Physics - EDEXCEL IGCSE - Finished

So that's all there is to IGCSE Physics. Once again now all you have to do is learn these notes, memorise them and then you're done.

Good luck in your exams!

PS. I've attached a complete copy in case you're too lazy to read it from the blog (it has a mighty 32 pages).

Click Here

Physics - EDEXCEL IGCSE - Radioactivity and Particles

Section 7 - Radioactivity and Particles:

Atomic number - the number of protons in the nucleus

Mass number - the number of protons and neutrons in the nucleus

Alpha, beta and gamma rays are all radiation that damages cells (ionises) and is emitted from unstable (full) nuclei.

Alpha - this type of radiation contains 2 neutrons and 2 protons which make it essentially the helium nucleus. This is the weakness type of radiation and cannot even penetrate paper.

Beta - this type of radiation contains only electrons created when a neutron turns into a proton and electron. This is stronger than the alpha radiation but cannot penetrate anything above aluminium.

Gamma - this type of radiation is part of the electromagnetic spectrum. It is very strong but cannot penetrate lead.

Alpha = -2 atomic number, -4 mass number

Beta = +1 atomic number, -1 neutron number, -0 mass number

Gamma = N/A

Uranium (Atomic number of 92, mass number of 235) —> Thorium (Atomic number of 90, mass number of 231) + alpha (atomic number of 2, mass number of 4)

Carbon (Atomic number of 6, mass number of 14) —> Nitrogen (atomic number of 7, mass number of 14) + beta (atomic number of 0, mass number of 0)

Radiation:

Ionising radiation imprints on camera film.

The Geiger-Muller detector beeps in the presence of radiation.

Background Radiation Examples:

• Radon gas in the ground.
• Cosmic rays
• Food and drink
• Buildings
• Boron in the soil
• Medical instruments.

The radiation from a radioactive source will decrease over time. The half-life is the time taken for the radiation to decrease by a half. It is different for different sources of radiation.

Uses of radiation:

1. Tracers - a radioactive source is put into a system such as a piping network. It will then build up at the blockage and can then be detected to tell people where the fault is.
2. Medical tracers - these are similar to the normal tracer except that these are put int a body. The radioactive source builds up, for example, at a blocked blood vessel and doctors will then know where to operate on.
3. Radiotherapy - radiation is used to target cancer cells.
4. Carbon dating - the amount of radiation is measured and carbon’s half-life is used to date the object.

Dangers of radiation:

Radiation can damage the structure of the cells DNA, when these damaged cells replicate, cancerous tissue may form. Therefore, some radiation is said to be carcinogenic. It damaged cells and tissues by changing their atomic structure, thereby causing them to stop functioning properly.

Radioactive waste can poison waters, destroy ecosystems and cause widespread harm to nature.

Experiment involving the alpha particles:

Rutherford designed an experiment which his two assistants Geiger and Marsden carried out.

Geiger and Marsden beamed alpha particles at a gold foil. They expected the particles to go straight through the gold foil. However, they found, rather surprisingly, that a few went through but emerged at a bent angle, some even got deflected. Using this surprising result, Rutherford formed out present day view of atoms. This new model explained why the positive alpha particles were sometimes repelled and why the faster they went the faster they were repelled.

Nuclear fission:

The nucleus of a uranium-235 atom can be split through fission whereby a neutron is fired at the uranium. This splits the uranium nuclei into 2, leaving 2 ‘daughter nuclei’ and some neutrons. These neutrons are then used to cause a chain reaction through hitting other uranium nuclei.

In nuclear fission, control rods are used to absorb neutrons to prevent there being too many of them. If there were too many neutrons then the reaction would get out of hand.

A moderator is also used. This is usually water and is used to slow the neutrons down enough to be able to hit the nuclei at the right speed.

Physics - EDEXCEL IGCSE - Magnetism and Electromagnetism

Section 6 - Magnetism and Electromagnetism:

Magnetically hard material - retains its magnetism for a long time. It is also hard to demagnetize.

Magnetically soft material - loses its magnetism almost as soon as it leaves the magnetic field.

Magnetic field lines represent the direction (through the direction of the lines) and magnitude (through the density of lines) of a magnetic field on a single North Pole.  

The three pictures above show the magnetic field lines present in the presence of bar magnets.

The two pictures shown to the left show the magnetic field lines of a straight wire and a solenoid. The direction of the magnetic field lines can be shown by using the right-hand grip rule shown on the first picture to the left.

A coil of wire carrying current acts like a magnet and as such has filed lines as shown to the left. 

The way to test for the magnetic field lines and its direction is by using a compass. The compass will point always in the direction of the magnetic field line. You can then draw dots at the end points of the compass and connect the dots to show the magnetic field lines.

To increase the strength of the magnetism you can:

1. Increase current
2. Increase the number of coils in the wire
3. Adding a magnetic soft material in the solenoid

An electromagnet is created by wrapping a soft magnetic material with a current carrying wire. These are then used in relays and circuit breakers.

How do Electric Motors work:

1. A wire in a magnetic field feels a force and so turns.
2. This turns the split ring commutator.
3. The commutator reverses the current every half turn.
4. The wire continues to spin until the current is switched off.

How do Loud Speakers work:

1. A wire is pushed forwards and then moves back and forwards hundreds of times a second.
2. This pushes the cone / diaphragm.
3. Noise is created.

These both work because of the motor effect. When there is a magnetic field and current then a force will be created. Fleming’s left-hand rule is used to see which direction the force is in.

