12 PLANTS AND MAN 



vanced to the organ- type of body plan (fig. 5). Trees, shrubs 

 and other flowering plants have a body built up of six types of 

 organs, each with one or more definite functions to perform in 

 the economy of the life of the whole plant. These are the roots, 

 stems, leaves, flowers, fruits and seeds. The particular nature 

 and activity of each of these will be taken up in detail in the next 

 two chapters. 



Metabolism 



The common protoplasmic basis and cellular organization 

 of both plants and animals is an indication of their biological 

 kinship from the structural viewpoint. But there are also numer- 

 ous similarities in the activities taking place in the protoplasm 

 and within the cells. All living material is strikingly different 

 from the non-living world by being able to grow, to reproduce 

 and to adapt itself to changing environmental conditions. In 

 the performance of these living processes protoplasm takes in 

 substances from the environment, transforms and utilizes them. 

 To be alive means a consumption of materials and energy, with 

 a consequent dependence upon some sort of fuel. The only fuel 

 which can be utilized for energy release by plants or animals is 

 that found in compounds of carbon and hydrogen combined to 

 form either carbohydrates, fats or proteins. It is this organic fuel 

 which constitutes food, and food is a primary requisite of all 

 living things. That animals must eat in order to live is well 

 known to all; but the fact that plants need food is not as widely 

 appreciated. 



The series of physical and chemical changes taking place in 

 protoplasm during the securing and utilizing of food is known as 

 metabolism; metabolic activity is fundamental to the life of all 

 plants and animals (fig. 6). It is a dual process, with a con- 

 structive and a destructive phase. In its constructive phase 

 metabolism involves securing food and assimilating it into proto- 

 plasm, resulting in growth or storage ot food for future consump- 

 tion. In its destructive phase the food is oxidized with a consequent 

 release of potential energy and the excretion of waste products. 

 This oxidation phase of metabolism can be compared with burn- 

 ing wood, both being the result of the union of oxygen with a 



