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Mass Transport
THE NEED FOR TRANSPORT
Transport is needed to move substances from one place to another
...

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
...

A way of moving materials fast enough e
...
heart pumping
Way of making sure materials are going in the right direction e
...
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
...

• The systemic circulation carries oxygenated blood from the heart to the cells of the body and deoxygenated
blood back to the heart
...

This helps ensure that oxygenated and deoxygenated blood do not mix
...

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
...

The arteries branch out when leaving the heart - as they get further away from the heart the lumen
becomes smaller
...

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
...


Capillaries
Capillaries are very small vessels that branch throughout the tissues of the body forming capillary beds
...

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
...


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
...

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
...
:
– Larger veins contract when physical activity takes place allowing the blood to get back to heart,
valves aid in stopping the blood flowing backwards
...


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
...
The two sides are split by the septum to stop the blood from either side mixing
...

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
...
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
...
The blood
returns to the heart via the vena cava and the pulmonary vein, into the atria and the process starts again
...
Their primary function is
to transport oxygen around the body, the protein haemoglobin helps with this
...

- 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
...

- 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
...

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
...
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
...
This molecule
combining with the first haem group, causes the haemoglobin to
change shape
...
– 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
...
An acidic environment has a high
concentration of hydrogen ions, these hydrogen ions displace
oxygen from haemoglobin and improves the release into the
tissues
...
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
...

TRANSPORT OF CARBON DIOXIDE

-

-

-

Carbon dioxide is released by respiring cells and diffuses into the blood plasma
...

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
...

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
...
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
...
It acts as an oxygen store and only releases oxygen at
extremely low partial pressures
...
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
...
So the ODC shifts to the left as they release and
take in more oxygen, however the haemoglobin should have an equal affinity
...
It is a
progressive disorder and usually affects the coronary arteries and the carotid arteries; arteries of the neck
...
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
...
This is where blood cells, mainly macrophages, move into the area
damaged
...

• 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
...

• 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
...
These are soluble fatty proteins that carry cholesterol from the
liver to tissues
...

• A lesion begins to occur and lipids deposit in the arterial wall causing fatty streaks
Step 2 – Inflammatory response

•

•
•
•
•

•
•

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
...

Monocytes are white blood cells that differentiate into macrophages when moving into the tunica
intima
...
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
...
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
...

• If it were to rupture, blood coagulation occurs and thrombosis occurs to restrict blood flow, this can
lead to strokes or cardiac arrest
...
This increases the pressure on the arteries walls, and they become weakened
...

• 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
...

• 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
...
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
...
Lastly if the endothelial lining is
damaged then the clotting process is also triggered
...
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
...

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
...

– The collagen fibres of the damaged vessel are now exposed
...

– The thrombocytes cause a protein called thromboplastin to be released
...

– Thrombin then catalyzes the conversion of fibrinogen (soluble protein) to fibrin (solid insoluble fibres)
...

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
...
You can compare a group of
people who have the same factors to the average risk for the whole population
...

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
...
– metadata analysis (meta-analysis)
EVALUATING STUDIES
Check if the methodology is valid; answers the question/ hypothesis the scientists are asking
...

Important to know who carried out the research, who funded it and where it was published, to identify if
there is any bias
...
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
...
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
...

A – ACCURACY – reliability, truthfulness, and correctness of the data
...
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
...
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
...

When these dietary foods are digested, they can be converted to cholesterol
...
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
...
Unsaturated fats increase receptors for LDL, so it deposits less
...
Liver breaks down the cholesterol then to make bile
...


The Chemistry Of Life
IONIC AND COVALENT BONDING
Ionic bonding : atoms either gain or give electrons
...
The other atom loses one or more electrons and becomes positively
charged; the cation
...

Covalent bonding: atoms share electrons
...
However
sometimes the molecules are slightly polarised; this is when the electrons have an uneven distribution
...
The
molecule is described as a dipolar molecule and usually occurs if the bond consists of one or more
hydrogen atoms
...
This process is usually reversible
...

The chemical formula of water is H2O; meaning that two atoms of hydrogen are joined to one atom of
oxygen
...

An effect of this polarity is water forms hydrogen bonds
...
They form a weak electrostatic attraction; this is a hydrogen bond
...

Water has a high melting/ boiling point as a lot of energy is required to break all the bonds
...
Things that dissolve in water easily are hydrophilic
...
Its positive end is attracted to the other
molecules negative sides and the negative connects with the positive
...
Water can also carry substances like starch, therefore most chemical reactions in cells happen in
water
...
g
...
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
...
transpiration
Water molecules are adhesive, the molecules stick to other molecules
...


BUFFERS
Acids release hydrogen ions into solution and alkaline(bases) release hydroxide ions
...
In a base
even though hydroxide ions are covalently bonded, it is an ion because together they have an extra
electron(-)
...

