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Title: Biology AS AQA Unit 1 Notes
Description: AS Notes for Unit 1 of the AQA Biology A Level course
Description: AS Notes for Unit 1 of the AQA Biology A Level course
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UNIT 1
BIOLOGICAL MOLECULES
Many molecules in biology are large and known as polymers
...
-‐Lipids, however, are not polymers because they are made up
of 3 fa>y acids and 1 glycerol; fa>y acids and glycerol are not
similar therefore lipids are not polymers
...
Polymers are broken down into their consAtuent monomers in
hydrolysis, which involves the addi)on of water
...
Carbohydrates
All carbohydrates contain carbon, hydrogen and oxygen
...
Glucose can take a number of different shapes
...
Each isomer has the same chemical
formula, but different structural formula
...
There are 2 main forms: alpha glucose and beta glucose
...
Alpha glucose molecules
combine to form starch, whilst beta glucose combines to
form cellulose
...
This is called a condensaBon reacBon and
involves the loss of a water molecule
...
Disaccharides typically have the formula:
C12H22O11
Polysaccharides
Many monosaccharides units can join together by glycosidic bonds to
form a polysaccharide
...
Large molecules of repeaAng units are called polymers, each unit are
called monomers
...
• A condensaAon reacAon between the hydroxyl group of a carbon 1
of one monosaccharide and carbon 4 on the other results in a
bond called the 1-‐4 glycosidic bond
...
Test for reducing sugar
All monosaccharides and some disaccharides (eg maltose) are reducing
sugars
...
Benedict’s reagent is an alkaline solu)on of copper (II) sulfate
...
The test is carried out as follows:
Ø Add 2cm3 of the food sample to be tested to a test tube
...
Ø Add an equal volume of Benedict’s reagent
...
Ø Blue à Brick red
Benedict’s test has a semi-‐quanBtaBve nature
...
Different concentra)ons of reducing sugars give different colours
...
In order to detect a
non-‐reducing sugar it must first be broken down into its monosaccharide components
by hydrolysis
...
Ø Add 2cm3 of the food sample being tested to 2cm3 of Benedict’s reagent, and
heat in a boiling water bath for 5 minutes
...
2)
Ø Add another 2cm3 of the food sample to 2cm3 of dilute hydrochloric acid in a test
tube and place the test tube in a boiling water bath for 5 minutes
...
Ø Slowly add some sodium hydrogencarbonate to neutralise the hydrochloric acid
...
Ø Re-‐test the resulAng soluAon by hea)ng it with 2cm3 of Benedict’s reagent in a
boiling water bath for 5 minutes
...
Starch
Starch is a polysaccharide formed from alpha glucose units
...
In amylose, the units are linked mainly by 1-‐4 glycosidic bonds which
form unbranched chains, giving it a coil structure
...
AmylopecAn is good for plants because by
having a branched structure, it is easier to access the glucose
monomers as an energy source
...
² Starch is compact due to its coil structure, making it ideal for
storage
...
If starch is present,
orange brown à black
Glycogen
Glycogen is also a storage polysaccharide, parAcularly
abundant in liver and muscle cells
...
This makes glycogen less
dense and more soluble than starch
...
This is reflected
in the higher metabolic rate in animals compared with
plants
...
Cellulose
Cellulose is a tough, structural polysaccharide
...
Cellulose is completely permeable; it allows water
and dissolved substances to enter and leave plant
cells freely
...
Unlike starch and glucose, cellulose cannot be
hydrolysed easily
...
Lipids
Lipids all contain carbon, hydrogen and oxygen, but the proporAon of
oxygen to carbon and hydrogen is smaller than in carbohydrates
...
The main groups are triglycerides and phospholipids
...
Other roles include:
• Energy source-‐ when oxidised, lipids provide more energy than the
same mass of carbohydrates
...
• InsulaBon-‐ fats are slow conductors of heat and when stored
beneath the body surface help to retain body heat
...
Fats are solid at room temperature, whereas oils are liquid
...
Each fa>y acid forms an ester bond with a
glycerol in a condensa)on reac)on
...
As the glycerol molecule in all lipids is the same, the
difference comes from the faWy acid molecules
...
If there is no
carbon-‐carbon double bond, the fa>y acid is saturated
...
If
there is more than one double bond, it is poly-‐
unsaturated
...
