Our Threatened Planet

By Emmanuel Kenneth

ABOUT THE BOOK :

If extinctions are part of nature's course, then why does it matter that so many species are becoming extinct now?

Over the long course of man's occupance on Earth has been seemingly characterised by its dependence on nature and the ecology which has overtime greatly influenced homeostatic r

• Language: English
• Publisher: Blue Rose Publishers
• Release date: Jul 13, 2020
• ISBN: 9789390119844

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Preface

The planet Earth has an age long history of existence. Nature in its dynamism took 600 million years to develop the environment which we live and carry out our activities today, but man in barely one million years of existence has brought about such changes which threatens the very existence of a healthy biosphere. This emphasis is clear, thus as mankind witnessed the dawn of industrialization, it was accompanied with human population increase in leaps and bounds which invariably intensified production activities in all sphere, ranging from agricultural and industrial activities, the production of electricity, and modern modes of transportation. These activities as varied as they may seem, has greatly increased both the quantity and diversity of contaminants that entered the air, surface water and ground water, and even the varieties of life form. These pollutants include both natural and synthetic materials (in liquid, solid and gaseous forms), and have slowly become apparent because they are produced at a faster rate than can be absorbed or modified by the Earth system.

Majority of the environmental impacts of these anthropogenic activities stem from the fact that they can be persistent or perhaps resists demobilization into non-toxic state. To further complicate the burden of these pollutants in the environment, the developed economies are continually in a mad race to exploit every bit of natural resources to convert them into finished goods in order to take undue advantage of the developing nations due to their weak and precarious economic conditions to saturate their markets with products of low salvage value. In doing so, the industrialized countries seize the opportunity to dump lots of materials into their environment which invariably becomes polluted.

The central theme of this text is predicated upon the fact that much of these pollutant build-up in the environment becomes more imminent as the population grows and the standard of living improves leading to an overall increase in the per capita usage of resources; for agriculture and grazing, forest for wood, rock and dirt for construction, oil and coal for energy or plastics and ores for metals. Without any doubt, our usages of resources have impacted the Earth’s system profoundly, as thus humanity has become a major agent of environmental change. Perhaps, recognizing the need for a specialized book of this magnitude, it is the author’s expectation that it shall be a more comprehensive a complete resume of various aspects of environmental pollution, and shall be extremely relevant to development experts, planners, policy makers, and the students, both at undergraduate and post-graduate levels, who major in such diverse field as economics, sociology, engineering, political science, law, history, English language, and the likes, not just as ensemble in the multidisciplinary nature and magnitude of environment perse, but perhaps for the simple reason that it impinges on their health, well-being and their overall existence.

Chapter 1

Introduction to Man’s Cosmic Environment

The planet-Earth which we currently live in is home to millions of species. Of these species of floras and faunas, man tends to exercise dominance over other organisms. The dominance man is exhibiting on earth tends to paints a broad picture of its ingenuity, creativity or inventiveness and its widespread activities which have over time modified almost every part of our planet. In fact, we are having a profound impact on it sustainability as the cost of these our ingenuities are such which tend to manifest in most of the global problem that humanity is currently facing. The dynamism of world phenomena replicated all over especially in contemporary times indicates that the ecosystems, the fabric of life on which we all depend, are declining rapidly through man’s influence, innovation and technological advancement. Evidently, right from the number of people that inhabit the world today to our level of development and technological sophistication, agricultural production, forest depletion and biodiversity, urban sprawl and consumerism, there is an increasing evidence of change and variability (Aniah, E. J, and Okpilliya, F. I, 2003).

These variabilities are imminent due to man’s inalienable dependence on nature for food, shelter, clothing, transportation, and so on. In spite of this, the use of resources such as land in economic perspective is fixed and tends to influence the quantity of food that is produced. The demand for food, especially for developing countries is enormous, and threatens the ability of human existence (Abang, S. O, 2005). This gap between numbers and resources is all the more compelling because so much of the population growth is concentrated in low-income countries, ecologically disadvantaged regions, and poor households, especially in the developing economies of Latin America and the Caribbean, Sub-Saharan Africa and South Asia. Therefore, the questions now are not just becoming visible, but more complex; from how to guarantee the necessities of mankind, to satisfying the growing appetites’ of man’s geometric pattern of population growth in the face of declining food per capita, to how to use these current resources in such a way as to ensure minimum degradation and sustainability for future generations.

