Question 2 (1 point) Let's compare the proteins of Chlamydomonas with those of humans and the plant Arabidopsis. Which of the following is a protein that you find in all three species? A. ODA16, protein required for eukaryotic flagella assembly. B. Protochloriphylide reductase, and enzyme of the chlorophyl biosynthetic pathway. C. uS2, a protein required for DNA replication. D. Gas4, a protein required for assembly of cell walls. √ Saved

The correct answer is **C. uS2, a protein required for DNA replication.**<br /><br />Here's why:<br /><br />* **DNA replication is a fundamental process in all living organisms.** Humans, *Chlamydomonas* (a single-celled alga), and *Arabidopsis* (a plant) all require DNA replication for cell division and growth. Therefore, they all possess proteins involved in this process. uS2 is a ribosomal protein, and ribosomes are essential for protein synthesis, which is itself essential for DNA replication (among many other things).<br /><br />* **A. ODA16, protein required for eukaryotic flagella assembly.** While *Chlamydomonas* has flagella, humans only have flagella in sperm cells, and *Arabidopsis*, being a plant, does not have flagella at all.<br /><br />* **B. Protochlorophylide reductase, an enzyme of the chlorophyll biosynthetic pathway.** Only photosynthetic organisms like *Chlamydomonas* and *Arabidopsis* require chlorophyll. Humans do not perform photosynthesis.<br /><br />* **D. Gas4, a protein required for the assembly of cell walls.** Plants like *Arabidopsis* have cell walls, but humans and *Chlamydomonas* do not.<br />