Focus Science 2022 SPM F5

1Chapter Form 5

Microorganisms

Form

CHAPTER FOCUS 5

World of Microorganisms Microorganisms exist all around us
without us noticing.
Useful Microorganisms Can you identify the microorganisms
above?
Prevention and Treatment What tools can we use to ‘see’
of Diseases Caused by microorganisms?
Microorganisms Are all bacteria bad for humans?

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  Science SPM  Chapter 1  Microorganisms

1.1 World of Microorganisms 3. Microorganisms can be classified into five
groups based on their characteristics such as
1. Microorganisms are minute organisms that size, shape, habitat, nutrition and reproduction
cannot be seen with the naked eye but can be method:
observed with the use of microscopes. • Bacteria
• Fungi
2. Microorganisms are everywhere. • Protozoa
• Virus
• Algae

Bacteria

Slimy capsule Cell wall (made up of
presents in peptidoglycan which is a
some mixture of proteins,
bacteria sugars and lipids).

protects Cell membrane
from
dehydration Glycogen granules (stored food)
has food granules
DNA
Cytoplasm
no organelles

Flagellum presents in some bacteria
involves in movement

Figure 1.1  General structure of bacteria

Bacteria

• Unicellular microorganisms
• Does not have membranous organelles and nuclei

Size Respiration
0.2 µm to 10 µm (1 µm = 0.001 mm) • Anaerobic and aerobic respiration

Shape Nutrition
• Autotrophic: some bacteria have chlorophyll and are able
Coccus Diplococcus
to make their own food by photosynthesis. Some bacteria
Form synthesise food through chemosynthesis using chemical
Streptococcus energy from oxidising chemicals such as nitrite.
• Saprophytic: Feed on dead and decaying organisms.
5 Coccus (Spherical) • Parasitic: Obtain food from living organisms

Bacillus Spirilla Habitat
(Rod-shaped) (Spiral-shaped) • Air
• Water
Vibrio • Soil
(Comma-shaped) • Food
• On or inside other organisms. For example, some bacteria
Figure 1.2  Different shapes of bacteria
can live inside the human body without causing any disease
to the human. This is known as a normal flora. Normal
flora aids in digestion, vitamin production, stimulating cell
maturation and in fortifying the body immune system.

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Science SPM  Chapter 1  Microorganisms

Reproduction
Asexual
• Binary fission: A parent cell divides into two identical daughter cells during favourable conditions such as dark, moist, suitable

temperature and presence of nutrients.

Figure 1.3  Binary fission
• Spores formation: During unfavourable conditions such as extreme temperatures and absence of nutrients.

Sexual
• Conjugation: DNA is transferred from one bacterium to another bacterium through a conjugation tube.

DNA

Conjugation tube DNA transferred

Figure 1.4 Conjugation

Fungi Cell wall (made of chitin) Sporangium (produces
Cell membrane spores)
Vacuole

Glycogen granules (store food)

Nucleus (contains DNA) Hypha
Cytoplasm
Mycellium (made up
Figure 1.5  Structure of fungal cell
Yeast of network of brancing
Mucor hyphae)

Figure 1.6  Examples of fungi 

Fungi

• Does not contain chlorophyll
• Some fungi are unicellular, like yeast
• Some fungi are multicellular, like mucor

Size Habitat Form
• 10 µm to 100 µm • Dark and moist places, rotting material and on the bodies of other organisms
Shape 5
• Spherical Nutrition
• Filamentous network • Saprophytic: Secretes enzymes to break down and absorb organic materials from dead and

Reproduction decaying organic matter before absorbing the nutrients.
Asexual • Parasitic: Obtains nutrients from living organisms which live on human skin (athlete’s foot)
Budding, in yeast.
Formation of spore, in mucor. Sexual
Bud • Conjugation: Occurs when there is a lack of
Sporangium Spore
food and water.

Two hyphae
fused

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  Science SPM  Chapter 1  Microorganisms

SPM Highlights SPM Highlights

The following information shows the characteristics The figure below shows microorganism, X.
of microorganism P.
Sporangium
• Size: 10 µm or less Spore
• Spherical-shaped
• Cannot conduct photosynthesis Apakah X?
A Spirogyra
What is P? Hypha B Amoeba
C Yeast
A Bacteria C Virus D Mucor
B Fungus D Algae

Examiner’s Tip Examiner’s Tip
Fungi does not contain chlorophyll and cannot Mucor can be identified by their sporangium and
undergo photosynthesis. hypha.

