Topic 1- Cell Biology

Eukaryotic- cells that are complex and include all animal and plant cells.

Prokaryotic- cells that are smaller and simpler e.g. bacteria.

Eukaryotes are organisms made up of eukaryotic cells and a prokaryote is a prokaryotic cell (single-celled organism).

• Nucleus-has genetic material that controls the cell
• Mitochondria- where aerobic respiration takes place, respiration transfers energy that the cell needs to work.
• Cytoplasm- gel-like substance where chemical reactions take place. Contains enzymes that control chemical reactions.
• Cell membrane- holds the cell together and controls what goes in and out.
• Ribosomes- where proteins are made in the cell.

Has everything the animal cell has but a few extra things as well.

• Rigid cell wall made of cellulose supports the cell and strengthens it.
• Chloroplasts- where photosynthesis occurs. Contains chlorophyll which is a green substance that absorbs light needed for photosynthesis.

• Bacteria are prokaryotes 
• They don't have a nucleus but just a single circular strand of DNA.
• They may contain one or more small ring of DNA called plasmids.
• Bacteria don't have chloroplasts or mitochondria.

Light microscopes use light and lenses to form an image.

Electron microscopes use electrons and have a higher magnification then light microscopes.

Formula for magnification is MAGNIFICATION= IMAGE SIZE/REAL SIZE

PREPARATION OF SLIDE

1. Add a drop of water to the middle of a clean slide.

2. Cut up an onion and separate it into layers. Use tweezers to peel of epidermal tissue.

3. Place the epidermal tissue into the water on the slide.

4. Add a drop of iodine solution, it will create a stain and highlight objects in a cell.

5. Place a coverslip on top and try not to get any airdrops in there as it will obstruct your view.

USING THE LIGHT MICROSCOPE

1. Clip the slide onto the stage.

2. Select the lowest powered objective lens.

3. Use the coarse adjustment knob to get it to the lens.

4. Look down the eyepiece and get the object into focus.

5. Then draw what you see.

Differentiation is the process of a cell changing to become specialized.

In animal cells, this ability is lost in the early stages of the organism developing and they all become specialized. However, in plant cells, they don't lose this ability.

It is mainly used for repairing and replacing cells.

Sperm cells are specialized for reproduction.

1. It has a long tail and a streamlined head to help it swim to the egg.

2. Lots of mitochondria they're to help provide the energy needed.

3. It carries enzymes in its head to digest through the egg cell membrane.

Nerve cells are specialized for rapid signalling

1. Its function is to carry electrical signals from one place to the next.

2. The cells are long and have branched connections to connect to other cells and form a network through the body.

Muscle Cells

• Its function is to contract quickly.
  
• The cells are long and contain lots of mitochondria to generate the energy needed.

Root Hair Cells

• These are cells on the surface of the plant which grow into long hairs and stick out of the soil.
• This gives the plant a big surface area for absorbing water and mineral ions from the soil.

Phloem and Xylem Cells

• They form phloem and xylem tubes which transport substances such as food and water around plants.
• They are long and joined end to end.
• Xylem cells are hollow and phloem has few subcellular structures so that stuff can flow through.

These are Undifferentiated cells that can turn into any cell depending on what they are told.

Found in early human embryos and in adults but only in places like bone marrow.

Adult stem cells can't turn into whatever they want only certain ones like blood cells.

They can be cloned in a lab to be made to differentiate into specialised cells for research or medicine.

Adult stem cells are used to replace faulty blood cells and embryonic stem cells could be used to produce insulin-producing cells to stop diabetes or nerves cells for people who are paralysed...

In therapeutic cloning, an embryo is given the same genetic information and so stem cells would not be rejected by the body.

There are risks of the cells being contaminated and giving the patient a virus and making them sicker.

Some people think you should not use human embryos as you are killing a potential human life. Others think curing people who are already suffering is more important than the embryo. A convincing argument is that these are normally embryos that are unwanted and will be destroyed anyway by the fertility clinics.

In some countries, stem cell researched is banned but not in the UK as long as it follows strict guidelines.

In plants stem cells are found in meristems and can differentiate into any type of cell.

These stem cells are used to produce clones of the whole plant quickly and cheaply. Also can be used to grow more rare plants to prevent extinction.

