Q: Q: Several neuropeptides, relatively short chains of amino acids, serve as neurotransmitters that operate via metabotropic what? A: | OPTIONS:
- lipids
- membranes
- organelles
- receptors
A: receptors

Q: Q: Prior to birth, the lungs are filled with amniotic fluid, mucus, and what else? A: | OPTIONS:
- blood
- plasma
- air
- surfactant
A: surfactant

Q: Q: The first living cells may have evolved around how long ago? A: | OPTIONS:
- 900,000 years
- 6 billion years
- 2.2 billion years
- 4 billion years
A: 4 billion years

Q: Q: By what are skeletal muscles attached to bones? A: | OPTIONS:
- joints
- ligaments
- veins
- tendons
A: tendons