Ecology and the Environment

FOOD CHAINS :

Ecosystem :A unit consisting of a community of organisms and their physical environment (consisting of biotic and abiotic factors)

Habitat :A place / location in which an organism / group of organism lives – the physical environment of a community.

Community :All the groups of living organisms of different species in the same habitat

Population :The total number of organisms of the same species in a particular habitat a particular time

Plants are digested by consumers and the materials are assimilated in the body of consumer. Only 10% energy is transferred from one trophic level to another as energy is lost at each stage of the chainas heat from respiration, by defacation, excretion and in growth. Some materials are indigestible, like body hair. At high trophic levels (usually after four levels), little energy is left to support another consumer.

Note : Only 10% light energy falling on plants is available for other organisms, because

·       Some light is reflected and is not absorbed

·       Energy is lost as heat, due to respiration

·       Energy is lost via movement

·       Energy is lost via excretion / egestion

DECOMPOSERS :

·       Bacteria and fungi secrete extracellular enzymes onto dead and decaying organic materialand digest it.

·       For example, cellulose of cellulose cell walls of plants is digested to release the contents of the cells.

·       The soluble products are then absorbed by the saprophyte by diffusion.

·       This is an example of saprophytic nutrition.

·       Saprophytic bacteria and fungi respire carbohydrates to release carbon dioxide.

Conditions that increase decomposition :

·                Optimum temperature and pH to enable microorganisms to remain active and for efficient enzyme activity.

·                Damp conditions increase decomposition as water acts a medium for chemical reactions

·                More oxygen increases respiration of bacteria and fungi.

Significance :

·                Decomposition recycles nutrients in the ecosystem.

·                Saprophytic bacteria and fungi respire carbohydrates to release carbon dioxide.

·                Carbon dioxide is used by plants to photosynthesise and synthesisecarbohydrates.

·                Carbohydrates are eaten by animals / heterotrophs.

·                Materials, like nitrates are removed from the environment by plants and are returned to the soil by decay.

·                Nitrates are released as ammonia by decay of free living nitrogen fixing bacteria in the soil to the air.

Dependence of humans on green plants for oxygen and energy

Green plants are producers, and are thus autotrophic in nature. They photosynthesise.

·                Chloroplasts in the palisade mesophyll cells absorb light energy from the Sun.

·                Plants make their own food and incorporate energy into ecosystem.

·                Light energy is converted to chemical energy in chloroplasts.

·                Some light energy is lost by reflection. Only a small percentage is used.

·                Carbohydrates, like glucose are made and are then converted to starch.

·                Carbohydrates contain chemical energy.

·                Glucose forms the basis of all other molecules, like starch, fats and amino acids (by addition of nitrates).

·                Carbon dioxide via stomata and water are required for this process.

·                Oxygen is formed as a by-product and is released into the atmosphere.

·                Oxygen is removed from the atmosphere for respiration and is replaced by photosynthesis.

·                Glucose is converted to starch for storage ; to amino acids for protein formation.

·                Producer is eaten by herbivore / primary consumer.

·                Animals eat starch in plants for nutritionand as a store of energy.

·                Starch is digested in herbivores by enzymes.

·                Cellulose is digested by bacteria in herbivores and is absorbed in the intestine, carried in blood plasma and is used by body cells.

·                Humans then eat animals for energy and nutrition.

·                Energy is lost from one organism to another.

Note : Energy can only be converted, not created or destroyed. Energy is lost as heat. Chemicals can be broken down or synthesized and consist of atoms that can be broken down and synthesized into molecules.

Significance of green plants / photosynthesis :

·                They are called producers as they can trap sunlight, convert light energy to chemical energy. Thus, they form the basis of food chains.

·                They make their own food.

·                They are food for other organisms as they are eaten by animals for nutrition.

·                They provide oxygen for respiration and maintain supply.

Uses of carbohydrates in plants:

·                Glucose is converted to starch for storage

·                Glucose is combined with nitrates absorbed by the roots to form amino acids and proteins for growth

·                Glucose is used to make cellulose

·                Glucose is used as an energy source :glucose + oxygen → carbon dioxide + water (+ energy)

Note :

·                Carbon dioxide has to diffuse a short distance into the leaf if it is thin. Diffusion is more efficient as easier / rapid diffusion occurs across short distances.

