A jar holds 12 adult cockroaches. Each one has three pairs of legs, two pairs of wings and two…
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A jar holds adult cockroaches. Each one has three pairs of legs, two pairs of wings and two compound eyes with about ommatidia each.
- How many walking legs are in the jar?
- How many wings are in the jar?
- How many ommatidia are there in all?
Need a reminder? The key ideaShow
The cockroach (Periplaneta americana) is an insect, in the phylum Arthropoda. Its body is covered by a hard chitinous exoskeleton made of plates called sclerites, and is divided into the head, the thorax and the abdomen. The head has two compound eyes, two antennae and chewing mouth parts. The thorax has three segments with three pairs of walking legs, and two pairs of wings: the leathery forewings (tegmina) and the membranous hind wings. The abdomen has ten segments and ends in a pair of anal cerci. The alimentary canal has a foregut (mouth, pharynx, oesophagus, crop and gizzard), a midgut and a hindgut (ileum, colon and rectum). The gizzard grinds the food with six chitinous plates.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. cockroaches. Three pairs of legs, two pairs of wings, two eyes of about ommatidia.
Plan. Count in one cockroach, then multiply by .
Step 1. Legs. in one cockroach. In the jar: .
Step 2. Wings. in one. In the jar: .
Step 3. Ommatidia. in one. In the jar: .
Answer: legs; wings; ommatidia.
Check. appendages, and .
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