Perhaps, much of these environmental dilemmas since the dawn of civilization and our desire to opt for sustainable development have brought to the fore, the need for a greater understanding of the paradigms in population dynamics, the struggle for finite resources between regions and environmental phenomena. The most daunting situation is that much of these problems are overtly accelerating as our population continue to expand. There are now more than 7 billion of us on Earth. As our numbers continue to grow, we tend to increase our need for far more water, more and more food supplies, compelling cases of land acquisition, extensive transport and the need for more energy. As a result, we are accelerating the rate at which we're changing our climate. In fact, our activities are not only completely interconnected with but also of complex web of interaction with, the complex system we live on: Earth. It is important to understand how all this is connected. If population levels continue to rise at the current rate, the generations yet unborn will see the Earth plunged into unprecedented environmental crisis, particularly as man is somewhat approaching the limits of environmental resources and the unequivocal problems associated with externalities of production and consumption especially of finite resources which is in itself an unprecedented planetary emergency and a cause for serious concern.

What is a Planet?

The definition of planet has for some time been the subject of intense debate. Although the word dates back thousands of years, no officially decreed scientific definition of planet existed before the early 21st century. While many people can point to a picture of Jupiter or Saturn and call it a planet, or have it denoted as any of the large bodies that revolves round the sun in the solar system, to some, it is usually denoted as the Earth when perhaps they are referring to the planet as part of the universe.

The word Planet which dates back to ancient Greek planēt- (literally, wanderer), is derived from planasthai, a Greek verb which means to wander. The name planet was originally applied to any of seven visible celestial bodies which appeared to move independently of the fixed stars - the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn. In the 17th century, the ancient Greeks counted the Earth's Moon and Sun as planets along with Mercury, Venus, Mars, Jupiter, and Saturn. Earth was not considered a planet, but rather was thought to be the central object around which all the other celestial objects orbited. The first known model that placed the Sun at the center of the known universe with the Earth revolving around it was presented by Aristarchus of Samos in the third century BCE, but it was not generally accepted. It wasn't until the 16th century that the idea was revived by Nicolaus Copernicus.

However, contemporary observations especially since the advent of science and technology are however changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation planets. The International Astronomical Union in 2006 defined a planet as an object that: orbit a star (in our cosmic neighbourhood, the Sun); is big enough to have enough gravity to force it into a spherical shape; is big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun. The IAU also created a newer classification, dwarf planet, which is an object that meets planetary criteria except that it has not cleared debris from its orbital neighbourhood (such as the Pluto). Apparently, as human knowledge continues to deepen and expand the more complex and intriguing the universe appears. Today, researchers have found hundreds of extrasolar planets, or exoplanets, that reside outside our solar system; there may be billions of exoplanets in the Milky Way Galaxy alone, and some may be habitable (have conditions favourable to life). Whether our definitions of planet can be applied to these newly found objects remains to be seen.

For now, our immediate concern is the planet of mankind and its various productive activities which is the Earth – the planet on which we live, the world. It is the substance on the land surface of the Earth, for example, clay or sand in which plants grow – hence the word environment.

Meaning of Environment

What is environment? Environment comes from the French word environer, meaning to encircle or surround, or the circumstances or conditions that surrounds an organism or group of organisms. Cunningham, Cunningham, and Siago (2005) further assert that environment is the complex of social and cultural conditions that affects an individual or community. Webster Collegiate dictionary defines environment as the aggregate of all the external conditions and influences affecting the life and development of an organism. In the same vein, the new explorers encyclopaedic edition of Merriam and Webster (2005), defines environment as the complex of physical, chemical and biotic factors (as climate, soil, and living things) that act upon an organism or an ecological community, and ultimately determines its form and survival. According to Animashaun (2002), the term refers to the external conditions which influence the development or the existence of an organism such as man. Federal Environmental Protection Agency (FEPA) Act of Nigeria, Decree No 58 of 1988 defines environment to include air, water, land and all plants and animals therein, and the interrelationship which exists among these or any of them.

