Environment

What is environmental protection

By the notion of environmental protection we understand all activities whose aim is to exploit, maintain and, if possible, replenish sensible resources and riches of natural environment. Apart from informal activities (ecological organizations and movements), some ecological activities became formalized and made global. Furthermore, international legislative and executive institutions take care of the protection of natural resources.

The conception of environmental protection appeared in the 19th century when the processes of industrialization sped up (the development of industry, the growth of cities, the increased exploitation of natural resources) which entailed new threats, such as pollution. At that time people became conscious of human destructive influences and the necessity of protecting their resources.

In the 20th century the development of industry progressed. This intensive expansion, which often took the form of overexploitation, caused other dangers and, accordingly, the development of activities whose aim was to protect the environment. Nowadays these problems are more often than not, regulated by law.

The main activities concerning environmental preservation, some more global than others, include the introduction of restrictions on the emission of harmful chemical compounds, a prohibition on using particularly destructive substances, protection of valuable ecosystems (national and landscape parks) and specific riches (natural features of historic importance). Environmental protection also involves less spectacular actions, such as promoting cleanliness, waste segregation, saving natural resources by more sensible use of, for example, water and energy.

Types of environmental pollution

Human activity is characterized by a huge diversity and practically in every field pollution may be generated. Pollution can be divided in terms of environment or the area of contamination: air pollution, soil pollution, water pollution and landscape pollution. We distinguish various types of pollution: dust, gases, sewage, waste, radioactive contamination and also noise and light.

Anthropogenic air pollution is mainly the result of the emission of harmful dust, gases and aerosols into the atmosphere. These harmful substances come from industrial, food-processing and transport activity.

Water pollution is the effect of water contamination by sewage and waste. Additional factors which pollute are: water transport (direct influence) and using pesticides and chemical fertilizers in agriculture; these agents penetrate through soil into ground water and then into cycle. What is more, the cycle of water in the nature is disturbed due to forest destruction, improper farming and the development of cities.

Soil is usually polluted by extensive and irresponsible waste disposal, using fertilizers and plant protection agents. It is also polluted indirectly by air, rainfall and ground water pollution.

Landscape pollution includes, first of all, omnipresent rubbish, waste stockpiles, dumps, slag heaps and damage caused by the exploitation of fossil deposits, everything that lowers the aesthetic qualities of the environment and frequently results in the destruction of nearby ecosystems.

Although light and noise pollution does not cause damage to the particular environment (air, land or water) and it might seem to be exaggeration of the problem, it becomes more and more serious threat to big cities and their surroundings. Artificial light has a negative influence on animals' and people's vital functions. The negative influence of the excess of light affects especially organisms which are active at night. Birds suffer as well - city lights made them disorientated during migrations. People are advised against sleeping in places which are lit by street lamps since it causes sleep disorders and in extreme cases it may lead to insomnia and exhaustion of organism.

There is no doubt that noise has a negative influence and, as scientists discovered, about 40% of Europeans live in conditions in which the noise generated by traffic exceeds the 55 decibels, so it exceeds the safe level (serious hearing irritation) during day whereas 30% Europeans are subject to noise which goes above 30 decibels even at night and at this level sleep is disturbed.

The effects of the environmental pollution

Environmental pollution has a destructive influence on a global scale - the problem concerns our whole planet and also local places - the existing threats are different in various countries.

On a macro scale people and by-products of their activity in the form of harmful substances polluting the air, soil and water, led to the increase in the greenhouse effect and consequently to global climate warming, the ozone hole and acidified precipitation. And thus:
The greenhouse effect caused by the emission of gases which increase temperatures on the Earth (carbon dioxide, ozone, CFCs) and forest thinning (lower intake of carbon dioxide, lower production of oxygen) result in climate change, ice melting, disturbance of vital functions of fauna and flora and even extinction of some species. Climate changes cause a wide range of atmospheric phenomena (hurricanes, rain, floods, hailstorm) on an unusual scale and make climate unpredictable.
The ozone hole is the result of the emission of CFCs into the atmosphere, it exposes us to the harmful effects of solar ultraviolet radiation; fortunately people partly handled this problem by prohibiting the production and emission of harmful substances, due to which the level of ozone in the upper layers of the atmosphere will be probably restored.
Acid rain, caused by the emission of sulfur dioxide and nitric oxides, has a destructive influence on soil and water and, accordingly, an indirect effect on living organisms.

On a macro scale each threat mentioned above influences: separate elements of the natural environment, plants, animals, whole ecosystems. They also cause diseases associated with the progress of civilization, for example allergies incidence rate has increased, more and more people suffer from diseases of blood circulation system and cancer.

The methods of environmental preservation

To protect the environment it is necessary to take action at local level as well as cooperate at international level.

On a global scale United Nations and various international committees and ecological organizations deal with the environmental protection. The aim of formalized activities is to introduce legal articles regulating the issues of environmental protection: restrictions on the emission of harmful compounds, the methods of waste recycling, prohibitions and promotion of specific activities.

The general aim of such activities is to eliminate threats; however, it should not mean ceasing all kinds of activities since it would defeat the purpose and stop the development; the point is that we ought to learn how to exploit the natural resources sensibly and let technology develop, taking into consideration our and environmental protection. And these types of actions are possible even at specific unit's level. All of us have considerable influence on the use of natural resources and clean environment. Every person is able to limit the emission of exhaust fumes, they just have to choose transport public or a bicycle instead of a car from time to time. We will be also ecological-friendly if we save water and energy, support waste recycling (by rubbish segregation) and first and foremost we will be aware of all the existing threats and the fact that it is human mindlessness that often leads to accidents with tragic consequences (ecological catastrophes).

Diseases caused by environmental pollution

Harmful effect of environmental pollution manifests itself in lowered immunity to all kinds of diseases which means that human organism becomes more liable to pathogenic influence of various factors.

This influence can be direct or indirect. All harmful chemical compounds we take in with the air or water have direct, toxic impact on people. Animals and plants which are also influenced by pollution in the process of nourishment become the source of harmful substances which we assimilate indirectly while eating.

As far as specific diseases caused by pollution are concerned, they are, above all, all kinds of diseases associated with the progress of civilizations. Their development, variety and incident rate depend closely on industrialization and changes in the quality and style of life resulting from the progress of our civilization. These diseases include cancer, allergies, asthma, sight and hearing diseases (caused by the excess of light, noise, ultraviolet radiation), neurosis, diseases of blood circulation system, skin diseases.

All kinds of emitted pollution has impact on our health and it is impossible to discuss it briefly; nevertheless, their influence is indisputable, especially as in industrialized areas incidence rate of diseases associated with the progress of civilization has increased which is contrary to the areas with less developed industry or with no industry at all; in these areas contagious diseases are more frequent.

Even a special field of medicine was distinguished - environmental medicine. Its aim is to deal with diagnosis, treatment and, above all, prevention of health problems caused by environmental pollution.

http://ourecology.org/index.html

Climate change

As a result of abnormal weather conditions caused by climate changes (such as hurricanes), about 160 000 people die every year. Within 50 years even one third of all species of plants and animals may die. We are the last generation that can put an end to it.