Also grow entire crops with desirable features like disease resistance.

Within the nucleus, it contains genetic material in the form of chromosomes. They are coiled up lengths of DNA molecules. Each chromo carries a large number of genes which control different characteristics e.g. hair colour.

Each body cell normally has 2 copies of each chromo one from each parent.

Human has 23 pairs of chromos.

We use mitosis to grow or replace damaged cells.

To perform mitosis you first need to grow the number of subcellular structures and replicate its DNA.

What happens in mitosis:

• The chromos line up and cell fibres pull them apart. The two arms of the chromos go to opposite ends of the cell.
  
• Membranes form around the chromos. Thes become the nuclei.
  
• Finally the cytoplasm and cell membrane divide.
• Now it's created 2 sister cells that are identical with the same DNA.

How it works:

• The circular DNA and plasmids replicate.
• The cell gets bigger and the circular DNA moves to opposite ends of the cell.
• The cytoplasms begin to divides and new cell walls form.
• The cytoplasm divides and 2 daughter cells are produced. Each one has a copy of the circular DNA but variable amounts of plasmids.

FOR PROKARYOTIC CELLS

Root Hair Cell

Millions of microscopic hair give the plant a large surface area for absorbing water and mineral ions from the soil.

plants need mineral ions for healthy growth 

the concentration of minerals is usually higher in root hair cell than in the soil around them

Active Transport

minerals should move out of the root if followed rules of diffusion this method is active transport this allows the plant to absorb minerals from a dilute solution against a concentration gradient essential for growth but active transport needs energy and respiration to work. active transport also happens in humans glucose from the gut and from kidney tubules.

active transport is used in the gut when concentration is lower of nutrients in the gut but a higher concentration of nutrients in the blood

Villi provide a really big surface area

the small intestine is covered in tiny little projections called VILLI

a single layer of surface cells, a very good blood supply to assist quick absorption

Structure of leaves lets gases diffuse in and out of cells

underneath leaf is an exchange surface covered in little diddy holes called stoma which carbon dioxide diffuses through

oxygen ( produced in photosynthesis) water vapour also diffuse out of the stoma

water vapour also evaporates from the cells of the leaf. 

Gills have a large surface area for gas exchange 

gills are the gas exchange surface in fish

water(containing oxygen) enters through the mouth and passes through the gills oxygen then diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water. Gills are made up of tiny thin plates called gill filaments these have a big surface area for exchange gases. Gill filament is covered in tiny structures called Lamellae which increase surface area even more.LAMELLAE lots of blood capillaries to speed up diffusion, thin surface layer of cells to minimise the distance the gases have to diffuse. Blood flows from the lamellae in one direction and water flows over in the opposite direction. a large concentration gradient between water and the blood.concentration of oxygen in water is always higher than that in the blood so as much oxygen diffuses from water to the blood 

containing oxygen 

DNA - Deoxyribonucleic acid.

it is the chemical that the genetic material in a cell is made up from.

what is in our DNA this determines what inherited characteristic we have

DNA is found in the nucleus of animal and plant cells called long structures called chromosomes

Chromosomes come in pairs

DNA is a polymer made up of two strands coiled together in the shape of a double helix.

A gene is a small section of DNA found in a chromosome.

Each gene codes for(tell the cell to make) a particular sequence of amino acids which are put together to make a specific protein

only 20 amino acids are used but there are thousands of different proteins

Genes simply tell cells in what order to put the amino acids.

DNA determines what proteins cells produces eg haemoglobin, keratin

in turn determines type of cell eg red blood cell, a skin cell.

Every Organism has a Genome

Genome - the entire set of genetic material in an organism

understanding the human genome an important tool for science and medicine for many reasons

It allows the scientists to identify any genes in the genome linked to different types of disease

DNA is made up of Nucleotides

DNA strands are polymers made up of lots of repeating units called nucleotides

Each nucleotide consists of one sugar molecule, one phosphate molecule and one base

The sugar and phosphate molecules in the nucleotides form a backbone to DNA strands the sugar and phosphate molecules alternate one in four different bases A T C or G joins to each sugar

