Page 18 - 新思维科学活动用书7 样章

1.4 Cells, tissues and organs

Exercise 1.4C Sting cells in Hydra

Challenge

In this challenging task, you will practise finding relevant information in text and diagrams. You will
then apply this information, and your knowledge of cells, tissues and organs, to answer questions.

Hydra is a tiny animal that lives in freshwater ponds. It has tentacles that it uses to catch even

smaller animals, which it pushes into its mouth. The mouth opens into a cavity where digestion
takes place.

The body of Hydra is made up of two layers of cells. The diagram shows what Hydra would look like
if you cut one in two, from top to bottom, and looked at it through a microscope.

tentacle

mouth

sting cell

outer layer of cells

inner layer of cells

digestive cavity

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