Scientists investigated the effect of a drug called a proton pump inhibitor. The drug is given as a tablet to people who produce too much acid in their stomach. It binds to a carrier protein in the surface membrane of cells lining the stomach. This carrier protein usually moves hydrogen ions into the stomach by active transport.
The scientists used two groups of people in their investigation. All the people produced too much acid in their stomach. People in group P were given the drug. Group Q was the control group.
The graph shows the results.
(b)(i) The scientists used a control group in this trial. Explain why.
Q5.Scientists investigated the effect of drinking tea and coffee on reducing the risk of developing one type of brain cancer. The investigation involved 410 000 volunteers and was conducted in 10 European countries over a period of 8.5 years.
(a) (i) Apart from age, suggest two factors that the scientists should have considered when selecting volunteers for this trial.
(d) During the investigation, the volunteers were asked to estimate the volume of tea and/or coffee that they drank each day. The types of tea and coffee consumed in different countries varied. When the data from all the countries were collected there was a correlation between drinking more than 100 cm3of tea or coffee each day and a reduced risk of developing this type of brain cancer.
Tea and coffee contain caffeine. A newspaper reported the results of this investigation under the headline ‘Caffeine helps cut cancer risk’. Explain why scientists could not support this view solely on the basis of this investigation.
(e) Another group of scientists investigated the effect of caffeine on blood flow to certain parts of the brain. Volunteers were given different concentrations of caffeine solution to drink. A control group was also set up.
(i) Describe how the control group should have been treated.
(ii) Volunteers who drank the same concentration of caffeine solution often had different concentrations of caffeine in their blood. Suggest one reason for the difference in concentration of caffeine in the blood of volunteers.
Q6.Catalase is used in a number of industrial processes. It is normally obtained from a fungus called Aspergillus niger. Scientists produced a mutant strain of A. niger called K30. They wanted to know if this mutant strain produced more catalase than the normal strain of A. niger.
• The scientists grew samples of the normal strain of the fungus and of the K30 strain on jelly in separate Petri dishes. The jelly contained a blue substance which is turned colourless by catalase.
• They incubated the dishes for 3 days then measured the diameter of the colourless zone around the fungus.
• They calculated the ratio of the diameter of the colourless zone to the diameter of the fungus.
The diagram shows the dishes after incubation.
(a) The scientists grew both strains of fungi on dishes kept at 30 °C. Keeping the dishes at a temperature of 15 °C would affect the results. Use your knowledge of kinetic energy to explain why.