The oxygen produced by a plant comes most directly from

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: Eukaryotes is incorrect because eukaryotes are organisms that have cells with a nucleus and other membrane-bound organelles, such as animals, plants, fungi, and protists. Some eukaryotes, such as protists, are microscopic and require microscopy to be studied, but others, such as animals and plants, are macroscopic and can be seen with the naked eye.

Choice B rationale: Fungi is incorrect because fungi are a group of eukaryotic organisms that include mushrooms, molds, yeasts, and lichens. Some fungi, such as yeasts and molds, are microscopic and require microscopy to be studied, but others, such as mushrooms and lichens, are macroscopic and can be seen with the naked eye.

Choice C rationale: Prokaryotes is correct because prokaryotes are organisms that have cells without a nucleus or other membrane-bound organelles, such as bacteria and archaea. All prokaryotes are microscopic and require microscopy to be studied. Prokaryotes are the smallest and most abundant living organisms on Earth.

Choice D rationale: Plants is incorrect because plants are a group of eukaryotic organisms that have cells with a cell wall, chloroplasts, and a large central vacuole, such as mosses, ferns, and flowering plants. Some plants, such as mosses and algae, are microscopic and require microscopy to be studied, but others, such as ferns and flowering plants, are macroscopic and can be seen with the naked eye.