BACTERIA

• Only small number are pathogens
• Asexually reproduction by binary fission / 2 identical daughter cells
• Grow best at optimum conditions (human body)
  • Constant temperature
  • Neutral pH
  • Constant supply of food, H2O, O2
  • Mechanism removing waste

• Most bacteria are aerobic / obligated aerobes
• Aerobic bacteria growing with absent oxygen / facultative anaerobes
• Bacteria which find oxygen toxic / obligate anaerobes

Sigmoid growth curve shows the number of bacteria plotted against time:

• Bacteria MUST grow in closed system and nutrient medium → BACTERIAL CULTURE
  • 1) Population grows slowly - LAG PHASE
  • 2) Rapid increase of population growth - LOG PHASE
  • 3) Reaches equilibrium when number remains constant - STATIONARY PHASE
• Lag Phase → initial phase
  • Low number of reproducing organisms
  • Bacteria increase in size before division
  • This requires nutrients which need to be digested
  • Digestion requires enzymes, proteins → activation of genes → time consuming process
• Log Phase → exponential phase; max growth rate; steep curve
  • Optimum conditions: no limiting factors, waste does not accumulate to a toxic level
  • Bacteria most susceptible due to production of new cells
    • Antibiotics inhibit cell wall formation
    • Antibiotics inhibit DNA replication
    • Antibiotics inhibit protein synthesis
• Stationary Phase → reduced growth rate
  • New cell production balanced by death of cells
  • Limiting factors, declining nutrients, accumulating waste influence population size
• Decline Phase → bacteria stop dividing
  • Death rate increases; numbers may fall to zero
  • Lack of nutrients, build up of toxic waste products
• Aseptic conditions
  • Sterilise equipment, instruments, thus, to prevent contamination with the culture.
  • Use high temp and disinfectants

Total cell count:

• Number of cells whether living or dead
• Count cells with haemocytometer
• Stop bacteria entering the flask with a stopper. Important as bacteria would have been caused reduced growth rate of yeast/killed yeast and competed for space/nutrients
• Culture is shaken to achieve a uniform distribution of yeast cells/spread out yeast
• Larger number is taken to avoid anomalies/produce an average

Measurement of growth;

Generation time: time taken for a bacterial population to double

• Rate of population
  • = increase in number of yeast cells/time
  •  = number larger - number less/(time larger - time less)
• Suppose the number of cells in one square are 6 8 9 5 7
• The sum of the cells in 5 squares is 35
• The mean for one type B square is 7
• Therefore 25 squares have 25 x 7 = 175 in 0.1mm3
• In 1mm3 there will be 1750 cells or 1,8 x 103

Viable cell count

• Only living cells since these are the only ones capable of dividing
• 1cm3 original sample is diluted in 9cm3 distilled H2O
• Mix 1cm3 from last dilution with 9cm3 distilled H2O - serial dilution
• 1cm3 of each dilution is put on an agar plate and counted. Number is multiplied by the dilution factor

Measurement of growth

• Number of colonies on the 10-3 dilution plate = 35
• Number of viable colonies in 1cm3 of 10-4 dilution of milk
  • 35 x 1/0.1 = 350
• Sample was diluted by 10-3
• Number of bacteria in 1cm3 of the original sample = 350 x 103

Biological factors

• Bacteria are effected in growing by nutrients: C, H, N, P, S
• Temp: low → low speed of enzyme reactions; high → denaturisation of enzymes
• pH → tolerate a wider range of pH than plant and animal cells
• O2 → some grow better in presence, but some grow in absence

Koch's Postulates1;

• A list of postulates (criteria) must be fulfilled to proof an infective cause for a disease
  • "Organism must be sufficiently abundant in every case to account for the disease
  • Organism associated with the disease can be cultivated artificially in pure culture
  • Cultivated organism produces the disease upon inoculation into another member of the same species
  • Antibodies to the organism appear during the course of the disease"1
• Exceptions are possible
  • Number of organism causing disease might be very low (eg tuberculosis)
  • Cultivation might be difficult
  • Animals must be used as it is unethical to infect a human with a causative organism
  • Antibodies may not appear if the immune system is inhibited

Entry of Microorganisms (Pathogens) into the Body;

• Damaged skin
  • Skin acts as a barrier to infections
  • Tetanus occurs when the bacterium Clostridium tetani enters a wound
• Mucus membrane of respiratory tract
  • Air containing droplet of infectious material are breathed in
  • Mycobacterium tuberculosis causes tuberculosis
• Digestive track
  • Vibrio cholerae causes cholera when drinking water infected with faeces
  • Salmonella enteritis causes food poisoning when eating undercooked food
  • These organisms are resistant to acidic conditions in the stomach
  • Acid protects against microorganisms by providing a hostile environment
• Others
  • Transmission by vectors (e.g. malaria via Plasmodium parasite when mosquito vector takes blood)
  • Direct entry through the intact skin (e.g. Schistosomiasis where the larval stage schistosome burrows through the skin of the feet)