Earth's atmosphere is made of a gas layer. These gases, which trap heat, allow to maintain life on the Earth. This is natural greenhouse effect without which life on the Earth would be impossible. However, human activity contributes to the escalation of this effect. By burning fossil fuels necessary for the production of energy and for transport, people release milliards of tones of carbon dioxide. It is the main greenhouse gas emitted due to human activity. Changes in the land, for example caused by cutting down forests, also contribute to the increase in CO2 in the environment. For instance, trees naturally absorb CO2, so when they are cut down, all carbon dioxide they absorbed during their life is emitted into the atmosphere.

Furthermore, industry and other branches of human activity increase the number of gases which appear in the atmosphere naturally, such as methane (CH4) coming from the rice growing, animal breeding and waste fermenting on dumps, and nitrous oxide (N2O) which comes mainly from agriculture. Methane has 21 times higher potential for heating climate than carbon dioxide and it contributes to the greenhouse effect in 18%. The potential of nitrous oxide for heating is 310 times higher in comparison with carbon dioxide but it is emitted in less amount and it contributes to greenhouse effect in 6%.

These gases escalate the greenhouse effect, they thicken the natural layer of gases in the atmosphere and contribute to trapping more heat. As a result, temperature rises and upsets the balance of the atmosphere.

Whereas the presence of many greenhouse gases is natural, the pace with which people add them to the atmosphere differs a lot form the natural one. It was estimated that presently the amount of CO2 in the atmosphere is higher than before the industrial revolution during which people started to burn fossil fuels on a large scale. Owing to industrial activity, people also produce new gases such as HFC and PFC (compounds from the group of hydrofluorohydrocarbons).

Although there are doubts about the scale of climate change, there is general consensus that:
Warming by about 1.3oC is inevitable due to the concentration of carbon dioxide in the atmosphere. We have to keep warming below 2oC if we want to prevent the worst scenario of climate changes.
If the emission of gases is not stopped, climate changes will take place much faster during the next 100 years than now.

There is every likelihood that the mechanism of climate feed-back will result in even faster and irreversible climate changes. In this phenomenon thermal gases absorb rays reflected from the surface of the Earth which causes rise in temperature; secondary effects, associated with the increase in the amount of water vapour in the atmosphere, might cause changes in cloud cover, trapping even more heat, and consequently climate changes. Nobody knows how much time it will take global warming to fulfill the worst-case scenario.

http://ourecology.org/climate_change.html

Recycling

Recycling involves using waste, worn out elements (e.g. parts of machines) to make new products, e.g. waste paper to produce paper, worn out tyres to produce fuel used in cement plants. Waste includes all objects and solids as wells as liquid substances which are not sewage and which come from human economic and living activity. Types of waste include: agricultural, industrial and municipal.

Recycling is significant to environmental protection. Some car companies strive for the possibility of recycling above 90% of steel and coloured metals they use for the production of cars; they also use plastics which can be recycled.

Large amounts of paper, metal, plastic and glass waste are used again in the process of recycling (utilization). In western countries the majority of these materials are gathered in special containers at homes or in factories. However, the rest of rubbish also contains many valuable materials which can be separated in various stages of their processing before they land in dump. Dried rubbish is burnt in anaerobic conditions in order to get such useful substances as carbon oxide, methane, hydrogen, mineral oils, tar or charcoal. Ferromagnetic metals (including iron or nickel) are taken from a conveyor belt which transports rubbish by strong magnets which hang above it. Also glass, aluminum and other non-ferrous metals are separated in order to take advantage of their various physical characteristics.

The process of separating materials is often based on the difference in their density, namely specific gravity. One of the separators works in this way that powdered rubbish falls on a conveyor band which goes upwards; the material with higher density falls down and the lighter material goes up. If we burn rubbish, metals and glass melt and they fall on the bottom of a stove from where they can be easily gathered.

Later glass separated from rubbish can be sorted into coloured and white. In order to do that, ground glass goes through strong magnetic field. Pieces of white glass do not interact with the field whereas coloured glass does and it is separated. The pieces of glass go through streams of light and the changes in their colour are recorded by photosensitive elements. On the basis of the signal they send, machines sort the glass - each colour separately.

http://ourecology.org/recycling.html

Ecosystem

Ecosystem is a unit consisting of living organisms which form biocenosis with all elements of inanimate environment, namely biotope. Every natural ecosystem is an open system and functions due to the flow of energy and matter circulation. Energy flow is one-way whereas matter circles in ecosystem in closed circuit. Solar power is the most important power in ecosystems. Not all energy is accumulated in organisms. Some of it is used for basic metabolic processes and building structures of organisms; however, some of it is lost in the form of heat.

To make matter circulation possible, the presence of producers, consumers and reducers, or at least producers and reducers, is essential. Owing to producers organic matter is synthesized. Consumers eat organisms or dead organic matter. Decomposers (reducers) decompose dead organic matter and release inorganic nutrients for producers. Due to reducers and decay processes:
matter circulation in the environment is closed influencing growth and development of plants,
nutrients are included in the circulation,
food for heterotrophic organisms is produced.

Ecosystem is divided into:
autotrophic ecosystem which functions on the basis of the presence of light and organic matter called autochthonous matter which is produced in the process of photosynthesis mainly by green plants. The examples of such ecosystems are a forest, a peat bog, a meadow, a pond, a lake.
heterotrophic ecosystem which is incomplete, which is not self-sufficient, devoid of producers, where matter comes from outside and is called allochthonous matter. The example of such an ecosystem is a cave. The lack of light makes it impossible for plants to exist.

http://ourecology.org/ecosystem.html

Greenhouse effect

What is greenhouse effect

Greenhouse gases warm the atmosphere, thermal radiation is absorbed by the planet and the temperature increases. This phenomenon is called greenhouse effect as its mechanisms are similar to the processes which occur in a greenhouse. In this case the atmosphere of the planet functions as glass which enables to heat the surface from one side and from the other side it absorbs heat emitted by the surface thereby causing global increase in temperature. To be brief, the atmosphere and gases it includes allow the radiation emitted by the Sun to get inside; however, at the same time, they trap the radiation of the heated Earth and do not allow it to escape and direct it towards the surface again. We receive the same amount of energy but the accumulation of the compounds which trap the Earth radiation in the atmosphere favors the increase in temperature.

Gases and aerosols are responsible for this.

Greenhouse effect is a thoroughly natural phenomenon which was observed not only on the Earth but also on other celestial bodies in our solar system, namely on Mars, Venus and Titan (moon of Saturn).

Natural greenhouse effect

The greenhouse effect is essential to life on our planet. Due to the ability to absorb and trap part of heat, it was possible for life to be created and survive. The greenhouse effect, owing to the specific role of atmosphere on every planet, is a natural phenomenon. Only on the Earth it takes on alarming proportions due to human activity. Natural heating of the planet is the effect of heat exchange. This process looks as follows: solar radiation carries thermal energy, when it reaches the Earth, it heats the atmosphere and the surface; water, forests and whole environment are heated as well. The Earth does not absorb the whole radiation, some of it is reflected; every light surface which reflects light also reflects thermal energy. This process is increased by some compounds and formations contained in the air (clouds, some aerosols). On the other hand, clouds and some gases let in and absorb energy thereby increasing temperature. Heating is not a one-way process. Ultraviolet objects heated by radiation emit all or part of radiation in a reverse process - long-wave infrared radiation. But for the atmosphere and the presence of compounds limiting the emission outside, all radiation would be transmitted to space. Nevertheless, the returned emission is stopped, heat balance of the Earth is positive, i.e. the amount of heat which reaches the Earth exceeds the amount of heat which leaves the Earth. This process leads to increase in temperature.

