Exchange and Transport


Substances needed to keep organisms alive;

-Oxygen= for aerobic respiration

-Glucose= as a source of energy

-Proteins= for growth and repair

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Substances (waste products) that need to be remove

-Oxygen= in microorganisms and animals (+ any plants that are not actively carrying out photosynthesis).

-Carbon dioxide= from photosynthesis in plants and so protocists.

-Any other waste products= e.g. ammonia, urea etc (products that have an excessive amount of nitrogen).

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Exchange surfaces

  • Large surface area= -More space for molecules to pass through.

-This is achieved by folding membranes and walls.

  • Thin barrier= -Reduces diffusion distance.
  • Fresh supply of molecules on one side= -To keep the concentration high.
  • Removal of molecules on the other side= -To keep the concentration low.
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Maintaining a diffusion gradient

(This is in order for diffusion to be rapid)

The gradient consists of;

-A fresh supply of molecules on one side.

-A way of removing molecules from the other side.

The process=

-The blood brings carbon dioxide from the tissues to the lungs. This ensures that the concentration of carbon dioxide in the blood is higher than the in air in the alveoli.

-The blood also carries oxygen away from the lungs. This ensures that the concentration in the blood is kept lower than in the air in the alveoli. 

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Gaseous exchange in the lungs

-Gases pass both ways through the thin walls of the alveoli. 

-Oxygen passes from the air in the alveoli to the blood in the capillaries.

-Carbon dioxide passes from the blood to the air in the alveoli. 

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Adaptations of the lungs

  • Large surface area= -Provides more space for molecules to pass through.

-Alveoli= 100- 300 micrometres across (they are also very numerous).

  • A barrier permeable to carbon dioxide and oxygen= -There is a plasma membrane that surrounds the thin cytoplasm of the cell (forming a barrier of exchange that readily allows the diffusion of carbon dioxide and oxygen).
  • Thin barrier=                  -To reduce diffusion distance.

-Alveoulus and capillary wall= 1 cell thick.

              -Both walls consists of squamous cells (flattened and thin).

-Capillaries are close in contact with alveoulus wall.

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Inhaling- Inspiration

  • Diphragm contracts- to become flatter- this pushes digestive organs down.
  • External intercostal muscles contract- to raise ribs.
  • Volume of chest cavity- increases.
  • Pressure in chest cavity- drops below atmospheric pressure.
  • Air moves into lungs. 
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Exhaling- expiration

  • Diphragm relaxes- and is pushed up by displaced organs underneath.
  • External intercostal muscles realx- ribs fall.
  • Volume of chest cavity- decreases.
  • Pressue in chest cavity- rises above atmospheic pressure.
  • Air moves out of the lungs.
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What is where?

Cartilage= Trachea + Bronchus (some Bronchioles).

Smooth muscle= Trachea, Bronchus and Bronchioles (not in the tiniest).

Goblet cells= Trachea, Bronchus and Bronchioles.

Cilia= All (Trachea, Bronchus, Bronchioles and Alveolus).

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Function- Cartilage

  • Supports the trachea and the bronchi by holding them open.
  • Prevents collapse when the air pressure is low during inhaltion.
  • C shaped (incomplete)= flexible for food to pass the oesophagus.
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Function- Smooth muscle

  • Able to contract in order to make the lumen narrower. Therfore precenting any harmful substances from entering the body.
  • The contraction is involuntary.
  • Think of asthma attacks.
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Function- Elastic fibres

  • When smooth muscle relexes the elastic fibres recoil back to their original shape and size. This helps dilate (widen) the air way.
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Function- Goblet cells and Glandular tissue

  • They secrete mucus.
  • Mucus traps tiny particles in the air.
  • Therefore trapping bacteria so it can be removed. This reduces the risk of infection. 
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Function- Ciliated epithelium

  • Epithelium consisting of ciliated cells.
  • These cells contain numerous hair like structures projecting from their membranes.
  • They work in a synchronised pattern to waft mucus up to the throat. This means it can be swallowed and the bacteria will be killed off by the acidity of the stomach.
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Measuring lung capacity

Tidal volume= Normal breathing at rest.

