env sc slides

8/7/2019 env sc slides

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Life, Work & Leadership

FOOD RESOURCES

1) CAUSES OF THE WORLD FOOD PROBLEMWorld Wide Problems

1. Natural catastrophes___drought, heavy rain and flooding, crop

failures.

2. Environmental degradation___soil erosion and inadequate water

resources.

3. Food supply-and-demand imbalances.

4. Inadequate food reserves.

5. Warfare and civil disturbances.

Problems of the Developing World

1. Excessive population growth.

2. Lack of economic incentives_farmers using inappropriate methods

and laboring on land they may lose or can never hope to own.

3. Parents lacking knowledge of basic nutrition for their children.

4. Insufficient government attention to the rural sector.

Problems of the Industrialized World1. Excessive use of natural resources.

2. Pollution.

3. Inefficient, animal-protein diets.

4. Inadequate research in science and technology.

5. Excessive government bureaucracy.

6. Loss of farmland to competing uses.

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2) IMPACTS OF OVERGRAZING

Overgrazing can be defined as grazing plants before they have

recovered from a previous grazing. When a plant is grazed

severely, it uses energy stored in its roots to support regrowth.As

this energy is used, the roots die back. The dying of roots depends

on the severity of grazing. This root dieback is not a bad thing. It

adds organic matter to the soil, which increases soil porosity, the

infiltration rate of water and the soil's moisture-holding capacity.

After enough leaves have re grown, the roots will re grow as well.

Some of very dangerous impacts of overgrazing are listed below -

1. Soils have less organic matter and become less fertile.

2. Porosity of soils decreases.

3. The infiltration rate and moisture-holding capacity drop.

4. Weeds don't make the land unhealthy. They appear because the land is

unhealthy. Overgrazing is often the cause of this adverse and undesirable

condition.

5. Animals graze selectively. Given a chance, they will overgraze. The

newest growth is the most palatable, nutritious forage in the pasture.

Even one cow in a big pasture will overgraze plants if she's kept there

long enough.

6. Overgrazing isn't a function of animal numbers. It's a function of time.

Overgrazing happens when animals are kept in a paddock (enclosure)

too long or brought back too soon.

7. As overgrazing destroys the vegetation completely the entire area

becomes prone to desertification and heavy soil erosion that may cause

river leading to severe floods that may claim large number of lives and

great property.

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In view of above mentioned serious impacts of overgrazing, some strong

measures for checking it must be taken up. These may be -

1. To stop overgrazing, producers must move livestock out of a pasture

before regrowth of plants begins again. During the periods of fast

growth, overgrazing will occur if livestock are kept in a paddock for

more than three or four days.

2. Herders need to make sure that they don't bring the animals back

before plants have recovered.

3. Overgrazing can be stopped with 8-10 paddocks. When growth of

plants is fast, recovery periods of four to six weeks may be adequate.

3) IMPACT OF MODERN AGRICULTURE

I) Fertilizer Related problems

a) Reduction of Basic fertility

Using Chemical fertilizers reduces the productivity of the

soil.

b) Nitrate population

Nitrogenous fertilizers such as calcium ammonium nitrate

(CAN) etc. are highly soluble in water. When applied in

the fields, they seep deep into the soil and ultimately

contaminate the ground water.

c) Micronutrient imbalanceThe fertilizers commonly used are N, P, K fertilizers

which contain Nitrogen, phosphorous and potassium as

macro-nutrients for the plants. Excessive use of these

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causes deficiency of micronutrients such as Zn in the soil,

which affects the productivity of the soil.

d) Eutrophication

The process by which a body of water acquires a high

concentration ofnutrients, especially phosphates and

nitrates. These typically promote excessive growth of

algae. As the algae die and decompose, high levels of

organic matter and the decomposing organisms deplete the

water of available oxygen, causing the death of other

organisms, such as fish. Eutrophication is a natural, slow-

aging process for a water body, but human activity greatly

speeds up the process.

