B2 C2 P2

symptoms can be caused by cell damage or by toxins

• the effects that an infection has on the body are called the symtoms.different microrganisms cause differnt symptoms,but they all damage the body in one way or another.the damge is done to the bodys cells
• some microorganisms damge cells directly.for example,malaria parasites invade red blood cells and multiply inside them,eventually making the cells burst open.malaria causes flu-like symptoms
• many infectious microorganisms produce poisons(toxins) that damge cells

mircroorganisms reprodce quickly inside the human body

In the correct conditions (with warmth, moisture, nutrients) bacteria can multiply rapidly. The human body can provide these conditions for bacteria to multiply, for example in a cut. Each bacterium splits into two up to every 20 minutes.So, after one hour a single bacterium could have reproduced to give eight bacteria.

your immune system fights off invading microbes

the role of the immune system is to deal with any infectious microorganisms that enter the body.an immune response always involves white blood cells.

• anything that gets into the body should be picked up straight away by a certain type of white blood cell
• these white blood cells are able to detect things that are 'foreign' to the body,e.g microorganisms
• they then engulf the microbes and digest them
• these white blood cells are non specific-they attack anything that's not meant to be there

antibodies recognise foreign microorganisms

a different group of white blood cells attack specific microoganisms.The second produces antibodies to label microorganisms. Pathogens contain certain chemicals that are foreign to the body. These are called antigens. Each of this group of white blood cell carries a specific type of antibody - a protein with a chemical ‘fit’ to a certain antigen. When a white blood cell with the appropriate antibody meets the antigen, the white blood cell reproduces quickly to make many copies of the antibody that neutralises the pathogen.

some white blood cells stay around in the blood after the original infection has been fought off-these are called memory cells.memory cells can reproduce very quickly if the same antigen eneters the body again.they can prodce loads antibodies and kill off the microoragnisms before you become ill-this is known as immunity

vaccinations use a safe version of a dangerous microorganism

• immunisation involves injecting dead or inactive microorganisms.these still carry the same antigens,which means your body prodces antibodies to attack them -even though the microorganism is harmless
• the body also produces memory cellsthat recognise the antigens of the microorganisms and stay in the blood
• if live microorganisms of the smae type appear after,the memory cells can rapidly mass-produce antibodies to kill them off.
• this normally means you can get rid of the disease causing microorganism before they make you sick

epidemics can be prevented by vaccinating lots of people

• to prevent big outbreaks of disease(called epidemics)a large percentage of the population needs to be vaccinated
• if a significant number of people aren't vaccinated,diseases can spread quickly through them and lots of people will be ill at the same time
• but if most people are vaccinated,even the people who aren't vvaccinated are unlikely to catch the disease because there are fewer people able to pass it on.

vaccines and drugs hae different effects on different people

• vaccines and drugs can never be completely safe for everyone.people can have side effects when using them,but these can be more serious for some people than others.for example 1 in 4 children who have meningitis vaccination develop a painful swelling at the site of the injection
• genetic differences also mean that people react differently to drugs and vaccines.

antimicrobial can inhibit or kill bacteria,fungi and viruses

• they're very useful for clearing up infections that your own immune system is having trouble with.
• antibiotics are a type of antimicrobial that can kill bacteria.
• however,antibiotics don't kill viruses-flu and colds are caused by viruses,so antibiotics can't be used to treat treat them

microorganisms can envolve and become resistant to antimicrobial..

• The main steps in the development of resistance are:

• Random changes or mutations occur in the genes of individual bacterial cells.
• Some mutations protect the bacterial cell from the effects of the antibiotic.
• Bacteria without the mutation die or cannot reproduce with the antibiotic present.
• The resistant bacteria are able to reproduce with less competition from normal bacterial strains.

the more antibiotics used,the bigger the problem of antibiotic resistance becomes.its important that people only use antibiotics when they really need to.also that you take all the antibiotics your doctor prescribes you

drugs are tested first in a laboratory

1. The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.
2. Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.

drugs are then tested on humans in clinical trials

Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check they are safe. The substances are then tested on people with the illness to ensure they are safe and that they work.

