Chapter 8

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.


TYPES OF MICROORGANISMS.• Microorganisms can be classified into five

types based on their basic characteristics;a) Protozoab) Fungic) Algae d) Bacteriae) Virus


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)


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


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.


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


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.


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


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.


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.


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.


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.

Chapter 8

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