Whereas faWy acid molecules repel water (hydrophobic),
phosphate molecules aWract water (hydrophilic)
...
Test for lipids-‐ Emulsion test
1
...
2
...
3
...
4
...
Proteins
Amino acids
All amino acids have an amino group (-‐NH2) and a
carboxyl group (-‐COOH), as shown in their general
structure
...
The R group is different for each of the 20 amino
acids, and it determines the specific properAes of a
given amino acid
...
PepBde bonds join amino acids together
...
Further amino acids join
together to form a polypep)de chain
...
The specific sequence of amino acids, controlled by DNA
code, will determine which protein will be formed
...
In order for any protein to carry out its specific funcAon,
it must contain the correct amino acids arranged in a
precise order
...
It will be this sequence of amino acids that determines
the secondary and ter)ary structure formed, and hence
the func)on of the protein
...
This coiling or folding is the protein’s secondary
structure
...
Tertiary structure
The terBary structure refers to the overall 3-‐D shape of a polypep)de chain
...
Proteins are classified into
two main groups of the basis of their terAary structure:
Ø Fibrous proteins consist of parallel polypep)de chains, cross linked at intervals to
form long fibres or sheets
...
Eg:
collagen, keraAn
Ø In Globular proteins, the polypepAde chains are )ghtly folded to form a spherical
shape
...
Eg: enzymes, anAbodies and hormones
...
The
shape is maintained by various bonds:
•
Hydrogen bonds-‐ very common, very weak
•
Ionic bonds-‐ rela)vely weak bonds between nega)vely & posi)vely charged parts
•
Disulfide bonds-‐ covalent bonds between two sulfur atoms
...
These are very weak
...
Quaternary Structure
Many proteins consist of more than one
polypepBde chains chemically bonded together
...
The same three bonds are present:
• Hydrogen bonds
• Ionic Bonds
• Disulphide bonds
Eg: haemoglobin has four polypepAde chains and
four non-‐protein haem groups
...
Before cell fracAonaAon, the Assue is placed in a cold,
isotonic buffered soluAon for the following reasons:
Ø Cold-‐ to reduce enzyme ac)vity that might break
down the organelles
Ø Isotonic-‐ to prevent organelles burs)ng or shrinking as
a result of osmo)c gain or loss of water
Ø Buffered-‐ to maintain a constant pH
There are two stages to cell fracAonaAon
HomogenaBon
Ø Cells are broken up by a homogeniser
...
Ø The heaviest organelle, the nuclei, are forced to the boWom of the
tube where they form a pellet
...
• One layer of phospholipids has its hydrophilic heads poinAng
inwards
• The other layer of phospholipids has its hydrophilic heads poinAng
outwards
• The hydrophobic tails point into the centre of the membrane
Lipid soluble material moves through the membrane via the
phospholipid porAon
...
They are embedded in the phospholipid bilayer in two main ways:
• Extrinsic proteins occur either on the surface of the bilayer or only partly
embedded in it, but they never extend completely across it
...
Some act as
carriers to transport water-‐soluble materials, while others are enzymes
...
This
gives the membrane a flexible structure that is
constantly changing in shape
• Mosaic because the proteins embedded in the
phospholipid bilayer vary in shape, size and
paWern
DIGESTION
The digestive system
1)
2)
3)
4)
5)
IngesBon-‐ solid food is taken into the
mouth
...
Gives food a
larger surface area for enzymes to act
upon
Chemical digesBon-‐ hydrolysis of large
parAcles into smaller ones, allowing them
to be absorbed
...
Blood
transports molecules into cells
...
AssimilaBon
...
The use of the
absorbed molecules is either to build
other molecules, or in respira)on
Villi and Microvilli
Glucose is absorbed through the walls of the small intes)ne,
which is folded and possess finger-‐line projecAons called villi,
which have smaller foldings called microvilli
...
Ø Able to move, so able to maintain a diffusion gradient
...
Glucose-sodium co-transport
The actual mechanism by which glucose is absorbed is an example of
co-‐transport, as two molecules are involved
...
1
...
This takes place on
carrier-‐proteins found on the cell membrane of the epithelial
cells
...
There is now a higher concentra)on of sodium ions in the lumen
of the intesAne than inside the epithelial cells
...
The sodium ions diffuse into the epithelial cells down a
concentraAon gradient through a co-‐transport carrier protein in
the cell surface membrane
...