II) Pesticide related problems:

About 60 years ago, when DDT and other chlorine pesticides became

popular in agriculture, they were considered a safe and effective way to

get rid of pests. But over the years, more and more problems associated

with the use of pesticides have shown up. Major problems include:

a) Harmful side effects on non-target organisms (people, animals, soil,

water, etc.)

b) resurgence of pest populations (because natural control is disrupted)

c) the development of resistance

d) the cost

a)Toxicity for non-target organisms

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The use of pesticides (both synthetic and organic) always involves

certain risks because of their poisonous character. Who is at risk?

1) The users of the pesticides.2) The consumers of the pesticides.

3) The Environment

Soil, air and water bodies can easily be contaminated with these

poisonous chemicals. The unavoidable destruction of beneficial

insects and spiders interferes with natural pest control.

b) Resurgence

Pesticides kill not only the pests but also the natural enemies of these

pests. That means that natural control mechanisms are disrupted and it

allows the pest populations to rapidly build up again to levels that can

cause serious crop damage.

The disruption of natural control can even create new pest problems.

Minor pests that are usually kept at low numbers by their natural enemies

will multiply rapidly in the absence of their enemies and cause outbreaks.

So the control directed against one pests may result in the outbreak of

another pest.

The rebirth/resurgence of pest populations after removing natural

enemies creates a dependence on pesticides, which obviously is not

sustainable. A key element of Integrated Pest Management is therefore to

avoid resurgence. Conservation ofnatural enemies is required so that

natural control will not be disrupted.

c) Development of resistance

One of the first discovered problems of pesticides was that pests can

become resistant to the chemicals. Unaware of how to deal with this

issue, farmers then decide to spray more frequently and to apply higher

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doses. This just causes more problems.

d)The economic problems

There are two sides to the economics of pesticide use.

Direct costsThis refers to buying the products, which requires investment by the

farmers.

While many will argue that pesticides are cheap, they form a major

part of the farm inputs.

Many farmers have become trapped in a dependence on pesticides.

By using pesticides they have disrupted natural control, which results

in more pests and which leads to more pesticide use.

Indirect costs

This refers to all kind of expenses related to pesticide use, most of

which are paid by the government spending tax payers' money.

A hidden cost is all the medical costs related to health problems and

accidental deaths as a result of pesticide use.

Other costs born by the government include: costs for staff involved

in registration, labeling, disposal of obsolete pesticides, cleaning ofcontaminated sites, etc.

The import of pesticides requires large amount of foreign currencies.

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III) Water Logging

Another problem associated with excessive irrigation on poorly drained

soils is water logging. This occurs (as is common for salinization) in

poorly drained soils where water can't penetrate deeply. For example,

there may be an impermeable clay layer below the soil. What happens is

that the irrigation water (and/or seepage from canals) eventually raises

the water table in the ground -- the upper level of the groundwater --

from beneath. Growers don't generally realize that water logging ishappening until it is too late -- tests for water in soil are apparently very

expensive. The raised water table results in the soils becoming

waterlogged. When soils are water logged, air spaces in the soil are filled

with water, and plant roots essentially suffocate -- lack oxygen. Water

logging also damages soil structure.

IV) Salinity Problems

Salt affected soils are caused by excess accumulation of salts, typically

at the soil surface. Salts can be transported to the soil surface bycapillary transport from a salt laden water table and then accumulate due

to evaporation. They can also be concentrated in soils due to human

activity, for example the use ofpotassium as fertilizer, which can form

sylvite, a naturally occurring salt. As soil salinity increases, salt effects

can result in degradation of soils and vegetation.

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Salinization is a process that results from:

high levels of salt in the soils.

landscape features that allow salts to become mobile. (movementof water table)

climatic trends that favor accumulation.

ENERGY RESOUCES

Energy resources are generally defined as anything that can beused as a source of energy. Some important energy resourcesare oil, natural gas and coal.

I) GROWING ENERGY NEEDS

Energy is one of the central issues of the 21st century. We have to

find a way of satisfying the growing needs of the human population .

