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Exchange Systems
Size and surface area
Smaller animals have larger surface area to volume ratios compared to larger animals

Size

Shape

Exchange organs and mass transport
Small organisms
Large organisms
• Quick diffusion over a
• Some cells deep within
large SA with a very
the body
small distance
• Low SA: VOL means
• No need for organs
not enough surface to
exchange, needs
organs
Heat exchange
• Easy to lose heat
• Hard to lose heat
• However, need high
• Can have a low
metabolic rate to
metabolic rate
compensate
• Irregular shape to
• Rounded, compact
increase SA: VOL thus
shape to reduce SA:
increase heat loss
VOL this decreases
heat loss

Gas exchange
Gas exchange in the leaf of a plant:
Gas exchange in plants occurs in the leaves
...
The mesophyll cells have a large surface area for rapid diffusion
...
They open and
close due to the guard cells situated next to them
...

The movement of the water in and out of the guard cells is controlled by ions moving in and out
...
When ions move out, water follows causing the guard cell to become flaccid and shut
...
Adaptations can include reduced SA: VOL as leaves are reduced to spines also creating less
stomata, fleshy stems to hold water or silver surface to reflect sun
...

Layers of hairs on epidermis to trap moist air around the stomata, limiting the water
potential
...


Gas exchange in single cell organisms and insects:
Single celled organisms have a thin membrane, moist surface and permeable membrane, this allows
them to not require a specialised gas exchange system
...
The oxygen
then travels through the
tracheae when spiracles close as
the decrease in SA causes a
pressure to pass the gases
through the body
...

•
•

Goes down to
individual cells
Made of a
single cell
layer to
reduce
diffusion
distance

•
•

Tracheae and tracheales
give large SA
Lined with chitin to stop
the pressure from
collapsing them

•

•
•

Opened and closed by
the insect
...
If
not will result in
desiccation (drying out)

Gas exchange in fish:
Mechanics of fish ventilation:
Fish take in water through their mouth and push in out of their gills, pictured below, to take gases
from the ocean sea water to allow survival
...


Gill Physiology:

With the gill lamella blood flow flowing opposite to the flow of water between the lamella, it allows
for an efficient gas exchange through the counter-current system
...
Almost all oxygen from water diffuses into blood
...
External intercostal muscles contract, pulling the ribcage
upwards and outwards
2
...
External intercostal muscles relax, and the ribcage falls under its
own weight
2
...
Elastic recoil of lung tissue
• The combined effect of these:
- Volume of the thorax and lungs decrease
- Pressure is increased
- Air is forced out
Expiration forced – active process
1
...
Abdominal muscle contracts pushing the diaphragm upwards

•

The combined effect of these:
- Volume of thorax and lungs decrease further
- Pressure increased
- More air forced out

Measuring breathing:
Spirometry – measuring of the volume (FVC or forced vital capacity) and speed (FEV or forced
expiratory volume) of inhalation and exhalation
...
The
subject breaths in and out of the machine wearing a
mouthpiece until oxygen is used up
...

Residual volume: The volume of air left in your lungs when you have exhaled as hard as
possible
Total lung capacity: Residual volume + Total lung compacity
Oxygen consumption: Take 2 points on graph, see how many seconds they are apart, see
how much volume they are apart, divide seconds by volume (s/dm)
Ventilation rate= Tidal volume x breathing rate

Lung diseases:
Tuberculosis
•
•
•
•
•

Caused by bacteria
Immune system builds a wall around the bacteria in the lungs
Infected tissue within dies
SA reduced
Symptoms:
- Increased ventilation rate, persistent cough, coughing up blood

VC/FVC affected
TV decreased
FEV₁ decreased

Fibrosis
•
•
•
•
•

Formation of scar tissue – due to infection or exposure to substances
Creates thicker diffusion distance
No longer one cell thick
Not as elastic
Symptoms:
- Faster ventilation rate, shortness of breath, chest pain

Lung volume
affected
TV decreases
VC/FVC decreases
FEV₁ decreases

Asthma
•
•
•
•

VC/FVC decreases
Airways inflamed/irritated usually an allergic reaction
Bronchiole smooth muscle contracts
Bronchioles over produce mucus
Symptoms:
- Wheezing, tight chest, shortness of breath