In a blind trial, patients don't know if they've been given the drug or a placebo.this is because a patient who knows they;re being treated might feel better for psychological reasons,even if there hasn't really been an improvement.in the same way a patient who knows they're not being treated might not feel better even if they are recovering.blind trials eliminate these effects

in double blind trials,even the scientists carrying out the research dont find out until the end which patients got real drugs and which got placebos.this is so scientists monitoring the patients and analysing the results aren't subconsciously influenced by their knowledge

in open-label trials,both the patients and the research scientists are aware of the treatments that have been used.open label trials are used when you cant mask the treatments being tested,e.g if one is a drug and another is exercise

human trials usually last a very long time,but its important that they do.in some cases it takes a while for a drug to have the effect it was designed for,e.g treating cancer.its also important to find got if a drug has any side effects which may only appear after a long time.

Blood carries oxygen and nutrients to the body’s cells, and waste products away from them. The circulatory system consists of:

• the heart, which is the muscular pump that keeps the blood moving
• the arteries, which carry blood away from the heart.it comes out the heart at high pressure,so artery walls have to be strong elastic.
• the veins, which return blood to the heart.they have a bigger lumen than arteries,to help the blood flow more easily.they also valves to help keep the blood flowing in the right direction
• the capillaries, which are tiny blood vessels that are close to the body’s cells they supply nutrients and oxygen,and take away wastes like CO2

The diagram outlines the circulatory system. To make things clear, oxygenated blood is shown in red, and deoxygenated blood in blue.

your pulse rate can be used to measure your heart rate

• your heart rate is the number of times your heart beats in 1 minute-its measured in BPM(beats per minute)
• your pulse rate is the number of times an artery pulsates in 1 minute

blood is pumped around your your body under pressure

• when your heart muscle contracts,blood is forced out of the heart this increases the pressure of your blood.when your heat muscle relaxes,the heart fills with blood and blood pressure decreases
• you can measure your blood pressure by taking a reading of the pressure of the blood against the wallls of an artery
• blood pressure mesurements have two values,e.g. a person blood value might be witten as "135 over 85".the higher value is the pressure of the blood when the heart contracts,and the lower value is the pressure of the blood when the heart relaxes

a persons heat rate and blood pressure can be sed to check how healthy they are by comparing their measurements agaisnst "normal" measurements. normal measurements are usually given as a range of values beacuse individuals vary

high blood pressure increases the risk of heart disease

• the inner lining of an artery is usually smooth and unbroken,but high blood pressure can damge it.
• fatty deposits can sometimes build up in damged areas of ateries-these deposits restrict blood flow and cause the blood pressure in arteries to increase
• if a fatty deposit breaks through the inner lining of an artery,a blood clot may form around it
• the blood clot could block the artery complely,or it could break away and block a different artery
• if a coronary artery becomes completly blocked an area of the heart muscle will be totally cut off from its blood supply,recieving no oxygen.this causes a heart attack
• a heart attack can cause serious damge to the heart or may even cause the death of the heart muscle-which can be fatal.

lifestyle factors can increase the risk of heart disease

• heart disease can often be linked to lifestyle factors,such as what someone eats and how much exercise they do.some people might be more at risk because of their genes too in most people its a condition caused by one or both of these things

poor diet,high blood cholesterol level is linked to eating foods high in saturated fat,e.g. fatty meats and cheese. a diet high in salt also increases the risk of heart disease because it increases blood pressure

stress,if a person is stressed for a long period of time it can increase their blood pressure and so incrase the risk of heart disease

smoking,both carbon monoxide and nicotine,found in cigarette smoke,increases the risk of heart disease.carbon monoxide reduces the amount of oxygen the blood can transport.if heart muscle doesnt recieve enough enough oxygen it can lead to a heart attack.nicotine increases heart rate

misuse of illegal drugs,drugs like ectasy and cannabis can increase heart rate which increases blood pressure.drinking too much alchol has the same effect

regular moderate exercise reduces the risk of developing heart disease.this is because exercise burns fat,preventing it building up in the arteries.exercise also strengthens the heart muscle

heart disease is more common in industrialised counties,such as the UK and USA,that non-industrialised countries.this is mainly because people in these countries can afford a lot of high fat food and often don't need to be very physically active

epidemiological studies can identify possible risk factors

epidemiology is the study of patterns of diseases and the factors that affect them.

epidemiological studies can help identify the lifestyle risk factors.for example,you could study a group of people who all dies from heart disease to look for similarites in their lifestyle that may be linked to heart disease

they can also involve large scale genetics studies to identify the genetic risk factors.for example,you could map the genetic makeup of a large group of people,then see if there are any genetic similarities between the people who are affected by heart disease

homeostasis maintaing a constant internal enviroment

• the conditions inside your body need to be kept steady,even when the eternal enviroment changes.thsi is really important because your cells need the right conditions to funtion properly.
• you have loads of automatic control systems in your body that regulates your internal enviroment-these include both nervous and hormonal communication systems
• all your automatic control systems are made up of three main componets which work together to maintain a steady condition-receptors,processing centres and effectors

negative feedback counteracts changes

your automatic control systems keep your internal enviroment stable using a mechanism called negative feedback.when the level of something(e.g. water or tempreture)gets too high ot too low,your body uses negative feedback to bring it back to normal.