The picture below shows Fleming’s left-hand rule:

The motor effect can be increased by:

1. Increasing the amount of coils, the magnetic field strength or current strength.
2. Add a magnetically soft material in the centre.

Moving a wire back and forth across a field will induce a voltage.

Ways to increase the voltage are to increase the field strength, quicken the movement or increase the number of coils in the wire.

How do transformers work:

1. An AC current passes through a coil wrapped around a soft iron core (electro-magnet).
2. This induces a magnetic field.
3. The magnetic field makes a second wire move back and forth, creating voltage.

Step up transformers - this has fewer turns in the first wire compared to the second thereby creating a higher voltage and lower current as the output.

Step down transformers - this has more turns in the first wire compared to the second thereby creating a lower voltage and higher current as the output.

How is this used:

Transformers are used to change the voltage and current of electricity. Below shows one example of how transformers are used to deliver electricity to our homes safely:

power plant —> step up transformer (to avoid heat from high current) —> power lines —> step down transformer —> distribution lines —> homes

input (primary) voltage / output (secondary) voltage = primary turns / secondary turns

Vp * Ip = Vs * Is

primary voltage * primary current = secondary voltage * secondary current

The above only occurs, however, if the transformer is 100% efficient

Physics - EDEXCEL IGCSE - Solids Liquids and Gases

Section 5 - Solids, Liquids, and Gases:

This is one of the simplest sections. As such there is only a small amount of information that you need to know.

p = m / v

density = mass / volume

p  = F / A

pressure = force / area

The pressure at a point in gas or liquid at rest acts equally in all directions.

p = h * p * g

pressure difference = height * density * gravitational field strength

Particles within a liquid have random motion within a closely packed irregular structure.

Particles within a solid vibrate about a fixed position within a closely packed regular structure.

Brownian Motion - this is the principle that particles move randomly about a space and that when particles collide they exert a pressure on a surface.

Kelvin:

We are all familiar with the celsius and Fahrenheit scales which are used to measure temperature. In science, another scale called the kelvin scale is also used. The scale starts at the lowest temperature possible in the universe.

There is an absolute lowest temperature of -273ºC

This is where particles have no energy at all and, therefore, are not moving at all.

0 kelvin = -273ºC

higher temperatures means higher pressure.

pressure₁ / kelvin₁ = pressure₂ / kelvin₂

pressure₁  * volume₁ = pressure₂ * volume₂

Physics - EDEXCEL IGCSE - Energy Resources and Transfer

Section 4 - Energy resources and transfer:

Examples of energy transfer:

• Chemical energy (in food) —> Kinetic energy (in muscles)
• Electrical energy (in circuits) —> Heat energy (from heat leakage from excess current)
• Kinetic energy (in muscles) —> Sound energy (from voice box)
• Elastic potential energy (in taught string) —> Kinetic energy (when string is relaxed)
• Chemical energy (battery) —> Light energy (from phone screen)

Energy is never lost but transferred, this is the principle of conservation of energy.

Energy Efficiency:

Energy efficiency = useful energy output / total energy input

The energy efficiency can be shown by using a Sankey diagram as below: 

The above Sankey diagram shows a light bulb. Its energy efficiency is 0.1 as it loses most of its energy through heat.

Energy can be transferred through conduction (transferred through touch), radiation (infrared) and convection whereby particles with energy rise allowing others to fill the space. If the source of energy continues the convection will continue and repeat. Convection is responsible for the distribution of heat energy. An insulator is bad at conducting so insulating buildings will stop heat energy from conducting away.

W = f * d

work done = force * distance moved in the direction of the force

Work done is also equal to energy transferred.

GPE = m * g * h

gravitational potential energy = mass * gravity field strength * height

KE = 0.5 * m * v²

kinetic energy = 0.5 * mass * velocity * velocity

p = W / t

power = work done / time taken

Energy production:

The following three methods all use natural processes to generate energy. The advantage with this is that it is green and renewable. However, they produce generally less energy and also cause visual pollution 

• wind —> turns turbine —> runs generator —> creates electrical energy
• water —> turns turbine —> runs generator —> creates electrical energy
• geothermal reserves —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

The next two methods also use natural processes. However, these two rely on the weather. They again produce relatively less energy and can cause visual pollution 

• solar heating system —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy
• solar cells —> converter changes sunlight into electricity—> creates electrical energy

The next is probably the most common method of production energy. However, it causes pollution and is non-renewable. It does produce relatively more energy, though.

• fossil fuels —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

This final one is probably the most dangerous method and produces toxic nuclear waste. However, it produces large amounts of energy and is technically renewable.

• uranium —> nuclear fission —> heats water to make steam —> turns turbine —> runs generator —> creates electrical energy

Physics - EDEXCEL IGCSE - Waves

Waves:

Properties of waves:

Transverse waves - One which the vibrations are perpendicular to the direction of travel of the wave. e.g. a slinky jerked sideways, rope, water, the electromagnetic spectrum.

Longitudinal waves - One which the vibrations are parallel to the direction of the wave. e.g. sound waves, slinky jerked along its length. 

Time period = time / number of waves in that time

Frequency = 1 / time period

Wave velocity = frequency * wavelength

Waves transfer energy and information without movement of matter.