Similarly, UNESCO (1992) uses the word environment to denote also the stock of physical and social resources available at a given time in a given location for the satisfaction of human needs and aspirations. Furthermore, the Ontario Environmental Assessment Act defines the environment as consisting of (i) air, land, or water (ii) plant and animal including man (iii) social, economic and cultural conditions that influences the life of man or a community (iv) any building, structure, machine or other devices or things made by man (v) any part or combination of the foregoing and the interrelationship between any or more of them. Crozient (1980) has defined environment as the setting for man’s various productive activities. In the view of Hyde and Reeve (2001), environment could be defined as something in which an organization operates, including air, water, land, natural resources, floras, faunas, humans, and their interrelationship.

Environment, Organism Interaction

Organisms interact with the environment at many levels. The physical conditions that surrounds an organism, such as ambient temperature, moisture and light intensity all influence basic bio-physiological processes that are crucial to their survival and growth. The organism must forage to acquire essential resources from the surrounding environment and in the process must protect itself from becoming food from other organisms. It must recognise friends from foe, differentiation between mates and possible predators. All of this, in a desperate attempt to survive, is perhaps the ultimate goals of all living organisms, to pass their genes unto successive generation in the ecosystem. The ecological system is a dynamic system. The ‘’eco’’ part of the word refers to the environment, while the ‘’system’’ part of it implies the interactions, interrelationships and interdependencies. In other words, it simply refers to the interplay of functions in the biological system. To be more precise, any spatial or organizational unit which includes the living (biotic) and the non-living (abiotic) constituents interacting with each other and producing exchange of materials between the two is termed as an ecosystem. The automobile system is a clear illustration of a system, such as ignition, the alternator, piston, crankshaft, the injector, fuel pump, etc. all of which function together with the broader context of an engine. In a similar fashion, the ecosystem functions together with its component as a unit. Broadly, the ecosystem consists of two basic interacting components, the living or biotic, and the physical or abiotic.

Consider the natural ecosystem such as the terrestrial or a subunit of which is a forest. The physical (abiotic) component of the forest consist of the atmosphere, climate, (humidity, temperature, rainfall, wind, etc.) soil and water. The biological (biotic) includes the many different organisms, plants, animals, and microbes that inhabit the forest. The interrelationship existing among them is complex and dynamic in that each organism not only responds to the physical environment, but also modifies it and in doing so, becomes part of the environment itself. Trees absorbs/intercepts solar radiation and synthesizes it as nutrient through the process known as photosynthesis. In the process, the tree modifies the environment of the plant below them, reducing the sunlight and lowering atmospheric temperature. We will explore these complex interactions between the biological and the physical environment and its influence on man’s existence in greater details in subsequent sections of this chapter.

Distribution of Organism in the Sea

Each environment presents a different set of constraints with regard to the processes relating to survival, growth and reproduction. The set of characteristics that enables an organism to thrive in a particular environment equally precludes it from thriving when introduced to a different set of environmental conditions, (Smith and Smith, 2006). For instance, if a fish is taken out of water and placed on dry land, it experiences great difficulty in locomotion and breathing. The fish demonstrates the unsuitability of land as a habitat by a vigorous struggle for life. It tumbles about and after a while, it dies. This harsh condition is a consequence of its removal from its natural habitat. Every living organism has limits to the environmental conditions it can endure. Temperatures, moisture levels, nutrient supply, soil and water chemistry, living space, and other environmental factors must be within appropriate levels for life to persist. In the marine habitat, characteristics such as size, chemical composition, salinity, density, pressure, temperature, oxygen concentration, hydrogen - ion concentration, stability, waves, oceans currents and tides are survival determinants.

