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Bio F6 Gaseous Exchange

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GLASS AND CERAMICS

CHAPTER 1Gaseous ExchangeIntroductionWhy Gaseous Exchange?Living organisms need energy for cellular activitiesDuring cellular aerobic respiration, O2 is used up in cells & CO2 is given outG.E. process of swapping 1 gas for anotherUnicellular organisms have a large surface area/volume ratio & short distance for rapid diffusion G.E. sufficient for their needsMulticellular organisms have a low surface area/volume ratio & the bulk of body cells are deep in the inner parts of the body G.E. need a specialised respiratory system

7.1 Animals7.2 Plants 7.1 Animals1

Respiratory System in Mammals & Humans

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Respiratory System in Mammals & Humans1

Mechanism of Ventilation (Breathing)InspirationExpiration

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Mechanism of Ventilation (Breathing)InspirationExpirationContractExternal intercostal muscles RelaxRelaxInternal intercostal muscles ContractPulled upwards & outwardsRibcagePulled downwards & inwardsContractDiaphragm muscles RelaxMoves downwards, becomes flattenedDiaphragmMoves upwards, returns to dome shapeIncreasesThoraic volumeDecreasesDecreases to below atmospheric pressureAir pressure in the lungsIncreases to higher than that of the atmosphereAir is drawn into the lungs along a pressure gradientAir movementAir is moved out of the lungs along a pressure gradientIncreasesVolume of the lungsDecreases1

Microscopic Stucture of Alveolus1Tiny space surrounded by a thin wall that separates it from adjacent alveoliMicroscopic air sacs clustered at the distal ends of the alveolar ductsTiny alveolar pores in the walls permit air to pass to diffuse from 1 alveolus to another provide alternate pathways for diffusion of O2 & CO2

Microscopic Stucture of Alveolus12 types of epithelium: (a) Type I pneumocytes - 95% - large thin, flattened simple squamous cells

(b) Type II pneumocytes - 5% - septal cells or great alveolar cells - cuboidal cells - act as reserve cells which differentiate into new squamous cells to repair damage in the alveoli - secrete pulmonary surfactant to decrease the surface tension betw. the thin aqueous film thst covers the alveolar wals, prevents the alveoli from collapsing & speeds up gaseous exchange

Microscopic Stucture of Alveolus1Respiratory macrophages- mobile phagocytes- ingest bacteria & small debris

Microscopic Stucture of Alveolus1

Microscopic Stucture of Alveolus1

Adaptations for G.E in the Lungs1Large surface area for G.EMoist surfaces for gases to dissolve b4 diffusion can occurType II pneumocyte secrete surfactant that lowers the surface tension of the fluid lining the inner surface of alveolus & speeds up G.EThin walls / 1 cell thick that minimise the distance for gas diffusionWalls are permeable to diffusion of O2 & CO2Surrounded by numerous blood capillaries which bring CO2 for diffusion into the alveoli & carry away O2 to the circulatory systemAlveoli:

Adaptations for G.E in the Lungs1A good ventilation system provides a constant supply of O2 to the alveoli & removes CO2Stretch receptors in the lungs help to initiate the breathing reflexElastic fibres in the lungs permit optimum extension during inspiration

The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structure

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The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structureConsists of 4 polypeptide chains, 2 and 2 chains (coil closely together)

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The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structureConsists of 4 polypeptide chains, 2 and 2 chains (coil closely together)Each polypeptide chain made up of globin & a haem group

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The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structureConsists of 4 polypeptide chains, 2 and 2 chains (coil closely together)Each polypeptide chain made up of globin & a haem groupEach haem group comprises of a porphyrin ring with an iron atom (Fe II) attached in the center

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The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structureConsists of 4 polypeptide chains, 2 and 2 chains (coil closely together)Each polypeptide chain made up of globin & a haem groupEach haem group comprises of a porphyrin ring with an iron atom (Fe II) attached in the centerHaem group give blood its red colour transport O2

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The Respiratory Pigment, HaemoglobinStructure of Haemoglobin A complex, quaternary protein structureConsists of 4 polypeptide chains, 2 and 2 chains (coil closely together)Each polypeptide chain made up of globin & a haem groupEach haem group comprises of a porphyrin ring with an iron atom (Fe II) attached in the centerHaem group give blood its red colour transport O2Iron atom can bind to 1 O2 molecule;So, each haemoglobin molecule can carry 4 O2 molecule to form oxyhaemoglobin ( Hb(O2)4 )