Pathogenesis: How Microorganisms Cause Disease;

• Damage or destroy host cells - e.g. HIV, Salmonella
  • Organism is taken up by epithelial cells in the intestine
    • HOST SPECIFIC: ligand on pathogen must fit onto receptor proteins on host
    • Some hosts are more susceptible than others because proteins depend on gene coding
  • Destroy brush border of microvilli
  • Host creates a ruffled surface / Invaded cells detach from intestinal wall, creating inflamed lesions / Secretion of large amounts of watery fluid into the lumen of the gut → diarrhoea
• Produce toxic waste - e.g. Vibrio cholerae
  • Are harmless but produce harmful "exotoxins" - toxins released from the cell
  • Causes loss of chloride and hydrogencarbonate ions from the intestinal cells
  • Osmotic loss of up to 10 litres of water per day
  • Impaired absorption of water and salt from the gut
  • This explains severe watery diarrhoea and death from dehydration
• Body's own immune response to the presence of microorganisms which produce the symptom
  • e.g. Mycobacterium tuberculosis
  • Body tries do destroy the invading bacteria
  • This causes inflammation and damage to the surrounding cells occur
  • Lesions may become hard or spongy, leaving "holes" in the lungs, sometimes damaging blood vessels
• Some bacteria will cause all of the 3 ways above; Some require a large number of bacteria for a disease; Some will only a few number of bacteria
• Microorganisms may enter the lymphatic system via tissue fluid and are carried around the body in this way
• Ability of bacteria to cause disease relies on
  • Location - what tissue is colonised
  • Infectivity - how easily a bacterium can enter the host cell
  • Invasiveness - how easily a bacterium or its toxin spreads within the body
  • Pathogenicity - how a bacterium cause disease

Tuberculosis (Myobacterium tuberculosis);

Salmonella;

Evolution:

• Changes allele frequency in population.
• Individuals show variation.
• Phenotypic variation due to:
  • Genetic Factors,
  • Environmental Factors,
  • Combination of both.
• Competition results in differential survival and reproduction.
• Selection acts on populations.
• Organisms with a selective advantage:
  • more likely to survive
  • reproduce
  • pass on genes to next generation.
• Selection may change allele and phenotype frequencies.
• Populations reproducing in isolation can result in the formation of new species.
  • Allopatric Speciation:
    • Geographically separated sister species are now so different - no interbreeding is possible.
  • Sympatric Speciation:
    • Genetic variation occurring in same geographical location.
• Human activities have, and continue, to alter environment of many organisms.
  • Changes selection pressures
  • May effect evolution of species.

3.5.2 People change communities

Ecosystems and the stability of populations

• Introduction of plant/animal species to different countries
• Changes stability of native species:
  • populations
  • communities
  • ecosystems.
• ECOSYSTEMS include:
  • living organisms
  • physical factors
  • chemical factors
• POPULATION = All organisms of one species in particular habitat
  • Populations of different species form COMMUNITIES.
• COMMUNITY:  found in one particular habitat
  • based on Dynamic Feeding Relationships
• Species occupy particular NICHE within habitat.
• Governed by:
  • adaptation to food availability
  • and/or prevailing abiotic conditions.
• Ecosystem supports certain size population of any single species.
• Influencing factors:
  • Abiotic Factors
  • inter-organism interactions
  • inter-organism competition
  • predation
• NOTE:  Be able to evaluate evidence and make balanced judgements between meeting human demands and the need to conserve the environment.

Winners and Losers

• Domesticated/introduced plants/animals affect ecosystems by competing with native species.
  • Examples:
  • domestic cats
  • grey squirrels
  • Japanese knotweed
• Growth of the urban environment has increased habitat and niches for:
  • foxes
  • rats
  • pigeons
  • and others

GM Organisms

• Environmental Impact Assessment.
  • Impact of large-scale introduction of GM organisms
  • Eg. Soya and Maize.

