264 FIRST YEAR COURSE IN GENERAL SCIENCE 



IV V 



FIG. 139. DIVISION OF CELLS 



1. Cell I has attained its greatest possible size. What change has 

 begun in II? 2. How does the size of each cell in V compare with the size 

 of I? 3. What does this show about the method of growth of an organism? 



When a new cell, instead of helping to make new plant or 

 animal tissue, separates from the plant or animal and develops 

 into a new organism, reproduction has taken place. The 

 new cell that left the tissue of which it formed a part is called 

 an egg cell or a sperm cell. 



EXERCISES 



1. (a) What are the physical properties possessed by all bodies? 

 (6) What other properties are possessed by organisms only? 



2. Why is food a universal necessity for all living things? 



3. What are the symptoms of starvation in an animal? In a plant? 



4. Why can animals live longer without food than without oxygen? 

 6. (a) Why is breathing necessary? (6) When is breathing the 



slowest? Why? 



6. What property makes possible the closing of a flower at night? 



7. Why does a humming bird need more food than a snail? 



8. Give an illustration, drawn from this chapter, of the Law of 

 Conservation of Matter. 



9. Why cannot the leaves of most plants live separated from the 

 plant? 



10. How could cells have been mistaken, in early microscopic study, 

 for empty spaces? 



11. What is the object of reproduction? 



12. What makes division of labor possible in higher forms of life? 