The kidneys maintain our body's water balance by controlling the water concentration of blood plasma. The kidneys also control salt levels and the excretion of urea. Water that is not put back into the blood is excreted in our urine.

Our bodies take in water from food and drinks. We even get some water when we respire by burning glucose to release energy.

We lose water in sweat, faeces, urine and when we breathe out (on a cold day you can see this water as it condenses into vapour).

For the cells of our body to work properly, it is important that their water content is maintained at the correct level. This means our body must maintain a balance between the water we take in and the water we lose. This is done by the kidneys.

your urine isn't always the same

the kidneys balance water levels by producing dilute or concentrated urine.the concentration of the urine depends on the concentration of the blood plasma,which can vary with the external tempreture,exercise level,and the intake of fluids and salt.

External temperature - when it is hot, we sweat more and lose water thereby making the blood plasma more concentrated.this means when its hot the kidneys will reabsord more water back into the blood

Amount of exercise- if we exercise, we get hot and increase our sweating so we lose more water and the blood plasma becomes more concentrated.

• Fluid intake - the more we drink the more we dilute the blood plasma. The kidneys respond by producing more dilute urine to get rid of the excess water.
• Salt intake - salt makes the plasma more concentrated. This makes us thirsty and we drink more water until the excess salt has been excreted by the kidneys.

the concentration of urine is controlled by a hormone

The concentration of our urine is controlled by a hormone called ADH.ADH is produced by the pituitary gland that is situated just below the brain. The pituitary gland monitors the concentration of the blood plasma. It releases ADH into the bloodstream, which travels in the blood to the kidneys.

the whole process of water content regulation is controlled by negative feedback.this means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal

The more concentrated the plasma, the more ADH is released into the blood. When the ADH reaches the kidneys, it causes them to reabsorb more water. This keeps more water in the body and produces more concentrated urine.When the plasma is more dilute, less ADH is released into the bloodstream. This allows more water to leave the kidneys, producing more dilute urine.This method of control is an example of negative feedback.

Alcohol suppresses ADH production. This causes the kidneys to produce more dilute urine. It can lead to dehydration.Ecstasy increases ADH production. This causes the kidneys to reabsorb water. It can result in the body having too much water.

all materials are made up of chemicals

we use a wide range of materials,including metals,ceramics and polymers.absolutly every material is made up of chemicals,either individual chemicals or mixtures of chemicals

some materials are mixtures of chemicals.a mixture contains different substances that are not chemically bonded together.for example,rock salt is a mixture of two compounds-salt and sand

materials from plants-wood and paper are both made from trees.cotton comes from the cotton plant materials from animals-wool comes from sheep. silk is made by the silkworm larve.  leather comes from cows.

we also use man-made(synthetic)materials:  alll rubber used to come frrom the sap of the rubber tree.you can make rubber in a factory.advantage is you can control its properties.alot of clothes are made of man-made fabrics like nylon or polyester you can also control its properties e.g super strecthy.most paints are mixtures of man made chemicals the pigment and stuff that holds it together are designed to be tough and to stop the color fading

different materials have different properties

melting point,most materials that are pure chemicals have a unique melting point.this si the temperature where the solid material turns into liquid.

strength,is how good a material is at resisting a force.you can judge how strong it is by how much force is need to either break it or permanently change its shape(deform it).strength in tension (when pulled) strength in compression (when pushed)

stiffness,a stiff matertrial is good at not bending when force is applied to it.materials like steel are very difficult to bend-they're very stiff   

hardness,the hardness of material is how difficult it is to cut into

density,density is a materials mass per unit volume(e.g/cm3).don't confuse density with mass or weight.objects that are less dense than water will float(like ice). objects that are more dense than water will sink

Many of the products that we use are made using plastics such as polythene and rubbers; and fibres such as cotton. The suitability of a material to a particular job depends on its properties.

