Matter and Energy 3.5

Introduction to Energy in Biological Systems

Energy is a fundamental concept in chemistry and biology, playing a crucial role in all living systems. In the context of General, Organic, and Biological (GOB) Chemistry, understanding how energy is measured, transferred, and utilized in the body is essential for interpreting nutritional information and metabolic processes.

Energy and Nutrition

Measuring Energy Expenditure

• Energy Expenditure: Physical activities, such as swimming, require energy. For example, one hour of swimming uses approximately 2100 kJ of energy.

• Units of Energy: The energy content of food and the energy used by the body are commonly measured in kilojoules (kJ) or kilocalories (kcal).

• Learning Goal: Be able to use energy values to calculate the number of kilocalories (kcal) or kilojoules (kJ) in foods.

Calorimeters

Definition and Function

• Calorimeter: A device used to measure the amount of heat transferred during a chemical or physical process.

• Bomb Calorimeter: Nutritionists use a type of calorimeter called a bomb calorimeter to determine the energy content of food.

• Structure: Consists of a steel container (combustion chamber) filled with oxygen and surrounded by a measured amount of water.

• Operation: The food sample is combusted inside the chamber, releasing heat that is absorbed by the surrounding water. The temperature increase of the water is used to calculate the energy value of the food.

How Calorimeters Measure Energy Values

• Process: The heat released from burning a food sample is transferred to water, and the temperature change is measured.

• Calculation: The energy value of the food is determined from the heat gained by the water.

Equation:

• q: Heat absorbed (in joules or kilojoules)

• m: Mass of water (in grams)

• c: Specific heat capacity of water (4.184 J/g°C)

• ΔT: Change in temperature (°C)

Energy and Nutrition: Food Labels

Units of Energy on Food Labels

• Calorie (Cal): On food labels, energy is shown as the nutritional Calorie (with a capital C), which is equivalent to a kilocalorie (kcal).

• International Units: In many countries outside the United States, energy is listed in kilojoules (kJ).

• Conversions:

  • 1 Cal (nutritional Calorie) = 1 kcal = 1000 calories (small 'c')

  • 1 kcal = 4.184 kJ

Caloric Food Values

Energy Content of Macronutrients

The caloric or energy value for 1 gram of a food is given in kilojoules (kJ) or kilocalories (kcal). Different macronutrients provide different amounts of energy per gram.

Example: Calculating Energy Content of Food

• Problem: A cup of whole milk contains 13 g of carbohydrate, 9.0 g of fat, and 9.0 g of protein. How many kilocalories does a cup of whole milk contain?

• Solution:

  • Carbohydrate:

  • Fat:

  • Protein:

  • Total:

Chemistry Link to Health: Weight Loss and Energy Requirements

Daily Energy Requirements

• Energy Needs: The number of Calories or kilojoules needed daily depends on factors such as gender, age, weight, and level of physical activity.

• Physical Activity: More active individuals require more energy.

Additional info: Actual values may vary based on individual characteristics and specific activity levels.