Temperature regulationEdexcel A-Level Biology B: Subtopic test

1. 1
   A scientist measures the body temperature of a desert lizard and of a mouse at air temperatures of 10 °C and 35 °C. At 10 °C the lizard's body temperature is 11 °C and the mouse's is 37 °C. At 35 °C the lizard's is 34 °C and the mouse's is 37 °C. The mouse uses more oxygen at 10 °C than at 35 °C. In the wild the lizard lies on warm rocks in the morning and shelters in a burrow at midday.

   (a)

   Which statement correctly describes the lizard?

   [1 mark]

   • AIt is an endotherm because its body temperature stays almost constant
   • BIt is an ectotherm because its body temperature depends mainly on the temperature of its surroundings
   • CIt is an endotherm because it uses behaviour to control its temperature
   • DIt is an ectotherm because it generates heat by shivering

   (b)

   What is the best explanation of the mouse's higher oxygen consumption at 10 °C?

   [1 mark]

   • AThe mouse is less active at 10 °C
   • BIts cells absorb more oxygen to cool the blood
   • CIts metabolic rate is lower because the enzymes work more slowly
   • DMore aerobic respiration releases heat that replaces the heat lost to the cold air

   (c)

   Explain why the lizard basks on warm rocks in the morning and shelters in a burrow at midday.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A man walks from a warm room into cold air outdoors. Within a few minutes the skin on his hands looks pale, the hairs on his arms stand up and he begins to shiver. His core body temperature remains at about 37 °C.

   (a)

   In which two places are the thermoreceptors that provide information for temperature regulation found?

   [1 mark]

   • AThe hypothalamus and the skin
   • BThe pituitary gland and the skin
   • CThe medulla oblongata and the liver
   • DThe cerebellum and the hypothalamus

   (b)

   Why does the skin on the man's hands look pale?

   [1 mark]

   • AThe arterioles supplying the skin capillaries dilate
   • BThe sweat glands secrete more sweat
   • CThe arterioles supplying the skin capillaries constrict, reducing blood flow near the surface
   • DThe erector pili muscles contract

   (c)

   Explain how shivering and the raising of the hairs help the man to maintain his core temperature.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   On a hot day a marathon runner's core temperature rises towards 38.5 °C. Her skin becomes flushed and she sweats heavily. The air is humid and she notices that the sweat drips off her rather than drying.

   (a)

   Describe how the autonomic nervous system brings about the flushed skin and the sweating.

   [3 marks]

   (b)

   Explain how vasodilation and sweating lower the runner's core temperature, and suggest why sweating is less effective in the conditions described.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher compares an Arctic fox with a frog during winter. The fox stays active at an air temperature of −20 °C and keeps its core temperature at about 38 °C, but its metabolic rate rises to five times the summer value and it must hunt almost every day. The frog buries itself in mud at the bottom of a pond, its body temperature falls close to that of the water and its metabolic rate drops almost to zero.

   (a)

   Evaluate the advantages and disadvantages of the temperature strategies of the fox and the frog in winter.

   [6 marks]

   (b)

   Describe how the fox's body detects and responds physiologically to a fall in air temperature.

   [6 marks]

   Total for question 4: 12 marks

End of questions