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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1:12 minutes

Problem 6

Textbook Question

Which of the following statements is false?
a. A healthy human has enough stored fat to supply calories for several weeks.
b. An increase in leptin levels leads to an increase in appetite and weight gain.
c. The interconversion of glucose and glycogen takes place in the liver.
d. After glycogen stores are filled, excessive calories are stored as fat, regardless of their original food source.

Verified step by step guidance

Step 1: Begin by analyzing each statement individually to determine its validity based on biological principles.

Step 2: Evaluate statement (a): 'A healthy human has enough stored fat to supply calories for several weeks.' This is true because fat is a long-term energy storage molecule, and humans can survive on stored fat during periods of caloric deficit.

Step 3: Evaluate statement (b): 'An increase in leptin levels leads to an increase in appetite and weight gain.' This is false because leptin is a hormone produced by adipose tissue that typically suppresses appetite and signals the brain to reduce food intake when fat stores are sufficient.

Step 4: Evaluate statement (c): 'The interconversion of glucose and glycogen takes place in the liver.' This is true because the liver plays a central role in glycogen storage and breakdown, converting glucose to glycogen (glycogenesis) and glycogen back to glucose (glycogenolysis) as needed.

Step 5: Evaluate statement (d): 'After glycogen stores are filled, excessive calories are stored as fat, regardless of their original food source.' This is true because once glycogen storage capacity is reached, surplus calories are converted into triglycerides and stored in adipose tissue, regardless of whether the calories come from carbohydrates, proteins, or fats.

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Key Concepts

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

Leptin and Appetite Regulation

Leptin is a hormone produced by adipose (fat) tissue that helps regulate energy balance by inhibiting hunger. Higher levels of leptin typically signal the brain to reduce appetite and increase energy expenditure. An increase in leptin levels generally leads to decreased appetite, not an increase, making this concept crucial for understanding the relationship between hormones and weight management.

Glycogen Storage and Utilization

Glycogen is a stored form of glucose primarily found in the liver and muscles. When the body requires energy, glycogen can be converted back into glucose through a process called glycogenolysis. Understanding how glycogen is synthesized and broken down is essential for grasping how the body manages energy reserves and responds to dietary intake.

Energy Storage and Conversion

The body stores excess energy from food in the form of glycogen and fat. Once glycogen stores are full, any additional calories consumed are converted into fat through lipogenesis. This process highlights the body's ability to adapt to varying energy intakes and is fundamental for understanding weight gain and metabolic health.