Which of the following is NOT a product of the light reaction?

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

Choice A rationale: Diffusion is correct because it is the passive movement of molecules from an area of high concentration to an area of low concentration. Small lipid soluble molecules can easily cross the plasma membrane by diffusing through the hydrophobic core of the phospholipid bilayer.

Choice B rationale: Filtration is incorrect because it is the process of separating solid particles from a fluid by passing it through a porous medium. Filtration does not involve the plasma membrane, and it does not depend on the solubility of the molecules.

Choice C rationale: Osmosis is incorrect because it is the diffusion of water across a selectively permeable membrane. Osmosis does not apply to lipid soluble molecules, which are not water molecules.

Choice D rationale: Active transport is incorrect because it is the movement of molecules across a membrane against their concentration gradient, which requires energy and transport proteins. Active transport does not depend on the solubility of the molecules, and it is not a passive process.

Choice E rationale: Pumping is incorrect because it is a type of active transport that involves the use of specific pumps to move ions or molecules across a membrane. Pumping does not apply to lipid soluble molecules, which are not ions or polar molecules.