What do we get from air? With every breath, your lungs fill up with air, but you don’t breathe out all of the oxygen you took in. What happens to the oxygen that you breathe in? Lungs have tiny spaces where the air goes, and each space is surrounded by tiny blood vessels. Some of the oxygen you breathe in goes into these blood vessels. The blood then takes oxygen to cells all over your body.
What do we get from food? You’ve already learned that we get organic matter from the foods we eat. These are carbohydrates, proteins, and fats. This organic matter is digested and broken down to monomers and taken to cells by the blood. Sometimes cells rebuild the monomers back into polymers in order to grow. But most monomers are used by cells in a different way: they are “reacted” with oxygen in the cells. Food contains molecules which are made of atoms and bonds. While the atoms can be used for growth the bonds can be used for energy.
How do we get energy from food? Every cell in your body needs energy, but how does it get energy? At first the energy is stored in food moleculesas chemical energy. The food molecules have carbon-carbon and carbon- hydrogen bonds. In order to release the energy from the bonds in the food the bonds must be broken. Breaking the bonds releases the energy and the cell can then use the energy. However, the atoms that were once connected by bonds have to go somewhere. The atoms rearrange into molecules that the cell does not need (carbon dioxide and water) and can get rid of as waste. How can it get rid of the waste products? Give them back to the blood! And the blood takes these waste products back to the lungs so you can breathe them out and get rid of them. This process of breaking down food molecules into carbon dioxide and water, in order to release energy, is called cellular respiration.
Glucose + Oxygen --> Carbon Dioxide + Water
Chemical energy in glucose is converted into kinetic energy used by the cell
C6H12O6 + 6O2 --> 6CO2 + 6H2O
Evidence of Cellular Respiration
We Breathe Out CO2 and H2O: As cells work, they give off carbon dioxide and water that they do not need. Carbon dioxide and water are inorganic molecules that do not have chemical energy. These molecules leave the cells and go back into the blood vessels. Eventually the H2O and CO2 leave our bodies. Carbon dioxide leaves when we breathe out. Water leaves when we breathe and sweat and urinate. What ways could you measure the H2O and CO2 animals give off when they breathe?
We Give Off Heat: Just like when you burn a piece of wood, burning food in your body also changes chemical energy to heat. Animal cells do this during cellular respiration. In fact, the heat you get from the food you eat is the same amount of heat that would be given off if you burned the food in a pan on the stove! A scientist name Max Rubner proved this to be true over 100 years ago. He found that burning dog food released the same amount of energy as was released if the dog ate and metabolized the food! The heat created when our cells do cellular respiration helps our body maintain its 98.6° temperature in warm and cold weather.
Our “Energy Level” Changes With Food: If animals do not get enough food and chemical energy they get tired. But when animals eat, they feel “energized.” That’s why athletes eat certain foods before a big race. Our bodies react the food with oxygen, changing the chemical energy in food into motion energy we use to move around and be active.