soil": both are signs that they have not yet separated the two rules.
02
Classroom Activities
3 Activities
1
Pill Bug Terrarium: Watching Matter Cycle
20 min to set up, then 5 min a week for 4 weeksGroups of 3-4
Groups set up two open terrariums and track what happens to the matter in dead leaves. Pill bugs are small land animals, related to crabs, that eat dead plant matter. They are decomposers, along with the fungi and bacteria in the soil.
Setup
Fill two clear plastic tubs with 5 cm of bagged potting soil and mist the soil with water.
Weigh 10.0 g of dry leaves for each tub, put them in a mesh produce bag and lay the bag on the soil.
Weigh 20 pill bugs together and add them to tub A only. Tub B has no pill bugs. Cover both tubs with cloth held by a rubber band so air can move in and out.
Mist both tubs twice a week. After 4 weeks, take out the leaf bags, let the leaves dry on paper for 2 days, and weigh them again. Weigh the pill bugs again.
Safety: wear gloves when handling soil and leaves, wash hands afterward, handle pill bugs gently with a spoon, and return them outdoors where they were found, or to the supplier's instructions, at the end.
Sample Data (invented)
Tub A, with 20 pill bugs: dry leaves 10.0 g at the start and 8.6 g after 4 weeks; the pill bugs together weighed 1.6 g at the start and 1.7 g at the end. Tub B, no pill bugs: dry leaves 10.0 g at the start and 9.7 g after 4 weeks.
Discussion Questions
The leaves in tub A lost 1.4 g, but the pill bugs gained only 0.1 g. Where did the other 1.3 g of matter go? (Think about the soil and the air.)
Tub B also lost 0.3 g with no pill bugs. Which decomposers could have done this?
Draw a boundary around tub A. Which matter crosses the cloth cover, and which energy enters and leaves?
Modification for Distance Learning
Students look under a log or a flowerpot at home, with an adult, and sketch what they find, or use the sample data to draw a matter model of tub A.
2
Yarn Models of Three Ecosystems
20 minGroups of 4
Groups build a large table-top model of one of three ecosystems with 10 cards, blue yarn for matter and black tape for energy. Then the class compares the three models and finds the rules they share.
Coastal ocean: sunlight, air, seawater, sea-floor mud, phytoplankton (tiny drifting algae), zooplankton (tiny drifting animals), herring, tuna, crabs that eat dead matter on the sea floor, bacteria.
Arctic tundra: sunlight, air, soil, meltwater, sedges and mosses, lemmings, caribou, arctic foxes, snowy owls, bacteria and fungi.
Each set has 4 nonliving cards and 6 living cards.
Procedure
Lay out the cards with the nonliving cards around the edge and the living cards in the middle.
Connect cards with blue yarn wherever matter moves, and with black tape wherever energy moves without matter (sunlight in, heat out). Put a sticky-note arrowhead on each piece.
Check two rules: can you follow blue yarn from any living card back to it again? Does every piece of black tape point away from the sun or toward a heat note?
Gallery walk: visit the other two models and list two things all three models have in common.
Discussion Questions
In each of the three sets, which living card does the job that decomposers do in the pond model?
The ocean and the tundra have very different living things. What is the same about how matter and energy move in both?
Which ecosystem would change the most if its decomposers were removed, and how would the model show it?
Modification for Distance Learning
Students build the model on a shared digital whiteboard with two colors of arrows, then post a screenshot and one sentence about each rule.
3
Schoolyard System Boundary Walk
20 minPairs
Pairs choose a small system in the schoolyard, such as one tree, a patch of lawn or a flower bed, draw a boundary around it on a sketch, and record the matter and energy that cross the boundary.
Procedure
Sketch the system and draw its boundary as a dotted line. Label the living and nonliving parts inside it.
Make a four-column table: matter in, matter out, energy in, energy out. Observe for 10 minutes and fill in at least two entries per column, such as a bird landing to eat seeds or a leaf blowing away.
Back in class, turn the table into a model with arrows that cross the boundary.
