Bacteria virus fungi

• Viruses 


  Tiny particles that can only be seen by using an electron microscope
• Viruses

  • Obligate parasites that infect all kinds of cells
  • non cellular
  • Consist of a string of dna or rna
  • rod spherical complex shapes

  
• features of viruses

  Living

  • have genetic material (dna rna)
  • can replicate
• Features of viruses 


  non living

  • non cellular
  • one type of nuclei acid (DNA/RNA)
  • cannot replicate outside a living cell
• Viral replication

  Viruses are obligate parasites of plants, animals and bacteria. This means they can only replicate in a living cell
• Stages of viral replication

  1. The virus attaches to the host cell (Wall or membrane).
  2. Viral DNA (or RNA) enters the host cell, its protein coat stays outside.
  3. Viral DNA replicates. The virus uses the host's organelles to produce copies of viral DNA and protein.
  4. New virus are made by assembling the viral DNA and protein.
  5. The host cell bursts and releases up to 100,000 new viruses.(The new viruses may infect other cells, be attacked by antibodies or white blood cells or released into the environment.)
• Structure of virus

  .

  
• Harmful effects of viruses

  1. Human disease : common cold, flu, rabies, cold sores and aids. Disease may be contracted by exchange of body fluids by contact with infected person 2. plant disease :mosaic disease in potato. The leaves develop a spotted mosaic appearance and growth is stunted.

  3. animal disease: foot and mouth, rabies
• Beneficial effects of viruses

  1. Genetic engineering : viruses may be used to transfer genes from one organism to another
  2. formation of vaccines: give resistance to disease
  3. medical research
  4. control bacteria
• Viruses are not affected by antibiotics because they have no enzymes
• bacteria

  • Belong to kingdom monera
  • unicellular
  • prokaryotes ie they dint have a nuclear membrane or any membrane bound organelles

  
• Structure of a bacterial cell

  
• Nutrition in bacteria 


  Autotrophic- make their own food

  • photosynthetic use sunlight
  • chemosynthetic use energy from chem reactions
  • parasitic
  • saprophytic

  heterotrophic- can’t make their own food
• Bacteria reproduction 


  Asexually by binary fission

  1. dna chromosome replicates
  2. dna bacterium grows and elongates
  3. bacterium divides forming two identical bacteria

  
• Mutation in bacteria 


  Reproduce every 20 min. Mutation occurs frequently. This allows bacteria to evolve quickly, producing new strains that suit the environment better.
• Factors affecting growth of bacteria

  1. temp : affects enzyme action, most bacteria grows well at 20 and 30°
  2. O2 concentration: aerobic (need o2 for respiration) anaerobic don’t need oxygen.
  3. ph: affects enzyme action, work best at 7
• Growth curve for a population of bacteria growth

  A: lag phase: number stays constant, bacteria are adapting

  B: number increases, bacteria producing rapidly because there is plenty of food, o2 and space

  C: stationary: numbers constant, reproduction rate slow down because of shortage of food o2 and space

  D; decline phase: number decreases, more shortage of materials needed

  E: survival phase: small number may survive as dormant sphores (endospore)
• Growth curve

  
• Endospores


  Under adverse conditions some bacteria form dormant Spores.
• Endospore formation 


  Bacterial DNA replicates

  one chromosome becomes surrounded by a thick wall

  Endospore is formed and loses water

  outer bacterial wall breaks down and the endospore is released. It can survive all sorts of adverse conditions. When conditions are suitable the endospore germinates. Thick wall breaks down and single bacterial cell is formed.
• Nutrition in bacteria

  1. beneficial bacteria: production of drugs(antibiotic), food (yogurt), waste disposa, scientific research.
  2. harmful bacteria: human disease(food poisonin), tooth decay, food decay (lactobacilli cause milk to go sour)
• Food processing bacteria 


  Use of bacteria and other organisms to produce a wide range of foods and other products eg yogurt cheese
• Batch processing 


  Fixed amount of sterile nutrient is added to the microorganism in a sterile bioreactor in the beginning. Microorganism population goes through the lag, log and stationary phases of the growth curve.
• Continuous flow processing 


  Nutrients are continuously fed into a bioreactor. At the same time the culture medium with the products is continuously removed. The volume of materia in the bioreactor remains constant.
• Advantages of batch culturing

  • Only one batch is spoiled if the culture becomes contaminated.
  • bioreactor can be used for a variety of diff purposes.

  advantages of continuous flow processing

  • product is formed more quickly
  • there is no regular shutting down of the process
• Nitrogen cycle 


  Bacteria in the soil play a major role in the decay of dead plant and animal bodies. This result in the formation of humus and the recycling of minerals, eg nitrogen. These minerals can be used again by microorganisms.

  Nitrogen is needed by living organisms for molecules such as protein, DNA RNA ATP. Plants in nitrogen as nitrate.
• Nitrogen fixation 


  Nitrogen gas (N2) converted into nitrates (NO3) or ammonia (nh3) some n2- fixing bacteria eg rhizobium, live in nodules or swellings on the roots of plants. These bacteria take in N2 gas and convert it to nitrate, which is given to plant, plant in return gives food to bacteria.
• recycling of nitrogen 


  Nitrates are reformed from protein in dead organisms by saprophytic and nitrifying bacteria
• .


  nitrification

  
• Fungi

  • Yeasts moulds, mushrooms- unicellular
  • eukaryotes ie they have a nuclear membrane and membrane bound organelles
  • mainly multicellular
• Characteristics of fungi

  • Long filaments called hyphae. Groups of hypae is mycelium
  • heterotrophic, may be parasites or saprophytes
  • reproduce by spores
  • cell wall made of chitin
• Rhizupus black bread mould

  
• Nutrition fungi 


  Rhisoups is a saprophyte, found on bread and other starchy foods. Hyphae secrete enzymes onto substrate to digest the root, soluble products of digestion are then absorbed into hyphae.
• Yeast 


  Unicellukar, saprophytic fungus

  reproduces asexually by budding

  
• Budding

  1. Parent cells form a bud That fills with cytoplasm
  2. nucleus divides by mitosis
  3. one nucleus moves into the bud
  4. bud is cut off from the parent cell forming a new daughter cell
  5. new cells separate from parent cell
• Economic importance if fungi

  Beneficial

  • produce antibiotics eg penicillin
  • brewing: alcohol fermentation by yeast
  • food: bread using yeast
• Economic importance of fungi

  Harmful

  • disease in humans eg athletes foot
  • disease in plants eg mildew on fruit trees
  • Dry rot of timber
  • Food spoilage e.g. mould on bread
• Edible and poisonous fungi

  Edible mushrooms

  • Field mushroom, truffles

  Poisonous mushrooms

  • Death caps
• Culturing microorganisms


  Bacteria and fungi can be cultured or grown on a nutrient agar plate. agger is a jellylike substance extracted from seaweed. It provides a solid medium for the growth of microorganisms. When working With microorganisms aseptic measures are taken. aseptic measures Prevent contamination. Nutrient medium must be sterile i.e free of organisms. An autoclave is used to sterilise medium and equipment.
• Curing microorganisms


  Asepsis- free of pathogens

  Sterile- free of organisms

  Needles are sterilised by flaming (Bunsen flame) or washing with disinfectant