A student uses iodine to visualize cells under the light microscope. Iodine stains starch deep blue and glycogen granules dark brown.
Observation of the cells reveals the presence of cell walls, dark brown granules, mitochondria, and a prominent nucleus. If the chemical composition of the cell wall is determined, which of the following molecules would MOST likely be the major constituent?
A.
cellulose ****
B.
chitin
C.
lignin
D.
peptidoglycan
The answer is B. Chitin. Peptidoglycan is present in bacteria and bacteria do not have mitochondria so you can cross that off. Cellulose and lignin are present in plants and they generally store their energy (glucose) in the form of starch rather than glycogen. Lastly, chitin is present in the exoskeleton of animals like lobsters and crickets, and fungi, but since animals do not possess cell walls it would be fungi and therefore B. Chitin.
The major constituent of the cell wall is most likely cellulose (Option A).
Cellulose is a complex carbohydrate that serves as a structural component in the cell walls of plants, algae, fungi, and some bacteria. It is composed of long chains of glucose molecules linked together.
Chitin (Option B) is another carbohydrate that can be found in the cell walls of fungi and the exoskeleton of arthropods but is not the major constituent of most cell walls.
Lignin (Option C) is a complex polymer that provides rigidity to plant cell walls, but it is not the major constituent.
Peptidoglycan (Option D) is a polymer that makes up the cell walls of bacteria, but it is not the major constituent of the cell walls in this case, as the question mentions the presence of mitochondria, which are not present in bacteria.
To determine the major constituent of the cell wall, we need to analyze the given information and apply knowledge about the composition of cell walls in different organisms.
From the information provided, we know that the cell wall is visible when using iodine staining. Iodine primarily stains starch deep blue and glycogen granules dark brown, but it does not specifically stain cellulose, chitin, lignin, or peptidoglycan.
Cellulose is a complex carbohydrate found in the cell walls of plants and some algae. It is not stained by iodine, so it is unlikely to be the major constituent of the cell wall in this case.
Chitin is another polysaccharide found in the cell walls of fungi and the exoskeletons of arthropods. Chitin is not stained by iodine either, so it is also unlikely to be the major constituent of the cell wall.
Lignin is a complex polymer found in the cell walls of woody plants. While it is possible for lignin to be partially stained by iodine, it is not the main constituent of a typical cell wall. Therefore, it is not the most likely major constituent.
Peptidoglycan is a unique molecule found in the cell walls of bacteria. Iodine staining is not typically used to visualize peptidoglycan, so it is an unlikely major constituent of the cell wall in this case.
Considering the information given and the known composition of cell walls, the most likely major constituent of the cell wall in this case is cellulose (option A).