How Photosynthesis Works (explained in 2 minutes)
How plants turn light, water and carbon dioxide into glucose and oxygen, step by step inside the leaf, with a worked example of the molecules.
- Subject: Science
- Age group: 10-14
What this video covers
- Plants use light energy captured by chlorophyll to make glucose.
- Light-powered photosynthesis joins simple ingredients into glucose, which the plant uses or stores.
- Water travels from roots to leaves, while carbon dioxide enters through stomata.
- Inside a leaf, light helps water and carbon dioxide react to produce glucose and oxygen; glucose stays and oxygen exits.
- The worked example begins with enough light, six carbon-dioxide molecules, and six water molecules.
- The six molecules of each input are rearranged into one glucose molecule and six oxygen molecules, with the stated atoms in glucose.
- Six oxygen molecules leave the leaf, showing that the plant makes food and releases breathable gas.
- Plants use glucose for growth and repair, or change it into starch when light is scarce.
- Humans cannot photosynthesise because their cells lack chlorophyll, so they get energy by eating plants or animals that ate plants.
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Transcript
Photosynthesis is the process plants use to make glucose. Green plants take in light energy from the Sun. A green pigment called chlorophyll catches that energy inside leaf cells.
It gives the plant power to join simple ingredients together. The product is a sugar called glucose, which can be used straight away or stored for later.
Water enters a plant through its roots and travels up thin tubes to the leaves. Carbon dioxide, a gas in the air, enters through tiny openings called stomata, usually found on the underside of a leaf.
Inside the leaf, light energy helps the water and carbon dioxide react. This reaction produces glucose and oxygen. The plant keeps most of the glucose. Oxygen leaves through the stomata and enters the air.
Here is a worked example. Suppose a leaf receives enough light and takes in six molecules of carbon dioxide and six molecules of water. A molecule is a tiny group of atoms joined together.
During photosynthesis, these ingredients are rearranged to make one molecule of glucose and six molecules of oxygen. The glucose contains six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.
The six oxygen molecules can leave the leaf. This is why the plant has made food while releasing a gas that animals can breathe.
The plant can use glucose to release energy for growing leaves, making roots, repairing cells, and producing flowers or seeds. It can also change glucose into starch, a storage material, so food remains available when light is scarce, such as at night or during winter.
Humans cannot photosynthesise because our cells do not contain chlorophyll. We get energy by eating plants or animals that ate plants.