Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

39. Digestive System

Digestion

General Biology

39. Digestive System

Digestion

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0:56 minutes

Problem 14

Textbook Question

Consider the relationship between correlation and causation with respect to some pairs of human traits. For example, are freckles and red hair correlated? Is there causation? How does this concept relate to the study of human nutrition? Can you name examples of correlation in humans with respect to obesity? Explain each answer.

Verified step by step guidance

Understand the difference between correlation and causation: Correlation refers to a statistical relationship between two variables, meaning they tend to occur together, but it does not imply that one causes the other. Causation, on the other hand, means that one variable directly influences or causes the other.

Analyze the example of freckles and red hair: Freckles and red hair are correlated because they are both influenced by the same genetic factor, specifically the MC1R gene. However, this is not a case of causation because having red hair does not directly cause freckles, nor do freckles cause red hair. Both traits are simply linked through shared genetics.

Relate this concept to human nutrition: In the study of human nutrition, it is important to distinguish between correlation and causation. For example, a study might find that people who eat more fruits and vegetables tend to have lower rates of heart disease. This is a correlation, but it does not necessarily mean that eating fruits and vegetables directly prevents heart disease. Other factors, such as overall lifestyle, could also play a role.

Provide examples of correlation in humans with respect to obesity: One example is the correlation between sedentary behavior (e.g., watching TV for long hours) and obesity. Another example is the correlation between high sugar consumption and obesity. These correlations do not necessarily prove causation, as other factors like genetics, metabolism, and overall diet may also contribute to obesity.

Explain the importance of critical thinking: When studying human traits or nutrition, it is crucial to critically evaluate whether observed relationships are merely correlations or if there is evidence of causation. This helps avoid drawing incorrect conclusions and ensures that interventions or recommendations are based on sound scientific evidence.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Correlation

Correlation refers to a statistical relationship between two variables, indicating that when one variable changes, the other tends to change as well. This relationship can be positive (both increase) or negative (one increases while the other decreases). However, correlation does not imply that one variable causes the change in the other; it merely shows that a relationship exists.

Causation

Causation indicates a direct cause-and-effect relationship between two variables, where a change in one variable directly results in a change in the other. Establishing causation typically requires controlled experiments or longitudinal studies to rule out other influencing factors. Understanding causation is crucial in fields like nutrition, where specific dietary choices can directly impact health outcomes.

Human Traits and Nutrition

The study of human traits, such as obesity, often involves examining both genetic and environmental factors, including nutrition. Certain traits may show correlation with dietary habits, but understanding the causative factors behind obesity requires analyzing how specific nutrients affect metabolism and health. For instance, high sugar intake is correlated with obesity, but it is essential to explore how it contributes to weight gain through mechanisms like increased caloric intake and insulin resistance.

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Related Practice

Textbook Question

The media report numerous claims and counterclaims about the benefits and dangers of certain foods, dietary supplements, and diets. Have you modified your eating habits on the basis of nutritional information disseminated by the media? Why or why not? How should we evaluate whether such nutritional claims are valid?

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Textbook Question

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times.

What changes in digestive structure and function are associated with the evolution of herbivory?

Which of the following is true of the digestive tracts of minnows?

a. They are incomplete but have both a mouth and an anus.

b. They are complete, facilitating compartmentalization of digestion in different organs.

c. They are incomplete, with no accessory organs.

d. They are complete and include a large gastrovascular cavity.

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Textbook Question

It is estimated that 15% of Americans do not always have access to enough food. Worldwide, more than 1 billion people go to bed hungry most nights, and millions of people have starved to death in recent decades. In some cases, war, poor crop yields, and disease epidemics strip people of food. Many say instead that it is not inadequate food production but unequal food distribution that causes food shortages. What responsibility do nations have for feeding their citizens? For feeding the people of other countries? What do you think you can do to lessen world hunger?

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Textbook Question

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times.

What changes in digestive structure and function are associated with the evolution of herbivory?

Researchers compared the relative gut length—the length of the digestive tract divided by body length—in four species of herbivorous minnows and four species of carnivorous minnows. The results are shown in the graph provided here. Based on these data, what conclusion can you draw about the relationship between diet and gut length?

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Textbook Question

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times.

What changes in digestive structure and function are associated with the evolution of herbivory?

Suggest a function of the difference in relative gut lengths of herbivorous and carnivorous minnows.

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Textbook Question

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times.

What changes in digestive structure and function are associated with the evolution of herbivory?

Which minnows, herbivorous or carnivorous, should exhibit higher cellulase activity in the gut? Explain.

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Textbook Question

Minnows are mainly carnivorous, eating insects and other small animals. However, herbivory has evolved independently in minnows several times.

What changes in digestive structure and function are associated with the evolution of herbivory?

Why did the researchers compare relative gut length instead of absolute gut length?

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Multiple Choice

Which of the following is NOT an example of mechanical digestion?

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