Module 2Exchange and Transport

Unit OneCells, Exchange and Transport

AS BiologyOCR Specification

Learning Outcomes

• Explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.

Exchanges between organisms and their

environment• Exchange can take place in two ways

– Passively (no energy is required)• E.g. diffusion and osmosis

– Actively (energy is required)• Active transport• Pinocytosis and phagocytosis

Surface area to volume ratio

• Exchange takes place at the surface of an organism, but the materials absorbed are used by cells that mostly make up its volume.

• For exchange to be effective, the surface area of the organism must therefore be large compared with its volume.

Learning outcomes

• Explain, in terms of surface area:volume ratio, why multicellular organisms need specialised exchange surfaces and single-celled organisms do not.

Evolution of organisms

• A flattened shape• A central region that is hollow• Specialised exchange surfaces

– Large areas to increase the surface area to volume ratio

Why organisms need special exchange surfaces

• Oxygen for…• Glucose as a source of …• Proteins for … and …• Fats • Water• Minerals• To remove waste materials

Features of a specialised exchange surface

• Good exchange surfaces have:– A large surface area– Thin barrier to reduce diffusion distance– Large concentration gradient

• Fresh supply of molecules on one side• Removal of required molecules on other side

Specialised Exchange Surfaces

• Alveoli in the lungs• Small intestine• Liver• Root hairs in plants• Hyphae of fungi

Progress Question

• Very small organisms such as the amoeba do not have specialised gas exchange systems.

• Mammals are large, multicellular organisms and have a complex gas exchange system.

• Explain why the mammal needs such a system when an amoeba does not.

Progress Question - suggestions

• Why do we need gas exchange?– Oxygen is needed for respiration– Body needs to get rid of waste carbon

dioxide.

• How do simple animals take in the oxygen they need?– Diffusion through the surface

membranes e.g. amoeba or flatworm

Progress Question - suggestions

• Why can’t multi-cellular organisms do this?– Cells are too far away from the oxygen

in the external environment.– Need a specialised exchange surface.

• In humans the specialised gas exchange surface is the alveoli.

Learning Outcomes

• Describe the features of an efficient gas exchange surface, with reference to diffusion of oxygen and carbon dioxide across and alveolus.

Gas Exchange

• Gaseous exchange is the movement of gases between an organism and its environment.

• Gas exchange takes place by diffusion.– The rate of diffusion depends on three

factors.• The surface area of the gas exchange surface• Difference in concentration• The length of the diffusion pathway

Alveoli

• Adaptations of alveoli to gas exchange – Large surface area– Thin walls of alveoli and blood capillaries– Steep concentration gradient– Good blood supply– Ventilation

• Blood is constantly moving through the lungs to maintain the concentration gradients.

• The air in the alveoli is continually refreshed by ventilation.

Alveoli and gas exchange

• Large surface area – 70m2

• Extremely thin – lined with squamous epithelium – allows for rapid diffusion– 0.1μm to 0.5μm thick

• Kept moist / surfactant• Extensive capillary network

– Capillaries 7-10μm in diameter– Blood flow through capillaries is slowed

• Ventilation

Applying your knowledge

• Alf smoked for 40 years. He had a bad “smoker’s cough” and easily got out of breath. His health got worse so he went to see his doctor. The doctor said that he had emphysema. She explained that the coughing had damaged a lot of the alveoli in his lungs and reduced their surface area.– Explain as fully as you can why Alf got out of

breath easily.– Alf’s illness got worse. He couldn’t walk very

far and he had to breathe oxygen from a cylinder. Explain why.

Structure of the Mammalian Lung

Learning Outcomes

• describe the features of the mammalian lung that adapt it to efficient gaseous exchange;

• outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm;

Think!!

