2cm
1cm
Total SA= 6 24 54
Total Vol= 1 8 27
SA:Vol= 6:1 3:1 2:1
An amoeba exchanges with the environment by occurring across the entire body surface through the cell membrane. An elephant exchanges with the environment by taking in oxygen into the respiratory tract and carbon dioxide, which is produced by respiration in the body of the elephant is released into the atmosphere. Since an elephant has large flat ears this increases the surface area of an elephant for radiating body heat in hot climates. For an elephant respiratory gases cannot reach its body tissues by only diffusion. Elephants need a specialised gas exchange surface (lungs) and a circulatory system to maximise the speed of the movement of substances through the body. As an organism increases in size there is an increase in bulk and therefore this means that the diffusion distance becomes greater and as a result the rate of diffusion becomes slower.
Fish on the other hand use different method to extract oxygen from water. Fish use gills to take the dissolved oxygen from the water. However the process is not easier, this is because the water is much heavier and thicker than air, so it takes a lot of energy to extract. Since fish are cold blooded they do not need oxygen that much. But warm-blooded animals such ourselves and whales are in demand of more oxygen so they have lungs to get oxygen from the air.
There are advantages for organisms being large such as they can avoid being eaten because they are too large to be eaten. They can eat more things because they are large. They can move longer distances to new food sources or more favourable environments.
They can be endothermic, which means that they can generate their own heat to maintain their body temperature, typically above the temperature of their surroundings.
Large organisms such as humans have constant core temperatures, normally around 37 degrees Celsius. This maximises reaction rates without denaturing enzymes, therefore this is another advantage of being a large organism. However, small organisms such as mice which are in large numbers to be the same mass as one human need 17 times food and oxygen consumption of that of a man to maintain constant core temperatures. This is because mice have a large surface area, so they radiate a lot more heat than humans therefore they lose a lot of heat to their surroundings.
Bergman’s rule
RULE: Within any one group of organisms, those of the largest body size are found at high latitudes and those of small body size are found nearer the equator.
EXPLANATION: This is because small organisms have a larger surface area than large organisms so by radiation of heat they can lose heat, however, since these small organisms are found near to the equator the hot climate will replace the lost heat, and so the small organisms will stay warm and not be cold. For large organisms they have a small surface area so they do not lose heat by radiation therefore most of their heat is kept in. Endothermy is also possible in large organisms so they are kept warm and so can survive in cold climates. This is why they are found at high latitudes because high altitudes have low temperatures.
Allen’s Law
Within any one group of organisms, those at the highest latitudes have smaller extremities than those in the tropics.
Transpiration rates
Large leaves get more water needed for photosynthesis, which makes food for the plant. Large leaves are needed to catch more light to trap the chlorophyll needed for photosynthesis. Large leaves can cause more water to be lost by transpiration because surface area: volume ratio is decreased.
Vaaheesan Sundaraanantham