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HbHaemoglobin4 O2HbO8OxygenOxyhaemoglobin+high partial pressure of O2(associates)low partial pressure of O2(dissociates)1Oxygen Transport

Oxygen Transport1O2 is carried in the blood:1. 98.5% O2 bound to haemoglobin in the red blood cells2. 1.5% O2 dissolved in the plasma

Oxygen Transport11. 98.5% O2 bound to haemoglobin in the red blood cells- the binding of the 1st O2 molecule to a haem group causes a slight change in the shape of the haemoglobin (allostery) which facilitates the binding of the other O2 molecules- 1 haemoglobin molecule can bind loosely & reversibly with 4 molecules of O2 to form an unstable oxyhaemoglobin molecule

Oxygen Loading & UnloadinggasesArea of high partial pressureArea of low partial pressureoxygenAlveolusBlood capillaries(PO2)(PO2)Haemoglobin + O2Oxyhaemoglobin1

Oxygen Loading & UnloadingO2 Dissociation Curve Sigmoid/S-shape graph relationship betw. The degree of haemoglobin saturation with O2 at different values of PO2

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Oxygen Loading & UnloadingO2 Dissociation Curve When 1st O2 is bound to haemoglobin, it changes the conformation of the haemoglobin molecule & facilitates the 2nd & 3rd O2 to bind. The binding of the 4th O2 is not facilitated so there is a slight delay

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Oxygen Loading & UnloadingO2 Dissociation Curve The facilitation of 1 molecule of O2 for the binding of the 2nd & 3rd O2 give rise to the S-shaped sigmoid curve of the O2 dissociation curve

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Oxygen Loading & UnloadingO2 Dissociation Curve 95% - loading tension of haemoglobin (in alveolus, high affinity of haemoglobin for O2 to form oxyhaemoglobin)

50% - unloading tension of haemoglobin (in respiring tissues, oxyhaemoglobin dissociates, release its bonded O2, freed haemoglobin is then circulated to the lungs for rebinding with O2)1

Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve Partial pressure of Carbon DioxideTemperatureMyoglobin vs HaemoglobinFetal Haemoglobin vs Adult Haemoglobin1

Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve Partial pressure of Carbon DioxideWhen PCO2 & pH , there is a reduction of the affinity of haemoglobin for O2.So, dissociation of oxyhaemoglobin , O2 dissociate curve shifts to the rightBohr effect

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Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve TemperatureWhen tissues respiration that occurs in skeletal muscles during exercise. Heat is generatedThe rise in blood temperature lowers the affinity of haemoglobin for O2The O2 dissociation curve shifts to the right

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Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve Myoglobin vs haemoglobinMyoglobin (acts as a store of O2 in resting skeletal muscles) binds strongly to O2 to form oxymyoglobin which is more stable than oxyhaemoglobinThe myoglobin dissociation curve is hyperbolic in shape & is to the left of the haemoglobin

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Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve Fetal haemoglobin vs Adult haemoglobinThe fetal haemoglobin has a higher affinity for O2 (enables it to obtain O2 from the maternal haemoglobin at low PO2)The fetal haemoglobin dissociation curve is to the left of the maternal haemoglobin

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Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve Fetal haemoglobin vs Adult haemoglobinThere is Double Bohr Effect- In maternal circulation, there is a high PCO2, which helps to release O2

- In fetal circulation, there is a low PCO2, which increases the binding of haemoglobin with O2O2 dissociation curve of HbA & HbF is shift in opposite directionsHbA curve - rightHbF curve - left1

Oxygen Loading & UnloadingFactors that affect the O2 Dissociation Curve

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Carbon Dioxide Transportcellsinterstitial fluidblood plasmaCO2CO23 ways of CO2 transport: 1. 85% CO2 convert to bicarbonate (hydrogencarbonate) ions (HCO3-)2. 10% CO2 combine with amino (NH2) group of Hb to form carbaminohaemoglobin (HbNHCOOH)3. 5% CO2 carried in physical solution1

Carbon Dioxide TransportCO2 + H2OH2CO3carbonic anhydrase1234H2CO3H+ + HCO3-carbonic acidcarbonic anhydrasehydrogencarbonate ionHb(O2)44O2 + HbCO2 , H+ , pH freed haemoglobin5H+ + HbHHbhaemoglobinic acidHCO3- diffuse out, convert back to CO2, expelled into atmosphere from alveoliCl- diffuse in, restore the electroneutrality of red blood cell, Chloride shift(act as buffer)1. 85% CO2 convert to bicarbonate (hydrogencarbonate) ions (HCO3-)1

