HS-LS2-4: Energy Pyramids and Conserved Matter
Also called NGSS HS-LS2-4 · Topic: Matter and Energy in Organisms and Ecosystems · Life Science
The Official Wording
Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
Clarification statement: Emphasis is on using a mathematical model of stored energy in biomass to describe the transfer of energy from one trophic level to another and that matter and energy are conserved as matter cycles and energy flows through ecosystems. Emphasis is on atoms and molecules such as carbon, oxygen, hydrogen and nitrogen being conserved as they move through an ecosystem.
Assessment boundary: Assessment is limited to proportional reasoning to describe the cycling of matter and flow of energy.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-LS2-4 Means in Plain English
Students use numbers, such as the energy stored in the biomass at each feeding level, to back up claims about how energy moves through a food web. They show that only a small share passes up each level, while atoms like carbon and nitrogen cycle without being lost.
The math is proportional reasoning, like percentages and ratios between levels, not complex equations. It builds on MS-LS2-3 and the cellular respiration in HS-LS1-7, and leads to HS-LS2-5, where carbon moves among air, water, rock and life.
HS-LS2-4 I Can Statements
- I can calculate how much energy reaches each trophic level.
- I can explain where the energy that does not move up goes.
- I can show that atoms are conserved as matter cycles.
HS-LS2-4 Worked Example
A worked energy pyramid for a grassland food chain, using the rough rule that about a tenth of the energy moves up each level.
Grass in a meadow stores 10,000 kJ of energy per square meter in a year. About 10% of the energy at each level reaches the next. How much reaches grasshoppers, shrews and owls, and where does the rest go?
- Grasshoppers get about 10% of the grass energy.10,000 kJ × 0.10 = 1,000 kJ
- Shrews eat grasshoppers and get about 10% of theirs.1,000 kJ × 0.10 = 100 kJ
- Owls eat shrews and get about 10% of that.100 kJ × 0.10 = 10 kJ
- Find what share of the grass energy reaches the owls.10 ÷ 10,000 = 0.001, or 0.1%
- Account for the energy that did not move up.Lost as heat from respiration, or left in uneaten parts and waste
Check it: Multiply back up: 10 kJ × 10 × 10 × 10 = 10,000 kJ. The carbon in waste and dead bodies is not lost either, because decomposers return it to the air and soil.
Common Mistakes with HS-LS2-4
Thinking energy is destroyed
“90% of the energy is used up and gone”
Try this: Energy is conserved. It leaves the food chain mostly as heat from respiration, which is why energy flows instead of cycling.
Treating 10% as an exact law
Using exactly 10% for every level in every ecosystem
Try this: Ten percent is a rough average. Real transfers run from about 5 to 20%, so use the data's own numbers when given.
Mixing up matter and energy
“Carbon is lost at each level just like energy”
Try this: Matter cycles. Carbon released by respiration returns to the air and gets captured again by plants, so the atoms are reused, not lost.
Where HS-LS2-4 Fits
Practice HS-LS2-4
Quick Check
- If producers store 50,000 kJ, about how much reaches secondary consumers?
- Why are there fewer owls than shrews in a meadow?
- Does the amount of carbon on Earth shrink as it passes through food webs?