• a washing-up bowl may be made from the plastic poly(ethene), commonly called polythene, because this material is waterproof and can be melted and reformed into the desired shape
• a bicycle tyre is made from rubber because it needs to be flexible and tough
• a pair of tights may be made from nylon fibres because these are flexible and elastic.

a products properties depend on the materials itss made from

the effectiveness of a product is how good it is at the job its supposed to do.a products effcetiveness depends on the materials its made from.materials also affect a products dursbilty-how long it would last

you would nees to be able to look at the properties of a material and work out what sort of purposes it might be sutible for e.g clothing fabric musnt be stiff,but need a good tensile strength(so it can be made into fibre) and high flame resistance,especially if its for nightwear or childrens clothes

crude oil is a mixture of hydrocarbons

crude oil is a mixture of hydrocarbons.hydrocarbons are molecules that are made of chains carbon and hydrogen atoms only.these chains are of varying lengths

hydrogen properties change as chain gets longer

as length of the carbon chain changes,the properties of the hydrocarbon change.short chain molecules have lower boiling points-they're often gases.long-chain molecules have high boiling boiling points and can be quite viscous(thick and sticky).its all down to the forces in between hydrocarbons

there are two important bond in crude oil: a) the strong covalent bonds between the carbons and hydrogen's within each hydrocarbon molecule b) the intermolecular forces of attraction between different hydrocarbon molecules in the mixture

the intermolecule forces break a lott more easily in small molecules than they do in bigger molecules.because the intermolecular forces of attraction are much stronger between big molecules.

crude oil is separated by frational distilation

Crude oil is not very useful until it has been processed at an oil refinery. The process of refining involves separating the hydrocarbons into fractions or batches using a technique called fractional distillation.

polymerisation means loads of small molecules linked together

plastics are formed when lots small molecules called monomers join together to make a very long molecule called a polymer.they're usually carbon-based. under high pressure many small molecules"join hands"(polymerise)to form long chains called polymers

there are lots of different types of polymers

polymerisation reactions involving different monomers can be used to make a wide range of polymers.different polymers have different physical properties-some are stronger,some are stretchier.some are more easily moulded,and so on.these physical properties make them suited for different uses

polymers have replaced natural materials for uses

polymers are used as alternatives to traditional materials in loads of applications,for example:synthetic fibres like nylon and polyester are often used to replace cotton,wool and silk fabrics.rigid PVC has largely replaced wood as a material for new window frames

if the polymer chains are packed close together,the material will have a high density.if the polymer chains are spread out,the material will have a low density

polymer chains-Long polymer chains have stronger forces of attraction than shorter ones. By making the chains of a polymer longer, a stronger and less flexible material is produced.

plasticers-Plasticisers are small molecules that can be added to polymers during their manufacture. They push the polymer molecules slightly further apart, weakening the forces between them and making the material softer and more flexible.

cross links-Chemical bonds can be formed to link together the chains of some polymers. These cross-links make the material tougher and less flexible.

the polymer can be more crystalline. a crystalline polymer has straight chains with no branches so the chains can fit close together.crystalline polymers have higher density,are stronger and have a higher melting point

The use and control of tiny matter is called nanotechnology. The tiny matter is referred to as nanoparticles.

These particles are measured in nanometres (nm). A nanometre is one billionth of a metre (0.000 000 001m). Nanotechnology is concerned with the use and control of structures that are 1-100 nanometres in size.

Some of these nanoparticles occur naturally, for example in volcanic ash. Some occur by accident, for example during the combustion of fuels. Many occur by design.

Nanoparticles of a material show different properties compared to larger particles of the same material. Forces of attraction between surfaces can appear to be weak on a larger scale, but on a nanoscale they are strong.

One reason for this is the surface area to volume ratio. In nanoparticles this is very large. Atoms on the surface of a material are often more reactive than those in the centre, so a larger surface area means the material is more reactive.

Nanoparticles are used in products that are currently available.

• sports equipment: nanoparticles are added to materials to make them stronger whilst often being lighter. They have been used in tennis rackets, golf clubs and shoes
• clothing: silver nanoparticles have been added to socks. This stops them from absorbing the smell of sweaty feet as the nanoparticles have antibacterial properties
• healthcare: nanoparticles are used in sunscreens. They offer protection and can be rubbed in so there are no white marks.