4
...
Digestion
In humans, digesAon takes place in two stages; physical and chemical
digesAon
...
This also provides a large surface area for
chemical diges)on
...
Chemical digesBon
Chemical digesAon breaks down large, insoluble molecules into
smaller, soluble ones
...
Carbohydrases break down carbohydrates
...
Amylase
hydrolyses glycosidic bonds of the starch molecule to produce the disaccharide
maltose
...
This process takes place as follows:
•
Food is taken into the mouth and chewed
...
•
Saliva enters the mouth, which contains salivary amylase
...
•
The food is swallowed and enters the stomach, which is acidic
...
•
Aaer a Ame, the food is passed into the small intes)ne, where it is mixed with
secreAons from the pancreas called pancreaBc juice
...
Hydrogencarbonate ions are secreted by
the pancreas, which neutralise the stomach acid
...
•
Muscles in the intesAne create peristal)c waves which moves the food along the
small intesAne
...
Lactose intolerance
Lactose intolerant people do not produce the enzyme lactase, so cannot hydrolyse
lactose into glucose and galactose
...
If you have high amounts of lactose, it will causer the lowering of the water poten)al
in the small intesAne, so the cells lining the small intesAne will have a higher water
poten)al, so water will move out of the cells lining the intesAne into the lumen,
causing water to move out of blood by osmosis into cells, then lumen
...
TesAng for lactose intolerance:
1
...
Monitor blood glucose levels
3
...
4
...
ENZYMES
Enzymes are globular proteins which act as catalysts
...
Enzymes do not make reacAons happen, they simply alter the speed of
the reacAons that already occur
...
• The energy of the products must be less than that of the
substrates
...
The
minimum amount of energy needed to ac)vate the reac)on is
called the acBvaBon energy
...
In this way,
enzymes allow reacAons to take place at a lower temperature than
normal
...
Consequently, an enzyme reduces the ac)va)on energy of the
reacAon it catalyses
...
Their
molecules have a very precise shape (terBary
structure) which includes an ac)ve site
...
The
substrate has a complementary shape to the
acAve site
...
Once the complex is formed, the enzyme then
helps change the substrate
...
This explains why
enzymes are specific and why any change in acAve
site shape alters its effecAveness
...
The acAve site is able to change its shape to enfold the
substrate molecule
...
The shape of
the enzyme is affected by the shape of the substrate
...
This
makes the substrate less stable, reduces its poten)al
energy and thus lowers the ac)va)on energy of the
reacAon
...
The flexible enzyme then returns to its original shape,
ready to bind with the next substrate molecule
Active site
The terBary structure of the enzyme protein is
vital for the formaAon of the 3D structure of
ac(ve sites
...
The enzyme’s acAve site is a specific shape into
which only one type of structure that is a
complementary shape can fit
...
Enzyme concentraBon
The rate of enzyme-‐catalysed reacAon increases as enzyme concentra)on increases
unAl it reaches a maximum rate, aaer which the enzymes will be in excess so there will
be more empty ac)ve sites
...
Increasing the temperature increases the kine)c
energy of the reacAons
...
Above the opAmum temperature, the increased energy causes bonds that maintain
the enzyme’s shape to break, so enzyme becomes denatured
...
Within this range there will be
an opBmum pH at which ac)vity is greatest
...
Inhibitors
Many substances can interfere with enzymes, reducing or
even completely destroying their acAon
...
Reversible inhibitors generally bind to the enzyme with
weak bonds such as hydrogen bonds which are easily
broken
...
Irreversible inhibitors a>ach to an enzyme with strong
covalent bonds which are difficult to break without
damaging the enzyme
...
A compeBBve inhibitor of a parAcular enzyme has
a shape resembling the enzyme’s normal
substrate
...
If the inhibitor occupies the site, it
prevents the enzyme from combining with its
substrate
...
A non-‐compeBBve inhibitor does not a>ach to
the acAve site, but binds with the enzyme at
another site
...
GASEOUS EXCHANGE SYSTEM
A gaseous exchange system is used to exchange
oxygen and carbon dioxide between air and the
blood
...
For gaseous exchange to happen, there must be
a con)nual flow of air into and out of the lungs
...
Alveoli
The lungs consist of microscopic sacs called alveoli
...
The alveoli have the following adaptaAons:
Ø A large surface area to volume raBo-‐ to speed up the rate of exchange
...
