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B3 - Evolution
How did life start?
• the Earth is about 4,500 million years old
• there is evidence living things existed on Earth at least
3,500 million years ago
• no-one was there to record how life began.
• Over many millions of years these molecules joined with
other molecules, becoming gradually more complex and
dependent on each other. The process of evolution by
natural selection eventually led to all of the different living
things that we see on Earth today.
Darwin’s finches
• He noticed that the
finches (songbirds) on
the different islands
were fundamentally
similar to each other,
• but showed wide
variations in size,
beaks and claws from
island to island.
• For example, their
beaks were different
depending on the
local food source.
• Darwin concluded
that, because the
islands are so distant
from the mainland,
the finches which had
arrived there in the
past had changed
over time.
Natural selection
• Individuals in a species show a wide range of variation.
• This variation is because of differences in their genes
• Individuals with characteristics most suited to the environment
are more likely to survive and reproduce.
• The genes that allow these individuals to be successful are passed
to their offspring.
Lamarck
His theory involved two
ideas:
• the law of use and
disuse, and
• the law of inheritance of
acquired characteristics.
Evidence for
evolution: fossils
• All the main stages of its
evolution have been
preserved in fossil form.
• Over 60 million years, the
horse evolved from a dogsized creature that lived in
rainforests into an animal
adapted to living on the
plains, and standing up to 2
metres high.
Evidence for evolution: rapid changes
• Evolution is difficult to
observe because it usually
occurs over many years.
This is one reason why the
theory of evolution is
still a theory, not a law
• Before the Industrial
Revolution in Britain, most
peppered moths were of
the pale variety
• Moths with a mutant black
colouring were spotted
easily by birds and eaten
• Airborne pollution in
industrial areas blackened
the birch tree bark with
soot
Antibiotic-resistant bacteria
Microorganisms such as bacteria and
viruses reproduce rapidly and can
evolve in a relatively short time
Extinction
• changes to the
environment,
such as the
climate
• new diseases
• new predators
• new competitors
The dodo was a large flightless bird that lived in the Mauritius, a group of islands in
the Indian Ocean. These were uninhabited, and the dodo had no natural predators.
Then Mauritius were colonised by the Dutch in 1638. Dodos were hunted for
food and easy to catch, because they were not afraid of people. New competitors
were brought to the islands, including pigs, cats and rats, which ate the dodos'
eggs and young. Within 80 years, the dodo was extinct..
Evolution of humans
• Humans did not evolve from apes such as gorillas and
chimps. Instead, humans and apes share a common
ancestor that lived millions of years ago. This diverged over
time to form many species of hominid. All, including early
humans, became extinct - except modern humans
• The ability to stand upright, so predators and prey could be
seen more easily.
• Having a larger brain, providing the ability to plan ahead,
work together, and eventually speak.
Hormones
• chemicals
• secreted by glands
• transported by the
bloodstream to target
organs.
The nervous system
• The nervous system uses
electrical impulses to bring
about fast, but shortlived,
responses. It consists of
the:
• brain and spinal cord
(which make up the central
nervous system, or CNS)
• neurones.
• Nerve cells are also called
neurones
• Receptors
• Effectors
Reflex actions
• When a receptor is
stimulated it sends a
signal to the central
nervous system, and the
brain co-ordinates a
response. But sometimes a
very quick response is
needed, one that does not
require the involvement of
the brain. This is a reflex
action.
• Receptor detects a stimulus
(change in the
environment).
• Sensory neurone sends a
signal to a relay neurone.
• Motor neurone sends a
signal to an effector.
• Effector produces a
response.
Control of internal conditions
• Water content of the
body
This is controlled to protect
cells by preventing too
much water from entering
or leaving them. Water
content is controlled by
water loss from
• the lungs when we exhale
• the skin by sweating, and
• the body, in urine produced
by the kidneys.
