Where did the apple come from, and where does it go?

In numbers

• ≈ 86%of an apple is water
• 1 treethe source of every tree of an apple variety (by grafting)

In five stops

1. 1

   Where were its atoms born?

   The hydrogen in an apple's water comes from the Big Bang and its oxygen from stars. The carbon in its sugar and fibre was also born in stars. Minerals such as potassium formed in massive stars and stellar explosions and ended up in Earth's rocks.

2. 2

   How did nature prepare it?

   An apple tree takes carbon dioxide from the air through its leaves and makes sugar by photosynthesis; its roots draw water and minerals from the soil. Bees pollinate its flowers, a pollinated flower grows into an apple, and the tree sends sugar and water into the fruit.

3. 3

   What did people do?

   DNA studies in 2010 showed that the main ancestor of the domestic apple is a wild apple from the Tian Shan mountains of Kazakhstan (Malus sieversii). A tree grown from an apple seed does not resemble its parent; every seedling is different. That's why favourite varieties are propagated by grafting: all the trees of one variety are really copies of a single tree.

4. 4

   What happens when we use it?

   When you eat an apple, its sugars are digested and turned into energy in your cells. You can't digest some of its fibre; the bacteria in your gut feed on it instead. The apple's water joins your body's water.

5. 5

   Where does it go next?

   The carbon from the sugar returns to the air as carbon dioxide in your breath. The peel and core feed fungi and bacteria in compost and become part of the soil, where another plant will one day use their minerals.