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PHOTOSYNTHESIS

Unlike animals, most plants do not need to find food, because they can make it for themselves. Plants use energy from sunlight to turn water and carbon dioxide into an energy-rich sugar called glucose. This process is called photosynthesis, which means “making things with light”. Photosynthesis takes place inside capsules in the leaf cells, called CHLOROPLASTS.

MAKING FOOD AND OXYGEN

Plants use their leaves to make food. Oxygen is created as a by-product. During photosynthesis, plant leaves take in carbon dioxide from the atmosphere. Using the energy from sunlight, this is combined with water drawn up from the roots to make glucose. Oxygen is also produced in this chemical reaction and exits the leaves into the surrounding air.

FOOD-PRODUCING CELLS

Different plant cells perform different tasks. Palisade cells and spongy cells are located just below the epidermis and are a plant’s main food-producers. The tall palisade cells are packed with green chloroplasts, which carry out photosynthesis. The irregularly shaped spongy cells also have chloroplasts. Air spaces between the cells are filled with carbon dioxide, water vapour and other gases.

CHLOROPLAST

Many leaf cells contain tiny, lens-shaped organelles called chloroplasts. These can move around the cell towards the direction of sunlight. Chloroplasts contain a green, light-capturing pigment called chlorophyll. This chemical helps the chloroplasts to act like minute solar panels.

INSIDE A CHLOROPLAST

Chloroplasts are made up of stacks of tiny disclike membranes called grana, held in a dense mass of material known as the stroma. The grana are where water is split into hydrogen and oxygen, using some of the light energy captured by the chlorophyll. The rest of the light energy is used in the stroma to combine the hydrogen with the carbon dioxide to make glucose.

Copyright © 2007 Dorling Kindersley

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