Man and His Environment notes

MDCAT Biology

This chapter explains ecosystems, their biotic and abiotic components, energy flow, food relationships, nutrient cycles and population interactions. It also covers pollution, its effects, biological control, conservation of biodiversity, endangered species and methods for protecting natural resources.

Ecosystem and Its Components

An ecosystem is a functional unit of nature in which living organisms interact with one another and with the non-living environment. A pond, forest, grassland, desert and maize field can all function as ecosystems.

The two main components of an ecosystem are biotic components and abiotic components. Biotic components are living organisms, while abiotic components are the physical and chemical factors of the environment.

The organisms of an ecosystem are linked through feeding relationships and the movement of energy and minerals. Decomposers return minerals to the environment and help maintain the functioning of the ecosystem.

Biotic components include plants, animals, fungi, bacteria and other living organisms.
Abiotic components include light, temperature, water, air, soil, minerals, pH and humidity.
Producers make organic food from inorganic substances, usually by photosynthesis.
Consumers obtain food by eating plants or other organisms.
Decomposers break down dead organic matter and release inorganic minerals.
Animals are a biotic component, while sunlight, water and soil are abiotic components.

Energy Flow and Food Relationships

Most ecosystems receive their energy from the Sun. Green plants capture a small part of the incident solar radiation through photosynthesis. The part of sunlight useful for photosynthesis is called photosynthetically active radiation, or PAR.

Energy passes from producers to consumers and then to decomposers. At each trophic level, much energy is lost as heat during respiration, so energy flow through an ecosystem is unidirectional and cannot be completely recycled.

A food chain shows a single pathway of feeding. A food web consists of interconnected food chains and gives a more realistic picture of feeding relationships in an ecosystem.

PAR is the part of solar radiation used in photosynthesis and is less than 50% of total incident solar radiation.
A trophic level is a feeding level in an ecosystem.
Producers occupy the first trophic level.
Primary consumers are herbivores that feed directly on producers.
In a maize field, a grasshopper is a primary consumer.
Secondary consumers eat primary consumers, while tertiary consumers may eat secondary consumers.
Food chains may be grazing food chains or detritus food chains.
Energy decreases as it moves from one trophic level to the next.

Population Interactions and Community Relationships

A population is a group of organisms of the same species living in a particular area. A community consists of populations of different species living and interacting in the same area. The place where an organism lives is its habitat, while its role and position in the ecosystem are described as its niche.

Competition occurs when organisms require the same limited resource. Competition is usually strongest between closely related organisms that occupy the same area and have similar niches.

Competition may occur within a species or between different species. A high density of elephants in one area can cause intraspecific competition because the elephants of the same species compete for food, water and space.

Intraspecific competition occurs between members of the same species.
Interspecific competition occurs between members of different species.
Competition may be for light, nutrients, water, food, shelter or space.
Competition for light, nutrients and space is most severe between closely related organisms growing in the same area or niche.
Predation is an interaction in which one organism kills and eats another organism.
Parasitism benefits the parasite and harms the host.
Mutualism benefits both participating organisms, while commensalism benefits one and does not significantly affect the other.

Nutrient Cycles and Decomposers

Matter is continuously recycled between organisms and the physical environment. Important biogeochemical cycles include the carbon, nitrogen, oxygen and water cycles.

Carbon dioxide is removed from the atmosphere by photosynthesis and is returned by respiration, decomposition and combustion. A large proportion of the global carbon is stored in the oceans. About 71% of total global carbon is found in oceans.

Decomposers are essential in nutrient cycling. If decomposers are completely removed, dead organic matter will accumulate and mineral movement will be blocked. Producers would then receive fewer mineral nutrients from the soil.

The carbon cycle involves photosynthesis, respiration, decomposition, combustion and exchange with oceans.
Oceans act as a major reservoir of carbon.
Nitrogen gas in the atmosphere cannot be used directly by most plants.
Nitrogen fixation changes atmospheric nitrogen into usable nitrogen compounds.
Nitrifying bacteria convert ammonia into nitrites and nitrates.
Denitrifying bacteria return nitrogen gas to the atmosphere.
Decomposers include bacteria and fungi that digest dead organic material.
Without decomposers, nutrient recycling and ecosystem functioning are seriously disturbed.

