Temperature regulation in mammals & birds.

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Experiment Aim:

To investigate how the shape and size of an organism affects the rate of temperature loss away from the organism.

Background Knowledge:

Most of the substances transported in the blood are carried dissolved in plasma. The main constituent of blood plasma is water (90% of blood plasma) (RESOURCE 1), from which heat can be lost by conduction, convection, radiation or evaporation.

(RESOURCE 2)

The limbs of a mammal or bird can easily be simulated using water-filled test tubes of differing sizes, to represent ‘models’ of a real life situation. The main method of transferring heat energy in a fluid (e.g.: water) is by convection. As a generalisation, most mammals and birds live in habitats where their body temperature is above that of their surroundings. (RESOURCE 3) Therefore, heat energy is principally lost from the bodies of mammals and birds by convecting and radiating away. Any liquid that is warmer than its surroundings will expand, so its particles occupy a greater volume than before (as they vibrate with the heat energy supplied). This in turn means that there is a decrease in density of the liquid, and the warmer particles move upwards (convection) and away (radiation) from the organism, through the blood vessels and protective skin. (RESOURCE 2)

Mammals and birds (which are all warm-blooded organisms) have the ability to regulate their body temperatures, keeping their bodies within a set optimum range. Therefore, any heat energy lost is replaced by expending energy from food taken in, to keep body temperatures constant (37degrees in humans). (RESOURCE 1)

 

Prediction:

I predict that the larger the surface area / volume ratio of a ‘model’, the greater the rate of heat loss away from the simulation will be. Therefore, the surface area / volume ratio of a ‘model’ is directly proportional to the rate of heat loss away from the ‘model’.

 

Prediction Reasoning:  

As the surface area / volume ratio of a ‘model’ increases, more heat energy is, in reality, able to escape away from the test tube at one time. The surface area / volume ratio is effectively the amount of heat energy that is in contact with the external surroundings at one time (surface area) divided by the amount of heat energy that is actually inside the test tube to begin with. The greatest surface area / volume ratio can come about when the surface area is at its greatest, and the volume is at its smallest.

Therefore, if a test tube with the highest surface area / volume ratio was used, it would take far less time to lose      of temperature than a test tube with the smallest surface area / volume ratio. Therefore, the same amount of temperature would have been lost in a shorter space of time, and the rate of heat loss would be directly proportional to the surface area / volume ratio of ‘model’ used. (RESOURCE 2)

Prediction Graph:

Key factors to vary: Variables:

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Preliminary work:

Certain pieces of preliminary work have to be completed before the actual investigation can begin. This is to check that the things that I plan to do are possible, and to find out what control variables to use (values).

For the preliminary work of this investigation, I need to find 6 test tubes that have surface area / volume ratios that are sufficiently well spread. I intend to find all of the different test tubes that are available, and find the surface area and volume of each. I will then work out ...

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