B6 Beyond the microscopeMicrobes

• Bacteria

• Fungi

• Viruses

These are microscopic, some are useful to humans, some are harmful (pathogens).

Order of size- largest Fungi, bacteria, virus smallest

Bacteria

Named according to their shape

You can see bacteria under a light microscope but only fine detail using an electron microscope

Part of a bacterium FunctionCell membrane Controls the movement of substances in and out of the cellCytoplasm Is a jelly-like substance where most of the cell reactions

occurCell wall Maintains the shape of the cell and stops it burstingLoop of DNA Not inside a nucleus. Controls the cell and its replicationCapsule Slimy and protective coating outside the cell wall (protects

some bacteria against antibioticsFlagellum Whip-like structure used to help the bacterium move

Binary fission- bacteria reproduce by dividing in two, and they can do it as quickly as every two hours. If food is left out in a warm room, the bacteria can reproduce very quickly, and it makes you ill as the reproduction is too fast for your immune system to cope with.

Bacteria can survive in extreme environments e.g. deep oceans

Safely growing bacteria in the laboratory

They are grown on dishes of agar jelly and they are kept warm for the bacteria to grow quickly.

You need to keep all surfaces free from bacteria (sterile technique), and do not infect yourself e.g. licking fingers that have been handling plates of bacteria.

Fungi

Include mushrooms, moulds, yeasts (used in bread and beer making)

Cell wall in fungi made of chitin

• Yeast- reproduce asexually by budding (Nucleus divides first, then a bulge appears on side of parent cell which becomes a new cell)

Speed of budding affected by temperature, pH, availability of food, and amount of waste products present.

Viruses

• Much smaller than bacteria or fungi and can only be seen by electron microscope

• Reproduction in viruses-

Transmission of disease

Disease caused by microbes called pathogens

Feature How it prevents entry of microbes

How microbes overcome the barrier

Skin Acts as a physical barrier to prevents microbes enteringWashing reduces the number of microbes on the skinBlood clots to seal a cut to form a scab

Cuts in the skin allow microbes inInsect bites penetrate the skinInfected needles carry microbes through the skin

Digestive system (through the mouth)

Acid in the stomach kills bacteria

Eating undercooked food or drinking infected water containing large numbers of microbes

Respiratory system (through the nose)

Cells lining the airways produce a sticky mucus which traps microbesCilia move the mucus with trapped microbes to the back of the throat for swallowing

Some airborne microbes get past the cilia

Reproductive system Acidic urine kills many microbes

Some microbes are resistant to acidMicrobes are passed from one person to another by sexual contact

Ways in which microbes can get into the body

Contaminated food e.g. salmonella Contaminated water e.g. vibrio cholera (causes cholera). Usually caused by sewage

getting into drinking water Contact- microbes spread from person to person or surface to person e.g.

Trichophyton is a fungus which causes athletes foot. In air- droplets in the air e.g. flu virus which gets breathed in

Natural disasters and spread of disease

Volcanoes and earthquakes causes cholera and food poisoning

Damage to sewage pipes, contaminates drinking water cholera Electricity cut off, no refrigeration for food food poisoning Loss of homes overcrowding greater spread of disease Lack of supplies puts health services under pressure

Examples of diseases caused by microbes

Disease microbe Name of pathogen and transmissioncholera bacterium Caused by a vibrio bacterium and transmitted in

infected water. Diarrhoea and vomiting dehydration. Often fatal

Food poisoning bacterium In contaminated food, stomach aches, diarrhoea and vomiting. Can be fatal in elderly

Influenza virus Flu virus causes headaches, fever, aching joints, cough sneezing. Can be fatal in old and sick

Chickenpox virus Spread by direct contact. Itchy rash and can give headache and fever. Not fatal

Athletes Foot fungus Fungus causes cracked skin between toes which can be painful and bleed

How infection develops

History and microbes

Louis Pasteur (1822-95)

• Proved decay was caused by microbes in the air

• Said if microbes got in body, they would cause disease, so need to prevent their entry

Joseph Lister (1827-1912)

• Developed ideas of antibiotics which are solutions that kill microbes (e.g. Dettol)

• Lister was a surgeon and he sprayed his instruments with carbolic acid, and this reduced infection after operations

Alexander Fleming (1881-1955)

• Left an agar plate out which had bacteria growing on it, and a mould grew which caused bacteria around it to die.