• Why is the volume of oxygen that has to be absorbed and the volume of carbon dioxide that has to be removed in mammals so large?– Large organisms with large volume of

living cells– Maintain a high body temperature

• High metabolic rate• High respiratory rate

Mammalian Lungs

• Structure of the lungs– Trachea– Rib cage– Intercostal muscles– Bronchi– Bronchioles– Alveoli (site of gaseous exchange)

• 100μm – 300μm in diameter• 300 million in each lung

Revision Activity

• Design a poster• Your poster should show the distribution of

tissues and highlight the functions of each of the tissues– cartilage – Cilia– goblet cells– smooth muscle– elastic fibres

Learning Outcomes

• describe, with the aid of diagrams and photographs, the distribution of cartilage, ciliated epithelium, goblet cells, smooth muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the mammalian gaseous exchange system

• describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic fibres in the mammalian gaseous exchange system;

Ciliated Epithelium

Cartilage

Smooth Muscle

Squamous Epithelium

DistributionTissue / cell trache

abronch

usbronchiol

esalveolu

s

Cartilage (not in the

tiniest)

Goblet cells Ciliated cells Smooth muscle

Very little

Squamous epithelium

Elastic fibres

Functions of cells, tissues and fibres

Cartilage

• Flexible supporting material• Incomplete rings support the smooth

muscle keeping the tubes open.• Prevents trachea and bronchi from

collapsing when air pressure lowers during inhalation

Cilia

• Synchronised movement to transport mucus towards the pharynx

Goblet cells

• Produce the mucus that forms a thin layer over surface of the trachea and bronchi

• The mucus is sticky and traps bacteria. Pollen and dust particles, the air is “filtered”.

Smooth muscle

• Contraction of the smooth muscle allows the bronchioles to constrict.

• This controls the flow of air to the alveoli.

Elastic fibres

• Elastic fibres become stretched when the smooth muscle contracts, when the smooth muscles relaxes the elastic fibres recoil back into their original positions.

• This dilates the bronchioles.

Difference in structure of Trachea, bronchi and

bronchioles• Cartilage in trachea and bronchi

keep airways open and air resistance low.– Trachea has c-shaped rings– Bronchi has irregular blocks

• Bronchioles have smooth muscle which contracts and elastic fibres to control their diameter

Learning Outcomes

• outline the mechanism of breathing (inspiration and expiration) in mammals, with reference to the function of the rib cage, intercostal muscles and diaphragm;

Inhalation

Exhalation

Inspiration ExpirationDiaphragm Contracts and

flattensRelaxes and pushed up by organs in abdomen

Rib cage (ribs and intercostal muscles)

External intercostal muscles contract raising the ribs

Internal

Volume of thorax

Pressure in chest cavity

Air movement

Fill in the gaps Mammalian Lungs (1)

• Two reasons why mammals require a large and constant supply of oxygen are (1) and (2). The main organs for gaseous exchange are the lungs, which are connected to the outside by a tube called the (3). This branches into two (4), one of which enters each lung.

Fill in the gaps Mammalian Lungs (2)

• The actual site of gaseous exchange is in the alveoli, which have a diameter of (5) and have walls made of (6) which is very thin, being only (7) in thickness. The total number of alveoli for both lungs is around (8) giving them a very large surface area of about (9).

Fill in the gaps Gaseous Exchange in the

alveoli (1)• Gaseous exchange occurs in the

alveoli, with the gas called (1) moving into the blood and the gas called (2) moving in the opposite direction. The diameter of an alveolus is (3) and it is surrounded by squamous epithelial cells that are only (4) thick and so allow rapid (5) of gases across them.

Fill in the gaps Gaseous exchange in the

alveoli (2)• Each alveolus is surrounded by a

network of (6) that are around (7) in diameter, causing (8) within them to be flattened against their surface, thus improving the rate of exchange of gases between themselves and the alveoli.

Learning Outcomes

• explain the meanings of the terms tidal volume and vital capacity;

• describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake;

• analyse and interpret data from a spirometer

Breathing Rate

• Breathing refreshes the air in the alveoli so that concentration of O2 and CO2 remains constant

Lung Capacities

• Tidal volume– The volume of air breathed in or out in a single

breath

• Residual volume – The amount of air that remains in the alveoli

and airways after forced exhalation.

• Vital Capacity– The volume of air that can be exchanged

between maximum inspiration and maximum expiration

• The effect of exercise on breathing is measured by calculating ventilation rate, which is the total air moved into the lungs in one minute.

