Transcript New B1 B2 B3 Revision

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B1 B2 B3
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B1 – You and your Genes
Locating genes
cell
nucleus
Genes are located in chromosomes which are in the nucleus of cells
23 pairs = 46 chromosomes altogether
Sperm cells can have an X or Y sex chromosome
Egg cells can only have an X sex chromosome
Most characteristics are
determined by genes called alleles
Alleles mostly come in pairs
An allele can be dominant,
recessive (or co-dominant)
The alleles you inherit is called your
genotype
Your phenotype is what you look like, your
characteristics
Punnett
square
If both the alleles you inherit are the
same you are homozygous for that
characteristic e.g. NN or nn
If you inherit different alleles you
are heterozygous e.g Nn
Disease
What it affects
Type of allele
cystic fibrosis
the lungs – sticky
mucus – difficulty in
breathing
recessive
haemophylia
the blood can’t clot
recessive
the nervous system
– uncontrollable
movements
dominant
Huntington’s disease
sickle cell anaemia
the bloods ability to
pick up oxygen
These are the key ones to remember
co-dominant
Characteristics depend on
inherited
environment
eg eye colour
eg dyeing your hair
both
eg weight
Natural clones
Identical twins (formed
when a fertilised egg
starts to divide and
splits to form 2 babies
instead of one).
Asexual reproduction
(eg bacteria)
Clones have got identical genes
Plant cuttings can be grown into clones of the original plant.
early embryo
Shows stem cells being extracted from a blastocyst
Stem cells are unspecialised cells
Making stem cells using the DNA from a patient means the cells
wont be rejected when they are transplanted into the patient
This means that the patient’s immune system
wont attack the transplanted stem cells
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The antibodies
help to kill the
foreign cell
foreign cell
with antigen
White blood cells
recognise it as a
foreign cell and
make antibodies
With this technique the white
blood cells do not recognise the
transplanted stem cells as foreign
and therefore don’t attack them
IVF – In Vitro Fertilisation
The fertilised egg can now be tested for genetic diseases if desired.
The fertilised egg can now be implanted into the uterus of the mother
Embryos left over from IVF treatment can be used to obtain stem cells
controversial
The right decision is the one which leads to the
best outcome for the majority of people involved
Some things are considered to be unnatural or wrong
Opinion. Against
cloning and against
using embryos.
Opinion. Seems to be against using stem cells.
Points out possible risks. Uses exaggerated
language. No mention of embryos.
Gordon is supposed to be impartial, ie he should give a balanced view.
The other people could have a vested interest, ie they could have a
direct benefit or are campaigners for a cause.
Seems to be for using stem
cells. Hasn’t said anything
about using embryos.
For using stem cells
and using embryos.
These people
could be biased.
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Spend 10 min writing down everything you can remember about B1
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a gene
recessive
chromosomes
John
Kate
Reshma
Lucy
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46
XY
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Higher material
understand that genes are instructions for a cell that describe how
to make proteins, which may be structural or enzymes;
recall that the sex of a human embryo is determined by a
gene on the Y chromosome;
understand the link between this gene and the development of
sex organs into either ovaries or testes.
understand the implications of testing embryos for embryo
selection (pre-implantation genetic diagnosis);
understand the implications of the use of genetic testing by
others,(for example for genetic screening programmes, by
employers and insurance companies.);
in the context of use of genetic testing by others can:
• distinguish what can be done (technical feasibility), from
what should be done (values);
• explain why different courses of action may be taken in
different social and environmental contexts.
understand how clones of animals occur:
• naturally, when cells of an embryo separate (identical twins);
• artificially, when the nucleus from an adult body cell is
transferred to an empty unfertilised egg cell;
Spend 10 min writing down everything you can remember about B1
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Jane must be a
carrier because
her mother Kate
has the condition.
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B2 - Keeping Healthy
viruses
bacteria
fungi
m i c r o o r g a n i s m s
cold
flu
Warmth and moisture are good
conditions for microorganisms to grow.
Symptoms of disease are caused
by damage to cells and by toxins.
antibiotics
Antibiotics are only effective against bacteria or fungi.
X
animation
The antibodies
help to kill the
foreign cell
foreign cell
with antigen
White blood cells
recognise it as a
foreign cell and
make antibodies
Memory cells “remember” how to make these
antibodies so if you are infected again your immune
system can make the right antibodies quickly – you
become immune to that particular form of microbe.
What is a vaccine ?
a vaccine is a dead or weakened form of bacteria or virus.
When administered the vaccine causes an immune
response and eventually antibodies are produced.
You are now immune to that particular microbe so if
you get infected with a real version you won’t get ill.
Why is it important for at least 95% of people in a
society to take a vaccine against a a particularly harmful
virus or bacteria ?
