Which of the following tests is used to detect the presence of lipids?
Biuret test
Gram's iodine test
Ninhydrin test
Brown paper test
Benedict's test
The Correct Answer is D
Choice A reason: Biuret test is a test for the presence of proteins or peptides in a solution. It involves adding Biuret reagent, which is a blue solution of copper (II) sulfate and sodium hydroxide, to the solution. If proteins or peptides are present, they form a complex with the copper (II) ions, which changes the color of the solution to violet or pink. ³
Choice B reason: Gram's iodine test is a test for the presence of starch in a solution. It involves adding iodine solution, which is a brown solution of iodine and potassium iodide, to the solution. If starch is present, it forms a complex with the iodine molecules, which changes the color of the solution to blue-black. ⁴
Choice C reason: Ninhydrin test is a test for the presence of amines or amino acids in a solution. It involves adding ninhydrin reagent, which is a purple solution of ninhydrin, to the solution. If amines or amino acids are present, they react with ninhydrin to produce a purple color, often called Ruhemann's purple. ¹
Choice D reason: Brown paper test is a test for the presence of lipids, such as fats or oils, in a solution. The test involves placing a drop of the solution on a piece of brown paper and letting it dry. If lipids are present, they leave a translucent spot on the paper, which can be seen by holding the paper against a light source. The test is based on the fact that lipids are nonpolar and do not dissolve in water, but can dissolve in organic solvents and stain the paper. ²
Choice E reason: Benedict's test is a test for the presence of reducing sugars, such as glucose or maltose, in a solution. The test involves adding Benedict's reagent, which is a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, to the solution and heating it in a water bath. If reducing sugars are present, they reduce the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. ⁵
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Related Questions
Correct Answer is C
Explanation
Choice A rationale: Starch solution is not a protein solution, but a carbohydrate solution. Starch is a polysaccharide, which is a polymer of glucose molecules. Starch does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, starch solution would not react with the biuret reagent and would not produce a violet color.
Choice B rationale: Olive oil is not a protein solution, but a lipid solution. Olive oil is mainly composed of triglycerides, which are esters of glycerol and fatty acids. Olive oil does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, olive oil would not react with the biuret reagent and would not produce a violet color.
Choice C rationale: Albumin solution is a protein solution. Albumin is a globular protein that is found in blood plasma and egg white. Albumin contains many peptide bonds, which are the bonds that link amino acids in proteins. Therefore, albumin solution would react with the biuret reagent and would produce a violet color.
Choice D rationale: Distilled water is not a protein solution, but a pure solvent. Distilled water is water that has been purified by boiling and condensing. Distilled water does not contain any solutes, such as proteins, carbohydrates, or lipids. Therefore, distilled water would not react with the biuret reagent and would not produce a violet color.
Choice E rationale: Glucose solution is not a protein solution, but a carbohydrate solution. Glucose is a monosaccharide, which is a simple sugar. Glucose does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, glucose solution would not react with the biuret reagent and would not produce a violet color.
Correct Answer is D
Explanation
Choice A rationale: Body tube is incorrect because the body tube is the part of the microscope that connects the eyepiece to the objective lenses, not the part that holds the objective lenses. The body tube is a hollow cylinder that allows the passage of light from the objective lenses to the eyepiece.
Choice B rationale: Stage is incorrect because the stage is the part of the microscope that supports the slide and the specimen, not the part that holds the objective lenses. The stage is a flat platform that has a hole in the center to allow the light source to illuminate the specimen.
Choice C rationale: Base is incorrect because the base is the part of the microscope that supports the whole microscope, not the part that holds the objective lenses. The base is the bottom part of the microscope that provides stability and balance.
Choice D rationale: Rotating nosepiece is correct because the rotating nosepiece is the part of the microscope that holds the objective lenses and allows them to be changed. The rotating nosepiece is a circular structure that has four or more objective lenses attached to it. The rotating nosepiece can be rotated to switch between different magnifications of the objective lenses.
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