Vertebrates_Concept_3
Magnets
Magnets
The first time that you handle a reptile can be a surprise: they are by no means cold. So where does this idea of the 'cold-blooded reptile come from? In order to avoid having to cool their bodies by evaporation (sweating), reptiles, fish and amphibians regulate their internal temperatures by movement to a few degrees below that of the surrounding environment. In a reasonably warm environment, they are warm; in a cold environment they are cold.
So-called *warm-blooded' animals function best within a narrow range of temperatures. They metabolise energy in their bodies at a high rate, releasing heat to maintatn a constant body temperature. When they are too cold they shiver increasing metabolism through muscle contraction. When they are too hot, they sweat or pant, evaporating more water to cool down.
The more correct terms are endotherm (temperature controlled from within) and ectotherm (temperature controlled externally), Endotherms require energy to control their metabolism in order to maintain a relatively constant temperature. As a result they require more food than ectotherms.An ectotherm's level of activity depends on the ambient temperature: if it gets too cold, an ectotherrn will become torpid and avoid movement. Within a particular temperature range, it will be at its most active. If it becomes too hot, it will have to adapt its behaviour once more and seek shade or shelter where it is cooler.
Reptiles are frequently referred to as 'cold-blooded' animais, which is technicallv untrue. Through coming to understand the inappropriateness of this term, the children will gain a valuable insight into the internal workings of animal bodies and their response to external conditions.
Humans have a 'normal body temperature of 37.5 0C, but individuals have survived body temperatures as high as 46,5C and as low as 16C. However, an average person could expect to die of hypothermia with a core body temperature below 35C or of heatstroke with a temperature above 41C.
'Cold-blooded' animals are cold to the touch.
It really depends on the environmental temperature. A fish pulled out of the Arctic Ocean will feel cold because its temperature will be near that of the water that surrounds it. A lizard picked up from the desert in daytime will feel hot for the same reason. The temperature of ectotherms varies with temperature of their environment, whereas endotherms will attempt to remain at a constant temperature though they may get colder at their extremities, where the blood circulation is less strong (which is why we need gloves and thick socks in winter).
So why are some animals called 'cold-blooded'?
In cold conditions, the blood temperature of an ectotherm's blood will become lower than the temperature of human blood. Unlike humans and other endotherms, who will die if their core temperature falls too far below the normal level, most ectotherms can survive extreme cold and revive when the environment warms up once more. Some fish can survive well in near-freezing waters: due to a natural 'anti-freeze' in their blood.
Were dinosaurs ectotherms, like lizards?
There is significant debate about whether the dinosaurs were ectotherms or endotherms. From the most recent research, it would seem that they developed from ectotherms to endotherms, or at least to having greater control over their metabolism, as they evolved. There is a growing body of convincing evidence to suggest that key bodily functions of dinosaurs, such as respiration and digestion, had much more in common with endotherms than ectotherms,
Most natural history programmes concerned with life in desert environments — very hot in the day and cold at night - will address the issue of activity and temperature in relation to snakes and lizards.
Resource: www.bbc.co.uldnature/iife/Reptile/by/rank/all
The children can use books, multimedia CD-ROMs and the internet to discover more about endotherrnic and ectothermic animals.