> to eradicate the virus or bacteria
Why do vaccines against influenza have to be developed
regularly ?
> because the virus changes very quickly
Over a period of time, bacteria and fungi may become
resistant to antibiotics.
How can we reduce antibiotic resistance ?
> we should only use antibiotics when necessary
and always complete the course
Developing drugs
• test them on cells and animals in a laboratory
• test them on healthy volunteers for safety
• test them on people with the illness
Why do heart muscle cells need their own blood supply ?
> because the heart has thick muscular walls
Why do arteries have
thick muscular walls ?
> to control blood flow by
contracting or dilating
Why do veins have valves ?
> to prevent blood from
flowing backwards
A common cause of heart attack
A healthy artery
A partly blocked artery
HDL (high density lipoprotein) cholesterol is good for you
LDL (low density lipoprotein) cholesterol is bad for you
What is a peer review ?
> a review by fellow scientists to check that a study
was done properly
- large enough sample
- fair test
What increases the confidence in a scientific claim ?
• if it has been peer reviewed
• if it has been replicated by other scientists
Risk of heart attack
Reading age
Correlation or cause ?
Shoe size
LDL cholesterol levels
There is a correlation between
shoe size and reading age.
But is there a causal link ? No
There is a correlation
between LDL cholesterol
levels and the risk of
having a heart attack.
But is there a causal link ? Yes
Homeostasis is the maintenance of a constant
internal environment.
Strenuous exercise, survival in hot or cold climates
affects homeostasis (eg temperature and water balance).
scuba diving
The cold water convects a lot of
heat away from the body.
The air gets thinner with less
oxygen as you climb higher.
Control of water balance
Water is gained from drinks, food and respiration and is
lost through sweating, breathing, faeces and the
excretion of urine.
A balanced water level is important for maintaining the
concentration of cell contents at the correct level for
cell activity.
The kidney works by:
• filtering small molecules from the blood to form
urine (water, salt and urea)
• reabsorbing all the sugar
• reabsorbing as much salt as the body requires
• reabsorbing as much water as the body requires
• excreting the remaining urine, which is stored
in the bladder
The kidneys balance water levels by producing dilute or
concentrated urine as a response to the concentration of
blood plasma.
The concentration of blood plasma varies with external
temperature, exercise level, intake of fluids and salt.
The concentration of urine is controlled by a hormone
called ADH, which is released into the bloodstream by the
pituitary gland.
water level in the blood
ADH secretion is controlled by negative feedback
Play animation
ADH levels
increased
danger
time
danger
ADH levels
decreased
Alcohol results in a greater volume of more dilute urine,
due to ADH suppression, which can lead to dehydration.
more dilute = less concentrated
The drug Ecstasy results in a smaller volume of less
dilute urine, due to increased ADH production.
less dilute = more concentrated
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Draw a straight line from the correct description to the correct explanation
ADH
hypothalamus
pituitary
increases
{because more water ends up in the urine}
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Why is it necessary to vaccinate a high percentage of a population ?
to prevent epidemics
Can distinguish what can be done (technical feasibility) from what
should be done (values).
Can explain why different courses of action may be taken in different
social and economic contexts.
How can antibiotics become less effective ?
due to random changes (mutations) in the genes of microorganisms
What is a ‘blind’ trial ?
one where the patient doesn’t know whether they have received the
real treatment or a placebo
What is a double ‘blind’ trial ?
one where the patient and the medical staff do not know whether the
real treatment or a placebo is being used
What is an open label trial?
Both the patient and the doctor know the treatment, no one is
given a placebo
Why are ‘blind’ and double ‘blind’ trials used ?
they reduce the influence of psychological factors and enable
evaluations to be more objective
Why are placebos not commonly used in human trials ?
when not giving a real treatment could result in patient deaths etc
or when patients could benefit from treatment
Can use data to develop an argument that a factor does/does not
increase the chance of an outcome.
Can identify the presence (or absence) of a plausible mechanism as
significant for the acceptance (or rejection) of a claimed causal link.
Epidemiological studies are the study of diseases in
populations of humans or other animals, specifically how, when and
where they occur.
Genetic study studies the types of genes a person has to look for alleles
that increase the risk of disease
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B3 - Life on Earth
Adaptations
• Species – similar organisms that are capable of breeding
to produce fertile offspring
Adaptations – features that
species have that help
them survive in their
environments
Cactus – spines to
Extinction can occur
if a species can’t adapt to
• Increased competition
• New predators
• New diseases
reduce water loss
deep, widespreading roots to
obtain water
Fish – gills to take
oxygen
Streamlined to move
easily
Swim bladder to
maintain position in
water
Food chains and webs
Food chains (start with plants, the producers)
•Animals are dependent upon each other
and their environment for survival.
