Which reagent is used to detect the presence of starch?
Iodine
Biuret
Benedict's
Phenol red
Sudan IV
The Correct Answer is A
Choice A rationale: Iodine is a chemical element that forms a brown solution of iodine and potassium iodide, known as iodine solution. When this solution is added to a sample that contains starch, it forms a complex with the starch molecules, which changes the color of the solution to blue-black. This is based on the fact that starch is a polysaccharide that has a helical structure, which can trap the iodine molecules inside. ²
Choice B rationale: Biuret is a chemical compound that forms a blue solution of copper (II) sulfate and sodium hydroxide, known as biuret reagent. When this reagent is added to a sample that contains proteins or peptides, it forms a complex with the copper (II) ions, which changes the color of the solution to violet or pink. This is based on the fact that proteins and peptides have peptide bonds, which have nitrogen atoms that can coordinate with the copper (II) ions. ³
Choice C rationale: Benedict's is a chemical compound that forms a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, known as Benedict's reagent. When this reagent is heated with a sample that contains reducing sugars, such as glucose or maltose, it reduces the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. This is based on the fact that reducing sugars have free aldehyde or ketone groups that can donate electrons to the copper (II) ions. ⁴
Choice D rationale: Phenol red is a chemical compound that forms a red solution that is used as a pH indicator. When this solution is added to a sample that has an acidic or neutral pH, it remains red or turns yellow. When this solution is added to a sample that has an alkaline pH, it turns pink or fuchsia. This is based on the fact that phenol red has a sulfonated hydroxyquinone group that can lose or gain protons depending on the pH of the solution. ⁵
Choice E rationale: Sudan IV is a chemical compound that forms a red powder that is used as a stain for lipids. When this powder is dissolved in a solvent and added to a sample that contains lipids, such as fats or oils, it dissolves in the lipids and stains them red. When this solution is added to a sample that does not contain lipids, it remains in the solvent and does not stain the sample. This is based on the fact that Sudan IV is a nonpolar compound that can dissolve in nonpolar substances like lipids, but not in polar substances like water. ⁶.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is {"dropdown-group-1":"B","dropdown-group-2":"B"}
Explanation
Choice A rationale: Low, high is incorrect because it is the opposite of the direction of simple diffusion. Simple diffusion is the passive movement of molecules along their concentration gradient, which means from high to low concentration.
Choice B rationale: Low, equal is incorrect because it is not the final state of simple diffusion. Simple diffusion will continue until the concentration of molecules is equal on both sides of the membrane.
Choice C rationale: Equal, low is incorrect because it is not possible for simple diffusion. Simple diffusion will stop when the concentration of molecules is equal on both sides of the membrane, and there will be no net movement of molecules.
Choice D rationale: Equal, high is incorrect because it is not possible for simple diffusion. Simple diffusion will stop when the concentration of molecules is equal on both sides of the membrane, and there will be no net movement of molecules.
Choice E rationale: High, low is correct because it is the definition of simple diffusion. Simple diffusion is the passive movement of molecules along their concentration gradient, which means from high to low concentration.
Correct Answer is B
Explanation
Tonicity is the ability of a solution to cause water movement across a semi-permeable membrane, such as the cell membrane. In the lab, tonicity can be tested by observing the effects of different solutions on cells, such as red blood cells or plant cells. However, the items that have been contaminated with blood, such as slides, pipettes, or gloves, cannot be thrown away in the regular trash can, because they pose a biohazard risk. Biohazardous waste is any material that contains or has been exposed to infectious agents, such as blood, bacteria, viruses, or parasites. Biohazardous waste must be handled and disposed of according to specific safety protocols, such as using autoclaves, incinerators, or biohazard bags. Therefore, after testing tonicity in the lab, the items that have been contaminated with blood cannot be disposed of in the trash can.
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