What Is Photosynthesis — for Kids

Plants make their own food

Photosynthesis is how plants make food.

Plants grow and thrive through photosynthesis. It is a process that turns sunlight into energy.

A leaf is like a food factory. It is the flat part of a plant or tree.

What a plant needs

A plant uses sunlight. A plant uses water. A plant uses a gas in the air called carbon dioxide.

Plants get the things they need to grow chiefly from air and water.

Sunlight matters a lot. A plant in deep shade can die. Big tree tops can block the sunlight on the rainforest floor.

The green helper

Leaves have a green helper called chlorophyll.

Energy from the Sun lands on plants. Chlorophyll collects it.

With chlorophyll, plants make sugar and oxygen.

What the plant makes

The plant makes sugar. Sugar is food and energy for the plant.

The plant also makes oxygen. Oxygen goes into the air.

People and animals breathe oxygen. People and animals eat plants, too. The sugar in plants is food for the animals that eat them.

It starts with the Sun

All food chains begin with green plants.

Green plants are called primary producers.

Plants are less active at night. When the Sun comes up, they wake up to the day.

Photosynthesis, in words

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

You can write it as an equation in words: sunlight + water + carbon dioxide → sugar + oxygen.

Plants absorb sunlight to convert carbon dioxide and water into food. That process is called photosynthesis.

The sugar is a carbohydrate. It stores energy for the plant.

Chlorophyll and chloroplasts

Chlorophyll is a green compound found in leaves and green stems of plants.

Chlorophyll can channel the energy of sunlight into chemical energy through photosynthesis. The energy it absorbs transforms carbon dioxide and water into carbohydrates and oxygen.

Chlorophyll is also the pigment that gives plants their green color and allows them to perform photosynthesis. One kind, chlorophyll b, is a special light-absorbing pigment. It reflects green light and absorbs almost all other colors of visible light, which is why plants look green.

Inside a leaf, disc-like structures called chloroplasts absorb most of the sunlight that strikes the leaf. They convert the light into carbohydrates through photosynthesis.

Chloroplasts re-emit about two percent of the light at longer, redder wavelengths. Scientists call that glow fluorescence. It is a byproduct of photosynthesis, and satellites can detect it from space, hundreds of miles above Earth. That gives scientists a direct view into the photosynthetic machinery of plants.

Not just plants on land

Plants, algae, phytoplankton, and other microorganisms use photosynthesis to convert energy from sunlight to sugar. Scientists call them producers.

Phytoplankton are tiny plant-like organisms at the base of the ocean food web. Like plants on land, they use chlorophyll and other light-harvesting pigments to carry out photosynthesis, absorbing carbon dioxide from the air to produce sugars for fuel.

Without producers, most life could not exist on Earth.

Why it matters for air and food

Photosynthesis is the foundation of food webs. Capturing and storing energy through photosynthesis fuels the living systems of our world.

The oxygen we breathe is a byproduct of this photosynthesis.

Scientists also measure how much carbon dioxide vegetation takes in during photosynthesis, minus how much it gives off during respiration. That measure is called net primary production. It helps scientists study how the Earth's carbon cycle works.

Food energy cycles through the ecosystem: from producers, to consumers that eat plants and other organisms, and then to decomposers that recycle nutrients.

Light, shade, and the daily rhythm

Sunlight is important for photosynthesis. A plant on the rainforest floor will not survive because the tree canopy blocks the sunlight. Once basic needs are met, plants begin to compete with each other for sunlight.

Plants also have a daily rhythm. They do not sleep the same way humans do, but they have more and less active times, and internal clocks called circadian rhythms. They are less active at night. When the Sun comes up, they awake to the day. An instrument on the International Space Station, called ECOSTRESS, has observed plants beginning photosynthesis in the morning.

Words to know

• Photosynthesis: the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar. Plants grow and thrive through it.
• Chlorophyll: a green compound found in leaves and green stems of plants. It collects energy from sunlight, and with it plants make sugar and oxygen.
• Chloroplast: a disc-like structure inside a leaf. Chloroplasts absorb most of the sunlight that strikes a leaf and convert it into carbohydrates through photosynthesis.
• Sunlight: light and energy from the Sun. Plants absorb sunlight to convert carbon dioxide and water into food.
• Carbon dioxide: a gas in the air. Plants take in carbon dioxide and use it, with water and sunlight, to make sugar.
• Oxygen: a gas that plants make during photosynthesis. The oxygen we breathe is a byproduct of photosynthesis.
• Sugar: the food and energy a plant makes in photosynthesis. In this form, it is a carbohydrate that stores energy.
• Producer: a living thing that uses photosynthesis to convert energy from sunlight to sugar. Green plants are primary producers, and all food chains begin with them.