Answer: B Answer: D

Protozoa 

Cytoplasm Nucleus Cilia Cytoplasm
Cell membrane Cell membrane
Pseudopodium Vacuole Food Nucleus
Nucleus vacuole Trypanosome

Oral groove

Contractile
vacuole

Amoeba    Paramecium   

Figure 1.7  Examples of protozoa

Protozoa

• Unicellular organism
• Contains nucleus, cytoplasm and plasma membrane
• Does not have cell wall

Form Size
5 µm to 250 µm
Habitat
Shape • Aquatic habitats (ponds, lakes, rivers, oceans)
• Spherical • Moist environments (moist soil)
• Living organisms (as a parasite)
5 • Coil
• Irregular Nutrition
• Saprophytic: Obtains food from dead and decaying matter, for
Reproduction
Asexual example Amoeba.
• Binary fission, for example, Amoeba. • Parasitic: Obtains food from living organisms such as

Plasmodium which feeds on cells in human body

Sexual
• Conjugation, for example Paramecium.

Figure 1.8  Binary fission in Amoeba Exchange of
genetic
196 materials

Figure 1.9  Conjugation in Paramecium

Science SPM  Chapter 1  Microorganisms

Viruses 

DNA Protein
coat

DNA

Protein
coat

Bacteriophage Influenza virus Tobacco mosaic virus Corona virus

Figure 1.10  Examples of viruses

Viruses Corona Virus
VIDEO
• The smallest microorganism
• Have no cell organisation
• Do not show characteristics of living cells
• Do not contain cytoplasm, plasma membrane or nucleus
• Can crystallise
• Do not eat, produce waste or grow
• Reproduce inside living cells
• Contain nucleic acids (DNA or RNA) and covered in protein sheath

Size Reproduction
• 0.2 µm to 0.4 µm • Reproduces when inside living cells by using the cell’s components

Shape to produce copies of itself.
• Spherical, for example influenza virus
• Helical, for example mosaic virus Bacterium Viral
• Polyhedral, for example adenovirus DNA
• Complex (combination of helical and polyhedral for Virus

example bacteriophage). Bacterial
DNA

1 A virus attaches itself 2 The virus injects
to a host cell. its DNA into the
cell’s cytoplasm.
Nutrition
• Do not need food

Habitat 3 The viral DNA replicates using Form
• Live in host cells material in the host cell.
• Form crystals outside a living cell The viral DNA then makes its 5
own outer protein coat.
SPM Tips
5 The host cell bursts to 4 New viruses formed
Many virologists view a virus as a non-living release hundreds of new
small particle because it does not have a cell viruses which will infect
membrane and does not undergo metabolic other cells.
processes like other microorganisms. Viruses
only undergo metabolic processes and Figure 1.11  Virus replication
are considered “alive” when inside the
host cell.

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  Science SPM  Chapter 1  Microorganisms

Algae 

Nucleus Chloroplast

Flagellum

Nucleus

Cell wall Chlamydomonas
Spirogyra

Figure 1.12  Examples of algae

Algae

• Unicellular, like Chlamydomonas sp.
• Multicellular, like Spirogyra
• Contains chloroplast, nucleus, cytoplasm, cellulose cell wall

Size Nutrition
• 1 µm to 100 µm Autotrophic: Most algae contain chlorophyll to conduct

photosynthesis.

Shape Reproduction
• Spherical Asexual
• Rod-shaped • Binary fission
• Filamentous • Fragmentation
• Spore formation
Habitat
• Ponds, lakes, rivers, oceans Sexual
• Moist environments such as moist soils and tree bark • Conjugation
• Some algae can also grow in the desert or in hotspring

Form Existence of Microorganisms

1. Microorganisms exist all around us.
2. Experiment 1.1 shows the existence of microorganisms on our hands.

Ekxsppeerirmimeennt 12.1

Aim: Using nutrient agar to compare bacterial growth from samples taken from different hands.
Problem statement: Does the hygiene state of hands influence bacterial growth?

5 Hypothesis: Unwashed hands yield the most bacteria.

Variable:
(a) manipulated: State of hygiene of hands (unwashed, washed with water only, washed with soap)
(b) responding: Growth of bacteria on nutrient agar
(c) constant: Type of nutrient, hands, temperature, incubation period
Materials: Sterile nutrient agar, soap, marker pen, cellophane tape
Apparatus: Three sterile Petri dishes with lids, incubator, magnifying glass

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Science SPM  Chapter 1  Microorganisms

Procedure:

Sterile nutrient agar

Petri B C
dish
A

Figure 1.13  Arrangement of apparatus

1. Three sterile Petri dishes containing nutrient agar are prepared and labelled A, B and C.
2. An unwashed hand is placed upon the surface of the nutrient agar in Petri dish A for one minute.
3. The hand is removed, and the Petri dish is closed tightly and taped together with its lid.
4. Steps 2 and 3 are repeated with a hand that has been washed with water in Petri dish B, and a hand that

has been washed with soap in Petri dish C.
5. All three Petri dishes are left in upside down in the incubator at 37oC for three days.
6. All three Petri dishes are removed after three days. Observations on the surface of the agar in each Petri

dish are recorded.
Observation:

A B C

Discussion:

1. Bacterial growth is highest in Petri dish A. This shows that the unwashed hand contains the most bacteria.

2. Bacterial growth is less in Petri dish B as a washed hand naturally contains less bacteria than an unwashed
hand.

3. Bacterial growth is lowest in Petri dish C. A hand that is washed with soap is the cleanest and hence has
the least number of bacteria colonies.

