*Question*
Q: What can prevent the passage of molecules and ions between cells, such as in the blood-brain barrier? Choices: - fatty junctions - solid junctions - special junctions - tight junctions A:
**Answer**
tight junctions

*Question*
Q: Is the heat of reaction positive or negative for an endothermic reaction? Choices: - Neither - Both - Negative - positive A:
**Answer**
positive

*Question*
Q: What element is released into the atmosphere by the burning of fossil fuels? Choices: - carbon - helium - oxygen - sulfur A:
**Answer**
sulfur

*Question*
Q: What does a pollinator pick from its body and carry directly to another plant of the same species? Choices: - spore - pathogen - egg - pollen A:
**Answer**
pollen