CHAPTER 5 • WHAT HAVE WATER AND AIR 



TO DO WITH BEING ALIVE? 



1 Is water necessary for all living things? 



2 How can there be any life in the desert? 



3 Do lichens growing on rocks need water? 



4 How long can we live without water? 



5 How long can one go without breathing ? . 



6 What has breathing to do with life ? 



7 Are all parts of the air necessary for life ? 



8 What makes dry seeds sprout ? 



9 What happens to the living things in a pond when the water 



freezes solid ? 



10 What happens to the life in a stream when all the water 



dries up? 



11 How does the air we breathe out differ from the air we 



breathe in? 



On a farm, the weather seems very important. Crops grow more luxu- 

 riantly where rains are frequent. Prolonged drought ruins them. Forest 

 vegetation likewise depends upon rainfall (see illustration, p. 78). What 

 makes things grow faster when water is plentiful? How does water act in 

 plants ? 



The amount of water varies not only from region to region, but from 

 season to season, in any one place. During winter there may be as little sign 

 of life as in a desert: most plants and animals of the preceding season are 

 dead. Of those plants that are not dead most are either bare of all foliage or 

 reduced to some kind of resting state. Roots and stems are lying dormant — 

 that is, sleeping — underground. Millions of seeds look as lifeless as pebbles. 

 In general, similar facts may be observed regarding animals. The winter 

 state is in some ways a dry state. Has water anything to do with the way 

 seeds behave in winter, as compared to the way seeds behave in spring or 

 summer ? What is the connection between water and being alive ? 



How Does Water Act in Protoplasm? 



Protoplasm a Chemical Machine Living machines differ from most 

 of our artificial machines in depending directly on chemical changes going 

 on within the protoplasm. The protoplasm itself is largely water — well over 

 90 per cent in many kinds of plant and animal cells. Of the various sub- 

 stances in the protoplasm in addition to water, some are in solution, like salt 

 that has dissolved in water. Others are suspended in water, like the solid 



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