Micro-organisms - Chapter 1 PDF

CHAPTER 1: BIODIVERSITY AND CLASSIFICATION OF MICRO-ORGANISMS Introduction Biodiversity in general, refers to the wide variety of plants, animals and micro- organisms on Earth. Organisms which are too small to be seen with the naked eye are referred to as micro-organisms. Micro-organisms can be uni...

CHAPTER 1: BIODIVERSITY AND CLASSIFICATION OF MICRO-ORGANISMS Introduction Biodiversity in general, refers to the wide variety of plants, animals and micro- organisms on Earth. Organisms which are too small to be seen with the naked eye are referred to as micro-organisms. Micro-organisms can be unicellular or multicellular. Some are harmful and cause diseases whilst others are very useful in the environment and to humans e.g. yeasts are used to make bread. Key terminology unicellular an organism consisting of only one cell multicellular an organism made up of many cells biodiversity the variety of organisms found in an area or on Earth The classification of organisms Scientists have placed all the organisms into specific groups so that it is easier to study them. There are five groups called kingdoms (Figure 1):  Kingdom Monera – bacteria  Kingdom Protista  Kingdom Fungi  Kingdom Plantae  Kingdom Animalia A scientist who is responsible for the placing of an organism within a specific group is called a taxonomist. Figure 1: The 5 Kingdoms of Life 7 Viruses Viruses are placed in a separate group and not in a kingdom because they display some non-living as well as living characteristics. Key terminology capsid a protein coat surrounding the nucleic material of a virus acellular non-cellular obligate = forced; a parasitic organism that cannot complete its obligate life-cycle without exploiting a suitable host (if an obligate parasite parasite cannot obtain a host it will fail to reproduce) host an organism that harbours a parasite pathogenic an organism that causes disease a type of virus that infects bacteria; the word "phage" means to bacteriophage eat” an irregularly shaped region within the cell of a prokaryote that nucleoid contains all or most of the genetic material Structure and characteristics of viruses Introduction to viruses: https://www.youtube.com/watch?v=8FqlTslU22s  Viruses are microscopic (20 – 300 nm) and can only be studied using an electron microscope.  Viruses consist of a core of either DNA or RNA enclosed by a protein coat called a capsid (Figure 2). Envelope DNA or RNA Protein coat Figure 2: Structure of a typical virus 8   Viruses occur in a variety of shapes,  cannot respire, feed or excrete waste,  do not have a cytoplasm and do not have any membrane bound organelles such as mitochondria or nuclei.  Viruses have either DNA or RNA which is surrounded and protected by an outer protein coat or capsid. All other living organisms have both DNA and RNA.  Viruses are acellular.  Viruses do not have chlorophyll and are therefore unable to make their own food by photosynthesis.  All viruses are obligate internal parasites. This means that they cannot multiply without infecting another living organism or host.  Viruses can infect bacteria, protists, plants and animals. Viruses that infect bacteria are called bacteriophages.  Viruses cause diseases and are said to be pathogenic.  In humans, viruses are responsible for diseases such as HIV/AIDS, poliomyelitis, chickenpox, herpes and influenza.  If a virus cannot find a host, they can become dormant. Bacteria Bacteria belong to the Kingdom Monera. Bacteria are found everywhere on earth. Some are pathogenic and cause diseases such as tuberculosis, while most are useful. Key terminology an organism where the nuclear material is not enclosed in a prokaryotic membrane any single or multicellular group of organisms that have a eukaryotic membrane-bound nucleus containing genetic material a whip-like, protruding filaments that help cells or micro- flagellum organisms move; plural of flagellum is flagella organisms which can synthesize their own food e.g. green autotrophic plants, algae and some bacteria any organism that sources food from its environment because heterotrophic it cannot make its own food, e.g. animals, fungi, most bacteria plant or fungal microorganisms that feeds on dead or decaying saprophytic tissues of other organisms 9  asexual reproduction of a single cell in which divides by binary fission mitosis; the cell regenerates as two or more separate cells having the same chromosomal identities as the parent cell a tough, protective, non-reproductive bacteria structure that contains DNA and cytoplasm and lies dormant to survive endospore unfavourable environmental conditions in order that it can germinate once conditions improve a plasmid is a small, circular, double-stranded DNA molecule plasmid that is distinct from a cell's chromosomal DNA Characteristics of bacteria Bacterial cell structure: https://www.youtube.com/watch?v=4DYgGA9jdlE  Bacteria are unicellular (one celled) organisms.  