Cold Blooded with an Exoskeleton All insects are cold blooded creatures. That is, they rely on the temperature of their environment to increase their body heat. During cold days they remain motionless because they have very little energy to search for food. During warm days, insects will absorb the heat from their surroundings and increase their body temperature high enough to search for food. Creatures such as mammals are known as warm blooded. Their body temperature is kept constant irrespective of the environment's temperature. It might surprise you to know that even during the coldest days your body temperature remains constant at around 37^oC. Creatures exposed to low temperature for great lengths of time will die. Unless of course they hibernate like bears do during the winter months. This way the body, in effect, shuts down. Chemical reactions that take place in their body require heat in order to proceed. If heat is not present these reactions can not produce the energy that is vital for to sustain life.
Insects have a thick inflexible skin known as an exoskeleton. This exoskeleton must be shed several times in an insect’s life as it grows in size. The skin is high in protein and some insects, such as caterpillars, will eat the skin they have shed. The exoskeleton provides the insects with protection and support. The shedding of the tough outer skin is not a simple task. The image on the right shows a cicada during its last moulting. The adult emerges with wings and must spend time drying and stretching them. Cicada nymphs, are subterranean dwellers, suck sap from the roots of various species of tree. Nymphs can remain underground for up to 17 years.
	The exoskeleton has several functions 1) Provides structure 2) Protects the insect from physical and chemical damage by its environment,. This also includes infection. 3) Prevents water loss. 4) Provides muscle attachment for locomotion 5) Lines the trachae that take air to the internal organs. The stick insect will outgrow its skin several times throughout its life. It will have to shed this inflexible exoskeleton and grow a new and bigger one. The discarded exoskeleton is a rich source of protein and it is not unusual for insects to eat the skin. Not only does the exoskeleton serve as a protective cover but it also allows for muscle attachment and movement.
Flight would be impossible if muscle had no where to attach themselves. The exoskelton provides points of attachment for muscles which makes flight possible.
All insects that have a tough exoskeleton also have a segmented body. The exoskeleton is a hard armour that protects the insect from dehydration and predators. Why is it important for the armour to have many joints or segments along its length. Refer to the picture on the right.
	How does an insect remove its inflexible suit of armor only to replace it with a bigger one? During molting the cuticle degrades and then reforms. First the hormone ecdysone stimulates epidermal cells to multiply and grow in size. This is the period where the skin of the insect under the exoskelleton grows before the new exoskeleton is formed. The existing cuticle detaches from the epidermal cells. This is called apolysis. The space between the cuticle and the epidermal cells is filled with a gel that contains inactive enzymes, such as chitinase and proteases, that can digest the cuticle. Next, the enzymes in the gel are activated and start to digest the cuticle from within. Most of the products of digestion are used by the epidermal cells to make a new cuticle. The digestion continues up to the exocuticle. Before the old exocuticle is discarded a new one is laid down. New endocuticle is deposited.
1) Which one is not a function of th eexoskeleton prevent dehydration of the insect help the insect move prevent bacteria from entering the insect keep air inside the insect 2) The exoskeleton is very flexible true false 3) The exoskeleton can grow in size to accomodate the growing insect. true false 4) Special enzymes in the molting gel help break down proteins that form the endocuticle. true false 5 ) Epidermal cells are the cells that make up the exocuticle. true false 6) The broken down proteins of the endocuticle are msotly recycled and used by the epidermal cells to from a new exocuticle. true false 7) The part of the exoskelton that is shed by the insect is known as the epidermal layer epicuticle endocuticle exocuticle 8) The skin under the exoskeleton grows just before the exoskeleton is shed. This happens when epidermal cells divide and or grow in size. endocuticle grows in volume and strethes the exoskeleton exocuticle grows in size

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