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Revision
B1
What is DNA?
Chromosomes…
are X-shaped
objects found in
the nucleus of
most cells
They consist of long
strands of a
substance called
deoxyribonucleic acid,
or DNA for short.
A section of DNA that has
the genetic code for
making a particular
protein is called a gene.
Sex cells and chromosomes
Human body cells each contain 23 pairs of chromosomes.
Parents pass on their genes to their offspring in their sex
cells:
• Female sex cells are called egg cells, or ova.
• Male are called sperm.
Sex cells and chromosomes
Human body cells each contain 23 pairs of chromosomes.
Parents pass on their genes to their offspring in their sex
cells:
• Female sex cells are called egg cells, or ova.
• Male are called sperm.
Female
Male
Gender
• All normal egg
cells produced
by a human
ovary have an X
chromosome.
• Half of the sperm
carry an X
chromosome,
and half a Y.
Variation in a species
Most characteristics, such as height, are determined by
several genes working together. They are also influenced by
environmental factors. These include:
• climate
• diet
• physical accidents
• culture
• lifestyle.
For example, an individual might inherit a tendency to
tallness, but a poor diet during childhood will result in poor
growth and a shorter individual.
Alleles (pronounced al-eels)
• Chromosomes carry genes
• Different versions of the
same gene are called
alleles
• For any gene, a person may
have the same two alleles
or two different ones:
• If both the alleles are the
same, the individual is
homozygous for that
gene.
• If the alleles are different,
they are heterozygous for
that gene.
• Alleles may be either
recessive or dominant.
• A recessive allele only
shows if the individual
has two copies of the
recessive allele. For
example, the allele for
blue eyes is recessive.
You need two copies
of the allele to have
blue eyes.
• A dominant allele
always shows, even if
the individual only has
one copy of it. For
example, the allele for
brown eyes is
dominant. You only
need one copy of it to
have brown eyes (and
two copies will still
give you brown eyes).
Cystic Fibrosis
• Cystic fibrosis
(CF) is caused
by a recessive
allele, written
as f.
• You need to
inherit two
copies of the
faulty allele to
be born with CF.
If you have just
one copy, you
are a carrier,
but will not
experience any
symptoms. If
two carriers
have a child
together, there
is a one in four
chance of it
inheriting the
disorder. The
genetic diagram
shows why.
Huntington’s disorder
• Huntington’s disorder is
caused by a dominant
allele, written as D.
• The symptoms usually
develop in middle age, and
include problems
controlling your muscles
and forgetfulness.
• You only need to inherit
one copy of the faulty allele
to have Huntington’s
disorder
Genetic Testing
• http://news.bbc.co.uk/player/nol/newsid_6230000/newsid_
6235300/6235373.stm?bw=bb&mp=rm
Gene Therapy
• Gene therapy involves inserting
copies of a normal allele into the
chromosomes of an individual
who carries a faulty allele.
The basic process
Gene therapy involves these
basic steps:
1. Doing research to find the gene
involved in the genetic disorder.
2. Cutting out the normal allele
(special enzymes are used to do
this).
3. Making many copies of the
allele.
4. Putting copies of the normal
allele into the cells of a person
with the genetic disorder.
Asexual reproduction
• Asexual reproduction only requires one parent, unlike
sexual reproduction, which needs two.
• As a result, the offspring are genetically identical to the
parent, and each other. They are clones.
Cloning
• Twins are genetically
identical because they
are formed after one
fertilised egg cell splits
into two cells. They are
natural clones.
• Fusion cell cloning
involves replacing the
nucleus of an unfertilised
egg with one from a
different cell. The
replacement can come
from an embryo. If it is
from an adult cell, it is
called adult cell cloning.
Revision
C1
The Atmosphere
The Earth is surrounded by a
mixture of gases called the
atmosphere. The main gases
in the atmosphere are:
• nitrogen (about 78%)
• oxygen (about 21%)
• argon (about 1%).
There are smaller proportions of
other gases, including:
• water vapour
• carbon dioxide.
The pie chart shows the relative
amounts of the three main
gases.
Burning…
• When a hydrocarbon burns it joins with oxygen…
Methane
+
oxygen
→
Burning…
Oxygen
Hydrogen
• When a hydrocarbon burns it
joins with oxygen…
Methane
+
oxygen
Carbon
→
The heat you supply with a match
Splits up the atoms…
This bit needs energy, lets say 10 Joules
Burning…
Oxygen
Hydrogen
Carbon
• When a hydrocarbon burns it
joins with oxygen…
Methane
+
oxygen
→
→ Carbon dioxide + water
The atoms then recombine to make carbon dioxide and water
This bit needed 10
Joules…
When these atoms
recombine, they release 15
Joules
Combustion
compound
carbon
monoxide
carbon
dioxide
sulfur
dioxide
nitrogen
monoxide
nitrogen
dioxide
water
formula
CO
CO2
SO2
NO
NO2
H2O
carbon
atoms
1
1
1
1
sulfur
atoms
1
nitrogen
atoms
hydrogen
atoms
oxygen
atoms
diagram
2
1
2
2
1
2
1
Pollutants from burning fossil fuels
• Most of the UK’s electricity is produced by power stations
that are fuelled by fossil fuels, which contain carbon.