3.5.3 Humans’ health can be affected when they change their environment

Diet, Crops, Food Allergies

• Our diet has changed.
• Vegetable oil seen large increase in demand.
• Linked to increase in range of allergies.
  • Nut allergy.
  • Hay fever
• Allergic responses produce illness.
• Allergens = antigens that produce abnormal immune response.
• Hypersensitivity:
  • Allergic Reactions involving Histamine production:
    • Hay fever
    • Food allergies
    • Allergic asthma
    • Hives
  • B cells produce antibody (IgE) in presence of allergen.
  • IgE binds to Mast Cells.
  • Mast Cells produce histamine when exposed to the allergen.
  • Histamine leads to symptoms of allergy.
• Anaphylaxis = Sudden, Acute reaction to allergen.
• Can result in:
  • oedema (inflammation) in airways
  • large, sudden fall in blood pressure.
• Treated with adrenaline.
• Use:
  • skin test for possible allergies
  • antihistamines

Air pollution and Respiratory illnesses

• Claims of links between air pollution and respiratory illnesses, Eg:
  • Asthma
  • bronchitis

Water Pollution and illness

• Polluted water can lead to illness.
• Beaches and coliform standards:
  • Coliform bacteria and faecal streptococci = pollution indicators
  • Blue Flag Beaches meet water quality standards.
• Cryptosporidium:
  • single celled parasite.
  • Causes cryptosporidiosis.
  • Oocyst = resistant form
  • Present in infected faeces (human and animal)
  • Oocyst infects new host.
  • Pollution of waterways from:
    • Infected farm animal slurry → rivers
    • Sewage discharge → rivers

3.5.4   Human activities can damage ecosystems and create new ones

Succession

• Ecosystems are dynamic systems.
• Communities move from: Colonisation → Climax
• Known as Succession.
• Communities change with time, due to interaction between:
  • Species
  • Environment.
• Certain species may change their environment -
  • result may be more beneficial for other species!

Local Wildlife

• Human activities may produce 'bare' areas of land and water.
• Wasteland = unmanaged land, vegetation in early stages of succession.
  • Includes corridor habitat, eg. railway/roadside embankments.
• Brownfield sites = sites previously developed for human use.
  • Can be reclaimed
  • Provide habitats for flora and fauna threatened by urbanisation/intensive agriculture
• Ecosystems range greatly in size.
• Increase area by 10 - doubles number of species.
• Important to enhance biodiversity in urban environment.
• Corridor habitats allow movement of plants/animals between habitats.
• NOTE: Be able to describe techniques to measure biotic/abiotic factors in an ecosystem.

Waste Disposal

• Should be environmentally sustainable.
• BPEO = Best Practical Environmental Option.
• The waste hierarchy:
  • Prevented/Reduced at source
  • Re-used
  • Re-cycled (used as raw material)
  • Or (if not pos) use as substitute for non-renewable energy source
  • Only landfill if none of above possible.
• Microorganisms decompose organic remains.
• Anaerobic bacteria produce methane.
• Collect from landfill sites to use as a fuel.
• Polluter Pays Principle:
  • Polluter pays for direct/indirect environmental consequences.

3.5.5 Plants can reduce the impact of the use of fossil fuels on climate change

• Carbon Footprint:
  • Measure of greenhouse gasses produced by human activities.
  • Units of kilograms of CO2 produced per year.
• NOTE: Be able to describe how:
  • primary /secondary contributions are calculated
  • to reduce household contributions
  • to off-set CO2  emissions.

Climate Change

• Burning of fossil fuels → production of greenhouse gasses.
• Changing climate: UK is getting warmer.
• Affecting distribution of plants and animals
• NOTE: be able to describe effects of climate change on:
  • Natural range of species
  • breeding seasons
  • availability of food
• Plants can reduce the impact of fossil fuels on climate change.
• They remove CO2  from the atmosphere via Photosynthesis
• Photosynthesis is the major route energy enters ecosystems
• Energy transferred through trophic levels of food chains/food webs
• and is dissipated.
• Energy transfer used to produce ATP and reduced NADP
  • in light-dependant stage of photosynthesis
• ATP and reduced NADP used in light independent stage
• incorporation of  CO2  → produces sugars.
• ATP synthesis associated with electron transfer chains -
• located in the chloroplasts.
• Therefore: tree planting used to off-set CO2  emissions.
• Carbon is sequestered in bio-mass of trees.
• Biofuels reduce use of fossil fuels.
• Renewable energy sources.
  • Biomass from fast-growing plants = fuel to burn
  • Vegetable oils = diesel substitute
  • Ethanol from fermented plants = petrol substitute/additive.
• Large scale production of plants needed.
• Impacts environmental
• Reduces food available for human consumption.

Respiration → CO2   → Atmosphere

• ATP = source of energy for biological processes.
• All cells/organisms respire
• In respiration:
  • Glycolysis occurs in cytoplasm,
  • is anaerobic.
  • Remaining steps occur in mitochondria.
  • Associated with electron transfer chain,
  • in membranes of mitochondria.
  • Oxygen = the final electron acceptor.
  • CO2  = waste product.

