INTRODUCTION 



Figure 2. — Plant Cell. 



Sexual reproduction is the name given to a process in 

 which two special cells, called the egg and the sperm, 



unite to form one cell, the 

 fertilized egg cell. The fer- 

 tilized egg grows into the 

 new organism. In some 

 plants the fertilized egg 

 forms part of a seed which 

 later develops into the plant. 

 These eight life processes 

 are seen in all forms of liv- 

 ing things, but it is often 

 hard to stuclv them. For 

 instance, the locomotion of a clam is harder to study 

 than that of a cat, and the respiration of a plant than that 

 of a man. 



The Parts of Bodies. — These life 

 processes tell us what the parts 

 of bodies do, but they tell us 

 nothing about these parts them- 

 selves. There are four words 

 which are used in biology to 

 describe these parts. They are: 

 cell, tissue, organ, and organ 

 system. 



1. The Cell. —When the bi- 

 ologist takes apart the plant or 

 animal as you used to take down 

 your block houses, he finds that 

 he can separate the parts until 

 he comes to a unit so small that 

 a microscope is necessary to see 



it. These microscopic parts are called cells and are 

 alike in the following respects : each one has a clear 



Figure 3. — Animal Cell. 