A buffer helps moderate any changes in pH when an acid or base is added
...
If
there is a sudden change in pH, some of the water molecules break apart to form a hydrogen ion and a
hydroxide ion
...
However r this won’t work for large changes in pH
...
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
...


Carbohydrates
ORGANIC COMPOUNDS
Biological molecules are often organic compounds
...
In your body, what isn’t water, is usually made up of
those molecules
...
They bond strongly with each other to make a
longer chain of carbon atoms
...
In some carbon compounds, small molecules (monomers) bond with other similar molecules
to make a large molecule known as a polymer
...

CARBOHYDRATES
Carbohydrates are important in cells as an energy source and important for storing energy
...

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
...

General formula : (CH2O)n
Triose sugars (n = 3): have three carbon atoms; formula C 3H6O3
...

Pentose sugars (n = 5): have five carbon atoms; formula C5H10O5
...

Hexose sugars (n = 6): have 6 carbon atoms; formula C 6H12O6
...
Contains
glucose, galactose and fructose
...


DISACCHARIDES
These are two monosaccharides joined together
...
g
...

Two molecules join in a condensation reaction(a reaction in which a water molecule is
removed from the reacting molecules, to allow them to bond) to form a disaccharide
and a molecule of water is released
...
Numbers
are used to show which carbon atoms are connected
...
g
...

Disaccharide
Source
Monosaccharide
Sucrose
Stored in plants such as sugar cane
Glucose + Fructose
Lactose
Milk sugar – main carbohydrate in milk
Glucose + Galactose
Maltose
Malt sugar – germinating seed, e
...
barley
Glucose + Glucose
TESTING FOR SUGARS
Benedicts solution is used for testing reducing sugars, sugars that react with benedicts and reduce the copper ii to
copper I, giving an orange/red precipitate
...
Sugars that don’t react with benedicts solution are non-reducing sugars
...
This produces a monosaccharide that is a reducing sugar
...

Three most abundant - starch, glycogen and cellulose, these are known as homopolymers as they are only type of
monosaccharide (glucose) after complete hydrolysis
...

Starch is a long chain of alpha glucose molecules but a mixture of two compounds:
Amylose : unbranched polymer of between 200 and 5000 glucose units
...

Amylopectin : branched polymer of glucose units
...

These are both alpha glucose chains however they differ because Amylose has only 1,4 glycosidic bonds whereas
amylopectin has 1,4 glycosidic bonds but there are also some 1,6 glycosidic bonds
...

Therefore starch has a combination of straight chain amylose and branched chain amylopectin molecules
...

Amylose is structure allows it to accommodate the iodine molecule - blue/violet color as amylose-iodine complex is
formed
...


GLYCOGEN
Glycogen is the carbohydrate store found in animals - also important in fungi
Glycogen is very similar to amylopectin molecules in starch and has many alpha glucose units
It is very compact like amylopectin however it contains more 1,6 glycosidic bonds - giving it many side branches
This means it can be broken down rapidly which is necessary for animals when they are at high activity levels
When treated with iodine, it gives a reddish brown color
...


CELLULOSE
A fibrous carbohydrate found in all plants, structural component of plant cell walls
A linear polymer of glucose, however it differs from starch and glycogen because the units are joined by β-1,4glycosidic bond, producing a more extended structure
...

This means cellulose has little interaction with water/solvents and because it isn't a helical structure It doesn't bind
onto iodine to form a colored product
...
When lipids are oxidized in the respiration process, the bonds are broken,
resulting in carbon dioxide and water as the final products
...

Other than glycerol, they are insoluble in water and are less dense than water, but dissolve In organic substances
such as ether
...

– Fatty acids differ in either the length of the carbon chain (most between 14-22) or the fatty acid maybe
saturated or unsaturated
...
g
...
E
...
linoleic acid
– Fatty acids long hydrocarbon chain makes it insoluble in water (hydrophobic)
Glycerol + fatty acid --> triglyceride + water(3 molecules)
A triglyceride is made when glycerol combines with three fatty acids, a bond is formed between the carboxyl and
hydroxyl groups in a condensation reaction
...

– If glycerol forms a triglyceride with saturated fats they produce fats that are solid at room temp and are fats
often found in animals
– If glycerol forms a triglyceride with unsaturated fatty acids, oil is produced - liquid at room temp and mostly
found in plants

WAXES
Esters of fatty acids with long chain alcohols - they are hard and form protective waterproof coverings on biological
surfaces
PHOSPHOLIPIDS
– Most involve glycerol, the glycerol forms two ester bonds with fatty acids and one with a phosphate group
– The negatively charged polar head contains the phosphate group which is hydrophilic and the two non polar
fatty acid side chains are hydrophobic
...
This enables the membrane to be self sealing If punctured and allows materials to
be taken in by forming a vacuole around it

Proteins
STRUCTURE
20 types of amino acids occur that form the parts that make up a
protein
...

