Question 22N.2.SL.TZ0.2
| Date | November 2022 | Marks available | [Maximum mark: 5] | Reference code | 22N.2.SL.TZ0.2 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Annotate, Describe, Outline | Question number | 2 | Adapted from | N/A |
The image shows a phospholipid bilayer that is a component of the cell membrane.
[Source: Boundless Learning. Course Hero. Phospholipids. [diagram online] Available at:
https://www.coursehero.com/study-guides/introchem/phospholipids/ [Accessed 1 November 2021].]
Annotate the diagram to illustrate the amphipathic nature of phospholipids.
[2]
- line to circle labelled phosphate (head) and (tail) labelled fatty acid/hydrocarbon/lipid (tail);
- label hydrophilic/polar/attracted to water/ and hydrophobic/non polar/not attracted to water;
Part (a) was a variation on a classic Section B question on the phospholipid bilayer. Approximately 1 in 10 students left it blank, suggesting that many did not think that they had to reply to it as there was no answer box. Cholesterol's function in reducing fluidity and permeability was not well known in (b). In (c) poorer candidates described endosymbiosis, rather than answering the question. Many knew about double membranes, own DNA and 70s ribosomes, but did not score any marks as they failed to say that they were in mitochondria and/or chloroplasts. This is perhaps a case where planning the answer was lacking, rather than rushing in.
Outline a function of cholesterol in cell membranes.
[1]
reduces fluidity of membrane / reduces permeability of membrane (to some molecules);
Accept ‘controls’ or ‘maintains ‘ as a BOD.
Describe two pieces of evidence that show that eukaryotic cells originated by endosymbiosis.
[2]
- mitochondria/chloroplasts have their own DNA;
- mitochondria can self-replicate/undergo a process like binary fission;
- mitochondria/chloroplasts have double membranes;
- mitochondria/chloroplasts have(70s) ribosomes;
- mitochondria/chloroplasts are sensitive to antibiotics;
- similar in size to bacteria