The causes of the greenhouse effect

The atmosphere of our planet is the air which is the mixture of various gases and aerosols. The composition of the atmosphere depends on the height. To put it simply, this is a composite mixture of gases. The most common gases are nitrogen (over 78%) and oxygen (28%). Other gases constitute only a fraction of the whole mixture; however, we cannot ignore their importance.

The main greenhouse gas is water vapour. According to scientists, it is responsible for the greenhouse effect in 30 to 60 per cent. The amount of the vapour in the atmosphere is not fixed and it fluctuates depending on a time of the day, season or area. Clouds are made of vapour, its presence can be easily stated with our own eyes. The vapour is also significant due to the fact that, on one hand, it absorbs perfectly some solar radiation and, on the other hand, it substantially limits heat return in the form of infrared radiation. Its presence in the atmosphere is the result of evaporating water: seas, lakes, oceans and also evaporating water from ground, plants and other organisms. The atmosphere is cleaned by rainfall and the process of vapour exchange and water cycle in the nature is dependant on temperature: the higher temperature the higher water evaporation rate; as a result the content of water vapour in the air increases and so does the greenhouse effect.

Another greenhouse gas is carbon dioxide. It was discovered in the atmosphere a long time ago and it is one of the factors responsible for life-friendly temperature. However, as the result of the emission of carbon dioxide in the process of fuel burning and forest burning, its greenhouse effect increases and so does its influence on climate. Carbon dioxide is responsible for the greenhouse effect at about 9 to 26% and the ability to absorb infrared radiation is 1. Methane has a considerable influence on climate warming. This gas is produced in natural processes, mainly by bacteria which decompose organic matter (remains of plants and animals). The excess of methane in the air and thereby enhancing the greenhouse effect are caused by mining industry and stockpiles of organic waste (dumps). The ability of methane to absorb infrared radiation is thirty times higher than the ability of carbon dioxide.

Other gases which cause and enhance the greenhouse effect (as a result of emission caused by people) are nitric oxides, including nitrous oxide, ozone and CFCs. The ability of nitrous oxide to absorb thermal radiation is 150 higher than the ability of carbon dioxide; this gas is produced in the emission of exhaust fumes and while using nitric fertilizers in farming.

Ozone, which is the protective ozone sphere in upper layers, in lower layers prevents heat produced on the Earth from escaping and its absorbency is 200 times higher than the same abilities of carbon dioxide. The content of greenhouse ozone increases due to chemical reactions of carbon monoxide, hydrocarbons and nitric oxides emitted in industrial burning processes.

And finally CFCs which are not natural as they were produced by people. Although there are not many CFCs in the air, their ability to trap radiation is from ten to twenty thousand higher than the ability of carbon dioxide.

Greenhouse effect and global warming

The issue of the greenhouse effect on climate change is debatable even in a scientific environment. Nevertheless, it is widely assumed that the greenhouse effect or its intensification resulting from human activity, has impact on global warming. The facts are clear: within the space of one century, i.e. from the beginning of the 20th century to the beginning of the 21st century, average temperature increased by 0.7%. What is more, there was a rise in the emission of carbon dioxide and other greenhouse gases. The estimated probability that it was caused by human activity and not by natural reasons is 90% (data from IV Report of the Intergovernmental Panel on Climate Change). Scientists who are skeptical about this theory claim that this change was caused by change in the activeness of the Sun which always influenced our planet, even before the intensification of human industrial activity.

There are other examples of climate change, such as a rise in average temperature on poles (the Arctic - average yearly temperature increased by 3oC and by 7oC in winter), changes in a moderate climate - which can be observed in hot summers and relatively warm winters. Furthermore, climatic zones are shifting to the Equator and, as a result, areas on which droughts occur are extending.

If this process continues, in the next century the consequences will be much more worrying: permafrost melting will cause the creation of bogs which consequently will increase the emission of methane and carbon dioxide. Due to the increase in the amount of carbon dioxide and methane in the air, the temperature of the Earth will rise by about 2oC which will influence ice melting and cause level of water to rise, as a result vast areas of the Earth will be threatened with flooding. From 1880 to 1990 the level of seas and oceans increased by about 11 cm.

Air circulation may be disturbed, climatic zones will shift, we will lose huge areas of farming lands and forest areas. Paradoxically global warming may lead to another Ice Age (ice melting will prevent warm sea currents).

To sum up, scientists agree that the greenhouse effect enhanced by people will speed up the process of global warming and global climate changes which may lead to unpredictable consequence in the future - even extermination of humankind and life on the Earth.

Forests and greenhouse effect

One of the main greenhouse gases responsible for the greenhouse effect, i.e. gases which absorb heat and trap it in the Earth atmosphere, is carbon dioxide. It is widely known that this gas is converted into oxygen by plants (photosynthesis). It means that the presence of carbon dioxide in the air is closely associated with the condition of plants on the Earth. Being a treasure trove of plants and lungs of our planet, forests are of great importance.

Most of forest areas have been destroyed and some of them are still being destroyed due to territorial expansion. They are cut down and burnt down. As a result of both processes we lose vast areas of forests which regulate gas and thermal economy of our planet. By burning forests we contribute to increase in the emission and concentration of carbon dioxide in the atmosphere.

Forests also absorb humidity thereby protecting the air from the excess of carbon dioxide. High humidity facilitates storing carbon dioxide in lower layers of the atmosphere owing to which it is kept in forests and does not escape to higher layers where it could cumulate heat. According to scientists' opinion, about 15% of the emission of carbon dioxide to the atmosphere is the effect of the destruction of forest areas.

Another problem connected with the greenhouse effect is destruction of rain forests. Not only are these huge green areas the treasure trove of nature and a place where oxygen is produced, they also regulate the amount of heat and light absorbed and reflected by the Earth. The ration of light reflection is called albedo. The colors of forests are dark so they absorb light radiation. If forests are destroyed, the light is reflected. Significant changes in the albedo ration influence winds, sea currents and rainfall, in other words, they cause climatic changes.

http://ourecology.org/greenhouse_effect.html

Environ Sci - Lecture 17

Environmental Issues

1. What is pollution?
Pollution is the contamination of an ecosystem by factors that are harmful for the equilibrium of its biotic or abiotic constituents.

 2. Is pollution always caused by humans?

In most cases pollution is caused by human activity. Other species and some abiotic factors however can also pollute an ecosystem. For example, the red tide is created by proliferation of some algae and volcanic dust is a consequence of the internal activity of the planet.

3. Why is waste considered one of the major environmental issues?

The environmental problem concerning waste worsens with industrial development and the global growth of consumption societies in the 20th and 21st centuries, factors that cause the immense volume of residuals produced by mankind in the last decades. The increased waste generation raises the issue about what to do with waste since nature is not able to degrade and resorb with adequate speed and efficiency most of the residuals. Therefore the various kinds of waste accumulate, polluting the environment and creating danger to humans and nature. (The present destination of waste has been public waste depositories where the waste volume is compressed and buried underground, an environmentally risky method. Another method has been incineration, with the grave consequence of causing air pollution.)

4. What are the main types of waste?

The waste can be classified into many types, each of them carrying its own different environmental problem: organic waste, recyclable waste, non recyclable waste, toxic waste, nuclear toxic waste and space waste.

