Identify which electron micrograph shows a mitochondrion, providing one observation to support your choice.

Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.

«micrograph» C cristae/double membrane is visible/«folds of» membranes inside ✔

Must state observation

a. «double» membrane may have formed when engulfed ✔

b. replicate by binary fission like free-living prokaryotes
OR
reproduce separate from «host» cell replication ✔

c. they have their own «circular» DNA AND reproduce on their own ✔

d. they have «70s» ribosomes AND can manufacture «their own» proteins ✔

e. have organelle«s» similar to free-living prokaryotes ✔

f. similar in size to free-living prokaryotes ✔

g. mitochondrial inner membranes manufacture ATP like bacterial membranes ✔

h. currently there is no free-living prokaryote like a mitochondrion ✔

Most candidates identified the correct micrograph but for the wrong reason such as 70S ribosomes visible, has a matrix, or correct shape. Only starch granules were visible in the image, not ribosomes.

The command term for this question was “discuss”. Connections were not made as many candidates just gave a list of features of mitochondria with no attempt at explanation or discussion. There was some confusion between the words endocytosis and endosymbiosis. In spite of the many shortcomings, there were a few brilliant responses