Chapter 3

1. III Functions of Biosphere

2. A- Significance of the Biosphere • The biosphere is the source of all human being's food energy. • Plants and algae are the only organisms capable of photosynthesizing, the process of transforming light energy to chemical energy. • Human being eats the plants, or he/she eats animals – herbivores and carnivores. • In all instances, he/she is completely dependant upon the producers and other consumers as source of food energy. • In food industry, biosphere members are also important. • For instance, wine, beer, cheese and yogurt industry are completely dependant upon fermentation caused by bacteria

3. A- Significance of the Biosphere • It also plays a significant role in removing air pollution. • During photosynthesis, carbon dioxide moves into the leaves of plants • If present, gaseous pollutants such as sulphur dioxide, nitrogen oxides, and ozone also move into the leaves. • Some of the molecules of these gases remain in the leaves; plants act, therefore, as natural filter. • But they have limited tolerance, and overloading by pollutants will impair their growth and even kills them.

4. A- Significance of the Biosphere • It is also important in cleaning water. • We will discuss later the function of decomposers in removing the Biological Oxygen Demand BOD wastes (dead bodies of living organisms decomposed in water). • Without decomposers, all water bodies would become completely polluted by organic wastes.

5. A- Significance of the Biosphere • Other members of biosphere are important in terms of human health, both from positive and negative viewpoint. • On the positive side, certain members of it produce antibiotics (chemical compounds produced by living microorganisms that are capable of killing other microorganisms), the famous is penicillin, a powerful antibiotic derived from a green fungus (mold) called Penicillium. • On other hand, some members of biosphere are the causes of several of human being's most serious diseases, including malaria (caused by a single-celled animal), typhoid fever (caused by bacteria) ..etc.

6. A- Significance of the Biosphere • Another important role of biosphere is the prevention of soil erosion. • If vegetative cover is removed, the soil is exposed and made susceptible to movement by wind and water. • Fertile soils are probably our more valuable resource. • soil is the main reservoir for plant nutrients; most of them are concentrated in the upper soil layers. • When nutrients are lost by erosion of topsoil, plant production decreases in less food energy available for consumers.

7. B- The Concept of Carrying Capacity • There is a finite amount of energy available to producers and consumers in a given area. • If this amount energy available by unit area is divided by the minimum energy demand per organism, the resultant number of organisms per unit area called carrying capacity, which is expressed by the following formula: Energy available / unit area = number of individuals Energy demand / individual unit area

8. C- Environmental Resistance 1- Biotic Factors a- overcrowding i- predation and parasitism • Predation generally is a short-term interaction between individuals in which the predator kills and eats the prey and then moves on. • On other hand, parasitism is usually an interaction of long duration in which a parasite may obtain nourishment from its host for weeks and longer. • It is a basic principle of predation and parasitism that if two populations (predator-prey or parasite-host) have a common evolutionary history, a stable interaction tends to evolve will benefit both populations. • Predation is beneficial for the prey population because it tends to hold the number of prey within the carrying capacity. • Conversely, a stabilized interaction assures the predator population of sufficient food source. • If the predator killed all of prey population, it would die off unless alternative food source were available.

9. ii- competition • There are two basic types of competition: interspecific that occurs between the populations of two different species, and intraspecific that occurs among the population of single species. • Two basic conditions must exist before there can be competition. • First, both populations must depend upon the same environmental factors e.g. food source or nesting sites. • Second, the demand of the total populations must exceeds the supply i.e. the carrying capacity.

10. b- Under-crowding • The above discussion dealt with over population as a limiting factor, but under-population can also be a limiting factor. • Observation shows that members of large coveys of bobwhite quail, which form a compact circles at night, survive severe winter temperatures, where single birds or small coveys die.

11. 2- Abiotic • As we mentioned previously, limiting factors are always composed by environmental components e.g. climatic factors. • For example, long severe winter in Northern America often kills off wildlife. • However, the long-term significance of such a control is questionable • Observations indicate that when there is a large winter kills, the resultants decrease in intraspecific competition during the following summer leads to a high reproductive rate. • It appears that unless abiotic factor such as food, drought, high wind, and temperature extremes decrease population to levels where the effect of undercrowding is significant, abiotic factors are not important for long-term regulation.