Ventilation rate = tidal volume X breathing rate

• Ventilation brings about changes in lung volume, these changes can be ,measured by a spirometer.

Measuring Oxygen Uptake

• If someone breathes in and out of a spirometer for a period of time, the carbon dioxide level increases to dangerous levels.

• To avoid this, soda lime is used to absorb the carbon dioxide exhaled.

• This means the total volume of gas in the spirometer will go down.

Measuring Oxygen Uptake

• The volume of CO2 breathed out is the same as the volume of O2 breathed in.

• This allows us to make calculations of oxygen used under different conditions.

Spirometer trace (4 marks)

• A spirometer measures the volume of gas breathed in and out of the lungs.

• The spirometer trace shows the results obtained from a 17 year old male who was sitting down while breathing in and out of a spirometer.

• Describe this person’s breathing between points J and K on the spirometer trace

Spirometer trace answers

Transport

Unit OneCells, Exchange and Transport

AS BiologyOCR Specification

Learning Outcomes

• Explain the need for transport systems in multi-cellular animals in terms of size, activity and surface area to volume ratio

• Explain the meaning of the terms single and double circulatory systems with reference to the circulatory systems of fish and mammals

• explain the meaning of the terms open circulatory system and closed circulatory system, with reference to the circulatory systems of insects and fish

The Mammalian Transport System

Why do multi-cellular animals require a transport System?

The Internal Transport System

• Cell Metabolism – What do cells need?– Amino acids, glucose, oxygen– Removal of waste products

• What is important in determining whether an organism has a transport system?– Size– Surface area to volume ratio– Level of activity

Pupil Activity

• Using the table on the next slide, determine the importance of the three factors and give information to support your answers?

• Size• Surface area to volume ratio• Level of activity

Different Transport Systems

Type of organis

m

Size range

ExampleLevel of Activity

Type of transport system

Single celled Microscopic ParameciumMove in search of food

No special transport sys.

CnidariansMicroscopic 60cm

Sea AnemoneSlow swim or sedentary

No special transport sys.

Insects 1mm 13cm Locust Move actively (fly)

Blood system with pump

Fish 12mm 10m Goldfish Move activelyBlood system with pump

Mammals 35mm 34m Human Move activelyBlood system with pump.

Determining the need for a transport system!

Size•Important, but not the only factor•Small mammals and insects have a transport system•Large cnidarians – no transport system

Determining the need for a transport system!

Size•Important, but not the only factor•Small mammals and insects have a transport system•Large cnidarians – no transport system

Surface area to volume ratio•Small organisms have a large S.A to volume ratio, and have no transport system

Determining the need for a transport system!

Size•Important, but not the only factor•Small mammals and insects have a transport system•Large cnidarians – no transport system

Surface area to volume ratio•Small organisms have a large S.A to volume ratio, and have no transport system

Level of Activity•Fish, mammals and insects more active have a transport system•Larger but sedentary cnidarians do not

Why transport systems?

• Diffusion only works effectively in large surface area to volume ratios

• Small organisms. Oxygen diffuses into cells, to mitochondria for use in respiration

• Large organisms can not rely on this• Body surface is not large enough• Distances from surface are too great

• Less active organisms have a smaller requirement for glucose and oxygen.

Surface Area:Volume ratios

Length of side (mm)

Volume(mm3)

Surface area

(mm2)

Surface area:volum

e ratio

1

5

10

Surface Area:Volume Surface Area:Volume ratiosratios

Length of side (mm)

Volume(mm3)

Surface area

(mm2)

Surface area:volum

e ratio

1 1 6 6 : 1

5 125 150 1.2 : 1

10 1000 600 0.6 : 1

Surface area: volume ratio

• With a cube shape– As it gets bigger the volume increases

faster than the surface area– Larger multi-cellular animals need a

transport system and special gas exchange surfaces

Open Circulation

• Insects have an open circulation– Blood is not enclosed in vessels, and it

circulates in body spaces.

Closed circulation

• Blood flows inside vessels

• Single circulation e.g. Fish– Blood flows through

heart once in every circulation of the body.