Bacteria are larger than viruses and can be seen using a light microscope.  Bacteria are distinguished from one another by their shape (Figure 3). These shapes include: coccus – round, bacillus – rod-shaped, spirillum – spiral- shaped, and vibrio – comma-shaped. Cocci Bacilli Others coccus diplococci spirilla coccobacillus coryne- tetrad sarcina bacterium bacillus diplobacilli streptococci vibrios staphylococci palisades spirochete Figure 3: Bacterial shapes 10 Structural characteristics All bacteria have the following structural characteristics (Figure 4):  A cell wall made up of polysaccharides.  Some bacteria have a slime capsule to protect them from drying out.  Cytoplasm surrounded by a cell membrane.  No membrane-bound organelles.  The DNA is in the form of an irregular loop and is called a nucleoid. Since there is no membrane around the nuclear material, bacteria are said to be prokaryotic.  A plasmid, small, circular, double-stranded DNA molecule is also found in the cytoplasm of bacteria.  Many bacteria have a whip-like flagellum which they can use to move in a liquid. The flagella can rotate to propel the organism forwards. slime layer cell wall cell membrane ribosomes nucleoid plasmid flagella Figure 4: Basic structure of a bacillus shaped bacterium 11 Nutrition of bacteria Autotrophic bacteria can manufacture their own food.  Photosynthetic bacteria use sunlight energy, while  Chemosynthetic bacteria get their energy from chemical processes. Heterotrophic bacteria cannot manufacture their own food. This includes:  Parasitic bacteria that obtain their food from other living organisms.  Saprotrophic bacteria that play an important role as decomposers. They obtain their food from dead organic plants and animals.  Mutualistic bacteria that form a relationship with another organism. Both organisms benefit from the relationship. Reproduction of bacteria Bacteria multiply very quickly under favourable conditions. This simple form of cell division is called binary fission (Figure 5). Figure 5: Binary fission in bacteria Bacteria form endospores when conditions are unfavourable for example, when there is a lack of food, extreme heat or a lack of moisture. Protista The Kingdom Protista is a collection of eukaryotic organisms. Protists do not fit into the plant, animal or fungi kingdoms. 12 Key terminology aquatic living in or around water phytoplankton very small plants (algae) that float on or near the surface of water zooplankton consisting of small animals and the immature stages of larger animals which float on or near the surface of the water sessile organisms are usually permanently attached to sessile something and can cannot move on their own but can move through outside sources (such as water currents) Characteristics of the Protista  simple unicellular or multicellular eukaryotic organisms  no tissue differentiation  found mainly in water  autotrophic or heterotrophic  usually microscopic but can be several meters in length for example the seaweeds  some are sessile or free-floating while others can move using flagella (e.g. Euglena) or move using false feet called pseudopodia (e.g. Amoeba)  they can reproduce both sexually and asexually Three groups of Protista are recognized: Plant-like Protista:  mainly unicellular organisms found in aquatic (water) environments  most are autotrophic  free floating aquatic plant-like protists are called phytoplankton (Figure 6) Figure 6: Phytoplankton 13  Animal-like Protista:  mainly heterotrophic free-living unicellular animals living in an aquatic environment e.g. Amoeba  some are parasitic and cause diseases such as malaria  free-floating aquatic animal- like protists are called zooplankton (Figure 7) Figure 7: Zooplankton Algae  multicellular, macroscopic organisms commonly called seaweeds (Figure 8)  seaweeds contain various photosynthetic pigments which give them a green, red or brown colour  seaweeds may be free-floating Figure 8: A species of red seaweed or sessile (attached to a (Gelidium pristoides) harvested along the substrate) South African coast