The first problem we face is the explosion in demand, due both to

the huge increase in population and to the efforts of some of the

most densely populated regions of the world to develop their

economies. In just one generation, the world population has increased

by nearly 2 billion, a rise of 33 per cent.

Fortunately, there are abundant immediate energy resources: 250 years

of coal reserves, 40 years of oil, 70 of gas. The problems mainly lie inmaking energy choices that are careless of the future of the planet

and its inhabitants.

Fossil fuels will have to be used for a long time to come: their

consumption will continue to rise even if we manage to reduce their

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relative proportion in the worlds mix of fuels. At the same time, we

should be developing renewable energies, especially the first and most

powerful of them, water. The worlds hydroelectric power potential is

far from being fully exploited.

Nuclear power remains the main method of electric power generation in

Europe, where it represents 35 per cent of total output.

Although the necessary resources and technology already exist, we have

to ensure that everyone can benefit from them.

II RENEWABLE AND NON-RENEWABLE ENERGY SOURCES

A) RENEWABLE SOURCES

Renewable energy has been in use for thousands of years in one

way or another. An example of this is how our ancestors used the

wind for sailing, and we now use the wind to generate electricity.

Below is a list of renewable energy sources: Biomass, Hydro,

Geothermal, Solar, Tidal, Wave, Wind and Wood.

B) NON-RENEWABLE SOURCES

An energy resource that is not replaced or is replaced only very

slowly by natural processes. Primary examples of non-renewable

energy resources are the fossil fuels--oil, natural gas, and coal.

Fossil fuels are continually produced by the decay of plant and

animal matter, but the rate of their production is extremely slow,

very much slower than the rate at which we use them. Any non-

renewable energy resources that we use are not replaced in a

reasonable amount of time (our lifetime, our children's lifetime,...)

and are thus considered "used up", not available to us again.

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III RENEWABLE OR NON-CONVENTIONAL ENERGY

SOURCES

A)SOLAR ENERGY

Solar power is produced by collecting sunlight and converting it

into electricity. This is done by

a) SOLAR CELLS

A solar cell (also called photovoltaic cell) is a solid state device that

converts the energy ofsunlight directly into electricity

b) SOLAR COOKER

A solar oven orsolar cooker is a device which uses sunlight as its

energy source.

c) SOLAR WATER HEATER

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SWH systems are designed to deliver the optimum amount of hot

water for most of the year.

d) SOLAR FURNACE

A solar furnace is a structure that captures sunlight to produce

high temperatures, usually for industry. This is done with a curved

mirror(or an array of mirrors) that acts as a reflector, concentrating

light (Insolation) onto a focal point. The temperature at the focalpoint may reach 3,500 C (6,330 F), and this heat can be used to

generate electricity, melt steel etc.

e) SOLAR POWER PLANT

Solar energy is harnessed on a large scale by using reflectors

which can boil water to produce steam.

B)WIND ENERGY

C)HYDROPOWER

Hydropower, hydraulic power orwater power is powerthat

is derived from the force orenergy of moving water, which may

be harnessed for useful purposes.

D)TIDAL ENERGY

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Tidal power, also called tidal energy, is a form ofhydropowerthat

converts the energy oftides into electricity .

E)OCEAN THERMAL ENERGYF) GEOTHERMAL ENERGY

Geothermal energy (from the Greek roots geo, meaning earth,

and thermos, meaning heat) is thermal energy stored in the

Earth.

G)BIOMASS ENERGY

Biomass, a renewable energy source, is biological material from

living, or recently living organisms such as wood, waste,

(hydrogen) gas, and alcohol fuels

H) BIOGAS

Biogas plants can be fed with energy crops such as

biodegradable wastes including sewage and food waste. Duringthe process, an air-tight tank transforms biomass waste into

methane producing renewable energy that can be used for

heating, electricity, and many other operations that use any

variation of an internal combustion engine.

I) BIOFUELS

Biofuels are a wide range of fuels which are in some way

derived from biomass.