Closed Circulation

• Double Circulation e.g. mammals– Blood passes through the heart twice in

every circulation of the body.– Two circuits

• Pulmonary circuit• Systemic circuit

Advantages of a double circulation

• Simultaneous high pressure delivery of oxygenated blood to all regions of the body

• Oxygenated blood reaches respiring cells undiluted by deoxygenated blood.

The Mammalian Heart

Structure of the HeartDissection

Learning Outcomes

• describe, with the aid of diagrams and photographs, the external and internal structure of the mammalian heart;

• explain, with the aid of diagrams, the differences in the thickness of the walls of the different chambers of the heart in terms of their functions;

External Structure of the heart

• Observe and draw the external structure of the heart, identifying the following parts.– Cardiac muscle– coronary arteries– Aorta– pulmonary artery– Vena cava– pulmonary vein

Internal structure of the heart

• Observe and draw the internal structure of the heart

• Identify and describe – Septum– atrium and ventricle– Atrio-ventricular valves

• mitral/bicuspid• tricuspid

Revision of structure of heart

• Label the diagram of the heart– Right atria / left atria– Right ventricle / left ventricle– Aorta / pulmonary artery– Vena cava / pulmonary vein

• Colour in deoxygenated blood blue / oxygenated blood red

• Fill in the missing gaps in the summary.• You have got 10 minutes for this activity

The Mammalian Heart

The Cardiac Cycle

Learning outcomes

• describe the cardiac cycle, with reference to the action of the valves in the heart;

Cardiac Cycle

• The sequence of events of a heart beat

• Alternate contractions (systole) and relaxations (diastole)

• Between 70 and 75 bpm

Cardiac Cycle

• Blood flows through the heart– Muscles contract– Volume chamber decreases– Pressure increases– Blood forced to a region of lower

pressure– Valves prevent backflow

Cardiac Cycle

• There are 3 main stages to the cardiac cycle– Atrial systole– Ventricular systole– Diastole

Atrial Systole

• Heart is full of blood and ventricles relaxed

• Both atria contract• Blood passes into ventricles• A-V valves open due to pressure• 70% blood flows passively atria -

ventricle

Atrial Systole

Ventricular Systole

• Atria relax• Ventricles contract• Forces blood into pulmonary artery

and aorta• A-V valves close (lub)• S-L valves open• Pulse is generated

Ventricular systole

Diastole

• Ventricles relax• Pressure in ventricle < pressure in

arteries• High pressure blood in arteries cause

S-L valves to shut (dub)• All muscles relax• Blood from vena cava and pulmonary

vein enter atria

Diastole

Structure and function of heart muscle

• Ventricle walls are thicker– Need greater force when contract

• R. Ventricle –force relatively small, pumps to lungs

• L. Ventricle – sufficient to push blood around body

• Thickness left > right

Exam Question

• Answer the exam question– You have got 15 minutes for this

Pressure and volume changes of the heart

Pupil Activity

• June 2003 2803/1 question 2

Learning outcomes

• Describe how heart action is coordinated with reference to the sinoatrial node (SAN), the atrioventricular node (AVN) and the Purkyne tissue.

• Interpret and explain electrocardiogram (ECG) traces, with reference to normal and abnormal heart activity.

Control of Heart Beat

• Myogenic – heart muscle contracts and relaxes without having to receive impulses from the nervous system– Sino-atrial node– Atrio-ventricular node

Sino-atrial Node

• Special cardiac muscle tissue in right atrium

• a.k.a. SAN or Pacemaker• Sets the rhythm at which all other

cardiac muscle cells beat• Sends excitation wave

(depolarisation) over atrial walls

What happens next?

• Collagen fibres prevent the wave of excitation from passing from the atria to the ventricle walls

• Allows the ventricle to fill before they contract

Atrio-ventricular Node

• Patch of conducting fibres in the septum

• a.k.a AVN• AVN picks up impulses that have

passed through atrial tissue• Wave of excitation runs down

purkyne tissue to the base of the septum

Atrio-ventricular Node

• Wave spreads upwards and outwards through the ventricular walls

• Blood is squeezed up and out through arteries.

