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Mass Transport
THE NEED FOR TRANSPORT
Transport is needed to move substances from one place to another
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Diffusion is the movement of particles in a liquid or gas from an area of high particle concentration to an area of low
particle concentration (down the concentration gradient)
In single celled organisms and very small multicellular organisms, diffusion can be used alone for transport:
The distance required for oxygen and nutrients to diffuse in and waste to diffuse out is very short
It has a large surface area to volume ratio (SA:V), meaning there is a large area surface area for substances to
diffuse into
They have low metabolic demands
For large multicellular organisms, every cell requires oxygen and glucose to carry out respiration in order to carry out
all life processes
...

Since diffusion alone would be too slow, large multicellular organisms have a mass transport system as well - series
of structures that allow substances to be moved systematically through an organism
...
This system allows nutrients and
waste to be transported around the body and then into the cells using osmosis, active transport and diffusion,
allowing the cells to carry out functions efficiently
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A way of moving materials fast enough e
...
heart pumping
Way of making sure materials are going in the right direction e
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valves
A transport medium
Way of adapting the rate for the organisms needs e
...
HR

CIRCULATION SYSTEMS
Plants have a open circulatory system however most animals have a closed circulatory system, the advantages of this
are:
The pressure can be increased to increase the flow of blood
The flow can be directed towards the organs that are in the most need of oxygen and nutrients
Animals like fish have a single circulation system; this is where the heart pumps the blood to the organs of gas
exchange and the blood travels around the body before returning to the heart
...
They move more when away from water and
produce more waste that needs to be removed quickly, therefore they require a faster supply of oxygen and
nutrients
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• The systemic circulation carries oxygenated blood from the heart to the cells of the body and deoxygenated
blood back to the heart
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This helps ensure that oxygenated and deoxygenated blood do not mix
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Deoxygenated blood travels in small vessels in the lungs to allow gas exchange to take place, this happens at a low
pressure to prevent the vessels from bursting
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Blood and Blood vessels

Arteries
Arteries carry blood away from the heart to cells in the body
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The arteries branch out when leaving the heart - as they get further away from the heart the lumen
becomes smaller
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Blood is pumped out of the heart regularly and with every pump there is a high pressure of blood in the
arteries, the arteries closest to the heart have to withstand the pressure:
– Their walls have a lot of elastic fibers so they can stretch and recoil depending on the volume of the
blood without causing damage and also a lot of collagen that increases the strength to help
withstand pressure
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Capillaries
Capillaries are very small vessels that branch throughout the tissues of the body forming capillary beds
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There is a capillary close to every cell therefore substances easily diffuse between cells and the blood,
blood also flows relatively slow therefore giving more time for diffusion to occur
...
This helps them fit In tissues and allows
rapid diffusion to occur
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Veins
Veins carry blood towards the heart, the blood is usually deoxygenated apart from the pulmonary vein that carries highly oxygenated blood from the lungs to the heart and the umbilical vein that carries
oxygenated blood from the placenta to the fetus
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Tiny venules leave from the capillaries and they keep combining till they form only two large veins that
carry the blood from the tissues back to the heart :
– Inferior vena cava : blood from the lower parts of the body
– Superior vena cava : blood from the upper part of the body
Veins hold a large volume of blood - more than half of the body's volume of blood is in the veins at once
...
The low pressure blood then returns to the heart and lungs to get oxygenated again before
recirculating
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:
– Larger veins contract when physical activity takes place allowing the blood to get back to heart,
valves aid in stopping the blood flowing backwards
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Cardiac Cycle
THE HEART
The heart is made of cardiac muscle(intrinsic rhythm and does not fatigue) The right side of the heart receives blood
from the body and pumps it to the lungs
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The two sides are split by the septum to stop the blood from either side mixing
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Tricuspid valve - an atrioventricular valve and
consists of three flaps, prevents back flow of
blood from the right ventricle into the right
atrium
Right ventricle - walls contract to pump blood
out the pulmonary arteries
Pulmonary valve - semilunar valve that
prevents the back flow of blood into the right
ventricle
Pulmonary arteries - carry deoxygenated
blood to capillaries in the lungs
Pulmonary veins - carries oxygenated blood
from the lungs to the heart
Left atrium - walls contract to force blood into
the left ventricle when pressure increases
Bicuspid valve - atrioventricular valve that prevents the back flow of blood into left atrium
Left ventricle - walls contract to pump blood out the aorta
Aortic valve - semilunar valve that prevents the back flow of blood into the right ventricle
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Because the pressure in
the ventricles is higher than the pulmonary artery and aorta, the aortic valve and pulmonary valve are forced open
and blood flows out into the arteries and cardiac diastole begins to take place
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The blood
returns to the heart via the vena cava and the pulmonary vein, into the atria and the process starts again
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Their primary function is
to transport oxygen around the body, the protein haemoglobin helps with this
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- Affinity: attraction between molecules
- Partial pressure: Pressure exerted by one gas in a mixture of gases
TRANSPORT OF OXYGEN