·                More / easy light penetration due to large surface area provided by flat leaf, so the chloroplasts absorb maximum amount of light energy from sunlight.

Benefits of photosynthesis to humans :

·                Glucose is converted to starch. Animals eat starch for nutrition, forming the basis of the food chain.

·                Photosynthesis produces oxygen needed for respiration.

Accumulation of chemicals in the human body, for instance, herbicides

·                Herbicides are incorporated into the plant.

·                Plants are eaten directly by humans, or are eaten by herbivorous animals.

·                The herbicides are not excreted or broken down.

·                Herbicides are rather passed along the food chain.

·                Hence, they accumulate in top carnivores, like humans.

Nitrates :Plants need nitrates for :

·                Manufacture of proteins for growth

·                Nitrates are needed for the conversion of glucose to amino acids

·                Amino acids are formed into proteins

·                Larger plants

·                Larger seeds / fruits / increased yield

Their supply is increased by :

·                Use of compost / humus

·                Use of chemical fertilisers

·                Use of leguminous plants –they have nitrogen fixing bacteria in their root nodules that convert atmospheric nitrogen to nitrates for uptake by root hair cells of plants by active transport against concentration gradient using energy from ATP.

Leguminous plants :

·                Leguminous plants contain nitrogen fixing bacteria, such as, Rhizobium, Bacillus Radicicola

·                Nitrogen fixing bacteria convert atmospheric nitrogen to nitrogen compounds, such as, amino acids

·                Plants convert amino acids into proteins.

Examples include :

·                Bean

·                Clover

·                Pea

·                Lentil

·                Alfalfa

Methods used by farmers to increase the production of food crops :

·                Glasshouses contain heaters or fire that increase temperature and carbon dioxide supply. More light is provided. These increase the rate of photosynthesis.

·                Polythene tunnels can be used.

·                Inorganic fertilisers, containing nitrates and phosphates, are added to the soil.

·                Organic fertilisers, such as, manure, are added to the soil.

·                Pests are controlled by the use of pesticides and insecticides, so that less plants are eaten by pests. This prevents competition.

·                Herbicides are used to kill weeds.

·                Fungicides are used to kill fungi.

·                Biological control can be used.

·                Selective breeding can be used.

·                Plants can be cloned.

·                Plants can be genetically modified.

·                Irrigation is used to supply water.

·                Hydroponics can be used.

·                Crop rotation. Legumes can be grown.

·                The soil can be ploughed.

Note :Infection by rust fungi can damage plant tissue and reduce growth. Infection can also reduce photosynthesis and thus, reduce crop yields.

NITROGEN CYCLE

·                Lightning converts nitrogen gas to nitrates.

·                Nitrogen gas is converted to amino acids by nitrogen fixation in soil by nitrogen fixing bacteria, such as,Azotobacter, Clostridium

·                Nitrifying bacteria, such as, Rhizobium, Bacillus Radicicola, in root nodules of legumes*

WATER CYCLE

·                Condensation :Raining converts gaseous water vapour to liquid water.

Reasons for being an endangered species :

·                Loss of habitat

·                Loss of food

·                Hunting / Predation

·                Less reproduction

·                Disease

SEWAGE TREATMENT :

Reasons for treatment :

·                Sewage contains human faeces, which has large quantities of pathogenic bacteria, like that of cholera, typhoid bacilli, etc.

·                Faeces may contain eggs of blood flukes, hookworms, tapeworms, roundworms and amoeba.

·                Amoeba causes dysentery.

·                Faeces / urine provide nutrients and good conditions for the pathogenic typhoid bacilli and cholera bacteria to multiply.

·                Treatment renders pathogens harmless.

·                This can attract insects to lay eggs and transfer pathogens onto food.

·                This can attract vectors of diseases, like rats, flies. After treatment, faeces can no longer be reached by vectors.

·                Hence, risk of contamination of food by pathogens is reduced.

·                This prevents contamination of water supply.

