BIOLOGY

DYNAMIC ECOSYSTEM

&

ENDANGERED ECOSYSTEM

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CHAPTER 8: DYNAMIC ECOSYSTEM

1.0 Abiotic and Biotic Components

An ecosystem is a system formed by the interaction of living organisms with one another

and with their environment.

Examples of ecosystems are forest, grassland, pond, field, river, lake and sea.

An ecosystem consists of two components:

a) Abiotic components (physical factors)

b) Biotic components (biological factors)

Abiotic components are the non-living components in the ecosystem such as air, water,

soil, temperature and light intensity.

Biotic components are the living components in the ecosystem such as plants and

animals.

1.1 The Abiotic Components

In any ecosystem, abiotic components such as pH, temperature, light intensity, humidity,

topography and microclimate determine the population size and distribution of the biotic

components.

The pH value of the soil and water affects the distribution of organisms.

a) Most organisms live in a neutral or nearly neutral environment (pH6-7.5)

b) Some plants, like the maize, grows well in an acidic condition while coconuts

grow well in an alkaline condition.

Temperature affects the biochemical reactions in the organisms.

a) Organisms can live within a certain range of temperature.

b) Poikilotherms are animals that cannot control their body temperature as their

body temperature varies with the environmental temperature.

c) Homoiotherms are animals that can maintain their body temperature.

d) Plants and animals have specific characteristics to help them adapt to areas of

extreme temperature.

Light intensity affects the rate of photosynthesis.

a) The distribution of green plants will be more extensive in areas with higher light

intensity.

b) All organisms that live in soil prefer a dark environment.

Topography refers to the shape of the Earth’s surface.

a) Topography of a place determines the temperature, light intensity and humidity in

an area.

b) Three tomography factors that affect the distribution of organisms are altitude,

slope(gradient) and aspects.

Microclimate refers to the climate in a small habitat such a the climate in the soil and

the climate below a tree trunk or a large rock.

a) Microclimate has specific temperature, humidity and light intensity within its

small habitat.

b) Each type of organisms finds a habitat that has a microclimate that is suitable

for it.

1.2 The Abiotic Components

The abiotic components are classified into three groups:

a) Producers

b) Consumers

c) Decomposers

The green plants are the producers because they can synthesise food through

photosynthesis.

Consumers are organisms that feed on plants or other organisms.

a) Primary consumers are herbivores that feed on plants directly.

b) Secondary consumers are carnivores that feed on primary consumers directly

while tertiary consumers are carnivores or omnivores that feed on secondary

consumers.

Decomposers are the bacteria and fungi that break down dead plants and dead animals

into simple substances.

1.3 Food Chain, Food Web and Trophic Levels

A food chain shows a sequence of organisms through which energy is transferred.

Each stage in a food chain is known as a trophic level.

Through the food chain, organisms obtain energy.

In an ecosystem, several food chains interact to form a network called a food web.

In a food chain, energy is transferred from one trophic level to another trophic level.

When energy is transferred from one trophic level to another trophic level as much as

90% of the chemical energy in the food consumed is used for its metabolic activities and

lost as heat, excretory products and undigested matter.

Only 10% of the energy in an organism is passed on to the organism at the next trophic

level.

2.0 Interactions between biotic components

Based on the feeding relationship, the interaction between biotic components is divided

into three main types which are symbiosis, saprophytism and prey-predator interaction.

2.1 Interaction between Biotic Components in Relation to Feeding

Symbiosis

Symbiosis is an interaction between two organisms of different species that live

together.

in symbiosis, one organism will live in or with another organism called the host.

The organism that interacts with the host will benefit from the interaction.

Symbiosis is further classified into three types:

a) Commensalisms

b) Paratism

c) Mutualism

i. Commensalism

Commensalisms is an interaction between two organisms where only one organism

benefits from the relationship. The other is neither benefit nor harmed.

The organism that benefits is called the commensal while the other organism is called

the host.

Examples of commensal are epiphytes and epizoites.

Epiphytes are green plants which grow on other plants to obtain more sunlight and for

support.

Examples of epiphytes are:

a) Pigeon orchid

b) Staghorn fern

c) Birds nest fern

Epizoites are animals that live in external surface of another animal.

