Explanation:
With each breath you exchange the gases oxygen (O2) and carbon dioxide (CO2). Why is this exchange important? Why does your body need oxygen? What happens to the CO2? Where do we get O2? These are some of the questions that this section will help you answer.
Every cell in your body needs oxygen to function. You get the oxygen your cells need from the air you breathe. The air you breathe is made up of 20 percent oxygen. The rest of the air is mostly nitrogen (79%). Your body cells use the oxygen you breathe to get energy from the food you eat. This process is called cellular respiration. During cellular respiration the cell uses oxygen to break down sugar. Breaking down sugar produces the energy your body needs. This is very similar to wood burning in a fire. As the wood burns, it combines with oxygen and releases heat energy and carbon dioxide. When the cell uses oxygen to break down sugar, oxygen is used, carbon dioxide is produced, and energy is released. But instead of heat energy, much of the energy produced in cellular respiration is stored chemically for the cell to use later. Carbon dioxide is the waste product of cellular respiration that you breathe out each time you breathe. Blood picks up oxygen and releases carbon dioxide in the lungs. The opposite takes place in the cells where the blood releases oxygen and picks up carbon dioxide.
The Breath of Life
Think about where the O2 you inhale comes from and where the CO2 you exhale goes. The exchange of gases doesn't only take place in the cells in your body. Actually, gas exchange is taking place all around you. In fact, oxygen and carbon dioxide are involved in the most important relationship that exists between plants and animals.
[Figure 2]
Figure 3.1 The blood in your lungs picks up oxygen and releases carbon dioxide. In your cells blood picks up carbon dioxide and releases oxygen.
Do you know where the oxygen your body needs comes from? Almost all the oxygen you breathe comes from green plants. They produce oxygen during a process called photosynthesis. During photosynthesis green plants manufacture the sugar molecules fructose and glucose. Green plants use energy from sunlight to build sugar molecules from carbon dioxide and water. Oxygen is produced when the plant combines the carbon dioxide and the water by using the Sun's energy. Plants use the sugar they produce to make plant structure and to provide the energy they need to live. Green plants use some of the oxygen they produce for their own life processes. But they release most of the oxygen produced during photosynthesis into the air as a waste product.
Unlike plants, which can get energy directly from sunlight, animals (including humans) must get energy from the food they eat. That food can be plants and/or other animals. Now think about the process of cellular respiration again. During cellular respiration animal cells combine oxygen with food molecules to release energy to live and function. Remember that cellular respiration produces carbon dioxide as a waste product. Animals use energy to grow, reproduce, and to function. They release the carbon dioxide into the air as a waste product. Plants help animals and animals help plants.
Did You Know?
It wasn't until the 1850s that scientists realized the Earth is a closed system-nothing comes in or goes out. Elements in our environment have cycles. They are used again and again. Recycling is a natural part of our existence. That's one reason we need to be careful and keep our environment clean and healthy.
[Figure 3]
Figure 3.2 Plants use carbon dioxide during photosynthesis to produce sugars and oxygen. Animals and plants use oxygen in respiration to produce carbon dioxide.
Respiration
All living organisms-plants and animals-carry out cellular respiration 24 hours a day. Cellular respiration takes place every minute of every day of every month of every year, and so on. The process of respiration can be shown with words or in a chemical equation. Both are written below.
Oxygen+Glucose ⟶Energy + Carbon dioxide+water6O2 +C6H12O6⟶36 ATP+6CO2+6H2O
Let's read the chemical equation for cellular respiration. The equation shows that cells use six molecules of oxygen (6O2) to break down one molecule of glucose (C6H12O6). The arrow shows that when the sugar is broken down something else is produced. Energy, water, and carbon dioxide are produced. When the chemical bonds of the glucose molecule are broken, energy is released. The cell is able to store that energy in the chemical bonds of a special molecule called adenosine triphosphate or ATP. The energy stored in ATP can be used by the cell to do various kinds of work. For each molecule of glucose broken down, 36 molecules of ATP can be produced. Finally when the glucose molecule is broken down, the waste products are six molecules of carbon dioxide (6CO2) and six molecules of water (6H2O).
