LIFE PROCESSES 



into living animal and plant parts. In animals the blood 

 vessels, into which the digested food passes, carry it to all 

 parts of the body, and as it circulates, 

 each part takes the food needed and 

 builds it into living material. 



6. Respiration is the life process that 

 uses oxygen taken from the air or water 

 and forms a waste product known as 

 carbon dioxide. This life process should 

 not be confused with breathing, which 

 is limited to animals with lungs or air- 

 tubes. In such animals the breathing 

 is simply a mechanical process in which 

 the air is brought into the lungs or 

 air-tubes. This allows the oxygen to 

 pass by diffusion into the blood, where 

 it is carried to all parts of the body, or 

 it may pass directly to the living cells. 

 See section 6, page 14. 



7. Excretion is the life process in 

 which waste products, like perspiration, 

 are made and cast off by the body. On 

 page 1 we saw that energy was pro- 

 duced by oxidation. After this the 

 waste is thrown off by excretion, as 

 the ashes are thrown out of a steam 

 engine. 



8. Reproduction is the life process by means of which 

 each generation of plants and animals is brought forth. 

 There are two kinds, asexual (a'sex-u-al) and sexual. 

 Figure 47 on page 49 shows a simple animal, the amoeba 

 (a-me'ba), dividing into two young amoebae by asexual 

 methods. The same kind of reproduction in a simple 

 plant, the yeast, is illustrated in Figure 374, page 355. 



Figure 1 . — Simple 

 Osmometer show- 

 ing Osmosis. 



The water in the 

 glass passes through 

 the egg-membrane 

 and forces the egg- 

 white up in the glass 

 tube ; while the egg- 

 white does not pass 

 out into the sur- 

 rounding water. 