The organic waste is more easily resorbed by nature, but the speed and the geographical concentration of its production due to urbanization generate pollution of rivers, lakes, proliferation of disease vectors and environmental degradation of towns. The recyclable waste is composed of residuals that can be reprocessed, used again by humans, like plastics and metals; the problem regarding recyclable waste is that the separation of such material is not culturally diffused and there is not enough social organization to use them; so the recyclable waste is mixed to other wastes increasing the volume of waste depositories even more. The non recyclable waste is formed of residuals that technology cannot yet recycle, like ceramics, photographic paper, mirrors, cigarettes, plasticized papers, etc; this kind of waste in the future may become recyclable waste and should be separated. The toxic waste includes industrial chemical residuals that are harmful for life and the environment, like contaminated medical waste and the domestic waste containing insecticides and medicines; the toxic waste is one of the major environmental problems since it puts the life of humans and other living beings in danger. The nuclear toxic waste is made of materials that release invisible dangerous radiation for many years; nuclear toxic waste is produced in the extraction of nuclear minerals (like uranium), by nuclear reactors and nuclear plants, in hospitals where Nuclear Medicine is performed and in research centers; although the nuclear waste is often put into armored receptacles the risk of accidents is permanent. Space waste is the waste produced by the activity of humans in space from the second half of the 20th century; it consists of non operating satellites, rocket piece and other equipments that remain orbiting the earth or other celestial bodies or even travelling across space.

 5. What is selective waste collection?

Recyclable waste is waste that can be reprocessed and used again. Waste recycling depends on the separation of the recyclable residuals from non recyclable ones and on the classification of the recyclable into plastics, metals, papers, etc. The function of the selective waste collection is to simplify that separation for the waste to be sorted at the point of origin. Selective collection also helps the creation of an environmental conscience in the people that produce the waste.
 
6. What is the cost-benefit relationship regarding sewage treatment as a strategy to fight water pollution?

To treat sewage is much cheaper for society. The non treated sewage pollutes rivers, lakes and the sea, being a cause of diseases transmitted through water. For the society the costs of these diseases are much higher than the cost of the sewage treatment.

One of the most economical systems to treat sewage is the aerobic treatment system, reservoirs kept very oxygenated for aerobic bacteria to decompose organic material.
 
7. What is eutrophication?

Eutrophication is the process of excessive increasing of nutrients, like phosphate and nitrate, in water due to direct deposit of non treated sewage. The nutrients act as fertilizers leading to abnormal proliferation of aquatic algae. With the exaggerated growth of the alga population the number of aerobic bacteria that cause decomposition of organic material also increases. The proliferation of these bacteria depletes the dissolved oxygen killing fishes and other animals. Besides, the lack of oxygen causes the decomposition to be assumed by anaerobic bacteria. Anaerobes multiply and release hydrogen sulfide that makes water improper to other living beings and creates a putrid smell.
 
8. What is a biodigester?

A biodigester is equipment that produces carbon dioxide, hydrogen sulfide and fuel gases (biogases) like methane from organic material under decomposition (dung, food waste, sugar cane waste, etc.). The biogas is used in heating, as energy for motors and machines and it even has industrial uses. Biodigesters are widely used in public waste depositories and in rural areas. Besides producing biogas the organic waste can be turned into good quality fertilizer.

 9. What are the environmental harms caused by mercury pollution? What are the main sources of mercury pollution?

Mercury is a metal that when present in the water of rivers, lakes and seas contaminates fishes, crustaceans, molluscs and other living beings. The mercury accumulates along the food chain and in each following trophic level the amount of the metal within the individuals is higher. When humans eat contaminated animals they also become contaminated and severe nervous system injuries may emerge. The main sources of mercury pollution are gold mining and the use of derived substances in industry and agriculture.

10. Besides mercury which other heavy metals cause toxic pollution?

Examples of other heavy metals that cause toxic pollution are lead, cadmium and chromium.

11. What are persistent organic pollutants (POPs)?

POPs, or persistent organic pollutants, are toxic substances formed from organic compounds. POPs are made in several industrial processes, like the production of PVC, paper whitened by chlorine, herbicides, insecticides and fungicides, and also in the incineration of waste. Examples of POPs are dioxins, furanes, chlordane, DDT, dieldrin, heptachloride, toxaphen and hexachlorbenzene.

POPs are toxic and highly harmful since, like the heavy metals, they are bioaccumulative, i.e., they are not degraded by the body and accumulate even more in each following trophic level of the food chains. In humans POPs can cause cancer and nervous, immune and reproductive impairments.

 12. Is the upward move of warm air good or bad for the dispersion of pollutants?

The upward movement of warm air is a natural method of dispersion of pollutants. The air near the ground is hotter because the sun heats the soil and the soil heats the air nearby. Since it is less dense, the warm air tends to move towards higher and colder strata of the atmosphere. Such movement helps the dispersion of pollutants.

13. Does thermal inversion occur in the winter or in the summer?

Pollutant low altitude thermal inversion occurs in the winter. In this period of the year the sun heats the soil less and the natural upward move of warm air decreases. Therefore the pollutants form a low altitude layer between the cold air layer near the ground and another layer of warmer air above. The pollutant layer over industrial areas or big urban concentrations reduces the penetration of the sun's energy and the air bellow takes an even longer time to warm.

 
14. Why does thermal inversion increases air pollution? What harm can thermal inversion cause to humans?

Thermal inversion confines at low altitude a layer of pollutants that would have been dispersed by the natural upward move of warm air. The solid particles present in the atmosphere cause health problems, like the exacerbation of asthma and other pulmonary diseases, cough, respiratory unease and ocular discharges; later the pollution can also trigger the appearance of cardiovascular and neoplastic diseases.

15. What is the role of the ozone layer for living beings?

Ozone, O3, is a gas of the atmosphere that filters ultraviolet radiation from the sun disallowing most of that radiation from reaching the surface of the planet. Ultraviolet radiation is harmful for living beings because it is a mutagen and can cause cancer (mainly skin cancer), other DNA mutations and even burns.

16. What are the main chemical compounds that destroy the ozone layer?

The mains chemical compounds that destroy the ozone layer are the CFCs, chlorofluorocarbons, or freons, substances used in the past in refrigerators, airconditioners and spray cans.

Chlorofluorocarbons react with ozone in the high atmosphere releasing molecular oxygen and therefore the amount of ozone in the atmosphere is reduced.

Another substance that destroys the ozone layer is methyl bromide, used in agricultural insecticides.

17. What is nuclear pollution?

Nuclear pollution consists of radiations emitted from atomic nuclei, these radiations are highly injurious to living beings. They can be originated from the extraction of radioactive minerals, nuclear plant reactors, nuclear research centers, hospitals and medical centers that use radioisotopes, nuclear bomb explosions or accidents with transportation, handling or storage of nuclear material. Nuclear materials remain dangerous for many years, contaminating the environment with radiation that can cause cancer, immune impairment, congenital deficiencies, burns and even death. The damage is proportional to the intensity of the exposition to the radiation.

Its persistent feature and high aggression power make nuclear pollution one of the major environmental problems of our time.

18. What is plutonium reprocessing? Why is it a big environmental issue?

Plutonium is the highly radioactive chemical element produced from uranium by nuclear plants. Plutonium can be reprocessed to be used again in nuclear plants or in other destinations, like the making of nuclear bombs. Plutonium reprocessing nowadays, however, is done only in some countries like France, Russia and Britain. The countries that have nuclear plants, like Japan, Australia, etc., send their atomic waste by ship to those plutonium reprocessing centers. Besides the inherent risks of the storage of nuclear waste, plutonium reprocessing brings the risks of the transport of radioactive material across the oceans. The “nuclear ships” often travel near the coast of many countries posing danger to their populations.

