Question 19M.2.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ1.b |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Explain how mitochondria could have been formed from free living prokaryotes.
[2]
a. endocytosis/engulfing of prokaryote by a larger/another/anaerobic prokaryote/cell ✔
b. double membrane of the mitochondrion is the result of endocytosis
OR
inner membrane of mitochondrion from engulfed cell and outer from food vacuole ✔
c. «engulfed prokaryotic cell» was aerobic/respired aerobically/consumed oxygen
OR
«engulfed prokaryotic cell» provided energy/ATP ✔
d. «engulfed prokaryotic cell» not destroyed/not digested
OR
«endo»symbiotic/mutualistic relationship developed ✔
e. «engulfed prokaryotic cell» had its own DNA/own «70S» ribosomes ✔
Do not award mpc for “mitochondrion makes ATP”.
This was generally well answered with candidates explaining how endocytosis would have got a free-living prokaryote into a larger cell and because it made itself useful, there was a selective advantage in developing a mutualistic relationship rather than digesting the engulfed cell. Some candidates gave valid evidence for endosymbiosis – presence of DNA, 70S ribosomes or the double membrane.
