18 Food and Nutrition-Mid

Food and Nutrition Written by Katherine Follett

What Needs Food? All living things need energy. They need it to live, to do all the things they do each day, and to stay healthy. Living things get this energy from food. In this book, you will learn about two very important processes: how living things get food and how living things use food for energy. Before reading on, think about how plants get food and how they use it for energy.

How Do Plants Get Food? Plants and animals get the energy they need in different ways. Animals get energy by eating food. But plants do not eat. Plants make their own food in a process called photosynthesis. During photosynthesis, plants make a simple kind of sugar. This becomes their food source. You may think that plants get their food from the soil, but they don't Green plants contain chlorophyll, which absorbs the sunlight plants use to make sugar. Plants also use a gas called carbon dioxide, which is found in the air. The carbon dioxide gets absorbed through tiny holes that are mainly found on the bottom of a plant's leaves. Plants make food using sunlight, carbon dioxide, and water. It is true that soil does not provide plants with food. But soil does supply plants with water and minerals, which are both absorbed through the roots. Water and minerals are important during photosynthesis. Study the diagram of a plant on page 6. It explains the steps of photosynthesis that take place inside green plants.

Photosynthesis in Green Plants 1 Roots absorb water and minerals. The plant transports the water to the plant's cells. 2 The cells contain a green pigment called chlorophyll Chlorophyll. captures the Sun's energy. 3 The plant takes in carbon dioxide from the air through tiny holes on the bottoms of its leaves. 4 The leaf cells use the Sun's energy to break down the carbon dioxide and water. They convert the chemicals into a simple sugar, which is the plant's food. 5 The plant uses some of the sugar it makes. It stores the rest in its leaves, stem, roots, and other parts. 6 Oxygen gas is given off as a waste product when sugar is made. The leaves release the oxygen back into the air through the tiny holes.

In the formula below, the left side explains what plants use during photosynthesis. The right side explains what plants produce during photosynthesis. The arrow is like an equal sign. How Do Plants Use Food for Energy? After photosynthesis, the plant has sugar it can use for energy. Some of that energy remains stored inside the plant's leaves, stem, fruit, roots, and other parts. The plant uses the rest of the energy to grow by making new cells. The plant then breaks down the sugar in a different process, which is called respiration. Respiration is the opposite of photosynthesis. This time, the plant takes in oxygen from the air. The oxygen reacts with the sugar, creating the energy the plant needs in order to live. During respiration, water and carbon dioxide are also produced. They are released back into the air. Plants perform photosynthesis when the Sun is shining. But plants can perform respiration in either the dark or the light. The next formula explains what plants use (on the left) and what they produce (on the right) during respiration.

To review, plants make their own food during photosynthesis. Plants use that food for energy during respiration. Photosynthesis can only happen in the light. Respiration can happen in the dark or the light. All living things use respiration. Plants also use photosynthesis. Use this chart to compare the two processes. PHOTOSYNTHESIS RESPIRATION produces food uses food stores energy releases energy uses water uses sugar (glucose) uses carbon dioxide uses oxygen produces sugar (glucose) produces water vapor produces oxygen produces carbon dioxide occurs in sunlight occurs in the dark or light used mainly by plants used by all living things Try This You can prove that plants give off water vapor during respiration. Seal a bag over a few leaves of a living plant for a few days and see what happens.