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Microbiology LO1
Bacterial structure, reproduction and growth, soil and water bacteria
| Question | Answer |
|---|---|
| Draw an example of a bacterium and label 5 of the main components. | MUST SHOW : nucleoid, ribosomes, cytoplasm, cell membrane, cell wall, capsule |
| Give 2 functions of the bacterial cell membrane | - Provides a permeable barrier - Site of cellular processes eg respiration - Site of biosynthesis of eg lipids - Coordination of DNA replication - Contains receptor molecules for eg chemotaxis |
| Give 2 functions of the bacterial cell wall | - Shape - Protection from lysis and toxins - A role in division / motility - May contribute to pathogenicity |
| Describe the key differences between a gram negative and a gram positive cell wall. What colour does each stain during gram staining? | Negative : thick, have an outer membrane, periplasmic space, LPS, porins stain pink Positive : thin, one layer, very small / no periplasmic space, techoic acids, stain purple |
| State 2 functions of the outer membrane in Gram negative bacterial cells | - Creates a negative charge to help evade phagocytosis - attachment site - receptor for F pilus - permeable barrier with porins for passage of nutrients - outer limit of periplasmic space |
| What is the definition of an endospore? Name 3 conditions that an endospore can survive. | An endospore is a highly resistant structure that allows bacteria to survive hostile environments. Occur due to high temp, irradiation, dessication, strong acid, solvents, disinfectant. |
| Describe the difference between a capsule and a slime layer / biofilm. | A capsule is a more permanent , detectable layer whereas a slime layer / biofilm is unorganised and less discrete and is easily removed. |
| Give 2 possible functions of the capsule / slime layer / biofilm. | - Aid in attachment - Protection from phagocytosis and microbial attack - Protection against desiccation - Aids pathogenicity |
| The growth curve of a bacterial culture has four distinct phases. List them | Lag phase, log phase, stationary phase and death phase. |
| State what is happening at the first stages of the growth curve | Lag phase: Cell number remains constant, cells are adapting to their new environment, synthesising enzymes, copying DNA, repairing damage. |
| State what is happening at the second stages of the growth curve | Log phase: Cell number increases exponentially, cells dividing, numbers doubling. At regular intervals, binary fission. |
| State what is happening at the third stages of the growth curve | Stationary phase: Cell number remains constant – number of new cells being formed is balanced by the number of cells dying, multiplication rate decreases. Cells start to die due to build up of acid. |
| State what is happening at the fourth stages of the growth curve | Death phase: The number of cell dying exceeds the number of new cells being formed. Cell division has halted, cells killed by low pH, toxic waste and lack of oxygen and space. |
| Give 2 reasons why a bacterial culture enters the stationary phase. | Lack of nutrients, lower pH of media. |
| At which stage would bacteria form endospores? | At beginning of death phase. |
| Name 2 species of bacteria that produce endospores | Clostridium and Bacillus. |
| State whether the following statement are true or false: Microaerophiles find high concentrations of oxygen toxic | True: they lack the enzymes need to deal with toxic oxygen products. |
| State whether the following statement are true or false: Acidophiles survive conditions of low external pH by pumping out hydrogen ions | True: allows them to maintain a neutral internal environment. |
| State whether the following statement are true or false: Thermophiles have long -chain unsaturated fatty acids in their membranes; | False: they are saturated. |
| State whether the following statement are true or false: Psycrophiles grow in a temperature range of 0-20ºC; | True. |
| State whether the following statement are true or false: Halophiles withstand conditions of high external osmotic pressure by pimping out sodium ions. | False: they would actually take them in to help them retain water or else they would ‘dehydrate’ in hypertonic environment. |
| State the oxygen requirements of : | Obligate aerobes: require oxygen at normal levels = 20% |
| State the oxygen requirements of : | Microaerophiles: require low oxygen levels 2-10% |
| State the oxygen requirements of : | Obligate anaerobes: killed by oxygen |
| State the oxygen requirements of : | Facultative anaerobes: prefer oxygen but can grow without it |
| Give the temperature ranges for growth of the following groups of microbes: Psychrophiles, Thermophiles, Mesophiles | psychrophiles: <20ºC mesophiles: 20-45ºC thermophiles: >45ºC |
| What happens to bacteria at very high temperatures and what adaptations do these bacteria possess to cope with these extremes? | At temperatures higher than the optimum, enzymes become denatured, membrane disrupted (too fluid), DNA double helix disrupted. Thermostable proteins, membrane fatty acids with long saturated chains and high melting points. |
