Question at position 5 What evidence indicates mitochondria evolved before chloroplasts in eukaryotic cells?Mitochondria are larger and more complex than chloroplasts.Mitochondria contain linear chromosomes, whereas chloroplasts have circular chromosomes.Chloroplasts can reproduce independently, while mitochondria cannot.All eukaryotes have mitochondria, but only some groups have chloroplasts.Clear my selection

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Question at position 5 What evidence indicates mitochondria evolved before chloroplasts in eukaryotic cells?Mitochondria are larger and more complex than chloroplasts.Mitochondria contain linear chromosomes, whereas chloroplasts have circular chromosomes.Chloroplasts can reproduce independently, while mitochondria cannot.All eukaryotes have mitochondria, but only some groups have chloroplasts.Clear my selection

BlackTom AI · Accepted Answer

Question at position 5 asks about evidence that mitochondria evolved before chloroplasts in eukaryotic cells. We'll evaluate each option in turn.
Option 1: 'Mitochondria are larger and more complex than chloroplasts.' At first glance, size and complexity differences do not reliably indicate the relative timing of origin. Both organelles evolved from endosymbiotic ancestors and have vast diversity in size and complexity across lineages; this statement oversimplifies and does not constitute evidence for the order of evolution.
Option 2: 'Mitochondria contain linear chromosomes, whereas chloroplasts have circular chromosomes.' In reality, both mitochondria and chloroplasts typically carry circular DNA molecules in most lineages. While there are rare exceptions or structural variations found in some organisms, the general rule is that these organelles harbor circular genomes, so this claim is not a robust indicator of evolutionary timing.
Option 3: 'Chloroplasts can reproduce independently, while mitochondria cannot.' This is a common misconception. Both organelles replicate by division and are constrained by the host cell; neither truly reproduces independently in the sense of a free-llying organism. Thus, this option does not provide valid evidence about which arose first.
Option 4: 'All eukaryotes have mitochondria, but only some groups have chloroplasts.' This statement aligns with the widely accepted phylogenetic sequence: the mitochondrion lineage is found across virtually all eukaryotes, reflecting its ancient origin in the first eukaryotic cells, whereas chloroplasts are present only in photosynthetic lineages (plants and certain algae). The ubiquity of mitochondria across eukaryotes, contrasted with the restricted distribution of chloroplasts, supports the idea that mitochondria appeared earlier in eukaryotic evolution, and chloroplasts were acquired later through secondary endosymbiotic events in specific lineages.
In summary, the first three options rely on properties that are not reliable indicators of evolutionary order and can be misleading due to variability and misconceptions. The fourth option, describing the broad presence of mitochondria across all eukaryotes and the narrower distribution of chloroplasts to certain groups, provides the most coherent evolutionary signal consistent with the idea that mitochondria predate chloroplasts in eukaryotic history.

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