The alveoli have only a single layer of epithelial cells and the blood
capillaries have only a single layer of endothelial cells
...
Ø There is rapid movement of environmental medium, eg air to maintain a
diffusion gradient
...
Ø There is rapid movement of the internal medium, eg blood to maintain a
diffusion gradient
...
Being thin, the alveoli are easily damaged so are located inside the organism for
protecAon
...
Around each
alveolus is a network of pulmonary capillaries, so narrow that red blood cells are
flaWened against the thin capillary walls
...
The human respiratory system
1
...
3
...
5
...
Air entering via the nose
cavity is filtered by hairs in the nasal passages, warmed and moistened by cells in
the mucous membrane of the nasal cavity
...
These membranes contain goblet cells which secrete mucus, a slimy
material rich in glycoproteins
...
The nasal and buccal caviAes lead into the pharynx, a tube that conducts both
food and air
...
This is a reflex acAon which prevents food from going down the
trachea
...
This single tube forms a major
airway
...
Without them, the trachea
would collapse during breathing out, when the external atmospheric pressure is
higher than the pressure inside the trachea
...
The trachea is lined with mucus membrane containing ciliated epithelium cells,
which have microscopic hair like extensions called cilia
...
The trachea subdivides into two main branches; the right and lea bronchus
...
Small bronchioles can constrict completely because they lack carAlage
...
For inhalaBon (breathing in) to occur, the gas
pressure in the alveoli must be less than that in
the atmosphere
...
Inhalation (or Inspiration)
Humans inhale by enlarging the thoracic (chest) cavity, which enlarges the lungs as
well
...
•
During inhalaAon, the external intercostal muscles contract
...
•
The internal intercostal muscles relax
...
•
The diaphragm also contracts; the central porAon of this muscle moves
downwards
...
Atmospheric pressure is now greater than pulmonary pressure, so air
is forced into the lungs
...
Enlargement
of the thorax during inhalaAon stretches the )ssues of
the thorax and lings, which recoil naturally during
exhalaAon
...
• The ribs move downwards and inwards, decreasing
the volume of the thorax
...
The pulmonary pressure is now greater than that of the
atmosphere, and so air is forced out of the lungs
...
•
The volume of air breathed in or
out of the lungs per breath is
called the Bdal volume
...
•
The volume of air remaining in
the lungs at the end of a
maximal expira)on is called the
residual volume
...
The rate at which a person breathes is called the venBlaBon rate, or
pulmonary venBlaBon
...
Cardiac
muscle is myogenic-‐ its contrac)on is ini)ated by
the muscle itself, rather than by nervous impulses
...
The heart is divided into a lec side and a right side
separated by a septum
...
Each side of the heart has two chambers; an atrium
which receives blood from the veins and a ventricle
which pumps blood into the arteries
...
As the atria fill, the pressure within them rises, pushing open the
atrioventricular valves and allowing the blood to pass into the ventricles
...
The relaxaAon of the ventricle wall reduces the pressure within the ventricle,
causing the pressure of the ventricles to be lower than the pressure of the aorta
and pulmonary arteries
...
ContracBon of the atria-‐ atrial systole
•
•
•
The muscle of the atria walls contract, forcing the remaining blood that they
contain into the ventricles
...
Muscle of the ventricle wall remains relaxed
ContracBon of the ventricles-‐ ventricular systole
•
•
•
Aaer a short delay to allow the ventricles to fill with blood, their walls contract
simultaneously
...
With the atrioventricular valves closed, the pressure rises further, forcing open
the semi-‐lunar valves and pushing blood into the pulmonary artery and aorta
...
The wall of the lec ventricle has to pump blood to
the extremi)es of the body, and so is much thicker than that of the right
ventricle
...
This is a small patch of Assue that
has its own inherent rhythm of contrac)on
...
The SA node is someAmes called the pacemaker because it determines the rate of
contracBon of the rest of the cardiac muscle
...
The SA node generates a wave of electrical impulses called the cardiac impulses
over the atria, causing the atria to contract
...
When the wave reaches the juncAon between the atria and ventricles, they are
delayed by the atrioventricular septum (a layer of non-‐conduc)ng )ssue)
...
3
...
4
...
5
...
6
...
7
...
This ensures
that all parts of the ventricles contract more or less simultaneously
...
