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Transcript
L.C. Biology Revision Kingdom Monera/Bacteria Bacteria are prokaryotes from the kingdom Monera. Distribution Bacteria are found in fresh water, salt water, soil, dust, air, plants and animals. They can be found at temperatures higher than 100⁰C, ponds of high salt concentration, sewage, swamps and human intestines. They can survive extreme temperatures and pressures and pH’s as low as 1 and 2. Bacterial Structure Cell wall flagella cytoplasm plasmid Strand of DNA capsule Function of parts of a bacterium Capsule/Slime layer Cell Wall Flagellum Cell membrane DNA Plasmid Mesosome Cell membrane Capsule is a dry layer, slime layer is moist – both help to prevent water loss Protects & prevents cell from expanding & bursting Allows the cell to move/swim Retains cell contents & controls what passes in & out of the cell The loop of DNA contains genes that control the cell Small loop of DNA that contains genes that may control antibiotic resistance Respiration (how cell gets energy) Size: bacteria are measured in micrometres (μm), most are 1-5 μm. Types of bacteria: Bacteria are classified according to their shape. 1. Round/coccus. Example: Staphylococcus Aureus causes pneumonia. 2. Rod/bacillus. Example: Bacillus Anthracis causes anthrax. Escherichia Coli live in human gut. 3. Spiral. Example: Treponema Pallidum causes syphillus. Reproduction Bacterial reproduction is asexual (one parent) and is called binary fission. Bacteria gets to a certain size & the DNA strand replicates Cell elongates and DNA strands move to opposite ends of cell Cell splits into two similar sized cells L.C. Biology Revision Bacteria can divide every 20 minutes – one bacterium could give rise to over a million bacteria in 7 hours!! Mutations in bacteria Bacteria can evolve very fast due to the speed at which mutations can spread throughout a population because of their short life cycles. This is how bacteria evolve resistance to new antibiotics. Endospores When growing conditions aren’t suitable the bacterial DNA replicates and a tough wall forms around one of the DNA loops inside the parent cell. Parent cell breaks down and endospore remains dormant (not growing/replicating). When conditions are suitable endospore absorbs water, the wall breaks and cell reproduces by binary fission. Nutrition Bacteria can be autotrophic or heterotrophic. 1. Autotrophic: means an organism makes its own food. Autotrophic bacteria can be photosynthetic or chemosynthetic. Photosynthetic: bacteria that make food using sunlight e.g. purple sulphur bacteria. Chemosynthetic bacteria make food using energy from chemical reactions e.g. nitrifying bacteria in the nitrogen cycle. 2. Heterotrophic: means an organism takes in food made by other organisms. Heterotrophic bacteria can be saprophytic or parasitic. Saprophytes are organisms that take in food from dead organic matter e.g. bacteria of decay Parasites are organisms that take in food from a live host usually causing harm e.g. bacillus anthracis Factors affecting bacterial growth Growth is affected by five factors, too much or too little of these is bad for bacteria. A limiting factor is something that slows down a process when in short supply. 1. Temperature: most bacteria grow best between 20 – 30⁰C, but some can tolerate higher temperatures. Low temperatures can slow down the rate of bacterial growth. 2. Oxygen concentration: Aerobic bacteria need oxygen for respiration (most bacteria are aerobic), a low oxygen concentration can slow down bacterial growth. Anaerobic bacteria do not need oxygen for respiration. Facultative anaerobes can respire with or without oxygen. Obligate anaerobes can only respire in the absence of oxygen. 3. pH: Bacterial enzymes work at specific pH values. Outside these values the bacterium’s enzymes will be denatured. Most bacteria grow best at neutral pH, some can tolerate low pH’s. Heliobacter in the human stomach can tolerate a pH of 2. 4. External Solute Concentration: bacteria gain or lose water by osmosis. If external solution has a higher solute (salt or sugar) concentration than the bacteria’s cytoplasm water will move out of the bacteria. This dehydrates the bacteria and stops its enzymes working. Used in food preservation. If external solution has a lower solute concentration than the bacteria’s cytoplasm water will move into the bacteria. Bacterial cell walls usually prevent the bacteria from bursting. L.C. Biology Revision 5. Pressure: Growth of most bacteria is inhibited by high pressures as their cell walls can’t withstand it. Bacteria found in deep sea vents can withstand high pressure. Pressure tolerant bacteria are sometimes formed by genetic engineering as some biotechnology processes require the use of