 19. What is transgenic food?

Transgenic beings are animals, microorganisms and plants that contain recombinant DNA, i.e., genes from other plants, microorganisms or animals artificially inserted into their genetic material. Transgenic beings are made for scientific and economic purposes, in this last case with the intention of improving their commercial features. For example, bacteria that produce human insulin are transgenic beings made by biotechnology. The main targets of the transgenic technology are edible vegetables, like soy, corn, potato and tomato.

 20. Why are transgenics considered a threat to the environmental safety?

Transgenics can be dangerous to the entire biosphere since the transfer of genes between species may have immediate and long term unpredictable consequences. The creation of new species by nature is a slow process, dependent on causal mutations and natural selection, a relatively safe process for the ecological equilibrium. It is impossible to know how the fast and artificial introduction of transgenic beings in nature affects ecosystems. Pathogenic agents may be involuntarily created in laboratories, spreading unknown diseases; transgenic species may uncontrollably proliferate destroying ecological interactions that have taken thousands of years to be established; the ingestion of transgenic food also has unpredictable effects.

21. What is biological control?

Biological control is a natural method to control the size of animal, microorganism or plant populations. Biological control is based on the knowledge of inharmonious (negative) ecological interactions between species. Using such knowledge a parasite, competitor or predator species is introduced in an ecosystem in order to attain reduction of the population of another species with which it has inharmonious ecological interaction. The biological control presents the advantage of substituting the use of pesticides and other toxic chemical products in the control of plagues and diseases. It however should be employed with caution under serious previous study to avoid harmful ecological disequilibrium.

A kind of biological control of some species can be done by the introduction of previously sterilized males, that do not generate offspring.

22. What is bioremediation?

Bioremediation is the use of microorganisms, like bacteria, protists and fungi, to degrade noxious substances turning them into non toxic or less toxic substances. Bioremediation employs microorganisms whose metabolism uses contaminants as reagents.

Bioremediation is used, for example, in the decontamination of environments polluted by oil spills. In this process bacteria that use hydrocarbons as substrate for their cellular respiration are employed.

 23. What is global warming?

Global warming is the increase in the temperature of the planet due to accumulation of some gases in the atmosphere, especially gases that retain the solar energy reflected by the planet surface. The main gas that causes the global warming is carbon dioxide, CO2, but other gases act as “warming gases” too, like methane, CH4, and nitrous oxide, N2O. The exaggerated increase of carbon dioxide in the atmosphere has been caused by the burning of fossil fuels (mainly oil and coal) in industrial and urban societies and by forest fires. (It is important to note that the natural warming provided by gases of the atmosphere is fundamental for the maintenance of the planet temperature.)

Predictions of studies sponsored by the United Nations stated that the global warming may cause life-threatening transformations to the planet in the near future. Countries that are the biggest emitters of carbon dioxide, like the United States and China, however, systematically ignore the warnings and continue to largely contribute to the danger.

Global warming is one of the most polemic environmental issues today.

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Population Ecology Basic Concepts

1. What is a population?

In Biology a population is a set of individuals of the same species living in a given place and in a given time.

 2. What is population density?

Population density is the relation between the number of individuals of a population and the area or volume they occupy. For example, in 2001 the human population density of the United States (according to the World Bank) was 29.71 inhabitants per square kilometer and China had a population density of 135.41 humans per square kilometer.

3. What is population growth rate?

Population growth rate (PGR) is the percent variation between the number of individuals in a population at two different times. Therefore the population growth rate can be positive or negative.

4. How different are the concepts of migration, emigration and immigration?

Migration is the moving of individuals of a species from one place to another. Emigration is the migration seen as an exit of individuals from one region (to another where they will settle permanently or temporarily). Immigration is the migration seen as the settling in one region (permanently or temporarily) of individuals coming from another region. Therefore individuals emigrate "from" and immigrate "to".

5. What are the main factors that affect the growth of a population?

The main factors that make populations grow are births and immigration. The main factors that make populations decrease are deaths and emigration.

6. What are some examples of migratory animals?

Examples of migratory animals are: southern right whales from Antarctica, that procreate on the Brazilian coast; migratory salmons that are born in the river, go to the sea and return to the river to reproduce and die; migratory birds from cold regions that spend the winter in tropical regions, etc.

7. What is biotic potential?

Biotic potential is the capability of growth of a given population under hypothetical optimum conditions, i.e., in an environment without limiting factors to such growth. Under such conditions the population tends to grow indefinitely.

8. What is the typical shape of a population growth curve? How can the biotic potential be represented in the same way graphically?

A typical population growth curve (number of individuals x time, linear scale) has a sigmoidal shape. There is a short and slow initial growth followed by a fast and longer growth and again a decrease in growth preceding the stabilization or equilibrium stage.

The population growth according to the biotic potential curve however is not sigmoidal, it is only crescent-shaped and points up to the infinite value of the scale (there is neither a decreasing stage nor equilibrium).
 
9. What is environmental resistance?

Environmental resistance is the action of limiting abiotic and biotic factors that disallow the growth of a population as it would grow according to its biotic potential. Actually each ecosystem is able to sustain a limited number of individuals of a given species.

The environmental resistance is an important concept of population ecology.

10. What are the main limiting factors for the growth of a population?

The factors that limit the growth of a population can be divided into biotic factors and abiotic factors. The main abiotic limiting factors are: availability of water and light, availability of shelter. The main limiting biotic factors are: population density and inharmonious (negative) ecological interactions (competition, predatism, parasitism, ammensalism).

11. How do the availability of water and light and the climate affect the growth of a population?

The availability of water and light and the climate are abiotic factors that limit the growth of a population. Since the producers are responsible for the synthesis of organic material transferred along the food chains of an ecosystem, water and light affect the availability of food and a population cannot grow beyond the number of individuals the environment is able to feed. For example, in the desert, the biomass is relatively small and populations that live in this ecosystem are smaller (compared to the same species in environments with large available biomass). The climate, including the temperature, affects the population growth because excessive change in this factor, as the occurrence of droughts or floods, may cause significant population decline; small climatic changes can also alter the photosynthesis rate and reduce the availability of food in the ecosystem.

12. How do populations of predators and prey vary in predatism?

Whenever a predator population increases at the first moment the prey population tends to decrease. At a second moment the decrease of the prey population and the bigger population density of predators cause the predator population to decrease. The prey population then reverts the tendency to decrease and begins to grow.

If variations in the size of populations occur in an unexpected intensity (different from the usual intensity of the ecological interaction) for example, due to ecological accidents killing many prey, the prey-predator equilibrium is disturbed and both species can be harmed. The existence of the predator sometimes is fundamental for the survival of the prey population, since the absence of predatism favors the proliferation of the prey and, in some cases, when the excessive proliferation creates a population size over the sustenance capacity of the ecosystem, environmental degradation occurs and the entire prey population is destroyed. 

13. What is the relationship between environmental resistance and the population growth according to the biotic potential curve and the real population growth curve?

The difference between the real population growth curve (number of individuals x time) and the population growth according to the biotic potential curve of a given population is a result of environmental resistance.