The benefits that epizoites get from their hosts are transport, protection and leftover

foods from the mouth of the hosts.

Examples of epizoites are

a) remora fish which attaches itself to the shark

b) protozoa which attaches itself to Cyclops sp.(water flea)

c) barnacles which attach themselves to shells of crabs or snails.

ii. Parasitism

Parasitism is an interaction between two different organisms where one organism called

the parasite benefits and the other organism called the host is harmed.

Two types of parasites:

a) Ectoparasites which live on the external body surface of the host

b) Endoparasites which live in the body of their host.

Ectoparasites depend on their hosts for food, protection and transportation.

Examples of ectoparasites that live on the bodies of animals are the various types of flea

and lice that feed on the blood of the host.

Endoparasites that live in animals arre the various types of worms that live in the

alimentary canals of their host and absorb nutrients from the intestines of their hosts.

iii. Mutualism

Mutualism is the interaction between two organism in which both organisms benefit.

Examples of mutualism:

a) Algae and fungi in lichen(both plants)

b) Hermit crabs and sea anemone(both animals)

c) Rhizobium bacteria and legume plants(one animal and one plant)

In the interaction between sea anemones and hermit crabs, the sea anemones attach

themselves to the shells of hermit crabs.

a) Sea anemone obtains transport and leftover food from the hermit crab

b) The hermit crab obtains protection from its predators because of the poisonous

tentacles of the sea anemone.

Saprophytism

Saprophytism is an interaction whereby an organism lives and feeds on decaying

organic matter.

Saprophytes refer to plants which obtain food from decayed organis matter.

Examples of saprophtes are the various types of fungi such as mushrooms, bread mould

and bracket fungus.

Saprozoites are microscopic animals that feed on decayed organic matter.

Some examples are paramecium sp. And amoeba sp. Which feed on organic matter

from dead organisms.

Prey-predator interaction

This is an interaction between two population of organisms in which one organism,

called the predator, hunts, captures and kills the other organisms, called the prey, for

food.

This interaction is a natural method to regulate the population size of the prey.

The size of the prey is usually smaller than the predator but the number of prey is always

more than the predator.

However, the population sizes of both predator and prey fluctuate together

a) When the population of a predator is high, the population of its prey decreases

because the prey are eaten by the predator.

b) When the population of the prey falls, there is insufficient food, which results in

a decline in the population of the predator.

c) When the population of the predator is low, the prey recovers and its population

increases. This will result in an increase in the population of the predator.

The population sizes of both predator and prey are maintained in dynamic equilibrium

even as they fluctuate together. However, the fluctuations in the predator population

usually lag slightly behind those of the prey.

The prey-predator relationship helps to control the population of organisms in an

ecosystem and maintain balance in nature.

2.2 Interaction between Biotic Components in Relation to Competition

Competition is the interaction between two organisms or two populations to obtain

common basic needs of life that are limited.

The common basic need are space, water, minerals, sunlight, food and mates for

plants and animals.

In a competition, organisms which are strong will obtain their common basic needs to

survive and hence win in the competition. The organisms which are weak will migrate

to other areas or die.

There are two types of competition:

a) Intraspecific competion

b) Interspecific competition

i. Intraspecific competition

Occurs between members of the same species of plants and animals to obtain their

common basic needs.

ii. Interspecific competition

Competition between individuals from different species.

3.0 Colonisation and Succession Process

The process of colonisation is a process in which plants start to inhabit an

uninhabited place and form a colony in the place.

The first plant species to inhabit a new place is called a pioneer species.

They have special adaptations that enable them to survive on dry and nutrient-poor

soil.

Pioneer plants are hardy plants which usually have dense root systems to bind the

sand particles and hold water and humus.

The pioneer species change the new habitat gradually to make the habitat more

suitable for another species to live.

As a result, the new habitat which is not suitable for the pioneer species is then

gradually replaced by another new species and succession begins.

The process of succession is a process in which a certain dominant plant species in

a habitat is gradually replaced by another plant species(successor species.)

These plants then become the new dominant species that can grow faster and so

they out-compete the pioneers which grow at a slower rate.

Succession is a very slow and continuous process which occurs in stages until a

stable and matured community which is equilibrium with the environment is formed.