Control of internal conditions
• Blood sugar level
This is controlled to
provide cells with a
constant supply of
energy. The blood sugar
level is determined by
the release and storage
of glucose, which is
controlled by insulin
Ion (salts) content of the body
This is controlled to protect cells by stopping too much
water from entering or leaving them. Ion content is
controlled by the loss of ions from
• the skin by sweating, and
• the body in urine produced by the kidneys.
Temperature of the body
This is controlled to maintain the temperature at which
enzymes work best. Body temperature is controlled by
• controlling blood flow to the skin
• sweating
• shivering.
C3 – Food, Plants
and Health
• Plants make their own food
through photosynthesis
• Carbohydrates
Sugars are carbohydrates.
They are small molecules
containing carbon, hydrogen
and oxygen
• Proteins
Amino acids are small
molecules containing carbon,
hydrogen and oxygen
• To make the compounds they
require, plants need these
elements:
• carbon
• hydrogen
• oxygen
• nitrogen.
Plant growth
Recycling elements
• As plants grow, they
remove elements such as
nitrogen, potassium and
phosphorus from the soil
through their roots. Over
time the soil loses these
elements and becomes less
fertile
• The elements needed by
plants are returned to the
soil when living organisms
die and decay. These
elements are also passed
on when animals eat other
living things.
• Plants can take up and use
nitrogen when it is in the
form of nitrates or
ammonium salts. Changing
nitrogen into a more reactive
substance is called nitrogen
fixation.
• Lightning
• Nitrogen fixing bacteria
• Nitrogen compounds are
returned to the soil through:
• excretion and egestion by
animals
• the death and decay of plants
and animals
• denitrifying bacteria in the
soil.
The nitrogen cycle
Intensive farming
1.
2.
3.
4.
•
•
•
To grow crops successfully,
farmers need to be able to:
Replace elements in the soil that
are removed by growing plants.
Stop weeds from competing
with their crops for space, water,
minerals and light.
Stop pests such as insects and
fungi from damaging crop
plants.
Stop the spread of disease by
insects and fungi.
Intensive farming methods
achieve these things by
using:
artificial fertilisers
herbicides (chemicals that kill
weeds)
pesticides (chemicals that kill
pests).
•
•
•
Removing hedgerows to make large
fields destroys animals' habitats, and
reduces species diversity.
Some of the lost species would have
eaten pests. So pest numbers grow,
and more chemical pesticides are
needed to control them.
Growing the same crop year after
year makes the soil less fertile, so
more chemical fertilisers are needed
Organic farming
People may choose organic food because they:
• believe it is a healthier
• think it tastes better
• feel it is kinder to livestock and the environment.
Organic farmers avoid using:
• artificial fertilisers (choosing natural ones such as manure
and compost instead)
• pesticides (they use hand-weeding and biological pest
controls, such as ladybirds that eat aphids)
• hormones and other additives in livestock feed
Food additives
• Processed foods, including vegetable oils, may have chemicals
added to them. These additives have different roles, including
extending a product’s shelf life and improving its taste and
appearance
Type of
additive
Example
Typical use
colouring
Tartrazine
(E102)
orange colouring for soft drinks, sweets and
sauces
emulsifier
Lecithin
(E322)
allows oil and water to mix to make margarine,
ice cream and salad cream
preservative
Benzoic
acid (E210)
used in many foods to stop harmful
microorganisms from growing
sweetener
Aspartame
(E951)
in low-calorie drinks and food
Food safety 1
• Food may contain chemicals that could be toxic or harmful.
These include:
• natural chemicals
• chemicals formed during food processing or cooking
• herbicides and pesticides used by farmers.
Moulds
Moulds may grow on crops before harvesting, or while they
are being stored. They may release harmful chemicals. For
example, nuts and cereals can contain aflatoxin - released
by a common fungus called Aspergillus. Aflatoxin is
poisonous and can cause liver damage.
Food safety 2
• Overcooking or burning food produces PAHs (polycyclic
aromatic hydrocarbons), which are suspected of causing
cancer.
• Frying food to make crisps and chips produces acrylamide,
a chemical known to cause cancer if given to laboratory rats
in high doses.
Herbicides and pesticides
Farmers may use herbicides to kill weeds, and pesticides to
kill insects and other pests. These chemicals remain on the
food unless they are washed away by rain. So it is
important to wash fruit and vegetables before use.
You may wish to view this funny BBC News video from 2006
about the need for accurate food labelling.
Digestion
• Digestion
• Our bodies cannot use most
of our food directly. First, it
must be broken down into
small molecules that are
soluble (they can dissolve).
This is called digestion, and
occurs in the digestive
system.
• Starch is broken down into
glucose (a sugar).
• Proteins are broken down
into amino acids.
Amino acids and proteins
• Cell growth
Cells grow by making new
proteins from amino acids that
are transported in the
bloodstream. Amino acids join
together end to end to make
proteins such as haemoglobin
Proteins are also found in:
• Hair
• Muscle
• Skin
• Tendons.
Excretion
Your body cannot store excess
amino acids. The liver breaks
them down to form urea. This is
removed from the blood by the
kidneys, and lost when you
urinate
Diabetes
• Too little glucose causes
confusion, unconsciousness,
even coma.
• Too much glucose causes
exhaustion and blurred vision.
• Processed foods often contain
a lot of sugar. This is
absorbed easily into the
blood, causing a rapid
increase in the blood glucose
level. Insulin is a hormone
that reduces the blood
glucose level.
Type 1 diabetes
Type 2 diabetes
How it
works
The pancreas stops
making enough insulin
The body no longer
responds to its insulin
How it is
controlled
Injections of insulin
Exercise and appropriate
diet
Occurs
Childhood
Later in life
P3 – Energy and Radioactivity
Atomic structure and radiation
• The protons and neutrons are found in the nucleus at the
centre. The electrons are arranged in energy levels, or
shells, around the nucleus.
• Radiation
Radioactive elements give out ionising radiation from their
nuclei. This happens all the time, whatever is done to the
substance.
• Alpha radiation
Alpha radiation consists of alpha particles. These are identical
to the nucleus of a helium atom, which comprises two protons and
two neutrons.
• Beta radiation
Beta radiation consists of high-energy electrons that are
emitted from the nucleus. These do not come from the electron
shells or energy levels around the nucleus. Instead, they form
when a neutron splits into a proton and an electron.
• Gamma radiation
Gamma radiation is very short wavelength (high frequency)
electromagnetic radiation. This is similar to other types of
electromagnetic radiation such as visible light and X-rays, which
can travel long distances.
Penetrating properties of radiation
Half-life
There are two definitions of
half-life, but they mean
essentially the same thing:
• The time it takes for the
number of nuclei of the
isotope in a sample to
halve.
• The time it takes for the
count rate from a sample
containing the isotope to fall
to half its starting level.
• Isotopes
All the atoms of a given element have the same number of
protons. The number of neutrons can vary. Atoms of the
same element that have different numbers of neutrons are
called isotopes of that element.
Radiation doses
Doses of radiation are measured in sievert
(Sv) - the amount of possible harm it could
do to the body. The dose is based on:
• the amount of radiation
• the type.
If the radioactive source is inside the
body, perhaps after being swallowed or
breathed in:
• Alpha radiation is the most dangerous,
because it is absorbed easily by cells.
• Beta and gamma radiation are not so
dangerous, as they are less likely to be
absorbed by a cell and usually just pass right
through it.
If the radioactive source is outside the
body:
• Alpha radiation is not as dangerous, because
it is unlikely to reach living cells inside the
body.
• Beta and gamma radiation are the most
dangerous sources, as they can penetrate the
skin and damage the cells inside.
Radiotherapy
Although ionising radiation can cause cancer, high doses can be
directed at cancerous cells to kill them. This is called radiotherapy.
About 40% of people with cancer undergo radiotherapy as part of
their treatment. It is administered in two main ways:
1. From outside the body using X-rays or the radiation from
radioactive cobalt.
