I20 



Liv'mg Things Are Basically Alike unit ii 



Fig. 148 Breaking up a log jcn/i. There are active cells in the viai and in the trees 

 along the bank. What activities are being carried on in these cells? In which cells is 

 there the greatest amount of oxidation? (American museum of natural history) 



\c)u will learn more about light as an 

 important form of energy in a later unit. 



You are acquainted with electrical en- 

 ergy, which can be transferred from one 

 place to another in wires. This form of 

 energy can be changed into other forms, 

 such as heat and light, or it can do work 

 directly as in causing a motor to turn. 

 You may have seen the inechajiical en- 

 ergy of moving water turn a Avaterwheel 

 or move a boat or e\en rocks in the 

 stream bed. It is easy to understand that 

 heat, electricity, and the mechanical en- 

 ergy of moving objects can do work. 



iMicrgy, or the al)ilit\- to do work, may 

 be stored. Coal contains stored eneriry, 

 and, since this cncrg\- lies in the chemical 

 make-up of the coal, it is also called 

 che7fiical energy, in biology chemical 



energy is of great importance; all living 

 things contain it. 



All forms of energy can be changed 

 into one another. For example, when 

 coal is used for making steam in an 

 engine its stored chemical energy is 

 changed into heat energy; this heat en- 

 ergy is used in machines to produce 

 electrical energy which is turned into 

 light energy in the lamps in our homes 

 or into mechanical energy in our wash- 

 ing machines. 



Oxidation in the cell changes stored 

 energy. You have learned that in all oxi- 

 dation heat energy is released. You just 

 read that when coal is burned the stored 

 energy of the coal is changed partially 

 into heat energy. The same thing hap- 

 pens in a cell. In a cell it is carbohydrates. 