14. How different is the growth according to the biotic potential of a viral population from the growth according to the biotic potential of a bacterial population?

The growth curve according to the biotic potential of virus and bacteria both present a positive exponential pattern. The difference between them is that in each time period bacteria double their population while the viral population multiplies dozens or hundreds of times. The viral population growth curve thus has more intense growth. This happens because bacteria reproduce by binary division, each cell generating two daughter cells, while each virus replicates generating dozens or even hundreds of new viruses.

15. What are age pyramids?

Age pyramids are graphical representations in form of superposed rectangles each representing the number of individuals included in age ranges into which a population is divided. Generally the lower age ranges are represented more to the bottom of the pyramid, always below higher ranges, and the variable dimension that represents the number of individuals is the width (there are age pyramids however in which the variable dimension is the height).

 16. What are the analyses provided by the study of human age pyramids?

The study of human age pyramids can provide the following analyses: proportion of individuals at an economically active age; proportion of elderly (indicating the quality of the pension and health systems); proportion of children and youth (indicating need for job generation and educational services); reproductive profile (shows the population growth tendency); postnatal survival rate (indicates quality of the health system, hygiene conditions, nutrition and poverty); longevity profile; etc.

It is possible to predict whether a population belongs to a rich and industrialized society or to a poor country since the patterns of the age pyramids differ according to these conditions.

17. What are the main characteristics of the age pyramids of developed countries?

In a stabilized human population the age pyramid has a narrower base since the reproduction rate is not so high. The adult age ranges are generally wider than the infantile ranges showing that in practice there is no population growth. There is a proportionally high number of older individuals meaning that the life quality is elevated and the population has access to health services and good nutrition. These are features of the age pyramids of developed countries.

 18. What is the typical conformation of the age pyramids of underdeveloped countries?

The age pyramids of peripheral countries or underdeveloped countries have characteristics related to the poverty of such populations, with a wider base and narrow apex. The base age range, if much wider than the other levels, indicates a high birth rate. The levels just above the base may present an impressive reduction in poorer populations due to infant mortality. Ranges that represent the youth are also wide showing future pressure on job and habitation needs. The widths of the rectangles diminish as age increases to the apex that represents the elderly, demonstrating difficult life conditions, precarious health services and low life expectancy.

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What is Ecological Succession?

1. What is ecological succession?

Ecological succession is the changing sequence of communities that live in an ecosystem during a given time period.

 2. What are pioneer species? What is the role of the pioneer species?

Pioneer species are those first species that colonize places where previously there were no living beings, like, for example, algae that colonize bare rocks. In general, pioneer species are autotrophs or those that maintain harmonious ecological interaction with autotrophic beings (like autotrophic bacteria, herbaceous plants, lichens).

The pioneer community is formed of species able to survive under hostile environments. The presence of these species modifies the microenvironment generating changes in abiotic and biotic factors of the ecosystem undergoing formation. Therefore they open the way to other species to establish in the place by the creation of new potential ecological niches.

3. What is the difference between primary ecological succession and secondary ecological succession?

Primary ecological succession is the changing sequence of communities from the first biological occupation of a place where previously there were no living beings. For example, the colonization and the following succession of communities on a bare rock.

Secondary ecological succession is the changing sequence of communities from the substitution of a community by a new one in a given place. For example, the ecological succession of the invasion of plants and animals in an abandoned crop or land.

4. What is the climax stage of an ecological succession?

The climax stage is the stage of the ecological succession in which the community of an ecosystem becomes stable and does not undergo significant changes. In the climax community practically all ecological niches are explored and greater biodiversity is possible. In this stage the biomass, the photosynthesis rate and the cellular respiration reach their maximum levels and thus the net primary production (NPP = organic material made by the producers – organic material consumed in the cellular respiration of the producers) tends to zero. At the climax the amount of oxygen released by photosynthesis is practically equal to the oxygen consumed by respiration. (This is one more reason why it is wrong to say that the Amazon Rainforest, an ecosystem at climax stage, is “the lung” of the earth. Other reasons are: lungs are not producers of oxygen; the algae and cyanobacteria of the phytoplankton are the main producers of the molecular oxygen of the planet.)

5. How do biodiversity, the total number of living beings and the biomass respectively vary during the ecological succession?

Biodiversity, the number of living beings and the biomass of an ecosystem tend to increase as the succession progresses and they stabilize when the climax stage is reached.

At the initial stage of the succession the use of carbon dioxide and the fixation of carbon into the biomass are high, since the total number of living beings in the ecosystem is increasing. At the climax stage the use of carbon dioxide by photosynthesis equals the production by cellular respiration and the fixation of carbon into the biomass tends to zero.

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Symbiosis and Other Ecological Interactions

1. What is inharmonious ecological interaction?

Inharmonious, or negative, ecological interaction is that in which at least one of the participating beings is harmed.

2. How are ecological interactions classified?

Ecological interactions are classified as intraspecific or interspecific interactions and as harmonious or inharmonious interactions.

3. What are intraspecific and interspecific ecological interactions?

Intraspecific ecological interactions are those between individuals of the same species. Interspecific ecological interactions are ecological interactions between individuals of different species.
4. What is inharmonious ecological interaction?

Inharmonious, or negative, ecological interaction is that in which at least one of the participating beings is harmed.

5. What is harmonious ecological interaction?

Harmonious, or positive, ecological interaction is that in which none of the participating beings is harmed.

6. What are the main intraspecific ecological interactions?

The main harmonious intraspecific ecological interactions are colonies and societies. The main inharmonious intraspecific ecological interactions are intraspecific competition and cannibalism.
7. What are colonies and societies?

Colonies are functional integrated aggregates formed by individuals of the same species. Colonies are often confused with a single individual. Examples are the coral reefs, by-the-wind sailors and filamentous algae.

Societies are interactions for labor division and collaboration among individuals of the same species. Human societies are examples of ecological societies; other species, like bees, ants, termites, wolves and dolphins, also form societies.

8. What is competition? Which type of ecological interaction is competition?

Competition is the ecological interaction in which the individuals explore the same ecological niche or their ecological niches partially coincide and therefore competition for the same environmental resources takes place. 

Competition is harmful for all participating beings and thus it is classified as an inharmonious (negative) ecological interaction.

9. What is an example of intraspecific competition?

Intraspecific competition occurs in practically all species, for example, the competition of humans for a job.

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Biological Diversity

1. What is biodiversity?

Biological diversity is the variety of species of living beings of an ecosystem. In ecosystems which are more biodiverse, like tropical forests, a great variety of plants, microorganisms and animals live; in ecosystems less biodiverse, like deserts, there are less variety of living beings.
 
2. How does biological diversity relate to the characteristics of the abiotic factors of an ecosystem?

The availability of abiotic factors like light, moisture, mineral salts, heat and carbon dioxide, more or less conditions the biodiversity of an ecosystem. Photosynthesis depends on water and light, and plants also need mineral salts, carbon dioxide and adequate temperature for their cells to work. In environments where these factors are not restrictive the synthesis of organic material (by photosynthesis) is at a maximum, plants and algae can reproduce easier, the population of these beings increase, potential ecological niches multiply and new species emerge. The large mass of producers makes viable the appearing of a diversity of consumers of several orders. In environments with restrictive abiotic factors, like deserts, the producers exist in small numbers and less diversity, a feature that thus extends to consumers and conditions fewer ecological niches to be explored.