Safety: stay within sight of the teacher, keep away from roads and parking lots, do not touch animals, animal waste or unknown plants, and tell the teacher about any bee-sting allergy before going outside.
Sample Data (invented)
One pair studied a maple tree. Matter in: water taken up by roots, air through the leaves, a squirrel that climbed up. Matter out: 3 leaves and a seed that fell, the squirrel leaving with a seed. Energy in: sunlight on the leaves. Energy out: heat from the leaves and the squirrel.
Discussion Questions
How did your list change when you made your boundary bigger, for example to include the soil around the tree?
Is the squirrel a part of the tree system, or something that crosses its boundary? Does the answer depend on where you draw the boundary?
Which of your entries were matter and which were energy, and how did you decide?
Modification for Distance Learning
Students do the walk in a yard, a park or near a window at home, or study a houseplant indoors.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Model of Matter and Energy in a Pond
A model of a pond ecosystem. Solid blue arrows show matter, and food arrows carry both matter and energy. Dashed arrows show energy that moves without matter: sunlight coming in and heat going out. The matter arrows form loops through the decomposers and the water and mud, while every energy path ends at the heat box.
Diagram 2: Dead Leaves on a Forest Floor Through One Year
Invented monthly measurements of dead leaves on the ground in one forest plot, drawn to scale. Leaves pile up in October and November when they fall from the trees, then decomposers break them down through the winter, spring and summer, fastest in the warm months.
04
Homework Assignment
~30 min
MS-LS2-3 Homework: Modeling Matter and Energy in Ecosystems
Directions: All data sets are invented for practice. Draw your models with labeled boxes, solid arrows for matter and dashed arrows for energy. Show each calculation. You do not need any chemical equations.
Part 1: Developing Models (Problems 1-3)
A salt marsh has these parts: cordgrass, fiddler crabs, marsh snails, bacteria in the mud, sunlight, seawater, mud and air. (a) Sort the parts into living and nonliving. (b) Draw a model with at least 8 arrows, using solid arrows for matter and dashed arrows for energy. (c) Describe one complete loop that a bit of matter could follow in your model.
A class rabbit eats 4.5 kg of dry food (hay and pellets) in a month. Over the month it gains 0.1 kg, and its dry droppings collected from the cage weigh 1.8 kg. (a) How much of the food's matter is not accounted for by the weight gain and the droppings? (b) Where did that matter go? (c) The droppings are dug into the school garden. Draw a model that shows where their matter goes next.
A mouse eats seeds that contain 600 energy units. It stores 18 units in new body tissue, and 120 units leave in its droppings. (a) How many units leave the mouse as heat? (b) What percent of the energy it ate did the mouse store? (c) Explain why the heat cannot be used again by the plants that made the seeds.
Part 2: Boundaries and Revising Models (Problems 4-6)
Seabirds catch fish at sea and nest on a small rocky island, where their droppings fall on the ground: about 400 g per m² each year. Plants on the island grow 900 g per m² each year; on a similar nearby island with no seabirds they grow 300 g per m². (a) How many times as much plant growth is there on the seabird island? (b) Draw a model with a boundary around the island that shows where the extra matter came from. (c) Predict what would happen to the plants if rats arrived and the seabirds stopped nesting there.
A student writes: "Energy and matter both cycle. Energy goes from the sun to plants, to deer, to decomposers, and then back to the plants." (a) What part of the statement is correct? (b) What part is wrong, and why? (c) Rewrite the statement and draw a model that fixes it.
Engineers are planning a greenhouse on Mars where astronauts would grow lettuce, keep fish in tanks and use decomposers to break down plant scraps and fish waste. Nothing can be shipped in after it is built except electricity for the lights. (a) Draw a model with the boundary at the greenhouse walls, and show which matter is recycled inside. (b) What energy must cross the boundary going in, and what energy goes out? (c) Explain why the greenhouse would fail without decomposers.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Model Parts
Model includes living and nonliving parts, decomposers and a clear system boundary where asked
Model is missing one kind of part or the boundary
Matter and Energy Arrows
Matter arrows form a loop; energy enters as light and leaves as heat with no loop back
Arrows are mostly correct, but energy loops back or matter has no loop
Calculations and Explanation
Budgets and percents are correct, and the explanation uses "matter in = stored + out" or names where the energy goes
Correct method with one calculation error, or a correct answer with no explanation
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All data sets are invented, and no chemical equations are needed. 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
A student is building a model of a forest. Which pair contains only nonliving parts that matter moves through?