Harmful effects

There are some concerns that nanoparticles may be toxic to people. They may be able to enter the brain from the bloodstream and cause harm. Some people think more tests should take place before nanoparticles of a material are used on a wider scale.

light is type of electromagnetic radiation

radiation is just a transfer of energy

visible light(the colours of the rainbow,from red to violet)is just radiation our eyes can detect.radiation that's further along in the'red' direction is called infrared.similarly,radiation that's further along in the 'violet' direction called ultraviolet

electromagnetic radiation transfers energy in 'packets'

all types of EM radiation transfer energy.this energy as photons.a photon is a packet of energy.

some types of EM radion transfer more energy than others

the amount of energy carried by a photon depends on the frequency of the radiation.the frequency,and so photon energy,increases as you go along the EM spectrum.radio wave photons have the lowest frequency and the least energy,and gamma ray photons have the higest frequency and the most energy

EM radiation is emitted from a sourceonce emitted, all types of EM radiation can travel through space.All types of electromagnetic radiation travel at exactly the same speed through a vacuum, 300,000 km/s. (3*10^8)

..and transmitted,reflected or absorbed somewhere else

when radiation is emitted from a source,it spreads out until it reaches some matter(a substance-like air,glass,walls..)three things can happen: 1)the radiation might be transmitted-just keep going,like light passes through glass 2)it could be reflected-bounce back.like light reflected from a mirror 3) or the radiation could be absorbed-like a sunbather UV rays from the sun

objects that absorb radiation are called detectors-or eyes are light detectors for instance

intensity decreases as distant from the source increases

when radiation is absorbed by matter,the photons transfer their energy to the matter.the intensity(or strength) of radiation means how much energy arrives at each square metre of surface per second.the intensity of a beam of radiation decreases with distance from the source because the beam spreads out,the beam gets partially absorbed as it travels.

some EM radiation causes ionisation

when a photon hits an atom or molecule,it sometimes has enough energy to remove an electron and change the atom or molecule.this process ionisation.the changed atoms or molecules can go on to initiate(start) other chemically reactions.it takes a lot of energy to remove an electron from an atom or molecule.so the only types of radiation with high enough photon energy that can cause ionisation-UV,x-rays and gamma rays.some substances(radioactive materials)emit ionising gamma radiation all the time.

ionisation is dangerous if it happens in your cells

The ions produced when ionising radiation breaks up molecules can take part in other chemical reactions. If these chemical reactions are in cells of your body, the cells can die or become cancerous. This is the reason that ionising radiation can be damaging to health.

EM radiation can cause heating

non-ionising radition,e.g light,doesnt have enough energy to change atoms.when its absorbed by a substance it transfers energy tot he atoms or molecules of the substance-and heats them up.

Microwaves are used to heat materials such as food. The water molecules in the material absorb the energy delivered by the microwaves. This makes them vibrate faster, so the material heats up.The heating effect increases if:the intensity of the microwave beam is increasedhe microwave beam is directed onto the material for longer.

So you need to cook food for longer in a less powerful microwave oven. This is why they have power ratings, and food labels recommend different cooking times depending on this.

some people say here are health risks with using microwaves

when you make a call on your mobile,the phone emits microwave radiation.some of this radiation is absorbed by your body,and causes heating of your body tissues.there are concerns that heating tissues like brain and jaw increase the the risk of some medicak conditions,possibly including cancers.

the greenhouse effect helps regulate earths tempreture

Some gases in the Earth’s atmosphere absorb infrared radiation. One of these is carbon dioxide. Even though carbon dioxide is only about 0.04 per cent of the atmosphere, it is a very important greenhouse gas because it absorbs infrared well.

1)The Sun’s rays enter the Earth’s atmosphere 2)Heat is emitted back from the Earth’s surface at a lower principal frequency than that emitted by the Sun 3)Some heat passes back out into space 4)But some heat is absorbed by carbon dioxide, a greenhouse gas, and becomes trapped within the Earth’s atmosphere. The Earth becomes hotter as a result.

Other greenhouse gases are water vapour, and also methane. Even though methane is present in trace (tiny) amounts only, it is a very efficient absorber of infrared.

in part of the atmosphere,there's a gas called ozone which absorbs UV radiation.

