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

Biological Membranes

General Biology

6. The Membrane

Biological Membranes

Previous problemNext problem

Struggling with General Biology?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

Which of the following will pass through a cell membrane most easily?

Ions such as Na$^+$

Large polar molecules such as glucose

Proteins

Small nonpolar molecules such as O$_2$

Previous problemNext problem

Verified step by step guidance

Understand the structure of the cell membrane: The cell membrane is primarily composed of a phospholipid bilayer, which has hydrophilic (water-attracting) heads on the outside and hydrophobic (water-repelling) tails on the inside. This structure makes the membrane selectively permeable.

Identify the types of molecules and their properties: Small nonpolar molecules like O$_2$ are hydrophobic and can easily dissolve in the hydrophobic core of the phospholipid bilayer. In contrast, ions like Na$^+$ are charged and require specific transport proteins, large polar molecules like glucose are too big and hydrophilic, and proteins are even larger and require specialized mechanisms to cross the membrane.

Recall the principle of passive diffusion: Small nonpolar molecules such as O$_2$ can pass through the cell membrane via passive diffusion, which does not require energy or transport proteins. This is because they can move directly through the hydrophobic core of the membrane.

Compare the ease of transport for each molecule: Ions like Na$^+$ are repelled by the hydrophobic core due to their charge, large polar molecules like glucose cannot pass due to their size and polarity, and proteins are too large and complex. Small nonpolar molecules like O$_2$ face no such barriers and pass through most easily.

Conclude based on the properties of the molecules and the cell membrane: Small nonpolar molecules such as O$_2$ are the most likely to pass through the cell membrane easily due to their compatibility with the hydrophobic core of the phospholipid bilayer.