3. How does the vegetal stratification of an ecosystem influence the biological diversity?

The vegetal stratification of an ecosystem, like the strata of the Amazon Rainforest, creates vertical layers with peculiar abiotic and biotic factors, dividing the ecosystem into several different environments. Therefore in the superior layer near the crowns of big trees the exposition to light, rain and wind is greater but moisture is lower compared to the inferior layers. As one goes down the strata the penetration of light diminishes and moisture increases. Regarding the biotic factors, communities of each stratum present ing differcomposition and features, food habits, reproduction strategies, etc. Such variations in the abiotic and biotic factors make the selective pressure upon living beings to be also diversified, there are more ecological niches to be explored and more varied beings emerge during the evolutionary process.

4. Despite having a great biodiversity why is the Amazon Rainforest under risk of desertification?


The natural soil of the Amazon Rainforest is not very fertile but it is enriched by the vegetal covering made of leaves and branches that fall from the trees. Deforestation reduces this enrichment. In deforestation zones the rain falls directly on the ground causing erosion, “washing” large areas (leaching) and contributing to make the soil even less fertile. Besides that, the deforestation disallows the recycling of essential nutrients for plants, like nitrogen. In this manner those regions and their neighboring regions undergo desertification.

5. How can a great biological diversity protect an ecosystem from environmental damage? Why are less biodiverse ecosystems at risk of suffering deep biological harm if submitted to even small changes?

In ecosystems with more biodiversity the food webs and ecological interactions among living beings are more complex and diverse. In these ecosystems environmental changes can be more easily compensated by the multiplicity of available resources, foods and survival options.

In ecosystems with less biodiversity the individuals are more dependent on some beings that serve them as food and they interact with a small number of different species. In these ecosystems generally abiotic factors are restrictive and the species are more specialized to such conditions and more sensitive to environmental changes. So even small environmental harm can cause big disturbances in the equilibrium of the ecosystem.

6. Is monoculture a system that contributes to great biological diversity of an ecosystem?

Monoculture means that in a large area a single crop (only one species of plant) is cultivated. Therefore monoculture does not contribute to the formation of a community with great variety of species in the area. Since there is only a single type of producer the types of consumers that can live in the area are also restricted.

7. What are some economic applications that can be generated by very biodiverse ecosystems?

Very biodiverse areas present enormous economic potential. They can be a source of raw material for the research and production of medicines, cosmetics, chemical products and food. They are depositories of genetic wealth that can be explored by biotechnology. They are sources of species for agriculture. They can also be explored by 'ecological tourism'.

8. What are the main causes of the loss of biological diversity nowadays?

The biggest dangers to biological diversity today are the action of humans. The main of them is the destruction of habitats caused by the growth of the cities, deforestation, pollution and fires. The second is the invasion of ecosystems by nonnative species introduced by humans; these species change the equilibrium of ecosystems causing harm. Other big dangers are predatory hunting and fishing and global warming.

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Biogeochemical Cycles

1. What are biogeochemical cycles?

Biogeochemical cycles are representations of the circulation and recycling of matter in nature.

The main biogeochemical cycles studied in Ecology are the water cycle, the carbon cycle and the nitrogen cycle.

2. What is the respective importance of water, carbon and nitrogen for living beings?

Water is the main solvent of living beings and it is necessary practically for all biochemical reactions, including as reagent of photosynthesis. Many properties of water are very important for life.

Carbon is the main chemical element of organic molecules; carbon dioxide is also reagent of photosynthesis and product of the energetic metabolism of living beings.

Nitrogen is a fundamental chemical element of amino acids, the building blocks of proteins that in their turn are the main functional molecules of living beings; nitrogen is also part of the nucleic acid molecules, the basis of reproduction, heredity and protein synthesis.

3. What is the water cycle?

The water cycle represents the circulation and recycling of water in nature.

Liquid water on the planet surface is heated by the sun and turns into water vapor that gains the atmosphere. In the atmosphere large volumes of water vapor form clouds that when cooled precipitate liquid water as rain. Therefore water comes back to the planet surface and the cycle is completed. As possible steps of the cycle, water may still be stored in subterranean reserves or in the form of ice in mountains and oceans and it may also be used in the metabolism of living beings, incorporated into the body of the individuals or excreted through urine, feces and transpiration.

 4. Why is the sun the “motor” of the water cycle?

The sun can be considered the motor of the water cycle because upon its energy the transformation of liquid water into water vapor depends. So the sun is the energy source that causes water to circulate in nature.

5. What is the carbon cycle?

The carbon cycle represents the circulation and recycling of the chemical element carbon in nature as a result of the action of living beings.

Photosynthetic beings absorb carbon as carbon dioxide available in the atmosphere and the carbon atoms become part of glucose molecules. During the cellular respiration of these beings part of this organic material is consumed to generate ATP and in this process carbon dioxide is returned to the atmosphere. The other part is incorporated by the photosynthetic organisms into the molecules that compose their structure. The carbon atoms incorporated into the producers are transferred to the next trophic level and again part is liberated by the cellular respiration of the consumers, part becomes a constituent of the consumer body and part is excreted as uric acid or urea (excretes later recycled by decomposer bacteria). Therefore carbon absorbed by the producers in photosynthesis returns to the atmosphere through cellular respiration along the food chain until the decomposers that also liberate carbon dioxide in their energetic metabolism. Under special conditions in a process that takes millions of years carbon incorporated into organisms may also constitute fossil fuels stored in deposits under the surface of the planet; as fossil fuels burn the carbon atoms return to the atmosphere as carbon dioxide or carbon monoxide. The burning of vegetable fuels, like wood, also returns carbon to the atmosphere.

6. What is the main biological process that consumes carbon dioxide?

The main biological process that consumes carbon dioxide is photosynthesis. 

7. How is carbon dioxide made by producers and consumers?

Carbon dioxide is made by producers and consumers through cellular respiration.

8. What are fossil fuels?

Fossil fuels, like oil, gas and coal, form when organic material is preserved from the complete action of decomposers, generally buried deep and under pressure over millions of years. Under such conditions the organic material transforms into hydrocarbon fuels.

Fossil fuels are a natural reservoir of carbon. When oxygen is present these fuels can be burned and carbon dioxide and carbon monoxide are released into the atmosphere.

9. What is the most abundant form under which nitrogen is found in nature?

The most abundant nitrogen-containing molecule found in nature is molecular nitrogen (N2). The air is 80% constituted of molecular nitrogen. 

10. Under which form is nitrogen fixed by living beings?

Most living beings cannot use molecular nitrogen to obtain nitrogen atoms. Producers fix nitrogen mainly from nitrate (NO3-). Some plants also fix nitrogen from ammonia. Consumers and decomposers acquire nitrogen through digestion of mainly proteins and nucleic acids from the body of other living beings.

11. What is the nitrogen cycle?

The nitrogen cycle represents the circulation and recycling of the chemical element nitrogen in nature.

The nitrogen cycle basically depends on the action of some specialized bacteria. Bacteria of the soil called nitrogen-fixing bacteria present in plant roots absorb molecular nitrogen from the air and liberate nitrogen in the form of ammonia. The decomposition of organic material also produces ammonia. In the soil and roots (mainly of leguminous plants), a first group of chemosynthetic bacteria called nitrifying bacteria, the nitrosomonas, produces energy consuming ammonia and releasing nitrite (NO2). The second group of nitrifying bacteria, the nitrobacteria, uses nitrite in chemosynthesis releasing nitrate (NO3). In the form of nitrate, nitrogen is then incorporated by plants to be used as constituent of proteins and nucleic acids and the element then follows along the food chain. Nitrogen returns to the atmosphere by the action of denitrifying bacteria that use nitrogen-containing compounds from the soil and release nitrogen gas (molecular nitrogen).

