GCSE Biology 1: You And Your
Genes
Keywords & Definitions
+ Nucleus- The nucleus contains almost all of the genetic
material. It controls what and when the cell does something
and is in charge of cell growth and reproduction.
+ Chromosomes- Chromosomes are found in the nucleusthere. They come in pairs and there are 23 individual pairs.
They carry genetic information.
+ DNA- DNA make up the chromosomes. They are coiled
up and carry the genes.
+ Genes- Genes are portions of DNA found at a specific
place of a chromosome depending on what they are for.
They carry genetic instructions for making different
proteins.
+ Alleles- Alleles are different versions of genes which
determine how a characteristic of a living thing is shown.
There are two alleles for every trait, one from either parent.
Proteins
Depending on a gene’s make up, different proteins can be
made for different uses.
+ Structural proteins are used to help the design and build
of a part of the body. E.g. Keratin in hair and nails.
+ Function proteins contribute to the daily workings of the
body and serve a specific duty. E.g. Enzymes to help
digest food.
Genetic Testing
Genetic testing is the examination of a foetus during
pregnancy to see if the child will be born with a genetic
disorder.
+ Chorionic Villus Sampling- CVS is usually done between
the 11th and 14th weeks of pregnancy. The test involves
taking a sample of cells (Chorionic Villus Cells) from the
placenta. This can be done by inserting a needle through
the abdomen (transabdominal CVS) or inserting a tube or
forceps through the cervix (transcervical CVS).
+ Amniocentesis- Amniocentesis is usually carried out
between 15 and 20 weeks of the pregnancy. A needle is
used to take a sample of the amniotic fluid which
surrounds the foetus.
+ Pre-implantation Genetics- Pre-implantation Genetics is
carried out during the process of IVF. When the eggs of
the mother have been fertilised by the father’s sperm, the
embryos are tested for any genetic disorders. Once this
has been done, some of the healthy embryos are inserted
into the mother’s uterus while the others are discarded.
Cloning
Clones are genetically identical. They have the same
genes and the same alleles for those genes. If there are
any differences between clones, it means it’s a result on
an environmental factor, e.g. Diet and living conditions.
Types Of Cloning
+ Asexual- Asexual reproduction means that there is only
one parent and the offspring and parent are genetically
identical. Sexual reproduction is not involved (asexually)
+ Natural- Identical twins are clones. Twins are formed
when a single embryo splits into two and each separate
embryo starts to develop and two identical babies will be
born.
+ Artificial- Artificial cloning is when the nucleus of an egg
cell is removed, a nucleus from an adult donor is inserted
into that empty egg cell, the cell is stimulated so that it
starts to divide and develop as if it were a formal embryo
(fertilised egg). The embryo produced will be genetically
identical to the donor cell.
Stem Cells
Stem cells are unspecialised cells which can develop into
many different types of cells.
+ Embryonic stem cells- Embryos contain stem cells.
They can develop into any type of cell. They can be
removed from early human embryos. Often scientists use
left over embryos from fertility treatment.
+ Adult stem cells- An adult stem cell is another
unspecialised cell. However, there are limits as to what
type of cell it can develop into.
What They Can Be Used For
+ Growing new brain cells for people with Parkinson’s
Disease.
+ Rebuilding bones and cartilage.
+ Growing new skin for burns victims
Saviour Siblings
Sometimes when children are ill, their parents resort to
having another child in order to save their ill child because
procedures and transplants etc. can be done to the
saviour sibling to save the life of the ill child.
+ Saviour siblings can be produced through IVF and preimplantation genetics can be done in order to make sure
the child has no genetic disorders and will be able to help
the ill child.
+ Once the child is born, the umbilical cord is usually
taken away for the extraction of stem cells or the saviour
sibling will do through certain procedures to help it’s ill
brother or sister.
Problems With Genetic Testing
+ The risk of miscarriage from genetic testing is about 1%
+ The placenta may be punctured from the needle.
Usually the wound will heal but sometimes their may be
issued with it developing.
+ Rarely, infections will occur if bacteria gets into the
amniotic sack.
+ The procedure may result in the baby being born with
Club foot- this is when the ankle and foot are deformed.
The risk of this happening is higher if the procedure is
under taken before the 15th week of the pregnancy.
