B6 - Beyond The Microscope (OCR Gateway Science B)

Bacteria have:

• bacterial DNA ('naked')
• flagellum (for movement)
• cell wall (not cellulose)
• cell membrane
• plasmid (small DNA circles with genes that help bacteria to survive)

Bacteria are different from plant cells and animal cells:

• 10x smaller
• don't have nuceli or mitochondria 
• smaller ribosomes 

There are four different shapes of bacteria:

• curved rod

• spherical 

• spiral

• rod

Bacterial Reproduction:

• bacterial cell

• cell divides into two

• two new cells form and get ready to divide 

binary fussion: each bacterium splits into two (a form of asexual reproduction that's not mitosis)

Yeast is a very important fungus:

• yeast is a single-celled fungus that has many uses, such as making bread and alcohol.
• yeast cells reproduce asexually using budding

Fungi have:

• cytoplasm
• bud (forming a new cell, made then breaks away)
• cell wall (made of a different material, NOT cellulose)
• nucleus

Viruses are:

• much smaller than bacterium or fungi
• not classified as living cells
• can only reproduce inside other cells, by taking over the cell to make new protein
• can cause some illnesses, for example: influensa, common cold and chicken box
• cannot be killed by antibiotics
• made up of strands of genetic material, surrounded by a protein coat

Viruses have:

• protein coat
• genetic material (RNA not DNA)
• enzymes (to take over cell machinery)

Virus reproduction:

• The virus attaches to a specific cell, called the host cell

• The genetic material from the virus is injected into the host cell where it enters the nucleus to make mRNA

• New viruses are made using material inside the host cell and the genetic material from the virus. This happens in the cytoplasm of the cell.

• The cell splits open, allowing the viruses to leave but killing the host cell.

Microorganisms that cause disease are called pathogens. There are different types of these:

• bacteria - eg: cholera, food poisoning
• virus - eg: influenza, chicken pox
• fungus - eg: athlete's foot

Disease transmission:

• method: in food 
• how it happens: food is contaminated with bacteria
• prevention: good hygiene through food cooking

• method: in water
• how it happens: bacteria in water contaminated with sewage
• prevention: good hygiene and proper sewage handling

• method: airborne droplets
• how it happens: microscopic in size, produced through coughing and sneezing, entering the airways or eyes
• prevention: using tissues, good gygiene, campaigns like 'catch it, bin it, kill it'

• method: contact
• how it happens: with damp surfaces where fungi thrive or through sexual activities
• prevention:  avoidance or use of barriers

Four stages of infection:

1. First the microorganism enters the body

2. It then reproduces to build up numbers. This is called the incubation period

3. The microorganisms then start to make harmful toxins (harm cells)

4. Symptoms start to appear, such as a fever

• Earthquakes can lead to diseases such as cholera and food poisoning.
• Tsunamis can lead to ruined water supplies, damage to electrical supplies and overcrowded places, therefore it's difficult to keep food and water fresh and there's poor sanitation, leading to disease.

• Damage to water supply systems and sewage systems means that water is no longer safe to drink or clean to wash in.
• If sewage gets onto land it can contaminate crops, therefore disease is more likely to spread.

• Overcrowded areas and cramped shelters lead to poor sanitation and disease would spread easily through high populated areas.
• Water and crops could be contaminated with sewage, making it unsafe to eat, but some people may anyway, leading to disease.

Bacteria are used to make lots of important things:

• Yoghurt - made when bacteria turns milk sour.
• Silage - made from fermented grass and is fed to cows.
• Cheese - made from milk using bacteria to help it ripen.
• Vinegar - made when bacteria makes acids from alcohol.
• Compost - made by bacteria breaking down dead plant material.

How to make yoghurt:

• All equipment is sterilised.
• Milk is pasteurised by heating to 95°c for 20 minutes then cooled until 46°c.
• A bacterial culture is added and milk is incubated at 46° c for about 4 hours.
• Samples are taken to find out when the yoghurt is ready.
• Flavours and colours are added.
• The yoghurt is cooled and packed ready to sell.

• The bacterium used to make the yoghurt are called 'Lactobacillus'. The bacteria are used to break down a sugar in the milk called lactose. Lactobacillus converts the lactose into lactic acid. The lactic acid then changes protein in the milk to give yoghurt its texture.

Beer Brewing Stages:

• Barley is mixed with water and left to sprout. This is called malting.
• (converts starch into sugar)
• Malted barley is dried and crushed to extract the sugar.
• Hops are added for flavour.
• The mixture is sterilised by heating in a brew kettle.
• This kills any unwanted microorganisms.
• After cooling, yeast is added and the mixture is put into tanks to ferment. The mixture is ket warm enough for the yeast to grow. The deep tanks and the layer of carbon dioxide that forms stops air getting into the yeast.
• This is important because it stops unwanted microbes from the air getting into the beer and turning it bad.
• The beer is clarified. A chemical is added to make the yeast settle out, leaving a clear liquid.
• The beer is pasteurised to destroy unwanted microorganisms. It is then put into bottles or casks ready to sell.

• Biomass is the mass of living materials.
• Plant biomass can be used to make biofuels (eg: biogas, wood)
• Biogas (mainly methane - CH4) is produced by bacteria when organic material (dead plants and animals) decay. This can be done on a large, industrial scale, using a digester.

Biogas:

• 70% (or 60%) matheane and 30% (or 40%) CO2.
• Also contains H2, N2, H2S (hydrogen sulfide).
• >50% methane burns easily, but as low as 10% methane is explosive.
• Temperature affects biogas production because enzymes are involved (eg: denaturing) in anaerobic respiration/ fermentation

When biogas burns it releases energy. This energy can be used in different ways:

• to generate electricity
• to produce hot water and steam for central heating
• as a fuel for vehicles

Gasohol:

• Gasohol is a type of biofuel. Yeast is used to turn sugar from sugar cane into a type of alcohol called ethanol. The ethanol is mixed with petrol to make gasohol. 
• Gasohol is then used in cars as a cleaner alternative to petrol.
• This is very useful in countries like Brazil. This is because they have lots of sugar cane but small oil reserves.

Advantages:

• They are an alternative to fossil fuels.
• Burning fossil fuels increases the level of carbon dioxide in the air; burning biofuels only recycles carbon dioxide used by plants.
• No participates (fine particles like soot) are produced when they burn.

Disadvantages:

• Large areas on natural habitats are destroyed to grow crops for biofuels, leading to some species being wiped out.