Emphysema
•
•

Mainly effects middle age to old long-term smokers
Damage to the air sacs in the lungs

Chronic bronchitis
•
•
•
•

Long term inflammation of the airways
Smoking or long-term air pollution
Particles become trapped in alveoli as the respiratory bronchioles collapse
Inflammation – phagocytes arrive, enzymes break down elastin = collapse

Interpreting data – Lung disease:
Correlation – when one variable clearly interacts with the other
Cause – cannot be stated definitively, must be investigated further to test correlation

FEV₁ greatly
reduced

Digestion
Digestive system:
Mechanical
digestion by
action of teeth
Peristalsis
...
Bile
production stored
in gall bladder
...
Turns
excess amino acids
into area

Takes water
out of
digestive food

Salivary amylase
coats food breaking
down starch into
maltose
...
The wall is
made of both elastic
fibres and smooth
muscle
...

Duct cells secrete a
bicarbonate solution
...
Enzyme fixed
within cell membranes in
the small intestines such as
maltase, lactose, sucrose
...
Maltase, sucrase, lactase breaks down
disaccharides into monosaccharides
...


Protein digestion:
Endopeptidase break down proteins from the inside to
protease and peptone
...
Then reducing them to
amino acids
...
When it goes back to being
oxygen and haemoglobin it is said to disassociate
For efficient oxygen transportation, Hb must:
- Readily associate with oxygen at the lungs where gas exchange takes place
- Readily disassociate with oxygen at the body tissue where respiration is occurring
The amount of oxygen present changes the Hbs affinity
- When low O₂ is present – low affinity
- When high O₂ is present – high affinity
- Other factors can also affect affinity
Haemoglobin + oxygen = oxyhaemoglobin
Hb + 4O₂ = HbO₈
It is a reversible reaction

Region of the
body

O₂ concentration

Blood at gas
High
exchange surface
Blood at respiring Low
tissues

CO₂
concentration
Low

Affinity of
haemoglobin for
oxygen
High

High

Low

Result

O₂ associates
with Hb
O₂ disassociates
from Hb

Oxygen disassociation curves:
Sigmoidal curve – binding of oxygen #1 and #4
1
...
Haemoglobin loads oxygen when in the
lungs where the O₂ saturation and O₂ pressure are high
...
This allows for O₂ to bind to haemoglobin easier
...
As the pressure of O₂ decreases, O₂ saturation will
too so the oxygen will be unloaded
...


Effect of CO₂ - Bohr Shift effect:
Affinity of Hb for CO₂:
-

By lowering the pH by CO₂ dissolving in the blood creating an acid, the bonds between a Hb
molecule is altered, changing its shape
...

So, in respiring, CO₂ rich tissues, O₂ is given up more readily

The greater the concentration of CO₂, the more readily available the Hb releases its O₂

Adaptations of Hb in different animals:
Lugworms:
•
•
•

Not very active
Oxygen diffuses from water into blood
When tide goes out = no circulation of water = no O₂

This means they can survive at low concentrations of O₂ as they
have a high affinity
...

Birds and Fish:
•
•
•

Flight and swimming are energetically demanding
Higher affinity – low O₂ environment, low MET rate, low
CO₂
Lower affinity – high SA: VOL, high MET rate, high CO₂
when respiring so needs O₂

Mouse:
•
•

Large SA: VOL causes high MET rate
Heat is lost quickly due to short diffusion distance

•
•

Shifted to right as there is more CO₂ due to respiration
...

Mouse’s unloading pressure is larger than humans

Foetal:
•

Foetal haemoglobin must have high affinity compared to
mother blood so it can take up oxygen

The Heart:
Aorta

Superior vena cava

Pulmonary vein

Pulmonary artery
Pulmonary artery
Left atrium
Right atrium

Tricuspid valve

Semilunar valves

Bicuspid valves
Septum

Right ventricle
Left ventricle
Inferior vena cava
Muscle layer

Protected by the pericardium which also facilitates pumping
Atriums have thin walls, ventricles thick walls to pump blood through arteries
Oxygenated blood – pulmonary artery → left atrium → left ventricle → aorta
Deoxygenated blood – vena cava → right atrium → right ventricle → pulmonary artery

Heart beats:
The Sino-atrial node (SAN) is a specialised bundle of thin,
cardiac, muscular fibres buried in the right atrial wall
...
When the electrical impulses reach
the atrioventricular node, the impulses will spread rapidly
through special fibres from the interventricular septum to
the walls of both ventricles, where muscle fibre cells are
stimulated to contract
...