Each base links to a base on the opposite strand to the helix

An always pairs up with T and C always pairs up with G

Its the order of bases in a gene that decides the order of amino acids in a protein

mRNA Carries The Code to the Ribosomes

To make the proteins ribosomes use the code in the DNA DNA is found in the nucleus of the cell and can't move out of it because it is really big. A cell needs the code from the DNA to the ribosome

This is done using the molecule mRNA made by copying the code from the DNA.the mRNA is the messenger between and DNA and the ribosome it carries the code between the two the correct amino acids are brought to ribosomes in the correct order by carrier molecules

Mutations are Changes to the Genetic Code

A mutation is a random change in an organisms DNA. Sometimes it can be inherited

Mutations occur continuously

Most mutations have very little or no effect on the protein 

some mutations can seriously affect a protein

Mutation in non-coding DNA it can alter how genes are expressed

There are different types of Mutation

Insertions are where a new base is inserted into the DNA base sequence where it should be

Deletions are when a random base is deleted from the DNA base sequence

Substitutions mutations are when a random base in the DNA base sequence is changed to a different base

Sexual Reproduction Produces Genetically Different Cells

SEXUAL REPRODUCTION involves the fusion of male and female gametes.

Because there are two parents the offspring contain  a mixture of their parents' genes

In ASEXUAL REPRODUCTION there is only one parent. there is no fusion of gametes no mixing or chromosomes and no genetic variation between parent and offspring they are genetically identical to the parent they're clones

Gametes are Produced by Meiosis

Meiosis produces cells which have half the normal number of chromosomes

before the cell starts to divide it duplicates its genetics 

Sexual reproduction has its advantages over asexual reproduction:

• Variation increases the chance of a species surviving a change in environment. While the change would kill a few individuals, the offspring will be able to survive in the new environment. Survival advantage.
• There more likely to breed successfully and pass the genes on. This is known as natural selection.

But asexual reproduction has advantages over sexual reproduction.

• One parent.
• Its faster than sexual reproduction.
• Many identical offspring can be reproduced in favourable conditions.

Some organisms can reproduce by both methods.

Malarial parasites:

• Malaria is caused by a parasite that is spread by mosquitoes. 
• The parasite reproduces sexually when it's in the mosquito and asexually when it's in the human host.

Fungi

• Many species of fungi can reproduce both asexually and sexually.
• They do this by realising spores which become new fungi. Spores produce sexually and asexually.

Plants

• Lots of species of plants produce seeds sexually but can reproduce asexually.

Density is a measure of compactness

• It relates the mass of a substance to how much space it takes up 

• The internal energy of a system is total energy that is particles have in their kinetic and potential energy stores
• Heating the system transfers energy to its particles increasing the internal energy
• A change in state occurs if the substance is heated enough 

A change of state conserves mass

• A change of state is a physical change 
• The number of particles don't change 

A change in pressure can cause a change in volume

•  The pressure of gas causes a net outwards force

Doing work on gas can increase its temperature

• If you transfer energy by applying force then you do work Doing work on a gas increases its internal energy which can increase its temperature

Developing the model of the atom

The total mass and atomic numbers must be equal on both sides

Alpha decay decreases the charge and mass of the nucleus

• Alpha particles are made up of two protons and two neutrons It is atomic number reduces by 2 and its mass number reduces by 4

Beta decay increases the charge of the nucleus

• When beta decay occurs a neutron in the nucleus turns into a proton
• The number of protons in the nucleus has increased by 1 this increases the positive change of the nucleus the atomic number

Gamma rays don't change the charge or mass of the nucleus

• Getting rid of excess energy from a nucleus 
• There is no change to the atomic mass or atomic number of the atom

Alpha particles are helium nuclei

• They don't penetrate very far and are stopped quickly travel a few cms in the air and absorbed by a sheet of paper
• They are strongly ionising 
• Alpha radiation is used in smoke detectors

Beta particles are high-speed electrons

• Virtually no mass and a charge of 1 
  
• Moderately ionising 
•  penetrate moderately range of a few metres they are absorbed by a sheet of aluminium
• Beta emitters are used to test the thickness of sheet metal 

Gamma rays are em rays with a short wavelength

• Penetrate far into materials will travel a long distance through the air
• They are weakly ionising 
• They can be absorbed by thick sheets of lead or metres of concrete
  