The stable and matured community is called the climax community. An example is

the tropical rain forest in Malaysia.

3.1 Colonisation and Succession in a Mangrove Swamp

Mangrove swamps are found in tropical and subtropical regions where freshwater meets

salt water.

The environmental conditions in the mangrove swamp which make it unsuitable for

habitation are:

a) Soft muddy soil

b) Waterlogged soil which lacks oxygen

c) Seawater with high salinity(high salt content)

d) Strong sunlight and extreme heat.

There are three types of mangrove trees which are involved in the process of

colonisation and succession in a mangrove swamp:

a) Avicenni sp. and Sonneratia sp. (pioneer species)

b) Rhizophora sp. (successor)

c) Bruguiera sp. (successor)

Mangrove trees have adaptive characteristics to overcome the problems it faces in the

environment.

a) A root system that spreads out widely to provide support for the mangrove

trees in the soft muddy soil.

b) Breathing roots that protrude out of the soil and which are called

pneumatophores. In waterlogged soil, which lacks oxygen the

pneumatophores enable gaseous exchange occur at the roots.

c) The leaves of mangrove trees have thick cuticle and sunken stomata to

reduce transpiration in a hot environment due to the strong sunlight. The leaves

are also thick and succulent to store water.

d) Many mangrove trees have viviparity seed that begin to germinate while still

attached to the parent tree. This ensures that the seeds will get sufficient

oxygen from the atmosphere during germination and will not be suffocated for

lack of air in a waterlogged environment. It also prevents the seed from

dehydration in the highly saline sea water.

The profile of a beach in a mangrove swamp can be divided into three zones according

to the dominant flora.

a) Avicenni sp. and Sonneratia sp. (pioneer species)

b) Rhizophora sp. (successor)

c) Bruguiera sp. (successor)

i. Avicennia sp. and Sonneratia sp. zone

The pioneer species in a mangrove swamp are the Avicennia sp. and Sonneratia sp.

The Avicennia sp. grows in the part of the mangrove swamp that faces the sea while

Sonneratia sp. grows at the mouth of the river which is sheltered.

The adaptations of the pioneer species to the soft muddy soil and waterlogged area are

as follows:

a) A root system that spreads out widely to give support to the trees in the soft

muddy soil.

b) The Avicennia sp. and Sonneratia sp. have asparagus-shaped

pneumatophores that grows vertically upwards from the main roots through the

mud into the air. The pneumatophores are very spongy and take in air for

respiration of the root system.

ii. Rhizophora sp. zone

This zone is higher and less waterlogged.

The adaptations of Rhizophora sp. for this zone are as follows:

a) The Rhizophora sp. has prop roots to support and anchor the tree in the soft

muddy soil.

b) The Rhizophora sp. has viviparity seed to ensure that the seedlings can grow

and are not carried away by the seawater.

iii. Bruguiera sp. zone

Trees of Bruguiera sp. grow well in hard clay soil that subjects to flooding during the high

tide.

Trees of Bruguiera sp. have buttress roots for support and knee-shaped

pneumatophores for gaseous exchange.

As more sedimentation of decayed substances occur, new mud banks are being built up

seawards while the old banks move further inland, away from the sea. The soil become

harder and dry land is formed.

Finally, after a few hundred years, the process of succession stops and a tropical rain

forest, which is the climax community, is formed.

4.0 Sampling Techniques

The distribution of organisms in a community is affected by the biotic factors and abiotic

factors.

A sampling technique is used to study the population size of an organism.

A sampling technique involves collecting, counting, and making observations on the

organism studied.

Sampling is done at random and systematically.

The sampling technique to estimate the population size of an organism in a habitat is the

capture-mark-release and recapture technique.

The sampling technique to determine the distribution of plants in a habitat is the quadrat

sampling technique.

4.1 The Quadrat Sampling Techniques

The quadrat sampling technique is primarily used in estimating the size of the plant

populations.

The technique uses quadrat of specific size.

A quadrat is a square frame made of wood, string or metal.

The size of a quadrat used depends on the organisms being studied.

Quadrat sampling is carried out at random in the habitat studied.

