Topic 1 Core Practicals

1.	Investigate the effect of caffeine on heart rate in daphnia.
2.	Investigate the vitamin C content of food and drink.
3.	Investigate the effect of caffeine on heart rate in daphnia.
4.	Investigate the vitamin C content of food and drink.

Questions

Q1.
 
The photograph below shows Daphnia (a water flea). Daphnia can be used to 
investigate the effect of chemicals on heart rate.

(i)  Give two reasons why Daphnia is a suitable organism for investigating the 
     effect of chemicals on heart rate.
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(i)  State two variables that you would need to control for a valid investigation 
     into the effect of caffeine on the heart rate of Daphnia.
     Describe how to control each of these variables.
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Q2.
 
Ascorbic acid (vitamin C) is named from the Latin word for scurvy, scorbutus.
Scurvy is caused by vitamin C deficiency and used to be a serious concern for sailors. These sailors had no access to fresh fruit and vegetables during long sea voyages.
Sauerkraut (fermented cabbage) contains vitamin C. Ships stored sauerkraut because it does not decompose easily.
Vitamin C is water soluble and is found in cabbage cells. These cells also contain an enzyme, ascorbic acid oxidase, that can oxidise vitamin C.
(a)  (i)  Suggest why the vitamin C content is reduced by boiling cabbage in water.
(2)
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(ii)  Suggest why less vitamin C is lost when the cabbage is added to boiling water rather than cold water before being boiled for 5 minutes.
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(b)  Suggest why sauerkraut was more useful than cabbage on a long sea voyage.
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(Total for question = 4 marks)

Q3.
 
A number of different drinks contain the drug caffeine. These drinks may be consumed to increase mental alertness. Caffeine also increases the heart rate and can interrupt sleep in some people.
A student found that certain drinks affected her sleep, so she carried out some research into the caffeine content of these drinks. The graph below shows the caffeine content of the drinks that the student researched.

(a) Using the information in the graph, describe the conclusions that the student could make about the caffeine content of these drinks.
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(b) A friend of the student suggested that herbal tea might have a lower caffeine content than these drinks. The student decided to use Daphnia to compare the caffeine content of herbal tea with the caffeine content of these other drinks.

(i) Describe an experiment that the student could perform, using Daphnia, to confirm that herbal tea has the lowest caffeine content.
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(ii) The friend did not agree with using Daphnia in this experiment. Give one ethical reason for the use of invertebrates and one ethical reason against the use of invertebrates in experiments of this type.
(2)
Reason for the use of invertebrates
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Reason against the use of invertebrates
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(Total for question = 9 marks)

Q4.
The concentration of vitamin C in a solution can be determined using the chemical DCPIP.
DCPIP is blue when it is in its oxidised form and colourless when it is in its reduced form.
(a)  The diagrams below show the structure of DCPIP in its oxidised form and in its reduced form.

(i)  Using the diagram, describe two differences between the structure of oxidised DCPIP and reduced DCPIP.
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(ii)  Suggest why these differences occur when DCPIP is used to determine the concentration of vitamin C.
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(b)  Mangaba fruit is produced by a tropical plant native to Brazil. As this fruit is a good source of protein and vitamins, it is important to study changes that take place in the fruit after picking.
The photograph below shows mangaba fruit.

A study was carried out to measure the changes in pH of mangaba fruit at different storage temperatures. Mangaba fruits were picked and stored at four different temperatures for four days. Each day the pH of the fruits was measured.

The graph below shows the results of this study.

(i)  Using the information in the graph, describe the effects of storage temperature on the pH of mangaba fruits during this four-day storage period.
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*(ii)  Describe an experiment that could be carried out to compare the changes in the vitamin C content of the mangaba fruit stored at 6 °C and 8 °C.
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(Total for Question = 11 marks)

Mark Scheme

Q1.

Q2.

 

Q3.

Q4.