"Critical thinking question" for Chapter 4 Student name: Dilnaz Kairzhanova Student ID: 20240968 Question: Several lines of evidence support the hypothesis that mitochondria and chloroplasts evolved from parasitic prokaryotic cells living in the cytoplasm of primitive eukaryotic cells. What types of evidence would you look for to support or refute this hypothesis? Interestingly, compared to other organelles, mitochondria and chloroplasts contain their own DNA and ribosomes (see Figures 1 and 2), which then interact to synthesize proteins (Simon & Dickey, 2019). Their genetic systems are very different from the genome of the eukaryotic cell they reside in. Firstly, according to Simon and Dickey (2019), every mitochondrion and chloroplast may have only one circular DNA chromosome. Also, they reproduce themselves by dividing into two parts. This is done by replication of their DNA and transmission of the genes to ribosomes at each division. These characteristics of mitochondrial and chromosomal genetic systems resemble those of prokaryotic cells. Moreover, if we pay attention to the very structures of these organelles, we can notice many similarities, too. For example, the presence of a double membrane in both organelles is similar to those of bacterial cells. Moreover, the size of the mitochondrion and chloroplast is nearly the same as the size of the tiny prokaryotic cell (Cooper, 2000). Thus, since mitochondria and chloroplasts are similar to prokaryotic cells both physiologically and biochemically, there is a basis for this hypothesis of organelle evolution. Also, this hypothesis can be reasoned by the fact that even if prokaryotic cells lived in the host organism by symbiosis, over time they could become interdependent on the host and turn into its organelles. Figure 1. Inner structure of mitochondrion (Rogers, 2024) Figure 2. Inner structure of chloroplast (Bashir, 2023) References Bashir, R. (2023, February 10). Chloroplast - Its structure and function - Microbial notes. https://microbialnotes.com/chloroplast#google_vignette Cooper, G. M. (2000). The origin and evolution of cells. The Cell - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK9841/ Rogers, K. (2024, August 23). Mitochondrion Structure [Schematic]. Encyclopedia Britannica. https://cdn.britannica.com/89/22489-050-EB3B8C59/membrane-mitochondrion-crista e-structures-Proteins-majority-components.jpg Simon, E. J., & Dickey, J. L. (2019). Campbell Essential Biology, Global Edition. Pearson UK.