Wave behaviour:

Reflection - this is where a wave hits a surface and bounces back. The angle of incidence (angle at which the wave hits the surface) must be the same as the angle of reflection (the angle at which it  bounces back)

Refraction - this occurs as wavelength decreases when a wave goes from a less dense to a denser material. The light bends to the normal or away if from a dense to rare material. The way to calculate the angle of refraction is through the formula:

n₁ * sini = n₂ * sinr

where n = refractive index (speed of light / speed in material)

Diffraction - when waves move past an obstacle or through a gap it spreads out. This is called diffraction. Diffraction is largest when the gap is the same size as the wavelength.

The Electro-Magnetic Spectrum:

In order of increasing frequency and decreasing wavelength:

radio waves —> microwaves —> infrared —> light —> ultraviolet —> X-ray —> gamma rays

Uses:

• Radio waves - used in broadcasting and communications. Also used to transmit radio and TV.
• Microwaves - used in cooking and satellite transmissions.
• Infrared - used in heaters, optical fibre communication, remote controls and light vision.
• Light - used in optical fibres and photography.
• Ultraviolet - used in sunbeams, fluorescent lights, and security coding of bank notes.
• X-ray - used to produce internal structures of objects and materials. Used in medicine and security.
• Gamma rays - used for sterilisation and killing cancer cells.

Dangers:

• Microwaves - can cause internal heating of body tissue.
• Infrared - causes burning of skin if under the presence for too long.
• Ultraviolet - causes changes to surface cells, blindness and skin cancer.
• Gamma rays and X-ray - changes the DNA of cells and causes cancer and mutations.

Light:

Light waves are transverse waves that can be reflected, refracted and diffracted.

Examiners often like to ask for a part of the ray diagram to be drawn, drawing it similar to this will get you full marks on that question.

In an exam, the paper may ask to work out the real or apparent depth of an object in water, here is the formula to work it out:

real depth / apparent depth = n (the refractive index of the dense material)

Measuring the refractive index of glass:

1. Place a glass block on paper and draw around it.
2. Mark the normal and draw a few different angles of incidence.
3. Send the light rays along the angle and draw the emerging rays from the block.
4. Connect the ray and measure the angle of refraction.
5. Draw a graph of sini and sinr with sini on the y-axis and sing on the x-axis.
6. The gradient of the graph will be the refractive index.

Critical angle - the angle of incidence where the refractive angle is 90º. The equation to work it out is:

n₁ * sinc = n₂

Where n₁ is the refractive index of the denser material, c the critical angle, and n₂ is the refractive index of the rarer material.

Total Internal Reflection - this occurs when the angle of incidence is large than the critical angle when this happens the light reflects and does not refract. This principle is used in bike reflectors and fibre optic cables which are used in communication and endoscopy.

Sound:

Sound waves are longitudinal waves that can be reflected, refracted and diffracted.

Sound waves move through the vibrations of particles in the air. These vibrations are carried. However, although energy is transferred, matter is not.

The human range of hearing is 20Hz to 20,000Hz.

The Speed of sound is around 340m/s in air. This can be tested by performing the following experiment:

1. Measure the distance between 2 places.
2. Have a sound be made at one end.
3. As soon as the sound is made start a stopwatch.
4. When you hear it return stop the stopwatch.
5. The distance the sound travels divided by the time taken will give the speed.

Sound waves can be displayed by using a microphone to detect sounds and then feeding the information gained from it into an oscilloscope which displays the sound wave.

Pitch is controlled by the frequency of the sound wave.

Loudness is controlled by the amplitude of the sound wave.

Analogue and Digital:

Analogue - varies continuously in amplitude

Digital - only two different states exist - on or off

Advantages of digital:

• Less likely to be corrupted by noise as it is harder for the data to be changed by noise since it can only be either 1 or 0.
• Can be restored to its original form relatively simply.
• No loss of quality in amplification while in analogue signals it is very easy for noise to also be amplified therefore decreasing the quality.
• Can be stored in small memory and is processed very quickly by processors.
• More information can be carried by multiplexing.

Physics - EDEXCEL IGCSE - Electricity

Section 2 - Electricity 

V = I * R

voltage = current * resistance

p = I * V

power = current * voltage

e = I * V * t

energy transferred = current * voltage * time taken

I = Q * t

current = charge * time taken

V = J / Q

voltage = joules / charge

mains supply = AC (alternating current) whereby the current is inverted very rapidly.

cell/battery = DC (direct current) whereby the current is always in one direction.

RMS (root mean square) = is a way to convert from peak voltage to shown voltage. The equation is:

RMS = peak AC voltage / √2

The following three graphs show the relationship between current and voltage.

As the voltage on a resistor increases, the current increases directly proportional to the voltage.

As the voltage on a filament lamp increases, the current increases but decelerates. This is because as current increases so does heat, the extra heat causes the atoms in the filament lamp to vibrate more, this creates more resistance thereby meaning less current can pass.

The current of a diode only increases when a certain set amount of voltage has been reached. After this point, current increases directly proportional to voltage. 

Benefits of series and parallel circuits :

Series:

• Energy efficient
• Less wiring

Parallel:

• Practical (can be independently controlled)
• If one part of the circuit was to break the entire circuit would not.
• Each closed loop would always receive the same amount of voltage so if for example, a lamp was added in parallel, all the lamps would remain bright while in a series circuit it would dim.

LDR = as light decreases so does the resistance

Thermistor = as heat decreases so does the resistance

The mains supply is 230V (RMS) with a peak voltage of 325V. Because of this, it is very dangerous if the mains charge is transferred to humans. Therefore, mains plugs have many safety features.

