The main barrier that limits the diffusion of polar molecules across a plasma membrane is the of the membrane.

Researchers randomly divide participants into groups. each group takes a different amount of omega-3 fatty acid supplements daily for a month. one group receives a placebo. the researchers measure the impact on cholesterol levels in the blood. what is the purpose of random assignment in this experiment? a, to produce treatment groups with similar characteristics b, to ensure that all people with high cholesterol have an equal chance of being selected for the study c, to increase the accuracy of the research results and prevent skewness in the data

Read the following scenario to answer the following question. in some zoos, rare crosses between a male lion and a female tiger have produced hybrid offspring called "ligers." male ligers are sterile but some female ligers are fertile. in the wild, lion and tiger ranges do not naturally overlap, making such a cross unlikely. furthermore, the solitary behavior of tigers and the social organizations of lions create behavioral differences. applying the biological species concept, the sterility of ligers reveals that a. lions are probably a subspecies of tigers b. tigers and lions are the same species c. a new species called "ligers" is forming d. tigers and lions are separate species

Interpret the model. a three-part model with black right-arrows between the parts. left part: a large green apple-shaped component with a w-shaped indentation centered on top. a small blue apple-slice shape sits above the left indentation and an arrow points from the shape to the indentation. a small purple apple-slice shape and arrow sit above the right indentation and an arrow points from the shape to the indentation. middle part: a large green apple-shaped component with a square indentation centered on top. sitting in the left side of the indentation is a blue apple-slice shape with a flat bottom, fused to a purple apple-slice shape with a flat bottom on the right side of the indentation. right part: a large green apple-shaped component with a w-shaped indentation centered on top. an up-arrow is centered above the indentation pointing to a fused blue and purple apple-slice-shaped flat-bottom component sitting above the indentation. assigne "true" or "false" to the end of each statement. the model shows a shape change occurring in the enzyme after the substrate is bound in the active site. t/fthere are two products in this model. t? f there are three substrates in this model. t/f the model shows two different enzymes. t/f