It
then gradually falls, but
never below 12kPa
because of the elas)city
of its wall, which
creates a recoil acBon
...
It is highest when they
are contrac)ng, but
drops when the lea
atrioventricular valve
closes and its walls
relax
...
The lea atrioventricular
valves close and pressure
rises drama)cally as the
thick muscular walls of the
ventricle contract
...
Pressure
falls as the ventricles empty
and the walls relax
Ventricular volume rises
as the atria contract and
the ventricles fill with
blood, and then drops
suddenly as blood is
forced out into the aorta
when the semilunar
valve opens
...
Valves in the control of blood flow
Valves in the cardiovascular system are designed so that they open whenever
the difference in blood pressure either side of them favours the movement of
blood in the required direc)on
...
Ø Atrioventricular valves between the atrium and the ventricle prevent
backflow of blood when contrac)on of the ventricles means that
ventricular pressure exceeds atrial pressure
...
Ø Semi-‐lunar valves in the aorta and pulmonary artery
...
Ø Pocket valves in veins that occur throughout the venous system
...
DISEASE
Cholera
Caused by: A water-‐borne bacterium called Vibrio Cholerae that produces a
toxin called choleragen
Symptoms: An acute intes)nal infec)on
...
This lowers water potenAal of the lumen, and causes water to move
out of the cells into the lumen and consequently out of the blood from
capillaries, into the cells and lumen
...
Any oral
treatment rarely has )me to be effec)ve as it is
flushed from the intesAnes by diarrhoea
...
Pathogens are disease causing microbes
The first thing a pathogen needs to do is:
• Gain entry to the host
• Resist the defences of the host
• Colonise )ssues of the host
• Cause damage to the host
They cause damage by:
-‐Producing toxins
...
If created inside the bacteria, these are endotoxins
and are only released upon death of the cell
-‐Damage (ssue or cells of the host
It is the transmission of microbes that causes diseases
Koch’s postulates
• The same microorganism must be found in all
cases of the disease
• It must be possible to isolate the suspected
microorganism from the diseased host and
grow it in a pure culture
• It must be possible to isolate the same
microorganism from an experimentally
infected animal
Entry into the body
Microorganisms may enter the body via:
-‐>The gas exchange system
-‐>The digesBve system
To help prevent entry of the pathogens, the body
has a number of natural defenses which include:
-‐A mucous layer that covers exchange surfaces and
forms a thick s)cky barrier that is difficult to
penetrate
-‐Enzymes which break down pathogens
-‐Stomach acid which kills microorganisms
Non-‐specific response:
-‐Response is the same for all pathogens
-‐Present since birth
-‐Does not provide long las)ng immunity
-‐Provides an immediate response
Eg: InflammaAon, swelling, temperature rise
The non-‐specific response includes physical barriers which
are designed to prevent entry of the pathogen, for instance
sweaAng and tears
...
This is caused by the leakage of plasma from the
capillaries which causes swelling
...
This involves the recogni)on of specific an(gens
...
The immune system is normally tolerant of the
body’s own an)gens-‐ self anBgens
...
The defensive reacAon of this system makes up the immune response
...
If we come in contact with these pathogens,
we will not have the specific memory cells to
produce an immediate response and so we will get
symptoms while we wait for the correct B cell to be
ac)vated
...
This process is called
phagocytosis
...
1) The phagocyte is a>racted to the pathogen by chemoagractants
(chemical products of the pathogen)
...
2) The phagocyte binds to the pathogen
...
4) Lysosomes within the phagocyte migrate towards the vesicle and fuse
with it
5) The lysosomes release lyBc enzymes into the phagosome, where they
break down the bacterium
...
Response to non-self antigens
White blood cells called lymphocytes will respond
...
They produce specific
an)bodies for the non-‐self anAgens
...
T lymphocytes are produced in the bone marrow and
mature in the thymus gland
Cell-mediated immunity
T lymphocytes respond to an organism’s own cells that have
been invaded by non-‐self material
...
As T lymphocytes will only respond to anAgens that are aWached to a
body cell, this type of response is called cell-‐mediated immunity
...
All three types of cell will possess receptors on their
cell membranes that will be a complementary shape to
the an)gens they act against
...
These produce chemicals called cytokines
that s)mulate specific B cells to divide and then produce
plasma cells
...
>T Killer Cells
...
