A student looks at three animals: a snail, an earthworm and a rat…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student looks at three animals: a snail, an earthworm and a rat.
- Which of them has an open circulatory system?
- In which of them does the blood always stay in vessels?
- Which of them has a heart with chambers?
- Why can the flow of blood be controlled better in a closed system?
Need a reminder? The key ideaShow
Arthropods and molluscs have an open circulatory system, with sinuses. Annelids and chordates have a closed one. A fish heart has chambers and a single circulation. Amphibians and reptiles, except crocodiles, have chambers and mixed blood. Crocodiles, birds and mammals have chambers and a double circulation, so the blood passes the heart twice in each round.
The worked solution
Have you tried it?
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.
Step 1. (a) The snail, a mollusc. Its blood bathes the organs in sinuses.
Step 2. (b) The earthworm and the rat. Annelids and chordates have closed systems.
Step 3. (c) The rat. All vertebrates have a muscular chambered heart.
Step 4. (d) In a closed system the blood stays in vessels, so it can be sent to the organs that need it.
Answer: (a) snail; (b) earthworm and rat; (c) rat; (d) the flow is directed by the vessels.
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