Science Sem 1 Year 10
a force is an interaction between two or more objects
it may be attractive or repulsive
it is a push, a pull or a twist
gravity - all objects with a mass are attracted to one another. The bigger the mass, the greater the attraction
electromagnetic - due to charged particles interacting
weak force - a force inside a proton
strong nuclear force - binds protons together in the nucleus
all other forces are just forms of these four
they always come in pairs - every action has an equal opposite reaction (3rd Law)
they can be balanced or unbalanced
an object can continue moving without a force being applied to it - inertia (1st Law)
forces act on an object, they are not a feature of the object
there are both contact and non-contact forces
Contact forces | Non-contact forces |
|---|---|
contact forces are types of forces that result when two interacting objects are perceived to be physically in contact with one another | a non-contact force is a force which acts on an object without physically coming into contact with it |
- frictional forces- tension forces- normal forces- applied forces- air resistance forces | - magnetism- gravity |
if forces in opposite directions are equal then they are balanced - there is no acceleration
the object will stay still (if not moving) or will move with constant speed and direction
if forces in opposite directions are not equal then they are unbalanced - there is acceleration
an object will remain at rest, or remain in motion with constant speed and direction, unless acted on by an unbalanced force
this is often called inertia. inertia is the reluctance of an object to change. the greater the mass, the greater the inertia
If the resultant force is unbalanced, the object will move
How quickly it changes its speed is dependent on the force applied and the mass of the object
F=ma
This relates to inertia. The larger the mass, the more difficult it is to get the object to accelerate
The acceleration of an object is directly proportional to the force applied. The acceleration of an object is also inversely proportional to the mass of an object
E | write down the equation |
|---|---|
V | write down the given values (check for conversion) |
E | enter the values into the equation |
R | calculate the result |
Y | add the (Y)units |
In reality, the acceleration of the object depends on the forces applied. You cannot apply an acceleration to get a force!
a = F/m
For every action there is an equal an opposite reaction
when body A exerts a force on object B, then object B will exert an equal force on A in the opposite direction
Remember: forces are interactions between bodies
Newton’s 3rd Law states that both bodies are always affected in an interaction
Whenever there is an action, there is always a reaction
F(ab) = -F(ba)
Key points
forces always come in pairs. we call these ‘newtonian pairs’
these forces act on different objects( each other). this is why they don’t cancel out
forces are always of the same type, eg. pushing a box on the floor (contact) and the friction on the floor (contact)
the forces are always equal in magnitude but opposite in direction
they have different effects on the objects they are acting on because of Newton’s 2nd Law
We can take Newton’s 2nd Law and apply it to our weight
F(grav) = ma
when we calculate the force due to gravity, the acceleration is called ‘the acceleration due to gravity’ and is given the symbol ‘g’
F(grav) =mg
on earth, g=9.8m/s/s
consider an object falling through a fluid such as air
at first, the object will accelerate due to the gravitational force (its weight)
as the object’s speed increases, the air resistance (reaction force) increases
after a time, the reaction force is equal to the weight. At this point the resultant force on the object becomes 0
Speed is how fast an object moves. It is how much time it takes to cover a certain distance
Speed is distance divided by time: speed = distance/time
Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs and equations
Kinematics is a branch of mechanics
The goal of any study of kinematics is to develop sophisticated mental models that serve to describe (and ultimately, explain) the motion of real-world objects
Scalars | Vectors |
|---|---|
only have a magnitude | have a magnitude and a direction |
- time- distance- volume- speed | - position- displacement- velocity- acceleration- force |
distance: total length of journey travelled
displacement: change in position, most direct route from start to finish
SI units: metres (m)
other units: kilometres (km) (needs to be converted to m)
speed: how far an object travels in a given time interval
average speed: distance travelled along an object’s path divided by the time it takes to travel this distance
average speed = distance travelled / time elapsed
velocity: how far an object has been displaced in a given time interval