They produce proteins that make
holes in cell surface membranes, meaning the cell becomes
freely permeable to all substances and dies
...
These give long las)ng immunity to the cell
B Lymphocytes and Humoral Immunity
Each type of B lymphocyte possesses a specific-‐shaped receptor on its
cell surface membrane
...
ANTIBODIES-‐ AnAbodies are globular proteins secreted by B-‐
Lymphocytes in response to the presence of non-‐self an)gens
...
AnAbodies have four polypep)de chains which have a complementary
structure
...
AnAbodies possess anBgen binding sites, which are specifically shaped
due to their specific sequence of amino acids
...
Each different anAbody will fit only one complementary shaped
an)gen, forming an an)body-‐an)gen complex
...
There need
to be many B Cells because pathogens reproduce quickly
...
These produce the anBbodies with specific an)gen
binding cites
...
-‐Memory B Cells, which will remain in the lympha)c system for
many years
...
Therefore, you get no symptoms
meaning you are immune
1) The surface an)gens of the invading pathogen are taken up by B
Cells
...
3) T Helper cells aWach to the processed anAgens on the B cells,
thereby acBvaBng them
...
5) The cloned plasma cells produce an)bodies that exactly fit the
anAgens on the pathogen’s surface
...
This is the primary immune response
...
These can respond to
future infec)ons of the same pathogen by dividing rapidly and
developing into plasma cells
...
Monoclonal Antibodies
Single types of anAbody can be isolated and cloned,
forming monoclonal anBbodies
...
They can
then acAvate a cytoxic drug
...
AcBve immunity is produced by s)mula)ng the produc)on of
an)bodies by the persons own immune system
...
-‐Individuals may develop disease immediately acer vaccina)on,
but before immunity levels are high enough to prevent it
...
New anAgens may not be
recognized by the immune system
...
Cardiovascular diseases
Atherosclerosis is a thickening of the inner layers of arterial walls with
deposits of cholesterol, fibrous Assue, dead muscle cells and blood
platelets
...
The fibrous Assue within an atheroma oaen becomes calcified and
hardened, contribuAng to loss of elas)city of the arteries, known as
arteriosclerosis
...
If the atheroma breaks through the smooth endothelial wall of an
artery and penetrates into the lumen, the rough surface of a plaque
can trigger the formaAon of a blood clot
...
It may be large enough to block an artery
...
If the weakening is
severe enough, the arterial wall may rupture causing an internal
haemorrhage
...
Blockage or severe narrowing of one of the
coronary arteries that supplies the heart may
lead to a “myocardial infarcBon”
...
Risk factors
High blood pressure: If the arteries become narrower and hardened by
atherosclerosis, the blood pressure increases causing persistent high blood
pressure called hypertension
...
To resist
high blood pressure, walls of arteries tend to become thicker and may
harden, resis)ng flow of blood
...
As such, it is transported in the blood plasma by Any spheres of lipoproteins:
• High density lipoproteins remove cholesterol from )ssues and transport
it to the liver for excreAon
...
Excess cholesterol accumulates in the blood, and is unloaded by low density
lipoproteins in the walls of blood vessels
...
High levels of saturated fat
increase low-‐density lipoprotein levels
...
As disease
progresses, fever and coughing up of blood may occur
...
The body’s immune system responds and white blood cells accumulate at
the site of infecAon to ingest the bacteria
...
This is the primary infecBon and usually occurs in
children
...
However, a few bacteria usually remain
...
This is called post-‐primary tuberculosis and typically occurs in adults
...
The bacteria destroy the )ssue of the lungs, resulAng in cavi)es
and scar )ssue where the lungs repair themselves
...
Without treatment, the TB spreads to the rest of the body and
can be fatal
1) Bactria transmi>ed in droplets
2) Bacteria engulfed by phagocytes
3) Bacteria encased in wall
4) Bacteria are dormant
5) If immunosupressed, bacteria acAvated
6) Bacteria destroy alveoli/ epithelial cells
7) Leads to fibrosis/scar Assue/ caviAes
8) damage leads to less diffusion due to less surface
area
Pulmonary fibrosis
Pulmonary fibrosis arises when scars form on the epithelium of the lungs,
causing them to become irreversibly thickened
...
In paAents
with fibrosis, oxygen cannot diffuse into the blood as efficiently because the
diffusion pathway has been considerably lengthened and the volume of air
that the lungs can hold has been reduced
...
