(d) the physiological and behavioural responses involved in temperature…

The idea

Temperature control keeps core temperature near an optimum so enzymes work at a suitable rate. Ectotherms gain most heat from the environment, so they use behaviour: basking in sunlight, seeking shade, pressing the body onto warm ground, burrowing, changing posture to alter surface area exposed, and sheltering from wind. Some also use physiological responses such as altering heart rate or metabolic rate. Endotherms generate heat metabolically and regulate it physiologically: sweating and panting increase evaporative cooling, vasodilation of skin arterioles increases heat loss by radiation, vasoconstriction reduces it, shivering and increased metabolic rate raise heat production, and erector muscles raise fur or feathers to trap an insulating air layer. Behaviour such as seeking shade or huddling supports these.

What earns the marks

• Ectotherms obtain most of their heat from the environment and rely heavily on behavioural responses such as basking, seeking shade, burrowing or changing posture.
• Endotherms generate heat from metabolism and use physiological responses including sweating, panting, vasodilation, vasoconstriction, shivering and raising fur or feathers.
• Vasodilation of skin arterioles increases heat loss by radiation; vasoconstriction reduces heat loss.
• Evaporative cooling by sweating or panting removes heat; shivering and raised metabolic rate increase heat production.
• The hypothalamus detects blood temperature and coordinates nervous and hormonal responses.
• Behavioural responses in endotherms, such as seeking shade or huddling, supplement physiological mechanisms.

Common mistakes and how to put them right

• Thinking ectotherms cannot control body temperature at all.

  Put it right: Is that they regulate largely through behaviour and some physiological adjustments.

• Confusing vasodilation with vasoconstriction.

  Put it right: Is that vasodilation widens skin arterioles to lose heat and vasoconstriction narrows them to conserve heat.

• Assuming sweating cools an endotherm in all conditions.

  Put it right: Is that evaporative cooling depends on water evaporating, so high humidity reduces its effectiveness.

Exam tips

• Link each response to the direction of heat change (gain or loss) rather than listing responses without purpose.
• Distinguish clearly between ectotherm behaviour and endotherm physiology when the question names a group.
• Use precise terms such as vasodilation, vasoconstriction, evaporative cooling and shivering rather than vague wording.