The mechanical stage upper knob causes the stage to move

Choice A rationale: Movement of water into the blood from the dialysis solution is incorrect because it is not the main goal of dialysis. Dialysis aims to remove excess water and solutes from the blood, not to add more water to it. The dialysis solution is usually isotonic to the blood, which means it has the same osmotic pressure and does not cause water movement.

Choice B rationale: Simple diffusion across a semi-permeable membrane is correct because it is the process of dialysis. Dialysis is the separation of small molecules from large molecules by using a membrane that allows only the small molecules to pass through. The dialysis membrane is semi-permeable, which means it is selective in what it allows to cross. The dialysis solution contains a lower concentration of wastes than the blood, which creates a concentration gradient that drives the diffusion of wastes from the blood to the solution.

Choice C rationale: Active transport across a semi-permeable membrane is incorrect because it is not involved in dialysis. Active transport is the movement of molecules across a membrane against their concentration gradient, which requires energy and transport proteins. Active transport is not necessary for dialysis, since the concentration gradient is favorable for diffusion.

Choice D rationale: Active transport of glucose from the blood to the dialysis solution is incorrect because it is not beneficial for dialysis. Glucose is a vital nutrient for the body, and it should not be removed from the blood. The dialysis solution usually contains glucose to prevent its loss from the blood by diffusion.

Choice E rationale: Facilitated diffusion across a semi-permeable membrane is incorrect because it is not relevant for dialysis. Facilitated diffusion is the passive movement of molecules across a membrane with the help of transport proteins. Facilitated diffusion is not needed for dialysis, since the wastes are small enough to cross the membrane by simple diffusion.

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