Module 3

• Large Surface Area
• Thin Layers
• Good Blood Supply/Ventilation

• Trachea
• Bronchi
• Bronchioles
• Alveoli

• Incomplete rings of cartilage offer support, are flexible and allow food to pass in the oesophagus
• Lined with ciliated epithelium & goblet cells that secrete mucus

• Divisions of the trachea
• Same structure as trachea

• Smaller bronchioles have no cartilage 
• Walls contain smooth muscle to contract & constrict or relax and dilate
• Lined with thin layer of flattened epithelium - some gaseous exchange occurs

• Tiny air sacs (200-300μm)
• Thin layer of squamous epithelial cells - gaseous exchange
• Collagen
• Elastic fibres - expand/return to normal size - elastic recoil
• Lung Surfactant - keeps alveoli from sticking shut
• Moist - solution of water, salts and surfactant allow oxygen to dissolve before diffusing to blood

• 1. Intercostal muscles contract
• 2. Diaphragm contracts
• 3. Chest cavity expands - low pressure, high lung volume
• 4. Air forced into lungs

• 1. Intercostal muscles relax, ribs move down & inwards under gravity
• 2. Diaphragm relaxes, moving upward to domed shape
• 3. Elastic Fibres return to normal length
• 4. Volume of thorax decreases, pressure increases above atmospheric pressure
• 5. Air is pushed out

• 1. Inspiratory Reserve Volume
• 2. Tidal Volume
• 3. Expiratory Reserve Volume
• 4. Residual Volume
• 5. Total Lung Capacity
• 6. Vital Capacity
• (7. Functional Residual Capacity)

• From the bottom of tidal volume to the top of total lung capacity
• The total amount of air you can breath in after breathing out normally

The volume that is inhaled with the strongest possible exhalation followed by the strongest possible inhalation

Ventilation Rate = Tidal Volume × Breathing Rate

• Thin gills
• High SA
• Tips of gills overlap, slowing flow of water to maximise O₂ intake
• Countercurrent system ~ blood and water flow in opposite directions to maintain conc gradient
• Lamellae have rich blood supply

• 1. Mouth and buccal cavity open
• 2. Volume of BC increases, pressure decreases ⇨ water is drawn in
• 3. Same time, opercular valve shuts & opercular cavity (containing gills) expands
• 4. Pressure in OC drops
• 5. BC floor moves up steadily ⇨ increases pressure ⇨ water moves towards the gills
• 6. Mouth closes, OV opens, OC sides move inwards
• 7. Increase in pressure ⇨ water moves over gills & out the operculum 

• Spiracles found along thorax and abdomen
• Opened or closed as required by sphincters
• Air moves in through diffusion 

• Tracheae Lined with spirals of chitin to keep them open (up to 1mm wide)
• Tracheoles divisions of tracheae, single elongated cell, freely permeable to gases
• Trachael fluid limits penetration of air for diffusion
• Muscle

• More spiracles opened
• Lactic acid build up in tissues causes water to move out by osmosis, exposing more SA for gas exchange

• Large insects/high energy demand:
• Mechanical Ventilation - air pumped in my muscular movements
• Collapsible enlarged tracheae or air sacs

• Only open spiracles when needed
• Hairs around spiracles trap humid air keeping a shallow concentration gradient

• Mammals: Double closed, high pressure, blood
• Fish: Closed, medium pressure, blood
• Insects: Open, low pressure, haemolymph

• Closed:
• -can carry varying amounts of blood to different parts of body
• -faster blood flow with double closed having the fastest

• Open:
• -unable to maintain steep concentration gradients
• -can't alter flow to meet different demands
• -haemolymph doesn't carry O₂ or CO₂ 
• -(does carry food & nitrogenous waste)

• Smaller lumen to maintain high pressure of the blood
• Smooth endothelium to reduce friction
• Thick layer of Elastic fibres - withstand force of the blood allowing the vessel to stretch & recoil evening out the surges to gain a continuous flow
• Thin muscle layer - doesnt need to change lumen size much
• Thick collagen layer maintains volume of vessel & gives structural support

• The further from the heart, the less elastic fibres
• The amount of smooth muscle increases to control the size of the lumen & blood flow
• Collagen decreases since there is less pressure and need for support

• 10μm - red blood cells travel in single file
• Gaps between endothelial cells are relatively large to allow substances out of the capillary into the tissue fluid
• One cell thick - efficient diffusion
• Total cross-sectional area of capillaries > than supplying arteriole so rate of blood flow drops - more time for exchange

• Larger Lumen - same flow rate as blood has slowed & reduces resistance 
• Smooth endothelium
• Thin elastic layer
• Some Smooth Muscle
• Lots of Collagen 
• Valves to prevent back-flow of blood
• Run between muscles, which squeeze the blood when they contract
• Breathing movement of chest acts as a pump