Background Radiation Comes From Many Sources

• Background radiation is the low-level radiation around us all the time 
• Naturally occurring unstable isotopes
• Radiation from space known as cosmic rays these come mostly from the Sun
• Radiation due to human activity eg fallout from nuclear explosions or nuclear waste

Exposure to Radiation is called Irradiation

• This simply means they're exposed to it  
• Irradiating something does not make it radioactive
• Keeping sources in lead line boxes standing behind barriers or being in a different room are all ways of reducing irradiation

Contamination is radioactive particles getting onto objects

• These contaminating atoms might decay releasing radiation 
• Gloves and tongs should be used when handling sources and protective suits

Exposure to some sources can be more harmful than others 

• Beta and gamma sources are most dangerous 
• Inside the body, alpha sources are most dangerous because they do all their damage in a very localised area

Gamma sources are usually used in medical tracers

• Isotopes which are taken into the body like this are usually gamma emitters so that the radiation passes out of the body without causing much ionisation this has a short half-life

Radiotherapy treating cancer with radiation

• High doses of ionising radiation will kill all living cells it can be used to treat cancers
  
• Gamma rays are directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells

There are risks to using radiation

• Lower doses tend to cause minor damage without killing cells  this can give rise to mutant cells which divide uncontrollably this is cancer
• Higher doses tend to kill cells completely 

Nuclear fission splitting a large unstable nucleus

• The nucleus has to absorb a neutron before it will split
• The atom splits it forms two new lighter elements 
• Two or three neutrons are also released when an atom splits theses neutrons are moving slowly so they can cause more fission to occur this is a chain reaction
• Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion 

Nuclear fusion joining small nuclei

• Two light nuclei collide at a high speed and join to create a larger heavier nucleus
• This heavier nucleus does not have as much mass as the two separate light nuclei did
  
• Fusion releases a lot of energy 

Contact and Non-Contact Forces

• Forces are very quantity vector quantities have a magnitude and a direction
• Lots of physical quantities are vector quantities
• Vector quantities force,velocity,displacement,acceleration,momentum etc
• Some physical quantities only have magnitude and no direction
• Scalar quantities speed,distance,mass,temperature,time, 
• Vectors are usually represented by an arrow 

Forces can be contact or non-contact

• A force is a push or a pull on an object
• When two objects have to be touching for a force to act that force is called contact force 
  
• Friction,air resistance,tension ropes,normal contact force
• If objects do not need to be touching the force is a non-contact force
• magnetic force,gravitational force,electrostatic force

Gravitational force is a force of attraction between masses

• On the surface of a planet, it makes all things fall towards the ground
• It gives everything a weight

Weight and mass are not the same

• Mass is just amount of stuff is an object this will have the same value anywhere in the universe
• Weight is the force acting on an object due to gravity 
• Weight measured using a calibrated spring balance or newton meter
• Mass is not a force it is measured in kilograms with mass balance 

Mass and weight are directly proportional

• If you have a number of forces acting at a single point you can replace them with a single force
• This single force is called the resultant force

When a force moves an object through a distance ENERGY IS TRANSFERRED and WORK IS DONE on the object

You can find out how much work has been done using

One joule of work is done when a force of newton causes an object to move a distance of one metre

• If all of the forces acting on an object combine to give a resultant force of zero the object is an equilibrium
• Not all forces act horizontally or vertically some act at awkward angles
• To make these easier to deal with they can split into two components at right angles to each other usually vertical and horizontal

Stretching Compressing or Bending Transfers Energy

• To do this you need more than one force acting on the object
• Work is done when force stretches or compresses energy elastic potential energy
• If it is elastically deformed All this energy is transferred to the objects elastic potential energy store

Elastic Deformation

• An object has been elastically deformed if it can go back  original shape and length after the force has been removed
  

Inelastic Deformation

• An object has been inelastically deformed if it doesn't return to its original shape and length after the force has been removed

• The extension of a stretched spring directly proportional to the load force applied 
• equation 
• The spring constant k depends on the material a stiffer spring has a greater spring constant
• The equation works for compression 
• There is a maximum force above which showing that extension is no longer proportional to the force
• This is known as the limit of proportionality

A force or several forces can cause an object to rotate

The turning effect of a force is called its moment

The size of moment of force is given by (book)