Safety features of mains plugs:

1. The body is made of plastic, a good insulator.
2. There is an earth pin to stop the plug from becoming charged. The earth pin is longer than the others so that it is always the first to make and the last to be broken.
3. The cable is clamped to stop the wire from being pulled out.
4. When there is no earth pin double insulation is used. This is where a layer of non-conductive material is wrapped around the body to stop it becoming charged.
5. A fuse is placed on the live wire. When there is high current, enough temperature is created to melt the fuse, which breaks the circuit causing it to stop working.

Mains plugs wire colours:

• live - brown
• neutral - blue
• earth - green and yellow

Physics - EDEXCEL IGCSE - Forces and Motion

Section 1 - Forces and Motion

average speed = distance moved / time taken

acceleration = change in velocity / time taken

Force - a push or pull of one body on another.

Examples of forces are:

• Applied force - transferred from a person or object to another. e.g. a man pushing a door.
• Gravitational force - a force caused by the attraction between objects by gravity.
• Normal force - when an object is in contact with another. e.g. a cup on a table.
• Friction force - when an object moves across a surface. e.g. a car driving.
• Air resistance - when an object travels through the air. e.g. a plane flying.
• Tension force - when an object is pulled in opposite directions.
• Spring force - when a compressed or stretched spring returns to its inert state.
• Electrical force - an attraction between oppositely charged objects.
• Magnetic force - an attraction caused by magnets.
• Upthrust force - buoyancy. e.g. the lift on a plane.

Vectors - something with both magnitude and direction. e.g. velocity, displacement.

F = MA

force = mass * acceleration 

W = MG

weight = mass * gravitational strength

p = Mv

momentum = mass * velocity

force felt = change in momentum / time taken

Airbags and such increase the time it takes for momentum to reach 0, thereby reducing the force felt.

Centre of mass - the point through which the weight of an object always acts through. 

Stability:

• Stable - the centre of gravity rises and returns to its equilibrium position. e.g. A ball in a bowl.
• Unstable - the centre of gravity falls and moves away from its equilibrium position. e.g. A ball in an inverted bowl.
• Neutral - the centre of gravity remains on the same level. e.g. a ball on a flat plane.

Moments:

Moment = force * perpendicular distance from the pivot

Taking the moment around ‘a’:

The anticlockwise moment = B * 10

The clockwise moment = 200,000 * 5 + 500 * 3

Therefore 10B = 1,001,500Nm

B = 100,150N

A + B = 200,500N

A = 100,350N

Taking the moment around ‘b’:

The clockwise moment =  A * 10

The anticlockwise moment = 200,000 * 5 + 500 * 7

Therefore 10A = 1,003,500Nm

A = 100,350N

A + B = 200,000 + 500

B = 100,150N

You can also take the moment around ‘c’:

Anticlockwise moment = B * (x + 10) + A * x

Clockwise moment = 200,000 * (x + 5) + 500 * (x + 3)

Therefore Ax + 10B + Bx = 1,001,500 + 200,500x

(A + B)x + 10B = 1,001,500 + 200,500x

(A + B - 200,500)x + 10B = 1,001,500

A + B = 200,500N

(0)x + 10B = 1,001,500

B = 100,150N

A = 100,350N

This proves that no matter where you take the moment from the result is always the same.

Stretching materials:

Hooke’s Law - the deformation of a body is directly proportional to the force applied to it, provided that the limit of proportionality is not exceeded.

This is translated into the formula F = kx where F is the force applied, x the extension of the spring and k the spring constant.

The limit of proportionality is the point at which the force and the extension of the spring are no longer proportional.

The elastic limit is the point at which the spring will not return to its original length when the force is removed. 

Elastic behaviour - materials are said to be elastic if they can regain their original size and shape.

Plastic behaviour - materials are said to be plastic if they do not return to their original size and  shape.

Human Biology - EDEXCEL IGCSE - Finished

So that's all there is to IGCSE Human Biology. Once again now all you have to do is learn these notes, memorise them and then you're done.

Good luck in your exams!

PS. I've attached a complete copy in case you're too lazy to read it from the blog (it has a mighty 32 pages).

Click here

Human Biology - EDEXCEL IGCSE - Environment

Environment:

Humans inhabit many of the Earth’s ecosystems. An ecosystem is a distinct, self-supporting system interaction with each other and with their physical environment.

Ecosystems have:

• Producers - green plants that photosynthesise.
• Consumers - animals that eat plants or other animals.
• Decomposers - Microorganisms that break down dead material and help in recycling nutrients.
• Physical environment - the non-biological components such as water, soil and air.

Plants are the source of all the food that animals, including humans, eat. They also create oxygen which aerobic organisms need for respiration. Plants can create from glucose, starch, sugars such as fructose or sucrose, cellulose and lipids.

Photosynthesis:

Carbon Dioxide + Water —> Glucose + Oxygen

Food chains are made up of trophic levels:

Producer —> consumer—> decomposers

Energy and substances are transferred along a food chain. Every time energy is transferred, a large amount of it is lost through the lack of digestion and therefore passes out as faeces. Some form excretory products such as urea and some is respired to release energy. Not only this, but a large amount of energy is also lost through respiration. Because of this, only around 10% of energy is used to create new cells and therefore can be passed on to the next trophic level.

Transfer of energy:

1. Photosynthesis creates glucose.
2. Respiration releases energy from compounds such as glucose.
3. Almost all biology processes use the energy released in respiration.
4. If the energy is used to create new cells then it can be passed on to the next trophic level.
5. If not then once used it will eventually escape as heat.

