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

6. The Membrane

Introduction to Membrane Transport

General Biology

6. The Membrane

Introduction to Membrane Transport

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2:20 minutes

Problem 2

Textbook Question

Add labels to the figure that follows, which illustrates some molecules that can and cannot pass through cell membranes unaided.

Verified step by step guidance

Step 1: Identify the molecules shown in the first image. The small molecules with red and white spheres represent water (H₂O), which can pass through the cell membrane unaided. The larger molecule shown in the inset represents a polysaccharide, which cannot pass through the membrane unaided due to its size and polarity.

Step 2: Label the green arrows in the first image as 'Water molecules passing through the membrane unaided.' This indicates that water can diffuse across the lipid bilayer due to its small size and polarity.

Step 3: Label the red arrow pointing to the polysaccharide in the first image as 'Large molecules like polysaccharides cannot pass through the membrane unaided.' This highlights the need for transport mechanisms for larger molecules.

Step 4: In the second image, label the small red spheres as 'Oxygen (O₂)' and the small white spheres as 'Water (H₂O).' These molecules can diffuse across the membrane unaided due to their small size and non-polar or polar nature.

Step 5: Label the protein channels and carriers in the second image as 'Facilitated transport for larger or charged molecules.' This indicates that molecules like glucose or ions require specific transport proteins to cross the membrane.

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Key Concepts

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

Cell Membrane Structure

The cell membrane, also known as the plasma membrane, is composed of a phospholipid bilayer with embedded proteins. This structure is crucial for maintaining the integrity of the cell and regulating the movement of substances in and out. The hydrophobic interior of the bilayer acts as a barrier to most polar molecules, while allowing nonpolar molecules to pass more freely.

Selective Permeability

Selective permeability refers to the ability of the cell membrane to allow certain substances to pass while blocking others. This property is essential for maintaining homeostasis within the cell, as it controls the internal environment by regulating the entry and exit of ions, nutrients, and waste products. Molecules that are small and nonpolar can often diffuse through the membrane, while larger or charged molecules require specific transport mechanisms.

Transport Mechanisms

Transport mechanisms are processes that facilitate the movement of substances across the cell membrane. These include passive transport, such as diffusion and osmosis, which do not require energy, and active transport, which requires energy to move substances against their concentration gradient. Understanding these mechanisms is vital for interpreting how different molecules interact with the cell membrane, as illustrated in the provided figure.

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