The effects of fibrosis are:
Ø Shortness of breath-‐ due to considerable volume of the air space within the
lungs being occupied by fibrous )ssue
...
The thickening also increases the
diffusion pathway, so diffusion of oxygen into the blood is very slow
...
The body’s reflex acAon is to try to remove the obstruc)on by
coughing
...
Ø Weakness and faBgue-‐ reduced intake of oxygen into the blood, meaning
release of energy by cellular respiraAon is reduced, leading to Aredness
...
Some of the most common
allergens that sAmulate asthma are: pollen, animal fur and faeces of house dust mite
...
This in turn has the following
effects:
– The lining of these airways becomes inflamed
...
– The muscle surrounding the bronchioles contracts and so constricts the
airways
...
The symptoms of asthma are:
Ø Difficulty breathing, due to the constric)on of the bronchi and bronchioles, their
inflamed linings and the addi)onal fluid and mucus within them
...
Ø A Bght feeling in the chest, due to not being able to ven)late the lungs adequately
due to constricted bronchi and bronchioles
Ø Coughing, the reflex response to obstructed bronchi and bronchioles
Emphysema
Healthy lungs contain large quan))es of elas)c )ssue, mostly made from the protein
elasBn
...
In emphysematous lungs, the elasAn has become permanently stretched and the
lungs are no longer able to force out all the air from the alveoli
...
As a result, liWle if any gas exchange can occur across the stretched and damaged air
sacs
...
If the lungs cannot be empAed of much of their air, then it is difficult to inhale
fresh air containing oxygen
...
Ø Chronic cough, due to lung damage and the body’s effort to remove damaged )ssue
and mucus that cannot be removed naturally due to cilia on the bronchi and
bronchioles being destroyed
...
Smoking greatly increases risk of genng emphysema
...
Explain how
...
-‐enters by osmosis from area of high water potenAal to area of low water potenAal
-‐through water channels
-‐by facilitated diffusion by carrier proteins
-‐down concentraAon gradient
-‐by acAve transport by carrier proteins
-‐against concentraAon gradient
-‐using energy from respiraAon
-‐by phagocytosis engulfing by cell surface membrane to form vesicle
-‐small, lipid soluble molecules diffuse through the bilayer by dissolving in it
Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the
alveoli and blood in the capillaries around them
...
•
Breathing in and out constantly venAlates the blood, moving carbon dioxide out and oxygen in,
thus maintaining a steep concentraAon gradient by constantly providing fresh oxygen
...
•
There are very many alveoli and they are incredibly small, meaning there is a large surface area to
volume raAo, thus meaning the diffusion pathway is shorter and there is more room for the
oxygen to diffuse into the blood
...
-‐glucose moves in with sodium
-‐via carrier proteins
-‐sodium removed from epithelial cells by acAve transport
-‐into blood
-‐MainAaning low concentraAons of sodium in epithelial cells
-‐glucose moves into blood by facilitated diffusion
Vaccines protect people against disease
...
What does an
ORS consist of and how does it work?
-‐Contains glucose
-‐Contains sodium
-‐Co-‐transport/symport
-‐Sodium and glucose taken up from lumen
-‐Lowers water potenAal in cells
-‐Water taken up by osmosis
Emphysema reduces the efficiency of gas exchange in the lungs
...
•
Alveoli break down and walls thicken
•
Less surface area for diffusion
•
Loss of elasAn
•
Alveoli/lungs cannot recoil
•
Reduced diffusion gradient
•
Less oxygen enters blood
•
Less respiraAon and so less energy released
Describe how these phagocyBc white blood cells destroy bacteria
...
Explain
how
...
Describe the transmission and course of infecBon of pulmonary tuberculosis
...
Describe how the structure of a cholera bacterium is different
...
Describe how
...
Explain
how
...
This releases the organelles from the cell
-‐Resultant fluid is then filtered to remove any complete cells and large pieces of debris
-‐Tube of filtrate placed in ultracentrifuge and spun at low speed
-‐heaviest organelle is forced to the bo>om where it forms a pellet
-‐fluid at top, supernatant, is removed
Title: Biology AS AQA Unit 1 Notes
Description: AS Notes for Unit 1 of the AQA Biology A Level course
Description: AS Notes for Unit 1 of the AQA Biology A Level course