Levers increase the distance from the pivot at which the force is applied this means less force is needed to get the same moment

Gears are circular discs with teeth around edges 

They are used to transmit the rotational effect of a force from one place to another

Different sized gears can be used to change the moment A force transmitted to a larger gear will cause a bigger moment as the distance to the pivot is greater

Pressure is the force per unit area

• So this means the particles exert a pressure
• A pressure of a fluid means a force is exerted normal to any surface in contact with the fluid
• Pressure book

The pressure in a liquid depends on depth and density

• Density is a measure of the compactness of a substance for a given liquid the density is uniform and it doesn't vary with shape or size
• The denser a given liquid is more particles it has in a certain space more particles that are able to collide so the pressure is higher
• As the depth of the liquid increases the number of particles above that point increase 
• The pressure at a certain depth due to the column of liquid above using a book

The pressure of the fluid exerts a force on it from every direction

Pressure increases with the depth the force exerted on the bottom of the object is larger than the force acting on the top

Causes a resultant force known as upthrust

Upthrust is equal to the weight of the fluid that has been displaced 

Upthrust equal to the weight of the object when the forces are balance and the object floats 

If an object weight is more than the upthrust the object sinks

Depends on its density

The atmosphere is a layer of air that surrounds earth it is then compared to the size of the earth

Atmospheric pressure is created on a surface by air molecules colliding with the surface

As the attitude increases atmospheric pressure decreases

As the altitude increases the atmosphere gets less dense so there are fewer air molecules 

Also fewer air molecules above a surface as the height increase weight of the air above decreases the altitude 

Distance is scalar displacement is a vector

• Distance is just how far an object has moved
• Displacement measures the distance and direction in a straight line from an object starting point to its finishing point 

Speed and velocity are both how fast you're going

There is usually a typical speed that each object travels at 

everyday objects 

, A person walking  1.5 m/s          A car 25m,s

                                                      A train 55m/s

                                                          A plane 250m/s

  A person running    3m/s

  A person cycling     5 m/s

Acceleration is the change in velocity in a certain amount of time 

Constant acceleration is sometimes called uniform acceleration

The equation for uniform acceleration 

If an object has no force it will always slow down and stop because of friction 

Friction always acts in the opposite direction to the movement

Drag is the resistance you get in a fluid Air resistance is a type of drag it is the frictional force produced by air acting on moving the object

Keeping the shape of the object streamlined where the object is designed to allow fluid to flow easily across it reducing drag

Drag increase as speed increase

Objects falling through fluids reach a terminal velocity

As speed increases the friction builds up 

This gradually reduces the acceleration until eventually, the frictional force is equal to the accelerating 

It  will have reached maximum speed or terminal velocity and will fall at a steady

Terminal velocity depends on shape and area

The accelerating force acting on all falling objects is gravity

Air resistance causes things to fall at different speeds and the terminal velocity of an object is determined by its drag in comparison to its weight 

Frictional force depends on its shape and area

THINK OF SKYDIVER

Newtons First Law says that a resultant is needed to make something start moving speed up or slow down

If the resultant force on a stationary object is zero the object will remain stationary. If the resultant force on a moving object is zero it will just carry on moving at the same velocity same speed and direction

A non zero resultant force will always produce acceleration in the direction of the force

This acceleration can take five different forms starting stopping speeding up slowing down and changing direction

Acceleration is proportional to the resultant force 

• The larger the resultant force acting on an object the more the object accelerates 
• An object with a larger mass will accelerate less than one smaller mass
•  The useful formula that describes Newtons Second Law is:

Inertia the tendency for the motion to remain unchanged

• An object inertial mass measures how difficult it is to change the velocity of an object
• Inertial mass can be found using newton second law 

Newtons third law interaction pairs are equal and opposite

• Newtons Third Law says 
• When two objects interact the forces they exert on each other are equal and opposite
• If you push something to say a shopping trolley will push back against you just as hard 
  

Stopping distance is the sum of two distances

• The longer it takes to perform an emergency stop the higher risk of crashing into whatever in front
• Is found by Stopping Distance= Thinking Distance +Braking Distance
• The thinking  distance how far the car travels during the driver's reaction time
• The breaking distance the distance taken to stop under a breaking force 

