← Back to course
Cells and Systems 6-8 / Week 09 / Friday
5/6
Week 09 · Food Becomes You

Friday

Energy out, and the week in review
// Molecules broken apart and put back together
⏱ about 20 min

Friday: Energy Out, and the Week in Review

Rocket races into the kitchen, out of breath from the stairs. "Why am I panting?" he gasps. "I only ran up one flight."

Raven hands him a glass of water. "What do you notice about your breathing after you run?"

"Faster," Rocket says. "And warmer. My face is hot."

Nova hovers beside Rocket. "Your muscles just spent a lot of energy," she says. "Where did it come from?"

Rocket thinks. "Glucose. From food. The mitochondria break it down." He pauses. "With oxygen. That is why I need more air."

"And the carbon dioxide and water go out with every breath," Raven adds. "Breakfast, leaving."

Releasing the energy

Living things use sugars as a major energy source, because sugar molecules have a great deal of energy stored within their bonds.

In cells that need oxygen, glucose is broken down in a series of reactions. Oxygen is used up, and carbon dioxide is released as waste.

Water is produced too. The whole process is called cellular respiration, and it happens mostly in the mitochondria you met in week 3.

Muscle cells have a very high number of mitochondria, because muscle cells need a lot of energy to contract.

Some of the energy does work, like moving your legs. Some leaves as heat, which is why Rocket felt warm.

Glucose from digested food reaches a muscle cell
Mitochondria break glucose down using oxygen
Energy is released for work and heat
Carbon dioxide and water leave in your breath
FOLLOW THE ENERGY
  • Read the question.
  • Tap your answer.
Which gas do cells use up when they release energy from glucose?
Which two substances are given off when glucose is broken down with oxygen?
Why do muscle cells have so many mitochondria?

Two directions, one set of atoms

Cells do two opposite kinds of work. Breaking down larger molecules releases energy. Building larger molecules requires energy.

Both are needed. Energy from glucose pays for linking amino acids into new proteins, which is how you grow.

In week 8 you learned that plants use light, carbon dioxide and water to make sugar and oxygen.

Respiration runs the other way: sugar and oxygen become carbon dioxide and water, and energy comes out.

The atoms travel in a loop between plants and you. Nothing is created or destroyed. It is rearranged.

Week reviewTrue or false?
Digestion breaks large food molecules into smaller ones.?
The body builds its own proteins from amino acids out of food.?
Breaking glucose down with oxygen releases energy.?
Atoms are destroyed when food is digested.?
Carbon dioxide and water are given off when cells release energy from glucose.?
WHY THIS EXERCISEThese five ideas are the whole model: broken apart, rebuilt, energy released, atoms conserved.
OUR WEEK, IN ORDER
  • ?We learned that food molecules are broken apart and rebuilt.
  • ?We built a paper-chain model and fogged a mirror.
  • ?We read a nutrition table of calories per gram.
  • ?We followed a bite through the digestive system.
  • ?We followed the energy out through respiration.
WHY THIS EXERCISEThe week moved from one sandwich to the loop of atoms between plants and people.
Which organelle breaks glucose down to release energy? Type one word.
WHY THIS EXERCISELinking this week to the cell parts you already know makes the body one connected system.
Try it
Sit still for one minute and count your breaths. Write the number down.
Walk briskly around the room for two minutes, then count breaths for one minute again.
Compare the two numbers in your Windowsill Log. This is a science reading, not a health check.
Safety first
Walk only as briskly as you are used to, on flat ground, with shoes on.
Anyone who feels dizzy sits down and drinks water.
Draw a loop. On the left, a leaf makes sugar and oxygen. On the right, a person uses them and breathes out carbon dioxide and water.

Strong week, biologist. Tomorrow is Nature Day: a family food-trail walk that traces every meal back to a leaf.

← Thursday