Insects (from Latin insectum, a calque of Greek ἔντομον [éntomon], "cut into sections") are a class of invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. They are the most diverse group of animals on the planet, including more than a million described species and representing more than half of all known living organisms. The number of extant species is estimated at between six and ten million, and potentially represent over 90% of the differing animal life forms on Earth. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, a habitat dominated by another arthropod group, crustaceans. 

The life cycles of insects vary but most hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat, and can include a passive pupal stage in those groups that undergo 4-stage metamorphosis (see holometabolism). Insects that undergo 3-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages. The higher level relationship of the Hexapoda is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22–28 in). The most diverse insect groups appear to have coevolved with flowering plants.

1. What is the life cycle of insects?
2. How is it's growth constrained?
3. How else?
4. How many stages of metamorphosis are there?
5. What are insects?
6. How many body parts do they have?
7. What are they?
8. Are they diverse?
9. How many species?
10. How many extant species are there?
11. What does that represent?
12. What kind of environment can they be found?
13. Even in oceans?
14. What have they found in the Paleozoic Era?
15. What kind was found in this era?
16. How big?
17. Have they coevolved with anything?
18. What?
19. What is the metamorphosis stage of an adult?
20. What do they lack when the go through 3-stage metamorphosis?

Numbered answers:
1. It varies but most hatch from eggs
2. by the inelastic exoskeleton
3. development involves a series of molts
4. Four
5. a class of invertebrates
6. Three
7. head, thorax and abdomen
8. Yes
9. more than a million
10. estimated at between six and ten million
11. represent over 90% of the differing animal life forms on Earth.
12. nearly all
13. Yes
14. Fossilized insects of enormous size
15. giant dragonflies
16. with wingspans of 55 to 70 cm
17. Yes
18. flowering plants.
19. series of nymphal stages
20. a pupal stage