7th grade · Science · Unit 3 of 10
Food Chains & Energy
Who eats whom, and the energy
What your child practices
Producers, consumers and decomposers, food chains and webs, how energy shrinks as it passes up a chain (about 10% each step), and what happens when part of a chain changes.
Alaska content standards learning standard: MS-LS2-3 · energy flowing through food chains and webs
How we explain it
Children can open this short lesson before they practice.
- Producers make food from sunlight. Consumers eat other living things. Decomposers break down dead matter.
- Arrows in a food chain point from the food to the eater.
- Only about 10% of the energy at one level passes to the next.
Example: Plants store 1000 units of energy. About how much reaches the rabbits that eat them? About 10% passes on. 10% of 1000 is 100. Answer: 100 units
Food Chains & Energy in Alaska
In the Alaska content standards, this is unit 3 of 10 in 7th grade Science, after Ecosystems and before Cycles & Succession.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Source: Alaska Department of Education and Early Development
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Put this food chain in order, from the organism that makes food to the last to eat.
- 🦗grasshopper
- 🦅hawk
- 🐍snake
- 🌾grass
grass → grasshopper → snake → hawk
Hint: Energy flows from the producer (grass) to the grasshopper, frog, snake and then hawk.
Question 2
Grass stores 50,000 units of energy. About 10% of the energy at each feeding level is passed on to the next. How many units reach the frogs that eat the grasshoppers?
answer boxunits
500 units
Hint: Two steps: grass to grasshoppers (divide by 10), then grasshoppers to frogs (divide by 10 again).
Question 3
What is a food web?
- A food chain with only one organism
- Many food chains linked together
- A spider's web full of insects
- A list of producers
Many food chains linked together
Hint: Most organisms eat more than one thing and are eaten by more than one thing.
Question 4
A grasshopper eats grass. A frog eats the grasshopper. The frog is a…
- producer
- primary consumer
- secondary consumer
- decomposer
secondary consumer
Hint: A primary consumer eats producers. A secondary consumer eats primary consumers.
Question 5
Producer, consumer or decomposer? Sort each organism.
Sort into: 🌿 producer · 🐇 consumer · 🍄 decomposer
- 🍞bread mold
- 🟢algae in a pond
- 🍁a maple tree
- 🦗a grasshopper
- 🍄a mushroom on a log
- 🐇a rabbit
🌿 producer: algae in a pond, a maple tree · 🐇 consumer: a grasshopper, a rabbit · 🍄 decomposer: bread mold, a mushroom on a log
Hint: Producers make their own food from sunlight (plants, algae). Consumers eat other living things. Decomposers break down dead matter (many fungi and bacteria).
Question 6
Why is a food web often more stable than a single food chain?
- It has no producers to run out
- Consumers can switch to another food source if one declines
- It has no top predators
- Each animal eats only one thing
Consumers can switch to another food source if one declines
Hint: More links mean more backup options.