• carbon dioxide, CO2
• carbon monoxide, CO (when there is not enough oxygen,
so burning is incomplete)
• particulate carbon, C (soot and smoke from incomplete
burning)
• sulfur dioxide, SO2.
Hazards of pollutants
• The pollutants generated by burning fuels do not disappear when
they enter the atmosphere. For example, carbon dioxide is used
by plants in photosynthesis
pollutant
where it goes
what it does
carbon dioxide
dissolves in rain water and
sea water
makes rain water and sea
water more acidic
(lowers their pH)
particulate carbon
lands on various surfaces,
such as walls and
buildings
makes the surfaces dirty
sulfur dioxide
reacts with water and
oxygen in the air
makes acid rain
nitrogen dioxide
reacts with water and
oxygen in the air
makes acid rain
Reducing pollution from power stations
• The only way to reduce the amount of carbon dioxide given
off by power stations is to burn less fossil fuels. This means
using less electricity
Reducing pollution from vehicles
• Designing engines that are more efficient.
• Using public transport, such as buses and trains, instead of
cars.
• Walking instead of driving.
Cleaning exhaust gases
• Catalytic converters are devices that convert harmful waste
gases into less harmful ones
• Nitrogen monoxide is reduced to nitrogen.
• Carbon monoxide is oxidised to carbon dioxide.
P3
How big? How old?
The Universe began with a
“big bang” about 14
thousand million years ago.
Our solar system was formed
about five thousand million
years ago
Diameter in kilometres
Number of times larger than
the Earth
Earth
12,756
1
Sun
1,380,000
108
Milky Way
1 million million million
74,000,000,000,000
The solar system
The solar system consists of:
• the Sun (a star)
• planets and dwarf planets in orbit around the Sun
• satellites (moons) in orbit around most of the planets
• comets and asteroids in orbit around the Sun
Comets and asteroids
• Comets
Comets are balls of ice and dust that orbit the Sun. Their
orbits are different to those of planets: they are elliptical.
• Asteroids
Asteroids are rocky objects, and smaller than planets. Most
are found in an “asteroid belt” in orbit around the Sun
between Mars and Jupiter.
• It is thought that an asteroid colliding with the Earth helped
to drive the dinosaurs to extinction.
Stars
The structure of the Earth
The Earth is almost a sphere.
These are its main layers,
starting with the
outermost:
• the crust (relatively thin
and rocky)
• the mantle (has the
properties of a solid, but
can flow - very slowly)
• the core (made from
nickel and iron).
Problems
Wegener’s theory of continental drift was
rejected by many geologists. Some of
the reasons for this were:
• The movement of continents could not
be detected (because they only move
by a few centimetres per year).
• No-one could provide a good
explanation of how whole continents
could move apart.
• Wegener was not a geologist (he
trained as an astronomer and
meteorologist).
• There were other, simpler, explanations
for the same evidence.
• It was felt his idea was too big for the
evidence at hand.
Magnetic field reversal
Seafloors spread by
about 10cm per year.
This spreading leaves a
characteristic pattern of
magnetism in the rocks
on the ocean floor that
can be "read" by
scientists.
The Earth’s magnetic
field has not always had
the same North-South
alignment. Every so often
it reverses direction for thousands or millions
of years. Iron-rich
minerals in molten
magma line up in the
magnetic field, and this
alignment is preserved
when the magma
solidifies.
Seafloor spreading
Earthquakes
Volcanoes
What they do
Constructive plate
boundary
Make new crust
Destructive plate
boundary
Make mountains
Conservative plate
boundary
Do not make or destroy
land
Stars
Galaxies and the Universe
• There are thousands of
millions of galaxies in
the Universe. Each
contains thousands of
millions of stars. The
Milky Way is the galaxy
that contains our Sun the star at the centre of
the solar system.
The Big Bang
• Scientists have gathered a lot of evidence and information
about the Universe.
• It states that about 14 thousand million years ago all the
matter in the Universe was concentrated into a single
incredibly tiny point. This began to enlarge rapidly in a hot
explosion, and it is still expanding today
• expand for ever
• eventually stop expanding, or
• eventually stop expanding, but then contract again in a “big
crunch”.
Hubble’s Law
• Astronomers have
discovered that distant
galaxies are moving
away from us. The
further away they are,
the faster they are
moving. This is called
Hubble’s Law.
Optical telescopes
• They can only be used at
night.
• They cannot be used if the
weather is poor or cloudy.
• They cannot be used in
areas where there is bright
street lighting (“light
pollution”).
Alien planets
• Astronomers have detected planets around some nearby
stars. As there are a lot of stars in the Universe, many
scientists think it is likely life exists on other planets. But
there is no evidence to support this view.
• You may wish to view this BBC News item from 2006
about how a new type of research radio telescope could
pick up TV transmissions from alien civilisations (if they
exist).