14 



ZOOLOGY 



the power of utilizing the simple inorganic compounds, as 

 oxygen, water, and carbon dioxid, in a larger measure than 

 that of animals. Plants may build these up into foods, whereas 

 animals must have the complex organised foods to start with. 



23. Growth and Reproduction.— The result of assimila- 

 tion is the addition of new molecules of complex organic 



Fig. I. 



ANIMAL SUBSTANCES- 



REPRODUCTION 



REPRODUCTION 



ENERGY 

 HEAT 

 MOTION 

 THOUGHT 



Pig. £. A diagram indicating the general cycle of events in the building up of inorganic sub- 

 stances into living matter. Sunlight enables the chlorophyll of plants to build up water and carbon- 

 didxide {photosynthesis) into carbohydrates. Plants may use these together with nitrogenous com- 

 pounds to form plant protoplasm and other proteins. Animals may by assimilation utilize these for 

 growth, reproduction, and in doing work of various kinds. Work results in waste. Plants may 

 again use these wastes. 



Questions on the figure. — What are the three main courses open to plant sub- 

 stances? In what sense are animals dependent on plants? For what? How 

 important is photosynthesis in life? What is the real source of the energy of 

 organisms? In what sense is the term cycle appropriate here? 



matter among the molecules of the old. This produces growth. 

 It is to be defined as increase in mass. If this continues in- 

 definitely in excess of whatever may tend to destroy the pro- 

 toplasm, the increase in size may lead to the division of the 

 protoplasm. The parts may separate and lead an independent 

 existence. Such is reproduction. In its simplest form it is 