·                It prevents transfer of pathogens to healthy individuals.

If sewage comes into contact, with the water supply :

·                They are easily transferred through the water supply and infect humans, when humans consume or drink contaminated water.

·                This can cause epidemics of cholera and typhoid.

·                Water contaminated by sewage may contain toxic material.

Eutrophication :

Sewage, farm waste, detergents and run off from fertilizer (manure) on fields contain excess nitrates. Faeces decompose to release nitrogen compounds. Nitrates are very soluble and are hence, easily leached into lakes / rivers. These cause eutrophication.

·                Excess nitrates cause algal bloom as algae reproduce rapidly.

·                Algae cover the water surface.

·                This blocks light to bottom rooted aquatic plants and prevents diffusion of oxygen into water.

·                Plants die as they can no longer photosynthesise.

·                Algae die as nitrates run out.

·                Decomposers, such as, aerobic bacteria feed on dead organisms and they reproduce rapidly.

·                Bacteria use up oxygen, making conditions anaerobic.

·                Fish and other animals die, due to lack of oxygen.

·                Oxygen is not replaced by photosynthesis anymore.

·                An unpleasant smell (due to sulphides) and look develops.

Note :Due to eutrophication, aquatic animals / fish die or migrate.

Method of Sewage Treatment :

·                Grid / Screen removes large objects.

·                Grit removal / chamber causes flow to slow down so that grit particles can settle out.

·                This causes sludge to settleto the bottom of settling tanks and is thus separated from the liquid effluent.

·                Anaerobic bacteria digest harmful, organic material.

·                The liquid is then free of harmful material – it is only clean water.

·                It (organic material) is thendrawn off to fermenters, where it is decomposed down by anaerobic bacteria to form methane. This generates heat, kills pathogens and speeds up chemical reactions.

·                Methane is used as fuel.

·                The digested sludge is used as fertilizer as it is rich in nitrates / phosphorus. The fertiliseris harmless in nature.

·                Liquid effluent flows over the top.

·                The effluent is taken to filter beds.

·                Liquid drips onto pebbles, clinker.

·                Liquid collects oxygen, thus aerating the clinker and pebbles.

·                Pebbles are coated with a slime of aerobic bacteria, which digest organic materials in sewage and kill pathogens.

OR

·                Effluent is taken to oxidation pond / aerobic tank, where oxygen is added for aerobic bacteria.

·                Aerobic bacteria and fungi digest any organic material. Protozoa feed on bacteria.

·                The clean water passes to a river.

PIT LATRINES

           

Structure :

·                Floor made of concrete slabs for easy cleaning.

·                There are no puddles around the top of the latrine.

·                The upper part is lined with concrete or bricks to prevent rats from burrowing.

·                The lid / cover prevents entry of flying insects, like, flies and mosquitoes, and cockroaches, as they spread disease.

·                They should contain suitable shelter with ventilation / mesh.

Location :

·                Pit is made deep and in permeable soil to allow the liquid to drain out. Liquid does not accumulate and overflow, which would otherwise, shorten the life of the latrine. This reduces the risk of spreading disease and allows bacterial decomposition.

·                Pit latrines are built away from wells and downhill. Otherwise, effluent could seep into water of wells or waterways and contaminate drinking water with pathogenic bacteria. Drinking water can cause diseases, like cholera, typhoid.

Note :

·                Disinfectants should not be used in a pit latrines as bacteria act as decomposers in the latrines, that break down solid material in the pit. Disinfectant kills all bacteria. Solid material would accumulate and would not be recycled.

·                Pit latrines are unsuitable for use in large towns as they can only accommodate a small amount of material. More people are present in larger towns, so more sewage is produced. There are not enough pit latrines, due to the less space available. There is higher risk of seepage into water supplies. A specialized sewage treatment plant is needed to deal with large volumes of material.

WATER TREATMENT

·                Water is pumped from river.

·                It is filtered / screened through a coarse grid to remove large objects.

·                Aeration allows gases and smells to escape.

·                Suspended matter settles in settling / sedimentation tanks.