Control of cardiac cycle - Summary

• Cardiac muscles is myogenic– Wave excitation spreads out from SAN across atria,

atria contract– septum prevents wave crossing to ventricles– Wave excitation passes through AVN, which lies

between atria– AVN conveys wave excitation between ventricles

along specialised muscle fibres known as bundle of His

– This conducts wave through septum to base of ventricles, bundles branch into smaller fibres known as Purkyne tissue

– Wave is released, ventricles contract from apex of heart upwards

electrocardiogram

• Record of wave of electrical activity caused by atrial systole (P), ventricular systole (QRS), and the start of ventricular diastole (T)

Translating ECGs

• Elevation of the ST section indicated a heart attack

• A small or unclear P wave indicated atrial fibrillation

• A deep S wave indicates abnormal ventricular hypertrophy (increase in muscle thickness)

ECG of an unhealthy heart

• An abnormal ECG could indicate– Arrhythmia

• Where the heart is beating irregularly

– Fibrillation• Where the heart beat is not co-ordinated

– Myocardial infarction• Heart attack

Fibrillation

• Excitation wave is chaotic• Small sections of the cardiac muscle

contract whilst other sections relax• Heart wall flutter• Possible causes

– Electrical shock– Damage to large areas of muscle in

walls of heart

Exam Question

• Answer the practice exam question

The Mammalian Transport System

Structure and function of Arteries, Veins and Capillaries

Learning Outcomes

• describe, with the aid of diagrams and photographs, the structures and functions of arteries, veins and capillaries;

Structure of Arteries, Veins and Capillaries

GCSE Revision• Arteries carry blood away from the

heart• Veins carry blood towards the

heart• Capillaries are a network of thin

tubes which link A to V, and take blood close to cell.

Basic Structure

Tunica intima

•Endothelium (single layer of cells)

Tunica media

•Middle layer containing smooth muscle and elastic fibres

Tunica externa

•outer layer containing collagen fibres.

Lumen (hollow centre of tube)

Microscope Artery

Microscope Vein

Microscope Capillary

Look at the image on the following page.

What are structures X and Y

What do parts 1 – 4 show or represent?

Blood Vessels

X

Y

1

3

2

4

Answers• X is an artery • Y is a Vein1. shows the smooth endothelial lining

cells which reduce resistance to blood flow.

2. shows red blood cells within the lumen of the artery

3. shows the thick muscular wall of the artery

4. shows blood capillaries note their size compared to arteries and veins.

Structure and Function of Arteries

Look at this cartoon.

What can you deduct about arteries?

(answers on a postcard please)

Structure of Arteries, Veins and Capillaries

Arteries Veins Capillaries

Thick muscular wallMuch elastic tissueSmall lumen

Capable of constrictionNot permeableValves

–(Aorta and P.A)

Thin muscular wallLittle elastic tissueLarge lumen

Not capable constrictionNot permeableValves throughout

No muscleNo elastic tissueLarge lumen (relative)Not capable constrictionPermeableNo valves

Arteries

• Function– To transport blood, swiftly and at high pressure

to the tissues.– The structure of the artery wall gives it

strength and resilience– The large amounts of elastic tissue in the

tunica media allow the walls to stretch as blood pulses through.

– As arteries move away from the heart there is a decrease in elastic tissue and an increase in muscle tissue.

Arteries (cont)• Elasticity of walls – 2 functions

– “give”– Blood at low pressure in an artery

gets a “push” as artery recoils evens out blood flow

• Arterioles– More smooth muscle– Contracts to help control the volume

of blood flowing into tissues (dilation and constriction)

Capillaries• Function

– To take blood as close as possible to all cells, allowing rapid transfer of substances between cells and blood

• Network of capillaries capillary bed

Veins• Venules/veins

– Return blood to the heart

• Low venous pressure

• Semi-lunar valves– Form from endothelium– Allow blood to travel to the heart– Prevents the back flow of blood

Systemic Circulation

Aorta artery

arteriole capillary

venule vein

vena cava

Summary of function of A, V and C

Arteries Veins CapillariesTransports blood away from heartOxygenated blood (except P.A)Blood High PressureBlood moves in pulsesBlood flow rapidly

Transport blood too heart.Deoxygenated blood (except P.V)Blood low pressureNo pulsesBlood flows slowly

Links arteries to veinsBlood changes from oxygenated to deoxygenated (except in lungs)B.P. reducingNo pulsesBlood flow slowing

Revision Questions (1)

– Suggest why arteries close to the heart have more elastic fibres in walls than arteries further away from the heart.