average velocity: displacement of an object divided by the time it takes to travel this distance
average velocity = displacement travelled / time elapsed
velocity and speed are very closely related but they are not the same
velocity is the rate of change of displacement
(an object’s speed in a given direction)
v = s/t
where:
v = velocity (m/s)
s = displacement (m)
t = time (s)
Speed | Velocity |
|---|---|
- scalar- how fast something is moving- = distance/time- units: m/s | - vector- speed in a given direction- = displacement/time- units: m/s |
normally, accelerate just means ‘go faster’
in physics, acceleration is the rate at which the speed or velocity of an object changes
a = (v-u)/t
v = final speed
u = initial speed
acceleration is a vector so it has magnitude and direction
the standard unit for acceleration is metres per second per second (m/s/s or m/s^2)
deceleration is just negative acceleration
speeding up (increasing speed)
starting to move from rest (increasing speed from 0)
changing direction of linear motion eg. ball bouncing (changing speed from + to - or vice versa)
slowing down - deceleration
stopping - deceleration
turning a corner (changing direction)
circular motion (changing direction)
speed up
slow down
change direction
car manufacturers are always introducing new safety features in cars such as
seatbelts
collapsible steering wheels
padded dashboards
head restraints
airbags
crumple zones
ABS (anti-lock Braking System
regulators are also reducing the likelihood of major damage by reducing the speed limit in built up areas and mandating that cars have newer safety features
inertia causes your head to keep moving in the direction it was before the crash. After the crash, the car bounces backwards and so does your head
without a properly configured headrest, your neck whips backwards - whiplash
airbags protect you from hard things and to slow down your deceleration
when you hit a wall, or another car or big object, Newton’s 3rd law tells us the other object will push the car back with an equal and opposite force. Airbags slow down the rate of deceleration
the smallest unit of life
all living things are made of cells
most cells are too small to see with the naked eye
cells contain organelles - small structures that perform specific functions and processes to keep cells alive
an organelle that controls the cells activity
the DNA is found in the nucleus
the chromosomes are very long strands of DNA, coiled up like a ball of string
most human cells contain 46 chromosomes but sex cells only contain 23 chromosomes
deoxyribonucleic acid is a molecule that contains genetic information
DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies
the DNA making up each chromosome is usually coiled up tightly. if we imagine it stretched out, it might look like beads on a string
each of these beads is called a gene
each gene is an instruction for a specific protein
thousands of genes make up each chromosome
the cell contains the nucleus, which holds the chromosomes, that contain tightly coiled strands of DNA, which are made of segments of genes that code for specific proteins that make up us
genes control the way a living thing looks, acts or works through the use of the proteins produced by those genes
genes dictate a lot about how an organism looks and acts, but the environment plays a role as well
genes are found in the nuclei of our cells, as specific lengths or segments of DNA
our DNA makes us who we are, because it contains all of our genes
DNA is a polymer molecule, which means it is a very large molecule made up of small repeating units
the repeating units in DNA are called nucleotides
nucleotides come in pairs:
Adenine always pairs with Thymine
Guanine always pairs with Cytosine
nucleotides are made of a sugar molecule, a phosphate molecule and a nitrogenous base (the A, T, G or C that makes it unique)
once the nucleotides are all connected, the DNA takes on a shape called a double helix - like a ladder that has been twisted around itself
the arrangements of As, Ts, Cs and Gs in a segment of DNA is what makes it a gene. A mechanism within the cell can read the code and turn it into a protein that will express the phenotype
the discovery of the structure of DNA was credited in 1952 to James Watson and Francis Crick. They were awarded Nobel prizes for their discovery
however, more recently it has been discovered that other scientists played important roles in the discovery of DNA’s structure, including Rosalind Franklin
Mendel, an Austrian monk, understood and proved as far back as the mid 1800s that traits were passed down from parent to child
our understanding of cell biology and genetics increased dramatically through the early 1900s, eventually leading to the structure of DNA in 1952
for years following that discovery, scientists were still unsure of one major process - how do the genes encoded in our DNA become the proteins that give us our phenotype (observable trait)?