Distribution of organisms in the forests

In the forest, there is a vertical distribution of plants according to their respective needs for light and their respective abilities to withstand exposures. On the forest floor, there are shades – tolerant plants, such as ferns, which can do with little light and prefer the protected humid environment of the forest floor to the exposed conditions higher up. The mistletoe is one of the light demanding epiphytes and it is usually found high up in the trees among the topmost smaller branches, where much light is available. The fig is another epiphyte found on forests trees. Fig fruit are usually consumed by birds; the seeds are coated with a stick thick juice which sticks to the beak of birds. The birds wipe their beak on the tree branches till the fig seed eventually falls on cracks or bark of the tree where they germinate. The young fig tree grows on other larger trees till its starts producing; eventually the fig tree may strangle the tree that helped it to grow. Many forest animals live on the tree. They include monkeys, squirrels, bats, birds, lizards, tree frogs and chameleons. Some forests animals such as earthworm and beetles live in the soil. Others such as millipedes, ants and snails, live amongst the leaf litter on the surface of the soil.

The different evolutionary solutions to life in various environments represent the product of trade-offs. In the balance of nature, one size does not fit all. There are 1.5 million known species that inhabit Earth’s myriads environment, which is 1.5 million different ways in which life exists on this robust planet.

Ecological Energy Budget and Transfer

Despite the diversity of species, all organisms (from single celled bacteria to the largest of all animals, the blue whale) represents solutions to the three basic functions shared by all living organisms; assimilation, reproduction, and the stability to respond to external stimuli. For organisms to function in the ecosystem, it must acquire energy and matter from the external environment for the synthesis of new tissues through the process of assimilation. To maintain the continuity of life, some of the assimilated resources (energy and matter) must be allocated to reproduction – the production of new individuals. Finally, organisms must be able to respond to external stimuli relating to both the physical (such as heat and humidity) and the biotic (such as recognition of potential mates or predators) environments.

Perhaps, the most fundamental concern on life is the acquisition and assimilation of essential nutrients and the processes associated with life – synthesis, growth, reproduction and maintenance requires energy. Chemical energy is generated in the breakdown of carbon compounds in all living cells, a process called respiration. But the ultimate source of energy for life on Earth is the sun. It is solar energy that fuels photosynthesis, the process of assimilation in green plants. Photosynthesis (and rarely chemosynthesis) is the bane of all ecosystems. Organisms that photosynthesize, mainly green plants and algae, are therefore known as producers. One of the major properties of an ecosystem is its productivity, the amount of biomass (biological materials) produced in a given area during a given period of time. Photosynthesis is described as primary productivity because it is the basis for all other growth in the ecosystem. Manufacture of biomass by organisms that eat plants is termed secondary productivity. Through the consumption of plant and animal tissues, all other organism use energy that comes directly or indirectly from photosynthesis.

The source from which an organism derives its energy is one of the basic distinctions in ecology. Organisms that derive their energy from sunlight are referred to as autotrophs or primary producers. The myriads or conglomeration of green plants that is found in the environment are the primary producers in this regard. These plants absorb carbon dioxide, mineral nutrients, water and built-up organic matter with the help of solar energy, releasing oxygen in the process (fig 1.1). Without producers, life activity in the system would either be stifled or sustained by biomass (i.e. organic material) but yet, survival would still not be feasible as green plant manufactures mineral nutrients. An organisms feeding level can be expressed as its trophic level. Other organisms in the ecosystem are consumers. An organism that eats producers is a primary consumer (e.g. grasshopper). An organism that eats primary consumer is a secondary consumer, which may in turn be eaten by tertiary consumers and so on, Most terrestrial food chain are relatively short (grass → grasshopper → toad → snake → hawk), but aquatic food chains may be quite longer (microscopic algae → copepods → minnow crayfish → bass → osprey). The length of food chain may also reflect the physical and biological characteristics of the ecosystem.

