Animal Physiology Surface Area to Volume Ratios

Animal Physiology: Surface Area to Volume Ratio 5

AnimalPhysiology: Surface Area to Volume Ratios

Physiologicalactivities in living organisms are affected by various factors. Therate of heat transfer in lower organisms is influenced by the factorsuch as surface area, volume, surface area to volume ratio,coloration, or insulation. A process such as diffusion is affected bythe surface area to volume ratio. Upper organisms have a smallsurface area to volume ratio. Simple organisms such as worms have alarge surface area to volume (Karafit,2014). As the surface area to volume ratio increases, the rate ofdiffusion also increases. Similarly, the larger the surface area tovolume ratio, the faster the rate of heat transfer due to a largesurface area of the organism exposed to the environment. Roundwormsare cylindrical or round whereas flatworms are flat in shape. Theexperiment below investigates the effect of the shape of a worm onthe rate of heating up. In this experiment round and flat tubes wereused to represent roundworm and flatworm respectively.


  1. The shape of the worm has no effect on how quickly it heats.

  2. The roundworm will heat up quicker.

  3. The flatworm will heat up quicker.


Flatand round copper tubes were used in place of a flat and roundworm. Each tube was heated by placing it under a heat lamp for 5 minutes,and the temperature was then measured. (A probe was used formeasurement of the temperature it was inserted inside of each tube).Each tube was the allowed to cool for 5 minutes and then, theexperiment was conducted two more times, which made a total of threetrials. The slope was then used to determine the rate of change oftemperature in the worms.


Comparisonof rate of change in temperature in a flat and roundworm is asfollows:



Experiment 1



Experiment 2



Experiment 3






Standard deviation



Standard Error



Therate of heating up in a roundworm is faster than in a flatworm.

Discussionand Conclusion

Theroundworm heated up at a faster rate than a roundworm because it hada large surface area. (It had round or cylindrical body). A roundwormhas a tube-within-a-tube body plan, and a body cavity called apseudo-coelom. Thus it has a small volume, unlike the flatworm thathas no body cavity. The roundworm has a large surface area to volumeratio as compared to the flatworm. The implication is that a largesurface area of the roundworm is exposed the environment, and thus itacquires heat faster than the flatworm. Thus, a direct relationshipexists between the heat gain and surface area to volume ratio(Karafit, 2014). The flatworm has a lower rate of heating because ithas a smaller surface area to volume ratio (it has a flat body).Aflatworm lives in a cold environment. Therefore, it needs to conserveheat. The smaller surface area to volume ratio helps it to conserveheat. On the other hand, lower rate of heating up enables theflatworms to regulate the rate of heat gain so that the can remainactive in a warm environment. The high rate of heating of theroundworm enables it to survive extremely hot and unfavorableconditions by quickly attaining an equal temperature to itsenvironment. Consequently, this enables it to achieve a uniformtemperature to its environment.

Theroundworms have a higher rate of acquiring heat because they arecolorless. Also, the fluid in the pseudo-coelom of the roundwormaccumulates heat as the roundworm acquires heat. It heats faster ascompared to the flatworm (Karafit, 2014).

Inconclusion, the shape of the worm influenced how quickly it heatedup, and the roundworm heated up quicker.


KarafitS.J. (2014). Biology 1441 Lab. Retrieved from as a reference.