Carbon Dioxide TransportCO2 + HbNH2HbNHCOOH12HbNHCOOHHbNHCO2- + H+carbaminohaemoglobincarbaminohaemoglobin iontransport to lungs where it dissociates release CO2 & being expelled2. 10% CO2 combine with amino (NH2) group of Hb to form carbaminohaemoglobin (HbNHCOOH)1

Carbon Dioxide Transport3. 5% CO2 carried in physical solutionCO2 + H2OH2CO312H2CO3H+ + HCO3-carbonic acidhydrogencarbonate ion transport to lungs where it dissociates release CO2 & being expelled1

O2 & CO2 Transport1

Carbon Dioxide Transport1

Control of BreathingBreathing automatic & rhythmic action, controlled by the respiratory centres (medulla of brain)Breathing main goal = maintain alveolar ventilation for normal blood O2 & CO2 concentration at all timesRespiratory central control centreMedulla & ponsSensorsEffectors Chemoreceptors Stretch receptors other receptors Respiratory muscles - Diaphragm - intercostal muscles - abdominal muscles1

Control of BreathingRespiratory central control centreInspiratory centre(ventral portion)Expiratory centre(dorsal & lateral portion)Increase in rate & depth of inspirationInhibit inspiration & stimulate expiration1

Control of BreathingSensorsChemoreceptorsStretch receptorsCentral chemoreceptorsPeripheral chemoreceptorsSensitive to PO2, PCO2, blood pHCarotid bodiesAortic bodiesSensitive to PO2, PCO2, pHSensitive to PO2, PCO21

Control of BreathingSensorsChemoreceptorsStretch receptorsCentral chemoreceptorsPeripheral chemoreceptorsSensitive to PO2, PCO2, blood pHCarotid bodiesAortic bodiesSensitive to PO2, PCO2, pHSensitive to PO2, PCO21

Control of BreathingStretch receptorsHelp in maintain any expansion in the lungs & size of airways

Send impulses to the expiratory centre to shorten inspiration1

Control of BreathingWhen changes in partial pressure of gases & pH are detected by chemoreceptors (central/peripheral), impulses are sent to the the inspiratory centre which then send impulses to the diaphagram & intercostal muscles12The respiratory muscles will react to increase or decrease alveolar ventilation as required by regulating amplitude & depth of each breath1

Control of Breathing1The rise in the carbon dioxide partial pressure in the blood (from respiration)detected by chemoreceptors in the carotid arteryimpulses are sent to the breathing centre to stimulate the inspiratory center and the cardiovascular center in the brain

The inspiratory centre sends out impulses through:intercostal nerve - stimulate the contraction of the external intercostal muscles of the rib cagephrenic nerve - stimulate the contraction of the diaphragm musclesBoth contractions bring the rib cage outwards and upwards to increase the volume of the lungs and decrease its pressure. Atmospheric air is inhaled into the lungsAs the bronchial tree of the lungs is stretched, it stimulates the stretched receptors which then send impulses to the expiratory centre through the vagus nerve to inhibit inhalation and stimulate exhalation

At the same time, the cardiovascular centre sends impulses through the sympathetic nerve to the heart to increase the cardiac frequencyInhalation

Control of Breathing1The rib cage and the diaphragm fall back to their original positions, decreasing the lung volume, but increasing its pressure. Air is exhaled out of the lungs. During forced exhalation, the internal intercostal muscles will contract to bring the rib cage downwards and inwardsThe expiratory centre then becomes inactive and inspiration begins again. At the same time, cardiovascular centre stimulate the heart to reduce its cardiac frequency, and the blood vessels to dilate thus lowering the blood pressure

The cycle is repeatedExhalation

Respiratory Volumes & CapacitiesTotal lung capacity (TLC) includes tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV) and residue volume (RV)TLC = TV + IRV + ERV + RVTV volume of air inhaled during a normal inspiration 400- 500 cm3 of airIRV additional volume of air that can be taken in after a normal tidal inspiration (deep breath) 1500 cm3 of airERV additional volume of air that can be forced out after a normal tidal expirationRV volume of air that remains in the lungs after a maximum expiration & cannot be expelled even after forced expiration air that always remains in the lungs, preventing lungs from collapsing 1500 cm3 of air 1

Respiratory Volumes & CapacitiesVital capacity (VC) is the maximum volume of air that can be breathed out in a forced breathVC = TV + IRV + ERVTLC = VC + RVSo, TLC can also be expressed as:Rate of respiration of a mammal:Ventilation rate = TV X inspiratory frequency (number of breaths per minute)1

Respiratory Volumes & Capacities

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7.1 Animals7.2 Plants 7.2 Plants 1

StomataGaseous exchange in plants occurs mainly through pores called stomataStomata- pores that found on the lower epidermis of leaves & stems

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StomataGaseous exchange in plants occurs mainly through pores called stomataStomata- pores that found on the lower epidermis of leaves & stems- formed by 2 guard cells (kidney-shaped, contains chloroplasts, involves in opening & closing of the stoma)Structure of stoma- has a thinner outer wall a thicker inner wall- cellulose microfibrils are radially orientated in the cell wall- the epidermal cells surrounding the guard cells are called subsidiary cells

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StomataGaseous exchange in plants occurs mainly through pores called stomataStomata- pores that found on the lower epidermis of leaves & stems- formed by 2 guard cells (kidney-shaped, contains chloroplasts, involves in opening & closing of the stoma)Structure of stoma- has a thinner outer wall a thicker inner wall- cellulose microfibrils are radially orientated in the cell wall- the epidermal cells surrounding the guard cells are called subsidiary cells- gaseous exchange respiratory gasesFunction of stoma absorption of CO2 (when photosynthesis, O2 diffuses out, CO2 diffuses in) regulation of water (under water deficit condition, stoma closes to prevent water lost)1

Stomatal Opening & ClosingThe opening & closing of stoma a response to an increase/decrease in the water potential (WPg) of the sap solution in the guard cells causing water to enter/exit the guard cells3 hypotheses- Bidirectional movement of water in & out of guard cells Starch-glucose equilibrium hypothesis123Potassium ion concentration hypothesisStarch-malate equilibrium hypothesis1

Stomatal Opening & ClosingStarch-glucose equilibrium hypothesis1Stomatal opening:- during photosynthesis, production of osmotically active glucose- water potential (WPg) - diffusion deficit gradient is esthablished, epidermal cells guard cells- water enters the guard cells by osmosis- guard cells becomes turgid- stoma opensStomatal closure:- during conversion of glucose to starch, osmotically inactive- water potential (WPg) - diffusion deficit gradient is esthablished, guard cells epidermal cells- water leaves the guard cells by osmosis- guard cells becomes flaccid- stoma closes1

Stomatal Opening & ClosingStarch-glucose equilibrium hypothesis1Stomatal opening: Starch Glucose (osmotically inactive) (osmotically active) starch , WPg glucose , WPg closing of stoma opening of stoma

CO2 lightCO2 dark1

Stomatal Opening & ClosingPotassium ion concentration hypothesis2Stomatal opening:- high light intensity, low mesophyll CO2- Potassium channels are activate, K+ ions diffuse into guard cells- diffusion deficit gradient is esthablished, epidermal cells guard cells- water enters the guard cells by osmosis- guard cells becomes turgid- stoma opens- guard cells contains chloroplasts, generate ATP- Blue Light (BL) activate a proton pump, ATP drive the proton pump- protons (H+) are pumped out of guard cells- water potential (WPg) - accumulation of K+ ions

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Stomatal Opening & ClosingPotassium ion concentration hypothesis2Stomatal closure:- low light intensity, rise of mesophyll CO2- diffusion deficit gradient is esthablished, guard cells epidermal cells- water leaves the guard cells by osmosis- guard cells becomes flaccid- stoma closes- hormone abscisic acid (ABA) is secreted & increase the permeability of Calcium channels- Ca2+ enter into the guard cells- water potential (WPg) - accumulation of Ca2+ ions, inhibit proton pump, H+ stop pumping out

1-potassium ion channel open, K+ diffuse out

Stomatal Opening & ClosingPotassium ion concentration hypothesis2

Closing of stoma Opening of stoma

K+ concentration , WPg ,entry of waterK+ concentration , WPg ,loss of water1

Stomatal Opening & ClosingStarch-malate equilibrium hypothesis3Stomatal opening:- during photosynthesis, CO2 conc. , pH - starch-malate equilibrium shifted to right, malate conc. - water potential (WPg) - water enters the guard cells by osmosis- guard cells becomes turgid- stoma opensStomatal closure:- night time, no photosynthesis, CO2 conc. , pH - starch-malate equilibrium shifted to left, malate conc. - water potential (WPg) - water leaves the guard cells by osmosis- guard cells becomes flaccid- stoma closes1

Stomatal Opening & Closing Starch Malate (osmotically inactive) (osmotically active) closing of stoma opening of stoma

CO2 , pH Starch-malate equilibrium hypothesis3pH-sensitive enzymesCO2 , pH 1

Stomatal Opening & Closing

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