1)ozone is a form of oxygen.an ozone molecule is just three oxygen atoms joined together

2) ozone occurs naturally at a certain height in the atmosphere-the 'ozone layer'.its formed:

most of the time,the amount of ozone is constant.but loss of ozone can cause holes in ozone layer.without ozone a lot more UV radiation(from the sun) would reach us here on earth.UV is ionising radiation so it can be harmful,especially to complex organisms.so the ozone layer is very important-it protects us from too much UV radiation.

all the carbon on the earth moves in a big cycle.some of these processes(mainly respiration)return carbon dioxide to the atmosphere as part of the carbon cycle:

respiration in plants and animals. respiration in decompose-rs-all plants and animals contain carbon.when they die decompose rs(bacteria and fungi)break them down.as they do so,they respire and produce carbon dioxide .burning(combustion,e.g trees or coal,also release carbon dioxide into the atmosphere

photosynthesis in green plants and other organisms remove carbon dioxide from the atmosphere.for thousands o years,these processes have all balanced out-carbon dioxide has been removed from the air in approximately equal quantities.so the concentration of carbon dioxide in the atmosphere has been almost constant or thousands of years

For thousands of years, the processes in the carbon cycle were constant, so the percentage of carbon dioxide in the atmosphere did not change. Over the past 200 years, the percentage of carbon dioxide in the atmosphere has increased steadily because humans are:

burning more and more fossil fuels as energy sources

burning large areas of forests to clear land, which means that there is less photosynthesis removing carbon dioxide from the air.

upsetting the greenhouse effect has led to global warming

ever since we started burning fossil fuels in a big way,the level o carbon dioxide in the atmosphere has increased.the global temperature has also risen during this time(global warming).there's a link between concentration of carbon dioxide and global temperature.

scientists use computer models to understand claimate change

the climate is very complicated-conditions in the atmosphere,oceans ad land all effect one anther

a climate model is a great big load of equations linking these various parts o the climate system.the idea is to mimic what goes on in the real climate by doing calculations.climate models can also be used to explain why the climate is changing now.we know that the earths climate varies naturally-changes in our orbit around the sun ice ages,or instance.climate modelling over the last few years has shown that natural changes don't explain the current global warming'-and that increase in greenhouse gases due to human activity is the cause

as the sea gets warmer,it expands,causing sea levels to rise.sea level has risen a little bit over the last 100 years.if it keeps rising it'll be bad news for people living in low-lying places like the Netherlands

higher temperatures also make ice melt.water that's currently 'trapped on land as ice runs into the sea,causing sea level to rise even More

global warming has changed weather patterns in many parts of the world.its thought that ,any regions will suffer more extreme weather because of this,e.g longer hotter droughts.hurricanes from over water that's warmer than 27 degrees- so with more warm water,you'd expect more hurricanes

changing weather patterns also affect food production-some regions are now too dry to grow food,some too wet.this will get worse as temperature increase and weather patterns change more

EM radiation has been used to send information for years-e.g. using light to send signals in morse code.different frequencies are used for different things: infrared-TV remote controls and night vision cameras. microwave-mobile phones and satellite communication.radio-TV ,radio transmissions and radar

radio waves and microwaves are good at transmitting information over long distances.this is because they don't get absorbed by the earths atmosphere as much as most o the spectrum(e.g gamma rays or x-rays).the radio waves used for TV and FM radio transmissions have very short wavelengths compared to most radio waves.microwaves used for mobile phone communications have very long wavelengths compared to most microwaves,but are still titchy compared to radio waves.

infrared and light are used in optical fibres

optical fibres work by bouncing waves off sides of a thin inner core of glass or plastic.the wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end

analogue signals vary but digital is either on or off

the amplitude or frequency of an analogue signal varies continiosly.an analogue signal can take any value in a particular range.digital signals can only take one of a small number of discrete values(usually two),e.g 0 or 1,on or off.the information is carried by switching the EM carrier wave on or off.this creates pulses-short burst of waves,e.g. where 0=off(no pulse) and 1=on(pulse).a digital receiver will decode these pulses to get a copy of the original signal.

both digital and analogue signals weaken as they travel,so they may need to be amplified along their route.they also pick up interference or noise from electrical disturbances or other signals.

noise is less of a problem with digital signals than with analogue.if you receive a noisy digital signal its obvious what its suppose to be.so its easy to clean up the signal so the noise doesn't get amplified.but if you receive a noisy analogue signal,its difficult to know what the original signal would have looked like.and if you amplify a noisy analogue signal,you amplify the noise as well.the amount of information used to store a digital image or sound is measured in bytes.images and sounds will be higher quality when the amount of information stored is higher