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Measuring lung capacity

Inspiratory reserve volume= The total amount of ar that can be breathed in.

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Measuring lung capacity

Expiratory reserve volume= The total amount of air that can be breathed out. 

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Measuring lung capacity.

Vital capactiy= The peak of your inspiratory and expiratory reserve volume. 

(Think of running)

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Measuring lung capacity.

Total lung capacity= Vital capacity + residual volume. 

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Measuring lung capacity

Residual volume= The amount of air left in your lungs so they don't collapse.

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Measuring lung capacity

The spirometer

  • A chamber filled with oxygen that floats on a tank of water.
  • There is a pen on a revolving drum in order to draw a trace.
  • When the person breathes out into the mouth piece there is soda lime that absorbs any carbon dioxide.
  • The concentration of oxygen also decreases.
  • When the trace displays a decrease this shows the volume of oxygen in the tank getting used up over time by the person breathing in.
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Transport in animals

Whether or not an animal has a transport system depends on the following;

Size= -Once an animals has several layers of cells, any oxygen or nutrients diffusing in from the outside will be used up by the outer layer of cells (they will not reach the cells deeper within the body)

Surface area: volume ratio= -If large...larger space for molecules to pass through.

-A shorter diffusion gradient.

Level of activity= -Animals need energy so they can move around.

-Releasing energy from food requires oxygen (therefore if the animal is very active it will need a good supply of oxygen and nutrients).

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SIngle circulatory system

  • Blood travels from the heart to the gills and then around the body.
  • Less efficient in comparison to the double circulatory system because= -Due to there only being one 'pump' the blood loses pressure as it travels around the body. This causes the flow to be slower and therefore limits the rate at which oxygen and nutruents are delivered to respiring tissues. 
  • The blood is not fully oxygenated.
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Double circulatory system

  • Blood travels from the heart to the lungs to be oxygeneranted and then back to the heart for a second pump in order to maintain a high blood pressure when travelling around the whole body.
  • More efficient in comparison to the single circulatory system because; -Higher blood pressure results in a faster flow meaning there is a faster delivery of oxygen and nutrients.
  • Blood will be fully oxyegenated.
  • Blood pressure must not be too high in the pulmonary circulation otherwise it might damage the capillaries in the lungs. 
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The two different types of Circulation.

Systemic= The circulation that carries blood around the body, excluding the circulation of the lungs.

Pulmonary= The circulation of the blood through the lungs. 

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Features of a good transport system


  • A fluid or medium to carry oxygen and nutrients around the body. 


  • A pump to create pressure that will push the fluid around the body.


  • Exchange surfaces that enable the oxygen and nutrients to enter the blood and to leave it again for where they are needed.


  • Tubes or vessels to carry the blood.
  • Two circuits... one to pick up oxygen and another to deliver oxygen to tissues. 
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The mammalian heart

  • A muscular double pump (divided into two sides).
  • The right side pumps deoxygenated blood to be oxygenated.
  • The left side pumps oxygenated blood to the rest of the body.

The main pumping chamber= Ventricles.

Thin walled chambers= Atria.

Veins= Carry blood into the heart.

Arteries= Carry blood away from the heart.

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External features of the heart

Coronary arteries= Lie over the surface of the heart. They carry oxygenated blood to the heart muscle itself. 

-Restricted blood flow resudes the delivery of oxygen and nutrients such as fatty acids. This could result in angina or a heart attack. 

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Internal features of the heart

Atrioventricular valves=

-Thin flaps of tissue arranged in a cup shape.

-When the ventricles contract the valves fill with blood and remain closed. This ensures that the blood flows upwards into the major arteries and not downwards into the atria. 

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Internal features of the heart

Tendinous cords= In the ventricles- attach the valves to the walls of the ventricles to prevent the valves from turning inside out. 

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Internal features of the heart

Septum= -A wall of muscle.

-Separates the ventricles from each other.

-This ensures that oxygenated blood on the left side and the deoxygenated blood on the right side stay separate. 

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Internal features of the heart

-Semilunar valves= They prevent the back flow of blood.

