Respiration is the process during which organic food, mainly glucose that is present in the cell, breaks down into simpler substances and liberates carbon dioxide and energy. The energy released during respiration is chemical energy. There are two types of respiration- aerobic and anaerobic respiration. During aerobic respiration, complete oxidation of carbohydrates takes place. Glucose is broken down by oxygen to release energy, while carbon dioxide and water are the by-products of the reaction. Aerobic respiration occurs in plants as well as animals and takes place in the mitochondria. Sometimes there is not enough oxygen around for animals and plants to respire, but they still need energy to survive, so they carry out respiration in the absence of oxygen to produce the energy they require. As the respiration takes place in the absence of oxygen, incomplete oxidation of food occurs and much less energy is released. However, carbon dioxide is still produced. This is called anaerobic respiration and the process occurs in the cytoplasm.
This video explains how to show experimentally that carbon dioxide is given out during respiration.