Conclusion: Form
The sample from the unwashed hand yields the most bacteria colonies. The hypothesis is accepted.

3. Our hands may appear to be clean but in fact, they house a lot of microorganisms. 5

4. Hence, we must wash our hands with water and soap to thoroughly VIDEO How to
clean them especially: Effectively Clean
• before and after handling food Your Hands
• after using the toilet
• after handling food waste
• after handling poisonous and dangerous materials

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  Science SPM  Chapter 1  Microorganisms

Factors that Influence the Growth of Microorganisms

Environmental pH Temperature Moisture

• Most microorganisms grow rapidly in • The optimum temperature • Microorganisms need water
neutral pH, pH 7 for microbial growth is mostly for biochemical reactions and
between 35oC to 40 oC growth
• Most bacteria thrive in a more
alkaline environment, pH 7.4 • Microorganisms become less • The condition is best when
active at low temperatures relative humidity is between
• Most protozoa and fungi grow well in (<5 oC) 25% to 40%
acidic environment, around pH 6.5
• Microorganisms will die at high • Most microorganisms will die
• Most microorganism will die temperatures (>60 oC) in dry conditions but some will
in extremely acidic or alkaline produce spores
environments • Spores can withstand
temperatures as high as
120 oC

Factors that influence microbial growth

Light Nutrients

• Microorganisms with chloroplasts such as algae can • Microorganisms apart from viruses, require nutrients
grow well in well-lit environments • Autotrophs synthesise their own food
• Parasites obtain food from the host cell
• Most other microorganisms prefer darker • Saprophytes obtain food from dead or decaying matters
environments

Ekxsppeerirmimeennt 12.21

Aim: To study the effect of nutrients on the growth of microorganisms.
Problem statement: What is the effect of nutrients on microbial growth?
Hypothesis: The availability of nutrient stimulates the growth and reproduction of yeast.
Variables:
(a) manipulated: Availability of nutrient
(b) responding: Yeast growth
(c) constant: Temperature, pH, moisture, light intensity

Form Operational definition:
Yeast undergoes respiration to produce carbon dioxide that turns limewater milky. Hence, yeast growth is
defined operationally as how cloudy limewater gets.

5 Material: Yeast suspension, glucose, distilled water, limewater
Apparatus: Boiling tube with delivery tube, test tube
Procedure:

Delivery tube Delivery tube

Boiling Test tube Test tube
tube

Yeast suspension + Yeast suspension +
glucose solution
Limewater distilled water Limewater

Set A Figure 1.14 Set-up of apparatus Set B

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Science SPM  Chapter 1  Microorganisms

1. Two sets of apparatus are prepared as shown in Figure 1.14.
2. The changes to the limewater are recorded.

Observation:
1. After a few minutes, the yeast suspension in set A will produce bubbles. The bubbles released causes the

limewater to be cloudy.
2. No changes can be observed in set B.

Discussion:
1. Glucose provides nutrients for yeast. Yeast breaks down glucose for energy and releases carbon dioxide.
2. No activity is detected in set B because distilled water does not contain any nutrient.

Conclusion:
Microorganisms grow and reproduce quickly when there is a nutrient source. The hypothesis is accepted.

SPM Highlights

The figure below shows an experiment to study the activity of a microorganism.

Boiling tube Delivery What is microorganism Z?
tube
Microorganism X Test tube A Bacteriophage
+ glucose solution B Chlamydomonas
Limewater C Paramecium
D Yeast

Examiner’s Tip
Yeast breaks down glucose to release carbon dioxide.

Answer: D

Ekxsppeerirmimeennt 12.31 Form

Aim: To study the effect of humidity on the growth of microorganisms. 5
Problem statement: How does humidity affect the growth of bread moulds?
Hypothesis: Bread mould grows and multiply faster when there is humidity. 201
Variables:
(a) manipulated: Humidity
(b) responding: The growth of bread moulds
(c) constant: Temperature, pH, light intensity, the amount and type of nutrients
Material: Two slices of fresh bread, transparent plastic bag, cellophane tape
Procedure:
1. Two slices of fresh bread are prepared.
2. A slice of bread is left to dry under sunlight for a few hours.

  Science SPM  Chapter 1  Microorganisms

3. One more slice of bread is placed in a transparent plastic bag. The edge of the bag is taped with cellophane
tape.

4. Both pieces of bread are kept in a drawer for a week.
5. After a week, observations are made about the two bread slices.

Caution: Wash your hands with soap after conducting this experiment.

Sealed plastic bag

Moulds

Bread Dried bread Bread Bread in
plastic bag

Figure 1.15

Discussion:

1. The bread inside the sealed plastic bag still remains moist. Moulds grow on this slice due to the humidity
present.

2. There is no mould growth on the dried bread slice because there is no moisture.

Conclusion:
Microorganisms can grow well in the presence of moisture. The hypothesis is accepted.