• The mould was producing penicillin and during the Second World War this

Microbe enters the body through nose, mouth or break in the skin

Microbe uses our body for warmth, food, and moisture, and reproduce rapidly (incubation period)

Microbes produce waste products which are toxins

High levels of toxins make you feel unwell. Different toxins cause different symptoms which doctors can use to

diagnose the disease

Resistance to antibiotics

• Antibiotics do not kill viruses

• Some bacteria have developed resistance and so the antibiotics do not kill them.

• Mutation occurs in some bacteria which gives them resistance to the antibiotic

• When antibiotics are given, all the bacteria are killed except those that are resistant

• The bacteria that remain pass on the gene for this resistance.

• Eventually all the bacteria are resistant

Changes over the last 20 years

• Doctors only prescribe antibiotics when really necessary

• Patients are encouraged to complete their course of antibiotics to kill the bacteria before resistance can fully develop.

Useful bacteria

Products from bacteria:

Yoghurt Cheese Vinegar Silage Compost

Yoghurt (all equipment must be sterile)

1. Milk is pasteurised (heated to 71.10C for 15-20s (kills 99% of bacteria)

2. Incubation- bacteria multiply using milk as food

3. Making the yoghurt- lactobacillus bacteria break down lactose in the milk into lactic acid, which converts the milk into yoghurt. Sample of yoghurt taken for quality control and added to next batch.

4. Flavouring and packing- colours and flavourings are added and product is marketed

Cheese

• Cheese is made by causing milk to curdle (by adding enzymes and bacteria such as lactobacillus) into solid curd and liquid whey

• Contains protein, calcium and vitamins

We are not all bad though!!

Vinegar

• Vinegar is produced by acidifying wine, cider, or beer, to produce wine vinegar etc.

• Production of vinegar uses bacteria such as Acetobacter

Silage

• Silage- winter cattle food which is made from vegetation which is broken down by fermentation, or anaerobic respiration in a silo.

• Lactobacillus is added to speed the process up.

Compost

• Compost- important in organic farming. Remains of animals and plants are digested by bacteria and fungi to form nutrient-rich soils. Harvest remains are allowed to rot down silage ready to put on soil next year.

Brewing

Wine made from grapes, beer and lagers from malted wheat, and cider from apples

Step Process Explanation1 malting This happens in beer- and larger making. The barley

seeds start to germinate (grow), which converts the starch stored in the seeds to sugar

2 Extracting the sugar The plant material is either crushed or soaked in water to get the sugar out

3 flavouring Wines get their flavour from the fruit juice used, beers from the hops used (female flowers of the hop plant Humulus lupulus)

4 Adding yeast The container is sealed to prevent air and microbes entering. The yeast can respire aerobically for a short time, until the oxygen in the container is used up. This gives the yeast a chance of reproducing. The liquid is kept warm

5 fermentation The culture quickly becomes anaerobic and the yeast starts to produce alcohol. If there is too much oxygen vinegar. Process happens in large stainless steel containers at a temperature of 25- 300C. This temperature produces the best rate of alcohol production and the best flavour

6 Extracting the wine and beer

After fermentation is over, the liquid is separated from the yeast cells (yeast usually sinks to the bottom), and liquid is filtered so clearer

7 Pasteurising and packaging/bottling

The product is heated and cooled quickly to kill microbes to give a longer shelf life in bottles

Fermentation is the anaerobic respiration reaction that occurs in yeast cells

Glucose (sugar) ethanol (alcohol) + Carbon Dioxide

C6H12O6 2C2H5OH +2CO2

Making alcohol stronger

There is a limit to concentration of alcohol produced by brewing. When the concentration is too high, it becomes toxic and destroys the yeast in the fermenter. Some yeasts can tolerate more alcohol than others- which results in drinks with different alcohol contents (Beers and lagers- 3-5% alcohol, Wines- 11-12% alcohol)

Spirits- Vodka and Whiskey contain high levels of alcohol (40%)

Rum- made from Sugar Cane, Whiskey-made from malted Barley,

Vodka- made using Potatoes

After the fermentation process the liquid is distilled. This is done by placing it in a large container (or a ‘still’) and heating it. Alcohol boils at 800C, lower than the boiling point of water. Alcohol therefore rises up the column as a vapour, leaving the water behind. This alcohol passes along a collecting arm where it is cooled.

