The fine adjustment knob on the microscope

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: H2O is a reactant or input for the light reaction of photosynthesis. In the light reaction, water is split by the energy from sunlight in photosystem II, releasing electrons, protons, and oxygen. The electrons and protons are used to reduce NADP+ to NADPH and to synthesize ATP from ADP and Pi. The oxygen is either used for respiration or released into the air¹².

Choice B rationale: Oxygen is not a reactant or input for the light reaction of photosynthesis, but a product or output. Oxygen is released as a by-product of the splitting of water in photosystem II. Oxygen is either used for respiration or released into the air¹².

Choice C rationale: NADPH is not a reactant or input for the light reaction of photosynthesis, but a product or output. NADPH is an electron carrier that is reduced by the electrons from water in photosystem I. NADPH provides electrons and hydrogen for the dark reaction, which uses CO2 to produce glucose¹².

Choice D rationale: ATP is not a reactant or input for the light reaction of photosynthesis, but a product or output. ATP is an energy molecule that is synthesized by the enzyme ATP synthase using the proton gradient created by the electron transport chain. ATP provides energy for the dark reaction, which uses CO2 to produce glucose¹².

Choice E rationale: Carbon dioxide is not a reactant or input for the light reaction of photosynthesis, but a reactant or input for the dark reaction. The dark reaction uses CO2 and energy intermediates from the light reaction to produce glucose, a type of sugar. The dark reaction does not require light and can occur in the day or night¹².