(They are at the base of the major arteries).

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Components of the heart to remember


Vena Cava= From the body

Pulumonary Vein= From the lungs


Aorta= To the body

Pulmonary artery= To the lungs

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Characteristics of components

Blood pressure= -The muscle of each chamber contracts increased pressure in the blood.

-The higher the pressure created in the heart, the further it will push the blood. 

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Characteristics of components

Atria= -The muscle of the atria is thin. This is because these chambers do not need to create much pressure....Their function is to push blood into the ventricles only.

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Characteristics of components

Right ventricle=

  • The walls of the right ventricle are thicker than the walls of the atria. This therefore enables the right ventricle to pump blood out of the heart.
  • However, the walls of the right ventricle are much thinner than the walls of the left. This is because the right ventricle only pumps blood to the lungs which sits right next to the heart. 
  • If the right ventricle created too much pressure, it coud damage the thing membranes in the lungs. This would lead to inefficient gaseous exchange. 
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Characteristics of components

Left ventricle=

  • Walls of left ventricle= 3 times thicker than right.
  • This is because the blood from the left ventricle is pumped out of the heart via the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation (going around the whole body).
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The Mammalian Heart

Systole= contraction

Diastole= relaxation

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Control of the cardiac cycle

-The heart is known as MYOGENIC.

-Muscles from the atria and ventricles each have their own natural frequecny of contraction.

-The atrial muscle contracts at a higher frequency that the ventricular muscle.

-This property of the muscle could cause inefficient pumping (FIBRILLATION) if the contractions of the chambers are not synchronised. 

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Controlling the cardiac cycle


  • An electrocardiogram is used to monitor the electrical activity of the heart.
  • It involved attaching a number of sensorts to the skin.
  • These sensors pick up electrical excitation created by the heart and convert this into a trace.
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Controlling the cardiac cycle

A Healthy Person

  • Consists of a series of waves that are labelled 'P, QRS and T'
  • Wave P= excitation of atria 
  • QRS= excitation of ventricles
  • T= shows diastole (relaxation)
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Controlling the cardiac cycle

An Unhealthy Person

  • The trace can show if the heart is breathing irregularly (arrhythmia).
  • If it is in fibrillation, the beat is not coordinated.
  • Shows it is has suffered a heart attack, the heart has enlarged or purkyne tissue is not conducing electrical activity properly. 


-Elevation of the ST section= Heart attack

-Small and unclear P wave= atrial fibrillation

-Deep S wave= abnormal ventricular hypertrophy (increase in muscle thickness)

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Open circulatory systems

Open circulatory system= The blood is not always in vessels.

INSTEAD, the blood fluid circulates through the body cavity, so the tissues and cells of the animal are bathed directly in blood. 

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Open circulatory system

Example= Insect

  • There is a muscular pumping organ much like a heart. This is a long muscular tube that lies just under the dorsal (upper) surface of the insect.
  • Blood from the body of the insects enters the heart through pores called Ostria. 
  • The heart pumps blood towards the head through the peristalis. 
  • At the forward end (near the head) blood simply pours out into the body cavity. 
  • Some larger and more active insects have open ended tubes attached to the heart. These direct the blood towards the active parts of the body. 
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Closed circulatory systems

Definition= Blood remains in vessels that carry it on a single pathway around the body. 

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Closed circulatory systems

  • In larger animals blood stays entirely inside vessels.
  • A separate fluid called tissue fluid bathes the tissues and cells.
  • This enables the heart to pump blood at a higher pressure meaning there will be a much faster delivery of oxygen and nutrients. 
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Blood, tissue fluid and lymph

Blood= held in the heart and blood vessels.

  • Consists of blood cells in a water fluid called plasma.
  • This plasma contains many dissolved substances, including oxygen, carbon dioxide, salts, glucose, fatty acids, amino acids, hormones and plasma proteins.
  • The cells are; red blood cells (erythrocytes), white blood cells (leucocytes) and fragments called platelets.

Tissue fluid= bathes the cells of individual tissues.

