A major difference between red blood cells and Elodea cells is that Elodea cells have a cell wall, which protects them from bursting.

True or False?

Red blood cells are animal cells that lack a cell wall, a rigid structure that surrounds the cell membrane of plant cells, such as Elodea cells. A cell wall provides support and protection for the cell, and prevents excessive water uptake or loss. Red blood cells, on the other hand, rely on the osmotic balance of their environment to maintain their shape and function. If red blood cells are placed in a hypotonic solution, where the water concentration is higher outside than inside the cell, they will swell and burst due to osmosis. This is called hemolysis. If red blood cells are placed in a hypertonic solution, where the water concentration is lower outside than inside the cell, they will shrink and lose their ability to carry oxygen. This is called crenation.

Elodea cells, however, can withstand hypotonic or hypertonic solutions without bursting or shrinking, because their cell wall prevents the water from entering or leaving the cell beyond a certain point. Therefore, a major difference between red blood cells and Elodea cells is that Elodea cells have a cell wall, which protects them from bursting.

Choice A rationale: Iodine is a chemical element that forms a brown solution of iodine and potassium iodide, known as iodine solution. When this solution is added to a sample that contains starch, it forms a complex with the starch molecules, which changes the color of the solution to blue-black. This is based on the fact that starch is a polysaccharide that has a helical structure, which can trap the iodine molecules inside. ²

Choice B rationale: Biuret is a chemical compound that forms a blue solution of copper (II) sulfate and sodium hydroxide, known as biuret reagent. When this reagent is added to a sample that contains proteins or peptides, it forms a complex with the copper (II) ions, which changes the color of the solution to violet or pink. This is based on the fact that proteins and peptides have peptide bonds, which have nitrogen atoms that can coordinate with the copper (II) ions. ³

Choice C rationale: Benedict's is a chemical compound that forms a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, known as Benedict's reagent. When this reagent is heated with a sample that contains reducing sugars, such as glucose or maltose, it reduces the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. This is based on the fact that reducing sugars have free aldehyde or ketone groups that can donate electrons to the copper (II) ions. ⁴

Choice D rationale: Phenol red is a chemical compound that forms a red solution that is used as a pH indicator. When this solution is added to a sample that has an acidic or neutral pH, it remains red or turns yellow. When this solution is added to a sample that has an alkaline pH, it turns pink or fuchsia. This is based on the fact that phenol red has a sulfonated hydroxyquinone group that can lose or gain protons depending on the pH of the solution. ⁵

Choice E rationale: Sudan IV is a chemical compound that forms a red powder that is used as a stain for lipids. When this powder is dissolved in a solvent and added to a sample that contains lipids, such as fats or oils, it dissolves in the lipids and stains them red. When this solution is added to a sample that does not contain lipids, it remains in the solvent and does not stain the sample. This is based on the fact that Sudan IV is a nonpolar compound that can dissolve in nonpolar substances like lipids, but not in polar substances like water. ⁶.