Q1.
A student investigated the effect of temperature on the decay of milk.
Figure 1 shows the apparatus the student used.
Figure 1
This is the method used.
1.
Set up the apparatus as shown in the figure above with the milk at 20 °C.
2.
Record the pH over 5 days using the computer.
3.
Repeat with another batch of fresh milk at 25 °C.
(a)
How could the student keep the milk at a constant temperature for 5 days?
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___________________________________________________________________
(1)
(b)
Give one variable the student should keep constant.
Do not refer to temperature in your answer.
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___________________________________________________________________
(1)
Q2.
This question is about the decay of milk.
(a)
Name two types of microorganism that cause decay.
1. ________________________________________________________________
2. ________________________________________________________________
(2)
(b)
Cows’ milk is pH 6.6.
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As milk decays, lipids in the milk are broken down.
One of the products of the breakdown of lipids causes the pH of milk to decrease.
Name the product that causes the pH to decrease.
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(1)
A student investigated the effect of temperature on the time taken for different types of
milk to decay.
This is the method used.
1.
Put cows’ milk in six test tubes.
2.
Keep each test tube at a different temperature.
3.
Measure the pH of the milk in each tube every day for 12 days.
4.
Record the number of days taken to reach pH 5.
5.
Repeat steps 1 to 4 with goats’ milk and with almond milk.
(c)
Give one way the pH can be measured.
___________________________________________________________________
(1)
(d)
Give two control variables the student should have used in this investigation.
1. ________________________________________________________________
2. ________________________________________________________________
(2)
The student improved the investigation to produce valid results.
The graph shows the results.
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(e)
Which type of milk stays fresh the longest at 10 °C?
___________________________________________________________________
(1)
(f)
Describe the effect of temperature on the time taken for goats’ milk to reach pH 5.
Use data from the graph above in your answer.
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(2)
(g)
The time taken for cows’ milk to reach pH 5 at 10 °C is less than the time taken for
cows’ milk to reach pH 5 at 5 °C.
Suggest one reason why.
___________________________________________________________________
___________________________________________________________________
(1)
(h)
Suggest two reasons why the different types of milk took different lengths of time to
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reach pH 5.
1 _________________________________________________________________
___________________________________________________________________
2 _________________________________________________________________
___________________________________________________________________
(2)
(i)
The student said:
‘The temperature milk is stored at affects
how likely the milk is to cause food poisoning.’
How can the investigation be developed to find out if the student is correct?
Tick (✓) one box.
Determine the types of bacteria present in the milk
Record the pH every 12 hours
Use more than three different types of milk
(1)
(Total 13 marks)
Q3.
A gardener wants to add compost to the soil to increase his yield of strawberries.
The gardener wants to make his own compost.
(a)
An airtight compost heap causes anaerobic decay.
Explain why the gardener might be against producing compost using this method.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
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(2)
(b)
The gardener finds this research on the Internet:
‘A carbon to nitrogen ratio of 25:1 will produce fertile compost.’
Look at the table below.
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Type of
material to
compost
Mass of
carbon in
sample in g
Mass of
nitrogen
in sample in g
Carbon:nitrogen ratio
8.75
1.25
7:1
10.00
0.50
20:1
9.80
0.20
X
Chicken
manure
Horse manure
Peat moss
Determine the ratio X in the table above.
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Ratio ________________
(1)
(c)
Which type of material in the table above would be best for the gardener to use to
make his compost?
Justify your answer.
___________________________________________________________________
___________________________________________________________________
(1)
(d)
Some of the leaves from the gardener’s strawberry plant die.
The dead leaves fall off the strawberry plant onto the ground.
The carbon in the dead leaves is recycled through the carbon cycle.
Explain how the carbon is recycled into the growth of new leaves.
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(6)
(e)
The diagram below shows two strawberries.
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•
Both strawberries were picked from the same strawberry plant.
•
Both strawberries were picked 3 days ago.
•
The strawberries were stored in different conditions.
Strawberry A
Strawberry B
A © sarahdoow/iStock/Thinkstock, B © Mariusz Vlack/iStock/Thinkstock
Give three possible reasons that may have caused strawberry A to decay.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
3. _________________________________________________________________
___________________________________________________________________
(3)
(Total 13 marks)
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Mark schemes
Q1.
