Jun 2015 Unit 1

Question 1

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.

Answer 1

1. Water potential in (bacterial) cells
higher (than in honey) / water
potential in honey lower (than in
bacterial cells);
2. Water leaves bacteria/cells by
osmosis;
3. (Loss of water) stops (metabolic)
reactions;

Question 2

Give two ways in which pathogens can cause disease.

Answer 2

1. (Releases) toxins;

2. Kills cells/tissues;

Question 3

Suggest three reasons why it is more efficient to attach lactase to the beads

Answer 3

1. (Lactase/beads) can be reused/not washed away;
2. No need to remove from milk;
3. Allows continuous process;

Question 4

Monosaccharides and disaccharides taste sweet.
The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow’s
milk containing lactose.
Suggest why.

Answer 4

1. (Lactose hydrolysed to) galactose
   and glucose;
2. (So) more sugar molecules;

Question 5

Suggest two reasons why the percentage of infants vaccinated decreased between
1973 and 1975.

Answer 5

1. (Decrease linked to) few(er) cases of
   whooping cough;
2. (Decrease linked to) risk of/fear of
   side effects;

Question 6

Between 1980 and 1990, there were three peaks in the number of reported cases of
whooping cough. After 1981, the number of cases of whooping cough in each peak
decreased.
Use the information from Figure 4 to suggest why

Answer 6

Vaccination rate increases

so more people are immune to the disease.

Question 7

The percentage of the population vaccinated does not need to be 100% to be effective in preventing the spread of whooping cough.
Suggest why

Answer 7

1. More people are immune / fewer
   people carry the pathogen;
2. So susceptible/unvaccinated people
   less likely to contact infected people;

Question 8

The scientists used the percentage change in the mean resting heart rate after the
exercise programme to compare the results for males and females.
Explain why they used percentage change in the resting heart rate

Answer 8

1. Allows comparison;
2. (Initial/resting) heart rates different
   (between males and females);

Question 9

Explain how their cardiac output could stay the same even when their resting heart rate
had decreased.

Answer 9

1. Cardiac output = stroke volume ×
heart rate;
2. (So) stroke volume increases /
increased size or volume of
ventricles;

Question 10

The scientists gave an injection to a mouse to make it produce the monoclonal antibody
used in this investigation (line 7).
What should this injection have contained?

Answer 10

Regulator protein;

Question 11

LDL enters the liver cells (lines 3–4).
Using your knowledge of the structure of the cell-surface membrane, suggest how LDL
enters the cell.

Answer 11

1. Lipid soluble / hydrophobic;

2. Enters through (phospholipid) bilayer;

Question 12

Explain how the monoclonal antibody would prevent the regulator protein from working
(lines 7–8).

Answer 12

1. (Monoclonal antibody) has a specific
tertiary structure/variable region / is
complementary to regulator protein;
2. Binds to / forms complex with
(regulator protein);
3. (So regulator protein) would not
fit/bind to the receptor / is not
complementary to receptor

Question 13

Explain how this treatment could reduce the risk of coronary heart disease (lines 8–9).

Answer 13

1. Less LDL in blood / more LDL taken
up (by liver cells);
2. So less atheroma/less chance of
blood clot in coronary artery;
3. (So) less chance of reduced/no
blood flow/oxygen to heart
muscle/cells/tissues;

Question 14

Describe how the control group should have been treated.

Answer 14

1. Injection with salt solution;

2. Otherwise treated the same

Question 15

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate
mitochondria from a suspension of animal cells.

Answer 15

1. Cell homogenisation to break open
cells;
2. Filter to remove (large) debris/whole
cells;
3. Use isotonic solution to prevent
damage to mitochondria/organelles;
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;
6. Re-spin (supernatant / after
nuclei/pellet removed) at higher
speed to get mitochondria in
pellet/at bottom;

Question 16

Describe the principles and the limitations of using a transmission electron microscope
to investigate cell structure.

Answer 16

Principles:
1. Electrons pass through/enter (thin)
specimen;
4. Electrons have short wavelength so
give high resolution;
Limitations:
5. Cannot look at living material / Must
be in a vacuum;
6. Specimen must be (very) thin
9. Image not in 3D