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Energy from food

Energy and power · level 1, lesson 2 of 6

A question to start

You have been running around all morning. Now you feel tired and hungry. Why does your body want food?

The idea

Your body is always using energy: to run and jump, to breathe, to keep your heart beating, to think, to grow, and to keep you warm. Even when you sleep, your body uses energy.

That energy comes from food. When you eat, your body breaks food down and takes the energy out of it. Running out of energy makes you feel tired and hungry, and eating fills you up again.

movingkeeping warmgrowingfood

Different foods hold different amounts of energy. Bread, rice, pasta, nuts and butter hold a lot. Lettuce and cucumber hold very little. A balanced meal gives you energy and everything else your body needs to grow.

Where does the energy in food come from? Plants make it from sunlight. Animals get theirs by eating plants, or by eating other animals that ate plants. So nearly all the energy in your dinner started as sunshine.

On Mars, people would grow food in greenhouses, under sunlight or under bright lamps. All the energy in a Mars salad would come from the Sun or from the city's power.

Worked examples

1. A sandwich before a hike. The bread and cheese give your muscles energy to walk for hours.

2. Shivering. When you are cold, your muscles shiver. Shivering uses food energy to make heat and warm you up.

Try it

  1. Name three things your body uses energy for.
  2. Does your body use energy while you sleep?
  3. Where did the energy in a carrot come from?
  4. Which holds more energy: a handful of nuts or a handful of lettuce?
Answers
  1. For example: moving, breathing, thinking, growing, keeping warm.
  2. Yes: for breathing, your heartbeat, and keeping warm.
  3. From sunlight. The carrot plant made it from sunlight.
  4. The nuts.

Common mistake

"Only running and playing use up energy." Your body uses energy all the time, even sitting still: about as much as an old-fashioned light bulb, just to keep you alive and warm.

Where it leads