274 Common Science 



of the blood vessels again and through the cell walls 

 into the cells. Waste is taken out of the cells into the 

 blood and passes from the blood into the lungs and 

 kidneys by this same process of diffusion. So you can 

 readily see why everything would die if diffusion stopped. 



Application 65. Explain how the roots of a plant can 

 take in water and food when there are no holes from the 

 outside of the root to the inside ; how bees can smell flowers 

 for a considerable distance. 



Inference Exercise 



Explain the following : 



401. A shell in the bottom of a teakettle gathers most of the scale 



around it and so keeps the scale from caking at the bottom 

 of the kettle. 



402. There is oxygen dissolved in water. When the water comes 



in contact with the fine blood vessels in a fish's gills, some 

 of this oxygen passes through the walls of the blood vessels 

 into the blood. Explain how it does so. 



403. Asphalt becomes soft in summer. 



404. When the trolley comes off the wire the car soon stops. 



405. You cannot see stars in the daytime on earth, yet you could 



see them in the daytime on the airless moon. 



406. Although the carbon dioxid you breathe out is heavier than 



the rest of the air, part of it goes up and mixes with the air 

 above. 



407. On a cold day wood does not feel as cold as iron. 



408. To make mayonnaise dressing, the oil, egg, and vinegar are 



thoroughly beaten together. 



409. A solution of iodin becomes stronger if it is allowed to stand 



open to the air. 



410. A drop of milk in a glass of water clouds all the water slightly. 



SECTION 44. Clouds, rain, and dew: Humidity. 



Why is it that you can see your breath on a cold day? 

 Where do rain and snow come from? 

 What makes the clouds ? 