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IV NON-RENEWABLE OR CONVENTIONAL ENERGY

SOURCES

These resources often exist in a fixed amount, or are consumed muchfaster than nature can create them.

a) Coal: Coal is a combustible black or brownish-black

sedimentary rock. Coal is composed primarily ofcarbon along

with variable quantities of other elements, chiefly sulphur,

hydrogen, oxygen and nitrogen.

b) Petroleum: Petroleum orcrude oil is a naturally occurring,

flammable liquid found in beneath the Earth's surface. Petroleum

is recovered mostly through oil drilling. It is refined and

separated, most easily by boiling point, into a large number of

consumer products, from gasoline and kerosene to coal tar etc.

c) Nuclear Energy: Nuclear power is produced by controlled (i.e.,

non-explosive) nuclear reactions. Commercial and utility plants

currently use nuclear fission reactions to heat water to produce

steam, which is then used to generate electricity.

LAND RESOURCES

I ) LAND AS A RESOURCE

Land is a valuable resource upon which we depend for our

food, fibre and fuel, the basic amenities of life.

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II) LAND DEGREDATION

Land degradation is a concept in which the value of the environment is

affected by one or more combination of human-induced processes actingupon the land. It is viewed as any change or disturbance to the land

perceived to be undesirable. It is estimated that up to 40% of the world's

agricultural land is seriously degraded.

III) SOIL EROSION

Erosion is the process ofweathering and transport of solids ( soil, rock

and other particles) in the natural environment or their source and

deposits them elsewhere. It usually occurs due to transport by wind,water, or ice; by down-slope creep of soil and other material under the

force ofgravity; or by living organisms, such as burrowing animals, in

the case ofbioerosion

Types of soil erosion

a) Normal erosion or geologic erosion:

It is causedby the gradual removal of top soil by natural processes.

b) Accelerated erosion

This is mainly caused by manmade activities and the rate of

erosion is much faster than the rate of formation of soil. Activities

that cause this are overgrazing, deforestation and mining.

IV CONSERVATION OF SOIL

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Soil conservation is a set of management strategies for prevention of

soil being eroded from the earths surface or becoming chemically

altered by overuse, acidification, salinization or other chemical soil

contamination.

It is based upon the following basic principles:

i) Protection of soil from the impacts of rain drops.

ii) Slowing down the water movement when it flows along the slope.

iii) Avoiding the concentration of water and its moving down in

narrow path.

iv)To adopt means so that more water enter the soil.

v) To reduce the wind velocity near the ground by growing vegetable

cover.

vi) To grow the strips of vegetable cover to hold the moving soil

particles.

V DESERTIFICATION

Desertification is a process leading to desert formation. It is either due

to a natural phenomenon linked with climatic changes or due to abusive

land use.

CAUSES OF DESERTIFICATION:

a) Overgrazing

Overgrazing was not as large of a problem long ago because

animals would move in response to rainfall. People would move

with the animals so it prevented overgrazing in such areas. Now,

humans have a steady food supply so they do not have to move

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about. Therefore, people use fences to keep their animals in one

place which causes overgrazing.

b) Destruction of Plants in Dry Regions

Destruction of plants in dry regions is causing desertification.

People are cutting down trees to use them as a source of fuel. Once

all these trees are cut down there is nothing to protect the soil.

Therefore, it turns to dust and is blown away by the wind.

c) Incorrect Irrigation in Arid Regions Causes a Build Up of Salt

in the SoilIncorrect irrigation is commonly used in poorer areas. Farmers are

using canal irrigation and other poor techniques because of the lack

of water. This type of irrigation causes a build up of salt in the soil.

Effects Of DESERTIFICATION:

a) Soil becomes less usable

The soil can be blown away by wind or washed away by rain.

Nutrients in the soil can be removed by wind or water. Salt can

build up in the soil which makes it harder for plant growth.

b) Vegetation is Lacked or Damaged

Loosened soil may bury plants or leave their roots exposed. Also,

when overgrazing occurs, plant species may be lost.

c) Food Loss

The soil is not suited for growing food. If the population is

growing, this will cause economic problems and starvation.