The distribution of plants in a habitat being investigated is based on the following

aspects:

a) Frequency = Frequency is the number of times a pasticular species is found

present when a quadrat is thrown a certain number of times.

b) Density = Density is the mean number of individuals of a species per unit area.

c) Percentage coverage = percentage coverage is an indication of how much

area of the quadrat is occupied by a species. The percentage is useful when it

is not possible to identify separate individuals.

4.2 The Capture, Mark, Release and Recapture Method

This method is used to estimate the population size of animals such as garden snails

and wood lice in a community.

In this technique, the first sample is the number of a certain animal that is caught,

marked and then released.

After a few days, a second sample is taken and recorded. The number of individuals

marked in the recaptured sample is counted and recorded.

Initially, a specific animal sample is captured and marked with a ring, a tag or with

waterproof coloured ink, paint or nail varnish.

The population size of the animals in the area can be estimated using the formula below:

5.0 Order of Classification

Taxonomy is a branch of Biology concerned with identifying, describing and naming

organisms.

It is also a systematic method of classifying plants and animals based on the similarities

in their characteristics.

It enables communication among scientists and allows information about a particular

organism to be found more readily.

In the classification system, organism are classified and grouped into kingdoms based

on their common characteristics.

All organisms on Earth can be classified into five kingdoms. The five kingdoms are

Prokaryotae, Protista, Fungi, Plantae and Animalia.

5.1 The Hierarchy in the classification of organisms

Organisms are classified from kingdom (the largest) to species (the smallest) in the

hierarchy system of classification.

Each kingdom is divided into phylum. Organisms in the same phylum have the same

specific characteristics. These characteristics differ from organisms in other phyla.

Each phyla is then divided into class. Organisms in the same class have the

characteristics but differ from organisms in other classes.

Subsequently, class is divided into order, order into family, family into genus, and

genus into species. Species is most specific classification based on the hierarchy.

6.0 Nitrogen Cycle

The nitrogen cycle is important in maintaining the balance of nitrogen content in the

water, soil and atmosphere.

Microorganisms such as bacteria, fungi and algae play important roles in nitrogen cycle.

The main processes in the nitrogen cycle are:

a) Nitrogen fixation

b) Decomposition

c) Nitrification

d) Denitrification

i. Nitrogen fixation

Nitrogen fixation is a process by which nitrogen in the air is converted to nitrogen

compounds required for growth.

The nitrogen in the air that is trapped in the soil is absorbed by nitrogen-fixing bacteria

which convert it to nitrogen compounds as nitrates.

The nitrogen fixation process is carried out by nitrogen-fixing bacteria and blue-

green algae.

During thunderstorms, the energy of the lightning causes the oxygen and nitrogen to

combine to form oxide of nitrogen. This gas involves in raindrops to form nitric acid

which combines with the minerals in the soil to form nitrates and nitrites.

ii. Decomposition

Bacteria and fungi that are saprophytes carry out decomposition.

These decomposers (putrefying bacteria and fungi) break down the protein in dead

plants and animals into ammonium compounds.

iii. Nitrification

Microorganisms that are involved in the nitrification process are nitrifying bacteria such

as Nitrosomonas sp. and Nitrobacter sp.

Nitrification is the process in which ammonium compounds are oxidized to nitrites and

then nitrates in two stages.

The nitrates formed are absorbed by plants for growth.

iv. Denitrification

Denitrification is the process which converts nitrates to gaseous nitrogen.

The microorganisms involved in denitrification is the denitrifying bacteria.

Through this bacterial process, nitrogen is returned to the atmosphere.

7.0 Microorganisms and its benefits in life

Microorganisms are microscopic organisms that cannot be seen with the naked eye.

Microorganisms are all around us and affect our life.

Microorganisms can be classified into five types based on their basic characteristics.

a) Protozoa

b) Fungi

c) Algae

d) Bacteria

e) Virus

7.1 Abiotic components affecting the activity of microorganisms

The activities of microorganisms such as respiration, growth and reproduction is affected

by the following abiotic components:

a) Temperature

b) pH level

c) Light

d) Nutrients

i. Temperature

The optimum temperature for the growth of most microorganisms is 35°C - 40°C.

At temperature above 60°C, most microorganisms die as the high temperature is not

suitable for growth and reproduction of microorganisms.

