LIFE PROCESSES AND ORGANIZATION 



93 



materials to the stems, and food storage. The func- 

 tions of stems include conduction of materials from 

 roots to leaves and from leaves to roots, production 

 of leaves and reproductive organs, plant support, and 

 food storage. The primary function of leaves is food 

 manufacture; they are the primary site of photo- 

 synthesis. 



Certain brown and red algae have structures that 

 approach, but are not, organs. These structures are 

 holdfasts, stipes, and blades. Holdfasts are rootlike 

 structures, but their only function is support of the 

 plant; stipes are stemlike stalks that have little com- 

 plexity in comparison to stems; blades are leaflike 

 but, again, are not as complex as leaf blades. 



The multicellular animals range from those with 

 no organs to forms that show a great many complex 

 organs. This range of variation does not lend itself 

 to a meaningful classification of organs per se. The 

 animal units of classification are organ systems. 



ORGAN SYSTEMS 



Organ systems are groups of organs that provide 

 an over-all function and are found almost exclusively 

 in the animal kingdom. Plants are assumed not to 

 surpass the organ basis of organization, because most 

 of their separate parts are organs. However, flowers 

 and most cones are organ systems. In the multicel- 

 lular animals one or more of the following ten organ 

 systems may be found: 



(1) Integumentary provides the body covering which 

 affords protection from the environment. (2) Skeletal 

 supplies levers for movement and structures for pro- 

 tection and support. (3) Muscular allows movement 

 and locomotion. (4) Digestive receives food and trans- 

 forms it to usable nutrients. (5) Circulatory transports 

 materials throughout the body. (6) Respiratory ex- 

 changes gases between the organism and its environ- 

 ment, or is a means of obtaining oxygen and removing 

 carbon dioxide. (7) Excretory disposes of excess fluid 

 and metabolic wastes. (8) .Nemous coordinates body 

 processes. (9) Endocrine chemically coordinates body 

 processes. (10) Reproductive perpetuates a species by 

 the production of new individuals. 



ORGANISMS 



The single plant or animal is most often the basic 

 independent unit of life. Units smaller than the or- 

 ganism are incapable of living by themselves, but 



individuals may be grown together into colonies. 

 Many colonies are composed of individuals each of 

 which could perform all life processes, but some 

 animal colonies are formed of diflferent kinds of spe- 

 cialized individuals. In such specialized colonies 

 marked division of labor can occur, individuals have 

 unique functions, and few if any of the distinct types 

 can survive alone. For example, a colony might be 

 made up of individuals that feed for the entire group, 

 others that do nothing but reproduce, and some that 

 are strictly protectors of the colony. In such cases all 

 types of individuals may be necessary for life to exist. 

 When division of labor is this strict, the organisms are 

 often physically attached to one another into a single 

 structural unit. 



In addition to being either solitary or colonial, 

 individuals are either sedentary or free-living. Most 

 multicellular plants and many animals are fixed to 

 soil, rocks, or some other substrate, at least during 

 their adult life. In these sedentary creatures only cer- 

 tain stages of the life history, but not the adult stage, 

 are motile. Free-living creatures, on the other hand, 

 are motile during most, if not all, of their life cycle. 



ORGANISM AND ENVIRONMENT 



Each creature is subjected to many environmental 

 variables that largely determine its function and place 

 within its surroundings. The organism's basic hered- 

 ity establishes its over-all ability to cope with varia- 

 tions within and among the physical and biological 

 features of its surroundings. Its reactions with these 

 environmental factors must still permit its receiving 

 all the necessities of life — especially suitable food, 

 shelter, and conditions for reproduction. 



The variations of organisms and environments 

 working together as a dynamic interacting phenome- 

 non demonstrate that no organism is independent of 

 its physical or biological surroundings. Their de- 

 pendence is summarized by the concept of a web of 

 life in which an organism is aflfected by its physical 

 environment and by other organisms acting as ene- 

 mies, competitors, or food. From all this, the obvious 

 assumption can be made that an organism is usually 

 found in a locality having conditions, within limits, 

 that allow the performing of its life processes. 



An additional organism-environment concept is 

 the balance of nature. This generalization refers to the 

 dynamic interrelationships that tend toward equilib- 

 rium in nature. Although there is an ever-changing 