Pollution of Air, Water and Soil

Pollution is the undesirable change in the physical, chemical or biological characteristics of air, water or land. A pollutant is a substance or form of energy that produces harmful effects in the environment.

Air pollutants may be gases, vapours or solid particles. Primary pollutants are released directly from a source. Secondary pollutants are formed in the atmosphere by chemical reactions involving primary pollutants.

Particulate matter is especially harmful when it is very small because it can enter deep into the respiratory system. According to the Central Pollution Control Board, particles with a diameter of 2.5 micrometres or less cause great harm to human health.

Examples of primary air pollutants include carbon monoxide, sulphur dioxide, nitrogen oxides, smoke and suspended particulate matter.
Carbon dioxide is not classified as a primary pollutant of the troposphere in the stated classification, although its increased concentration contributes to global warming.
Secondary pollutants include ozone and components of photochemical smog formed in the atmosphere.
Sulphur dioxide and nitrogen oxides can contribute to acid rain.
Particulate matter of 2.5 micrometres or less is called fine particulate matter and can reach deep lung tissues.
Water pollution may result from sewage, industrial waste, pesticides, fertilizers, oil and disease-causing organisms.
Soil pollution may result from excessive pesticides, industrial chemicals, plastics and heavy metals.
Pollution can reduce biodiversity and disturb food chains and nutrient cycles.

Eutrophication, Salinity and Agricultural Pollution

Eutrophication is the excessive enrichment of water with nutrients due to human activity. Nitrates and phosphates from fertilizers, sewage and detergents stimulate the rapid growth of algae and other living organic matter.

The dense algal growth is called an algal bloom. When algae die, decomposers use oxygen while breaking them down. The reduction in dissolved oxygen can kill fish and other aquatic organisms.

Agricultural practices can also damage soil. Prolonged and liberal irrigation, especially in poorly drained land, may cause waterlogging and the accumulation of salts at the soil surface. This condition is called salinity.

Eutrophication is excessive nutrient enrichment of water that causes abundant growth of living organic matter.
Phosphates and nitrates are important nutrients responsible for eutrophication.
Algal blooms reduce light penetration into water.
Decomposition of dead algae consumes dissolved oxygen.
Severe oxygen deficiency in water may cause the death of fish and other aquatic animals.
Extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies.
Prolonged liberal irrigation of agricultural fields is likely to create salinity.
Salinity reduces soil fertility and makes water absorption by plants difficult.

Radiation, Ozone Depletion and Biological Effects

Radiation pollution may result from nuclear power plants, nuclear tests, radioactive wastes and accidents. Ionising radiation can damage cells, chromosomes and DNA. Radioactive substances may enter food chains and become concentrated in organisms.

Strontium-90 is particularly dangerous because it behaves chemically like calcium. It may be deposited in bones and bone marrow, where its radiation can damage blood-forming tissues and increase the risk of disease.

The stratospheric ozone layer absorbs much of the harmful ultraviolet radiation from the Sun. Certain chemicals and high-altitude emissions can reduce ozone concentration, allowing more ultraviolet radiation to reach Earth.

Strontium-90 is a dangerous radioactive isotope for Homo sapiens because it can accumulate in bones.
Radioactive materials may undergo biomagnification through food chains.
Excess ultraviolet radiation can cause sunburn, skin damage, skin cancer and cataracts.
Ozone depletion may weaken the immune system and damage living organisms.
Increased liver cancer is not a prime health risk associated with increased ultraviolet radiation caused by stratospheric ozone depletion.
Supersonic jets can contribute to pollution and thinning of the stratospheric ozone layer.
The ozone layer should be distinguished from ground-level ozone, which can act as an air pollutant.

Biomagnification and Biological Control

Some pollutants are not easily broken down and become concentrated in organisms. Biomagnification is the increase in concentration of a persistent chemical at successive trophic levels of a food chain.

DDT is a persistent pesticide. It can accumulate in body tissues and become more concentrated at higher trophic levels. In an aquatic food chain, a seagull may contain the highest DDT concentration because it occupies a high trophic level.

Biological control uses living organisms to reduce pests or disease-causing organisms. It can reduce dependence on chemical pesticides, although the control organism must be selected carefully to avoid ecological damage.

