*Question*
Answer the following question given this paragraph: In addition to holding cells together, tight junctions play a role in the transport of materials. Tight junctions prevent the passage of molecules and ions through the space between cells. So these molecules and ions must actually enter cells (either by diffusion or active transport) in order to proceed through a tissue. This allows tight junctions to indirectly play a role over what substances are allowed into a specific cell. Tight junctions play this role in maintaining the blood-brain barrier. 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*
Answer the following question given this paragraph: Because the heat is absorbed by the system, the 177.8 kJ is written as a reactant. The heat of reaction is positive for an endothermic reaction. Q: Is the heat of reaction positive or negative for an endothermic reaction? Choices: - Neither - Both - Negative - positive A:
**Answer**
positive

*Question*
Answer the following question given this paragraph: water. Sulfur, critical to the 3D folding of proteins (as in disulfide binding), is released into the atmosphere by the burning of fossil fuels, such as coal. The cycling of these elements is interconnected. For example, the movement of water is critical for the leaching of nitrogen and phosphate into rivers, lakes, and oceans. Furthermore, the ocean itself is a major reservoir for carbon. Thus, mineral nutrients are cycled, either rapidly or slowly, through the entire biosphere, from one living organism to another, and between the biotic and abiotic world. Q: What element is released into the atmosphere by the burning of fossil fuels? Choices: - carbon - helium - oxygen - sulfur A:
**Answer**
sulfur

*Question*
Answer the following question given this paragraph: Wind-blown pollen might land anywhere and be wasted. Another adaptation solved this problem. Plants evolved traits that attract specific animal pollinators . Like the bee in Figure below , a pollinator picks up pollen on its body and carries it directly to another plant of the same species. This greatly increases the chance that fertilization will occur. 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