this became known as the central dogma (a principle laid down by an authority as incontrovertibly true) in biology, and wasn’t fully resolved for decades
proteins are large, complex macromolecules made up of one or more long chains called polypeptides. polypeptides are made up of amino acids
proteins perform the functions that help us live. they could be enzymes, structural, eg. muscles
DNA is a code which is read in groups of 3 nucleotides. Every group of 3 nucleotides in a gene codes for 1 amino acid. So, if a gene is 900 nucleotides long, it would produce a protein which is 300 amino acids long
the DNA sequence of a gene must be read, and the code translated into a sequence of amino acids
it’s as if your cells are translating from one language to another
since the DNA instructions must remain in the nucleus, an intermediate molecule-messenger RNA (mRNA) is created; this carries a transcribed copy of the relevant instructions from the nucleus to the ribosomes in the cytoplasm
the ribosomes can be considered as the ‘machinery’ that translates the message carried by the mRNA into a cell product such as protein
RNA uses uracil (u) instead of thymine when creating RNA
a mutation is a change in the genetic material of a cell
the sequence of nucleotides (A, T, G and Cs) is altered
can be spontaneous (through erroneous DNA replication) or induced (through mutagenesis)
mutations can result in a change to the RNA created during transcription and the polypeptides/proteins created during translation
mutations can be small (a single nucleotide) or large (whole chromosome) or anywhere in between
effects of mutations can be positive, negative or neutral
a mutagen is anything that has the potential to alter DNA in a living organism
the process of inducing a mutation in a living organism is called mutagenesis and the resulting mutations are called induced mutations
prior to the discovery of DNA (1952), mutagens were already being researched, as there were certain jobs/environments that lead more people to develop cancers (Eg people working with radiation and certain chemicals, people exposed to nuclear radiation/bombs)
there are three types of mutagens: chemical, physical and biological
we have studied the structure of DNA and its role within living things. our knowledge and understanding of DNA has revolutionised biology, not just because we now know how the traits in living things are controlled, but also because we are learning how DNA can be used and even changed to suit our purposes as humans
historically, people whose identities are unknown have been identified using fingerprinting. each individual has a different fingerprint, so if a fingerprint is found at a crime scene, it can be compared to existing databases of fingerprints to try and identify the owner
recently, we have been able to create DNA profiles from tiny amounts of DNA to be used in much the same way as fingerprints. DNA profiles created with the same basic tools will be identical if they come from the same person, but different if they come from different people. people who are closely related will have DNA profiles with more similarities than unrelated individuals
these profiles can now routinely be used to either identify potential suspects in criminal activities, potential parents where paternity is uncertain, and to establish evolutionary relationships between species
the DNA of living organisms can be modified using a variety of techniques
genes can be removed from the DNA of living organisms, or far more commonly, genes from other species can be cut, copy and pasted into the genomes of others
one of the most common ways this technology is used is in adding the genes for specific vitamins to foods where these vitamins aren’t naturally found. one example of this is Golden Rice - a strain of rice that has the gene for beta-carotene added to it. the rice grows with a slight golden/orange colour to it, and provides those who eat it with beta-carotene that they wouldn’t normally have access to
another incredibly useful application of GMO is the addition of the gene for insulin into bacteria - the bacteria will produce insulin which can be collected and used as medicine for people living with diabetes
cloning means making exact genetic copies of something - a gene, a tissue/organ, or an entire organism
cloning can have many useful purposes - in the case of gene cloning, it can be used as a first step towards genetic modification, as making many copies of the gene of interest is important before it can be pasted into the genome of another organism. in the case of tissue/organ cloning, a genetically identical organ to transplant eliminates the risk off rejection and medical complications. in the case of whole organism cloning, a whole crop of identical plants can be grown quickly and easily. this is the case in most banana plantations in Queensland - all plants are genetic clones of each other
whole organism cloning specifically can have some ethical implications
Chemical Reactions | Nuclear Reactions |
|---|---|
chemical reactions occur when electrons are transferred or shared between atoms | nuclear reactions occur when the nucleus in an unstable atom breaks apart to form a ‘daughter’ nucleus and releases particles and energy |
most atoms are stable. however, radioactive atoms are not - they are unbalanced and unstable.
they ‘want’ to become stable (balanced). so to try to achieve this state they emit energy in the form of radiation
this releases energy. sometimes a massive amount of energy
alpha decay
alpha - an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons)
