57082855 folio biology form 4 chapter 8 and 9

7/27/2019 57082855 Folio Biology Form 4 Chapter 8 and 9

http://slidepdf.com/reader/full/57082855-folio-biology-form-4-chapter-8-and-9 1/28

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 veryspongy 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 phylumhave 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 innitrogen 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 thenaked 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 andreproduction 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.

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.

v. 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 nitrifyingbacteria.

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. Theconcentration 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

Parasitism – the parasite destroys crops

Prey-predator – eventually removes the pest

For example,

Owls and snakes eat rats

Fire ants eat aphids on leaves

Rearing guppies in a pond to eat mosquitoe larvae

Rearing cats to eliminate rats.

57082855 folio biology form 4 chapter 8 and 9

Documents