Fig 1.1: Energy change in a hypothetical ecosystem

Organisms that derive energy from consuming plants and animal tissues, breaking down assimilated carbon compounds are called heterotrophs, or secondary producers. In ecosystem, some consumers feed on a single species, but most consumers have several food sources. Similarly, some species are prey to a single kind of predator, but several species in the ecosystem are beset by several kinds of predators and parasites. In this way, individual food chain becomes interconnected to form a food web. Fig 1.2 shows feeding relationships amongst organisms in a typical grassland community, where worm is being fed by grasshopper and grasshopper in turn is being eaten by mouse which invariably is being eaten by a snake, and a snake in turn is being preyed by a leopard which is a higher animal in the terrestrial – grassland community.

Fig 1.2: A food web illustrating feeding relationship in a typical grassland community: Arrows flow from prey (consumed) to predator (consumer)

Organisms can be identified both by the trophic levels at which they feed and by the kind of food they eat, (fig 1.2). Herbivores are plant eaters; they derive their food from primary producers (which belong to the class of ruminants, e.g. goat). Carnivores are flesh eaters (e.g. lion), and omnivores eats both plant and animal mater. Human beings belong to this category of animal by history and habits. The entire food web action is incomplete without the activities of decomposers; they remove and recycle the dead bodies, exudates and excreta of plants and animals. Scavengers such as crows, jackals, and vultures clean up dead carcasses of larger animals, while detritivores such as ants and beetles consume litter, debris and dung, while decomposers such as bacteria and fungi does the final disintegration process which brings the constituent elements of the plant and animal bodies back to the surrounding medium or to the soil, (Asthana and Asthana, 2005).

Plant Adaptation to the Environment

All life on Earth is carbon based. This means that all living organisms are made up of complex molecules built on a framework of carbon atoms. The means by which organism acquires and use carbon represents some of the most basic adaptation required for life. Human, like all other animals gain their carbon by consuming other organisms. However, the ultimate source of carbon from which life is constructed is carbon dioxide (CO2) in the atmosphere. Not all living organism can use this abundant form of carbon directly. Only one process is able to transform carbon in the form of CO2 into organic molecules and living tissues. The process carried out by green plants, algae, and some type of bacteria is photosynthesis. Photosynthesis is essential in the maintenance of life on Earth. All other life forms derive their energy (carbon) from the consumption of organic carbon compound in the form of plant and animal tissues.

Photosynthesis and Respiration

How does photosynthesis occur in green plants? Photosynthesis is the conversion of carbon dioxide in the presence of water into simple sugars. It is the process by which energy from the sun in the form of short wave radiation (photo-synthetically active radiation or PAR is harnessed to drive a series of chemical reactions that result in the fixation of CO2 into carbohydrates (simple sugars) and the release of oxygen (O2) as a by-product. Photosynthesis takes place in tiny membrane organelles called chloroplasts that resides within the plant cells, (fig 1.3). The process cannot take place without the chlorophyll, this is a green molecule in the chloroplasts that has the propensity of absorbing light energy which is being utilized to create high energy chemical bonds in compounds which fuels up other cellular metabolism.

The process can be simplified in the equation below;

The net effect of the above chemical reaction is the utilization of six molecules of water (H2O), oxygen (O2) and carbon dioxide (CO2) molecules for one molecule of sugar to be formed (C6H12O6). One would ask how imperative sugar is in the sustenance of plant life. Glucose is the end product of sugar, an energy rich compound that aids metabolic processes of cells. The synthesis of various other carbon-based compounds, such as proteins nucleic acid, fatty acids, lipids, carbohydrates and enzymes from these initial products occurs in both the leaves and other parts of plants. This process of releasing chemical energy is called cellular respiration.

Fig 1.3: Ultra structure of a plant tissue

Photosynthesis is a complex sequence metabolic reaction. It begins with two steps referred to as light dependent and dark dependent reaction. The light dependent begins with the initial photochemical reaction where chlorophyll, (light absorbing pigments) traps light energy within the chloroplasts cells. This enzyme in the process splits water molecules and releases molecular oxygen (O2). This is the source of all oxygen in the atmosphere upon which all living organisms, including man depends on for life. This light dependent reaction produces mobile energy molecules to another acceptor molecules resulting in the process of photosynthetic electron transport. This process results in the synthesis of ATP (adenosine triphosphate) and the NADPH (nicotinamide adenine dinucleotide phosphate). This high energy substance ATP and the strong reductant NADPH produce a high reaction for the next set of processes, the dark or light independent reactions.

