II 



How the Cell Lives 

 U 



Before we go any further, we must consider a little what goes on 

 inside the living cell. All living cells are necessarily the seat of 

 intense chemical activity. In order to live they must have food, which 

 enters into the cell and is transformed in various ways. It may be 

 burnt to provide energy or changed into substances needed for 

 growth, and the products which are not wanted are given out. 



Plants are extremely modest in their requirements. From carbon 

 dioxide taken from the atmosphere, water and simple inorganic 

 nutrients, which contain nitrogen, phosphorus and a few more in- 

 organic elements, they are able, with the help of the energy of light, 

 to construct all the chemical compounds, including proteins, which 

 they require. Animal cells have to be provided with a greater variety 

 of foods. As a rule they require, at least, the simpler compounds 

 synthesized in plants; but from these they obtain what they need to 

 live. From the oxidation of sugars they obtam the energy which is 

 required to keep them alive. While single living cells like bacteria 

 are able to carry out all the processes necessary for living, in higher 

 organisms there is some specialization, i.e. some cells perform one 

 task and others mainly another. 



It is obvious that the life of all cells involves a multitude of 

 chemical actions which are carried and with a speed and smoothness 

 which the laboratory chemist cannot approach. In practice, chemical 

 synthesis in the laboratory is often very diflficult. Compounds have 

 to be transformed one step at a time, often by wasteful processes, 

 using powerful chemicals, heat, and sometimes electrical actions, to 

 bring about the desired changes. It may take months to build up a 

 compound, by a complicated sequence of actions, which a cell can 

 make in a matter of minutes. Many bacteria completely reproduce 

 themselves in half an hour, and in tiat time everything they contain 

 is duplicated. 



How are these manifold changes brought about? We will take a 