– Suggest why there are no blood capillaries in the cornea of the eye. How might the cornea be supplied with its requirements?

Revision Questions (2)

• Suggest reasons for the following:1. Normal venous pressure in the feet is

about 25mm Hg. When a soldier stands at attention the blood pressure in their feet rises very quickly to about 90mm Hg.

2. When you breathe in (volume thorax increases), blood moves through the veins towards the heart.

Pupil Activity

• Bioviewer activity – slide set 68– Read the information on the front of the card.

• how does the human circulatory system help to maintain cell life?

• what are the three major parts of the human circulatory system?

– Observe the following slides• Slide 1 – human blood• Slide 2 – Phagocyte• Slide 3 – artery and vein• Slide 4 – capillaries in the lung

Blood, Tissue fluid and Lymph

Blood – the transport medium• Plasma

– Straw coloured, alkaline liquid– Consists mainly of water

• Functions of blood– Defends body against disease– Maintains diffusion gradients– Acts as a buffer– Provides pressure– Distributes heat around body

Blood plasma

• Water with dissolved substances– Nutrients e.g. glucose– Waste products e.g. urea– Plasma proteins

• Buffers• Solute potential

Red Blood CellsErythrocytes

• Origin– Bone marrow

• Mature RBC transport respiratory gases

• Life span 120 days• No nucleus/ cell organelles• Cytoplasm full of haemoglobin

• Biconcave disc• Large SA: volume ratio

White Blood CellsLeucocytes

• Protect body as part of the immune system

• Originate in bone marrow thymus and lymph for growth and development

• Lymphocytes– Production of antibodies

• neutrophils, monocytes– phagocytosis

Platelets(cell fragments)

• Tiny packages cytoplasm containing vesicles with thromboplastins– Clotting factors

• Made in bone marrow• Last 6 – 7 days

Pupil Activity

• Which of these functions could, or could not, be carried out by a RBC.

• Protein synthesis• Cell division• Lipid synthesis• Active transport

Answers SAQ

• Protein Synthesis– NO: no DNA so no

mRNA can be transcribed.

• Cell Division– NO; no

chromosomes, so no mitosis; no centrioles for spindle formation

• Lipid Synthesis– NO; occurs in

smooth ER

• Active Transport– YES; occurs across

plasma membrane, can be fuelled by ATP from anaerobic respiration.

Tissue Fluid

• Immediate environment of each individual body cell.

• Homeostasis maintains composition of tissue fluid at a constant level to provide the optimum environment in which cells can work.

• Contains less proteins than Blood plasma

Forces for exchange on capillaries

Blood in capillary

Arteriole end Venule end

Blood proteins (e.g. albumins) can not escape and maintain the water potential of the plasma,

preventing excess water loss, and help to return fluid to the capillary

Diff

usio

n g

radie

nt

Osmotic movement of water Ultrafiltration of

water and small molecules (O2, glucose and amino acids) due to hydrostatic pressure

Diff

usi

on g

radie

nt

Hydrostatic pressure reducedTissue fluid

Lymph• Similar composition to plasma with

less proteins• Lipids absorbed in lacteals, give

lymph milky appearance• Tiny blind ending vessels• Tiny valves in walls allow large

molecules to pass in.• Drains back into blood plasma in

subclavian vein.

oedema

• If lymph does not take away proteins in tissue fluid between cells, YOU could die in 24 hours.

• Get a build up in tissue fluid, called oedema.