In the dark reaction, CO2 is biochemically incorporated into simple sugars. The process does not necessarily require the presence of sunlight. They depend on the product of the light reaction and therefore invariably depend on the essential resource of light. The enzymes extract energy from ATP and NADPH to add carbon atoms to produce simple sugar molecules.

Carbon dioxide (CO2) uptake and water loss

Photosynthesis involves two key physical processes; diffusion and transpiration. CO2 diffuses from the atmosphere to the leaf through leaf pores or stomata. As photosynthesis slows down during the day and demand for CO2 lessens, stomata closes to reduce loss of water to the atmosphere. Water loss through the leaf is called transpiration. The amount of water loss depends on the humidity. Water lost through transpiration must be replaced by water taken up from the soil. Water moves from the soil into the roots, up through the stem and leaves, and out to the atmosphere. The process continues as long as water is available the soil.

Animal Adaptation to the Environment

The plethora of green plants that dots our landscape, whether the smallest of shrubs or the myriads of giant forest trees derive their energy from the process of photosynthesis. The process is quite different in animals because heterotrophic organisms derive their energy and nutrients from the consumption of organic compounds contained in plants and animals. In this regards, the adaptation of animals to its environment is much more complex than that of plants. However, there are number of processes that are common to all animals; the acquisition and digestion of food, the maintenance of body temperature and the adaptation to systematic variation in light and temperature.

In addition, there are a number of fundamentally different constraints imposed by aquatic and terrestrial environments.

Mechanisms of Energy Acquisition in Animals

Carbon fixed by plants in the process of photosynthesis directly or indirectly provides the nutritional resources for animals. The ultimate source of energy through which animals derives their potential food items in the form of organic compounds is plants. Because plants and animals have different chemical composition, the problem often encountered is the conversion of this plant tissue to animal tissue. Animals are high in fats and protein, whereas plants are high in carbohydrates and low in protein and much in the form of cellulose in lignin and cell walls which are complex in structure and form as well as difficult to breakdown.

The diversity of potential source of energy in the form of animal tissues requires an equally diverse array of physiological, morphological and behavioural characteristics that enables animal to acquire (fig 1.4) and assimilate these (energy) resources. The most general of most of this classification is the division based on how animals use plants and animal tissues as sources of food.

Fig 1.4: Mouth part depicts how organisms obtain their food. (a) Piercing/sucking mouth part as a mosquito (b) Chewing mouth part of a grasshopper (c) The burring and chewing mouth part of an ant (d) The strong conical bill of a seed eating bird (e) The grinding molars of a herbivores (a horse) (f) The shear grinding jaw of a snake (g) The tear breaking of a hawk (h) The canine and shearing teeth of a carnivorous mammal, and (i) The chewing and grinding teeth of an omnivore.

Those that feed exclusively on plant tissues are classified under the herbivores. Animals that derive their food from consuming other animals are called carnivores (e.g. lion), whereas those that feed both on plants and animal tissues are called omnivores (e.g. man). In addition, animals that feed on dead plants and animals matter are called detrivores (e.g. earthworm).

Herbivory

Herbivores are characterised based on their kind of food. Grazers, antelopes, etc. feed on leafy materials especially grasses. Granivores feed on seeds, browsers feed on woody material and frugivore feed on fruits, nectivore feed on plant nectar.

Ruminants such as cattle are exemplary case of herbivores, anatomically specialised for the digestion of cellulose. They pose a highly complex digestive system with compartmentalised stomach structure-rumen (the compartment through which the name is derived, reticulum, omasum and abomasum (the main stomach) (fig 1.5).