Biofuels

These are fuels that are from biological materials e.g. trees, biogas, and alcohol. When burnt they give up carbon dioxide but the trees grown for the fuel, takes the gas in and so balances it.

Advantages of biofuels Disadvantages of biofuelsReduces fossil fuel consumption Habitat loss as large areas are needed to grow

treesNo overall increase in levels of greenhouse gases

Habitat loss extinction of species

Burning biogas and alcohol does not produce smoke

Biofuels transfer less energy

Small scale biogas production

Remote areas use biogas digesters. Large tank is sunk into the ground and organic material like dead plants and animal waste is put in. Bacteria digest the waste releasing gas which can be used for cooking.

Larger scale production- produced commercially in large anaerobic tanks at a temperature of 32-350C. Biogas is used in vehicles, to generate electricity, and for heating systems.

Bioethanol- alcohol is produced on a large scale from plant material by yeasts . Bioalcohol can be used as a fuel in vehicles (mixed with petrol gasohol).

Life in the soil

Soil contains

Fragments of rock Air spaces Water Dead material from plants and animals Living organisms

Soil types

Soil type Particle size Air spaces Permeability to waterClay small Few and small Low- water stays in

the soil and so floods easily

Loam Mixture of large and small

Many and vary in size Medium- retention is good

Sand large Many and large Poor- little water is retained, it passes through

Testing for soil constituents

Soil constituent How to test a soil sample for itmoisture Weigh, bake, reweighhumus Weigh, burn, reweighair Weigh sample and measure the volume

Soil as a habitat

Organisms need water and oxygen and this varies in soil. Clay soil- few air spaces and loads of water, sandy soil- large air spaces but water drains away, loam soil- mixtures of particle size so are air spaces and some water retention.

Humus (decomposed dead material) can be added to soil improve aeration and water retention.

Soils vary in pH- heathers like acidic soil, most plants like neutral pH. Farmers add lime to neutralise acidic soils.

Worms- Neutralise acidic soils, mix the soil, improve nutrient content of the soil, aerate the soil, reducing chances of flooding.

Life in the water

Advantages-

Buoyancy- even a blue whale cane be supported Removal of animal waste Steady temperature- water has a high specific heat capacity so takes a lot of heat to

raise its temperature Ready water supply

Disadvantages

Movement-water is denser than air so more energy required to move through it Water balance- as water is everywhere it is a problem to balance the amount of

water in the body

Water regulation-

In fresh water, too much water can enter the body by osmosis (not problem in plants as cell walls prevent further expansion and more water getting in), but excess water must be removed from animals.

Freshwater fish urinate frequently

Microscopic organisms have a contractile vacuole into which excess water goes, and from here the water is released at the surface of the cell.

Sea water - Sea water is salty and affects osmosis. Many invertebrates have bodies at the same concentration of sea water no

problem

Larger fish do not so they actively get rid of salt in the water they drink

Aquatic food webs

Phytoplankton- are the microscopic producers of the sea

Zooplankton- are small animal- like organisms and they are consumers

Plankton is affected by seasonal factors

Seasonal changes of phytoplankton affect zooplankton numbers as they feed on these producers

In deep water, food webs do not start with phytoplankton as there is no light

Food chains rely on dead food falling from above- called detrital chains

Other chains start with bacteria- producers get their energy from a chemical process called chemosynthesis

Water pollution

Ways in which water is polluted

Eutrophication

Fertilisers are washed in water and causes algal overgrowth which stops light getting to plants deeper in the water. These plants die, and the bacteria that bring about their decay use up the oxygen in the water- eutrophication

Indicators of pollution-

Presence of Indicator Species

e.g.

• pH changes in streams and bogs can be indicated by a reduction in the number of amphibians

• Rat-tailed maggots present where there are reduced oxygen levels

Bioaccumulation- build-up of chemicals in the food webs

• Chemicals such as PCBs and DDT can be up to toxic levels in the food chains

• These chemical have built up in the bodies of killer whales and PCB has resulted in a suppression of their immune system and their numbers decreased (some people were eating the whale meat).