to produce agar Fungi The Kingdom Fungi includes moulds, yeasts, mildews, rusts, toadstools and mushrooms (Figure 9 – 12). Key terminology a fibrous substance consisting of polysaccharides, which is the chitin major constituent in the exoskeleton of arthropods and the cell walls of fungi a network of multi-celled threadlike filaments forming the hyphae mycelium of a fungus a vegetative mass or network of fungal hyphae found in and mycelium on soil or organic substrates 14  multinucleate cells that have more than one nucleus per cell, i.e., multiple nuclei shared in one common cytoplasm threadlike structures that anchor lower plants and fungi to a rhizoids surface a form of asexual reproduction which involves the pinching off budding of offspring from the parent cell; the offspring cell is genetically identical to the parent Figure 9: Toadstools Figure 10: Mushrooms Figure 11: Bracket fungi Figure 12: Breadmould Characteristics Fungi have the following characteristic in common:  Some are unicellular (yeasts) while others are multicellular (mushrooms).  Eukaryotic (i.e. have a nuclear membrane).  Heterotrophic since they lack chlorophyll. Fungi that live off dead organic matter are said to be saprotrophic. Parasitic fungi live off living organisms. Fungi cause diseases such as thrush, ringworm and athlete’s foot. 15   Cell walls which contain chitin. Plants have cellulose in their cell walls.  The bodies of multicellular fungi are made up of threads called hyphae. All the hyphae together form a mycelium.  The hyphae are often multinucleate (have many nuclei).  Fungi reproduce both sexually and asexually.  Asexual reproduction in unicellular fungi such as yeasts is by budding.  In multicellular fungi asexual reproduction is by means of spores. Activity 1: Kingdoms 1. Name the five kingdoms which represent all living organisms (5) 2. Make a labelled diagram to show the internal structure of a bacterium. (6) 3. Name one important characteristic which distinguishes fungi from algae. (2) 4. Explain why viruses are not placed into one of the five kingdoms. (2) 5. Complete the following table: (12) Unicellular/ Prokaryotic / Mode of Organism Multicellular Eukaryotic nutrition Viruses acellular neither Bacteria Phytoplankton autotrophic Zooplankton Fungi (27) Activity 2: Practical investigation Aim: Investigating the growth of bread mould under different temperature conditions A Grade 11 learner investigated the optimum (ideal) temperature for growth of bread mould. The learner used the following method:  The learner selected four black plastic containers with lids.  A slice of bread was placed in each container.  Before closing the containers, 30 ml of water was sprinkled over each slice.  Container A was placed in a fridge (cold), container B was placed in a cupboard (cool), container C was kept at room temperature (mild) and container D was placed on a window sill (warm).  After a week the slices of bread were removed from the containers and placed next to each other. 16 The results of the investigation are depicted below. 1. Formulate a hypothesis for the investigation. (2) 2. Name: (a) the dependent and (b) the independent variable in this investigation. (2) 3. State the relationship between the growth of bread mould and temperature. (2) 4. State three ways in which the learner made sure the results were valid. (3) 5. How could the learner have ensured that the results were reliable? (2) 6. Use the following scale to determine the percentage of bread mould growing on the slices of bread. Record the estimations in a table. (5) 7. Plot a bar graph to show the relationship between temperature (cold, cool, mild and warm) and the growth of breadmould using the table. (6) (22) The role that micro-organisms play in maintaining a balance in the environment Micro-organisms play an essential role in the natural recycling of living materials. Key terminology organisms that break down dead plant and animal (organic) decomposers material e.g. bacteria and fungi saprophytes organisms that live off dead organic matter 17 Micro-organisms as producers in food chains Autotrophic bacteria, phytoplankton and algae can manufacture their own food by photosynthesis. The carbohydrates they produce are available to consumers. These organisms form the first link in a food chain. Oxygen, the waste product of photosynthesis, is made available to other organisms for respiration. The role of micro-organisms as decomposers  Bacteria and fungi are the main decomposers.  