Form Ekxsppeerirmimeennt 12.41

Aim: To study effect of light on the growth of bread moulds.
Problem statement: How does light affect the growth of bread moulds?
Hypothesis: Bread moulds grow and multiply faster in darkness.
Variables:
(a) manipulated: Presence of light
(b) responding: The growth of bread moulds

5 (c) constant: Temperature, pH, moisture, the amount and type of nutrients
Operational Definition:
Bread mould grows and multiply faster forming mould colonies on bread. Growth of bread mould is defined
operationally as the area on the bread that is covered with moulds.
Material: Two fresh slices of bread
Apparatus: Table lamp, Petri dish
Procedure:
1. Two Petri dishes are labelled as A and B.
2. Two slices of fresh bread are placed in Petri dishes A and B.

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Science SPM  Chapter 1  Microorganisms

3. Set A is placed under a well-lit lamp.
4. Set B is placed inside a dark cupboard.
5. After a week, the two slices of bread are observed for changes. The observation is recorded.
Observation:

No bread mould Bread mould

Under bright light In the cupboard

Discussion: Figure 1.16

1. Bread mould grows quickly in the dark.

2. The presence of light inhibits the growth of bread moulds.

Conclusion:
Microorganisms grow well in the dark. The hypothesis is accepted.

Ekxsppeerirmimeennt 12.51 Form

Aim: To study effect of temperature on growth of microorganisms. 5
Problem statement: How does temperature affect the growth of bacteria?
Hypothesis: The growth of Bacillus subtilis is the highest at room temperature.
Variables:
(a) manipulated: Temperature
(b) responding: The growth of bacteria (Bacillus subtilis)
(c) constant: Light intensity, humidity, pH, the amount and type of nutrients
Operational Definition:
White spots will form on the nutrient agar indicating the growth of bacteria. Hence, the growth of bacteria is
defined operationally as the number of white spots on the nutrient agar.
Material: Nutrient agar, bacterial culture (Bacillus subtilis), cellophane tape
Apparatus: Petri dish, oven
Procedure:

Safety Precautions!
Please wear gloves when handling this experiment. Wash your hands with soap before and after the
experiment.

Sterile nutrient agar B C
Figure 1.17
Petri
dish
A

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  Science SPM  Chapter 1  Microorganisms

1. Three Petri dishes containing nutrient agar are labelled A, B and C.
2. 1 cm3 bacteria culture is poured onto the agar in the three Petri dishes.
3. The three Petri dishes are closed with their lids and sealed with cellophane tape.
4. The three Petri dishes are overturned.
5. Set A is stored in the refrigerator.
6. Set B is stored in the room temperature.
7. Set C is stored in the oven at 65oC.
8. The three Petri dishes are taken out after two days. The appearance of nutrient agar in each Petri dish is

observed and recorded.

Observation:

White spot

No spot No spot

Set A Set B Set C

Discussion: Figure 1.18

1. There are no white spots in set A. There is no bacterial growth on this set due to the low surrounding
temperature. Bacillus subtilis is not active at low temperatures.

2. There are white spots in set B, indicating the presence of bacterial growth. This is because Bacillus subtilis
grows well in room temperature.

3. There are no white spots in set C because Bacillus subtilis does not grow in high temperatures.

Conclusion:
Bacillus subtilis grows well at a room temperature. The hypothesis is accepted.

SPM Highlights

Form The table below shows the differences in the number of bacteria colonies in Petri dishes placed in different environment
temperatures.

Petri dish Temperature (oC) Number of bacteria colonies

P 10 3

5 Q 20 7
R 37 15

S 45 3

What is the optimum temperature for the growth of this bacteria?
C 37°C
A 10°C

B 20°C D 45°C

Examiner’s Tip
Petri dish R has the highest number of bacteria colonies, thus the optimum temperature for growth of the bacteria
is 37oC.

Answer: C

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Science SPM  Chapter 1  Microorganisms

Ekxsppeerirmimeennt 12.61

Aim: To study the effect of pH on the growth of microorganisms.
Problem statement: How does pH affect the growth of bacteria?
Hypothesis: Bacteria grow well in a neutral medium.
Variables:
(a) manipulated: pH
(b) responding: The growth of bacteria
(c) constant: Light intensity, humidity, temperature, the amount and type of nutrients
Operational Definition:
White spots will form on the nutrient agar indicating the growth of bacteria. Hence, the growth of bacteria is
defined operationally as the number of white spots on the nutrient agar.
Material: Nutrient agar, hydrochloric acid, sodium hydroxide, distilled water, bacteria culture (Bacillus subtilis)
Apparatus: Petri dishes, cellophane tape
Procedure:
1. Three Petri dishes containing nutrient agar are labelled A, B and C.
2. Five drops of hydrochloric acid are added into the nutrient agar in Set A.
3. Five drops of sodium hydroxide are added into the nutrient agar in Set B.
4. Five drops of distilled water are added into the nutrient agar in Set C.
5. A small amount of Bacillus subtilis culture is added to each of the Petri dishes.
6. All the Petri dishes are closed with their lids and sealed with cellophane tape.
7. All the Petri dishes are overturned and kept in a cupboard in the laboratory.
8. After two days, the Petri dishes are taken out. The appearance of each nutrient agar is observed and

recorded.
Observation:

White spot

No white spot No white spot

Set A Set B Set C Form

Figure 1.19 5

Discussion:
1. The white spots are bacteria colonies.
2. Set A and Set B do not have any white spots. Bacillus subtilis does not grow well in acidic or alkaline

environments.
3. There are many white spots (bacteria colonies) on the nutrient agar in Set C. Bacillus subtilis grows well in

neutral pH.

Conclusion:
Bacillus subtilis grows well in a neutral medium. The hypothesis is accepted.

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  Science SPM  Chapter 1  Microorganisms

Checkpoint 1.1

Q1 List five groups of microorganisms.

Q2 State two characteristics for:

(a) Virus (b) Algae

Q3 How is a bacterium named and classified?

Q4 List five factors that may affect the growth of bacteria.

Q5 Explain how the following factors influence the growth of microorganism:

(a) Nutrients (b) Light

Q6 How is vinegar used to preserve food? HOTS
Analysing

Q7 Give two reasons why clothes should be left to dry under sunlight. HOTS
Analysing

1.2 Useful Microorganisms

Application of Useful Microorganisms in Daily Life
1. Useful microorganisms play important roles in the medical, agriculture and industrial sectors.

Medical Agriculture

• Antibiotics are used to kill or inhibit the growth of • Bacteria and saprophytic fungi break down dead organic
microorganisms that cause diseases. compounds to simple compounds that can be returned to
the soil and used as nutrients by crops.
• Penicillin is an antibiotic produced from a fungus and can be
used to treat bacterial infections such as gonorrhea. • Crop residue can be recycled into compost.

• Streptomycin is an antibiotic obtained from a bacterium and • Nitrogen-fixing bacteria that exist freely in the soil or in
can be used to treat tuberculosis. root nodules for leguminous plants convert nitrogen in the
atmosphere into nitrates.
• Vaccines are produced by weakened or dead
microorganisms. Vaccines are injected into a person’s body
to stimulate the production of antibodies.

• Vaccination is important to help prevent diseases such as
tuberculosis, measles and mumps.

• Insulin made from genetically modified bacteria can be used
to treat diabetes.

Form

5 Figure 1.21 Root nodules of leguminous plant

Figure 1.20 Vaccination • Microorganisms can also be used in biological control.

• Enzymes produced by bacteria or fungi can be used for • Biological control is a method to control the population of
medical diagnosis such as sugar level and treatment of pests by using its natural predators. A type of bacteria can
diseases. be used to control beetles and caterpillars that attack crops,
while viruses can be used to kill rabbits.
• Some bacteria, fungi and even yeast can be used to produce
vitamins.

206

• Microorganisms are also important in food digestion. Science SPM  Chapter 1  Microorganisms
• The main food for herbivores such as cows and goats are cellulose-
Bacteria found in
rich plants. stomach of a cow
• Alimentary canals in herbivores contain bacteria and protozoa that

produce cellulase to digest cellulose into glucose.
• Protozoa in the alimentary canals of termites can also produce

cellulase to digest cellulose in wood into glucose (Figure 1.23).

Flagellum

Nucleus

Figure 1.22

Ingested food
Trichonympha (protozoa in termite)

Figure 1.23

• In human large intestines, E. coli bacteria produces vitamins K and B which are essential for health, and will be absorbed
by our body.

Industries
Food industry
• Alcoholic beverages
– Using yeast. Sugar fermentation in grapes to produce wine. Fermentation of wine or barley to produce beer.
• Bread
– Sugar fermentation by yeast to produce carbon dioxide which raises the dough used in bread production.
• Yogurt, cheese, cream, butter
– Milk fermentation by bacteria produces yogurt, cheese, cream and butter.
• Soy sauce
– Yeast and Lactobacillus (type of bacteria) are used to ferment a mixture of soya beans, wheat and water. Certain fungi

are used to act on the fermented soya beans to produce the desired flavor.
• Vinegar
– Bacteria oxidises ethanol into acetic acid and produce vinegar.
• Tea leaves
– Bacteria are used to act on tea leaves to produce the desired flavour.

Form

Figure 1.24  Food that are produced with the help of microorganisms 5
Rope, thread and textile industry
• Rope, thread and textile
– Bacteria is used to break down soft tissue in woody stems. The strong fibre that remains is used to produce rope, thread

and textile.

Leather industry
– Microbial enzyme is used to break down soft tissue on the skin of animals. The skin is then used to produce leather products.

Mining industry
• Petroleum and metal
– Bacteria are used to clean the impurities by decomposing organic matter in the purification of petroleum and metals.

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  Science SPM  Chapter 1  Microorganisms

Potential Use of Microorganisms in Biotechnology and Sustainability of the Environment

1. Biotechnology is the technology which uses Treating sewage
living organisms or biological processes to
produce beneficial products. Community Final
effluent
2. The genetic structure of bacteria is changed Preliminary
through genetic engineering to produce screening Primary Chlorine
bacteria that give benefits to us. settling tanks

Enzyme production tank

• Fruit peel and vegetable scraps are Sludge Activated
fermented together with sugar to produce drying sludge
eco enzymes which can break down fat
and proteins in stains. bed Settling
tank
• Eco enzymes also have cleaning properties Sludge
due to the alcohol or acetic acid produced digestion
in the solution. Alcohol (ethanol) or acetic
acid is produced by the metabolic processes tank
of bacteria that exist naturally on the fruit
peel or vegetable scraps. Sludge

• Eco enzyme liquids can be used as a eco- Activated Trickling filter
friendly cleaning agent comparable to the sludge tank tank
cleaning power of commercial detergents.
Figure 1.30 Sewage treatment plant
Oil spill clean-up
• Microorganisms are used in the sewage
• Genetically modified bacteria are used to treatment system to break down dangerous
clean up oil spills. organic material to safer byproducts.
Bacteria will reduce sewage water into
• Bacteria and a nutrient solution are sprayed water, carbon dioxide, mineral salts and
onto the oil spill. methane gas.

• The bacteria will break down the complex • The methane gas produced can be used as
oil components into simpler and safer fuel whereas dried sewage sludge can be
components. used as fertiliser.

Checkpoint 1.2

Production of bioplastic Q1 State two roles of microorganisms play in the

Form • Bioplastics are produced from renewable human digestive system.

biomass sources. Q2 State the beneficial roles of microorganisms

5 • Some bioplastics can be made from found in the alimentary canals of:
polyester produced by bacteria through
(a) Herbivores
(b) Termites

fermentation of sugars. Q3 Name microorganisms that are used in the
• Bioplastics produced by bacteria are production of:

biodegradable and thus, friendly to the (a) Bread

(b) Vitamin B

environment. (c) Vinegar

• The bioplastics produced can be used Q4 Explain two uses of microorganisms in the

to make device casings and packaging medical field.

material for goods.

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Science SPM  Chapter 1  Microorganisms

1.3 Prevention and Treatment of Diseases Caused by Microorganisms

“Prevention is Better than Cure” Sterilisation using Heat Form
Approach to Treat Diseases Caused by
Microorganisms 1. Heating food can kill microorganisms.

1. Microorganisms that are dangerous to humans 2. Boiling water can kill almost all
and can cause diseases are called pathogens. microorganisms, except for those with thick-
walled spores.
2. Diseases can spread when pathogens are
transmitted from a sick person to a healthy 3. Objects that can be sterilised this way are
person via food, water, air, touch or vectors milk bottles, metal spoons and forks, and
(disease carriers, e.g. Aedes mosquitoes). surgery equipment.

3. ‘Prevention is better than cure’ means that 4. Autoclave is a type of high-pressure pot that
taking efforts to prevent one falling sick is allows the water inside to be compressed
better than to seek treatment for the disease under high pressures and heated up to 120oC to
after one is infected. kill microorganisms and spores. Autoclave is
suited to sterilise glassware, culture mediums
4. Preventive measures must be taken and surgical tools.
seriously in controlling diseases spread by
microorganisms. Sterilisation using Chemicals

5. Failing to do so will involve high treatment 1. Antiseptics are chemicals used to kill or
costs, lead to a loss of valuable time and inhibit the growth of microorganisms on skin
threaten our lives. particularly on wounds to prevent the growth
of pathogens.
Aseptic Techniques in Controlling the
Spread of Microorganisms 2. Some examples of antiseptics include
iodine solution, hydrogen peroxide, ethanol,
1. Aseptic techniques involve taking actions acriflavine and potassium permanganate
and following procedures designed to solution.
minimise the possibility of infection from a
microorganism. 3. Disinfectants are stronger compared to
antiseptics. Disinfectants cannot be rubbed
2. Sterilisation is the process of destroying or onto skill because it causes damage to body
eliminating pathogens from an object, food tissues.
or environment.
4. Disinfectants are suitable to sterilise walls,
3. Here are some ways sterilisation can be
carried out: 5floors, blankets, bedsheets, toilet bowls and
• Heat treatment – boiling, heating, use of
autoclave medical tools.
• Chemical treatment – antiseptic,
disinfectant 5. Some examples of disinfectants are iodine
• Radiation treatment – ultraviolet rays, solution, chlorine gas, phenol, copper sulphate
gamma rays and Lysol.

Sterilisation using radiation

1. Gamma rays have high penetration power. This
ray can penetrate through microorganisms and
killing them.

209

  Science SPM  Chapter 1  Microorganisms Mattresses, pillows and clothes can be
sterilised when dried under sunlight.
3. Tools that are sensitive to heat or chemicals
have to be sterilised using gamma radiation. 5. Operating theatres are sterilised with a special
These include plastic tools, medication, lamp that emits ultraviolet rays.
vaccines, syringes and surgical tools.

4. Ultraviolet rays can kill many microorganisms.
The Sun is a source of ultraviolet rays.

Ekxsppeerirmimeennt 12.71

Aim: To study the concentration of antibiotics (penicillin) used against the growth of bacteria (Bacillus sp.).
Problem statement: How does the concentration of antibiotic affect the growth of bacteria?
Hypothesis: The higher the antibiotic concentration, the larger the clear surface area of the nutrient agar.
Variables:
(a) manipulated: The concentration of antibiotic
(b) responding: Surface area that is clear
(c) constant: Type of bacteria, type of antibiotic, temperature, pH
Operational Definition:
The area that is clear does not indicate the growth of bacteria. Hence, antibiotic is defined operationally as the
chemical which causes clear areas on nutrient agar.
Materials: Sterile nutrient agar, Bacillus subtilis culture, penicillin solution of concentrations 10% and 20%,

distilled water
Apparatus: Autoclave, sterile Petri dish, inoculation ring, filter paper discs, cellophane tape, labelling papers
Procedure:

Safety Precautions!
Wear gloves when conducting this experiment.

1. Three Petri dishes containing nutrient agar are prepared and sterilised in the autoclave.
2. Approximately 1 cm3 Bacillus subtilis culture is poured into nutrient agar as shown in Figure 1.26 (a).

Form Nutrien agar

5 Filter paper
disc

(a) (b)
Figure 1.26  Set-up of apparatus

Caution! Be careful when handling Bacillus subtilis culture

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Science SPM  Chapter 1  Microorganisms

3. The Petri dishes were labelled A, B and C.
4. Two filter paper discs are soaked in distilled water then placed on the surface of nutrient agar in Petri dish

A as shown in Figure 1.26(b).
5. Two filter paper discs are soaked in penicillin solution 10% then placed on the surface of nutrient agar in

Petri dish B.
6. Two filter paper discs are soaked in penicillin solution 20% then placed on the surface of nutrient agar in

Petri dish C.
7. All the three Petri dishes are closed and taped with cellophane tape.
8. The Petri dishes are placed upside down in the incubator at 37oC for two days to allow growth of bacteria.
9. After two days, the Petri dishes are taken out and observed.
10. All the observations are recorded.

Safety Precautions!
Wash your hands thoroughly with soap after carrying out this experiment.

Observation:

Filter paper Filter paper Filter paper
discs soaked discs soaked disc soaked
in distilled in penicillin in penicillin
water solution solution 20%
Petri dish A 10% Clear zone
Clear zone

Petri dish B Petri dish C

Discussion: Form
1. There is no clear zone surrounding the filter paper discs soaked in distilled water.
2. The clear zone around the filter paper discs soaked in 20% penicillin solution is larger than the clear zone

around the filter paper discs soaked in 10% penicillin solution.
3. Higher concentration of antibiotics can kill more bacteria.

Conclusion:
The higher the concentration of antibiotic, the larger the clear zone is on the surface of the nutrient agar.

Methods of Treating Infectious Diseases 5

1. Medication is used to treat infectious diseases. These include antibiotics, antifungal and antiviral
medication.

Antibiotic • Used to kill or inhibit the growth of bacteria
• Taken orally or via injection
• Example:

– Streptomycin (produced by Streptomyces griseus) is used to treat tuberculosis
– Penicilin (produced by Penicillium chrysogenum) is used to treat syphilis

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  Science SPM  Chapter 1  Microorganisms

Antifungal • Used to treat fungal infections
Antiviral • Available in powder, lotion or gel form
• Applied onto the affected area.
• Example:

– To treat athlete’s foot
– To treat skin conditions like a yeast or ringworm infection

• Used to inhibit virus growth
• Taken orally, via injection or applied on the affected area
• Example:

– To treat shingles

2. The full course of antibiotics must be 3. If the wrong type of antibiotics is prescribed,
completed. This is to ensure that all the beneficial bacteria in the alimentary canal may
pathogens involved will be eliminated. Any be killed and this will affect our digestive
spared pathogen will be able to produce a new system.
generation of pathogens which have some
form of resistance against the antibiotics. This Checkpoint 1.3
will cause us to require a higher amount of
antibiotics to overcome the same infection in Q1 What does aseptic technique mean?
the future. Q2 Explain three sterilisation methods.
Q3 What is the use of antibiotics?