Food preparation, storage and preservation:

Preparation: cooking food properly to kill any microorganisms present.

Storage:

• Packaging of food to prevent transmission of microorganisms.
• Display before and best before dates to tell you when the food is unsafe to eat.
• Placing cooked and raw food separately.
• Not refreezing after cooking as bacteria will multiply very quickly.
• Food should not be left open to the air on a work surface.

Preservation:

• Salting - bacteria lose water by osmosis and are killed. (e.g.fish, some meats)
• Pickling - food butler in vinegar (ethanoic acid). The low pH inactivates most microorganisms.
• Pasteurisation - 63-65°C for 30 minutes or 71.5°C for 15 seconds (milk)
• Canning - packed in cans, heated, sealed, then finally heats to 105-160°C. (e.g. soup, beans).
• Drying - blowing hot air to remove water (e.g.cereal, grains)
• Freezing - frozen to -10°C rapidly (e.g. meats, prepared meals)
• Irradiation - high energy gamma rays are passed through food (e.g.potatoes, onions)

Water purification:

1. Water is taken from a source.
2. It is then passed through a screen to filter large solid objects such as weeds and other debris.
3. It is pumped to a settling tank for particles to settle. The sludge is removed at intervals and used as fertiliser or in landfill.
4. Pumped to a filter bed where it is sprayed onto it from a revolving arm. It slowly trickles down from sand at the top to stones and gravel at the bottom. Bacteria and fungi among the particles break down any organic matter and protozoa feed on the bacteria, including pathogens.
5. Chlorine is added to kill any remaining pathogens.
6. It is then stored in covered reservoirs which prevent the growth of algae and contaminants from entering.
7. Water is finally pumped to homes.

Air pollution:

Carbon Monoxide:

This is a colourless, odourless and tasteless gas which can cause death by asphyxiation. Haemoglobin bind with this rather than oxygen and so a person may become unconscious if it’s breathed in for a certain time as a result of a lack of oxygen.

Sulfur Dioxide:

This is a major constituent of acid rain which kills plants and also ruins the landscape.

Green House Gases:

These include water vapour, carbon dioxide, nitrous oxide, methane and CFCs (chlorofluorocarbons).

The level of greenhouse gases has risen rapidly in the past 100 years. The increasing burning of fossil fuels such as coal, oil and natural gases as well as petrol and diesel in vehicle engines has led to this. The increasing deforestation also means that the greenhouse gas carbon dioxide is used less in photosynthesis.

The increasing levels of greenhouse gases have resulted in the enhanced greenhouse effect. The normal greenhouse effect is where gases absorb some long wavelength infra-red radiation from the sun and re-emit some as longer wavelength IR. This heats up the surface of the Earth. However, with too much greenhouse gases, global warming has occurred where the earth heats up quicker than it should. This has caused the melting of the ice caps and, therefore, sea level rises, changing ocean currents meaning warm water is redirected to cooler areas, more rainfall in some areas (climate changes), species to become extinct as they cannot adapt fast enough and changes to agricultural practices as some pests become more abundant.

Deforestation:

Each year tens of thousands of hectares of rainforests are cut down. This causes several problems:

• Soil erosion occurs as it is exposed due to lack of a canopy meaning the soil is down or washed away.
• Leeching occurs where minerals are washed out by rain. This occurs as there are no tree roots to hold the soil together.
• Destruction of habitats and reduced biodiversity occurs. Around 50-70% of all species live in rainforests.
• The water cycle is disturbed as trees are an important part of returning water vapour from the soil.
• The balance in atmosphere oxygen and carbon dioxide changes as photosynthesis decreases. This will cause global warming.

Human Biology - EDEXCEL IGCSE - Disease

Disease

The general course of a disease:

1.Infection:

• Droplet infection - coughs, sneezes e.g. cold, influenza
• Drinking contaminated water - e.g. cholera, typhoid
• Eating contaminated food - e.g. polio, salmonella
• Direct contact - skin to skin contact e.g. athlete’s foot, ringworm
• Sexual intercourse - e.g. AIDS, syphilis, chlamydia
• Blood to blood contact - e.g. AIDS, hepatitis B
• Animal vectors - e.g. malaria, sleeping sickness

2. Incubation period:

The time between when a person is infected and when they first show symptoms. This occurs as the pathogen may need time to multiply for the effects to become large enough. It also may need time to reach its destination.

3.Sign:

A disease that can be seen by other people. It can be seen, heard or be measured (e.g. blood sugar). A sign is different from a symptom as a symptom does not have to be visible to other people as it is what the patient experiences.

Endemic disease - a disease that is always present in the population of a particular geographical area.

Epidemic disease - a widespread outbreak of a disease spreading over a large area and many people.

Pandemic disease - a worldwide outbreak of a disease e.g. Swine Flu (2009).

Pathogens:

Viruses:

Structure:

Reproduction:

A virus takes over the host cell and its genetic machinery and uses it to make more virus particles. The host dies after more viruses are reproduced and the viruses then spread to other cells in the body.

Diseases:

Influenza: transmitted through airborne droplets produced when a person sneezes or coughs. Influenza primarily affects the cells in the upper airways of the respiratory system. There is little that can be done to treat the disease although antibiotics can be used to combat the secondary bacterial infections. The disease can, however, be prevented 60-70% of the time through vaccinations. Staying away from infected people also prevents transmission.

