Question 19M.2.SL.TZ1.2
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.2.SL.TZ1.2 |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Discuss, Identify | Question number | 2 | Adapted from | N/A |
Identify which electron micrograph shows a mitochondrion, providing one observation to support your choice.
[1]
«micrograph» C cristae/double membrane is visible/«folds of» membranes inside ✔
Must state observation
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.
Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.
[3]
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 ✔
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
