Practice question · Sort into groups
The blood-brain barrier admits small, lipid-soluble molecules but stops most others. Sort each item.
Groups: Crosses the barrier readily · Largely kept out
- Alcohol (small, lipid-soluble)
- Nicotine (small, lipid-soluble)
- Most large protein-based medicines
- A large water-soluble drug molecule
- Bloodborne bacteria
Hints
- The criterion is not 'good vs bad' - it is small AND lipid-soluble versus large or water-soluble.
- Alcohol and nicotine slip through; big or water-loving molecules and pathogens do not.
Show the answer
Crosses the barrier readily: Alcohol (small, lipid-soluble), Nicotine (small, lipid-soluble)
Largely kept out: A large water-soluble drug molecule, Bloodborne bacteria, Most large protein-based medicines
Why
The barrier's tight junctions favour small, lipid-soluble molecules (alcohol, nicotine) and exclude large or water-soluble ones and pathogens. Applying the size/solubility criterion - not a value judgement - is the skill being tested.
Practise Central Nervous System
The app has 6 more questions on this lesson, and keeps your place in the course. Psychology I is free to start.
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