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d) People near Affected Areas

Desertification can cause flooding, poor water quality, dust storms,

and pollution. All of these can affect people living near an affected

region.

VI CONSERVATION OF NATURAL RESOURCES (ROLE OF

AN INDIVIDUAL)

NEED FOR CONSERVATION

Different natural resources like forests, water, soil, mineral and energy

resources play a vital role in the development of a nation. We should

protect the present resources and situation so that good, clean and selfsufficient environment should be provided to the future generations.

CONSERVATION OF WATER

Water-saving technology for the home includes:

Low-flow shower heads sometimes called energy-efficient shower

heads as they also use less energy.

Using taps, which break water flow into fine droplets to maintain"wetting effectiveness" while using less water. An additional

benefit is that they reduce splashing while washing hands and

dishes.

Wastewater reuse or recycling systems, allowing:

o Recycling of wastewater through purification at a water

treatment plant.

Rainwater harvesting

CONSERVATION OF ENERGY

Advocates and critics of various forms and policies ofenergy

conservation debate some issues, such as:

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Some retailers argue that bright lighting stimulates purchasing.

However, health studies have demonstrated that headache, stress,

blood pressure, fatigue and worker error all generally increase with

the common over-illumination present in many workplace andretail settings. It has been shown that natural day lighting increases

productivity levels of workers, while reducing energy

consumption.

The use of telecommuting by major corporations is a significant

opportunity to conserve energy, as many Americans now work in

service jobs that enable them to work from home instead of

commuting to work each day.

Consumers are often poorly informed of the savings of energy

efficient products.

UNIT III ECOSYSTEM

I Concept :

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An ecosystem is a complete community of living organisms and the

nonliving materials of their surroundings. Thus, its components include

plants, animals, and microorganisms; soil, rocks, and minerals; as well

as surrounding water sources and the local atmosphere. The size ofecosystems varies tremendously. An ecosystem could be an entire rain

forest, covering a geographical area larger than many nations, or it could

be a puddle or a backyard garden. Even the body of an animal could be

considered an ecosystem, since it is home to numerous microorganisms.

II STRUCTURE OR COMPONENTS OF ECOSYSTEM

a) ABIOTIC COMPONENTS

These include air, water, soil, basic elements and compounds

of the environment.

i) LITHOSPHERE: The hard and rigid outer layer of

the Earth.

ii) HYDROSPHERE: A hydrosphere in physical

geography describes the combined mass of water

found on, under, and over the surface of a planet.iii) ATMOSPHERE: An atmosphere is a layer of

gases .

b) BIOTIC COMPONENTS

Biotic components are the living things that shape an

ecosystem. Biotic components usually include:

Producers, i.e. autotrophs: e.g. plants; they convert

the energy (from the sun,) into food. Consumers, i.e. heterotrophs: e.g. animals; they

depend upon producers for food. Decomposers: e.g. fungi and bacteria; they break

down chemicals from producers and consumers intosimpler form which can be reused.

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III FUNCTIONS OF ECOSYSTEM

In an ecosystem there are two processes proceeding simultaneously:

1 ) Energy flow and

2 ) Biogeochemical cycle

The energy flow is in a single direction and is non-cyclic where as

Biogeochemical flow is cyclic (Any mineral cycle)

Biogeochemical flow

Energy flow

Solar energy is converted by the producers (plants) into chemical

energy in the form of plant carbohydrates. Herbivores consume the plant

carbohydrates and so this chemical energy is transferred to them.

Carnivores consume herbivores. So the energy is circulated further to the

next trophic level. In these animals, this chemical energy is convertedmostly into mechanical energy (work done) and heat. The heat is lost to

the atmosphere at each trophic level. It is estimated that 90% of the

energy is used up at each trophic level and only 10% of it is transferred

to the next trophic level. Finally, at the last trophic level (decomposer)

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no energy is left for recycling. Hence, energy flows from sun through

producers to consumers in a single direction only.