The rumen and reticulum inhabited by millions of anaerobic bacteria and protozoans functions as fermentation aid. These microbes breakdown the cellulose into useable nutrients as found in ruminants. Ruminants have powerful salivary glands which secretes substances that regulate the acidity and the chemistry of the rumen. The food materials eaten by ruminants are stored in the rumen and the reticulum where it is soften to a pulp by addition of water, kneaded by muscular action and fermented by bacterial action. At leisure, these animals regulate their food material and further reduce them to a sizeable particle to aid digestion, thus making it more accessible to microbes before swallowing again back into the rumen. Finer materials move into the reticulum, contraction forces it into the third compartment where it is further digested and finally forced into the abomasums. Part of the food material in the rumen is converted into methane which is expelled from the body and is utilized as food for the body.

Fig 1.5: (a) Digestive tract of a non-ruminant herbivore, which is characterised by a long intestine and a well-developed caecum. (b) The ruminant stomach. The four compartment stomach consists of the rumen, reticulum, Omasum, and abomasums (c) The digestive tract of a monogastric animal (d) The digestive tract of a bird with a crop, the stomach or the gizzard (e) The digestive tract of a carnivorous mammal consisting of the oesophagus, a small caesum and large intestine for predation.

Seed eating birds, e.g. chicken, doves, pigeon, etc. have three separate chambers. The first chamber is a pouch in the oesophagus called the crop, which is a reservoir for food that passes through the stomach. Food then passes through the gizzard which secretes enzymes and grinds.

In the marine ecosystem, fishes and herbivores species are few and typically inhabits the coral reefs. These herbivores fish feed on algae growth which lacks lignin and other structural compounds like the terrestrial plants and as such makes digestion much easier. The gizzard like stomach ingests inorganic materials that mechanically breakdown algae cells to reduce nutrients. Other fishes depend on microbial fermentation in the hindgut to assist in breakdown of algae cells. Some reef fishes develop specialized jaws that grind algae materials before gaining its way into the intestine.

Carnivory

These are flesh eaters, herbivores are the major source of energy for this category of animals. Carnivorous are not faced with digestion issues because of the chemical composition of its prey, but rather problems of sufficiency.

Fig 1.6: Predation between a lion and a zebra

Carnivorous mammal stores processed food, adds mucus enzymes, and hydrochloric acid to expedite digestion. The carnivorous bird has a dissimilar stomach structure, its gizzard is little, with reduced muscle, and the implication of this is that digestion starts in the anterior stomach. In hawks, owls, and other carnivorous birds, the gizzard acts as a barrier against hair, bones, feathers which this birds discards before digestion.

Omnivory

Omnivory are categories of animal that derive their energy source from both plant and animal. Human beings (i.e. man) belong to this group. The red fox for example feeds on cherrus, acorns, grasses, grasshoppers, crickets and small rodents. The black bear feeds heavily on vegetation, birds, leaves, nuts, tree bark-supplemented with bees, beetles, cricket, fishes, small to medium scale mammals, etc. Human being is not an exception to this feeding patterns, although man’s food are to an extent processed before consumption, man eats raw food sources like vegetables and fruits e.g. mango, cabbage, carrots, lettuce, cherry, mango, guava, banana and apple, (just like the red fox) as well as myriads of animals such as cattle, goat, sheep, pig, etc. and even birds of all sort, including both marine animals, e.g. fish.

Biogeochemical Cycles and Anthropogenic Activities

In the succeeding discussions, we examined the internal cycling of nutrients driven by the process of net primary productivity and decomposition. The entire process of energy budget, material cycling and the overall processes on Earth is an aspect of biogeochemical processes. Each process of element transformation or movement from the environment (abiotic) to the organism (biotic) and back to the environment in more or less cyclic path is collectively referred to as biogeochemical cycle (from bio, ‘’living’’; geo for the rocks and soils; and chemical for the processes involved).

Types of Biogeochemical Cycles

There are two basic types of biogeochemical cycles, gaseous and sedimentary. The classification is based on the primary source of nutrient input to the ecosystem. In gaseous cycles, the main pool of nutrients is the atmosphere and the oceans, and as such is globally visualized. The gases most important for the sustenance of life on Earth are nitrogen, oxygen and carbon dioxide. These three gases are found in the atmosphere in a stable quantity of 78 per cent, 21 per cent, 0.03 per cent, respectively, and are dominant component of the atmosphere. Other gases found in the atmosphere