Biology Unit 6: Beyond the Microscope

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Bacteria

Bacteria cells have certain features:

  • flagellum (tail) for movement
  • cell wall to maintain shape and stop it bursting
  • DNA in it's plasmid to control the cell's activities

Bacteria reproduce by splitting in half in a process called binary fission, a type of asexual reproduction where the cell splits in half. You can reproduce bacteria on an agar plate using an aseptic technique to prevent contamination. 

Bacteria are very successful because they can:

  • survive on a variety of food
  • live in a wide range of habitats
  • produce their own food (in some cases)
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Fungi and Viruses

Yeast is a single-celled fungus that is grown commercially for use in foods like bread. Its growth is altrered by:

  • pH (due to enzyme optimums)
  • temperature (due to enzyme optimums) - growth rate doubles as temperature increases by 10 degrees until the optimum is reached
  • food availability
  • removal of waste products 

Viruses are dead cells made of only genetic material surrounded by a protein coat. This means that viruses can only reproduce in living cells and attack specific cells. A virus reproduces by:

  • attatching to a living cell
  • inserting its genetic information
  • reproducing inside the cell, using the cell to make new components of a virus
  • bursting host cell, killing it, to release new viruses
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Harmful Microorganisms

Microbes can be spread and prevented by:

  • food (salmonella) - cooling foods
  • water (vibrio cholera) - sterilising water
  • direct contact (many germs, like the common cold) - barrier methods
  • air droplets (influenza, aka flu) - barrier methods and isolation

Disease often occurs in areas of natural disasters as day to day life has been disrupted meanig there is a lack of food (rotten from no operating fridges as loss of electricity), water (water pipes burst) and health services (people are displaced).

The stages of an infectious disease are:

  • microbe enters body
  • microbe reproduces (incubation period)
  • microbes produce toxins 
  • symptoms produced (like fever) from toxins

Thanks to Louis Pasteur (germ theory) we know about these microbes, allowing Alexander Flemming to create penicillin and justifying Joseph Lister's aseptic surgery.

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Useful Microorganisms

A bacteria called lactobacillus is used to convert the lactose in milk into lactic acid to give yoghurt its sharp, distinctive taste. The steps of making yoghurt are:

  • sterilisation of all equipment
  • pasteurisation of milk to kill germs
  • milk incubated with a culture of lactobacillus 
  • yoghurt sampled with a variety of flavours and colours

Yeast is then used in a process called fermentation that produces alcohol:

glucose TO ethanol + carbon dioxide

This is through:

  • sugar extracted from grapes for wine and barley for beer
  • yeast added
  • kept warm and air kept out to ensure anaerobic respiration (if aerobic it produces ethanoic acid but initial oxygen allows aerobic respiration to reproduce yeast cells rapidly)
  • wine/beer is allowed to clarify and yeast is removed
  • wine/beer goes through distillation to increase alcohol% + pasteurised then bottled/cased
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Biofuels

Biofuels occur in different forms but use all of the energy trapped in biomass like burning trees or fermenting waste or sugar from plants. Despite sometimes destroying habitiat, biofuels are becoming more popular because:

  • fossil fuels are running out so alternative energy sources are required
  • they are carbon neutral as there is no net increase in greenhouse gases (not for all though!)
  • they do not release particulates (like dust/smoke) when they are burnt

Biogas is produced by inserting waste products continuously into a large digester where bacteria inside digest the organic waste producing gas. Due to the enzymes in bacteria, gas production is affected by pH and temperature. It can be used as a fuel or burnt for heating. Biogas is cleaner than petrol and diesal as it isn't as polluting but doesn't contain as much energy. It is made of:

  • 50% methane (less than 10% is explosive)
  • carbon dioxide
  • nitrogen
  • hydrogen sulfide

Gasohol is made by mixing petrol with alcohol made by fermentation, useful in places like Cuba.