It is found that there is maximum energy at the producer (plant) leveland as you go further and further the energy in food goes on decreasing.

Therefore, the herbivores get more energy rich food, than carnivores.

Biogeochemical cycles

Organic materials synthesized by the producers are eaten and assimilated

by the consumers. With the help of decomposers, all the organic

materials in the bodies of the consumers are eventually broken down

into inorganic materials. These are then rebuilt into organic compoundsby the synthetic activities of the consumers. Thus, matter circulates in

nature. Though it may constantly change it's form, there is no overall

loss or gain. The cyclic flow of nutrients between non-living

environment (soil, rocks, air, water) and living organisms is known as

biogeochemical cycle. The major nutrient element i.e. carbon, hydrogen,

oxygen and nitrogen, which form about 95% mass of the living

organism, are circulated again and again between living and non-living

components of the ecosystem.

IV PRODUCERS, CONSUMERS AND DECOMPOSERS

A) PRODUCERS

Definition

In an ecosystem, producers are those organisms that use

photosynthesis to capture energy by using sunlight, water and carbon

dioxide to create carbohydrates, and then use that energy to create more

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complex molecules like proteins, lipids and starches that are crucial to

life processes. Producers, which are mostly green plants, are also called

autotrophs.

Role

Producers funnel into the ecosystem the energy needed for itsbiological processes. The carbohydrates and other organic chemicals

formed by the producers are consumed and utilized by the heterotrophs,

or consumers; first by the herbivores who eat the plants--the primary

consumers--then by the predators who eat the herbivores--the secondary,

tertiary, and so on consumers. But at each step, much energy is lost. Lessthan 10 percent of the energy stored in plants is converted to herbivore

mass. The loss from herbivore to predator is similar. Thus energy needs

to be added to the ecosystem continuously. This is the producers' role.

B)CONSUMERS

A consumer is the organisms that obtain nutrients from other

organisms. This is also a heterotroph. Based on the type of food

they eat, consumers may be divided into four groups.

Herbivores, carnivores, omnivores and saprobes.

i) Herbivores are animals that feed only on plants..

ii) Carnivores are animals that feed on other animals.

iii) Omnivores are animals that feed on both plants and

animals. Examples of omnivores are humans and

bears.

iv) Saprobes are organisms that get nutrients bybreaking down the remains of dead plants and

animals. Examples of saprobes are bacteria and fungi

C)DECOMPOSERS

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When a plant or animal dies, it leaves behind nutrients and energy inthe organic material that comprised its body. Decomposers eventually

convert all organic matter into carbon dioxide (which they respire) and

nutrients. This releases raw nutrients (such as nitrogen, phosphorus, and

magnesium) in a form usable to plants and algae, which incorporate the

chemicals into their own cells. This process resupplies nutrients to the

ecosystem, in turn allowing for greater primary production.

V ENERGY FLOW IN THE ECOSYSTEM

Energy flow in the ecosystem is unidirectional. Energy obtained is used

for various body activities and to overcome entropy. Dissipation of

energy occurs as heat. Energy after it is being accumulated by theprimary producer is transferred through a food chain to differenttrophic levels. This phenomenon is called energy flow. Accordingto Lindemann (1942), about 10% of total energy is transmitted,during flow of energy through several trophic (relating to the

nutritive value of food) levels. This is known as 10 % law.

A) Pathway of energy flow :

1) Through Grazing food chain : It is started from a green plantbase, goes to grazing herbivores and onto carnivores like :

GRASS -------> HERBIVORES-----> CARNIVORES

2) Through detritus food chain : It starts from dead organicmatter (DOM) to microorganisms and then to others like :

DOM ------->Bacteria and fungi --------> Insect larvae -------->Fishes.

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B) Principles of energy flow:

Energy flow through food chain occurs as two laws of Thermodynamics,which are generally applied to closed systems.

The first law of thermodynamics is the law of conservation of energy,

which states that energy may be transformed from one form to another

but, is neither created nor destroyed.