Answer: B
Soil and air are both nonliving, and matter moves into and out of both. Choice A includes mushrooms, which are living fungi. Choices C and D each pair a living thing (trees, deer) with a nonliving one.
Question 2 of 20 · Multiple Choice
In a model of a meadow, which arrow shows energy leaving the ecosystem?
Answer: A
Living things release heat to their surroundings as they use energy, and that heat leaves the ecosystem. Choice C is energy entering, not leaving. Choice D moves energy from one living part to another inside the meadow. Choice B moves matter, not energy.
Question 3 of 20 · Multiple Choice
A model has an arrow from decomposers back to the sun, labeled "energy returns to the sun." What is wrong with it?
Answer: D
Energy flows one way: it enters as sunlight and leaves as heat to the surroundings. It does not return to the sun or to the plants. Choice B still makes energy loop back, which is the same error. Choice C confuses energy with matter, which does cycle. Choice A is wrong because decomposers get their energy from the dead matter they eat.
Question 4 of 20 · Multiple Choice
Invented data: a pet turtle eats 80 g of food in a month and gains 6 g. How much of the food's matter left the turtle as droppings and gases breathed out?
Answer: D
Matter in = matter stored + matter out, so 80 = 6 + out, and out = 74 g. Choice A adds the gain to the food instead of subtracting it. Choice B is the matter stored, not the matter that left. Choice C assumes none of the food stayed in the turtle.
Question 5 of 20 · Multiple Choice
Why must energy keep entering an ecosystem, while the same matter can be used again and again?
Answer: D
Heat cannot be turned back into food by plants, so sunlight must keep arriving. Matter is conserved, and decomposers return it to the soil, water and air, where plants take it in again. Choice A reverses the rules: matter is never destroyed. Choice B swaps where matter and energy come from. Choice C is wrong because living things use energy all the time.
Question 6 of 20 · Multiple Choice
What job do decomposers do in a model of matter cycling?
Answer: B
Decomposers break down dead organisms and wastes and release the matter into the soil, water and air, which closes the matter loop. Choice A describes plants and algae. Choice C is wrong because matter is never destroyed. Choice D describes energy looping back, which does not happen.
Question 7 of 20 · Multiple Choice
Deep in a cave there is no sunlight, but beetles, crickets and fungi live there. In a model with a boundary at the cave entrance, where does their energy most likely come from?
Answer: A
With no sunlight inside, the cave depends on food that crosses the boundary from outside, such as bat droppings and plant matter carried in by water. That food holds energy that was first captured from sunlight outside the cave. Choice C is wrong because plants need light to make food. Choices B and D name nonliving parts that are not food.
Question 8 of 20 · Multiple Choice
A frog eats insects that contain 250 energy units and stores 20 units in its body (invented model numbers). How many units left the frog as heat or in its wastes?
Answer: A
250 - 20 = 230 units left the frog. Choice B adds the two numbers instead of subtracting. Choice C is the energy stored, not the energy that left. Choice D divides 250 by 20.
Question 9 of 20 · Multiple Choice
A class wants to model how matter cycles in a school pond. Which system boundary will let them see the most loops inside the system?
Answer: C
A boundary around the whole pond puts the producers, consumers, decomposers, water and mud inside, so the matter loops stay inside the system. Choices A and D put one group of living things inside, so almost every arrow crosses the boundary and no loop is complete. Choice B leaves out the mud, where decomposers release much of the matter.
Question 10 of 20 · Multiple Choice
A maple tree grows from a 0.2 g winged seed to 1,500 kg of wood and leaves. Where did most of that matter come from?