Biomagnification is also called biological magnification.
Persistent pollutants remain in the environment and are not easily degraded.
The highest DDT concentration in an aquatic food chain is expected in a high-level predator such as a seagull.
Trichoderma species can be used for biological control against certain plant pathogens.
Biological control may use beneficial microbes, predators or parasites of pests.
Biological control is different from chemical control because it uses living agents rather than synthetic pesticides.
Excessive pesticide use may kill non-target organisms and contaminate soil and water.

Biodiversity, Conservation and Useful Microbes

Biodiversity means the variety of living organisms at genetic, species and ecosystem levels. Habitat destruction, pollution, overhunting, invasive species and climate-related changes can reduce biodiversity and cause species to become threatened or extinct.

The Red List contains information about threatened species. Conservation may be in situ, where organisms are protected in their natural habitats, or ex situ, where they are protected outside their natural habitats.

Microorganisms are useful in agriculture and industry. Biofertilizers contain living organisms that improve nutrient availability to plants. Industrial microbes produce substances such as acids, alcohols, antibiotics and enzymes.

Amphibians comprise the vertebrate group with the highest number of endangered species.
The indri-indri lemur is found in Madagascar.
Prosopis, Acacia and Capparis are examples of plants found in tropical thorn forests.
The Red List provides data on threatened species.
National parks, wildlife sanctuaries and biosphere reserves are examples of in situ conservation.
Zoos, botanical gardens, seed banks and gene banks are examples of ex situ conservation.
Rhizobium, Azotobacter and certain cyanobacteria are used as biofertilizers.
Agrobacterium is not generally listed as a biofertilizer in the relevant classification.
Aspergillus is a good producer of citric acid.
Clostridium butylicum is not correctly matched with lactic acid in the stated industrial product pairing.
Nitrogenase is an enzyme involved in nitrogen fixation, not the production of alcohol.
Conservation includes habitat protection, controlled use of resources, reforestation and prevention of illegal hunting.

Key terms

Ecosystem: A functional unit in which living organisms interact with one another and with their non-living environment.
Biotic component: Any living part of an ecosystem, such as plants, animals, fungi or bacteria.
Abiotic component: Any non-living environmental factor, such as light, water, temperature, soil or minerals.
Producer: An organism that makes organic food from inorganic substances, usually by photosynthesis.
Consumer: An organism that obtains food by feeding on producers or other organisms.
Decomposer: An organism, usually a bacterium or fungus, that breaks down dead organic matter and releases minerals.
Trophic level: A feeding level occupied by organisms in a food chain or food web.
PAR: Photosynthetically active radiation, the part of solar radiation used by plants for photosynthesis.
Intraspecific competition: Competition between members of the same species for limited resources.
Eutrophication: Excessive nutrient enrichment of water that causes abundant growth of algae and other organic matter.
Salinity: The accumulation of soluble salts in soil, often caused by excessive irrigation and poor drainage.
Pollutant: A harmful substance or form of energy that causes undesirable environmental change.
Biomagnification: The increase in concentration of a persistent pollutant at successive trophic levels.
Biofertilizer: A preparation containing living organisms that increases the availability of nutrients to plants.
Biological control: The use of living organisms to control pests or disease-causing organisms.
Biodiversity: The variety of genes, species and ecosystems present in a region or on Earth.
Red List: A record containing information about species that are threatened with extinction.
Stratospheric ozone layer: A layer of ozone in the stratosphere that absorbs much of the Sun's harmful ultraviolet radiation.

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Biology shortcuts

Recognising acellular organisms

If an entity has no cellular organisation and depends on a host for replication, identify it as a virus. Viruses are non-cellular and are not placed among cellular organisms.

Check whether it has cytoplasm, ribosomes and independent metabolism.
Viruses contain nucleic acid inside a protein coat but lack cellular structure.
Example: An infectious particle without cytoplasm or ribosomes is a virus.
Answer: Non-cellular virus.

This shortcut does not apply to bacteria, which are cellular prokaryotes.

Separating prokaryotic and eukaryotic cells

Use ribosomes as the common feature. Both cell types have ribosomes, but only eukaryotes have a membrane-bound nucleus and membrane-bound organelles.

Look for the feature present in both groups.
Ribosomes occur in prokaryotes and eukaryotes for protein synthesis.
Example: Which structure is common to both? Ribosomes.
Answer: Ribosomes.

Do not use mitochondria, chloroplasts or a membrane-bound nucleus as common features.

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