http://en.wikipedia.org/wiki/Cyanobacteria
Scroll to photosynthesis and read. Then think about how most plants and algae use chloroplasts to photosynthesise.
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 answer this question, you will need to compare the cellular structures of a cyanobacterium and a diatom.
First, let's understand the basic differences between cyanobacteria and diatoms:
Cyanobacteria: Cyanobacteria are a group of photosynthetic bacteria that obtain energy through photosynthesis, just like plants and algae. They are prokaryotic organisms, meaning they lack a true nucleus and membrane-bound organelles.
Diatoms: Diatoms, on the other hand, are a type of eukaryotic algae that also perform photosynthesis. They have a true nucleus and membrane-bound organelles, making them more complex than cyanobacteria.
Now, let's consider the given options:
a. DNA: Both cyanobacteria and diatoms have DNA, as DNA is a fundamental component of all living organisms. Therefore, DNA is not the structure that is absent in the cyanobacterium.
b. Chloroplasts: Chloroplasts are specialized organelles in which photosynthesis takes place. Most plants and algae, including diatoms, have chloroplasts. However, cyanobacteria do not have chloroplasts. They perform photosynthesis using specialized membranes called thylakoids within their cells. So, the presence of chloroplasts is what differentiates diatoms from cyanobacteria.
c. Plasma membrane: Both cyanobacteria and diatoms have a plasma membrane. Therefore, the plasma membrane is not the structure that is absent in the cyanobacterium.
d. A cell wall with peptidoglycan: Cyanobacteria possess a cell wall, but it does not contain peptidoglycan. Peptidoglycan is a component of the cell wall in many bacteria, but cyanobacteria have a different type of cell wall composition. Diatoms, on the other hand, have a cell wall that contains silica, which is absent in cyanobacteria. Therefore, a cell wall with peptidoglycan is the structure that is absent in the cyanobacterium.
e. "All of the above" is not the correct answer because only option (b) - chloroplasts, is the structure that is absent in the cyanobacterium.
Therefore, the correct answer is b. chloroplasts.