  • Does not contain most of the cells found in blood and contains no plasma proteins.
  • Its role is to transport oxygen and nutrients from the blood to the cells, and to carry carbon dioide and other wastes back to the blood.
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How tissue fluid is formed

  • At the arterial end of a capillary, the blood is under high pressure due to the contraction of the heart muscle. This is known as HYDROSTATIC PRESSURE.
  • It will tend to push the blood out of the capillaries.
  • The fluid can leave through tiny gaps in the capillary wall.
  • The fluid that leaves the blood consits of plasma with dissolved mutrients and oxygen.
  • All the res blood cells, platelets, and most of the white blood cells remain in the blood, as do the plasma proteins as they are too large to be pushed out through the gaps.
  • The fluid that leaves the capillaries is known as tissue fluid.
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How tissue fluid returns to the blood

By the following factors;

  • The tissue fluid itself has some hydrostatic pressure, which is tend to push the blood back into the capillaries.
  • Both the blood and the tissue fluid also contain solutes, giving them a negative water potential. The tissue fluid has a less negative water potential than the blood therefore water moves back to the blood from the tissue fluid by osmosis down the water potential gradient.
  • At the venous end (vein end) of the capillary the blood has lost hydrostatic pressue. This along with the osmotic force of the plasma proteins is enough to move fluid back into the capillary. The fluid brings back with it any dissolved waste substances such as cabron dioxide that has left cells.
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Formation of lymph

  • Not all the tissue fluid returns to the blood capillaries... some is drained into the lymphatic system.
  • Lymph contains the same solutes as tissue fluid but however, less oxygen and fewer nutrients due to it being absorbed by body cells and more carbon dioxide and waste products due to them being released by body cells.
  • The main difference between lymph and tissue fluid is that lymph contains many lymphocytes. Lymphocytes are produced in lymph nodes.

Lymph nodes= Swellings found at intervals along the lymphatic system. They filter any bacteria and foreign material from the lymph fluid. The Phagocytes can ten engulf and destroy these bacteria and foregin particles....this is the part of the immune system that protects the body from infection.

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Carriage of oxygen- Haemoglobin


  • Oxygen is transported in erythrocytes (red blood cells).
  • These cells contain the protein haemoglobin.
  • When the haemoglobin takes up oxygen it becomes oxyhaemoglobin.
  • Haemoglobin is a complex protein consisting of 4 subunits.
  • Each subunit consists of a polypeptide (protein) chain and a haem (non-protein) group.
  • Haem groups contain a single iron atom in the form of Fe2+.This iron can attaract and hold an oxygen molecule.
  •  Affinity= attraction for.
  • Haem group is said to have affinity for oxygen as each haem group can hold one oxygen molecule meaning each haemoglobin molecule consists of 4 oxygen molecules.
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Taking up oxygen

  • Oxygen is absorbed into the blood in the lungs.
  • Oxygen molecules diffusing into the blood plasma enter red blood cells.
  • Here they are taken up by the haemoglobin.
  • This takes the oxygen molecules out of the solution therefore mainting a steep diffusion gradient.
  • This diffusion gradient allows more oxygen to enter the cells.
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Releasing oxygen

  • In the body tissues cells need oxygen for aerobic respiration.
  • Therefore the oxyhaemoglobin must be able to release oxygen...this is known as DISSOCIATION.
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Haemoglobin and oxygen transport

·         The ability of haemoglobin to take up and release oxygen depends on the amount of oxygen in the surrounding tissues.

·         The amount of oxygen is measured by the relative pressure that it contributes to a mixture of gases (known as the partial pressure

(PO₂) or oxygen tension measured in units of kPa.

·         Haemoglobin can take up oxygen in a way that produces an S-shaped curve. This is known as the OXYHAEMOGLOBIN DISSOCIATION CURVE.

·         At low oxygen tension, the haemoglobin does not readily take up oxygen molecules. This is because the haem groups that attract the oxygen molecules are at the centre of the haemoglobin molecule. This therefore makes it difficult for the oxygen molecule to reach the haem group and associate with it. This as a result accounts for the low saturation levels of the haemoglobin at low oxygen tensions.