• 55% Plasma
• Red & white blood cells & platelets ~ erythrocytes and leucocytes
• dissolved glucose
• amino acids
• mineral ions
• hormones
• large plasma proteins e.g fibrinogen

• Hydrostatic: pressure from surges of blood every time the heart pumps
• ~ +4.6kPa (arteriole end) ⇨ +2.3kPa (venule end)
• Oncotic: the tendancy of water to move into the blood in capillaries by osmosis 
• ~ around -3.3kPa

• When hydrostatic pressure is greater than oncotic pressure:
• -water & other dissolved substances move out of capillaries through fenestrations

• When hydrostatic pressure is less than oncotic pressure:
• -about 90% tissure fluid moves back into blood

• Albumin has osmotic effect
• -causes low water potential in blood
• -meaning the osmotic pressure is higher

• Last 10% of tissue fluid drains into lymph capillaries
• -less O₂ & nutrients
• Moved by body movements
• Valves prevent backflow
• Returns to blood (subclavian veins)

• Lymph nodes
• -lymphocytes build up here & produce antibodies when necessary
• -intercept bacteria ⇨ injested by phagocytes

• Reversibly binds to haemoglobin 
• When the first O₂ binds, haemoglobin changes shape making it easier for the next to bind
• Up to 4 oxygen molecules can bind

At higher partial pressures of CO₂ haemoglobin gives up O₂ more easily

• 5% dissolved in plasma
• 10-20% combined with amino groups in haemoglobin to form carbaminohaemoglobin
• 75-85% converted to hydrogen carbonate ions (HCO3-) in cytoplasm of RBCs
• ~ CO₂ + H₂O ⇌ H₂CO₃ (carbonic acid) ⇌ H⁺ + HCO₃^-(hydrogen carbonate ion)
• ~ catalysed by carbonic anhydrase

• HCO₃^- ions diffuse out of RBC
• Cl^- ions diffuse in ~ maintaining electrical gradient
• ~converting & removing CO₂ from RBCs means there is a steep concentration gradient so that more CO₂ is collected from respiring tissues

• In lungs with low partial pressure of CO₂:
• -opposite diffusion directions
• -carbonic anhydrase converts carbonic acid back to carbon dioxide and water
• -CO₂ free to leave & exit lungs

• Accepts H⁺ ions from dissociated carbonic acid
• Forms haemoglobinic acid

• Diastole: ~ filling
• -volume & pressure build in heart
• -pressure in arteries at minimum

• Systole: ~ contracting
• -atrial systole followed by ventricular systole
• -high pressure inside heart during contraction
• -volume & pressure low at end
• -pressure in arteries at highest

• As the blood hits AV valves during ventricular systole 
• And hits semi-lunar valves after ventricular systole

• Myogenic 
• - has its own intrinsic rhythm (around 60bbp)

• Wave of excitation begins at Sino-atrial node (SAN)
• Causes atria to contract
• Layer of non-conducting tissue prevents impulse passing directly to ventricles
• Impulse picked up by Atrio-venticular (AV) node 
• Slight delay (to ensure atria finish contracting) before stimulating Bundle of His ~ made up of conductive Purkyne fibres in septum
• Bundle of His splits in two
• Carries impulse down to apex of heart
• Purkyne fibres spread up sides of ventricles
• Impulse causes upward contraction of ventricles

• Measures tiny electrical differences in the skin which result from the heart's activity
• Each lasts about 1 second

• Bradycardia 
• - reduced rate
• - fit people have more efficient hearts
• - may require pacemaker 

• Tachycardia 
• - very rapid
• - normal after exercise/fear etc.
• - can be caused by electrical control problems

• Ectopic Heartbeat 
• -out of normal rhythm 
• - normal around once a day
• - could be serious if frequent

• Atrial Fibrillation 
• - rapid impulses generated at atria which contract quickly
• - don't contract properly
• - only some impulses passed on to ventricles
• - heart does not pump blood very effectively

• Carries water and mineral ions
• Gives plant support
• Largely non-living
• Columns of cells fuse end to end
• Xylem parenchyma packs around vessels to store food and tannin deposits
• Lignin ~ rings/spirals for support
• Bordered pits ~ unlignified areas so water can leave

• Transports food - solutes - sugars, amino acids
• Living tissue
• Sieve Tube Elements: 
• -cells joined end to end
• -sieve plates between
• -vacuole membrane (tonoplast), nucleus, some organelles break down
• Companion Cells:
• -Linked to sieve tube elements by plasmodesmata
• -'life support'

• Symplast:
• -cytoplasm connected by plasmodesmata
• -water moves by osmosis from root hair cell to next cell along as the root hair has a higher water potential
• -water exits into xylem causing drop in water potential & maintaining gradient

• Apoplast:
• -cell walls and intercellular spaces
• -pulled through by cohesion

• Water reaches endodermis & Casparian strip forces water into symplast pathway ~ passing through selectively permeable membrane blocking out potentially toxic solutes
• Mineral Ions actively pumped into xylem ~ lowering its water potential
• Water moves through symplast into xylem cells