•

•

The long and low pitched ‘lubb’ – the
closure of the two valves between the
atria ventricles during ventricular
contraction
...


Phases of the cardiac cycle:
The heart pumps blood in rhythmic activity
...
Contraction - systole, relaxation –
diastole
...
No backflow due to presence of the bicuspid and tricuspid valves
...
1 seconds
...


Ventricular systole:
•

•

Takes place alongside atrial diastole
...
The closing
of the atrioventricular valves produces the
‘lubb’
...
The atriums are already in diastole
when ventricles are in diastole, the
pressure in the ventricles decreases
compared to pressure in the great arteries
...

Veins and arteries follow the same characteristics to some degree:
•
•
•
•
•

Tough outer layer – maintain structure and resist pressure
Muscle layer – contraction and controlling blood flow
Elastic tissue – return to shape, maintain blood pressure by stretching and springing back
Thin inner layer – minimise the friction and thin for diffusion
Lumen – allows blood flow

Artery:
•
•
•

Thick outer layer
Thick elastic layer
Thicker muscle layer

Arteriole:
•
•

Narrower than arteries
Muscular control – most regulated
blood vessels, contribute the most
to overall blood pressure

Capillary:
•
•
•
•
•

Massive numbers
Near all cells – bathe all cells with
oxygen etc
Tiny
Permeable
One cell thick

Venule:
•
•
•

Very small vessels
Start to carry blood from the
capillary beds
Feed into larger veins

Vein:
•
•
•
•

Carry blood in towards heart
Large lumen
Thinner outer layer/muscle/elastic
Valves

Tissue fluid:
Constituent parts of blood: WBCs, RBCs, platelets, plasma
Substances found in blood: oxygen, water, carbon dioxide, glucose, urea, lipids, amino acids, lactic
acid
...
The LDL cholesterol finds
weak spots within the endothelium and enters under it
...
P
...

Thrombosis:
A thrombus is a blood clot in the vascular system
...
It can also break off and flow with the blood until blocking a
passage
...

Myocardial infarction:
No blood flow to the heart tissue means no respiration can occur leading to
a heart attack
...

Stroke:
If an atheroma develops in the neck, it interferes with the flow of blood to
the brain
...


Risk of developing a CVD:
Blood pressure:
•
•
•
•

High BP caused by obesity, smoking, high blood cholesterol levels or diabetes, too much
alcohol, lack of physical activity, stress
Hereditary risk factors include family history, age, gender, race
Sleep apnea, pregnancy-induced hypertension, kidney disorders, heart defects
A high BP increases the hearts workload, making it thicken and stiffer
...


Diet:
•
•

High LDL cholesterol caused by eating more saturated fat increases the chance of an
atheroma forming
...
O =
-ve, H = +ve
Spontaneously arrange with +ve next to -ve
Molecules cohere or stick together – cohesion
Tension is created when molecules fill in space of drawn up water molecules
when the space has low density, low pressure
...
Water enters – water enters through osmosis into the root hair cells and enters
the xylem
2
...
Tension occurs when molecules have negative pressure exerted on column of
water
4
...


The phloem – translocation
1
...
Water enters the phloem with the solutes creating
a solution
...
The solutes enter the companion cell by active
transport meaning the water leaves the phloem
back to the xylem
The source – where the sugars are made, high
concentration
The sink – where the sugars are used up or stored, low
concentration
Sugars need to be translocated from source to sink

Translocation evidence
For
• Remove a ring of bark which includes
phloem but not xylem, bulge forms
above cut
• Pressure investigating using aphids
...
Sap flows quicker nearer the
leaf (source)
• Radioactive tracer evidence supports
• If a metabolic inhibitor is added, then
translocation stops

Against
• Sugar travels to many sinks not just the
highest water potential
• Lots of pressure needed to get through
sieve plates



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