Two amino acids join to form a dipeptide and many amino acids
join to form a polypeptide
...

The shapes may either be of alpha-helix type or beta-pleatedsheet – fibrous type structural proteins
...

Beta-pleated-sheet : the polypeptide chain folds into regular pleats held together by hydrogen
bonds between the amino and carboxyl ends of the amino acids
...

These structures are still single polypeptides, the quaternary structure of protein is how proteins
form
The different structures of proteins are cross-bonded by ionic, hydrogen, Sulphur and peptide
bonds formed between reactive groups in the amino acid side chains
...

Simple proteins : only contain amino acids in their structure and exist as several different types, e
...

albumins and globulins
...
g
...

Haemoglobin is a conjugated protein, consisting of 4 globular polypeptides which contains a
porphyrin ring which also contains iron

EFFECT OF pH
The hydrogen ions concentration, affects how the amino acids and proteins ionize
In a high hydrogen ion concentration the reaction R
...
COO- + H+ will tend to be pushed
to the left and the reaction R
...
NH3+ will be pushed to the right
...

In a lower hydrogen ion concentration, the opposite happens and the amino acid has many
negatively charged anions
...
Held together by peptide
bonds
Secondary structure – the polypeptide chain doesn’t remain flat and straight
...

Tertiary structure – the coiled or folded chain of amino acids is often coiled or folded further
...

o Ionic bonds : attractions between negative and positive charges on different parts of the
molecule
o Disulfide bonds: whenever two molecules of cysteine come close together, the sulfur atom
in one bonds to the a sulfur atom in the other
...
Hydrophilic groups are pushed to the outside, protein folds up to its final
structure
...
Weak bond – sensitive to high temperatures and pH changes
...
The quaternary structure is the way these polypeptide chains are assembled together
...
g
...
The bonds depends on the tertiary structure, so they can contain
any bond
...
The amino acid
sequence determines what bonds will form and how the protein folds
...

Since they are insoluble in water and strong, they are often found in supportive tissues such as
collagen in tendons and keratin in your nails and hair
...
This is due to
its structure
...

Its primary structure is repeating sequences of glycine with two other amino acids
...

The R group of the amino acid is important when forming the structure, as when they are
hydrophobic, they are usually found on the inside of the globular structure and if they are
hydrophilic, the outside
...


The carboxyl and amino ends, give them ionic properties, the molecules are very large, so they form
a colloid
...
g
...

They do not settle and can’t be easily separated, important as they hold molecules in position in the
cytoplasm
...

Each polypeptide chain surrounds an iron containing haem group
...

Enzymes are large so globular proteins that are biological catalysts – soluble due to many hydrophilic side
groups
A catalyst is a substance that changes the rate of reaction by lowering activation energy and providing an
alternative pathway without changing the substance produced
...

Enzymes can affect structures and functions in an organism
They can be intracellular – catalyze reactions inside cells e
...
DNA polymerase or extracellular – catalyze
reactions outside of cells e
...
lysosome – enzyme in your tears
...
Anabolic – reactions that build up new chemicals,
catabolic – reactions that break down substances
...

Enzymes have an active site which has a very specific shape, so enzymes are said to show great specificity,
this allows them to catalyze one specific reaction
...

LOWERING ACTIVATION ENERGY
In a chemical reaction, chemicals require a certain amount of
energy(heat) before the reactions starts; activation energy
Enzymes lower the amount of energy required allowing reactions to
happen at a lower temperature, speeding up the rate of reaction
...

HOW ENZYMES WORK
Induced fit hypothesis
Substrate and enzyme form an enzyme-substrate complex, then after the enzyme breaks/joins substrates,
once the reaction is complete, the products are not in the right shape to stay in the active site and the
complex breaks up, this releases the products and allows the enzyme to form new complexes
...

Therefore the enzyme needs to be specific in the way it changes shape as well(due to its tertiary structure),
once the products are released, the enzyme changes back to its inactive form
...


Increasing the substrate concentration causes a faster rate of reaction – as this means there is a higher chance that a
substrate collides to form a complex
...

COFACTORS
Activators – inorganic groups that are permanently bound to the enzyme and so are a type of prosthetic group e
...

iron, zinc, copper
Coenzymes – organic molecules that bind to the enzyme temporarily, transferring a chemical group required for the
reaction e
...
vitamin c and ATP

Cell Membranes
STRUCTURE OF MEMBRANES
– The membrane is mainly composed of two types of molecules, phospholipids and proteins
...

– So when the phospholipids
come in contact with water,
the two parts of the molecule
behave differently, since the
surface has water on both
sides, it forms a bilayer
instead of a monolayer
...