Poliomyelitis: this is spread through animal vectors such as flies and also through contaminated water and food. There is no effective treatment but this can be prevented by a vaccine and/or a good hygiene so that flies do not make contact with human sewage or food and drink.

AIDS: this is spread through the HIV virus through sexual intercourse or blood to blood contact. There is no cure or vaccine. It can be prevented by not sharing needles or limiting the number of sexual partners.

Bacteria:

Structure:

Nutrition:

Most bacteria are heterotrophic meaning they live on other organisms and eat organic matter. Saprobes are bacteria that live off dead organic material while heterotrophic parasites are those that cause disease. Some bacteria are also autotrophic meaning they produce their own food through photosynthesis.

Reproduction:

Bacteria reproduce asexually by binary fission. This is where the DNA of a bacterium duplicates creating two daughter bacteria with the same genetic information as the parent bacterium.

Diseases:

• Typhoid: spread through contaminated water containing the bacteria Salmonella Typhi or flies transferring the bacteria from faeces to food. It can be treated with antibiotics such as penicillin and the oral rehydration method is useful in combating the effects. It can be prevented by a vaccine, better sanitization and better hygiene.
• Tuberculosis (TB): this is spread through droplet infection of a bacteria called mycobacterium tuberculosis. Long-term use of antibiotics can treat the illness but it can take up to 15 months to treat it. In that time, the bacteria may become resistant to the antibiotics meaning it will have to constantly be changed. It can be prevented through better standards of living as if people are less crowded then there is less chance of infection. Also, the vaccine BCG can be used although it only works for children.
• Gonorrhoea: spread through sexual intercourse. It can be treated with antibiotics although resistance to them are growing. It is prevented through the use of condoms or through avoiding sexual intercourse with someone infected with the disease.

Fungi:

Diseases:

• Thrush: transmitted through direct contact of the fungus candida Albicans. It is treated with anti-fungal drugs and prevented through a good hygiene.
• Athletes Foot: transmitted through direct contact it can once again be treated with anti-fungal drugs and prevented through a good hygiene.

Parasites:

Schistosomiasis (or Bilharzia): this is spread by the parasite Schistosome.

1. Larvae of the worms are released by freshwater snail.
2. The larvae swim in the water and penetrate the skin of people in the water.
3. The larvae develop in the body to adult worms, living inside the liver, intestine and bladder. They feed of red blood cells.
4. They mate and release eggs which pass out in faeces or urine to infect more snails.

Effects: Schistosomiasis is a long term illness (chronic). Symptoms are generally quite mild although in serious cases symptoms may include fever, chills, diarrhoea, severe rashes and blood in the urine. Organs may also become damaged and the liver, spleen and/or lymph nodes may become enlarged.

Prevention:

1. Treatment with drugs to kill the worms in the body.
2. Killing the freshwater snails through chemicals or introducing natural predators such as crayfish. This interrupts the life cycle.
3. Improving sanitisation also disrupts the cycle as it prevents faeces containing the worms from faeces and urine from entering the rivers and lakes and infecting the snails.
4. Health education needed to inform the villagers about the dangers of going into the river.

Malaria and Typhoid: spread through animal vectors. Malaria parasites are spread by mosquitos while typhoid bacillus is spread through houseflies.

Malaria:

1. Mosquitos feed on an infected person’s sex cells.
2. Fertilisation occurs in female mosquitos. The zygote develops into malarial parasites.
3. Infected mosquitos infect the person.
4. Parasites enter liver cells and change form. They rupture the liver cells, enters the blood stream and infects the red blood cells.
5. The red blood cells burst, releasing more parasites and sex cells.
6. The process repeats.

Prevention:

1. Use of insecticides to kill mosquitos and houseflies.
2. Draining swamps and rubbish dumps where mosquitos and houseflies gather.
3. Use of drugs to target the life cycle of the malarial parasites.
4. Stocking ponds with a fish called Tilapia which feed on mosquito larvae.
5. Using insect repellents, wearing long-sleeved shirts and sleeping under insect nets prevent bites from mosquitos.
6. Improving hygiene and sanitisation.

Defence:

Immunity: immunity can be...

• Natural - created through organic processes.
• Artificial - created through man-made intervention.
• Active - created through an immune response and so is in the long term.
• Passive - created without an immune response. Normally this only happens twice in our lives. First when we receive antibodies across the placenta and second through our mothers in colostrum and breast milk.

Vaccines:

These are a form of an artificial active immunity and works by injecting a person with an “agent” that carries the same antigens as a specific disease-causing microorganism. This can be achieved by injecting…

• An attenuated (weakened) strain of the actual microorganism (e.g. polio, TB and measles)
• Dead microorganisms (e.g. a whooping cough, typhoid)
• A modified toxin of the bacteria (e.g. tetanus)
• Just the antigen (e.g.influenza)
• Harmless bacteria, genetically engineered to carry the antigen of a different disease carrying microorganism.

The Antibody/Antigen reaction:

1. Lymphocytes recognise individual marker chemicals called antigens on the surface of the pathogens.
2. Lymphocytes’ receptor proteins bind with the antigens.
3. When it binds the lymphocytes to divide rapidly, producing millions of the same type of lymphocyte that is capable of recognising the microorganism.
4. Most of this occur with B and T lymphocytes.
5. Most B-lymphocytes begin to produce antibodies which bind with the antigens, causing the pathogens to clump together. This makes it easier for phagocytes to ingest it through phagocytosis where pseudopodia enclose the pathogen. Some antibodies also cause the pathogens to burst apart. Some also develop into memory cells which remain  for a long time and if the cells re-infect, the memory cells will start to reproduce and produce antibodies. Because of these, the secondary immune response is much faster than the primary.
6. T-lymphocytes destroy our own cells. These cells have become infected with a virus or are cancerous. This is done by releasing chemicals that “punch a hole” in the cell or activates a “programmed cell death” that is put into the genetic coding of every cell. Some also become memory cells like B-lymphocytes.

