13.2 · The Sun Is Where It Starts

From Ohio 5th Grade Science Power Workbook · Chapter 13 · Lesson 13.2.

Big idea: Food carries energy, but the sun is where almost all of that energy came from in the first place.

Learning goals: Explain why food is not the original source of energy

Trace the energy in any food back to sunlight

Use a food chain to show where energy enters

Food carries energy. It does not make it.

A fish gets energy from the insects it eats. So the insect looks like the source.

It is not. The insect got its energy from algae. The algae made food using sunlight.

The sun is the original source. Food is how that energy is carried from one living thing to the next.

Follow any chain back

Every food chain starts the same way. Sunlight reaches a producer. The producer stores the energy in food.

Then the energy passes along, eater to eater. Start anywhere in the chain and trace backwards. You always reach the sun.

Worked examples

Question: Look at the pond food chain in this lesson. A student says the bluegill's energy comes from the water insect, so the insect is the source. Is the student right?

Steps: The bluegill did get its energy by eating the insect. That part is true.

But the insect had to get its energy from somewhere too — the algae. And the algae used sunlight to make food.

So the insect is one step in the chain, not the source. The source is the sun.

Answer: Partly. The insect passed the energy to the fish, but it did not make that energy. Trace the chain back and the energy started as sunlight.

Common mistakes

Food is a carrier, not the beginning

You eat, you get energy. So it is natural to think food is where energy begins.

Food only carries energy. The energy in a sandwich was in wheat and vegetables first, and those plants got it from the sun. Producers are the only living things that bring new energy into an ecosystem, and they get it from sunlight.

Check your thinking: If your answer names a plant or an animal as 'the source', keep going one more step. The source is the sun.

Ohio connection

Lake Erie starts with sunlight

Lake Erie is shallow, so sunlight reaches a lot of its water. Tiny algae use that light to make food.

Small animals eat the algae. Small fish eat those animals, and larger fish such as walleye eat the small fish. Every fish in the lake is living on energy that came in as sunlight.

Think: Suppose thick mud clouded the water for a whole summer and blocked the light. Predict what would happen to the fish, and explain the chain of reasons.

Remember

Back to the sun

Any organism, any food: ask 'and where did that get it?' Keep asking. The chain always ends at the sun.

Practice tip

Remember: 'Original source' is a signal.

Tip: When a question says original or trace back, it wants the sun. When it says gets its energy from, it usually wants the food. Read which one is being asked.

Written practice

A student says an owl gets its energy from mice, so mice are the owl's energy source. Explain what is missing from this answer.

Sample response: The owl does get its energy by eating mice, but the mice are not where the energy started. The mice ate seeds or plants. The plants made their food using sunlight. So the original source of the owl's energy is the sun, and the mice are just one step along the way.

Scoring guide: 1 point: agrees the owl gets energy by eating mice but says the mice are not the original source.

1 point: traces the energy back through what the mice ate to a plant, and to the sun.

This targets Ohio's listed misconception that food is the original source of energy for all organisms. Food carries energy that began as sunlight.