Haemoglobin – a respiratory pigment that enables blood to carry enough oxygen for the body’s needs
...
Therefore
the oxygen carried by plasma alone, isn’t enough
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- So the oxygen in the air diffuses into the blood and into the red blood cells
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- Hb + 4O2 HbO8
OXYGEN DISSOCIATION CURVE
Shows the percentage saturation of haemoglobin as it passes through areas of the body with different
partial pressures of oxygen
Low partial pressure would be expected at actively respiring muscles and the Hb saturation would also be
very low
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So if a blood cell was flowing through a capillary in the lungs, it would be
in an area of higher partial pressure (of oxygen) therefore it would
unload oxygen and haemoglobin saturation is increased
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As it enters the
capillaries in the muscles, it is in an area of low oxygen partial pressure,
therefore it offloads(dissociates oxygen) and decreases in Hb saturation
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This molecule
combining with the first haem group, causes the haemoglobin to
change shape
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– affinity increases rapidly
- The curve then flattens as it becomes harder for the last oxygen molecule to bind onto the haem
group – decreased area
THE EFFECT OF PH – Bohr effect
The number of oxygen molecules carried by haemoglobin depends on pH as well as oxygen tension
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An acidic environment has a high
concentration of hydrogen ions, these hydrogen ions displace
oxygen from haemoglobin and improves the release into the
tissues
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The carbon dioxide dissolves to form
carbonic acid – which stimulates the release of oxygen from
haemoglobin
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Haemoglobin acts as a buffer and a form of homeostasis – keeping the blood pH in the optimum range
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TRANSPORT OF CARBON DIOXIDE

-

-

-

Carbon dioxide is released by respiring cells and diffuses into the blood plasma
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then 25% diffuses into the red blood cells and attaches on to the amino acid side chains of
haemoglobin forming carbaminohaemoglobin – can still carry oxygen on its haem groups
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CO2 + H2O H2CO3 H+ + HCO-3
The hydrogen ions attach to the haem group (if they were free, they’d lower the bloods pH), they
displace the oxygen and limit the pH change
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Carbaminohaemoglobin releases CO2 and the higher
PO2 dislodges the H+ ions from the haem groups
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Carbonic acid then forms and dissociates due to the carbonic anhydrase to give water and CO2

FACTORS THAT EFFECT BLOOD GAS TRANSPORT
Carbon monoxide tension – gas released from car exhausts, it
competes with oxygen for the haem groups, which it binds with
irreversibly, causing death
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The fetal haemoglobin associate’s oxygen at the partial
pressure that the mother’s haemoglobin is dissociating oxygen
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Temperature – as temperature increases, less oxygen associates with
haemoglobin
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As
temperature rises more oxygen is released from haemoglobin
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Myoglobin – skeletal muscles contain their own respiratory pigment
myoglobin, this has a similar structure and function to haemoglobin,
it holds and stored oxygen in the muscle till its required
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It acts as an oxygen store and only releases oxygen at
extremely low partial pressures
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Diseases like anemia will reduce the
quantity of red blood cells and haemoglobin that can carry oxygen
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So the ODC shifts to the left as they have a higher affinity
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So the ODC shifts to the left as they release and
take in more oxygen, however the haemoglobin should have an equal affinity
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It is a
progressive disorder and usually affects the coronary arteries and the carotid arteries; arteries of the neck
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It is more likely to occur in arteries than veins as they contain blood flow at a high
pressure; endothelial walls are more likely to damage
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This is where blood cells, mainly macrophages, move into the area
damaged
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• These white blood cells and lipids from the blood join and form fatty streaks under the
endothelium
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• The plaque partially blocks the lumen of the artery and restricts blood flow, increasing blood
pressure
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• This blood clot can completely block an artery and restrict blood flow or block any blood vessel in
the body
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STEPS OF ATHEROSCLEROSIS
Step 1 – Endothelial damage
• The endothelium(tunica intima) is a very thin layer of cells within the blood vessel wall and the
damage is usually seen in the intima layer as the artery initially has a higher blood pressure
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These are soluble fatty proteins that carry cholesterol from the
liver to tissues
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• A lesion begins to occur and lipids deposit in the arterial wall causing fatty streaks
Step 2 – Inflammatory response