alpha radiation is the nucleus of a helium atom travelling at extremely high speed
the atomic number increases by a value of 1
beta
beta - an atom decays into a new atom by changing a neutron into a proton and electron
the fast moving, high energy electron is called a beta particle
the atomic structure doesn’t fundamentally change
gamma
gamma - after alpha or beta decay surplus energy is sometimes emitted. the atom itself is not changed
gamma radiation is part of the electromagnetic spectrum; a wave with a very high frequency, very short wavelength
they travel different distances
they have different strengths
they are stopped by different materials
Type of radiation | Symbol | What is it made from? | How far will it travel in air? | What stops it? | Charge |
|---|---|---|---|---|---|
alpha | helium nucleus, 2 protons and 2 neutrons | a few cm in air | sheet of paper | +2 | |
beta | high speed electron | a few m in air | cm of aluminium | -1 | |
gamma | high energy wave | very weakly absorbed in air | lead | no charge |
isotopes occur when an atom has the same number of protons but a different number of neutrons
when the number of neutrons is much greater than the number of protons, an atom becomes unstable
we know that each element is composed of atoms which are the same as each other… but this is not entirely accurate
within an element, all of the atoms have the same number of protons and the same number of electrons
however, the number of neutrons within atoms of the same element can vary. these are called isotopes
because all the protons are the same in each, they are all called the same name. but their mass numbers are different
spontaneous decay is the disintegration of an atom
an unstable nucleus tries to reach a more stable nuclear configuration
the process of radioactive decay occurs in general by three different methods
a nucleus that changes one of its neutrons into a proton with the simultaneous emission of an electron - this is beta decay
emitting a helium nucleus - this is alpha decay
spontaneous fission, that is splitting into two fragments
after decay, a resulting atom is often still radioactive
this results in that atom decaying again - attempting to reach a stable state
if often does this by emitting gamma rays
radioactive decay is a random event
for a given radioactive isotope, it’s impossible to predict when the nucleus will decay
this is like throwing dice or tossing coins. we can’t pick the result of a single coin toss, but we know that over a large sample size we will get 50% heads and 50% tails
the half life is the average time taken for half the nuclei in a sample to decay
the shorter the half life, the faster the rate of decay
nuclei have different degrees of stability, therefore they decay at different rates. the half life of an isotope is defined as the time required for half the initial number of radioactive nuclei to decay
it is also the time required for the intensity of the radiation to halve
each radioisotope has its own characteristic half life, which is unaffected by external conditions such as the composition of the compound it is found in, temperature and pressure
half lives may be as short as a fraction of a second or as long as millions of years
a decay curve shows how the number of nuclei of a radioactive element decreases with time
after each half life, one half of the original radioactive nuclei have decayed into atoms of a new element
note that the time for the material to halve its mass remains constant. after 5730 years, the mass of C has reduced to 5 g, after 11 450 years the mass has reduced to 2.5 and so on
we need to know the half life for a radioisotope when determining its suitability for a specific use
for example, radioisotopes that are to be injected into the body should have relatively short half-lives. this will minimise the exposure of healthy tissue to damaging radiation
technetium-99m and iodine-123 are used regularly in medical diagnosis and have half-lives of 6.0 and 13.3 hours respectively
all living things take in carbon-14 during their lifetime and this amount stays constant as new carbon-14 is taken in to replace the carbon-14 that decays
when an organism dies, it no longer replaces the decayed carbon-14 which converts back to nitrogen-14 due to beta decay
by measuring the amount of carbon-14 relative to carbon-12 in the sample, an estimate can be made of the number of half-lives have passed
nuclear reactions cause a lot of energy to be released
there are two methods to create energy
nuclear fission - a large nucleus is broken apart to form smaller daughter nuclei. in the process, energy is released. this is how nuclear power plants work
nuclear fusion - two smaller nuclei are fused together to form larger nuclei. energy is released as part of this process. this is what happens in stars such as our sun
neutral neutron particles aren’t deflected as it approaches the nucleus
neutral neutron fired at speed can force a large atom to split into smaller neutrons
energy can be released from within certain nuclei
if we can split the nuclei of heavy elements, the product will be approximately equal parts, with a release of neutrons and energy
a uranium-235 nucleus will be split if a neutron hits it and is captured by the uranium nucleus
a self sustaining ‘chain reaction’ can be created - these are the reactions that drive nuclear reactions, and nuclear bombs
only the U-235 undergoes fission and releases energy after it absorbs a neutron
the products of fission are neutron and highly radioactive
the three neutrons released can go on to hit other nearby U-235 nuclei, splitting them, and keeping the reaction going
