Which reagent is used to detect the presence of simple sugars?

Choice A rationale: Chlorophyll is the molecule that traps the sun's energy and initiates the process of photosynthesis. Photosynthesis is the process by which plants convert light energy into chemical energy, stored in the bonds of sugar molecules. Chlorophyll is a green pigment that is found in the thylakoid membranes of the chloroplasts, the organelles where photosynthesis occurs. Chlorophyll absorbs red and blue light from the sun and reflects green light, giving plants their characteristic color. Chlorophyll also transfers the light energy to electrons, which are then used to split water molecules and generate ATP and NADPH, the energy intermediates for the dark reaction of photosynthesis¹².

Choice B rationale: ATP is not the molecule that traps the sun's energy, but an energy molecule that is synthesized by the light reaction of photosynthesis. ATP stands for adenosine triphosphate, and it consists of a nitrogenous base, a sugar, and three phosphate groups. ATP stores energy in the bonds between the phosphate groups, and releases energy when one of the bonds is broken, forming ADP (adenosine diphosphate) and Pi (inorganic phosphate). ATP provides energy for the dark reaction of photosynthesis, which uses CO2 to produce glucose, a type of sugar³⁴.

Choice C rationale: Chloroplast is not the molecule that traps the sun's energy, but the organelle where photosynthesis occurs. Chloroplast is a membrane-bound structure that is found in the cytoplasm of plant cells. Chloroplast contains its own DNA and ribosomes, and can divide independently of the cell. Chloroplast has two main parts: the stroma, which is the fluid-filled space inside the chloroplast, and the thylakoid, which is a system of flattened sacs that contain chlorophyll and other pigments. The light reaction of photosynthesis takes place in the thylakoid, while the dark reaction takes place in the stroma⁵⁶.

Choice D rationale: Glyceraldehyde-3-phosphate is not the molecule that traps the sun's energy, but an intermediate molecule in the dark reaction of photosynthesis. Glyceraldehyde-3-phosphate, also known as G3P, is a three-carbon sugar that is formed from CO2 and energy intermediates from the light reaction. G3P can be converted to glucose, which is the main product of photosynthesis, or to other organic molecules, such as amino acids, lipids, and nucleotides. G3P can also be recycled to regenerate the five-carbon starter molecule called ribulose, which is needed for the dark reaction to continue⁷⁸.

Choice E rationale: Rubisco is not the molecule that traps the sun's energy, but an enzyme that catalyzes the first step of the dark reaction of photosynthesis. Rubisco stands for ribulose-1,5-bisphosphate carboxylase/oxygenase, and it is the most abundant protein on Earth. Rubisco combines CO2 with ribulose, a five-carbon sugar, to form a six-carbon intermediate that splits into two molecules of G3P. Rubisco is also responsible for a wasteful process called photorespiration, in which it binds O2 instead of CO2, resulting in the loss of carbon and energy⁹ .

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.