Answer: C
Most of a tree's mass is built from matter taken in from the air and water; the soil supplies only small amounts of nutrients, which is why the soil around a tree does not disappear. Choice B confuses energy with matter: sunlight has no mass to add. Choice D ignores that the seed is only 0.2 g.
Question 11 of 20 · Multiple Choice
Invented data: a forest floor holds 500 g of dead leaves per m² in October and 200 g per m² the next April. What percent of the October leaves broke down?
Answer: C
500 - 200 = 300 g broke down, and 300 ÷ 500 = 0.60, or 60%. Choice A is the share that was left (200 ÷ 500). Choice B treats the 300 g as a percent of 1,000. Choice D divides by the April value instead (300 ÷ 200).
Question 12 of 20 · Multiple Choice
A student's model shows only: sun to grass, grass to rabbit, rabbit to fox. What must be added so that the model shows matter cycling?
Answer: B
Matter cycles only if it can return from dead organisms and wastes to the soil and air, and then to the grass. That needs decomposers and nonliving parts. Choice C adds energy, not a matter loop. Choice D makes energy loop back, which is wrong. Choice A only makes the food chain longer.
Question 13 of 20 · Multiple Choice
A desert and a rainforest have very different living things. Which statement is true of the models of both ecosystems?
Answer: D
The same two rules hold in every ecosystem: energy enters as sunlight and leaves as heat, and matter cycles through producers, consumers, decomposers and nonliving parts. Choices A and C claim a rule works in only one ecosystem. Choice B names the wrong source of energy.
Question 14 of 20 · Multiple Choice
Salmon grow up in the ocean, swim up a river to lay eggs and die. Bears carry some of the dead salmon into the forest beside the river, and studies have found matter from the ocean in the trees there. With the boundary drawn around the riverside forest, which statement fits?
Answer: A
Salmon carry matter from the ocean into the river, and bears carry it across the forest's boundary. Decomposers release it into the soil, where the trees take it in. Choice D is wrong because matter often crosses ecosystem boundaries. Choice C is wrong because matter is conserved. Choice B is wrong because the forest's plants capture sunlight directly.
Question 15 of 20 · Short Answer
Develop a model of a backyard ecosystem. Name three living parts and three nonliving parts, describe one complete loop that matter follows, and describe the path of energy from where it enters to where it leaves.
Example: living parts grass, earthworms, robins (also fungi and bacteria); nonliving parts soil, air, rainwater (also sunlight). Matter loop: grass takes in air and water and nutrients from the soil; earthworms and decomposers break down dead grass; the matter returns to the soil and air; the grass takes it in again. Energy path: sunlight to grass, grass to insects or worms, then to robins, with heat leaving at each step and no arrow back.
Question 16 of 20 · Short Answer
A farmer cuts and removes about 4,000 kg of hay from a field every year (invented data). How much hay leaves the field in 3 years? Use a model of the field's system boundary to explain why farmers often spread manure on fields like this.
4,000 × 3 = 12,000 kg of hay leaves in 3 years. The hay carries matter, including nutrients from the soil, out across the field's boundary, and decomposers in the field never get to return it. Spreading manure brings matter back in, so the soil does not run low on nutrients.
Question 17 of 20 · Short Answer
In a model of a garden (invented numbers), the plants contain 2,000 energy units. Caterpillars eat leaves containing 320 units and store 32 units in their bodies. How many units leave the caterpillars as heat or in droppings? Explain why birds that eat the caterpillars get far less energy than the caterpillars ate.
320 - 32 = 288 units leave the caterpillars. The birds can get only the energy stored in the caterpillars' bodies, at most 32 units, because the caterpillars used most of the energy to move and stay alive, and that energy left as heat.
Question 18 of 20 · Short Answer
Sam's model of a lake has these arrows: sun to algae (energy); algae to fish (food); fish to heat (energy); dead fish to algae (energy). Find two problems with the model and describe how to fix them.