·                Slow sand filter :Fine sand is above gravel. Algae in water reproduce.Algae and bacteria form a jelly – like gelatinous layeron sand particles, which traps bacteria in water. Protozoa and midge larvae feed on bacteria.

OR

·                Rapid sand filter :Aluminiumsulphate is added to water, that forms jelly on sand particles. Jelly traps suspended particles and bacteria. Jelly is removed periodically by forcing water under pressure upwards from the base of the filter.

·                Chlorination tank :Chlorine is added to water todestroy any remaining bacteria by oxidation.

·                Water is stored in covered reservoirs to prevent contamination.

·                The purified water is distributed in closed pipes by gravity or by pumps.

SULPHUR DIOXIDE

Sources :Sulphur is present in many fossil fuels, like coal and oil. So, it is released by combustion into the atmosphere as sulphur dioxide by power stations and vehicles.

Effects on humans and the environment:

·                Sulphur dioxide irritates the lining of the lungs and aggravates bronchitis and asthma.

·                It irritates the eyes.

·                It causes choking.

·                It is an acidic gas that dissolves in rain water to form acid rain that dissolves limestone buildings.

·                It acidifies lakes and kills fish along with other aquatic invertebrates.

·                It damages forests by eroding the waxy cuticle of leaves of plants.

Why is it on the rise?

·                More fossil fuels need to be burnt to meet greater energy demands. This releases more sulphur dioxide into the air.

·                More vehicles are being used.

·                More factories

How to combat the situation?

·                Use alternative energy sources, like solar power

·                Use energy saving bulbs and lights to reduce energy demand

·                Sustain forestry by planting more trees

Note :Sulphur dioxide dissolves in moisture to form sulphuric acid. Acid rain corrodes limestone buildings, corrodes mortar and erodes stone. Acid rain damages leaves, which reduces photosynthesis.

CARBON MONOXIDE :

Source :Vehicle exhausts, Cigarette smoke

Effects on humans :

·                Carbon monoxide is poisonous. It combines with haemoglobin to form carboxyhaemoglobin, which is a stable and an irreversible compound. It reduces oxygen transported by the red blood cells. Less oxygen is available for cell respiration and less energy is released, resulting into death by asphyxiation / suffocation.

·                Fetuses born are underweight. Carbon monoxide is passed across the placenta into fetal blood. So, uptake of oxygen is reduced. This causes brain damage. It can cause premature birth.

CARBON DIOXIDE

Source :Combustion of fossil fuels

Effects on humans :

·                Global warming

·                Flooding due to rise in sea levels as polar ice caps melt due to the greenhouse effect

·                Acid rain and its effects, such as -

Why did it remain constant in volume in air for millions of years?

·                Carbon dioxide is removed from the atmosphere by photosynthesis.

·                It is replaced by respiration and combustion of fossil fuels.

·                These processes roughly balance out.

·                Oxygen is removed from the atmosphere by respiration and combustion.

Why is it on the rise?

·                Increased combustion of fossil fuels to meet increased energy demands in homes and in industries.

·                Increased use of vehicles

·                Deforestation, so less photosynthesis and less absorption of carbon dioxide

·                Increased population over recent years, cause more release of carbon dioxide by respiration

·                Original carbon dioxide removal over millions of years is replaced over a very short time

CHLOROFLUOROCARBONS (CFCs)

Source :Spraying aerosol

Effects of CFCs :

·                Ozone absorbs ultra violet light.

·                CFC’s thin ozone layer and form holes in it, causing more UV light to reach humans.

·                UV light damages skin by causing sunburns and skin tans.

·                UV light damages skin tissues and skin cells.

·                More DNA and chromosome mutations occur, resulting in skin cancer (melanoma).

·                CFCs damage the retina of the eye.

NITROGEN OXIDES

Source :Vehicle exhausts

Effects on humans :

·                Nitrogen oxides irritate the lining of the lungs and aggravate bronchitis and cause asthmatic attacks.

·                They dissolve in rain water to form acid rain that dissolves limestone buildings.

·                They acidify lakes and kills fish along with other aquatic invertebrates.

·                They damage forests by eroding the waxy cuticle of leaves of plants.

LEAD OXIDES

Source :Exhaust fumes of cars

Effects on humans :

·                They are toxic.

