3.5 The Circulatory System in Animals

This question should be answered in continuous prose. 

Quality of written communication will be assessed in this answer. 

Describe and explain how the structure of capillaries enables them to function efficiently as exchange surfaces. 

Figure 1 below shows part of the blood circulation in a mammal. 

Figure 1

Name the blood vessels represented by letters C, D and G in Figure 1. 

Figure 2 shows a section through a human heart. 

Figure 2

Use Figure 2 to name the chamber / blood vessel and state whether it fills with oxygenated or deoxygenated blood.  
  

Suggest why it is advantageous that the heart has four chambers, and therefore acts as a ‘double pump’, providing a double circulation system. 

Figure 1 below shows a dissected pig’s heart.

Figure 1

 Name the chambers and the valve the pencil passes through in Figure 1

There are many factors that can increase the risk of an individual developing coronary heart disease (CHD). Some factors are out of the individual's control such as their sex, genetics and increasing age while other factors can be influenced by the individual’s lifestyle.

Scientists used a risk factor points system to assess women's risk of developing CHD. They included the following risk factors: age, smoking, systolic blood pressure, blood cholesterol and blood HDL concentration. To calculate the point score of an individual you must add together the scores of all five categories. A higher score indicates a higher risk of developing CHD in the next 10 years. 

The effect of the chosen risk factors on an individual’s point score can be seen in Table 1 below. 

Table 1

Describe the effect of blood HDL content on an individual's point score shown in Table 1.

The point score can be directly related to the probability of developing CHD in the next 10 years, as shown in Table 2.

Table 2

Using the data in Table 1 and Table 2 work out the 10 year risk for a female smoker, aged 62, blood cholesterol 260 mg 100 cm^-3, blood pressure 20.5 kPa, and HDL 57 mg 100 cm^-3. 

Describe and explain the point scores for high cholesterol (>280 mg 100cm^-3) across the age groups.

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. One group was given plant sterols and stanols to eat every day 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 selected and treated. 

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

Table 1

The scientists concluded from Table 1 that there was sufficient evidence to assume a causal relationship between plant sterols and stanols and a reduced risk of coronary heart disease. 

Evaluate this conclusion. 

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

Table 2

Sketch a graph of the results shown in Table 2. 

Calculate the heart rate in beats per minute from the data in Table 2.

Figure 1 below represents a capillary and the surrounding tissue fluid.

Figure 1

Use the information in Figure 1 to explain the formation of tissue fluid.

The blood plasma in Figure 1 has a more negative water potential at the venule end of the capillary compared to the arteriole end of the capillary. Explain why.

Genetics and nutrition are two factors that influence blood pressure in humans. Explain how very high blood pressure may affect an individual’s circulatory and lymphatic system.

Molecules of different substances differ in size. Table 1 below shows the relative molecular mass of molecules and the relative permeability of capillary walls to them. 

Table 1

Haemoglobin is not present in the tissue fluid. Use Table 1 to explain why this could be considered surprising and your own knowledge to explain why it is, in fact, the case.

Figure 1 below shows changes in pressure in parts of a human heart during one second. 

Figure 1

At what time do the semilunar valves open? 

Use Figure 1 to calculate the heart rate in beats per minute (bpm)

Valves are important for maintaining blood pressure in the heart. Using a specific example, explain how they work.

Name which part of the heart causes the increase in pressure in the aorta and explain why this increase is important for the organism.

Figure 1 below shows the rate of blood flow in various blood vessels in the body. It also shows the total cross-sectional area of the vessels.

Figure 1

As shown in Figure 1 the rate of blood flow increases from the venules to the vena  cava. This is despite a large decrease in the total cross-sectional area. 

Suggest why. 

Table 1 below shows the relative thickness of layers in the wall of an artery and a vein.

Table 1

Describe and explain the difference in the thickness of elastic tissue for the artery versus the vein.

The diameter of a vein was 1.5 mm. 

Calculate the diameter of the lumen of the vein. Show your working.

Deep vein thrombosis (DVT) is a serious medical condition in which blood forms a clot in a vein, typically in the legs.

Sitting for long periods of time, such as on a long flight, can increase the risk of developing a DVT due to the fact that sitting for extended periods decreases blood flow. 

To reduce the risk, people are advised to stretch and move their legs often during long flights.

Using this information and your own knowledge, explain how blood returns to the heart from the legs.

Explain the formation of tissue fluid. 

Include why proteins are not found in it.  

Explain how high blood pressure may affect tissue fluid.

Molecules of different substances differ in size. Table 1 below shows the relative molecular mass of molecules and their relative permeability of capillary walls to them. 

Table 1

Using the table and your own knowledge, explain why the water potential of the plasma at the arteriole end is more positive than at the venule end. 

This question should be answered in continuous prose.

Quality of written communication will be assessed in this answer.

Describe and explain four ways in which the structure of capillaries enable them to function efficiently as exchange surfaces.

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. 

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

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?

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: