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BIOLOGY FORM 4
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CHAPTER 8 CHAPTER 8
DYNAMIC ECOSYSTEMDYNAMIC ECOSYSTEM
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
• Microorganisms are microscopic organisms that cannot be seen with the naked eye and it is all around us.
• Most microbes are harmless and useful to humans. Others can cause diseases in plants and animals including humans.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
TYPES OF MICROORGANISMS.• Microorganisms can be classified into five
types based on their basic characteristics;a) Protozoab) Fungic) Algae d) Bacteriae) Virus
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
PROTOZOA• Aquatic unicellular animal• Can be seen under a microscope at low power• Has nucleus, cytoplasm and is surrounded by a plasma
membrane• Takes in food (feeding), removes excretory products and
reproduces• They use flagella, cilia or pseudopodia to move• Reproduces sexually and asexually• Lives freely in the river, pond, fresh water, soil or on another
organism. Some live in parasites.• Examples: Amoeba sp., Paramecium sp., Plasmodium sp.
(parasite)
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
FUNGI• Heterotrophic multicellular or unicellular
eukaryotes which do not have chlorophyll• Can be seen under a microscope at low
power or with a magnifying glass• Cell walls are made up of chitin.• Feeds by secreting enzymes that break the
surrounding organic material down into simple molecules before they are absorbed
• Reproduces by budding and formation of spores
• Examples: Yeast, Mucor sp., mushroom
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
ALGAE• Exists as unicellular, in a colony and in
filaments • Contains chlorophyll• Carries out aerobic respiration• Reproduces asexually and sexually• Lives in sea, pond, river, paddy field, tree
stem, damp soil• Examples: Phytoplankton, Pleurococcus sp.,
Spirogyra sp.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
VIRUS• Smallest microorganisms which can only be
seen under an electron microscope• Consists of nucleic acid that is ribonucleic acid
(RNA) or deoxyribonucleic (DNA)• Has no cytoplasm, nucleus or plasma membrane• Has a layer of protein for protection• Exists as crystals outside host cells, no signs of
life• Examples: Bacteriophage, tobacco mosaic fluid,
influenza virus
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
BACTERIA• Unicellular organisms which have a basic cell
structure that includes a cell wall, plasma membrane and DNA that is not enclosed in a membrane
• Has cell walls made of a polymer called peptidoglycan
• Reproduces asexually by binary fission• Form spores when conditions are not suitable• Their shape may be spherical, rod-shaped or spiral.• Examples: Lactobacillus sp., Staphylococcus sp.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
THE EFFECTS OF ABIOTIC COMPONENTSON THE ACTIVITY OFMICROORGANISMS
The activities of microorganisms such asrespiration, growth and reproduction isaffected by the following abiotic components :a) Temperatureb) pH valuec) Light intensityd) nutrients
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
TEMPERATURE• The optimum temperature for the growth of
most microorganisms is 35-40 ˚C.• At low temperature, microorganisms such as
bacteria or yeast are not active and the growth rate is slow.
• 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 in the microorganisms are denatured.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
pH value• Every microorganism has its own optimum
pH value• Most microorganisms live best in a neutral
or nearly neutral pH environment.• However, 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.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
LIGHT INTENSITY• Microorganisms that are autotrophs need
light for photosynthesis.• At a suitable light intensity, the growth of
autotrophic microorganisms is at its optimum.• The activities of other microorganisms is
inhabited under a high light intensity because the ultraviolet rays can destroy these microorganisms.
• In the dark, growth and reproduction of microorganisms such as fungi, bacteria and protozoa occur actively.
8.5 THE IMPACT OF 8.5 THE IMPACT OF MICROORGANISMS ON LIFEMICROORGANISMS ON LIFE
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 acid by means of saprophytism or parasitism.
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