Antibiotics:

• Source - antibiotics such as penicillin are created by fungi. For example, penicillin is excreted by the fungus penicillium.
• Role - bacteria can be stopped by antibiotics. Antibiotics can be both bactericidal where bacteria are killed or bacteriostatic where the bacteria are stopped from multiplying. For example, penicillin and tetracycline are bactericidal while nalidixic acid is bacteriostatic.
• How - penicillin works by weakening cell walls by interfering with the manufacture of bacteria cell wall. Water, therefore, enters through osmosis and bursts the cell. Nalidixic acid interferes with DNA replication meaning bacteria cannot multiply. Tetracycline interfered with protein synthesis meaning no enzymes can be made to control the cell.

Non-pathogenic organisms and their importance:

Non-pathogenic bacteria and fungi are useful to humans because they are decomposers which break down complex organic materials into simple substances. These are then released into the environment. For example, decomposers are used to break down protein into ammonia and then nitrates which are essential for plants.

Decomposers are involved in sewage treatment. Sewage must be treated as they contain pathogenic bacteria which can cause diseases if drunk and also because aerobic bacteria in the water will deplete the amount of oxygen in the water by breaking down the organic material in the sewage. This then causes death to species not adapted to low oxygen levels. The sewage must, therefore, be treated first to remove any organic material.

There are two ways of treating sewage. The percolating (biological) filter method is one of them and works like this:

1. Sewage is screened to remove any large objects and left to stand in a large setting tank to allow other solid material to settle out.
2. The sewage is then pumped through sprinklers rotating over a filter bed. The filter bed contains bacteria, fungi, and protozoa which oxidise any organic material.
3. The treated sewage is discharged into a waterway.

The second method is called the activated sludge method:

1. Sewage is screened and stood in a large settling tank.
2. It is then passed into an aeration tank which when oxygen is pumped in, allows the bacteria to oxidise the organic material.
3. It passes to a sedimentation tank where the activated sludge settles.
4. Some are returned to the aeration tank carrying bacteria. The purified effluent is discharged.

A pit latrine is used in less developed countries and is basically a hole in the ground with a pit underneath containing microorganisms which can break down the urine and faeces.

All these different methods of sewage treatment rely on both aerobic and anaerobic microorganisms. Aerobic microorganisms are used to oxidise any organic matter in the sewage creating an effluent that contains much less organic material and fewer pathogens.

Anaerobic microorganisms are needed to treat the waste sludge that settles in the settling tanks. The microorganisms are placed with the sludge in a fermentation tank and the organic material is converted to biogas, a mixture of methane and carbon dioxide. The biogas can be used as a fuel in electricity generator or for heating. The remaining dry, solid material can be used for fertiliser or disposal of in a landfill site.

Eutrophication occurs when excess minerals such as nitrates and phosphates enter a body of water from sewage or fertilisers. Fertilisers can enter the water through leaching as nitrates and such are washed out of the soil by rain since it dissolves in water. This can also occur through surface run offs. Excess minerals stimulate the growth of algae. An algal bloom will develop and block out the light needed for photosynthesis and are also decomposed as they die. This is done by aerobic bacteria which uses up oxygen in the water. This causes oxygen depletion, causing many fish and plants to die. In severe cases, the water will become anoxic (containing very little oxygen) and become smelly from the gases such as hydrogen sulphide and methane which are released by the bacteria. Only anaerobic bacteria can survive conditions like these.

Human Biology - EDEXCEL IGCSE - Reproduction and Heredity

Reproduction and Heredity

The process of fertilisation involves the fusion of a male and female gamete (sex cell) to produce a single cell called a zygote.

Reproductive System:

Male:

Sperm is stored and created in the testes. During intercourse it travels along the sperm duct in the penis and mixes with secreted liquid from the seminal vesicle to form semen. One ovum is released into the fallopian tube each month and when it is in the tube a sperm can fertilise it.

Female:

Menstruation:

Hormones are very important for this process. First the follicle stimulating hormone (FSH) stimulates the growth of the follicle containing an ovum. At the same time, FSH stimulates the release of oestrogen which begins the re-thickening of the uterus lining and also slows the release of FSH and stimulates the release of LH (luteinising hormone). When LH is at its peak, ovulation occurs where the ovum is shed by the ovary. If sexual intercourse occurs, what is left of the follicle forms a structure called the corpus lute. This releases progesterone which completes the thickening of the uterus walls and inhibits production of FSH and LH, stopping any further ovulation. If the egg is not fertilised then the corpus luteum breaks down and the lining of the uterus is shed through menstruation. Progesterone is also used during pregnancy to stop menstruation. It is produced by the placenta.

Definitions:

• Genes - a small section of DNA that determines a particular feature by instructing cells to produce a particular protein are called genes.
• Alleles - an alternative form of a gene which gives rise to differences in inherited characteristics.
• Dominant - a feature will always have two alleles. If one allele’s characteristic is present while the other is not then it is said to be dominant.
• Recessive - if one allele is dominant then the other is said to be recessive.
• Homozygous - contains two copies of one allele (e.g. TT, aa).
• Heterozygous - contains two different alleles (e.g.Tt, Aa).
• Genotype - describes the alleles each cell has for a certain feature.
• Phenotype - a feature that results from the genotype.
• Codominance - if two alleles are expressed in the same phenotype.
• Diploid cells - cells with chromosomes in homologous pairs are said to be diploid.
• Haploid cells - cells with chromosomes not in a homologous pair is said to be haploid.