to maintain a sustained reaction for every 2 or 3 neutrons released, only one must be allowed to hit another uranium nucleus
if this ratio is less than one, then the reaction will stop
a chain reaction process is a balanced system
neutrons are released in fission, to produce another fission in at least one additional nucleus
that nucleus in turn produces neutrons, splits further atoms and the process repeats
chain reactions may be controlled - as in nuclear reactions, or uncontrolled - as in nuclear weapon detonation or a nuclear reaction meltdown
because fission is initiated by neutron absorption, it is an example of an artificial transmutation
nuclear fusion is the merging of two nuclei to form a new atom with accompanying energy release
another common fusion reaction is when two deuterium nuclei join together to form tritium - hydrogen-3 - and a proton
some elements decay naturally - by going under alpha, beta or gamma decay
uranium-238 decays into thorium-234 and an alpha particle
the atomic and mass numbers must balance on both sides of the equation
thorium-234 decays into protactinium-234 and a beta particle
the atomic number increases by one during beta decay as a neutron decays into a proton, an electron and an antineutrino
a force is an interaction between two or more objects
it may be attractive or repulsive
it is a push, a pull or a twist
gravity - all objects with a mass are attracted to one another. The bigger the mass, the greater the attraction
electromagnetic - due to charged particles interacting
weak force - a force inside a proton
strong nuclear force - binds protons together in the nucleus
all other forces are just forms of these four
they always come in pairs - every action has an equal opposite reaction (3rd Law)
they can be balanced or unbalanced
an object can continue moving without a force being applied to it - inertia (1st Law)
forces act on an object, they are not a feature of the object
there are both contact and non-contact forces
Contact forces | Non-contact forces |
|---|---|
contact forces are types of forces that result when two interacting objects are perceived to be physically in contact with one another | a non-contact force is a force which acts on an object without physically coming into contact with it |
- frictional forces- tension forces- normal forces- applied forces- air resistance forces | - magnetism- gravity |
if forces in opposite directions are equal then they are balanced - there is no acceleration
the object will stay still (if not moving) or will move with constant speed and direction
if forces in opposite directions are not equal then they are unbalanced - there is acceleration
an object will remain at rest, or remain in motion with constant speed and direction, unless acted on by an unbalanced force
this is often called inertia. inertia is the reluctance of an object to change. the greater the mass, the greater the inertia
If the resultant force is unbalanced, the object will move
How quickly it changes its speed is dependent on the force applied and the mass of the object
F=ma
This relates to inertia. The larger the mass, the more difficult it is to get the object to accelerate
The acceleration of an object is directly proportional to the force applied. The acceleration of an object is also inversely proportional to the mass of an object
E | write down the equation |
|---|---|
V | write down the given values (check for conversion) |
E | enter the values into the equation |
R | calculate the result |
Y | add the (Y)units |
In reality, the acceleration of the object depends on the forces applied. You cannot apply an acceleration to get a force!
a = F/m
For every action there is an equal an opposite reaction
when body A exerts a force on object B, then object B will exert an equal force on A in the opposite direction
Remember: forces are interactions between bodies
Newton’s 3rd Law states that both bodies are always affected in an interaction
Whenever there is an action, there is always a reaction
F(ab) = -F(ba)
Key points
forces always come in pairs. we call these ‘newtonian pairs’
these forces act on different objects( each other). this is why they don’t cancel out
forces are always of the same type, eg. pushing a box on the floor (contact) and the friction on the floor (contact)
the forces are always equal in magnitude but opposite in direction
they have different effects on the objects they are acting on because of Newton’s 2nd Law
We can take Newton’s 2nd Law and apply it to our weight
F(grav) = ma
when we calculate the force due to gravity, the acceleration is called ‘the acceleration due to gravity’ and is given the symbol ‘g’
F(grav) =mg
on earth, g=9.8m/s/s
consider an object falling through a fluid such as air
at first, the object will accelerate due to the gravitational force (its weight)
as the object’s speed increases, the air resistance (reaction force) increases
after a time, the reaction force is equal to the weight. At this point the resultant force on the object becomes 0
Speed is how fast an object moves. It is how much time it takes to cover a certain distance
Speed is distance divided by time: speed = distance/time
Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs and equations
Kinematics is a branch of mechanics
The goal of any study of kinematics is to develop sophisticated mental models that serve to describe (and ultimately, explain) the motion of real-world objects
Scalars | Vectors |
|---|---|
only have a magnitude | have a magnitude and a direction |