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Life in Soil

Soil can be found in 3 main forms:

  • clay soil: high water content (so low oxygen/air content) 
  • sandy soil: low water content with larger particles (so high oxygen/air content) and more humus (dead organic material that decomposes to release minerals and increases air in soil)
  • loam: a mixture of clay and sandy soil with high humus content

The content of soil can be found by conducting several experiments:

  • water: gently heating the soil to evaporate the water
  • air content: how much water is needed to fill the air spaces
  • humus: burning off humus using the bunsen burner

Charles Darwin highlighted the importance of earthworms:

  • bury humus for decomposition by bacteria and fungi
  • aerate and drain soil so organisms can respire aerobically
  • mixing up soil layers to ensure all organisms get minerals
  • neutralising soil allowing bacteria to survive
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Life in Water

There are several advantages and disadvantages of living in water. The advantages are:

  • water acts as support
  • endless water supply
  • waste products can be disposed of
  • temperature of the water varies less than air

But  the disadvantages:

  • water content can vary easily as organisms take in too much fresh water by osmosis and lose it in salt water 
  • harder to move as water is denser

Some organims like amoeba have adapted in order to dispose of water through their contractile vacuole. 

Organims in water rely on different food sources:

  • marine snow (dead material floating down to organisms)
  • green plants/bacteria acting as producers
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Life in Water 2

The numbers of phytoplankton (aquatic plants) and zooplankton (aquatic animals – think animals in a ZOO) vary in the water because photosynthesis and food is effected by:

  • deeper depths: results in lower temperatures and less light
  • winter season: results in less minerals as they are used up during summer

Water pollution like eutrophication is caused when fertiliser and sewage is run off into the ocean, killing organisms. Some species are killed by pollution and then act as indicator species. Some pollutants like PCBs and DDTs can kill organisms higher up the food chain as they are toxic and build up in food chains.

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Enzymes in Action

Biological washing powders often use enzymes in order to make dirt soluable and easier to wash out. Due to the enzymes, the washing powders work best at moderate temperatures with a neutral pH as organisms denature at excessive pH and temperatures. Some enzymes used are: 

  • amylase: to digest carbohydrates
  • protease: to digest proteins
  • lipase: to digest fats

They are also used commercially to convert sucrose, a common sugar, into a higher number of small linked units of sugar like glucose and fructose which are sweeter sugars. This means that less are required in the product and results in low calorie food. 

Lactase (the enzyme that converts lactose in milk into sugars) can be extracted and put directly into milk for people who are lactose intolerant (don't have the lactase enzyme naturally so lactose ferments in the gut producing wind and diarrhoea). 

Enzymes can also be immobolised in order to make them easier to use in chemical reactions and so the mixture doesn't become contaminated by enzyme and used in continuous flow processing (reused). This is done using alginate beads or in calcium chloride solution. 

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Gene Technology

Genetic engineering is when a gene from one organism is taken an place into another organisms, which is then called a transengic organism. The process is:

  • gene isolated and extracted (e.g. insulin)
  • restriction enzymes used to cut open the DNA of an organism (e.g. bacteria)
  • ligase enzymes used to 'stick' the gene into the organism's DNA (the plasmid of bacteria)
  • making sure the gene works using assaying techniques (like also giving organism resistance gene and then bombarding it with pesticides/antibiotics/whatever it is supposed to be resistant to and scientists choose the ones that survive)
  • transengic organisms can then be cloned to mass produce things like insulin with bacteria for people with diabetes

The genetic code is universal. This means that any gene can work in any organism, thus making genetic engineering possible. The plasmid of bacteria that is used to produce human insulin then acts as a vector for any gene. 

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DNA Fingerprints

DNA fingerprints can be used to identify individuals for crimes and other reasons, though some people don't like this information being accessible for many people.

The stages of producing a DNA fingerprint are:

  • extracting DNA from a sample
  • fragmenting DNA into smaller pieces for analysis
  • seperating DNA using electrophoresis (electricty runs through gel block seperating DNA)
  • making fragments visible using a radioactive probe
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