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•
•
•
•

•
•

Once the lipids accumulate, The LDL’s move into the tunica intima from the lumen and are oxidized
by metalloproteases that are released by endothelial cells causing the endothelial cells to express
receptor molecules that trigger an inflammatory response
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Monocytes are white blood cells that differentiate into macrophages when moving into the tunica
intima
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Therefore they try to reduce the levels of cholesterol by engulfing the
LDL’s
However many macrophages die in this attempt as they have a buildup of cholesterol within,
transforming them into foam cells
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Foam cells
also release chemokine to attract more macrophages
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This leads to a negative effect; platelets begin to form clots and cholesterol continue to deposit
within the arterial wall; forming an atheroma

Step 3 – Plaque/ atheroma formation
• Fibrous tissue is also present within the arterial wall alongside calcium salts that accumulate
...
Here they secrete
extracellular matrix enzymes that form a fibrous cap over the deposited plaque, sealing it into the
arterial wall and hardening the plaque
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• If it were to rupture, blood coagulation occurs and thrombosis occurs to restrict blood flow, this can
lead to strokes or cardiac arrest
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This increases the pressure on the arteries walls, and they become weakened
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• The large amount of blood loss and decreased blood pressure causes death; unless diagnosed
before bursting (surgery performed) then aneurysms are fatal
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This leads to an increase in blood pressure due to stress on the walls of the artery
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• Blood flow is reduced which reduces O2 supply and CO2 removal, this causes damage to arterial
walls
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•
•

Cells are unable to function, and the tissue eventually die, leading to ischemia
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Evident in damaged nephron units within the medulla and
cortex of the kidney
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During exercise, the
narrow arteries can’t supply enough oxygenated supply, anaerobic respiration begins to take place
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• Can help reduce it by losing weight and not smoking however if arteries continue to narrow then
angina gets worse and a person Is need of a stent(inserted in the coronary artery to hold it open) or
a heart bypass
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The walls of an artery are
hardened because of the plaque, making it prone to damage
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Lastly if the endothelial lining is
damaged then the clotting process is also triggered
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This can quickly block the entire artery
(especially when atherosclerosis has already occurred) and prevent blood flow; nutrients and
oxygen can’t reach the heart
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STROKES
• Strokes are due to a change in blood supply to the brain; bleeding form damaged capillaries or a
blocked vessel (usually carotid arteries) restricting blood flow to the brain
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• A blocked vessel can be a result of clotting or atheroma
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• Side effects happen very quickly; main arteries that get blocked can lead to death but blocks in
smaller arterioles are not as dangerous
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– The collagen fibres of the damaged vessel are now exposed
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– The thrombocytes cause a protein called thromboplastin to be released
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– Thrombin then catalyzes the conversion of fibrinogen (soluble protein) to fibrin (solid insoluble fibres)
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Factor that affects the personal perception of risk:
how familiar you are with the activity
how much you enjoy the activity
whether or not you approve of the activity
Epidemiology: the study of patterns of health and disease, to identify causes of different conditions and patterns of
infection
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You can compare a group of
people who have the same factors to the average risk for the whole population
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When two sets of data change together, they may have a correlation, however it doesn’t mean they cause
one another, they may be linked by another factor
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DESIGNING STUDIES
The larger the sample size, the more meaningful the study
Changing one factor and keeping the rest controlled would be the most accurate, however that can’t be
done when investigating humans, as lifestyles are very different and complex
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– metadata analysis (meta-analysis)
EVALUATING STUDIES
Check if the methodology is valid; answers the question/ hypothesis the scientists are asking
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Important to know who carried out the research, who funded it and where it was published, to identify if
there is any bias
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Examples are arteries that easily damage, a
tendency to develop hypertension, problems with cholesterol balance
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Gender: under the age of 50, men are more likely to develop CVD
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Identical twin studies are good for investigating genetic factors, as if anything different happens, its environmental
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High Blood pressure