Problem 1: the arrow from dead fish to algae is labeled energy, but energy does not loop back to producers; the dead fish carry matter. Problem 2: the model has no decomposers and no nonliving parts such as water and mud, so matter cannot cycle. Fix: dead fish to decomposers (matter), decomposers to water and mud (matter), water and mud to algae (matter), and heat arrows leaving the algae and the decomposers too.
Question 19 of 20 · Short Answer
Compare the system boundaries of a class aquarium and a pond in a park. Name two things that cross the boundary of each, and explain which system needs more help from people to keep matter cycling.
Aquarium: fish food added and dirty water removed by people cross the boundary, along with light in and heat out. Pond: rainwater and fallen leaves come in, and birds or insects fly in and out. The aquarium needs more help, because it is small and has fewer decomposers and plants, so wastes build up unless people clean the water and add food.
Question 20 of 20 · Short Answer
Explain why matter on Earth can cycle for billions of years, but energy from the sun has to keep arriving every day. Use an example from any ecosystem.
Matter is conserved: it is never destroyed, only moved, and decomposers return it from dead things to the soil, water and air for plants to use again. Energy leaves as heat at every step, and heat cannot be used by plants to make food. Example: the matter in a fallen leaf becomes part of the soil and then a new plant, but the energy the leaf captured is used by decomposers and leaves as heat.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-LS2-3 mean?
MS-LS2-3 asks middle school students to develop a model that describes how matter cycles and energy flows among the living and nonliving parts of an ecosystem. The code stands for Middle School, Life Science, core idea 2 (Ecosystems: Interactions, Energy, and Dynamics), performance expectation 3.
What is the assessment boundary for MS-LS2-3?
The official Assessment Boundary says that assessment does not include the use of chemical reactions to describe the processes. Students describe what happens in words, drawings and arrows; they are not asked to write or balance chemical equations for photosynthesis or for the way living things release energy from food.
What is the difference between matter cycling and energy flow?
Matter cycles: the same matter moves from air, water and soil into living things and back again, over and over. Energy flows: it enters as sunlight, passes along food chains and leaves as heat, so it does not come back around and must keep arriving.
Why does MS-LS2-3 ask students to define the boundaries of the system?
A model only makes sense once you decide what is inside it. The boundary tells you which matter and energy stay inside the system and which cross into or out of it, such as leaves falling into a stream or crops carried off a field.
What should a good MS-LS2-3 model include?
A good model has living parts (producers, consumers and decomposers), nonliving parts (sunlight, air, water, soil), a system boundary, and two kinds of arrows. The matter arrows form at least one loop, and the energy arrows start at the sun and end as heat.
Why are decomposers so important in these models?
Without decomposers, dead organisms and wastes would pile up and the matter in them would not return to the soil, water and air. Plants would run short of the materials they need, so the matter loop would break.
Is photosynthesis part of MS-LS2-3?
Only as an arrow in the model: plants and algae capture sunlight and take in matter from the air and water to make food. The details of photosynthesis belong to MS-LS1-6, and the chemical reactions are left out of this standard by its Assessment Boundary.
What are common mistakes students make?
Students often say that matter is "used up" or "disappears" when things decompose, draw energy looping back from decomposers to plants, or leave out nonliving parts and decomposers. Another common mistake is thinking that plants get most of their mass from the soil.
Do students need numbers for MS-LS2-3?
Simple numbers help but are not required. A matter budget such as "in = stored + out" shows conservation of matter, and invented energy units show that most energy leaves as heat. The heavier math of energy pyramids comes later, in HS-LS2-4.
What comes after MS-LS2-3?
In high school, HS-LS2-4 uses math to track matter and energy through food webs, and HS-LS2-5 models how carbon cycles among living things, air, water and rock. Both build on the matter and energy rules from MS-LS2-3.
07
Related Standards
6 standards
These standards connect to MS-LS2-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-LS2-1Prerequisite
Model the movement of matter among plants, animals, decomposers and the environment
Lesson coming soon
5-PS3-1Prerequisite
Use models to show that the energy in animals' food was once energy from the sun
Lesson coming soon
Alongside
MS-LS1-6Parallel
Explain the role of photosynthesis in cycling matter and energy into and out of organisms
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