What does the term motile mean?

Choice A rationale: The variant is a term used to describe a viral genome that may contain one or more mutations. It is not related to the difference in concentration between two areas. ³

Choice B rationale: The concentration gradient is the correct term for the difference in concentration between two areas. It is a measure of how steep the change in concentration is. ¹

Choice C rationale: Level gradient is not a term used in biology or chemistry. It may refer to the slope of a surface or a line, but not to the concentration of solutes in a solution.

Choice D rationale: The osmotic pressure is the minimum pressure required to prevent the flow of solvent molecules through a semipermeable membrane. It depends on the concentration of solute particles in the solution and is calculated with the formula π = iCRT. It is not the same as the concentration gradient, although it is related to it. ⁴

Choice E rationale: Turgid pressure is the force exerted by stored water against a cell wall. It is caused by the osmotic flow of water and occurs in plants, fungi, and bacteria. It is also called hydrostatic pressure and affects cell growth, movement, and dispersal. It is not the same as the concentration gradient, although it is influenced by it. ⁵

Choice A rationale: Sudan IV is a stain used to stain lipids. It is a red powder that dissolves in lipids and stains them red, but does not react with sugars. ¹

Choice B rationale: Benedict's is a reagent used to test for reducing sugars. It is a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate that reduces the copper (II) ions to copper (I) ions when heated with a reducing sugar, forming a red, orange, or green precipitate of copper (I) oxide. ⁴

Choice C rationale: Biuret is a reagent used to test for proteins and polypeptides. It is a blue solution of copper (II) sulfate and sodium hydroxide that forms a violet or pink complex with the peptide bonds in proteins or peptides. ⁸

Choice D rationale: Phenol red is a pH indicator. It is a red solution that changes color from yellow to red over the pH range 6.8 to 8.2, and from pink to fuchsia over 8.2 to 10.0. It does not react with sugars. ¹¹

Choice E rationale: Iodine is a reagent used to test for starch. It is a brown solution of iodine and potassium iodide that forms a blue-black complex with the starch molecules. It does not react with simple sugars. ¹⁴