Chapter 4. Chapter 6: Dietary Energy and Cellular Respiration

4.1 Introduction

Welcome to the Interactive Study Guide for Chapter 6: Dietary Energy and Cellular Respiration! This Study Guide will help you master your understanding of the chapter's Driving Questions, using interactive Infographics and activities, as well as targeted assessment questions. Click "Next" to get started, or select a Driving Question from the drop-down menu to the right.

DRIVING QUESTIONS

• Why do humans weigh more now than in the past?
• How does the body use the energy in food?
• How does aerobic respiration extract useful energy from food?
• When does fermentation occur, and why can’t it sustain human life?

4.2 Driving Question 1

Why should you care?

Well over 50% of American men and women, and an increasing number of American children, are classified as overweight or obese. This means that their body compositions – the proportion of muscle, fat, bone, etc. in their bodies -- include too much fat for their height. Being overweight or obese increases the risk of developing heart disease, diabetes, and some forms of cancer; the current trends are problematic, therefore, both for individuals and for society as a whole. The most common measure of body composition is the Body Mass Index (BMI), a number calculated by using a combination of an individual’s height and weight. BMI must be interpreted with some caution because it is only an indirect measure of body composition: some individuals might register as overweight or obese despite having healthy body compositions.

Understanding the reasons why Americans – and people in countries that adopt American eating habits – are increasingly overweight and obese is the first step toward solving the problem. The reasons are complex and include the interaction of our adaptations to a long evolutionary history of food shortage with a modern culture of eating large meals of calorie-dense foods. Which of these factors is easier to change?

What should you know?

To fully answer this Driving Question, you should be able to:

1. Discuss the aspects of our biological history and modern culture that contribute to the obesity epidemic and describe the consequences of their interaction.
2. Evaluate the data from Infographic 6.3 in light of the hypothesis that biology and culture interact to contribute to the growing problem of obesity in the United States.

Infographic Focus

The infographics most pertinent to the Driving Question are 6.1, 6.2 and 6.3.

Evaluate the data from Infographic 6.3 in light of the hypothesis that biology and culture interact to contribute to the growing problem of obesity in the United States.

Question 4.5

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Yes, these data could be used to test this hypothesis, since there is likely a cultural difference between U.S. and French food portion sizes.

Question 4.6

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These data support the hypothesis that biology and culture interact to contribute to the obesity problem in the United States because the food portion in the United States is at least twice as large as the portion in France in almost every restaurant studied. Since there is likely a cultural difference behind this difference and since Americans have a higher rate of obesity than the French, this supports the hypothesis that culture and biology are both contributing to the obesity problem.

4.3 Driving Question 2

Why should you care?

Physiologically, we become overweight/obese by consuming more food energy (Calories) than our body needs, and then storing the excess as fat. Foods vary in their energy content because they vary in the proportion of fats, carbohydrates, and proteins they contain. If we know the energy content of different macromolecules and the proportions of those macromolecules in different kinds of foods, we can better control our Calorie intake and, ultimately, our body composition.

Our bodies have evolved an efficient way to deal with excess calories (this is good news or bad news, depending on your perspective!). Excess simple sugars are bound into glycogen, a complex carbohydrate, and stored in our muscles and liver. Glycogen is an excellent short-term energy storage molecule because it is quickly broken down. Triglycerides (a type of fat), on the other hand, are better long-term energy storage molecules because they are so energy-dense: a little fat stores a lot of energy. Understanding how energy reserves are stored and mobilized can help with proper nutrition and smart exercise plans.

What should you know?

To fully answer this Driving Question, you should be able to:

1. List the energy-containing biomolecules and the approximate amount of energy each contains.
2. Explain the process by which excess nutrients are converted to energy storage compounds.
3. Compare and contrast glycogen and fat as energy storage molecules.

Infographic Focus:

The infographics most pertinent to the Driving Question are 6.4, 6.5 and Table 6.1.

4.4 Driving Question 3

Why should you care?

Just as you can’t take a bar of gold to a convenience store to buy coffee, our bodies can’t use a complex carbohydrate to fuel muscle contractions or other forms of cellular work. Instead, our cells carry out a complex process of energy conversion that results in the production of ATP, the single molecule that acts as energy “currency” for all living things.

Aerobic respiration is a metabolic process that uses oxygen to break down energy-rich food molecules in order to extract and store their energy in the form of ATP. This process takes place when we are at rest, of course, but also when we are performing aerobic exercise. Aerobic exercise is a critical component of weight control because it involves large muscles using up huge amounts of ATP. To keep the ATP supply going, we break down glycogen and fat and use their subunits as the raw material for aerobic respiration.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Explain the role of adenosine triphosphate (ATP) in living things.
2. List the major inputs and outputs of aerobic respiration.
3. Describe how the inputs are delivered to cells and the waste products removed.
4. Describe the three major stages of aerobic respiration.

Infographic Focus:

The infographics most pertinent to the Driving Question are 6.6, 6.7, 6.8 and 6.10.

4.5 Driving Question 4

Why should you care?

Fermentation is a metabolic process that, some of our body cells can use it to generate ATP when oxygen is scarce. Sprinters and power lifters train to build up their anaerobic capacity – their ability to power their muscles over relatively short intervals when their bodies cannot supply oxygen rapidly enough for their activities to be fueled aerobically. Because anaerobic activities can only be sustained for a few minutes, they are ineffective (by themselves) for weight control and building heart health.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Illustrate, outline, and describe fermentation.
2. Compare the ATP output from fermentation to the output from aerobic respiration.
3. Explain the role of fermentation in a healthy organism.

Infographic Focus:

The Infographic most pertinent to the Driving Question is 6.9.