CONCEPT MAP

Microorganisms

The World of Microorganisms Useful Microorganisms Prevention and Treatment
Group of Diseases Caused by
Microorganisms

Bacteria Protozoa Alga Application in Potential in
Daily Life biotechnology

Form5 Fungi Virus Medicine and ‘Prevention Effect of
Agriculture sustainability is better antibiotics
than cure’ towards
of the concept bacterial
environment
growth

Factors which influence

microorganism growth Aseptic technique

Industry

Nutrition Light pH value Treatment of
infectious diseases

Usage

Moisture Temperature

Antibiotic Antifungal Antiviral

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SPM Practice Science SPM  Chapter 1  Microorganisms

1

Objective Questions 4. Which of the following is the 7. Amirah wants to make
most suitable for the growth yogurt. Which of the following
1. Figure 1 shows a of bacteria that causes microorganism is needed?
reproduction process by a diseases to humans? A Bacteria
microorganism. A Temperature of 37oC B Yeast
B pH 2 C Mucor
Figure 1 C Bright area D Protozoa
D Dry medium
What is the process? 8. Which microorganism in
A Budding 5. Figure 3 shows two the intestine of humans
B Conjugation preserved food. can produce vitamin K and
C Fragmentation Vitamin B?
D Spore formation Pickled Pickled A Algae
chilles mangoes B Bacteria
2. The information below shows C Fungi
a group of microorganisms. Figure 3 D Virus

• Amoeba Which of the following factors 9. Figure 5 shows two industrial
• Euglena inhibits the bacterial growth in products.
• Paramecium the bottle?
A High temperature Leather shoes Rope
What is the group of the B Low pH Figure 5
microorganisms? C Low light intensity
A Algae D High humidity What microorganism is used
B Bacteria in the production of the
C Fungi 6. Figure 4 is a graph that
D Protozoa shows the relationship products shown?
between the number of
3. Figure 2 shows two types of bacteria colonies and the A Algae
microorganisms. temperature. B Bacteria
C Yeast
Z D Fungi
Number of bacteria
P Q calories 10. Which of the following Form
Figure 2 diseases are caused by
viruses?
What are microorganisms P A Tetanus 5
and Q? B Yeast infection
Temperature (°C) C Malaria
PQ D Hepatitis A
Figure 4
A Amoeba Yeast 11. What is streptomycin?
What is the possible value for A An antibiotic
B Euglena Bacteriophage Z? B An antibody
A 0°C C An antiserum
C Mucor Spirogyra B 15°C D An antiseptic
C 35°C
D Paramecium Chlamydomonas D 50°C

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  Science SPM  Chapter 1  Microorganisms

Subjective Questions

Section A
1. Figure 1.1(a) and 1.1(b) shows an experiment to study the effect of nutrients on the growth of microorganisms.

Boiling Delivery Delivery
tube tube tube

Test tube Test tube

Yeast suspension Yeast suspension
+ glucose solution
Limewater Limewater

Figure 1.1(a) Figure 1.1(b)

(a) Based on Figure 1.1(a), what is the observation that can be made of the limewater?
Mark (3) for your answer in Table 1.

Table 1

Figure Bubbles No bubbles
1.1(a)

1.1(b)

(b) State an inference for this experiment. [1 mark]
[1 mark]
(c) State the variable in this experiment.
(i) Manipulated variable [2 marks]
(ii) Responding variable [1 mark]

(d) State a hypothesis for this experiment.

2. A group of students carry out an experiment to study the effect of concentration of antibiotic towards the
growth of bacteria. The observation of this experiment is shown in Figure 2.

Form Filter paper soaked in Filter paper soaked in penicillin
penicillin of medium of low concentration
concentration
Filter paper soaked in penicillin
of high concentration

Nutrient agar Clear zone

5 Figure 2

(a) (i) State an observation from the experiment. [1 mark]
(ii) Based on the observation in 2(a)(i), state an inference. [1 mark]

(b) State the variable in this experiment. [2 marks]
(i) Constant variable
(ii) Manipulated variable

(c) Predict the clear zone around the filter paper disc that is soaked in distilled water that is placed on the
HOTS [1 mark]
surface of the nutrient agar. Analysing

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Science SPM  Chapter 1  Microorganisms

Section B
3. Figure 3 shows the medication made from bacteria.

Antibiotic

Streptomycin Hormone
insulin
(a) State the function of antibiotic.
Figure 3

[1 mark]

(b) Name another use for bacteria in the field of medicine apart from producing antibiotic and hormone.
[1 mark]

(c) State two uses of bacteria besides in the medical field. [2 marks]

(d) State two dangerous effects of bacteria. [2 marks]

Section C
4. Study the following information.

The growth of microorganisms is influenced by several factors such
as temperature, pH value, humidity, light and nutrients. Different
temperatures give different effects on the growth of fungi.

(a) State one problem statement from the above information. [1 mark]
(b) Suggest one hypothesis to investigate the above statement. [1 mark]

(c) Based on the given statement, design a laboratory experiment to test your hypothesis by using two
slices of bread, plastic bags, a magnifying glass, a shoe box and ice box that contains ice.

Your description should include the following criteria: [1 mark] Form
(i) Aim of experiment [2 marks]
(ii) Identification of variables [4 marks]
(iii) Procedure or method [1 mark]
(iv) Tabulation of data

5

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