1.1. Read the following passage. 

Plant sterols and plant stanols are found in a range of food, including vegetables, cereals, seeds and nuts.

Plant sterols and stanols have a similar structure to cholesterol and reduce the absorption of cholesterol in the small intestine, so more cholesterol is lost in the faeces. This helps to lower the levels of cholesterol in the blood and in turn, reduce the risk of coronary heart disease (CHD). 

A group of scientists wanted to investigate the effects of eating plant sterols and stanols on the risk of coronary heart disease. The scientists randomly divided healthy volunteers into two groups. Every day, one group was given plant sterols and stanols to eat for eight weeks. The other group acted as a control. 

Each week, the scientists measured the diameter of the lumen of the main artery in the arm of the volunteers. After the trial, the diameter of the lumen of the main artery in the arm of the volunteers who had eaten foods containing plant sterols and stanols had increased. 

Use the passage and your own knowledge to answer the questions.

Describe how the control group should have been treated. 

1.2. The scientists randomly divided the participants into two groups (line 8). Suggest how they may have done this.

1.3. The results of the experiment are shown in Table 1 below: 

Table 1

The scientists concluded that there was sufficient evidence to assume a causal relationship between plant sterols and stanols and a reduced risk of coronary heart disease. 

Use the standard deviations above and your knowledge of correlation to evaluate whether the scientist's conclusion is correct?

1.4. Table 2 below shows pressure changes during one cardiac cycle in the left side of the heart.

Table 2

During which times is the atrioventricular valve between the left atrium and ventricle closed?  Explain your answer. 

Times __________________s and ____________________s

Explanation: