Download Science - B3 Revision

DHFS Science
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a Molecules of life
b Proteins and mutations
c Respiration
d Cell division
e The circulatory system
f Growth and development
g New genes for old
h Cloning
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Liver and muscle cells have
large numbers of mitochondria
due to large amounts of
respiration taking place.
Ribosomes are in the cytoplasm
and are the site of protein
synthesis
Some structures in cells, such as
ribosomes, are too small to be
seen with the light microscope
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Structure of DNA: two strands coiled to form a double helix, each
strand containing chemicals called bases, of which there are four
different types, with cross links between the strands formed by
pairs of bases.
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Watson and Crick used
data from other scientists
to build a model of DNA
X-ray data showed that
there were two chains
wound in a helix
Chemical data indicated
that the bases occurred in
pairs.
New discoveries, such as
Watson and Crick’s, are
not accepted or rewarded
immediately
◦ Shows the importance of
other scientists repeating
or testing the work to get
the same results
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A chromosomes is a long, coiled molecules of DNA, divided up into
regions called genes
Each gene contains a different sequence of bases and codes for a
particular protein
Only some of the full set of genes are used in any one cell; some
genes are switched off.
The genes switched on determine the functions of a cell. For
example, only pancreas cells switch on the gene for making the
hormone insulin.
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Proteins are synthesised at
the ribosomes in the
cytoplasm
An mRNA copy of the gene is
made because the gene itself
cannot leave the nucleus.
The mRNA travels from the
DNA to the ribosomes
mRNA from DNA is
called transcription (in
nucleus)
Proteins from mRNA is
called translation (at
ribosome)
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Protein structure is
determined by the
DNA base code
The base sequence
determines amino
acid sequence and
each amino acid is
coded for by a
sequence of 3 bases.
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DNA controls cell function by controlling the production of proteins,
some of which are enzymes
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Proteins are made of long chains of amino acids. Each protein has
its own number and sequence of amino acids, which fold into
differently shaped molecules, which have different functions.
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The function of proteins includes:
◦ structural (e.g. collagen)
◦ hormones (e.g. insulin)
◦ carrier molecules (e.g. haemoglobin)
◦ enzymes
Enzymes
 biological catalysts
 catalysing chemical reactions occurring in living cells:
◦ respiration, photosynthesis, protein synthesis
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having a high specificity for their substrate -the ‘lock and key’
mechanism.
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Changing temperature and
pH, away from the optimum,
will change the rate of
reaction of an enzymecatalysed reaction.
Enzyme activity is affected by
pH and temperature:
◦ lower collision rates at low
temperatures
◦ denaturing at extremes of
pH and high temperatures
◦ denaturing as an irreversible
change inhibiting enzyme
function
◦ denaturing changing the
shape of the active site.
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Q10 value for a reaction over a 10°C
interval
Q10 = rate at higher temperature
rate at lower temperature
For example, if rate of a certain
reaction is 10 units/min at 20 °C and
24 units/min at 30 °C. What is its Q10?
Q10 = 24 ÷ 10 = 2.4
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Changes to genes alter, or prevent the production of the protein
which is normally made. Cystic Fibrosis
◦ The sequences of DNA bases is changes which may lead to a different sequence
of amino acids, which causes a different shaped protein
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Mutation may occur spontaneously but can be made to occur more
often by radiation or chemicals.
Mutations are often harmful but may be beneficial or have no
effect.
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Production of ATP using energy from glucose
ATP is the ‘universal energy currency’ and is used
for all cellular processes that require energy such
as active transport and muscle contraction
Aerobic respiration
C6H12O6 + 6O2→ 6CO2 + 6H2O
Glucose + oxygen → carbon dioxide + water
Energy released leads to production of 30-38
ATP molecules
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Production of ATP using energy from glucose
ATP is the ‘universal energy currency’ and is used for all cellular
processes that require energy such as active transport and muscle
contraction
Anaerobic respiration (in animals)
C6H12O6 → 2C3H6O3
Glucose + oxygen → lactic acid
Energy released leads to production of 2 ATP molecules
Takes place when there is insufficient oxygen available due to
hard exercise
Incomplete breakdown of glucose
Lactic acid (oxygen debt) accumulates in muscles causing pain
and fatigue
Recovery of oxygen debt
◦ continued panting replacing oxygen allowing aerobic
respiration
◦ increased heart rate ensuring that blood carries lactic acid away
to the liver
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Production of ATP using energy from glucose
Rate of respiration is influenced by changes in temperature and
pH because enzymes are involved
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The rate of oxygen consumption can be used as an estimate of
metabolic rate (rate of chemical reactions in cells) because
aerobic respiration requires oxygen
Use the respiratory quotient (RQ) formula
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RQ = carbon dioxide produced / oxygen used
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Advantages of being multicellular:
◦ organism can be larger
◦ Allows for cell differentiation
◦ organism can be more complex
Becoming multi-cellular requires the development of
specialised organ systems:
◦ communication between cells (nervous system)
◦ supplying the cells with nutrients (digestive system)
◦ controlling exchanges with the environment
(respiratory and excretory system)
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DNA replication must take
place before cells divide
(both mitosis and meiosis)
‘unzipping’ of the
chromosome to form
single strands
new double strands
forming by
complementary base
pairing.
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New cells for growth are
produced by mitosis
◦ genetically identical because
they contain the same genetic
information
◦ Body cells are DIPLOID (contain
two copies of each
chromosome).
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in mitosis the chromosomes:
◦ line up along the centre of the
cell
◦ they then split
◦ the copies move to opposite
poles of the cell.
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Produces Gametes
Gametes are HAPLOID
(contain one chromosome
from each pair)
Chromosome number is
halved and each cell is
genetically different
because:
◦ one chromosome from each
pair separate to opposite
poles of the cell in the first
division
◦ chromosomes divide and the
copies move to opposite poles
of the cell in the second
division.
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Fertilisation results in genetic variation
because:
◦ gametes (1 sperm and 1 egg) combine to form a
diploid zygote
◦ genes on the chromosomes combine to control the
characteristics of the zygote.
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Structure of a
sperm cell is
adapted to its
function:
◦ many mitochondria
to provide energy
◦ an acrosome that
releases enzymes to
digest the egg
membrane
Feature
Reason
Small size
Lets red blood cells pass through narrow
capillaries
Increases SA:V allowing rapid diffusion of
oxygen
Flattened disc shape (biconcave disc)
Provides a large surface area, allowing
rapid diffusion of oxygen
Contains haemoglobin
Reacts with oxygen in the lungs to form
oxyhaemoglobin. In tissues the reverse of
this reaction happens.
Does not contain a nucleus
Increases amount of space inside the cell
for haemoglobin
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Plasma transports dissolved substances
around the body, including:
◦ Hormones
◦ Antibodies
◦ Nutrients, such as water, glucose, amino acids,
minerals and vitamins
◦ Waste substances, such as carbon dioxide and urea
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Arteries transporting blood away from the heart thick muscular and elastic wall in arteries
Veins transporting blood to the heart - large lumen
(inside diameter) and presence of valves in veins
capillaries exchanging materials with tissues permeability of capillaries
atria receive blood
valves
prevent
back flow
ventricles pump blood
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One circuit links the
heart and lungs
The other circuit links
the heart with the rest
of the body
The advantage of the
double circulatory
system in mammals,
means it can
withstand higher
pressures and
therefore greater rate
of flow to the tissues
Plant cell
Animal cell
Bacterial cell
Cell wall
NO cell wall
Sometimes has a cell wall
chromosomes.
chromosomes.
single circular strand of DNA
presence of a nucleus
presence of a nucleus
Absence of a nucleus, mitochondria
and chloroplasts
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Advantages and disadvantages of measuring growth
◦ length
◦ wet mass
◦ dry mass.
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Height and wet mass can be measured when an
organism is alive, but dry mass can only be
measured when an organism has had all its water
removed and is dead.
However, dry mass is the best measure of growth.
growth of parts of an organism may differ from the
growth rate of the whole organism
◦ e.g the head of a human foetus in the womb grows faster
than the rest of the body for the first two months.
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Undifferentiated cells called stem cells can
develop into different cells, tissues and
organs.
Stem cell research in humans/animals.
◦ adult and embryonic stem cells.
 Human embryos (embryonic stem cells)
 Parkinson’s disease
 Paralysis
 Adult bone marrow (adult stem cells)
 Leukaemia
Feature
Plants
Animals
Pattern of growth
Often can grow
continuously
Tend to grow to a
maximum size
How growth happens
Mainly by cell
enlargement (increase
in cell size)
Increasing the number
of cells
Where cell division
happens
Mainly at meristems –
found at the tips of
shoots and roots
In most tissues
Cell differentiation
Many cells can
differentiate
Most cells lose the
ability to differentiate
at an early stage
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Selective breeding has been
used to produce plants and
animals with useful and
desirable characteristics for
human use
◦ Dairy cows with high milk yield
◦ Pugs with a friendly nature
◦ Wheat with large seeds
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Selective breeding may lead to
inbreeding, which can cause
health problems within the
species due to a build up of
recessive alleles
◦ Diabetes in Labradors
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Select desired characteristics
Isolate genes responsible
Insertion the genes into other organisms
Replication organisms
Organisms display characteristic
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Take the genes from carrots that
control beta-carotene production
Put them into rice
Rice produce beta-carotene
Humans can then convert the betacarotene from rice into Vitamin A
Aimed at solving the problem of
parts of the world relying on rice
but lacking vitamin A
Aimed at preventing vitamin A
deficiency and blindness
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Take a gene out of an organism that has
resistance to:
◦ Herbicides
◦ frost damage
◦ disease
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Insert into crop plants
Grow plants that display characteristic
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The
production
of human
insulin by
genetically
engineered
bacteria
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advantage – organisms with desired features
are produced rapidly
risks – inserted genes may have unexpected
harmful effects
Ethics – unknown health risks and harm
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Changing an individuals genetic code in order
to prevent disease
◦ Inserting or deleting sequences of DNA
◦ E.g. Attempts to cure cystic fibrosis by inserting
healthy gene
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Controversial if the therapy is carried out on
embryos or gametes
◦ Possible unknown effects for future generations
◦ Requires trials on embryos
 Status of the embryo
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nucleus removed from an egg cell
egg cell nucleus replaced with the nucleus
from an udder cell
egg cell given an electric shock to make it
divide
embryo implanted into a surrogate mother
sheep
embryo grows into a clone of the sheep from
which the udder cell came.
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Some possible uses of cloning include
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Possible risks
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Ethics
◦ Mass producing animals with desirable characteristics
◦ Producing animals that have been genetically engineered to provide
human products
◦ Producing human embryos to supply stem cells for therapy and
organ replacement
◦ Animal viruses could be introduced into humans if using genetically
modified animals to supply replacement organs for humans
◦ Animal clones may age prematurely
◦ Status of the embryo
◦ Psychological issues if used for human reproduction (illegal)
Advantages of cloning plants
Can be sure of the characteristics
of the plant since all plants will
be genetically
identical
It is possible to mass produce
plants
that may be difficult to grow
from seed
Disadvantages of cloning plants
If plants become susceptible to
disease or to change in
environmental conditions
then all plants will be affected
Lack of genetic variation.