– This allows non-polar substances such as oxygen and carbon dioxide to diffuse quickly and small polar
substances such as urea and water to diffuse slowly
...

THE FLUID MOSAIC MODEL
–
–
–
–

–

–

In this model, the bilayer is said to be fluid as the phospholipids are constantly moving
The cell membrane also contains proteins – some floating and some fixed
...

The proteins make pores or channels that allow specific molecules to move through the membrane some are
open or shut depending on the conditions of the cells, these are referred to as gated channels
Integral proteins (intrinsic or transmembrane) these proteins span the whole width of the membrane and
are protein channels that help transport substances that can’t diffuse across the membrane but are still vital
to a cell functioning
...

Peripheral proteins (extrinsic) these proteins are confined to the inner or outer surface of the membrane
...
– extracellular
side
...

Some proteins have a polysaccharide chain attached to them; these are called glycoproteins
...


–
–

Some lipids also have a polysaccharide chain attached; these are glycolipids
...

Cholesterol is also a type of lipid found in the cell membrane, it fits in between the phospholipids, forming
bonds and making the membrane more rigid
...


Diffusion
Diffusion is the net movement of particles in a liquid or gas from an area of high concentration to an area of low
concentration, down the concentration gradient
...

SIMPLE DIFFUSION
– Simple diffusion is the direct diffusion through phospholipids down the concentration gradient
...

– The random motion when molecules are tightly packed is that they spread out till they reach uniform
distribution
...

– The substances that diffuse by simple diffusion are oxygen and carbon dioxide
...

Facilitated diffusion uses either carrier proteins or channel proteins in the cell membrane
...

– Each type of channel protein is dedicated to one particular molecule e
...
sodium ion channels
– Some channels open only if a specific ion is present or if there is an electric change across the membrane
(passage of a nerve impulse along neurons)
...

Carrier proteins
– These proteins move large molecules into or out of the cell down the concentration gradient
...

– Protein carriers are also specific for particular molecules/groups of molecules depending on the shape of the
protein carrier and the substance to be carried
...

The carrier protein then releases the molecule on the opposite side of the membrane
...


FICK’S LAW
Rate of diffusion is proportional to

surface area x difference in concentration
membrane thickness(length of diffusion path)

Osmosis
Osmosis is the diffusion of free water molecules through a partially permeable membrane, form an area of high
water concentration to an area of low water concentration, down a water potential gradient
...

Partially permeable – allows some molecules through e
...
cell membrane or nuclear membrane
Water potential – measures the concentration of free water molecules; molecules that are not associated with
solute molecules
...

OSMOTIC CONCENTRATION
– This is a measure of the concentration of solutes in a solution that have an osmotic effect
...

– In an isotonic solution – the osmotic concentration of the solutes in the solution is the same as that in the
cells
...

– In a hypertonic solution – the osmotic concentration of solutes in the solution is higher than that in the
cytoplasm
...
The net movement of water in and out of cells has
to be kept at a minimum as animal cells are very fragile
...

OSMOSIS IN PLANT CELLS
– Plant cells are also fragile however they are surrounded by a cell wall made of cellulose
...

– If the surrounding fluid is hypotonic, water will enter the cell by osmosis
...

– The inward pressure of the cell wall on the cytoplasm increases until it cancels out the tendency for water
molecules to move in – pressure potential
...

– Incipient plasmolysis – when a large amount of water has moved out of the cell by osmosis that the state of
turgor is lost and the cell membrane begins to pull away from the cell wall due to the protoplasm shrinking
...


Active Transport
Active transport is the movement of molecules and ions across a membrane against a concentration gradient, low to
high concentration
...

PROCESS
– Active transport involves a carrier protein
...

– Antiporters are one type of carrier proteins, where the ion moves in the opposite direction to the actively
transported molecule
– The other type of carrier proteins are symporters, this is where the ion moves in the same direction as the
actively transported molecule
...
Cells that
carry out active transport tend to have a lot of mitochondria that supply the ATP needed
...
This provides the energy needed to change the shape of the protein, release the
transported substances and revert to the original
...

Therefore they only move substances in the direction required by the cell
...

SODIUM POTASSIUM PUMP

ENDOCYTOSIS AND EXOCYTOSIS
Endocytosis
– Some molecules are way too large to be taken in by carrier proteins e
...
lipids
– Instead a cell surrounds a substance with a section of its cell membrane, also uses ATP
– The membrane then pinches off to form a vesicle inside the cell containing the ingested substance
...

Exocytosis
– Some substances produced by the cell need to be released e
...
hormones need to be released from the cells
– exocytosis is used with energy provided by ATP
...

– The vesicles fuse with the cell membrane and release their contents outside the cell, some substances e
...

membrane proteins are inserted straight into the cell membrane

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