- time- distance- volume- speed | - position- displacement- velocity- acceleration- force |
distance: total length of journey travelled
displacement: change in position, most direct route from start to finish
SI units: metres (m)
other units: kilometres (km) (needs to be converted to m)
speed: how far an object travels in a given time interval
average speed: distance travelled along an object’s path divided by the time it takes to travel this distance
average speed = distance travelled / time elapsed
velocity: how far an object has been displaced in a given time interval
average velocity: displacement of an object divided by the time it takes to travel this distance
average velocity = displacement travelled / time elapsed
velocity and speed are very closely related but they are not the same
velocity is the rate of change of displacement
(an object’s speed in a given direction)
v = s/t
where:
v = velocity (m/s)
s = displacement (m)
t = time (s)
Speed | Velocity |
|---|---|
- scalar- how fast something is moving- = distance/time- units: m/s | - vector- speed in a given direction- = displacement/time- units: m/s |
normally, accelerate just means ‘go faster’
in physics, acceleration is the rate at which the speed or velocity of an object changes
a = (v-u)/t
v = final speed
u = initial speed
acceleration is a vector so it has magnitude and direction
the standard unit for acceleration is metres per second per second (m/s/s or m/s^2)
deceleration is just negative acceleration
speeding up (increasing speed)
starting to move from rest (increasing speed from 0)
changing direction of linear motion eg. ball bouncing (changing speed from + to - or vice versa)
slowing down - deceleration
stopping - deceleration
turning a corner (changing direction)
circular motion (changing direction)
speed up
slow down
change direction
car manufacturers are always introducing new safety features in cars such as
seatbelts
collapsible steering wheels
padded dashboards
head restraints
airbags
crumple zones
ABS (anti-lock Braking System
regulators are also reducing the likelihood of major damage by reducing the speed limit in built up areas and mandating that cars have newer safety features
inertia causes your head to keep moving in the direction it was before the crash. After the crash, the car bounces backwards and so does your head
without a properly configured headrest, your neck whips backwards - whiplash
airbags protect you from hard things and to slow down your deceleration
when you hit a wall, or another car or big object, Newton’s 3rd law tells us the other object will push the car back with an equal and opposite force. Airbags slow down the rate of deceleration
the smallest unit of life
all living things are made of cells
most cells are too small to see with the naked eye
cells contain organelles - small structures that perform specific functions and processes to keep cells alive
an organelle that controls the cells activity
the DNA is found in the nucleus
the chromosomes are very long strands of DNA, coiled up like a ball of string
most human cells contain 46 chromosomes but sex cells only contain 23 chromosomes
deoxyribonucleic acid is a molecule that contains genetic information
DNA sequences must be converted into messages that can be used to produce proteins, which are the complex molecules that do most of the work in our bodies
the DNA making up each chromosome is usually coiled up tightly. if we imagine it stretched out, it might look like beads on a string
each of these beads is called a gene
each gene is an instruction for a specific protein
thousands of genes make up each chromosome
the cell contains the nucleus, which holds the chromosomes, that contain tightly coiled strands of DNA, which are made of segments of genes that code for specific proteins that make up us
genes control the way a living thing looks, acts or works through the use of the proteins produced by those genes
genes dictate a lot about how an organism looks and acts, but the environment plays a role as well
genes are found in the nuclei of our cells, as specific lengths or segments of DNA
our DNA makes us who we are, because it contains all of our genes
DNA is a polymer molecule, which means it is a very large molecule made up of small repeating units
the repeating units in DNA are called nucleotides
nucleotides come in pairs:
Adenine always pairs with Thymine
Guanine always pairs with Cytosine
nucleotides are made of a sugar molecule, a phosphate molecule and a nitrogenous base (the A, T, G or C that makes it unique)
once the nucleotides are all connected, the DNA takes on a shape called a double helix - like a ladder that has been twisted around itself
the arrangements of As, Ts, Cs and Gs in a segment of DNA is what makes it a gene. A mechanism within the cell can read the code and turn it into a protein that will express the phenotype
the discovery of the structure of DNA was credited in 1952 to James Watson and Francis Crick. They were awarded Nobel prizes for their discovery
however, more recently it has been discovered that other scientists played important roles in the discovery of DNA’s structure, including Rosalind Franklin
Mendel, an Austrian monk, understood and proved as far back as the mid 1800s that traits were passed down from parent to child
our understanding of cell biology and genetics increased dramatically through the early 1900s, eventually leading to the structure of DNA in 1952
for years following that discovery, scientists were still unsure of one major process - how do the genes encoded in our DNA become the proteins that give us our phenotype (observable trait)?
