Raven spreads a printed diagram across the Windowsill. Red arrows point up into the sky. Green arrows point down.
"Carbon dioxide going up, carbon dioxide coming down," she says. "What do you notice about the green arrows?"
Rocket studies them. "Plants. The ocean. Soil. They all pull it out of the air."
"And the red ones?" Nova asks, hovering over the top of the page.
"Breathing out. Rotting leaves. Volcanoes. Burning fuel," Rocket reads. "I am a red arrow!"
Raven laughs. "And the seedlings are green arrows. Right there on our sill."
"Then the carbon in them was in the air last month," Rocket says. He breathes out slowly at the jar, then feels silly.
NASA's Earth science pages for kids describe the carbon cycle, how carbon moves through the planet.
The page says all living things on Earth contain carbon. One way carbon travels is as carbon dioxide gas in the air.
Carbon is added to the air by living organisms, like when we breathe out. It is also released when plants and animals decay.
Volcanic eruptions add carbon dioxide. So does burning fuels like gas, oil and coal for energy and transportation.
Carbon is removed from the air by plants, soil and the ocean. Plants absorb carbon dioxide during photosynthesis.
In NASA's words, photosynthesis is a process where plants use carbon dioxide, water and sunlight to make food and release oxygen.
| Direction | What moves carbon | Fast or slow? |
|---|---|---|
| Adds carbon dioxide to the air | Living things breathing out | Fast: a breath takes less than a second |
| Adds carbon dioxide to the air | Plants and animals decaying | |
| Adds carbon dioxide to the air | Volcanic eruptions | |
| Adds carbon dioxide to the air | Burning fuels such as gas, oil and coal | |
| Removes carbon dioxide from the air | Plants, on land and in water, during photosynthesis | |
| Removes carbon dioxide from the air | The ocean and soil, absorbing it directly | |
| Stores carbon for a very long time | Carbon sinking into the Earth and forming oil and coal | Slow: millions of years |
The OpenStax textbook Concepts of Biology sums up photosynthesis as a table of what goes in and what comes out.
It also explains the energy side. Plants convert the energy of sunlight to chemical energy stored within sugar molecules.
Energy cannot be created or destroyed. It can be transferred from place to place or transformed into different forms.
Sunlight becomes stored energy in sugar. Breaking down the sugar later releases it for work, such as moving a muscle.
| Photosynthesis | Matter | Energy |
|---|---|---|
| Goes in | Carbon dioxide and water | Sunlight |
| Comes out | Sugar and oxygen | Stored in the sugar |
| Statement | True or false? |
|---|---|
| All living things on Earth contain carbon. | ? |
| Decaying plants and animals remove carbon dioxide from the air. | ? |
| Plants in water carry out photosynthesis too. | ? |
| Energy cycles around and around like carbon. | ? |
Excellent reading. Tomorrow you will find photosynthesis in every meal and review the week.