·                They cause brain damage and damage to the nervous system.

·                They inhibit enzymes in the body.

·                They accumulate in young children.

Note :Cars give out oxides of nitrogen, carbon monoxide, sulphur dioxide and lead oxides in their poisonous exhaust fumes. Less cars means less exhaust as less fuels are burnt.

Effect of air pollution on photosynthesis :

·                Soot / smoke particles / smog coats leaves and blocks stomata. This reduces light entry and gaseous exchange. Photosynthesis is reduced.

·                Sulphur dioxide causes acid rain. This causes damage to leaves and leads to leaf fall.

·                Carbon dioxide may increase photosynthesis.

BIOLOGICAL CONTROL

Advantages of biological control :

·                It is specific. It affects the target species only and does not affect the food chain.

·                It does not cause pollution and no harm is done to the environment.

·                It does not kill all pests, so the pests are less likely to become extinct.

·                No residue is left on crops.

·                It does not accumulate along the food chain – no bioaccumulation.

Note :Weeds must be killed using herbicides to reduce competition with crop plants for

·                Light

·                Minerals and nutrients

·                Carbon dioxide

·                Water

·                Rooting space

FISH FARMING

Advantages of farming fish over catching fish :

·                No need for boat, fuel or nets

·                Harvest is guaranteed

·                Type, age and size of fish can be selected

Why is it more profitable to farm fish in seawater than catch wildfish?

·                Lower fuel costs

·                Fewer staff

·                Optimum feeding

·                Less predation of young fish

·                Desired species – profitable fish

·                Farm to desired size

·                Easier to catch as fish is abundant and readily size

Why might farming fish in freshwater be unsuccessful ?

·                High infection rate as disease spreads rapidly.

·                External predation

·                Need for aeration of water due to lack of oxygen in water

·                Pollution risk, due to build up of nitrogenous waste

·                Temperature fluctuation

·                Eutrophication leads to lack of oxygen

Harmful effect of fish farming on the local environment :

·                Eutrophication :Release of waste, urea and faeces into the water can cause algal growth. Algae die and bacteria reproduce rapidly, using up oxygen dissolved in water due to respiration.The water lacks oxygen.

·                Escape of antibiotics, insecticides and hormones can affect other fish

·                Fish farming attracts predators. This can affect food chain.

·                Fish farming can lead to spread of disease, affecting the food chain.

Methods used to farm fish :

·                Production of / caring for eggs

·                Caged areas / nets to control predators

·                Oxygen level is kept high

·                Water is cleaned / filtered / replaced to remove waste / faeces / ammonia to prevent growth of bacteria, and thus, reduce eutrophication

·                Intensive farming methods pose greater risk of disease

·                Use of antibiotics / fungicides / pesticides

·                Selective breeding / genetic engineering

·                Manipulation of sexes / all female for faster growth / placid natured fish

·                High protein diet is fed regularly in small amounts

·                Separation of ages / sizes to make it easier to catch fish / drain ponds and lakes

Note :A Case Study from January 2001 Paper 4(c)

·                Leaves falling into a tank disappear after a few months as they are decomposed by saprophytic bacteria and fungi.

·                Fungal spores are dispersed by wind, birds, animals.

·                The water turns green due to algal growth, which are dispersed by wind, birds and animals. Algae are producers

·                Fish appear after sometime as their eggs are dispersed by wind, birds and animals. Fish are consumers.

·                Water lily appears as their seeds are dispersed by wind, birds and animals. Water lilies are producers.

·                Here, algae and water lily compete for light, minerals, carbon dioxide.

·                Algae and bacteria / fish compete for oxygen.

·                Fish compete for mates.

·                Bacteria and fish compete for oxygen.

·                Fish compete for food.

·                Fish compete for oxygen.

GLOBAL WARMING

·                Melting of ice caps

·                Rise in sea level causing floods

·                Increased sweating causing dehydration

·                Increased transpiration from plants cause wilting

·                Changing weather patterns, such as, more flooding

Effect of urbanization on ecosystem :

·                Loss of plant

·                Loss of habitat

·                Damage to food chain