They break down dead plant and animal remains and return the nutrients to the soil.  Organisms which break down dead organic matter to obtain nutrients are called saprophytes. The role of bacteria in the nitrogen cycle Bacteria play an important role in the nitrogen cycle.  Free living bacteria can convert atmospheric nitrogen to ammonia and nitrates.  Higher plants can only use nitrogen when it is in the form of nitrates, so they rely on bacteria for the conversion.  Some plants form special relationships with nitrogen fixing bacteria.  When plants and animals die, de-nitrifying bacteria return nitrogen to the atmosphere by a process called denitrification. Symbiotic relationships Symbiosis refers to the living together of two or more species of organism. A symbiotic relationship may benefit one or both members or it can be beneficial to one but harmful to the other one. Key terminology mutualism a symbiotic relationship where both organisms benefit a symbiotic relationship where one organism benefits without commensalism harming or affecting the other organism 18  a symbiotic relationship where parasitic organisms benefit parasitism while causing harm to their hosts composite organisms made up of fungi that grow symbiotically lichens with algae or cyanobacteria an even-toed mammal that chews the cud regurgitated from its ruminant rumen e.g. cattle, sheep, antelopes, deer, giraffes, and their relatives. mycorrhiza The symbiotic association of fungi with the roots of trees. Three types of symbiosis occur:  mutualism – both organisms benefit e.g. lichens  commensalism – one species benefits whilst the other does not benefit, nor is it harmed  parasitism – one species benefits whilst the other is harmed Lichens Algae need a moist environment to survive and cannot live on dry land. They can, however, form a mutualistic relationship with a fungus and this called a lichen (Figure 13). The fungus provides the alga protection from the environment. Fungi however cannot produce food for themselves. They in turn obtain nutrients from the algae which can produce food by photosynthesis. In this way, both the alga and the fungus benefit. Figure 13: Lichens are often the first organisms to occupy a habitat 19 The relationship between nitrogen fixing bacteria and plants  Higher plants require nitrogen to manufacture proteins.  Plants cannot use nitrogen directly from the atmosphere.  Plants require nitrogen in the form of nitrates.  Some soil bacteria can convert free nitrogen to nitrates that can be used by plants. Some nitrogen-fixing bacteria live in special nodules in the roots of leguminous plants (i.e. pod producing plants such as beans and peas). They produce nitrates for the plant while the plant provides the bacterium with a place to live, carbohydrates and water. Both the plant and the bacteria benefit in this relationship. The relationship between E. coli and the human intestine  Not all the bacteria found in our intestines are harmful.  Mutualistic bacteria such as Escherichia coli (E. coli) (Figure 14) live on the undigested remains of food in the gut and in turn make vitamin K which can be used by humans.  Vitamin K plays an important role in blood clotting. Both humans and the bacteria benefit from the relationship. Figure 14: E. coli bacteria Mutualistic bacteria are also found in the digestive tracts of ruminants and termites where they are responsible for the digestion of cellulose into simple sugars. 20 Mycorrhizal fungi and the roots of higher plants Filamentous fungi known as mycorrhizas can penetrate and become associated with the roots of higher plants. The fungi increase the absorption surface area of the roots. The fungus in turn, gets sugars from the plant. Symbiosis in general: https://www.youtube.com/watch?v=zTGcS7vJqbs Activity 3: Nitrogen use 1. Name the form of nitrogen which higher plants use. (1) 2. Describe three ways in which nitrogen becomes available to higher plants. (3) 3. What is a lichen? (3) 4. Describe the role bacteria play in maintaining the nitrogen balance in an ecosystem. (6) 5. The photograph below (Figure 15) shows a seedling without mycorrhizal fungi (left-hand side) and one with mycorrhizal fungi (right-hand side). The seedlings are the same age. Study the photograph and answer the questions that follow. without & with mycorrhizae Figure 15: Seedlings with and without mycorrhizal fungi. 5.1 What is a mycorrhiza? (2) 5.2 Explain why the seedling on the right-hand side is bigger than the seedling on the left-hand side. (3) (18) 21