Which reagent is used to detect the presence of simple sugars?

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

Choice A rationale: Only use lower power magnification is incorrect because this does not solve the problem of the dark field of view, but rather avoids it. Using lower power magnification means that you will not be able to see the details of the specimen that you want to observe under the 40x objective lens. Lower power magnification also has a larger field of view and a lower resolution than higher power magnification.

Choice B rationale: Add more immersion oil is incorrect because immersion oil is only used for the highest magnification objective lens, which is the 100x oil immersion objective lens, not the 40x objective lens. Immersion oil is a type of oil that has the same refractive index as glass, which means that it bends light in the same way as glass. Immersion oil is applied between the slide and the lens to reduce the refraction of light and increase the clarity of the image.

Choice C rationale: Adjust the fine adjustment knob is incorrect because the fine adjustment knob is used to fine-tune the focus of the specimen, not the brightness of the field of view. The fine adjustment knob is a small knob that is located on the side of the microscope, next to the coarse adjustment knob. The fine adjustment knob is used to make small changes in the distance between the objective lens and the specimen, which improves the sharpness of the image.

Choice D rationale: Increase the light intensity is correct because the light intensity is the amount of light that reaches the specimen and the objective lens, which affects the brightness of the field of view. The light intensity can be adjusted by using the rheostat, which is a dial that is located on the base of the microscope, next to the light source. The rheostat can increase or decrease the voltage of the light source, which changes the brightness of the light. Increasing the light intensity can make the field of view brighter and easier to see.