Sugar is the source of energy for nearly all living things, including plants. In the presence of oxygen, this carbohydrate is broken down into energy, water and carbon dioxide. The process of converting sugar to energy is known as cellular respiration. Kids may find the concept of cellular respiration a little difficult to understand due to the various reactions and processes, such as glycolysis, citric acid cycle and electron transport. However, using experiments to demonstrate this reaction can help to make the concept clearer.
Cellular respiration in humans
Humans eat food to survive, develop and grow. During the process of cellular respiration, the cells in the body metabolise or break down the food and convert it into energy. The energy is temporarily stored in a molecule known as ATP (adenosine triphosphate) before it is transported to cells that require it. Carbon dioxide, which is produced during the conversion of carbohydrate into energy, is exhaled through the lungs. Cellular respiration in humans can be demonstrated using lime water. Take some lime and dissolve it in water. Get the child to blow into the lime water and let them watch the colour change. Lime water turns milky in the presence of carbon dioxide.
Cellular respiration in yeast
Yeast is a single-celled fungi used primarily to make bread. In yeast, cellular respiration takes place without oxygen and this is known as anaerobic respiration. However, even then carbon dioxide is produced along with energy. Take some brewer's yeast and mix it with some water and sugar. Place the mixture immediately into a small-mouthed bottle. Fix a rubber balloon on the mouth of the bottle. As cellular respiration takes place in the yeast, it will release carbon dioxide, which will cause the balloon to inflate.
Cellular respiration in seeds
After seeds fall from a plant, they go into a state of dormancy. They wait for ideal conditions to germinate. In order to survive, the seeds undergo cellular respiration using their stored sugar. Cellular respiration increases when seeds are about to germinate. Place some seeds in a test tube along with some calcium hydroxide. Invert the test tubes in a beaker of water. As cellular respiration occurs, the seeds will take in oxygen present in the test tube and release carbon dioxide, which will get absorbed by the calcium hydroxide. As a result, the air in the inverted test tubes will decrease allowing the water level to rise.
Cellular respiration in plants
Many people are not aware that besides photosynthesis, which is a process to manufacture food, plants also undergo cellular respiration for growth, development, reproduction and many other metabolic processes. In cellular respiration, the sugar stored in the cells is used to produce energy. The best way to conduct cellular respiration experiments on plants is by measuring the pH of water. During cellular respiration, plants release carbon dioxide, which makes the water acidic. Pour some distilled water in an empty jar and introduce elodea, which is an aquatic plant. Use just distilled water, as tap water contains minerals, which prevents the acidity of the water from changing. Place the jar in a dark area, such as a drawer, to prevent photosynthesis. During photosynthesis, plants release oxygen, which makes the water alkaline or neutral. After a few hours, use a mid-range pH indicator to test the water. Any pet shop with aquarium accessories will have this pH indicator. On testing the water sample, you will find that the water is acidic. This is due to the presence of carbon dioxide released during cellular respiration.