Problem 89 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) What is meant by the term fuel value? (b) Which is a greater source of energy as food, \(5 \mathrm{~g}\) of fat or \(9 \mathrm{~g}\) 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?

Step-by-Step Solution

Answer

(a) Fuel value refers to the amount of energy released when a specific amount of a substance is burned or metabolized in the body, usually measured in calories or joules. (b) 5g of fat provides 45 calories of energy, whereas 9g of carbohydrate provides 36 calories, so fat is the greater source of energy. (c) CO2 is expelled through the respiratory system during exhalation, and H2O is expelled through sweating, urination, and respiration.

Step 1: (a) Definition of Fuel Value

Fuel value is the amount of energy that is released when a specific amount of a substance (usually food) is burned or metabolized in the body. This value is typically measured in units of energy, such as calories or joules.

Step 2: (b) Comparing available energy from fat vs carbohydrate

To answer this question, we need to know the energy provided by 1 g of fat and 1 g of carbohydrate. 1 g of fat provides approximately 9 calories of energy. 1 g of carbohydrate provides approximately 4 calories of energy. Now, let's calculate the total energy provided by 5 g of fat and 9 g of carbohydrate. Energy from 5 g of fat = 5 * (9 calories/g) = 45 calories Energy from 9 g of carbohydrate = 9 * (4 calories/g) = 36 calories Thus, 5 g of fat provides a greater source of energy as food compared to 9 g of carbohydrate.

Step 3: (c) Expelling the reaction products from the metabolism of glucose

The metabolism of glucose results in the formation of carbon dioxide (CO2) and water (H2O). The human body gets rid of these reaction products in the following ways: 1. Carbon dioxide (CO2): It is expelled from the body through the respiratory system. During exhalation, lungs remove the carbon dioxide from the body, which is then replaced with oxygen during inhalation. 2. Water (H2O): Water produced from glucose metabolism is expelled from the body through various processes, including sweating, urination, and respiration. Sweat glands release excess water and salts through sweating, and the kidneys filter and expel water and waste products through urination. Additionally, a small amount of water is also expelled during exhalation along with carbon dioxide.

Key Concepts

Energy Metabolism

Energy metabolism is the process by which the human body converts food into energy. It's a fundamental process that maintains life by fueling various bodily functions such as movement, growth, and repair. This energy conversion takes place through biochemical reactions that occur primarily in the mitochondria, known as the "powerhouses" of the cell. During energy metabolism, the foods we eat—whether carbohydrates, fats, or proteins—are broken down, and their energy is stored in the form of adenosine triphosphate (ATP), the main energy currency in cells.

Understanding energy metabolism is crucial, as it influences all the body's energy expenditures, from maintaining body temperature to contracting muscles. The efficiency of energy metabolism can vary depending on factors like age, muscle mass, and overall health, affecting how quickly or slowly calories are burned.

• The breaking down of macronutrients provides the raw energy needed.
• ATP acts as an immediate energy source for cellular processes.
• Mitochondria play a key role in energy conversion.

Clean energy conversion and efficient metabolism are essential to meet daily energy requirements and maintain health.

Glucose Metabolism

Glucose metabolism focuses on how the body processes glucose to derive energy. Glucose, a simple sugar found in many carbohydrates, is one of the primary energy sources for our cells. When you consume foods rich in carbohydrates, they are digested into glucose, which then enters the bloodstream. This increase in blood glucose prompts the pancreas to release insulin, a hormone necessary for allowing glucose to enter cells.

Once inside the cells, glucose undergoes glycolysis, a series of reactions that convert glucose into pyruvate, producing a small amount of ATP. This pyruvate is further processed in the mitochondria via the citric acid cycle, leading to the production of more ATP and the release of carbon dioxide and water as by-products.

• Insulin is critical for regulating glucose entry into cells.
• Glycolysis is the first step in breaking down glucose.
• The citric acid cycle is where most energy extraction occurs.

Efficient glucose metabolism is vital for maintaining healthy blood sugar levels and supporting energy demands in the body.

Macronutrients Comparison

Macronutrients—carbohydrates, proteins, and fats—are the primary sources of energy in our diet. Each macronutrient contributes different amounts of energy and fulfills various roles in maintaining health and bodily function.

Carbohydrates typically provide 4 calories per gram and are the body's preferred energy source, especially for short-term, high-intensity efforts.Proteins, like carbohydrates, offer 4 calories per gram. They are essential for building and repairing tissues but are not primarily used for energy unless in a deficiency state.
Fats are the most energy-dense macronutrient, offering about 9 calories per gram. They serve critical functions, such as supporting cell structure and protecting vital organs. Fats are more suitable for long-term energy storage due to their high energy content.

• Carbohydrates: 4 calories/gram - preferred for quick energy.
• Proteins: 4 calories/gram - used mainly for growth and repair.
• Fats: 9 calories/gram - best for sustained energy and storage.

Understanding the different energy values of macronutrients helps in making informed dietary choices to meet individual energy needs.