Download - Folio Biology form 4 - chapter 8 and 9
1.0 Biotic and Abiotic 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.
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.