bacteria in pressurised bioreactors. Economic Importance of Bacteria Benefits: Lactobacillus convert milk to yoghurt/cheese Genetically modified bacteria can be used to make insulin, drugs, enzymes, alcohols Disadvantages: Cause human, animal & plant diseases like tuberculosis, septic throat, food poisoning Pathogens are micro-organisms that cause disease. Cause food to decay. Lactobacilli cause milk to go sour. Antibiotics Antibiotics are chemicals made by micro-organisms that stop the growth of or kill other micro-organisms without damaging human tissue. Antibiotics have no effect on viruses. Examples of antibiotics: streptomycin, penicillin. Antibiotic Resistance Antibiotics kill most bacteria but some bacteria have developed antibiotic resistance by mutations, these aren’t affected by the antibiotic, new antibiotics must be made continually to treat newly resistant bacteria. If a person is taking an antibiotics then all bacteria in that person are killed, if resistant bacteria evolve they’ve no competition and will reproduce quickly and take over the persons body. If a pathogenic bacterium then enters the body the antibiotic-resistant gene may be passed on to it. The person will develop an infection for which there is no antibiotic. In this way bacteria have developed that are resistant to most known antibiotics and are called multi-resistant bacteria. Abuse of the use of antibiotics Overuse of antibiotics results in increased growth of antibiotic-resistant bacteria. If you don’t complete your course of antibiotics bacteria are allowed to survive and re-grow, this means more antibiotics are needed and gives an increased risk of developing multi-resistant bacteria. Growth Curve of Bacteria Log Phase Stationary Phase Decline Phase Death Phase Number of Bacteria Lag phase Time (days) This diagram shows the growth curve of bacteria growing on a fixed amount of nutrient agar in a warm environment. The no. of bacteria is in the log scale. L.C. Biology Revision 1. Lag phase: Bacteria adapting to new environment and making enzymes to digest the substrate (agar), little if any increase in bacteria numbers. 2. Log phase: Bacteria reproducing rapidly due to ideal conditions of food, moisture, space, oxygen. 3. Stationary phase: No increase in bacterial numbers, production of new bacteria is cancelled out by death of equal numbers of bacteria due to lack of food, moisture, space, oxygen and the build up of toxic waste products. 4. Decline phase: Death rate is higher than reproduction rate and bacterial numbers fall. High death rate due to factors outlined in no.3. 5. Death/survival phase: Not all bacteria die, some survive as spores until conditions are suitable for growth. Food Processing Modern bioprocessing methods use bacteria to produce a range of products & food – yoghurts, cheese, vitamins, wine, beer. A bioreactor is a vessel in which biological reactions take place. The use of bacteria/fungi to produce edible forms of protein is called single-cell protein (SCP) production. Two main methods of food processing: Batch culture & Continuous flow. Both processes may/may not need oxygen bubbled through them & both need continuous rate of stirring. 1. Batch Culture Fixed amount of sterile nutrient is added to micro-organism in bioreactor. Organisms go through lag, log, stationary phases of growth Product formed at log and stationary phases Process stopped before decline phase as this phase produces very little product & there’s a danger the microorganism would burst or produce unwanted side products. At the end bioreactor is emptied , product separated from solution & purified. Bioreactor is cleaned& sterilised, process started again. Advantages: Simple process Small volumes of product can be formed Micro-organisms grow well (naturally) 2. Continuous flow Nutrients continuously fed into bioreactor Culture medium continuously withdrawn (allows volume in bioreactor to remain constant) Micro-organisms maintained in log stage of growth – reproducing rapidly & making product at quick rate Micro-organisms grow under steady state – constant conditions of Ph, temperature, rate of stirring, concentration of nutrients & oxygen. Difficult process to maintain constant conditions so limited to few applications like production of single-cell protein. Advantages: Production is continuous No need to sterilise bioreactor so often Product made more quickly L.C. Biology Revision Bioreactor for Batch Food Processing Nutrients and microorganisms added here Gas out here Stirrer Product is released at the end of the process Sparger Oxygen (if required) in here Bioreactor for Continuous Flow Food Processing Nutrients fed in continuously Gas out here Product (and culture medium) flows out continuously Stirrer Sparger Oxygen in here Product