(ii) Prevents osmosis / no (net) movement of water;
So organelle / named organelle does not burst / shrivel;
Q Allow reference to cell rather than organelle for first mark
point only.
Regard damage as neutral
2
(d) (Mitochondria) use aerobic respiration;
Mitochondria produce ATP / release energy required for muscles (to contract);
Q Do not accept reference to making / producing energy.
2
[8]
M2.(a) 1. Large / dense / heavy cells;
2. Form pellet / move to bottom of tube (when centrifuged);
3. Liquid / supernatant can be removed.
Must refer to whole cells.
3
(b) Break down cells / cell parts / toxins.
Idea of ‘break down / digestion’ needed, not just damage
1
(c) 1. To stop / reduce them being damaged / destroyed / killed;
Reject (to stop) bacteria being denatured.
2. By stomach acid.
Must be in context of stomach.
2
(d) 1. More cell damage when both present / A;
2. Some cell damage when either there on their own / some cell damage in
B and C;
MP1 and MP2 − figures given from the graph are insufficient.
3. Standard deviation does not overlap for A with B and C so
difference is real;
MP3 and MP4 both aspects needed to gain mark.
4. Standard deviations do overlap between B and C so no real
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, Cardinal Newman College
difference.
MP3 and MP4 accept reference to significance / chance for
‘real difference’
3 max
(e) 1. Enzyme (a protein) is broken down (so no enzyme activity);
Accept hydrolyse / digested for ‘broken down’.
2. No toxin (as a result of protein-digesting enzyme activity);
Must be in the correct context.
3. (So) toxin is protein.
This must be stated, not inferred from use of
‘protein−digesting enzyme’.
3
[12]
M3.(a) Any five from:
1. Cell homogenisation to break open cells;
1. Accept suitable method of breaking open cells.
3. Use isotonic solution to prevent damage to mitochondria / organelles;
3. Ignore to prevent damage to cells.
4. Keep cold to prevent / reduce damage by enzymes / use buffer to
prevent protein / enzyme denaturation;
5. Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments /
heavy organelles;
5. Ignore incorrect numerical values.
6. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to
get mitochondria in pellet / at bottom.
6. Must have location
Reject ref to plant cell organelles only once
5 max
(b) Principles:
1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
Principles:
Allow maximum of 3 marks
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex / long preparation time;
9. Image not in 3D / only 2D images produced.
Limitations:
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