False Positives/Negatives
Sometimes the results may come back wrong giving the
parents the wrong idea about their child’s condition
+ False Negative- The results may come back negative
when, in fact, they are positive. The parents may be
shocked to find they have an ill child and won’t have time
to prepare before they start caring for their child.
+ False Positive- They may come back positive when the
test results are negative. This can mislead the parents
and they may abort the baby when there’s no need.
Ethical Problems With Genetic Testing & Saviour Siblings
+ Whether or not to abort the baby if it has a genetic
disorder- would it be fair?
+ Should relatives be told if the condition may run in the
family?
+ Should they continue the pregnancy if the child were to
have a reduced quality of life? It’s still a human and has
the right to life.
+ The saviour sibling may feel they were born for the
wrong reasons and may feel unwanted.
+ The child might not like the procedure etc. they have to
go through in order to save their brother or sister.
+ The child might feel that they are loved less than their ill
sibling because if they hadn’t have been ill, the saviour
sibling would not have been born.
Positive Implications
+ The parents would know about their child’s condition
and would be able to prepare themselves.
+ They wouldn’t have as much of a shock at the birth and
would be able to start to educate themselves on their
child’s condition ahead of when it arrives.
+ They would be able to weigh up whether they should
keep the baby having improved knowledge on the
condition from health care professionals etc.
+ The ill child would survive or have, at least, an improved
quality of life or an extended life expectancy.
+ The family would be a lot happier if the ill child recovers
and they may become a lot close because of this.
Alleles: Dominant & Recessive
+ Alleles are different forms of genes.
+ In a gene, one allele comes from the mum and the other
allele comes from the dad.
+ Alleles work in pairs to determine how a characteristic is
portrayed.
+ They can be either dominant or recessive.
Punnet Squares
Punnet squares can be used to show what the
possibilities a living thing has of inheriting a characteristic.
From the diagrams you can work out the chance of
someone inheriting and not inheriting the trait.
+ Dominant allele- Only one dominant allele needs to be
present within a pair for the characteristic to follow it.
Dominant alleles are shown as capital letters.
+ Recessive allele- Two recessive alleles are required for
the characteristic to be like how the recessive allele
instructs. Recessive alleles are shown as lower cases
letters. However, if a recessive allele is present, the
offspring will be a ‘carrier’ of that trait.
Homozygous/Heterozygous
+ Homozygous- Homozygous means when something
has two alleles in a gene which are the same.
+ Heterozygous- Heterozygous means something has two
conflicting alleles that make up a gene.
Genotype/Phenotype
+ Genotype- The genotype shows which alleles are
present in the formation of a gene. The genotype is
expressed as two letters.
+ Phenotype- The phenotype is he actual physical
appearance which is the result of the alleles in a gene.
Amanda is homozygous for brown eyes (which comes
from a dominant allele) BB
Dave is homozygous for blue eye (which comes from
recessive allele) bb
E.g. Genotype- BB (two dominant alleles for brown eye)
Phenotype- Brown eyes
E.g.
b
b
B
B
Bb
Bb
Bb
Bb
From this punnet square, I can see that there is a 100%
guarantee that Amanda and Dave’s child will inherit brown
eyes.
1) Draw a box and on the top write the alleles of on
parent and down the side write the alleles of the other
parent.
2) In each box write the combination of the alleles (the
capital letter always go first).
3) Have a look at the combinations and write down the
chance of the offspring inheriting that form of the
characteristic.
Family Trees/ Pedigree Diagram
+ Family trees can be used to show how genetic disorders
were inherited.
+ In each diagram, those with the disorder have their
symbol shaded- squares for males and circles for
females.
+ From the diagram we can see if the disorder is because
of a recessive or dominant allele and we can work out the
chance of different people inheriting the condition.
Tim
Mary
Jill
Tom
Harry
Gender Inheritance
+ One of the 23 pairs of chromosomes in the nucleus
controls which gender something will be.
+ For a living thing to be male, it has to have two different
chromosomes, X and Y.
+ For something to be female, it has to have two X
chromosomes.
+ There is an equal 50, 50 chance that the offspring will
be a boy or a girl. Nothing can be done to increases the
chances of the offspring being one or the other.
Jim
Mel
Lyn
Scott
Fiona
Laura
This pedigree diagram is for Sickle Cell Disease. The
darker symbols mean they have the condition while the
lighter symbols show that they do not.
From this pedigree diagram, we can see that sickle cell
disease is from a recessive allele because Tim and Mary
both have the condition but, Jim, their son does not.
