Which of the following tests requires heating prior to observing results?

Choice A rationale: Distilled water is not a positive control, but a negative control for the iodine test. Distilled water is a pure solvent that does not contain any starch or other carbohydrates. It does not react with the iodine solution and does not produce any color change. A negative control is used to confirm that there is no response to the reagent or the microorganism used in the test. It is used to set the baseline and verify that the detecting reagent is working properly³.

Choice B rationale: Olive oil is not a positive control, but a negative control for the iodine test. Olive oil is a lipid that does not contain any starch or other carbohydrates. It does not react with the iodine solution and does not produce any color change. A negative control is used to confirm that there is no response to the reagent or the microorganism used in the test. It is used to set the baseline and verify that the detecting reagent is working properly³.

Choice C rationale: Albumin solution is not a positive control, but a negative control for the iodine test. Albumin is a protein that does not contain any starch or other carbohydrates. It does not react with the iodine solution and does not produce any color change. A negative control is used to confirm that there is no response to the reagent or the microorganism used in the test. It is used to set the baseline and verify that the detecting reagent is working properly³.

Choice D rationale: Starch solution is a positive control for the iodine test. Starch is a polysaccharide that contains many glucose units linked by glycosidic bonds. Starch reacts with the iodine solution and produces a blue-black color. A positive control is used to confirm that the test works and gives a positive result when the substance is present³.

Choice E rationale: Glucose solution is not a positive control, but a negative control for the iodine test. Glucose is a monosaccharide that does not contain any glycosidic bonds. Glucose does not react with the iodine solution and does not produce any color change. A negative control is used to confirm that there is no response to the reagent or the microorganism used in the test. It is used to set the baseline and verify that the detecting reagent is working properly³.

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 .