Enzymes

Use of enzymes in industry is called enzymes technology

Invertase (sucrase)- is an enzyme that is used to break down sucrose into glucose and fructose. These are sweeter, and fructose is so less is needed to make things taste sweeter, therefore used in low calorie products. This enzyme is used in the food industry to make slimming foods taste sweeter.

Biological cleaning powders- use of enzymes to

Digest stains

Digest fibres in the dirt, releasing bobbles

Allow stain removal to happen at a lower temperature which saves energy and money

Disadvantages of biological washing powders

Not work at high temperatures as enzymes are denatured

Not work in some parts of the country where water is alkaline or acidic

May cause allergies (people then use non-biological washing powder)

Enzymes in medicine

• Reagent strips contain enzymes which allow diabetics to test their glucose levels. Normal blood glucose levels 4-8mmol/l and it can rise in diabetics and cause damage to blood vessels in organ like eyes.

• Lack of the enzyme lactase- people lacking this enzyme cannot digest a sugar in milk called lactose, so bacteria in their gut does and causes wind and diarrhoea. These people can get lactose-free foods.

Immobilised enzymes- they are attached to inert substances like fibre mesh, or inside gel beads to stabilise them.

Producing gel beads-

enzymes are mixed with a solution sodium alginate the mixture is dropped into calcium chloride solution which caused small beads of

alginate bead to form The enzymes are now inside the alginate beads

Advantages of immobilised enzymes

• Beads are easier to use than free enzymes

• Beads support the structure of the enzyme making them less sensitive to heat and changes in pH.

• Enzyme can be removed from the reaction mixture by filtering out the beads, so the solution is not contaminated with enzymes.

• For lactose intolerant people- Beads containing immobilised lactase enzymes can be mixed with foods such as milk. The lactase digests lactose into glucose and galactose which can be absorbed into the gut.

Genetic engineering

• Biotechnology- using microorganisms in industry

• Genetic engineering- introduce a gene from organism (the donor) into another organism (the host)

• Transgenic bacteria- bacteria which have genes inserted into their DNA from other organisms.

• Examples of products made by gene tic engineering- Insulin and Human Growth Hormone

Steps in genetic engineering

• Identify the gene in the donor that codes for a particular organism

• Remove the gene from the DNA of the donor cell (human cell)

• Introduce the gene into the DNA of the host organism (bacterium)

• Grow the bacterium on a large scale and the introduced gene will make the bacterium produce the require protein e.g. insulin

Assaying techniques are required to check that the bacteria have taken up the human insulin gene into their plasmid.

Assaying-

The transgenic bacteria are grown on agar with coloured dye. The human gene had been introduced into the plasmid along with along gene which

codes for an enzyme which caused the dye in the agar to turn blue. If the human gene and the gene that codes for the enzyme are both taken up by the

bacteria, the human insulin gene damages the colour-change enzyme gene. The agar will not turn blue (they are the bacteria that are required, they are selected and cloned).

If the human gene is not present, the coloured change enzyme will turn the agar blue.

Genetically modified organisms

Organisms that have been genetically modified-

• Pesticide resistance in plants

• Frost resistance in fruit

• Increased shelf life in fruit

• Increased milk yield in cattle

Putting genes into DNA

• Restriction enzymes make a staggered cut in DNA leaving unpaired bases that make ‘sticky ends’

• A gene is cut using the same restriction ends so that it also has sticky ends, and the gene will easily fit into the vector’ cut DNA.

• The enzyme DNA ligase the DNA incorporating the gene into it.

DNA fingerprinting

• A DNA fingerprint is an image of certain parts of a person’s DNA

• All people even identical twins have a unique DNA sequence as over time there are mutations in their DNA so it will not be identical.

Making a DNA fingerprint-

• Sample of human tissue is collected (hair, blood, skin, hair, semen), and DNA is extracted

• DNA is cut into fragments using restrictions enzymes

• As people have different DNA the enzymes cut the DNA in different places so they will be different lengths

• These DNA fragments are separated using a kind of chromatography called electrophoresis where they are separated according to their size (smaller ones travel further).

• Visible bands are produced on a gel

• To make the bands visible a radioactive probe is added which attaches to the DNA which can detected on film.

• This film shows a series of black and white bands called an autoradiograph.

• It is possible to store DNA fingerprints on computer records for future reference

• Many people are concerned about this as they say it is an invasion of privacy if they have their DNA taken and they have done nothing wrong.