Cystic Fibrosis
+ Cystic Fibrosis is an inherited disorder that affects cell
membranes causing thick and sticky mucus to be
produced.
+ It is caused by a recessive allele. This means it must be
inherited by both parents to directly suffer from it or
become a carrier.
Huntington’s Disease
+ Huntington’s Disease is an inherited disorder which
affects the nervous system.
+ It is caused by a dominant allele which means it can be
passed down by only one parent with the condition.
GCSE Biology 2: Keeping Healthy
Pathogens
Pathogens are microorganisms, like viruses and bacteria,
that cause diseases. Bacteria release toxins into out
bodies while viruses damage cells. Bacteria and viruses
are the main types of pathogens.
+ Bacteria- Come in many shapes and sizes. They are
living cells and, in good conditions, can multiply extremely
quickly. They release harmful poisons and toxins, which
make us feel ill, once they get into the body. Diseases from
bacteria include food poisoning, cholera, typhoid and
whooping cough.
+ Viruses- Are a lot smaller than bacteria. They can only
reproduce once they are inside another cell (a host cell)
and damage the cell when they do this. Once inside
another cell, they can produce hundreds of thousands of
copies of itself and fill the host cell so that it bursts open.
Then, the viruses are passed out through into the
e routes. Diseases
bloodstream, the airways and other
caused by viruses include the common cold, measles,
chicken pox, influenza and AIDs.
How Diseases Can Spread
Diseases which can spread from one person to another are
called infectious diseases. There are various ways in which
the pathogens/microorganisms can spread:
+ The air
+ Contact with animals
+ Contaminated food
+ Touch
+ Water
+ Coughing/Sneezing
The Body’s Defence System
+ Acid in the stomach- kills many foreign microorganisms
+ Mucus in the lungs- traps microbes. Then cilia cells
sweep them out
+ Skin- prevents microbes from entering the body
+ Scabs- Form on the skin when it has been cut to stop
microbes entering the body
+ Tear- Contain things which kill bacteria
White Blood Cells
+ Lymphocytes (type of white blood cell) identify foreign
microbes in the body
+ Then, produce the correct antibody to engulf it to stop
the pathogen from reproducing or moving around the
body - because all microorganisms have different
antigens, it takes specific antibodies to destroy them.
+ The antibodies coat the pathogen. Then, the
Phagocytes (another type of white blood cell) comes
along to ingest it.
+ Antitoxins are produced to neutralise the toxins made by
the pathogen.
Remember- Pathogens are not diseases; they cause
them. Also, white blood cells do not eat the pathogens;
they ingest them. Finally, antibodies and antitoxins are not
living things; they are specialised proteins.
Antigens- Antigens are chemicals in the pathogens. There
are different antigens in different types of pathogens. This
requires white blood cells to produce specific antibodies
for different foreign microorganisms in order to destroy
them.
Antibodies
+ Can bind to the pathogens and damage or destroy
them.
+ Cover the pathogens to clump them together making it
easier or the white blood cell to come along and ingest it.
Antibiotics
+ Antibiotics are substances that kill bacteria or prevent
them from growing. They DO NOT work against viruses.
+ It is very hard to make drugs that kill viruses without
harming the tissue in our body.
+ They are made so that they will kill the desired bacteria
without damaging the cells in our body.
+ Each antibiotic affects a different bacteria and in a
different way.
How Antibiotics Work
+ A bactericidal antibiotic kills bacteria. This type of
antibiotic usually hampers with the development of the
bacteria’s cell walls or the content of the cell.
+ A bacteriostatic stops the bacteria from multiplying.
Antibiotic Resistance
+ Over time, bacteria can become resistant towards
particular antibiotics.
+ Resistance can happen for a number of reasons...
-Random changes and mutations in the genes of
individual bacteria cells- some of these mutations can
protect the bacteria against the antibiotics and its effects.
This leads to the non-resistant bacteria cells being killed
off my the antibiotics leaving just the mutated ones. When
this happens, the resistant cells reproduce to make a
whole other generation which is resistant to the antibiotic.
Taking The Full Course
+ When we are ill, we are given antibiotics in order to kill
the bacteria in our bodies.
+ When we start to take antibiotic, the number of bacteria
starts to go down because the medicine is killing them.