Many factors affect total stopping distance

• Thinking distance affected by your speed, your reaction time 
• Can be affected by tiredness drugs or alcohol
• Distractions can affect your ability to react
• Braking Distance is affected by Your speed, the weather or road surface
• condition of tyres
• how good your brakes are

Breaking relies on friction between the brakes and wheels

• The work done transfers energy from the kinetic energy of the wheels to the thermal energy stores of the brakes increase the temperature
• The faster a vehicle is going the more energy it has in its kinetic store so more work needs to be done to stop it 
• A larger braking force means a larger deceleration

Speed affects braking distance 

• As a car speeds up the thinking distance increases at the same rate as a speed
• Braking distance, however, increases faster the more you speed up the work done to stop the car is equal to the energy in the cars kinetic energy store
  

It is a property that all moving objects have

The greater the mass of an object or the greater its velocity the more the momentum the object has

We can work out the momentum of an object using 

In a closed system, the total momentum before an event is the same as after the event. This is called conservation of momentum

The force causing the change is equal to the rate of momentum

A larger force means a faster change of momentum

Likewise, if someone momentum changes very quickly like in  a car crash the forces on the body will be very large and more likely to cause injury

The longer it takes for a change in momentum the smaller the rate of change of momentum and so the smaller the force 

Cars have many safety features such as - CRUMPLE ZONES crumple on impact increasing the time taken for the wearer to stop

Seat Belts stretch on impact increasing the time taken for the wearer to stop

Waves transfer energy in the direction they are travelling

The particles of the medium oscillate and transfer energy between each other. BUT overall the articles stay in place only energy is transferred

Waves have amplitude wavelength and frequency

The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed position

The wavelength is the distance between the same point on two adjacent waves

Frequency is the number of complete waves passing a certain point per second Frequency is measured in hertz

In transverse waves, the oscillations are perpendicular to the direction of energy transfer

Most waves are transverse including

All electromagnetic waves ie flight

Ripples and waves in water

A wave on a string

Longitudinal waves have parallel vibrations

The oscillations are parallel to the direction of energy transfer

Other examples are soundwaves -ultrasound

Shockwaves-some seismic waves

All waves can be absorbed transmitted or reflected

Absorbed by the material the wave is trying to cross into -transfers energy to the materials energy stores

Transmitted - the waves carry on travelling through the new material leads to refraction

One simple rule to learn for all reflected waves

The angle of incidence is the angle between the reflected wave and the normal 

The normal is an imaginary line that perpendicular to the surface at the point of incidence

Refraction waves changing direction at a boundary

• How much its refracted by depends on how much the wave speeds up or slows down which usually depends on the density of two materials
• Crosses a boundary and slows down it will bend towards the normal.
• It crosses into a material and speeds up it will bend away from the normal
• Frequency stays the same 
• Travelling along the normal it will change speed but it's NOT refracted
• The optical density how quickly light can travel through, higher the optical density the slower light waves travel through it

• All EM waves transverse waves that transfer energy from a source to an absorber
• EM waves travel at the same speed through air or a vacuum
• They're grouped together into seven basic types based on the wavelength and frequency
• EM waves are made up of oscillating electric and magnetic fields
• Alternating currents are made up of oscillating charges 
• A frequency of the waves equal to the frequency of the alternating current

• All EM waves transverse waves that transfer energy from a source to an absorber
• EM waves travel at the same speed through air or a vacuum
• They're grouped together into seven basic types based on the wavelength and frequency
• EM waves are made up of oscillating electric and magnetic fields
• Alternating currents are made up of oscillating charges 
• A frequency of the waves equal to the frequency of the alternating current
• Produce radio waves using an alternating current oscillate to create the radio waves is called a transmitter
• Radio waves reach a receiver the radio waves are absorbed
• Energy transferred by the waves is transferred to electrons 
• Causes the electron to oscillate
•  Same frequency as the radio waves that generated it 

Radio waves are used mainly for communication

• Longwave radio waves can be transmitted from London and received halfway around the world
  
• Diffract bend around the curved surface of the earth
• Shortwave radio signals are reflected from the ionosphere
• Bluetooth uses shortwave radio waves to send data over short  distances

Microwaves are used by satellites

• For satellite TV signal from a transmitter is transmitted into space
• The satellite transmits the signal back to Earth in a different direction 
• There is a slight time to delay between the signal being sent and received because of long distance 