(a)
(put beaker in a) water bath
allow (put beaker in an) incubator
1
(b)
volume of the milk
or
type of milk
allow amount of milk
allow named type of milk, eg cows’ or
semi-skimmed
1
(c)
correct scale and axis labelled
scale must be at least 1 cm for 1 day
1
all points plotted correctly
allow a tolerance of ± ½ small square
allow 4 or 5 correct plots for 1 mark
2
suitable curved line of best fit
ignore line joined point to point with straight lines
1
(d)
similar shaped line drawn to left of 20 °C line on Figure 4
1
same start pH
allow a tolerance of ± ½ small square
allow from student’s line of best fit or student’s
plot for 0 days
1
[8]
Q2.
(a)
bacteria
allow singular
1
fungi
allow mould
ignore microbes / germs / decomposers
do not accept viruses
1
(b)
fatty acid(s)
1
(c)
any one from:
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•
universal indicator (paper / solution)
allow UI (paper / solution)
ignore pH paper unqualified
•
pH meter
allow pH probe
ignore datalogger unqualified
ignore Cresol red
ignore phenolphthalein / litmus
1
(d)
any two from:
•
volume of milk
allow amount of milk
•
exposure to air / oxygen
•
sterilise test tubes
allow bungs on test tubes
•
treatment of milk before investigation
allow example such as pasteurised or not
•
freshness / age of milk (at start)
•
time of day pH was measured
allow starting pH of milk
2
(e)
almond (milk)
1
(f)
as temperature increases up to 15 °C the time taken (to reach pH 5) decreases
allow converse
1
above 15 °C the time taken (to reach pH 5) stays the same
if no other mark awarded allow 1 mark for as
temperature increases the time taken (to reach 5
°C) decreases and then stays the same
1
(g)
any one from:
•
bacteria / microbes / microorganisms / fungi dividing faster (when
warmer)
allow converse if clearly describing 5 °C
allow number of bacteria / microbes /
microorganisms / fungi increasing (when warmer)
allow more bacteria microbes / microorganisms /
fungi
•
reactions (in the bacteria) are happening faster (to decay milk)
•
(because there is) more (kinetic) energy
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allow particles move faster
allow more collisions between particles
•
enzyme activity is higher (at 10 °C than at 5 °C)
allow enzymes work faster
ignore enzymes work better
1
(h)
any two from:
•
different concentration / type of fat / lipid
allow different amounts of fat / lipid
•
different concentration / type of proteins / carbohydrate / sugar
allow different amounts of proteins / carbohydrate
/ sugar
•
different (amount / type of) bacteria present
•
may have been pasteurised by a different process
allow may have been treated in different ways
(before the investigation)
•
different starting pH
ignore different oxygen concentration
2
(i)
determine the types of bacteria present in the milk
1
[13]
Q3.
(a)
methane is produced
ignore bad smell
1
which is a greenhouse gas / causes global warming
1
(b)
(9.80 / 0.20 = 49 therefore) 49:1
1
(c)
horse (manure)
allow ecf from 11.2
closest to 25:1 (ratio)
1
(d)
Level 3 (5–6 marks):
A detailed and coherent explanation is given, which logically links how carbon is
released from dead leaves and how carbon is taken up by a plant then used in
growth.
Level 2 (3–4 marks):
A description of how carbon is released from dead leaves and how carbon is taken
up
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by a plant, with attempts at relevant explanation, but linking is not clear.
Level 1 (1–2 marks):
Simple statements are made, but no attempt to link to explanations.
0 marks:
No relevant content.
Indicative content
statements:
•
(carbon compounds in) dead leaves are broken down by microorganisms /
decomposers / bacteria / fungi
•
photosynthesis uses carbon dioxide
explanations:
•
(microorganisms) respire
•
(and) release the carbon from the leaves as carbon dioxide
•
plants take in the carbon dioxide released to use in photosynthesis to produce
glucose
use of carbon in growth:
•
glucose produced in photosynthesis is used to make amino acids / proteins /
cellulose
•
(which are) required for the growth of new leaves
6
(e)
any three from:
(storage conditions)
•
(at) higher temperature / hotter
•
(had) more oxygen
•
(had) more water / moisture
•
(contained) more microorganisms (that cause decay)
allow reference to bacteria / fungi / mould
3
[13]
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