+ But, if we do not continue to take the full course of
antibiotics, the remaining bacteria, which have not yet
been destroyed, will start to reproduce again, the number
of bacteria in our bodies will go up and we will not get
better.
Immunity
+ Some Lymphocytes (the white blood cells which identify
pathogens and produce appropriate antibodies) stay
around in the blood after the infection has been
destroyed- they are then called memory cells.
+ These memory cells can reproduce extremely quickly if
the same type of antigen in a pathogen enters the body
again.
+ The memory cells then produce lots of the correct
antibodies and kill off the pathogens before you get ill and
suffer from any symptoms- this is immunity.
Vaccinations/ Immunisation
+ Vaccinations involve using a safe type of a dangerous
microorganism to make people immune to it.
+ Immunisation involves injecting a dead or inactive
microorganism into a person.
+ Even though the microorganism is completely harmless,
it still contains antigens and means the body produces the
right antibodies to attack them.
+ Once the antibodies attack the dead microorganism,
memory cells are produced that recognise the antigens of
the microorganism which was injected into the body
during the vaccination.
+ This means that if a live version of that microorganism
enters the body, the memory cells can produce loads of
antibodies to kill them off and the vaccinated person will
no longer become ill by that type of microorganism if it
enters the body again.
Large Scale Vaccinations
+ To prevent large outbreaks of diseases (epidemics) a
large percentage of the population is vaccinated.
+ If lots of people aren’t vaccinated, diseases can spread
quickly and affect lots of people.
+ If most people are vaccinated, even those who aren’t
vaccinated are unlikely to catch the disease because
there are less people who are able to pass it on.
Against
+ People should have a right to choose whether or not to
have the vaccination- putting themselves first and not
society as a whole.
+ Because there is a chance of small side effects, people
may choose not to have the injection and live with the
increased risk that they will get ill.
Problems With This
+ If fewer people have the vaccination, the number of
cases of disease will increase.
+ The chance of getting seriously ill, or even dying, from
the disease may be far greater the chance of experiencing
side effects.
+ Using a vaccine may be much cheaper than treating a
very ill person.
For
+ The risk of suffering from a side effect is smaller than
the risk of developing the illness if the vaccination is not
done.
+ A small, quick injection will remove the risk of
contracting a possibly life threatening illness in the future.
+ The cost of the vaccination is a lot less than the hospital
care of a person if they developed an illness which could
have been vaccinated against.
Weighing Up Arguments
1) Say clearly what the issue is: if the risk of suffering
side effects from the vaccination is greater or less than
the risk of catching the disease.
2) Summarise different views that could be held: some
people used to think there was a risk of a child
developing autism from the MMR vaccine. Others
though the MMR vaccine was safe and there was no
risk of children developing autism.
3) Identify and develop arguments based on the idea that
the right decision is the one that has the best outcome
for most of the people: even though there is a slight
risk from being vaccinated, society as a whole will
benefit because it will help reduce the risk of the
disease being passed on to other people.
4) Identify and develop arguments based on the idea that
certain actions ar never justified because they are
unnatural and wrong: most people think that the
Government should not pass a law making vaccination
compulsory because it would take away people’s
human rights to freedom of choice.
GCSE Biology 3: Life On Earth
Classification
+ Classification is the process of putting living things into
groups. Similarities and differences between organisms are
used to do this.
+ All living things are linked together because they all
belong to the biggest group called the Animal kingdom.
The Steps
+ The first group is called a kingdom. There are five
kingdoms based on what organisms’ cells are like:
1) Animalia (multicellular animals)
2) Plantae (green plants)
3) Fungi (mould, mushrooms, yeast)
4) Prokaryotae (bacteria, blue-green algae)
5) Protoctista (Amoeba, Paramecium)
Further Steps
1- Kingdom (animal)
2- Phylum
(vertebrate)
e
3- Class
(mammal)
4- Order
(carnivorous)
Lions’ classification
5- Family
(cat)
6- Genus
(big cat)
7- Species
(lion)
Differences Between Species
It is important for scientists to identify indivual species of
animals from different places. There are animals that
live in various countries and are different to one
another. By giving each one a different binomial name
there is no confusion.
+ Binomial name- Organisms are known by their binomial
name which is their Genus and species.
+ Binomial classification (naming different species) is
important because it means all species are clearly
identified, studies and conservation can be specifically
targeted at particular species.
Food Chains
+ Food chains are a way to show what organisms eat and
what they get eaten by themselves (their prey and their
predator).
