Question

(a) What is meant by the term fuel value? (b) Which is a greater source of energy as food, 5 g of fat or 9 g of carbohydrate? (c) The metabolism of glucose produces \(\mathrm{CO}_{2}(g)\) and \(\mathrm{H}_{2} \mathrm{O}(l) .\) How does the human body expel these reaction products?

Short answer

(a) Fuel value refers to the amount of energy released when a specific quantity of a substance is completely combusted or metabolized, measured in calories, kilocalories, or Joules per gram. (b) 5g of fat provides 45 kcal (188.5 kJ) of energy, while 9g of carbohydrate provides 36 kcal (150.3 kJ); therefore, 5g of fat is a greater source of energy than 9g of carbohydrate. (c) The human body expels carbon dioxide (CO₂) through the respiratory system, specifically during exhalation, and water (H₂O) through various means such as perspiration, urine, and exhaled air.

Step-by-step solution

(a) Definition of Fuel Value

Fuel value refers to the amount of energy that is released when a specific quantity of a substance is completely combusted or metabolized. It is usually measured in calories, kilocalories, or Joules per gram.

(b) Comparison of Energy Content of Fat and Carbohydrate

To compare the energy content of 5g of fat and 9g of carbohydrate, we need to know the energy content per gram of fat and carbohydrate: - Fat contains about 9 calories (or 37.7 kilojoules) per gram. - Carbohydrate contains about 4 calories (or 16.7 kilojoules) per gram. Now, let's calculate how much energy 5g of fat and 9g of carbohydrate provide: - Energy from 5g of fat: 5g x 9 kcal/g = 45 kcal (188.5 kJ) - Energy from 9g of carbohydrate: 9g x 4 kcal/g = 36 kcal (150.3 kJ)

(b) Conclusion

Since 45 kcal (from 5g of fat) is greater than 36 kcal (from 9g of carbohydrate), 5g of fat is a greater source of energy than 9g of carbohydrate.

(c) Expulsion of Carbon Dioxide and Water from Human Body

During the metabolism of glucose in the human body, carbon dioxide (CO₂) and water (H₂O) are produced as reaction products. The human body expels these products in the following ways: - Carbon dioxide (CO₂) is expelled through the respiratory system, specifically during exhalation. It is transported from the cells to the lungs via the bloodstream, where it is exchanged for oxygen, and then exhaled through the mouth and nose. - Water (H₂O) is expelled from the body through various means including perspiration (sweat), urine, and exhaled air. The kidneys play a crucial role in regulating the amount of water expelled from the body.

Key concepts

Energy Content

Energy content refers to the amount of energy a food or substance can release when it is metabolized in the body. Different types of foods provide varying amounts of energy, which is measured in units like calories, kilocalories (kcal), or joules (J).

• Fats provide approximately 9 calories per gram, making them a concentrated source of energy.
• Carbohydrates offer about 4 calories per gram, providing a quicker but less dense energy source.

Understanding the energy content of different foods can help in dietary planning and ensuring an adequate energy supply for bodily functions. Consider the balance between these two macronutrients for optimal energy provision.

Metabolism

Metabolism is the chemical process the body uses to convert food into energy. This process is essential for maintaining life by powering everything from breathing to thinking. Metabolism involves two main processes:

• Catabolism: Breaking down molecules, which releases energy.
• Anabolism: Building and storing energy in the form of molecules.

During metabolism, foods like carbohydrates and fats are broken down, releasing energy that the body uses for various activities. The efficiency of metabolism can vary depending on several factors, including age, muscle mass, and activity level.

Carbohydrates

Carbohydrates are a primary source of energy for the body, especially for the brain and during physical activity. They are converted into glucose, which is then metabolized for quick energy.

• Simple carbohydrates are broken down quickly and provide short-term energy.
• Complex carbohydrates take longer to break down, offering sustained energy.

Incorporating a balanced diet with both simple and complex carbohydrates can help maintain energy levels throughout the day. Foods rich in carbohydrates include fruits, vegetables, grains, and legumes.

Fats

Fats are a dense source of energy, providing more than twice the energy per gram than carbohydrates or proteins. They play a crucial role in absorbing vitamins and providing essential fatty acids.

• Fats serve as a major storage form of energy.
• They help protect vital organs and insulate the body.

Although essential, it's important to consume fats in moderation, focusing on healthy sources like nuts, seeds, fish, and avocados to maintain overall health and energy balance.

Respiratory System

The respiratory system is crucial for expelling carbon dioxide, a byproduct of glucose metabolism. It involves several key steps:

• Air travels through the nasal passage and mouth, down the trachea, and into the lungs.
• Oxygen is exchanged for carbon dioxide in the alveoli, tiny air sacs in the lungs.
• Carbon dioxide is carried back to the lungs via the bloodstream, where it is exhaled out of the body.

In addition to carbon dioxide, the respiratory system also helps expel some water vapor during exhalation. This process is vital for maintaining the body's pH balance and ensuring cellular efficiency in energy production.