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What is Photosynthesis?, Where Does Photosynthesis Happen?, Plant Cells, Respiration, Starch, Why Do Plants Need Energy?

The Sun is the source for all life on Earth. It gives out huge amounts of energy as light and heat. This energy travels across space to Earth. Here it is used by both plants and animals.

Plants, in particular, make good use of sunlight. A plant's leaves trap the energy from the Sun. They use it to make food. Plants in turn supply animals with food. Some animals eat the plants. Some eat the animals that eat the plants. In the end, all living things depend on the food from the Sun.

Food from the Sun A tree's leaves are arranged to catch as much sunlight as possible.

What is Photosynthesis?

Photosynthesis is how plants make food from sunlight. It begins with the water and carbon dioxide that plants take in. With the energy from the Sun, plants turn these into simple sugars, called glucose. Oxygen is also created. Some of this is given off into the air that we breathe.

Where Does Photosynthesis Happen?

Photosynthesis happens in a plant's green leaves. Leaves look green because they contain a coloring matter, called chlorophyll. It is the chlorophyll that absorbs the sunlight.

Food from the Sun Chloroplasts in the leaves contain chlorophyll. Chlorophyll traps the Sun's energy.

The photosynthesis equation is:

Food from the Sun


The Sun is about 93 million miles (149.5 million kilometers) from Earth. Can you imagine how far away that is? Say that you could fly to the Sun in an airplane. It would take you over twenty-one years to get there. Yet sunlight travels that far in just eight minutes.

Plant Cells

Photosynthesis happens in a plant's cells. The cells are tiny. You need a microscope to see them.

There are many types of plant cells. Each has a different job. But each has similar parts. One, the nucleus, controls what happens in the cell. The vacuole keeps the cell strong and rigid. Chloroplasts contain chlorophyll. This is where photosynthesis takes place. All of these parts sit in a jellylike matter called cytoplasm. These are protected by a cell membrane. Each plant cell also has a tough outer cell wall.

Food from the Sun This leaf cell contains all of the structures it needs to carry out photosynthesis.


Plants turn glucose into energy. This process is called respiration. They need the energy to live and grow. Plants only carry out photosynthesis when there is sunlight. Respiration happens all of the time. Inside the cells, plants use oxygen to turn glucose into energy. They also produce carbon dioxide and water.

The respiration equation is:

Food from the Sun


On a sunny day, plants make lots of glucose. This lasts them through the night and through several cloudy days. But they cannot store up lots of glucose. Glucose that isn't used in respiration is turned into starch. Starch can be stored in leaf cells for later use.

Food from the Sun In bright sunshine, you can be sure that green plants are making lots of glucose.

Why Do Plants Need Energy?

All living things carry out the seven life processes.

They need energy for these processes. They include:

  • Movement: Plants move their leaves to face the Sun.
  • Respiration: Plants turn glucose into energy.
  • Sensitivity: Plants react to their surroundings.
  • Growth: Plants grow from a seed to full plant.
  • Reproduction: Plants have offspring.
  • Excretion: Plants get rid of waste.
  • Nutrition: Plants make their own food.

Look at the first letter of each process. Together, they form the words “MRS GREN.” This will help you remember the seven life processes.

Food from the Sun This plant has pushed through the soil toward the Sun as it grows.


Some plants need darkness. Plants called poinsettias need twelve hours of darkness each day. They do not flower if there is too much light. Other plants are even more sensitive to light. If the night is interrupted by a blink of light, they will not flower.

Food from the Sun

Pale Plants

Plants need sunlight to grow properly. Stems hold the leaves so that they face sunlight. But sometimes, there is very little sunlight. Then, the stems grow longer as they try to find light. They may be weak and spindly. The leaves turn pale. The plants will die unless they get sunlight.

Additional topics

Science Encyclopedia for KidsFood from the Sun