If your blood pressure is regularly above 140/90 mmHg, you have high blood pressure or hypertension
This can be a sign of atherosclerosis, as the arteries become less flexible when there is a buildup of plaque or when
the artery narrows
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Being overweight can lead to high blood pressure and type 2 diabetes, which increases the risk of damage

LINKING DATA TO RISK FACTORS
Modifiable factors: risk factors that can be changed, may result in different figures over time depending on changes
e
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smoking, obesity, diabetes, high cholesterol, high blood pressure, psychological factors
Non-modifiable risk factors: factors that can’t be changed, such as age, genes and sex can also be aligned to data e
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Oestrogen release correlates to reduced plaque build up
Sample size: size of participant population is important, for example a CVD study on 20 young males compared to
1500 old males with family history of coronary defects would yield different results
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g
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Standard deviation: how much the data deviates from the mean
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g
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EVALUATING A STUDY
C – CURRENCY – timeliness of information, is the information revised or updated and does the topic require current
information
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A – ACCURACY – reliability, truthfulness, and correctness of the data
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Does the point of view
seem objective and impartial with no political, religious or personal bias?

CVD Treatments
BMI = weight/height2

Drug Type
Antihypertensives

Key Info

Benefits

Risks

Made to control hypertension
(high BP)
Diuretics - increase volume of
urine, to decrease blood
volume; decreased BP
Beta-Blockers - sympathetic
nervous system stimulates
arteries to constrict, betablockers are inhibitors that
prevent these signals from
being sent, arteries dilate

Lower BP
Reduces problems
associated with CVD
Reduces risk of damage to
kidneys and
eyes(capillaries)

BP may become too low
Side effects - swelling, fatigue
and impotence can
discourage used as risk may
redevelop

Statins

Lower cholesterol in the blood
by blocking the enzyme coenzyme Q10 that produces
cholesterol and the
production of LDLs

Lowers cholesterol
Balances HDLs and LDLs
Reduces arterial
inflammation
Few side effects recorded
Effective - 11
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5% without

Risk of relying on statin rather
than improving/ maintaining
healthy lifestyle
Side effects - muscle/ joint
aches
Links to degenerative
diseases such as dementia

Plant Sterols and Sterols
(Statins)

Contain compounds in foods
and reduce the amount of
cholesterol absorbed by your
gut; easier to metabolise
cholesterol and reduce LDLs

Not classed as a drug
Evidence suggesting they
are effective when
following a prescription
Can lower LDLs by 25% if
used correctly

Claims only supported by
data from meta-analysis
Strict recommended amount
to achieve results
More analysis necessary

Anticoagulants

Interferes with production
of prothrombin in the body,
making blood clotting more
difficult

Not classed as a drug
Evidence suggesting they
are effective when
following a prescription
Can lower LDLs by 25% if
used correctly

Claims only supported by
data from meta-analysis
Strict recommended amount
to achieve results
More analysis necessary

Platelet inhibitory drugs

Make platelets less
adhesive (less sticky)

Not classed as a drug
Evidence suggesting they
are effective when
following a prescription
Can lower LDLs by 25% if
used correctly

Claims only supported by
data from meta-analysis
Strict recommended amount
to achieve results
More analysis necessary