This is because at very high temperatures, enzymes (protein) in the microorganisms are

denatured.

ii. pH value

Every microorganism has it own optimum pH value.

A slightly alkaline medium is more suitable for the growth and reproduction of bacteria. A

slightly acidic medium is more suitable for the growth of fungi.

A pH value that is too low or too high can inhibit growth and destroy most

microorganisms.

iii. Light

Microorganisms that are autotrophs need light for photosynthesis.

The activities of other microorganisms is inhibited under a high light intensity because

the ultraviolet rays can destroy these microorganisms.

In the dark (low light intensity), growth and reproduction of microorganisms such as

fungi, bacteria and protozoa occur actively.

iv. Nutrients

Proper nutrients are required for the activities of microorganisms.

Autotrophs such as the algae obtain its inorganic nutrients from the surroundings.

Microorganisms that are heterotrophs obtain their nutrients in the form of starch, fat,

glucose and amino acis by means of saprophytism or parasitism.

7.2 The role of useful microorganisms in the ecosystem

Decomposition

a) Decomposition of dead organic remains is carried out by a group of saprophytic

bacteria and fungi, which are called the decomposers.

b) Decomposers breakdown the dead remains of plants and animals and waste

products of animals and release nutrients in the soil.

The nitrogen cycle

a) Nitrogen is an important element in the synthesis of plant and animal proteins.

b) Plants can only absorb nitrogen in the form of ammonium ions and nitrate ions.

c) Nitrogen fixing bacteria can convert atmospheric nitrogen to a form that can

be used by plants.

d) For example, Nostoc sp. can be found freely in the soil and Rhizobium sp. lives

in the nodules of leguminous plants.

e) They fix atmospheric nitrogen and convert it into ammonium compounds.

f) When animals eat the plants, the organic nitrogenis transferred into the body of

the animals.

g) When the animals and plants die, decomposition produces ammonia that can

be converted into nitrites(by Nitrosomonas sp.) and nitrates(by Nitrobacter sp.)

by nitrifying bacteria.

h) The denitrifying bacteria convert nitrates back into atmospheric nitrogen to

complete the nitrogen cycle.

Alimentary canal of termites

a) The flagellated protozoa called Trichonympha sp. lives freely in mutualism in

the alimentary canals of termites.

b) The protozoa secretes the enzyme cellulose to digest the cellulose into simpler

sugars which is then absorbed by the termite.

c) The protozoa enables the termite to digest cellulose which is found in the wood

it feeds on.

Digestive system in humans

a) The cellulose in humas is the undigested food which is channeled into the

caceum of the large intestine.

b) Useful symbiotic bacteria are found in the human colon.

c) They synthesise vitamin B12 and vitamin K. A deficiency in vitamin B12 can

lead to anaemia while vitamin K is essential for blood clotting.

7.3 The harmful microorganisms

Harmful microorganisms are microorganisms that can cause diseases, spoilage of

food and other materials through their activities.

Microorganisms that cause diseases are called pathogens.

Organisms which transmit pathogens are called vectors. Examples are mosquitoes,

houseflies, lice and rats.

Other diseases that are transmitted by vectors are as follows:

a) Elephantsiasis (caused by filarial worms) – Culex mosquitoes

b) Typhus fever (caused by virus) - lice

c) Plague – rats

7.4 Uses of microorganisms in Biotechnology

Biotechnology is the development of techniques for the application of biological process

to produce materials used in medicine and industry.

Microorganism plays an important role in biotechnology.

CHAPTER 9: ENDANGERED ECOSYSTEM

8.0 Green House Effect

The greenhouse effect is the phenomenon of an increase in the temperature of the

Earth’s atmosphere.

This due to the heat that is absorbed and trapped in the Earth’s atmosphere by certain

gases(greenhouse gases) such as carbon dioxide, methane, chlorofluorocarbon and

nitrogen dioxide.

These greenhouse gases, especially carbon dioxide, trap and absorb heat in the

atmosphere, causing a rise in the temperature of the atmosphere.

As a result, the Earth’s temperature increases causing global warming.

