Objective

Our objective is to show experimentally that carbon dioxide is given out during respiration.

Theory

Respiration is a biochemical process during which simple carbohydrates, like glucose, are broken down to release energy. Every cell of a living organism- man, animal and plant, respires.

Respiration in plants can be studied in moist germinating seeds that release carbon dioxide (CO₂) during respiration. The seeds are kept in an air tight conical flask. A small test tube containing potassium hydroxide (KOH) solution is placed in the flask. Potassium hydroxide absorbs carbon dioxide released by the seeds and a partial vacuum is created in the flask as a result. This causes the water level in the delivery tube to rise.

Respiration in humans can be studied with lime water. Carbon dioxide reacts with lime water on respiration to form calcium carbonate (CaCO₃) that turns lime water milky. Freshly prepared lime water is taken in a boiling tube and a cork with two glass tubes is inserted into the cork. The tip of one of the glass tube dips in the lime water and air is blown with full force through this glass tube. The bubbles of the air breathed out gradually turn lime water milky, showing that carbon dioxide is produced in human respiration.

Respiration

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.

Aerobic Respiration

Aerobic means ‘with air’. This type of respiration requires oxygen, so it is called aerobic 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. The released energy is used to make a special energy molecule called Adenosine triphosphate (ATP). ATP is where the energy is stored for later use by the body. Aerobic respiration occurs in plants as well as animals and takes place in the mitochondria.

The word equation for aerobic respiration is:

The chemical equation is:

Anaerobic Respiration

Anaerobic means without air. 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.

The word equation for anaerobic respiration in plants is:

The chemical equation is:

The word equation for anaerobic respiration in animals is:

The chemical equation is:

Factors Effecting Respiration

Here are some of the few factors that affect the rate of respiration.

• Temperature- At a very high temperature, the rate of respiration decreases with time and at very low temperature, the respiration rate is insignificant. Optimum temperature for respiration is 20 - 30^oC.
• Carbon dioxide concentration - Increase in CO₂ concentration and absence of O₂ adversely affects the rate of aerobic respiration.
• Light-  Light controls respiration by raising the temperature of an organism.
• Water- The respiratory rate increases with the increase in water content of the respiring organism.

Learning Outcomes

1. Students understand the terms respiration, aerobic and anaerobic respiration and ATP.
2. Students understand the two types of respiration.
3. Students understand the factors affecting the rate of respiration.
4. Students do the experiment better in the real lab having gone through the animation and simulation.