3.5.6 People and their microorganisms

The Human Ecosystem

• Human body supports populations of bacteria and fungi.
• These microorganisms:
  • carry out extracellular digestion of biological molecules
  • absorb products of digestion
  • use these in their own metabolism.

The ecology of the skin

• The skin supports communities of microorganisms, including:
• Staphylococci
• Micrococci
• Corynebacterium
• Fungi, eg. yeast.
• Can cause spots/blemishes, number of skin conditions.
• Acne vulgaris caused by Propionibacterium acnes 
• growing in/near sebaceous glands in the skin.
• Antibiotics/antiseptics can control populations.

The ecology of the gut

• The human gut supports populations of bacterial species,
• form a bacterial community.
• Human actions (eg. antibiotics) can change dynamic of community,
• may adversely affect functioning of the gut.

Antibacterial Resistance

• Humans have introduced large amounts of antibacterial agents into environment.
• This selective pressure → evolution of resistant microbes.
• Eg. MRSA
• Originally MRSA meant methylin resistant staphylococcus aureus -
• now means multiply resistant!

Variation

• Variation is the presence of any differences (genotypic and phenotypic), between individuals in a population, or between parents and offspring.
• Genotypic variation can be due to:
  • Mutation
  • Random assortment during Meiosis,
  • Crossing over during Meiosis,
  • Random fertilisation of gametes.
• Phenotypic variation can be due to:
  • Genetic Factors,
  • Environmental Factors,
  • Combination of both.
• Variation provides organisms with a means of producing new phenotypes.
• Variations to the structure or behaviour of an organism may confer a selective advantage to survive and reproduce

Evolution

• Evolution is the sum of changes of heritable characteristics in population.
• It is the development of life in geological time
• Natural selection is the process where organisms that are better adapted to their environment survive and breed.
• Those that fail to adapt will not survive. 
• The environment therefore exerts a selection pressure on the population.
• Allele frequency is the commonness of the occurrence of any particular allele in a population.
• Evolution changes allele frequency in population because:
  • Organisms with a selective advantage:
    • more likely to survive  →  reproduce  →  pass on genes to next generation.
    • This will increase the frequency of the allele that corresponds to the adaptation.
  • Organisms with a selective dis-advantage:
    • less likely to survive  →  die  → fail to pass on genes to next generation.
  • This will decrease the frequency of alleles possessed by these individuals.
• A population is a group of individuals of a species, living close together, and able to interbreed.
• Populations reproducing in isolation can result in the formation of new species
• This is known as Speciation.

Allopatric Speciation:

• Geographically separated sister species reproduce in isolation.
• Natural and man-made barriers may arise rapidly.
• For example: a population may be divided if a river breaks it's banks and takes a new route, or a new road may separate a population.
• Many generations may elapse.
• Sister species are now so different - no interbreeding is possible.

Sympatric Speciation:

• Genetic variation occurring in same geographical location.
• Reproductive isolation due to:
  • Temporal mechanisms
  • Behavioural mechanisms
  • Polyploidy
• Temporal (time) mechanisms may occur when two very closely related species occupy the same habitat, differing only in the time of year that they complete their life cycles.
• Reproductive isolation may develop within the population so that some members produce gametes at distinctly different times of the year from others.
• Thus, two distinctive gene pools start to evolve.
• Behavioural mechanisms results when members of a population acquire distinctive behaviour routines in their growth and development, courtship or mating process that are not matched by all individuals of the same species.
• For example: imprinting behaviour of birds.
• Polyploidy is a change in structure or number of chromosomes.
• Applicable mostly to Plants.
• This chromosomal mutation may instantly give rise to a new species.
• Human activities have, and continue, to alter the environment of many organisms.
  • Changes selection pressures
  • May effect evolution of species.
• Artificial Selection is an intentional selection process by humans,
• selecting certain organisms based on their phenotype, specifically for breeding purposes,
• In the hope offspring inherit the desired characteristics. (NOT a guarantee).
• Usually carried out by animal and plant breeders during Selective Breeding.
• Selective Breeding is use of artificial selection to modify and improve quality/yield
• In plants and animals.
• Eg. cross-fertilisation of maize variates to produce plants that:
  • mature faster,
  • larger fruit size,
  • higher yield,
  • resistant to disease.
• Eg. All modern race horses have been artificially selected.
  • Horses are selected for breeding on basis of success in races.
  • Gene pool is constantly improved.
• Humans are the selective agents.