2. From inside the body by putting radioactive materials into the
tumour, or close to it.
Some normal cells are also damaged by the radiation, but they
can repair themselves better than the cancer cells are able to.
Sterilising
Surgical instruments are sterilised using high doses of gamma
radiation. Food can also be sterilised by gamma radiation from
radioactive cobalt. The radiation kills microbes, preserving the
food for longer.
Monitoring radiation
• The human senses cannot detect radiation, so we need
equipment to do this.
• Photographic film goes darker when it absorbs radiation, like
when it absorbs visible light. The more radiation the film
absorbs, the darker it is when developed.
People who may be exposed to
radiation regularly include:
• medical staff
• workers at nuclear power stations
• research scientists.
Dose in sievert (Sv)
Sterilising surgical
instruments
25000
Typical radiotherapy dose
60
Legal dose limit for a worker
0.02
Mean annual dose from
natural radiation
0.002
Typical chest X-ray
0.00002
Flying from the UK to Spain
0.00001
Electricity – a secondary energy source
Coal, oil and natural gas are primary energy sources. Electricity is a
secondary energy source, because we use primary energy sources to
produce it.
Electricity is convenient because:
1. It is transmitted easily over distance (through electricity cables).
2. It can be used in many ways (think of electric lamps, heaters, motors,
and so on).
Generating electricity
• Generators are the devices
that transfer kinetic energy
into electrical energy. They
can be turned directly, for
example, by:
• wind turbines
• hydroelectric turbines
• wave and tidal turbines.
Efficiency of energy transfer
Electric lamps
Most of the electrical energy is
transferred as heat rather than
light energy. This is the Sankey
diagram for a typical filament
lamp
Modern energy-saving lamps
work in a different way. They
transfer a greater proportion of
electrical energy as light
energy. This is the Sankey
diagram for a typical energysaving lamp
Calculating efficiency
• The efficiency of a device such as a lamp can be calculated
using this equation:
• efficiency =
useful energy transferred
/
energy supplied
× 100
• The efficiency of the filament lamp is 10 ÷ 100 × 100 =
10%. This means that 10% of the electrical energy supplied
is transferred as light energy (90% is transferred as heat
energy).
Different energy resources
• Our renewable energy resources
will never run out. Their supply
is not limited. There are no fuel
costs, either. And they typically
generate far less pollution than
fossil fuels.
•
•
•
•
•
Renewable energy resources
include:
wind energy
water energy (wave machines,
tidal barrages and hydroelectric
power)
geothermal energy
solar energy
biomass energy (for example,
energy released from wood).
The fuel for nuclear power
stations is relatively cheap.
But the power stations
themselves are expensive to
build. It is also very expensive
to dismantle old nuclear power
stations or store radioactive
waste, which is a dangerous
health hazard
Nuclear power stations
• The main nuclear fuels are uranium and plutonium, both of which are
radioactive metals. Nuclear fuels are not burnt to release energy. Instead,
they are involved in nuclear reactions in the nuclear reactor which leads to
heat being released.
Category
Examples
Disposal
Low level
Contaminated equipment,
materials and protective
clothing
Put in drums and surrounded by
concrete
Intermediate
level
Components from nuclear
reactors, radioactive
sources used in medicine
or research
Mixed with concrete, then put in a
stainless steel drum in a purposebuilt store
High level
Used nuclear fuel and
chemicals from
reprocessing fuels
Stored in a purpose-built store where
air can circulate to remove the
heat produced
Nuclear fission (Higher Tier)
• Nuclear power stations use the
heat released by nuclear reactions
to boil water to make steam. The
type of nuclear reaction used is
called nuclear fission. In nuclear
fission:
• a neutron collides with an
uranium nucleus (which is large
and unstable)
• the uranium nucleus splits into
two similar-sized smaller nuclei
• more neutrons are released
• these neutrons can then collide
with more uranium nuclei.