Read the following information carefully:
Insects, like all arthropods, grow in stages. This is because they have an exoskeleton surrounding their body. The exoskeleton is hard and it cannot expand. Every so often the insect will lose its old exoskeleton and grow a new one (this is called moulting). The new exoskeleton is soft to begin with so
the insect's body can expand for a while. While the insect is moulting it cannot feed itself so it will not grow in mass.
Usually the insect inflates its soft new exoskeleton with air or with water (if it is an aquatic insect). This makes room for new growth inside the exoskeleton. When the exoskeleton hardens, the insect starts to feed again. The space inside the exoskeleton will be gradually filled up with body tissues, such as muscles. This will continue until the is no more room inside the exoskeleton so the insect will have to moult once again.
Usually an insect moults 5 times during its life.
Now study the two graphs below which show the growth of a stick insect.