this became known as the central dogma (a principle laid down by an authority as incontrovertibly true) in biology, and wasn’t fully resolved for decades
proteins are large, complex macromolecules made up of one or more long chains called polypeptides. polypeptides are made up of amino acids
proteins perform the functions that help us live. they could be enzymes, structural, eg. muscles
DNA is a code which is read in groups of 3 nucleotides. Every group of 3 nucleotides in a gene codes for 1 amino acid. So, if a gene is 900 nucleotides long, it would produce a protein which is 300 amino acids long
the DNA sequence of a gene must be read, and the code translated into a sequence of amino acids
it’s as if your cells are translating from one language to another
since the DNA instructions must remain in the nucleus, an intermediate molecule-messenger RNA (mRNA) is created; this carries a transcribed copy of the relevant instructions from the nucleus to the ribosomes in the cytoplasm
the ribosomes can be considered as the ‘machinery’ that translates the message carried by the mRNA into a cell product such as protein
RNA uses uracil (u) instead of thymine when creating RNA
a mutation is a change in the genetic material of a cell
the sequence of nucleotides (A, T, G and Cs) is altered
can be spontaneous (through erroneous DNA replication) or induced (through mutagenesis)
mutations can result in a change to the RNA created during transcription and the polypeptides/proteins created during translation
mutations can be small (a single nucleotide) or large (whole chromosome) or anywhere in between
effects of mutations can be positive, negative or neutral
a mutagen is anything that has the potential to alter DNA in a living organism
the process of inducing a mutation in a living organism is called mutagenesis and the resulting mutations are called induced mutations
prior to the discovery of DNA (1952), mutagens were already being researched, as there were certain jobs/environments that lead more people to develop cancers (Eg people working with radiation and certain chemicals, people exposed to nuclear radiation/bombs)
there are three types of mutagens: chemical, physical and biological
we have studied the structure of DNA and its role within living things. our knowledge and understanding of DNA has revolutionised biology, not just because we now know how the traits in living things are controlled, but also because we are learning how DNA can be used and even changed to suit our purposes as humans
historically, people whose identities are unknown have been identified using fingerprinting. each individual has a different fingerprint, so if a fingerprint is found at a crime scene, it can be compared to existing databases of fingerprints to try and identify the owner
recently, we have been able to create DNA profiles from tiny amounts of DNA to be used in much the same way as fingerprints. DNA profiles created with the same basic tools will be identical if they come from the same person, but different if they come from different people. people who are closely related will have DNA profiles with more similarities than unrelated individuals
these profiles can now routinely be used to either identify potential suspects in criminal activities, potential parents where paternity is uncertain, and to establish evolutionary relationships between species
the DNA of living organisms can be modified using a variety of techniques
genes can be removed from the DNA of living organisms, or far more commonly, genes from other species can be cut, copy and pasted into the genomes of others
one of the most common ways this technology is used is in adding the genes for specific vitamins to foods where these vitamins aren’t naturally found. one example of this is Golden Rice - a strain of rice that has the gene for beta-carotene added to it. the rice grows with a slight golden/orange colour to it, and provides those who eat it with beta-carotene that they wouldn’t normally have access to
another incredibly useful application of GMO is the addition of the gene for insulin into bacteria - the bacteria will produce insulin which can be collected and used as medicine for people living with diabetes
cloning means making exact genetic copies of something - a gene, a tissue/organ, or an entire organism
cloning can have many useful purposes - in the case of gene cloning, it can be used as a first step towards genetic modification, as making many copies of the gene of interest is important before it can be pasted into the genome of another organism. in the case of tissue/organ cloning, a genetically identical organ to transplant eliminates the risk off rejection and medical complications. in the case of whole organism cloning, a whole crop of identical plants can be grown quickly and easily. this is the case in most banana plantations in Queensland - all plants are genetic clones of each other
whole organism cloning specifically can have some ethical implications
Chemical Reactions | Nuclear Reactions |
|---|---|
chemical reactions occur when electrons are transferred or shared between atoms | nuclear reactions occur when the nucleus in an unstable atom breaks apart to form a ‘daughter’ nucleus and releases particles and energy |
most atoms are stable. however, radioactive atoms are not - they are unbalanced and unstable.