Example- A common household example of this law shows conversion

of electric energy into light and heat energy.

The second law of thermodynamics states that there can be no

transformation of energy unless the energy change is from aconcentrated to a dispersed form. In other words energy cannot flow

from a cold body to a hot body by itself.

Example-In the process of photosynthesis, where conversion of light

energy into potential chemical energy is accompanied with the

dispersion of some energy as heat energy.

V FOOD CHAINA food chain shows how each living thing gets its food. Plants are

called producers because they are able to use light energy from the Sun

to produce food (sugar) from carbon dioxide and water.

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1. Animals cannot make their own food so they must eat plants

and/or other animals. They are called consumers. There are three

groups of consumers.

a. Animals that eat ONLY PLANTS are called herbivores (or

primary consumers).

b. Animals that eat OTHER ANIMALS are called carnivores.

carnivores that eat herbivores are called secondary

consumers

carnivores that eat other carnivores are called tertiary

consumers

e.g., killer whales in an ocean food web ...

phytoplankton small fishes seals killer whales

2. Animals and people who eat BOTH animals and plants are called

omnivores.

3. Then there are decomposers (bacteria and fungi) which feed on

decaying matter. These decomposers speed up the decayingprocess that releases mineral salts back into the food chain for

absorption by plants as nutrients.

Characteristics of food chain

In a food chain,

a) there is repeated eating in which each group eats the smaller one and

is eaten by the larger one. Thus, it involves a nutritive interaction

between the biotic components of an ecosystem.

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b) the plants and animals which depend successively on one another

form the limbs of a food chain.

c) there is unidirectional flow of energy from sun to producers and then

to a series of consumers of various types. Thus, a food chain is alwaysstraight and proceeds in a progressing straight line.

d) usually 80 to 90% of potential energy is lost as heat at each transfer

on the basis of second law of thermodynamics (transformation of energy

involves loss of unavailable energy).

e) usually there are 4 or 5 trophic levels. Shorter food chains provide

greater available energy and vice - versa.

Types of food chain

i) GRAZING FOOD CHAIN

A food chain in which the primary consumerfeeds on living plants is called a grazingpathway.a) Terrestrial food chains

Some animals eats plants, and then are

eaten by other animals, which are in turneaten by other animals.Grass-> grasshopper->birds->hawks

b) Aquatic food chains

The food chain which occurs in aquatic water is called aquatic food

chain.

e.g. Algae Protozoa Small Insects Large aquatic

Insects Small fish Large fish

.

The main function of Aquatic food chain is that:

It depicts the structure of the living components of

hydrosphere.

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It transfers energy and materials.

ii)DETRITUS FOOD CHAINA food chain in which the primary consumer feeds on

dead plant matter is known as a detritus pathway. Example

Mangrove leavesdetritus (non-living organicmaterial)micro-organisms-crabs and shrimpssmall fisheslarge fishes

VI FOOD WEB

A food web is a graphical description of feeding relationships among

species in an ecological community, that is, of who eats whom (Fig. 1).

It is also a means of showing how energy and materials (e.g., carbon)

flow through a community of species as a result of these feeding

relationships. Typically, species are connected by lines or arrows called

"links", and the species are sometimes referred to as "nodes" in food

web diagrams.

A food web differs from a food chain in that the latter shows only a

portion of the food web involving a simple, linear series of species (e.g.,

predator, herbivore, plant) connected by feeding links.

A food web aims to depict a more complete picture of the feeding

relationships, and can be considered a bundle of many interconnected

food chains occurring within the community.

All species occupying the same position within a food chain comprisea trophic level within the food web. For instance, all of the plants in

the food web comprise the first or "primary producer" tropic level, all

herbivores comprise the second or"primary consumer" trophic level,

and carnivores that eat herbivores comprise the third or "secondary

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consumer" trophic level. Additional levels, in which carnivores eat

other carnivores, comprise a tertiary trophic level.

Fig: Food Web of a Forest

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