The following human activities can increase the concentration of carbon dioxide in the

atmosphere to cause a greenhouse effect:

a) Burning of fuels in factories

b) Forest fires

c) Deforestation

d) Open burning of rubbish

e) Coal-fueled power stations

f) Motor vehicles

g) Use of chlorofluorocarbon(CFC)

8.1 Thinning of the ozone layer

The ozone layer is located at the atmospheric layer called the stratosphere which is 20 –

50km away from the Earth’s surface.

The ozone layer absorbs the harmful ultraviolet rays and prevents them from reaching

the Earth’s surface.

Today, the ozone layer is becoming thinner because of the destruction of the ozone gas.

The atmosphere in this area has very low ozone concentrations, resulting in the

formation of an ozone hole.

The destruction of the ozone layer is mainly due to the increasing levels of

chlorofluorocarbon(CFC) in the atmosphere.

CFCs are a group of chemical compounds that contain chlorine, carbon and fluorine.

These gases are used as coolants in air conditioners and refrigerators, as propellants in

aerosol cans and as foaming agents in the making of styrofoam packaging.

Effects of the thinning of the ozone layer which allows excessive ultraviolet radiation to

reach the Earth.

a) On the environment

o Increases in the temperature of the environment

o Changes in the climate and weather patterns

o Changes in wind direction.

b) On plants

o The rate of photosynthesis decreases due to the destruction of the

stomata and chlorophyll in the leaves.

o Disturbs the ecological balance by destroying aquatic organisms such

as planktons.

c) On human health

o Causes skin cancer

o Damages eyesight and causes cataract

o Weakens the human immune system

8.2 Impact of the thinning of the ozone layer and the global warming

The average increase in the Earth’s temperature could change weather patterns and

agricultural output.

There is also convincing evidence from research that links the melting of the polar ice

caps into global warming.

This in turn leads to a corresponding rise in sea levels.

By absorbing most of the ultraviolet radiation, the ozone layer shields living organisms

on Earth from the damaging effects of ultraviolet radiation.

9.0 Eutrophication process

Eutrophication occurs as a result of an abundant supply of fertilizers or sewage in lakes,

pond or rivers.

Fertilizers and sewage contain high concentration of nitrates and phosphates which

encourage eutrophication. They promote rapid growth of algae and subsequently a rapid

increase in the population of algae.

The algae that grow extensively cover up the surface of the lake, pond or river.

This prevents sunlight from reaching the plants in the lower depths of the water.

As a result, the plants in the water die.

The number of aerobic bacteria that decompose the dead plants also increases using

more of the oxygen in the water.

This reduces the concentration of oxygen in the water and results in the death of

aquatic organisms.

The rapid growth of the algae and the process of decomposition by the bacteria use up

the oxygen supply in the water and thus increase the biochemical oxygen

demand(B.O.D).

10.0 Biochemical Oxygen Demand (B.O.D)

Biochemical oxygen demand is the amount of oxygen taken up by the microorganisms

(bacteria and algae) that decompose organic waste matter in water.

B.O.D is used as a measure of the amount of certain types of organic pollutants in water.

Hence, B.O.D can be used to measure the level of water pollution.

A high B.O.D indicates the presence of a large number of microorganisms which

suggest a high level of pollution.

The higher the B.O.D value, the more polluted is the water sample.

Polluted water contains a large amount of organic waste matter. This process of

decomposition requires oxygen. As a result, much oxygen supply in the water is used up

and the B.O.D value is high. The concentration of oxygen in the water is low.

Good quality water has a B.O.D value of less than 0.5mg of oxygen per litre.

Methylene blue solution is used to analyse the presence of oxygen in water.

11.0 Biological control

Biological control is a method in which a predator, which is a natural enemy to a certain

pest(prey), is used to control the population of that pest in an area.

Biological control is usually used in agriculture to control populations of pests without the

use of pesticides.

The prey-predator interaction is applied in biological control.

Biological control has many advantages as compared to using pesticides.

a) Does not pollute the environment

b) Does not kill other organisms

c) Is cheap and safe to use

The two types of interaction that happen in biological control are

a) Parasitism – the parasite destroys crops

b) Prey-predator – eventually removes the pest

For example,

a) Owls and snakes eat rats

b) Fire ants eat aphids on leaves

c) Rearing guppies in a pond to eat mosquitoe larvae

d) Rearing cats to eliminate rats.