• Results from active pumping of mineral ions into xylem
• ⇨ So water follows due to decreased water potential in xylem
• Gives water a small push up the xylem

• Cyanide affects mitochondria & stops ATP production
• ⇨ no root pressure when cyanide is applied

• Increases with temperature
• ⇨suggesting chemical reactions are involved

• Decreases with falling oxygen and respiratory substrate levels
• ⇨ not a passive process

• Xylem sap forced out of pores in leaves
• ⇨ when transpiration levels are low (e.g. at night) there must be something else pushing water up

"The loss of water vapour from the leaves and stems as a result of evaporation from cell surfaces in the plant and diffusion down a concentration gradient out through the stomata"

• Water evaporates from meosphyll cells in leaves into air spaces ⇨ diffuses out via stomata
• This water loss lowers the water potential ⇨ water moves in from adjacent cells
• Water replaces this from the xylem
• Adhesion & cohesion result in capillary action ⇨ water is drawn up xylem by transpiration pull
• Resulting in tension in the xylem which helps pull water from the soil
• ~ Cohesion-tension theory

• Changes in diameter of trees
• ⇨ tension during the day reduces their diameter

• Air drawn into cut stems
• ⇨ instead of water leaking out
• ⇨ water no longer drawn up if this happens since the stream is broken

Using a potometer

• Favourable conditions:
• -solutes actively pumped into guard cells
• -in order to increase turgor pressure
• -guard cells expand lengthways ~ cellulose hoops prevent expansion widthways
• -thicker, less flexible inner cell wall causes them to become bean shaped

• When water is scarce:
• -hormonal signals from roots trigger turgor loss
• -stomata close

• Light intensity: more light ⇨ more stomata open for photosynthesis
• Relative Humidity: higher humidity ⇨ smaller concentration gradient ⇨ less transpiration 
• Temperature: Higer temp ⇨ more kinetic energy ⇨ increased evaporation
• -ALSO higher temp ⇨ increases ability of air to hold water before becoming saturated ⇨ decreasing relative humidity ⇨ less transpiration
• Air movement: more wind ⇨ greater concentration gradient ⇨ more transpiration 
• Soil Water Availability: dry conditions ⇨ plant is under water stress ⇨ reduces transpiration

• From source to sink
• Transporting the products of photosynthesis ~ assimilates
• Mainly sucrose
• Mainly an active process

• The apoplast route:
• Sucrose travels from source via apoplast
• Companion cells acvtively pump sucrose into cytoplasm
• -pump H⁺ ions out using ATP for proton pump
• -H⁺ ions return down concentration gradient via cotransport protein
• -Companion cells have many infoldings for high SA and many mitochondria for ATP
• Build up of sucrose in companion cells & sieve tube elements means water moves in by osmosis
• Build up of turgor moves water & assimilates into sieve elements
• Solute accumulation in source phloem increases turgor pressure ⇨ forcing sap to regions of lower pressure by mass flow

• Sucrose diffuses to any points that need it
• Converted to another substance ⇨ maintaining concentration gradient
• -e.g. glucose for respiration or starch for storage
• Loss of solutes from phloem cause rise in water potential 
• ⇨ water moves out to surrounding cells
• ⇨ some water is drawn into transpiration stream

Not used in metabolism as readily ⇨ less likely to be used during transport process

• The adaptations of the companion cell for active transport ~ seen via microscope
• Translocation stops if the mitochondria are poisoned
• The flow of sugars is 1000X faster than diffusion alone
• Positive pressure in phloem forces sap out of an aphid's stylet

• Xerophytes ~ dry
• Hydrophytes ~ live in water

• Thick Waxy Cuticle
• Sunken Stomata ⇨ in pits, reducing air movement and forming microclimate of humid air
• Reduced no. of stomata
• Reduced leaves ⇨ reducing SA:V ratio
• Hairy leaves ⇨ microclimate of humid air
• Curled Leaves ⇨ confines stomata in microclimate of humid air
• Succulents ⇨ store water in specialised parenchyma tissue
• Leaf loss ⇨ lose leaves during dry times
• Root adaptations
• -long tap roots access water deep in ground
• -widespread shallow roots collect water during a shower
• Avoiding the problem
• -become dormant
• -die and leave seeds behind
• -some survive as storage organs

• Thin/No waxy cuticle ⇨ no need to conserve water
• Many stomata, always open, on upper surfaces ⇨ maximise gaseous exchange
• Reduced structure ⇨ since water supports the plant
• Wide, flat leaves ⇨ capture lots of sunlight
• Small roots ⇨ water is able to diffuse directly into the stem and leaves
• Air sacs ⇨ keep plant afloat
• Aerenchyma ⇨ specialised parenchyma 
• -many large air spaces
• -helps with buoyancy 
• -low resistance pathway for substances like oxygen