+ Food chain diagrams contain arrows pointing in the
direction of where the energy is going (from the food to
the eater).
+ The sun is always at the start (bottom) of every food
chain because it provides the energy for the producer
organism to make it’s own food.
Food Webs
+ Food webs are simply different food chains joined
together. They are used to help us figure out what the
effect is on a particular organism if another organism dies.
It shows us how, in the end, all different living things rely
on each other to survive- this is called interdependency of
living things.
+ You will probably be given a question involving a food
web. For example:
Considering the food web above as an example, what
would happen if the population of slugs decreased?
+ Producer- They make their own food through
photosynthesis (green plants and algae).
+ Primary Consumers- Usually eat plant
material/herbivores (grass hopper)
+ Secondary Consumers- Eat the primary
consumers/animal material (shrew).
Tertiary Consumers- At the top of the food chain. A
carnivore who eats the secondary/ or primary consumer
(depending on how long the food chain is).
+ Scavengers- Feed on dead animals (crows, vultures,
hyenas).
+ Decomposers- feed on dead and decaying organisms
and on undigested parts of plant and animal waste.
+ To answer this question you need to explore all the
possibilities. Basically, think about who would die and who
would thrive.
+ From there you can consider what would happen to
other animals. Work back through the arrows connected
to the linked animals and work out how they would be
affected.
+ Answer- Slugs, rabbits and insects all eat grass. If there
were fewer slugs there would be more grass for the
rabbits and insects. With more food the populations of
rabbits and insects would increase. However, the thrushes
would have to eat more insects to maintain their
population, so it is also possible that the population of
insects could decrease. This is turn may reduce the
populations of voles and frogs.
Environmental changes
+ Changes in the environment can cause organisms to
change. There are many ways in which the environment
of an organism can change and each environmental
change can cause different things to happen to the
organism there.
+ Predators and prey- If the number of prey grows,
predators will respond by increasing too. Eventually, the
prey number will start to decrease as the predators eat
them. As the food supply slowly reduces, the predator
level will fall because there isn’t enough food to feed on.
+ Climate- Over millions of years, continental drift cause
plates to move and, in turn, countries too. Because of this,
over time climates change and organisms are no longer
suited or able to live in that environment. Some die and
over the next generations the organisms are born with
suitable characteristics leaving a species who can survive.
(natural selection).
Ethical Problems With Genetic Testing & Saviour Siblings
+ Whether or not to abort the baby if it has a genetic
disorder- would it be fair?
+ Should relatives be told if the condition may run in the
family?
+ Should they continue the pregnancy if the child were to
have a reduced quality of life? It’s still a human and has
the right to life.
+ The saviour sibling may feel they were born for the
wrong reasons and may feel unwanted.
+ The child might not like the procedure etc. they have to
go through in order to save their brother or sister.
+ The child might feel that they are loved less than their ill
sibling because if they hadn’t have been ill, the saviour
sibling would not have been born.
Positive Implications
+ The parents would know about their child’s condition
and would be able to prepare themselves.
+ They wouldn’t have as much of a shock at the birth and
would be able to start to educate themselves on their
child’s condition ahead of when it arrives.
+ They would be able to weigh up whether they should
keep the baby having improved knowledge on the
condition from health care professionals etc.
+ The ill child would survive or have, at least, an improved
quality of life or an extended life expectancy.
+ The family would be a lot happier if the ill child recovers
and they may become a lot close because of this.
•Nucleus
•Chromosome
•DNA
•Genes- Protein (Structural + Functional)
•Alleles
•Problems with genetic testing + saviour
siblings
•Positives of: genetic testing + saviour siblings
•What is:
Genetic Testing: CVS, amniocentesis, Preimplantation Genetics
Cloning: asexual, natural, artificial
Stem cells- embryonic and adult
•Recessive/Dominant
•Homozygous/Heterozygous
•Genotype/Phenotype
•Punnet Squares
•Family Trees
•Gender
•Cystic Fibrosis
•Huntington’s Disease
•How Diseases can be spread
•How the body prevents microbes entering it
•How your immune system responds when
you’re ill
• Antibiotics- how they work: antibiotic
resistance and the importance of taking the
full course.
• Immunity
• Vaccines- how they work step-by-step
• Arguments for and against giving out
vaccines on a large scale (vaccines are usually
a very good thing).