•Food webs – show how all food chains
are inter-related and dependent on each
other (interdependence)
•Environmental changes can alter the
food web.
•All living things ultimately get their
energy from the sun
Energy transfer
•Plants capture energy from sunlight to build organic compounds
(photosynthesis).
•The compounds can be broken down to release
energy (respiration).
•Animals are consumers and break down food
molecules in respiration to release energy, used
for e.g. growth, keeping warm etc
•Only about 10% of the energy at each stage of a
food chain gets passed to the next level. The rest
-Escapes as heat and used for movement
-Excreted or cannot be eaten and passes to decomposers (bacteria
and fungi)
Energy flows into decomposers and detritivores (e.g.woodlice) as they
feed on dead organisms and waste material
The carbon cycle
Carbon dioxide is taken out of the atmosphere by photosynthesis
and the glucose produced is broken down during respiration, this
releases carbon dioxide back into the atmosphere
Dead organisms are broken down by microorganisms (decomposition)
to release carbon and this becomes part of a new organism.
Carbon dioxide is also added to the atmosphere by combustion (burning)
Measuring environmental change
Measuring environmental
change
Carbon dioxide levels are
rising, this is thought to be
linked to rises in
global temperature.
Climate change can be measured by
looking at the impact on living organisms
like phytoplankton.
Many species are threatened with extinction
if conditions change beyond their ability to
adapt.
The Nitrogen cycle
Life on Earth started at least 3,500 million years ago.
complex
How did this
incredible variety
of life evolve ?
simple
Some of the finches on the Galapagos Islands
Natural Selection
Charles Darwin
The key ideas relating to natural selection
Variation: All members of a particular species have
variations in their characteristics.
Environmental Changes in the environment whether due to
pressure:
climate or disease or other species can make it
difficult or impossible for some members of a
species to survive.
Population size: Population size tends to increase which means
more competition for resources.
Survival of
the fittest:
Members of a species which have the
characteristics to survive in an environment
will pass their successful characteristics on to
the next generation by passing on their genes.
Those that do not have successful
characteristics will tend to die out.
The fossil record is evidence for evolution
Embryonic evidence
Early embryonic development among vertebrates is very similar.
common ancestry
Evolution takes a long time
For 3 billion years life on Earth was single
celled organisms or very simple multi-celled
Then for the next 600 million years …
“Hi, my name is
Adam and this is
my partner Eve”
Only joking !!
X
This cartoon is incorrect. We didn’t evolve from apes.
common ancestor
We evolved from ape-like mammals.
3 theories about
human evolution
The branches in the
diagram show divergence
Tattersal
All of the species are
extinct except one – us.
Notice there are a lot
of question marks
Wood
Johanson
The evolution of a
larger brain gave some
early humans a better
chance of survival.
Not everyone agreed with the idea of natural selection.
Clarence Darrow and William Jennings Bryan, lawyers in
the famous 1925 Scopes trial in Tennessee, America.
To this day, the idea of natural selection is still challenged.
Creationism
This kind of explanation is not scientific
It is not based on observable evidence and cannot be tested.
If the conditions on Earth had, at any stage, been
different from what they actually were, evolution by
natural selection could have produced different results.
eg humans might not have evolved
Selective breeding
(“human” selection as opposed
to natural selection)
cabbage
cauliflower
broccoli
brussel sprouts
How to get sweet tomatoes
(basic idea)
1. Grow some normal non sweet tomatoes
2. Select seeds from the sweetest one and
breed some more tomatoes
3. Keep doing step 2 until you have tomatoes
with the desired sweetness
What can cause a species to become extinct ?
• the environmental conditions change;
• a new species that is a competitor, predator or
disease organism of that species is introduced;
• another organism in its food web becomes extinct;
Human activity is the main cause of modern extinctions.
Directly:
Indirectly:
The passenger pigeon – mainly due to hunting.
The dodo – destruction of habitat and the
introduction of other animals (eg pigs) to
the island (Mauritius) who ate the eggs
Maintaining biodiversity is an important part of
using the environment in a sustainable way.
Biodiversity may be important for the future
development of food crops and medicines.
Biodiversity means the variety of life that exists on Earth.
Sustainability means that the needs and requirements of
People are met without damaging the Earth for future
generations
Specimen paper questions on B3 - Foundation
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evolution
natural
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the brain
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Higher material
• interpret data on changes in a species in terms of
natural selection;
• recall that changes can occur in genes (mutations)
• understand that mutated genes in sex cells can be
passed on to offspring and may occasionally produce new
characteristics
• understand that the combined effect of mutations,
environmental changes and natural selection can produce
new species
Specimen paper questions on B3 - Higher
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