Photosynthesis: how plants make sugar from light

0:00Plants do not eat. So where does a plant's food come from?

0:05Plants make food in their leaves. This thin slice across a leaf is called a cross-section.

0:13The tall cells near the top are palisade cells, packed with chloroplasts, where food is made.

0:20Light shines in through the top of the leaf.

0:23Carbon dioxide from the air enters through tiny pores called stomata, then spreads through air spaces.

0:30Water comes up from the roots in tubes called xylem, inside the veins.

0:36Now zoom in on one chloroplast. Here, light energy is used to make sugar. This is photosynthesis.

0:45Chloroplasts contain chlorophyll, a green substance that absorbs light.

0:50It absorbs mostly red and blue light. It reflects more green light, so leaves look green.

0:57Carbon dioxide and water go in. These starting substances are the reactants.

1:03Light energy turns them into glucose, a sugar, and oxygen. These are the products.

1:10Carbon dioxide plus water, using light energy, makes glucose plus oxygen.

1:17In symbols, six carbon dioxide and six water molecules make one glucose and six oxygen molecules.

1:25Look at the carbon. Every carbon atom in glucose comes from carbon dioxide in the air.

1:32A plant uses glucose to build its body, so most of its dry mass, the mass without water, comes from the air, not the soil.

1:41Photosynthesis uses light energy to turn carbon dioxide and water into glucose and oxygen.