| What happens to bacteria at very low temperatures and what adaptations do these bacteria possess to cope with these extremes? | At temperatures lower than the optimum, metabolism slows right down due to decreased enzyme activity. At very low temperatures, cytoplasm might freeze. They accumulate solutes in their cytoplasm to stop them freezing, create protein anti freezes which |
| Explain what is meant by the term ‘microhabitat’. | Area within a layer of soil where particular conditions determine which microbes are found there. Conditions include types of surfaces eg cavities between soil aggregates will have different nutrients available than spaces between the surface litter. |
| What is the rhizosphere? | The zone of soils surrounding the roots of plants |
| How does the rhizosphere support large numbers of microbes? | The presence of the microbes stimulates the plants to release growth factors which the microbes can use. |
| Name a nitrogen-fixing bacterium | Rhizobium. |
| State where this microbe is usually found | Root nodules in leguminous plants. |
| Starting with atmospheric nitrogen (N2), list the stages in converting this element to forms useable by animals | N2: 1) NH4+ 2) NO2- 3) NO3- ------> Amino acids USED BY ANIMALS |
| Identify the type(s) of microbes which play a major role at each of these stages | Step 1= Nitrogen fixing bacteria Step 2= Gram negative bacteria Step 3 =Bacteria such as Nitrobacter |
| What is a photoautotroph? | Microbe which can use energy from sunlight to convert CO2 to organic matter (ie carries out photosynthesis). |
| State why high levels of N and P stimulate algal growth (think about which molecules N and P are components of) | Nitrogen is a component of nucleic acids and proteins and phosphorous is a component of nucleic acids and so can be used in the synthesis of nucleic acids and proteins during growth. |
| Fully explain why the turbidity increases and light penetration decreases | Increased nutrients stimulate algal growth (and other aquatic plants). Photosynthesis increases, nutrient regeneration increases leading to further growth. High levels of phytoplankton in upper layer lead to turbidity and low penetration. |
| Describe why levels of dissolved oxygen become depleted as a lake becomes eutrophic | Algal blooms provide a large amount of organic matter which is decomposed by bacteria. As a result of a rich food supply for bacteria, bacteria multiply, oxygen is used up as they respire, and oxygen in the lake becomes depleted. |
| During which seasons are algal blooms more likely to occur? Explain your answer | Autumn and spring. The large level of nutrient recycling, lack of stratification and constant oxygen and temperature leads to algal blooms |
| Typhoid fever, Shigellosis, Cholera and Campylobacerosis are all water-borne, bacterial diseases of man. Describe how the bacteria which cause these diseases enter the body. | Ingestion of contaminated food and water |
| Typhoid fever, Shigellosis, Cholera and Campylobacerosis are all water-borne, bacterial diseases of man. Describe any disease symptoms which are common to all four diseases. | Abdominal pain, loose watery stools |
| Typhoid fever, Shigellosis, Cholera and Campylobacerosis are all water-borne, bacterial diseases of man. In the UK, how is drinking water chemically treated to prevent these diseases? | Chlorination |
| Typhoid fever, Shigellosis, Cholera and Campylobacerosis are all water-borne, bacterial diseases of man. Water-borne infections are more prevalent in India than in Britain. Give a reason as to why this is the case. | Lack of sanitation in India and lack of water treatment leads to more water-borne bacteria. |
| Name the water-borne disease of man which causes paralysis and state the type of micro-organism which causes the disease | Poliomyelitis - virus |
| What is a pathogen | A pathogen is an organism that causes disease in the body. |
| Name the main pathogen infective agents | Virus, Bacteria, Fungi/Yeast and Ptotozoa |
| Describe the virus | Virus are the simplest organism but nonetheless are highly successful parasites. They take over the host cell and make millions of virus particles. Viruses can't reproduce outside host cell. |
| Describe the bacteria | Bacteria are capable of surviving outside host and can be found in many places such as: food, water supplies and on object. |
| Describe fungi/yeast | Fungi/Yeast sometime are described as opportunistic infections. They tend to go only as far as the skin. |
| Describe protozoa | Protozoa includes single celled parasites such as the malaria protozoa. |
| What is approximately the size of bacteria | Their size is approximately 0.1 - 10.0 µm in lenght. |
| Explain what is meant by the term 'microhabitat' | Area within a layer of soil where particular conditions determine which microbes are found there. Conditions include types of surface, eg cavities between soil aggregates will have different nutrients available than spaces between the surface litter. |
| What is the rhizosphere? | The zone of soils surrounding the roots of plants |
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Pigall609
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