Cellular examination of a cyanobacterium and a diatom reveals that the diatom has (which structure?) that is absent in the cyanobacterium?
a. DNA
b. chloroplasts
c. plasma membrane
d. a cell wall with peptidoglycan
e. all of the above
To determine which structure is present in a diatom but absent in a cyanobacterium, we can analyze the cellular characteristics of both organisms.
First, let's consider the options:
a. DNA: Both cyanobacteria and diatoms possess DNA as their genetic material. Therefore, this cannot be the structure that differentiates the two.
b. Chloroplasts: Chloroplasts are specialized structures involved in photosynthesis, and they are found in diatoms. Cyanobacteria, however, do not possess chloroplasts. This is due to the fact that diatoms are eukaryotic organisms and possess membrane-bound organelles like chloroplasts, while cyanobacteria are prokaryotes and lack membrane-bound organelles. Therefore, the correct answer is b. chloroplasts.
c. Plasma membrane: The plasma membrane is a fundamental structure that is present in all living cells, including both cyanobacteria and diatoms. Therefore, this cannot be the structure that distinguishes the two.
d. A cell wall with peptidoglycan: Cyanobacteria are prokaryotes, and one of the defining features of prokaryotes is the presence of a cell wall. However, cyanobacteria have a cell wall composed of different types of materials, such as peptidoglycan, glycoproteins, and polysaccharides. Diatoms, on the other hand, are eukaryotes and have a cell wall made of silica. Thus, the presence of peptidoglycan is characteristic of cyanobacteria and not diatoms. Therefore, the correct answer is d. a cell wall with peptidoglycan.
Based on the above analysis, the structure absent in the cyanobacterium but present in the diatom is a cell wall with peptidoglycan (answer d).