they ‘want’ to become stable (balanced). so to try to achieve this state they emit energy in the form of radiation
this releases energy. sometimes a massive amount of energy
alpha decay
alpha - an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons)
alpha radiation is the nucleus of a helium atom travelling at extremely high speed
the atomic number increases by a value of 1
beta
beta - an atom decays into a new atom by changing a neutron into a proton and electron
the fast moving, high energy electron is called a beta particle
the atomic structure doesn’t fundamentally change
gamma
gamma - after alpha or beta decay surplus energy is sometimes emitted. the atom itself is not changed
gamma radiation is part of the electromagnetic spectrum; a wave with a very high frequency, very short wavelength
they travel different distances
they have different strengths
they are stopped by different materials
Type of radiation | Symbol | What is it made from? | How far will it travel in air? | What stops it? | Charge |
|---|---|---|---|---|---|
alpha | helium nucleus, 2 protons and 2 neutrons | a few cm in air | sheet of paper | +2 | |
beta | high speed electron | a few m in air | cm of aluminium | -1 | |
gamma | high energy wave | very weakly absorbed in air | lead | no charge |
isotopes occur when an atom has the same number of protons but a different number of neutrons
when the number of neutrons is much greater than the number of protons, an atom becomes unstable
we know that each element is composed of atoms which are the same as each other… but this is not entirely accurate
within an element, all of the atoms have the same number of protons and the same number of electrons
however, the number of neutrons within atoms of the same element can vary. these are called isotopes
because all the protons are the same in each, they are all called the same name. but their mass numbers are different
spontaneous decay is the disintegration of an atom
an unstable nucleus tries to reach a more stable nuclear configuration
the process of radioactive decay occurs in general by three different methods
a nucleus that changes one of its neutrons into a proton with the simultaneous emission of an electron - this is beta decay
emitting a helium nucleus - this is alpha decay
spontaneous fission, that is splitting into two fragments
after decay, a resulting atom is often still radioactive
this results in that atom decaying again - attempting to reach a stable state
if often does this by emitting gamma rays
radioactive decay is a random event
for a given radioactive isotope, it’s impossible to predict when the nucleus will decay
this is like throwing dice or tossing coins. we can’t pick the result of a single coin toss, but we know that over a large sample size we will get 50% heads and 50% tails
the half life is the average time taken for half the nuclei in a sample to decay
the shorter the half life, the faster the rate of decay
nuclei have different degrees of stability, therefore they decay at different rates. the half life of an isotope is defined as the time required for half the initial number of radioactive nuclei to decay
it is also the time required for the intensity of the radiation to halve
each radioisotope has its own characteristic half life, which is unaffected by external conditions such as the composition of the compound it is found in, temperature and pressure
half lives may be as short as a fraction of a second or as long as millions of years
a decay curve shows how the number of nuclei of a radioactive element decreases with time
after each half life, one half of the original radioactive nuclei have decayed into atoms of a new element
note that the time for the material to halve its mass remains constant. after 5730 years, the mass of C has reduced to 5 g, after 11 450 years the mass has reduced to 2.5 and so on
we need to know the half life for a radioisotope when determining its suitability for a specific use
for example, radioisotopes that are to be injected into the body should have relatively short half-lives. this will minimise the exposure of healthy tissue to damaging radiation
technetium-99m and iodine-123 are used regularly in medical diagnosis and have half-lives of 6.0 and 13.3 hours respectively
all living things take in carbon-14 during their lifetime and this amount stays constant as new carbon-14 is taken in to replace the carbon-14 that decays
when an organism dies, it no longer replaces the decayed carbon-14 which converts back to nitrogen-14 due to beta decay
by measuring the amount of carbon-14 relative to carbon-12 in the sample, an estimate can be made of the number of half-lives have passed
nuclear reactions cause a lot of energy to be released
there are two methods to create energy
nuclear fission - a large nucleus is broken apart to form smaller daughter nuclei. in the process, energy is released. this is how nuclear power plants work
nuclear fusion - two smaller nuclei are fused together to form larger nuclei. energy is released as part of this process. this is what happens in stars such as our sun
neutral neutron particles aren’t deflected as it approaches the nucleus
neutral neutron fired at speed can force a large atom to split into smaller neutrons
energy can be released from within certain nuclei
if we can split the nuclei of heavy elements, the product will be approximately equal parts, with a release of neutrons and energy
a uranium-235 nucleus will be split if a neutron hits it and is captured by the uranium nucleus
a self sustaining ‘chain reaction’ can be created - these are the reactions that drive nuclear reactions, and nuclear bombs
only the U-235 undergoes fission and releases energy after it absorbs a neutron
the products of fission are neutron and highly radioactive
the three neutrons released can go on to hit other nearby U-235 nuclei, splitting them, and keeping the reaction going
to maintain a sustained reaction for every 2 or 3 neutrons released, only one must be allowed to hit another uranium nucleus
if this ratio is less than one, then the reaction will stop
a chain reaction process is a balanced system
neutrons are released in fission, to produce another fission in at least one additional nucleus
that nucleus in turn produces neutrons, splits further atoms and the process repeats
chain reactions may be controlled - as in nuclear reactions, or uncontrolled - as in nuclear weapon detonation or a nuclear reaction meltdown
because fission is initiated by neutron absorption, it is an example of an artificial transmutation
nuclear fusion is the merging of two nuclei to form a new atom with accompanying energy release
another common fusion reaction is when two deuterium nuclei join together to form tritium - hydrogen-3 - and a proton
some elements decay naturally - by going under alpha, beta or gamma decay
uranium-238 decays into thorium-234 and an alpha particle
the atomic and mass numbers must balance on both sides of the equation
thorium-234 decays into protactinium-234 and a beta particle
the atomic number increases by one during beta decay as a neutron decays into a proton, an electron and an antineutrino