LDL and HDL – cholesterol
Cholesterol as a lipid is an important waxy-like substance made primarily by the liver that acts as a steroid
(forms vital components to cell membranes and/or signaling molecules; such as hormones)
Cholesterol production primarily takes place in the liver
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When these dietary foods are digested, they can be converted to cholesterol
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To aid transport in the blood, cholesterol may be combined with protein to make a lipoprotein (lipid
and protein) of which there are multiple types
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Unsaturated fats increase receptors for LDL, so it deposits less
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Liver breaks down the cholesterol then to make bile
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The Chemistry Of Life
IONIC AND COVALENT BONDING
Ionic bonding : atoms either gain or give electrons
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The other atom loses one or more electrons and becomes positively
charged; the cation
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Covalent bonding: atoms share electrons
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However
sometimes the molecules are slightly polarised; this is when the electrons have an uneven distribution
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The
molecule is described as a dipolar molecule and usually occurs if the bond consists of one or more
hydrogen atoms
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This process is usually reversible
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The chemical formula of water is H2O; meaning that two atoms of hydrogen are joined to one atom of
oxygen
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An effect of this polarity is water forms hydrogen bonds
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They form a weak electrostatic attraction; this is a hydrogen bond
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Water has a high melting/ boiling point as a lot of energy is required to break all the bonds
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Things that dissolve in water easily are hydrophilic
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Its positive end is attracted to the other
molecules negative sides and the negative connects with the positive
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Water can also carry substances like starch, therefore most chemical reactions in cells happen in
water
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g
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A lot of
energy is required to break the hydrogen bonds, meaning bodies of water don’t change much
through the year – good habitat
Water Is a liquid meaning it can’t be compressed – important for hydraulic mechanisms in living
organisms
Water molecules are cohesive, the forces allow the molecules to stick together – e
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transpiration
Water molecules are adhesive, the molecules stick to other molecules
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BUFFERS
Acids release hydrogen ions into solution and alkaline(bases) release hydroxide ions
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In a base
even though hydroxide ions are covalently bonded, it is an ion because together they have an extra
electron(-)
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A buffer helps moderate any changes in pH when an acid or base is added
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If
there is a sudden change in pH, some of the water molecules break apart to form a hydrogen ion and a
hydroxide ion
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However r this won’t work for large changes in pH
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Therefore ice floats
and forms a layer at the surface that protects the rest of the water from freezing and because it is at the
surface the ice melts quickly
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Carbohydrates
ORGANIC COMPOUNDS
Biological molecules are often organic compounds
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In your body, what isn’t water, is usually made up of
those molecules
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They bond strongly with each other to make a
longer chain of carbon atoms
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In some carbon compounds, small molecules (monomers) bond with other similar molecules
to make a large molecule known as a polymer
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CARBOHYDRATES
Carbohydrates are important in cells as an energy source and important for storing energy
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Sucrose: familiar white crystalline table sugar
Glucose: used as a fuel by the cells of our body
The structure of carbohydrates consist of carbon, hydrogen and oxygen and the three main groups are
monosaccharides, disaccharides and polysaccharides
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Amylopectin produces a reddish/brown when mixed with iodine as its helical structure is disrupted by the branching
chain
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They can be broken down into the D-glucose sub units by hydrolysis or the same enzymes that break down starch
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Extreme linearity allows many hydrogen bonds to happen between OH groups on adjacent chains, causing them to
pack closely into fibers - forming microfibrils; these are strong
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LIPIDS
Lipids contain the elements carbon, hydrogen, oxygen and many carbon-hydrogen bonds and almost no oxygen; low
proportion of oxygen than carbohydrates
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The reaction can aid the production of ATP, lipids
(especially triglycerides) store three times the amount of energy for the same mass of carbohydrates
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FUNCTIONS
– Glycerol and fatty acids - energy source as soluble, mobile, respiratory substrate
– Fats in animals and oils in plants - energy store as insoluble respiratory substrate
– Fats - thermal insulation against heat loss via body surface, buoyancy in aquatic animals, cushioning and
protection against knocks
– Waxes - waterproofing on surfaces of leaves, insects, skins
– Fats and oils - solvent, enabling storage and transport of fat soluble vitamins
– Phospholipids, glycolipids and cholesterol(Sterols) - major components of cell membranes
STRUCTURE
– Fats and oils are made of two structures - fatty acids and glycerol(C3H8O3) and are combined using ester
bonds
– Glycerol is a three carbon alcohol that contains three -OH (hydroxyl) groups, each of these groups can
condense with a fatty acid to form a ester bond, this forms a triglyceride
– Fatty acids have a long hydrocarbon chain (general formula R-COOH) and a -COOH (carboxyl) group at one
end, the R is hydrogen or an alkyl group such as -CH3
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Saturated fatty acid - each carbon is joined to the next one by a single covalent
bond (e
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stearic acid) unsaturated fatty acid - the carbon chains have one(monounsaturated)or
more(polyunsaturated) double covalent bonds between them
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g
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A molecule of water is removed and an ester bond is formed - this type
of condensation reaction is called esterification
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– This property allows the polar heads to face the water and keeps the tails hidden, forms the membrane of
many biological molecules
– The phospholipid bilayer is dynamic fluid since the individual molecules can move sideways and exchange
places in their own row
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Amino acids join together by peptide bonds, these form due to a
condensation reaction between the acid group of one amino acid
and the amine group of another
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Polypeptide chains fold to make a specific 3D shape, known as
the secondary structure of protein
...

