Heat loss from a human body – interpreting a graph
Task
Read the information and statements below.
a. The total heat content of a human body is indicated by its temperature.
b. It is helpful to think of the body as having a central 'core' surrounded by an outer
'shell' made up of skin and layers of fat.
c. The skin is the main heat exchanger of the body. Skin temperature depends on
the core temperature and conditions such as temperature and humidity in the
environment. Therefore, skin temperature may be many degrees lower than the
normal core temperature of 37 ºC.
d. Heat can be lost from the body by the evaporation of sweat and by forms of 'dry'
heat loss i.e. conduction, convection and radiation. Dry heat loss is proportional
to the temperature difference between the body shell and the surroundings. The
greater the difference, the greater the amount of dry heat loss.
Statements to use as annotations;

For a person sitting in a room temperature of 37 ºC the dry heat loss from their body is
zero.

If the room temperature starts to fall then the amount of dry heat loss begins to
increase.

At a room temperature of 20 ºC and below the body maintains its core temperature by
increasing its metabolic rate.

At very low temperatures, less than 5ºC, the dry heat loss becomes larger than the heat
produced by the metabolism and the body core begins to cool down. Hypothermia sets
in.

If the temperature of the room rises to 35 ºC, heat loss occurs only through the
evaporation of sweat.

Hyperthermia sets in at an environmental temperature of 37 ºC and above. The
maximum rate of sweat evaporation is reached and it is not enough to cool the body.

Heat begins to enter the body causing heat death.
© www.teachitscience.co.uk 2016
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Heat loss from a human body – interpreting a graph
Now study the graph and answer the questions below.
Heat loss from human body in different environmental temperatures
160
Heat energy (Watts)
140
120
100
Heat loss through evaporation
Dry heat loss (radiation,
conduction, convection)
metabolic rate
80
60
40
20
0
-20
0
5
10
15
20
25
30
35
40
45
Temperature of environment ºC
© www.teachitscience.co.uk 2016
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Heat loss from a human body – interpreting a graph
Describing the graph:
Q1. What does the title tell you about the graph?
Q2. What variables are represented by the x-axis and the y-axis?
Q3. What units of measurement are used and what are the intervals on each scale?
Q4. What do each of the coloured lines mean?
Describe the data and trends:
For each line describe what it shows in a short, simple statement.
Interpreting the graph:
Read the information again and select statements to annotate
different points on the graph.
Can you add any of the following key phrases to the annotations?
Key phrases: shivering, blood vessels dilate, blood vessels contract,
hairs stand on end.
© www.teachitscience.co.uk 2016
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Heat loss from a human body – interpreting a graph
Suggested answers
Describing the graph:
Q1.
What does the title tell you about the graph?
The effect of environmental temperature on the amount of heat lost from the
human body
Q2.
What variables are represented by the x-axis and the y-axis?
X-axis = temp of environment; y-axis = heat energy
Q3.
What units of measurement are used and what are the intervals on each scale?
Temp = °C; heat loss = Watts
Q4.
What do the coloured lines mean?
Blue shows heat loss through evaporation (of sweat); orange shows 'dry' heat loss
through conduction, convection and radiation from body; yellow shows energy
produced through respiration by the metabolism.
Describe the data and trends:
For each line describe what it shows in a short, simple statement.
Blue =
steadily increasing rate of heat loss through evaporation as temp
increases; rate increases greatly between 35 – 37 °C;
Orange =
steadily decreasing dry heat loss as environ temp increases; no heat loss
when environ temp matches body temp; heat gain when environ temp
rises above body temp. (Link to Newton's law of cooling).
Yellow=
heat energy produced by metabolism decreases with increasing
environment temp (less shivering as environ gets warmer); levels off as
near 37°C; rate increases as temp rises and thermoregulatory systems in
body are overwhelmed, heart and respiration rates increase.
Interpreting the graph:
Read the information again and select statements to annotate different points on the
graph.
Can you add any of the following key phrases to the annotations?
Key phrases: shivering, blood vessels dilate, blood vessels contract, hairs stand on end.
© www.teachitscience.co.uk 2016
23627
Page 4 of 5
Heat loss from a human body – interpreting a graph
At a room temperature of 20 ºC
and below the body maintains its
core temperature by increasing
its metabolic rate.
At very low temperatures,
less than 5ºC, the dry heat
loss becomes larger than
the heat produced by the
metabolism and the body
core begins to cool down.
Hypothermia sets in.
Hyperthermia sets in at an environmental
temperature of 37 ºC and above. The
maximum rate of sweat evaporation is
reached and it is not enough to cool the body.
Heat loss from human body in different environmental temperatures
If the temperature of the room rises to 35 ºC,
heat loss occurs only through the evaporation
of sweat.
160
Heat energy (Watts)
140
120
100
Heat loss through evaporation
Dry heat loss (radiation,
conduction, convection)
metabolic rate
80
60
40
20
0
-20
0
5
10
15
20
25
30
35
Temperature of environment ºC
The room temperature
starts to fall then the
amount of dry heat loss
begins to increase.
© www.teachitscience.co.uk 2016
40
45
For a person sitting in a
room temperature of 37 ºC
the dry heat loss from
their body is zero.
Heat begins to enter
the body causing heat
death.
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