4. Mammals are endothermic homeotherms, which is a very precise way of saying they regulate their own body temperature. It is worth noting that not all organisms do so because it would in fact be disadvantageous for some to do so. Furthermore some organisms regulate their body temperature solely through behavioural methods. Temperature Regulation
5. In humans it is the core body temperature which is maintained by homeostasis. Temperature Regulation
13. Skin based effectors – responding to heat gain Effector Response Arterioles supplying skin capillaries The muscles relax – this is known as vasodilation. The effect of this is to increases the blood flow to the surface of the skin causing increased heat loss by radiation. Sweat glands The glands secrete sweat onto the surface of the skin. The sweat is composed mainly of water, which evaporates from the skin surface. As water has a high latent heat of evaporation the evaporating sweat removes heat from the surface of the skin. Hair erector muscles The muscles relax – this lowers the hairs on the skin surface. The hairs do not trap air when laid flat so they allow heat to be removed more easily by convection.
14. Skin based effectors – responding to heat loss Effector Response Arterioles supplying skin capillaries The muscle contract – this is known as vasoconstriction. Blood flows through the shunt vessel as this is the path of least resistance. Less blood flows to the surface of the skin so there is less heat loss by radiation. Sweat glands The sweat glands stop producing sweat therefore stopping the heat loss of evaporating sweat. Hair erector muscles The muscle contract – this raises the hairs on the surface of the skin. The effect of this is to reduce airflow therefore reducing convection of heat from the skin.
20. 1. All living organisms exist in changing external environments and many are able to control their internal environments. (a) Explain how the body of a mammal may respond to a rise in the environmental temperature. (8marks) Exam questions
21.
22. 2. Size matters for marathon runners. Big athletes produce more heat and find it harder to keep cool. Shape matters too - a tall, thin runner has fewer problems keeping cool than a short, tubby runner of the same body mass. A 65 kg athlete running a marathon in 2 hours 10 minutes in reasonably dry conditions can avoid overheating at air temperatures up to 37 °C, but in humid conditions the same level of performance is possible only at temperatures below about 17 °C. (a) Explain how athletes produce heat when they run. (2) (b) Why does a ‘tall, thin runner have fewer problems keeping cool than a short, tubby runner of the same body mass’? (2) (c) Explain why runners are more likely to overheat in humid conditions. (3) (d) Describe how the body responds to a rise in core body temperature. (5) (Total 12 marks) Exam questions
23. 2. (a) Respiration for muscular activity; (energy ‘needed/used’ for respiration’ etc, disqualifies) respiration inefficient / releases waste heat / all energy ‘ends up as ‘heat’ 2 (b) Larger surface area: volume ratio, or less fat under skin; more rapid / more heat loss from body surface. 2 (c) Humidity reduces diffusion gradient / less difference in water potential; less evaporation of sweat; less cooling due to use of heat energy for evaporation of sweat. 3 (d) Temperature receptors stimulated in; (in skin disqualifies) hypothalamus; heat loss centre stimulated; nerve impulses to sweat glands; increase rate of / start sweat production; nerve impulses to skin arterioles; vasodilation (ref to vessels moving disqualifies) max 5 [12] Exam answers
