19 Food and Nutrition-High

Food and Nutrition Written by Barb Davis

What Needs Food? All living things, or organisms, need energy in order to live, complete their daily activities, and remain healthy. This energy comes from food. This book explains two life-sustaining processes: how organisms get food and how food goes through changes inside organisms so they can use the food for energy. Before reading on, think about how plants get food and how they turn the food into energy.

How Do Plants Get Food? As you know, animals get the energy they need to survive by eating many kinds of food found in their environment. But plants don't eat food. Unlike other living things, they have the ability to make their own food. Plants produce food through a chemical process called photosynthesis. During photosynthesis, plants make a simple kind of sugar, called glucose, which becomes their food source. You may have thought that plants get their food from the soil, but this is not the case. Green plants contain chlorophyll, a pigment that absorbs the sunlight used to produce glucose. During photosynthesis, plants also use a gas called carbon dioxide, which is found in the air. The carbon dioxide gets absorbed through tiny holes called stomata, which are mostly found on the underside of a plant's leaves. Although soil does not provide plants with their food, it does supply plants with water and minerals, both of which are absorbed through the roots. Water and minerals aid in the process of photosynthesis. The diagram on page 6 reviews the process of photosynthesis.

Photosynthesis in Green Plants 1 Roots absorb water and minerals, and transport them to the plant's cells. 2 A green pigment in plant cells, called chlorophyll, captures the Sun's light energy, which the plant turns into chemical energy. 3 Carbon dioxide from air enters the leaf through tiny holes called stomata. 4 The energy from the Sun helps carbon dioxide molecules react with water molecules to make a simple sugar called glucose. 5 The plant uses some of the glucose it makes and stores the rest. 6 Oxygen, a waste product from the food-making process, passes out of the leaf and enters the air.

Photosynthesis takes place inside the smallest parts of a plant— its cells. Much like bricks in a building, cells join together to make up most living things. The left side of the formula below explains what plants use during photosynthesis. The right side explains what plants produce during photosynthesis. How Do Plants Use Food for Energy? Some of the glucose (sugar) that a plant makes during photosynthesis remains stored in its leaves, fruit, stem, roots, and other parts. To use the rest of the food for energy, the plant must break down the glucose in its cells. This involves a different chemical process, called respiration. During respiration, glucose reacts with oxygen to release energy that plants need to live. Respiration also forms carbon dioxide and water vapor as waste products. These waste products exit the plant through the stomata. The left side of the next formula explains what plants use during respiration. The right side explains what plants produce during respiration.

To review, photosynthesis is how plants make their own food. Respiration is how plants use that food for energy. While photosynthesis occurs in sunlight, respiration can occur in the dark or the light. All organisms use respiration, but plants also use photosynthesis. Use the chart below to compare these two important processes. Photosynthesis Respiration produces food uses food stores energy releases energy uses water uses glucose uses carbon dioxide uses oxygen produces glucose produces water vapor produces oxygen produces carbon dioxide occurs in sunlight occurs in the dark or light used primarily by plants used by all organisms Try This When plants lose water vapor through their leaves, it is called transpiration. To prove that plants give off water, try sealing a few leaves of a living plant in a bag for a few days and watch what happens!