Meiosis:

1. Each chromosome in the nucleus duplicates itself.
2. The cell divides into two as in mitosis.
3. The cell divides again to form four cells containing half the number of chromosomes. This results in the formation of genetically different haploid (half the number of chromosomes) cells that are not in homologous pairs.

A zygote is formed when two gametes (sex cells) formed through meiosis fuse to form a cell with a full chromosome count. Following this, mitosis duplicates the cell millions of times to form an embryo.

The embryo in the uterus develops a placenta which not only anchors the embryo to the uterus but also allows the embryo to obtain nutrients such as oxygen and glucose from the mother’s blood. It also allows the embryo to get rid of waste products such as urea and carbon dioxide. An embryo also is enclosed by a membrane called the amnion. This secretes amniotic fluid which protects the embryo from jolts and bumps.

Secondary Sexual Characteristics:

Boys: controlled by testosterone

• Growth of penis and testes.
• Growth of facial and body hair.
• Muscle development.
• Breaking of the voice.

Girls: controlled by oestrogen

• The breast develop.
• Menstruation starts.
• Growth of armpit and pubic hair.

Birth Process:

1. Cervix dilates to allow the baby to pass through. The muscles of the uterus contract strongly and rupture the amnion, allowing the amniotic liquid to escape. This is called the water break.
2. Strong contractions of the uterus push the baby head first through the cervix and vagina.
3. After the birth, the uterus continues to contract to push out the placenta and the amnion. This is called the afterbirth.

Breastfeeding:

Advantages:

• Perfect food for healthy growth of the baby.
• Contains antibodies which protect the baby against infection diseases.
• Forms an emotional bond between the mother and the baby.

Growth and development:

gametes—> zygote—> embryo—> foetus—> baby—> child —> adolescent —> puberty—> adult

Contraception:

Hormonal - oral contraceptive pill such as the combined pill (oestrogen and progesterone) or the mini pill (progesterone). The mini pill creates a thickening of the mucus in the cervix which acts as the barrier and the combined pill prevents the production of FSH and LH, preventing menstruation. Its advantage is that it has a low failure rate however it must be taken every day and at a certain time.

Barrier - uses a barrier to prevent sperm from reaching the ovum. Examples include the condom and femidom. The advantages are that they are easy to obtain and use and that they also protect against STI. However, they may slip off during intercourse.

Natural - withdrawal from intercourse or having intercourse during a “safe period” is easy however there is a high failure rate and women will also have to have a regular cycle and will need to keep track of it.

Inter-uterine - an IUD (inter-uterine device) or coil is inserted through the cervix into the uterus. It is a piece of plastic or copper that prevents a fertilised egg from implanting in the uterus. Its main advantage is that it has no effect on intercourse however it does have to be fitted by a doctor and cause heavy periods.

Sterilisation - a surgical process that prevents sperm from passing to the penis or eggs from passing to the uterus. In men, it is called a vasectomy and is where the sperm ducts are cut and tied under general anaesthetic. In women, a similar process occurs in the fallopian tubes and is called tubal ligations. Its advantage is that it has a very low failure rate while its disadvantages are that it is non-reversible and that it has to be performed by a doctor.

The nucleus of a cell contains chromosomes which contain DNA. A small section of DNA that determines a particular feature by instructing cells to produce a particular protein are called genes. In humans, the diploid number of chromosomes is 46 and the haploid number is 23.

ABO blood groups are determined by multiple alleles (more than two alleles) with each allele determining which antigens are on red blood cells. The alleles are: I^A, I^B, I^O

 I^A and I^B are codominant and I^O is recessive to both.

To show patterns of inheritance we often s a genetic diagram called a pedigree.

The sex of a person is determined by a pair of chromosomes, XY in a male and XX in a female. The overall ratio of male and female births is 1:1

This can be shown by this diagram:

There are certain diseases which are sex-linked. This means that they exist on the X chromosome and means that often boys are more susceptible to them. An example of this is a blood disorder called haemophilia. The allele for this is recessive and is “h”. It is only found on the X chromosome. A woman with the gene X^HX^h would not have haemophilia but would be a carrier.

A carrier female and a healthy male have a 25% chance of a having a haemophiliac boy but no chance of a haemophiliac girl.

Another example of a sex-linked disease is red-green colour blindness.

The offspring formed through intercourse vary genetically because of the huge variation in sex cells. It is also because of the random nature of fertilisation where over a billion different sperms can fertilise one of the thousands of ova

Variation can be produced both by genes and by the environment. e.g. body mass, height, skin colour, intelligence.

Mutations are rare, random genetic changes to the genetic material that can be inherited.

Most mutations are harmful, some are natural and a few are beneficial.

Mutations that are beneficial can cause the mutant organism to increase in population through natural selection. An example of this is in bacteria that have mutated to be resistant to antibiotics. These bacteria live for longer and can, therefore, multiple more.

The chances of mutations can be increased by mutagens. Examples of these are ionising radiation such as ultraviolet light, X-rays and gamma rays and many different chemicals, both natural and man-made (e.g. benzene).