Alpha-helix : a spiral coil with the peptide bonds forming the
backbone and the R groups protruding in all directions
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The secondary structure may then be folded tightly to give a tertiary structure of protein – globular
protein
...

TYPES OF PROTEIN
Proteins are classed as fibrous or globular depending on their structure, however they can also be
classed as simple or conjugated
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g
...

Conjugated proteins : contain amino acids and some other type of chemical molecule e
...
lipids in
lipoproteins
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COOH ⇌ R
...
NH2 + H+ ⇌ R
...
– amino acid has
many positively charged cations
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STRUCTURAL LEVELS
Primary structure – the sequence of amino acids in the polypeptide chain
...
Hydrogen bonds form
between the amino acids and makes it automatically coil into an alpha helix or fold into a beta
pleated sheet
...
More
bonds form between parts of the polypeptide chain
...
One of the strongest, most important bonds
– doesn’t get affected by the temperature or pH
o Hydrophobic interactions : when hydrophobic groups are close together, they tend to clump
together
...
Very weak force
o Hydrogen bonding : shared electrons spend longer at atoms, leaving them slightly negatively
charged
...

Quaternary structure – some proteins are made of several polypeptide chains held together by
bonds
...
E
...

haemoglobin, insulin, collagen
...

A proteins primary structure determines the proteins 3D structure and properties
...

FIBROUS PROTEINS
Little to no tertiary structure
Made up of long insoluble parallel polypeptide chains with occasional cross links that form them
into fibers
...

Collagen is the most common type of fibrous protein found and are extremely strong
...
Its quaternary structure has three polypeptide alpha chains each up to 1000 amino
acids long
...

GLOBULAR PROTEINS
Complex tertiary and sometimes quaternary structures
They are round(spherical), compact proteins made up of many polypeptide chains
...

This makes them soluble, so they are easily transported
...
This is when microscopic particles of one substance are suspended throughout another
substance e
...
protein in water
...

Haemoglobin is a globular protein made of four polypeptide chains connected by disulfide bonds, it
carries oxygen and is easily soluble, so it can be transported in the blood
...
The iron allows the haemoglobin
to bind and release oxygen molecules and the arrangement of the polypeptide chains, determines
how easily this is done
...
The catalyst is unaffected at the end of the
reaction and can be used again
...
g
...
g
...

They catalyze both anabolic and catabolic reactions
...
The two reactions together is metabolism
...

Temperature and pH affect how efficient enzymes are as they affect the intermolecular bonds that form the
shape of the enzyme
...

When a substrate fits into the enzyme’s active site and forms an
enzyme-substrate complex this lowers the activation energy
In an anabolic reaction, two substrate molecules need to join, being
attached to the enzyme holds them closer together, reducing any
repulsion so they can bond more easily
In a catabolic reaction, fitting a substrate into the active site puts a
strain on the substrate, causing it to breakdown more easily
...

The lock and key hypothesis claimed that the active site had the perfect shape for the substrate to fit into,
however the active site actually has a similar shape and it is flexible allowing it to modify around the
substrate to form the complex
...


ENZYME AND SUBSTRATE CONCENTRATION
Increasing the concentration of enzymes, increases the rate of reaction – more active sites present that the
substrates can collide with to form a complex,
However this is only up until a certain point as the number of substrates is limited, so when the amount of enzymes
exceeds the amount of substrates, it no longer has an affect on the rate of reaction
...

Only true until a saturation point – all the enzymes are occupied, so adding more doesn’t make a difference
Substrate concentration also decreases over time, unless more substrate is added ; substrates are getting broken
down – so rate of reaction decreases over time and the initial rate is the highest
...
g
...
g
...

The phospholipid bilayer
– These lipids are polar lipids as
they contain a hydrophilic
head(contains phosphate
group) and a hydrophobic
tail(two fatty acids)
...

– The hydrophobic heads are
pointing into the water and
the hydrophilic tails are
protected in the middle
...

– Charged particles such as ions, amino acids and glucose are unable to diffuse directly
...
The proportion of unsaturated
fatty acids, controls how freely the proteins move in the membrane
...
Some are receptors for hormones and neurotransmitters, and some are enzymes for
catalyzing reactions
...

They are receptors for hormones or neurotransmitters or are involved in cell recognition
...
Involved in cell signaling or chemical reactions, can dissociate from the membrane and move into the
cytoplasm – cytosolic side
...
Their function
is to either act as antigens or are recognition sites for substances such as insulin and acetylcholine

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