12. Why is a leguminous crop rotation used in agriculture?

Leguminous crop rotation and other crop rotations are used in agriculture because in these plants many bacteria important for the nitrogen cycle live. The leguminous crop rotation (or cojointly with the main crop) helps the soil to become rich in nitrates that are then absorbed by the plants.

Green manure, the covering of the soil with grass and leguminous plants, is also a way to improve the fixation of nitrogen and it is an option in avoiding chemical fertilizers.

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Food Chains and Trophic Pyramids

1. What is the primary energy source for life on earth?

The primary energy source for life on earth is the sun. The sun plays the important role of keeping the planet warmed and it is the source of the luminous energy used in photosynthesis. This energy is converted into organic material by the photosynthetic autotrophic beings and consumed by the other living beings.

 2. What is the main means by which autotrophic beings obtain energy? 

The main means by which autotrophs obtain energy is photosynthesis. (There are also chemosynthetic autotrophs.)

 3. Which is the autotrophic group responsible for the production of most part of the molecular oxygen of earth?

Algae and cyanobacteria of the phytoplankton are the organisms that contribute most to the production of molecular oxygen.

 4. In the ecological study of food interactions, what are the autotrophic beings called?

In Ecology autotrophic beings are called producers because they synthesize the organic material consumed by the other living beings of an ecosystem.

An ecosystem cannot exist without producers.

5. How are the heterotrophic beings divided in the ecological study of food interactions?

Heterotrophs are divided into consumers and decomposers. An ecosystem can exist without consumers but it cannot be sustained without decomposers. Without the decomposers the organic material would accumulate causing environmental degradation and later death of the living beings.

6. What is a food chain?

The food chain is the linear not branched sequence in which a living being serves as food for another, starting with the producers and going up to the decomposers.

7. How is energy transferred along a food chain?

The energy flux along a food chain is always unidirectional, from the producers to the decomposers.

8. What are trophic levels? How many trophic levels can a food chain have?

Trophic levels correspond to positions on a food chain. Therefore producers always belong to the first trophic level and decomposers to the last trophic level, consumers that directly eat the producers belong to the second trophic level and so on.

There is no limit regarding the number of trophic levels on a chain, since many orders of consumers can exist.

9. What are primary consumers? Can a food chain present quaternary consumers without having secondary or tertiary consumers? Can a tertiary consumer of one chain be a primary or secondary consumer of another chain?

Primary consumers are living beings that eat autotrophic beings, i.e., they eat the producers. Primary consumers always belong to the second trophic level of a chain.

A food chain cannot have consumers of superior orders without having the consumer of the inferior orders. A consumer however can participate in several different chains not always belonging to the same consumer order in each of them.

10. What is the difference between the concepts of food chain and food web?

The chain concept is a theoretical model to study the energy flux in ecosystems. Actually in an ecosystem the organisms are part of several interconnected food chains, forming a food web. Therefore the chain is a theoretical linear sequence and the web is a more realistic representation of nature in which the food chains interconnect forming a web.

11. What are the three main types of trophic pyramids studied in Ecology?

The three types of trophic pyramids studied in Ecology are the numeric pyramid, the biomass pyramid and the energy pyramid.

Generally the variable dimension of the pyramid is the width, and the height is always the same for each represented strata of living beings. The width therefore represents the number of individuals, or the total mass of these individuals or the available energy in each trophic level.

 12. What do numeric pyramids represent? 

Numeric pyramids represent the number of individuals in each trophic level of a food chain.

 13. In a numeric pyramid to which trophic level does the base always refer? What about the top level? 

In a numeric pyramid the base corresponds to the first trophic level, i.e., to the producers. The top level of the pyramid corresponds generally to the last consumer order of the food chain (since the number of individual decomposers, most of them microorganisms, is too large to be represented). 

14. In a numeric pyramid is it possible for the base to be smaller than the other levels?

Since the numeric pyramid represents the quantity of individuals in each trophic level of the food chain, inferior trophic levels with less individuals than the superior trophic levels may exist. For example, a single tree can serve as food to millions of insects.

15. In the short term what will happen to the levels above and below a population of secondary consumers of a numeric pyramid if a large number of individuals from this population dies?

If an intermediate level of a numeric pyramid has its variable dimension decreased, i.e., if the number of individuals of that level is reduced, the number of individuals of the level below will increase and the number of individuals of the level above will be reduced. That happens because the individuals of the level below will face less predators and the individuals of the level above will have less available food.

16. What do biomass pyramids represent? 

Biomass pyramids represent the sum of the masses of the individuals that participate in each trophic level of a food chain.

 17. What is dry mass?

When biomasses are compared often the concept of dry mass is used. The dry mass is the total mass less the water mass of an individual. The total mass is also called fresh mass. To use dry mass instead of fresh mass is useful because among living beings there are differences related to the proportion of water within their body and such differences can distort the quantitative analysis of incorporated organic material.

18. What do energy pyramids represent?

Energy pyramids represent the amount of available energy in each trophic level of the food chain.

 19. Into which type of energy is the light used in photosynthesis transformed? 

The luminous energy used in photosynthesis is transformed into chemical energy.

20. Can the amount of available energy in a given trophic level be larger than the available energy in inferior trophic levels? What does that condition means to the conformation of the energy pyramids?

A superior trophic level always has less available energy than inferior trophic levels. This is because in each trophic level only a fraction of the organic material of the level below is incorporated into the consumers (into their bodies). The other part is eliminated as waste or is used in the metabolism as energy source. Therefore it is never possible to have energy pyramids with inverted conformation, i.e., with the tip to the bottom and the base to the top. It is also not possible to have superior trophic levels with a variable dimension larger than inferior ones. In every energy pyramid, from the base to the top, the size of the variable dimension decreases.

21. What is the gross primary production of an ecosystem? How does GPP relate to photosynthesis? 

Gross primary production of an ecosystem, or GPP, is the quantity of organic material found in a given area in a given period.

Since only autotrophs produce organic material and photosynthesis is the main production process, GPP is a result of the photosynthesis.

22. What are the factors that for influencing photosynthesis also interfere with the gross primary productivity? 

Mainly water and light, but also mineral salts, temperature and carbon dioxide are factors that interfere with the gross primary productivity. 

23. What are the destinations of the organic material fabricated by the producers?

Part of the organic material synthesized by the producers is consumed as energy source for the metabolism of the own producer individual. The other part is incorporated (into the body) and becomes available to heterotrophic beings of the ecosystem. In each following trophic level part of the organic material is used in the metabolism of the individuals of the level, the other part is eliminated as waste and only a fraction is incorporated and becomes available as food for the following level.

24. What is the formula of the net primary production (NPP)? How does NPP relate to the energy pyramids?

Net primary production is the gross primary productivity less the organic material consumed as energy source in the metabolism of the producers: NPP = GPP – (organic material spent in aerobic respiration). It represents the organic material available in the first trophic level.

The base of the energy pyramids must represent the NPP and not the GPP since the idea of these pyramids is to show the available energy in each trophic level of the food chain.

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