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Fetal Haemoglobin

  • A fetus is not exposed to the outside air. It gains oxygen from its mother's blood. It must be able to 'pick up' oxygen at a PO ₂ that is low enough to make the maternal haemoglobin release oxygen.
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How carbon dioxide is transported.

  • Carbon dioxide is released from respiring tissues.
  • It must be removed from these tissues and transported to the lungs.
  • Carbon dioxide in the blood is transported in 3 ways;

-About 5% is dissolved directly in the plasma.

-About 10% is combined with haemoglobin to form a compound called CARBAMINOHAEMOGLOBIN.

-About 85% is transported in the form of hydrogencarbonate ions.

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How are hydrogen carbonate ions are formed

  • As the carbon dioxide diffused into the blood, some of it enters the red blood cells.
  • It combined with water to form a weak acid called carbonic acid.
  • This is catalysed by the enzyme carbonic anhydrase.
  • This carbonic acid dissociates to release hydrogen ions and hydrogen carbonate ions.
  • The hydrogen carbonate ions diffuse out of the red blood cells into the plasma.
  • The charge inside the red blood cells is maintained by the movement of chloride ions from the plasma into the red blood cell.... THE CHLORIDE SHIFT. 

In order to prevent hydrogen ions making the content of red blood cells very acidic, the hydrogen ions are taken up by the acid to produce haemoglobinic acid. The haemoglobin acts a buffer (a compound that can maintain the pH). 

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Releasing oxygen

  • Blood enters respiring tissues with the haemoglobin carrying oxygen in the form of oxyhaemoglobin.
  • Oxygen tension of respiring tissues is lower than in the lungs due to oxygen being used in respiration.
  • As a result, the oxyhaemoglobin begins to dissociate and releases oxygen to the tissues. 
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The Bohr effect

The amount of O2 carried and released by Hb depends not only on the pO2 but also on pH.

An acidic environment causes oxyhaemoglobin to dissociate (unload) to release the O2 to the tissues. Just a small decrease in the pH results in a large decrease in the percentage saturation of the blood with O2.

An acidic environment causes oxyhaemoglobin to dissociate (unload) to release the O2 to the tissues. Just a small decrease in the pH results in a large decrease in the percentage saturation of the blood with O2.

Acidity depends on the concentration of hydrogen ions.

H+ displaces O2 from the oxyhaemoglobin, thus increasing the O2 available to the respiring tissues.

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The Bohr effect

  • During respiration, CO2is produced. 
  • This diffuses into the blood plasma and into the red blood cells. 
  • Inside the red blood cells are many molecules of an enzyme called carbonic anhydrase. 
  • It catalyses the reaction between CO2and H2O. 
  • The resulting carbonic acid then dissociates into HCO3+ H+. (Both reactions are reversible.)

CO2 + H2O → H2CO3 carbon dioxide   water   carbonic acid H2CO3 → HCO3 + H+ Carbonic acid   hydrogencarbonate ion   hydrogen ion

Therefore, the more CO2, the more the dissociation curve shifts to the right:

Dissociation curve  (

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Haemoglobin and oxygen transport (part 2)

· Eventually an oxygen molecule diffuses into the haemoglobin molecule and associates with one of the haem groups. This causes a slight change in the shape of the haemoglobin molecule known as the CONFORMATIONAL CHANGE. This allows more oxygen molecules to diffuse into the haemoglobin molecule and associate with the haem groups relatively easily as the oxygen tension rises.

· Once the haemoglobin molecule contains 3 oxygen molecule it becomes difficulty for the 4th molecule to diffuse down and associate with the haem group. This therefore means it is difficult for the haemoglobin molecule to reach 100% saturation even when the oxygen tension is high. This as a result causes the curve to level off.

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The Bohr effect (part 2)

H+ + HbO2 → HHb + O2

HHb is called haemoglobinic acid.

This means that the haemoglobin mops up free H+. That way the Hb helps to maintain the almost neutral pH of the blood. Haemoglobin acts as a buffer.

This release of O2 when the pH is low (even if the pO2 is relatively high) is called the Bohr effect.

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