Fig. 5.1 shows a vertical section through a small piece of human skin as seen under a microscope. Some structures involved in controlling body temperature c...
Question 1 Report
Fig. 5.1 shows a vertical section through a small piece of human skin as seen under a microscope. Some structures involved in controlling body temperature can be seen. The epidermis, the dermis, the fat layer and a hair are labelled. Two further structures are labelled only with the letters X and Y. Structure X lies close to the skin surface and structure Y is a coiled tube deeper in the dermis with a duct leading to the surface. The section had been cut thinly, stained and mounted on a slide so that the layers of the skin and the structures within them could be seen clearly. The student was asked to identify the two lettered structures and then explain how the skin responds to changes in body temperature.
(a) Name the structures labelled X and Y in Fig. 5.1. [2]
(b) State whether the blood vessels near the skin surface become wider or narrower when the body is too hot. [1]
(c) Explain how this change in the blood vessels helps to cool the body. [3]
(d) Describe what happens to these blood vessels when the body is too cold, and explain the effect this has on heat loss. [3]
(e) Explain the role of the sweat glands when the body is too hot. [3]
(f) Explain how the hairs and the muscles attached to them respond when the body is too cold, and how this helps to keep the body warm. [3]
(g) Make a large, labelled drawing of the section in Fig. 5.1. Label the hair, structure X and structure Y. [3]
Answer Details
This question identifies skin structures and explains how the skin controls body temperature by negative feedback.
(a) Structures X and Y [2] X, lying close to the surface, is a blood vessel (capillary) [1]; Y, a coiled tube deep in the dermis with a duct to the surface, is a sweat gland [1].
(b) Vessels when too hot [1] The surface blood vessels become wider (vasodilation). [1]
(c) How this cools the body [3] More blood then flows through the vessels near the skin surface [1]; this carries more heat close to the surface [1]; so more heat is lost by radiation to the surroundings and the body cools [1].
(d) Vessels when too cold [3] The surface vessels become narrower (vasoconstriction) [1]; less blood flows near the surface [1]; so less heat is lost and the body stays warm [1].
(e) Role of sweat glands when hot [3] The sweat glands release more sweat onto the skin [1]; the water in the sweat evaporates [1]; evaporation takes heat energy from the body, cooling it [1].
(f) Hairs and their muscles when cold [3] The erector (hair) muscles contract so the hairs stand up [1]; this traps a layer of air next to the skin [1]; the trapped air insulates the body and reduces heat loss [1].
(g) Labelled drawing of the section [3]
Marks: clean single continuous lines, no shading, drawn large [1]; the hair and structures X and Y placed in roughly correct positions [1]; three correct labels on straight ruled label lines [1].
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