Microwaves ovens use a different wavelength from satellites

• Microwaves penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food
• Water molecules then transfer this energy to the rest of the molecules in the food by heating 

Infrared radiation can be used to monitor the temperature

• Infrared is given out by all objects

Or increase it 

Absorbing IR radiation causes objects to get hotter

Fibre optic cable uses visible light to transmit data

• Optical fibres are thin glass or plastic fibres that can carry data
• As pulses of visible light
• Work because of reflection .light rays are bounced back and forth
• Light is not easily absorbed or scattered as it travels along a fibre

Ultraviolet radiation 

• Fluorescence is a property of certain chemicals where ultraviolet UV radiation is absorbed and then visible light emitted 
• Fluorescence lights generate UV radiation and re-emitted as visible light by a layer of phosphorus

Xrays and gamma rays are used in medicine

The effects of each type of radiation are based on how much energy the wave transfers

Low-frequency waves like radio waves pass through soft tissue without being absorbed

High-frequency waves like UV Xrays and gamma rays all transfer lots of energy so can cause lots of damage

UV radiation damage surface cells lead to sunburn and cause the skin to age prematurely some serious effects are blindness and an increased risk of skin cancer

Xrays and gamma rays are types of ionising radiation cause gene mutation or cell destruction and cancer

Radiation dose measured in sieverts is a measure of the risk of harm 

Not a measure of the total amount of radiation that has been absorbed

Risk depends on the total amount of radiation absorbed and how harmful the type of radiation is 

Often see doses in millisieverts where 1000 mSv= 1Sv

Risk can be different for different parts of the body 

• A convex lens bulges outwards it causes rays of light parallel to the axis to be brought together converge at the principal focus
• A concave lens caves inwards
• It causes rays of light parallel to the axis to spread diverge
• Axis of a lens is a line passing through the middle lens
• The principal focus of a convex lens is where rays are hitting the lens parallel to the axis all meet
• The principal focus of a concave lens is the point
• where rays hitting the lens parallel to the axis appear to all come from 
• There is a principal focus on each side of the lens distance from the centre of the lens to the principal focus is called the focal length

There are three rules of refraction in a convex lens

• An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
• The incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
  
• Incident rays passing through the centre of the lens carries on in the same direction

Three rules for refraction in a concave lens

• Incident rays parallel to the axis refracts through the lens and travels in line with the principal focus
• The incident ray passing through the lens towards the principal focus refracts through the lens and travel parallel  to the axis
  
• The incident ray passing through the centre of the lens carries on in the same direction

A lens can produce real and virtual images

• Real images are where the light from an object comes together to form an image on a screen 
• A virtual image is when the rays are diverging so the light from the object appears to be coming from a completely different place 
• Through the magnifying lens
• To describe an image properly you need to say 3 things
• How big it is compared to the object 
• Whether its upright or inverted upside down relative to the object 
• Whether is real or virtual

• Colour filters are used to filter out different wavelengths of light
• A primary colour filter only transmits that colour 
• If you look at a blue object through a blue colour filter look blue Blue light is reflected from objects surface and is transmitted by the filter
• Filters that arent for primary colours let through both the wavelengths of light for that colour AND the wavelengths of the primary colours that can add together to make that colour

All objects are continually emitting and absorbing infrared {IR} radiation

• The hotter an object is the more infrared radiation it radiates in a given time
• An object that's hotter than its surroundings emits more IR radiation than it absorbs as it cools down the object that is cooler than its surroundings absorbs more IRradiation than it emits as it warms up
• Objects at a constant temperature emit infrared radiation at the same rate that they are absorbing it

A perfect black body is an object that absorbs all of the radiation that hits it No radiation is reflected or transmitted

• Black bodies are the best possible emitters of radiation All objects emit electromagnetic EM radiation due to the energy in their thermal energy stores This radiation isn't just in the infrared it covers a range of wavelengths and frequencies
• The intensity and distribution of the wavelengths emitted by an object depend on the objects temperature Intensity is the power per unit area
• As the temperature of an object increases the intensity of every emitted wavelength increases
• Intensity increases more rapidly for shorter wavelengths causes the peak wavelength to decrease