Movement in lymph capillaries

• Contraction of muscles around vessels

• Valves• Slow movement

– Diagram: the relationship between blood, tissue fluid and lymph at a capillary network

» Diagram: the lymph system

Table summary

feature blood Tissue fluid Lymph

Cells

Proteins

Fats

Glucose

Amino acids

Oxygen

Carbon dioxide

Antibodies

Table summary

feature blood Tissue fluid Lymph

Cells Erythrocytes, leucocytes, platelets

phagocytes Lymphocytes

Proteins Hormones and plasma proteins

hormones, proteins secreted by body cells

some

Fats Transported as lipoproteins

None Absorbed by lacteals

Glucose 80-120mg per 100cm3

Less Less

Amino acids more less less

Table summary

feature blood Tissue fluid Lymph

Oxygen more less Less

Carbon dioxide

little Released by body cells

More

Antibodies yes yes yes

The Mammalian Transport System

Transport of Oxygen and Carbon Dioxide

Partial Pressure• In a mixture of gases, each component

gas exerts a pressure that is proportional to how much of it is present.

• Concentration of gas is quoted as its partial pressure, in kilopascals kPa.

• pO2 partial pressure of oxygen• pCO2 partial pressure of carbon dioxide

pO2 = atmospheric pressure x % O2

100

Pupil Activitycalculation of partial pressure

• Assume the composition of air is 20% oxygen and 80% nitrogen, and is approx. the same at sea level (atmospheric pressure = 101.3kPa) and at 5000m above sea level (atmos. Pressure = 54.0 kPa) and at 10000m above sea level (atmos. Pressure = 26.4 kPa)

• What is the partial pressure of oxygen at these altitudes?

Transport of Oxygen

• Haemoglobin in red blood cells (RBC)

Hb + 4O2 HbO8

Haemoglobin dissociation curve

• A graph showing the amount of oxygen combining with haemoglobin at different partial pressures.

• High pO2 – haemoglobin saturated with oxygen

• Low pO2 – oxyhaemoglobin gives up its oxygen to respiring cells (dissociates)

Haemoglobin dissociation curve

S-shaped curve

• Each Hb molecule has 4 haem groups

• 1st O2 combines with first haem group

• Shape of Hb distorted

• Easier for other 3 O2 to bind with haem group

Bohr Shift

• high pCO2 increases dissociation of oxyhaemoglobin

• Oxyhaemoglobin releases oxygen where it is needed most – actively respiring tissues.

Fetal Haemoglobin

• Fetal Hb has a higher affinity for O2 than adult Hb.

• This allows the fetal Hb to “steal” O2 from mothers Hb

Myoglobin

• Oxymyoglobin is more stable than oxyhaemoglobin

• Only gives up O2 at very low pO2.

• Myoglobin acts as an oxygen store

Carbon Dioxide Transport

• CO2 carried in three ways

– 5% in solution in plasma as CO2

– 10% combines with amino groups in Hb molecule (carbamino haemoglobin)

– 85% hydrogen carbonate ions

Carbon dioxide transport

• Transported in blood as hydrogen carbonate ions

• Carbonic anhydrase catalyses the reaction

CO2 + H2O H2CO3

Carbon Dioxide Transport

• Carbonic acid dissociates

H2CO3 H+ + HCO3-

• H+ ions associate with haemoglobin (buffer)

• Haemoglobinic acid (HHb)

• Contributes to Bohr effect

Chloride Shift

• Build up HCO3- causes them to diffuse

out of RBC

• Inside membrane positively charged

• Cl- diffuse into RBC from plasma to balance the electrical charge

Problems with Oxygen Transport

Carbon Monoxide• Haemoglobin combines readily with

carbon monoxide to form carboxyhaemoglobin (stable compound)

• Carbon monoxide has a higher affinity with haemoglobin than oxygen does

• 0.1% CO in air can cause death by asphyxiation.

High Altitude

• Pupil activity– question sheet on high altitude– Question

• Atheletes often prepare themselves for important competitions by spending several months training at high altitude. Explain how this could improve their performance.

Training at high altitude

• Spending a length of time at high altitude stimulates the body to produce more red blood cells

• When an athlete returns to sea level, these “extra” RBC remain in the body for sometime, and can supply extra oxygen to muscles enabling them to work harder and for longer than they would otherwise.