Blood vessels and the Daphnia heart-rate practicalEdexcel A-Level Biology A: Subtopic test

1. 1
   Blood leaving the left ventricle of a mammal travels through an artery, then arterioles, then capillary networks in the muscles. It returns to the heart through venules and a vein.

   (a)

   Which feature makes a capillary well suited to exchange of substances between blood and tissues?

   [1 mark]

   • AIts wall contains a thick layer of elastic fibres
   • BIts lumen contains valves
   • CIts wall is a single layer of thin endothelial cells
   • DIts wall contains a thick layer of smooth muscle

   (b)

   Which type of blood vessel contains valves?

   [1 mark]

   • AArteries
   • BCapillaries
   • CArterioles
   • DVeins

   (c)

   Explain why the wall of an artery contains elastic tissue.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates the effect of caffeine on the heart rate of Daphnia. She places one Daphnia in a drop of caffeine solution on a cavity slide, with a few cotton wool fibres to restrict its movement, and counts the heartbeats seen under a microscope in 20 s.

   (a)

   Which is the main reason Daphnia is used to investigate the effect of caffeine on heart rate?

   [1 mark]

   • AIts heart is much larger than a mammal's heart
   • BIts body is transparent so the heart can be seen and counted under a microscope
   • CIt has a double circulation like a mammal
   • DIt is a vertebrate so the results apply directly to humans

   (b)

   Which of the following is a variable that should be kept constant in this investigation?

   [1 mark]

   • AThe concentration of caffeine
   • BThe heart rate of the Daphnia
   • CThe temperature of the caffeine solutions
   • DThe colour of the cotton wool

   (c)

   In the control, the student counted 56 beats in 20 s. Calculate the heart rate in beats per minute.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The student repeated the investigation using five Daphnia in each of four caffeine concentrations. The mean heart rates were 186 beats per minute in 0.0 %, 201 in 0.1 %, 219 in 0.2 % and 255 in 0.4 % caffeine solution.

   (a)

   Describe the effect of caffeine on heart rate and calculate the percentage increase in heart rate between 0.0 % and 0.4 % caffeine.

   [3 marks]

   (b)

   Suggest four improvements to the method that would make the results more reliable and valid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school biology department plans a practical in which students expose Daphnia, a freshwater invertebrate, to caffeine solutions and measure heart rate. The students will also compare the three types of blood vessel in a mammal. A parent has written to the school asking whether it is acceptable to use animals in this way.

   (a)

   Compare the structure and function of arteries, veins and capillaries.

   [6 marks]

   (b)

   Discuss the ethical issues involved in using invertebrates such as Daphnia in research.

   [6 marks]

   Total for question 4: 12 marks

End of questions