Organisms exchange substances with their environment

• • Surface area: Volume ratio
  • as size increases -> volume increase disproportionately
  • small organisms:
  • larger SA:V -> shorter diffusion distance -> transport across their body is sufficient
  • large organisms: can't rely on body surface for exchange
  • distances too great -> SA:V insufficient
  • active organisms -> demand for nutrients increase disproportionately
  • to meet demand: specialised exchange surface & efficient transport system
  • features of specialised exchange surface:
  • large surface area
  • short diffusion distance
  • steep concentration gradient
• Insect Gas Exchange -> very active

  1. Air enters (diffuses) via spiracles found on insect
  2. cell & tracheoles provide conc. gradient & O2 goes straight into muscle
  3. can pump abdomen to ventilate tracheole system

  • During major activity:
  • anaerobic respiration forms lactate -> lowers water potential in cells -> fluid at tracheole ends moves into cells via osmosis -> more SA in tracheole ends for diffusion
  • Limiting water loss:
  • small SA:V -> minimises area over which water is lost
  • waterproof coverings -> outer skeleton with waterproof cuticle
  • spiracles can close -> only at rest when less O2 is needed
• Fish gas exchange

  • Gill structure:
  • 2 rows of filaments with lamellae (folds) -> increased SA
  • extensive blood capillary network -> steep conc. gradient
  • distance between water & RBCs is 5 ɥm -> short diff. distance
  • Countercurrent flow = when blood flow is in the opposite direction to water flow
  • maintains a conc. gradient along whole length of gill lamellae
  • ensures O2 uptake can happen at all distances
• Plant gas exchange

  • gases diffuse in/out via stomata controlled by guard cells
  • air spaces in mesophyll increase SA for diffusion -> easy contact between all cells & gases
  • Limiting water loss
  • can't have small SA:V -> needed for photosynthesis
  • waterproof coverings & guard cells can limit water loss in terrestrial plants
  • xerophytes = plants adapted to live in dry areas/areas with limited water
• xerophytic features:

  • leaves:
  • thick cuticle
  • rolling up leaves -> increases humidity
  • stomata in pits/grooves -> increases humidity
  • hairs -> increases humidity
  • reduced SA:V -> increases humidity
  • roots:
  • extensive root network -> takes advantage of superficial rainfall/deep water reserves
  • thin cortex -> short diffusion distance
• Lung structure

  A) nasal cavity

  B) pharynx

  C) alveoli

  D) right lung

  E) diaphragm

  F) nose

  G) larynx

  H) trachae

  I) bronchi

  J) bronchioles

  K) left lung

  L) pleural membrane

  M) pulmonary arteries

  N) ribcage

  
• Lung structure

  • larger organisms have larger volume of living cells -> higher metabolic rate -> higher respiratory rate
  • trachea/bronchi:
  • rings of cartilage keeping trachea open during pressure changes
  • cartilage is C-shaped to allow food down
  • lined with ciliated epithelial cells & goblet cells which produce mucus
  • bronchioles:
  • branches get increasingly smaller & end in alveoli
  • contain smooth muscle & elastic fibres -> allows diameter to be altered depending on ventilation needs
• Gas exchange surface in lungs

  • large number of alveoli -> larger SA
  • covered in network of capillaries -> rich blood supply -> steep conc. gradient
  • one cell thick -> short diffusion distance
  • elastic fibres -> expand & recoil during ventilation
• Mechanism of breathing pt 1

  A) Active

  B) Passive

  C) external intercostal muscles contract

  D) internal intercostal muscles relax

  E) ribcage moves up & out

  F) diaphragm contracts - moves down & flattens

  G) volume of thorax increases

  H) air pressure decreases in lungs

  I) air moves in down pressure gradient

  J) external intercostal muscles relax

  K) forced exhale - internal intercostal muscles contract

  L) ribcage moves down & in

  M) diaphragm relaxes - moves up & domes

  N) volume of thorax decreases

  O) air pressure increases in lungs

  P) air moves out down pressure gradient

  
• Mechanism of breathing pt 2

  • gases move for high to low pressure down pressure gradient
  • intercostal muscles - antagonistic pair
  • external intercostal muscles - contract for inspiration
  • internal intercostal muscles - contract for FORCED expiration
  • elastic recoil from alveoli/diaphragm enough for normal expiration
  • pulmonary ventilation (dm3/min) = tidal volume (dm3) x ventilation rate (min)
  • pulmonary ventilation = total volume of air moved into the lungs during 1 minute
  • ventilation rate = no. of breaths take per minute (12-20 in healthy adult)
  • tidal volume = total volume of air moving in 1 breath
• Lung disease

  pulmonary fibrosis = build up of scar tissue in lungs

  • walls lose elasticity -> lowers tidal vol -> lowers conc. gradient
  • scarring increases diffusion distance

  asthma = inflammation of airways & bronchioles constrict due to allergic reaction

  • bronchoconstriction reduces ventilation -> deprives body of O2
  • excess mucus production -> lumen diameter decreases -> airflow reduced -> deprives body of O2

  emphysema = alveoli breakdown causing lungs to be baggy with bigger holes

  • alveoli fuse together -> larger alveoli -> small SA:V
  • lung tissue dilates & thickens -> increases diff. distance
• Digestion = breaking down of large insoluble molecules into small soluble molecules that can be assimilated into cells


  alimentary canal = entire digestive system

  ileum is main site of absorption of nutrients

  A) mouth

  B) oesophagus

  C) liver

  D) stomach

  E) gallbladder

  F) pancreas

  G) small intestine

  H) duodenum, jejunum, ileum

  I) large intestine

  J) rectum

  K) anus

  L) gallbladder, liver & pancreas are accessory organs

  
• Mechanical digestion

  teeth, stomach & small intestine muscle contraction mechanically digests

  • increases SA of food particles for hydrolysis
• Chemical digestion: carbohydrates

  • amylase produced in saliva & pancreas hydrolyses glycosidic bonds
  • salivary amylase denature in stomach acid
  • pancreatic juices release pancreatic amylase + with alkaline salts maintains pH in small intestine
  • maltase, sucrase & lactase found on ileum lining (membrane-bound disaccharidases)
• Chemical digestion: lipids

  • lipase produced by pancreas hydrolyses ester bonds in triglycerides to form monoglycerides & fatty acids
  • Bile salts made in liver & stored in gallbladder
  • neutralise stomach acid for better enzyme activity
  • emulsify fats by splitting large globules into micelles which increases SA for faster hydrolysis
  • micelles = monoglycerides & fatty acids in association with bile salts
• Chemical digestion: proteins

  peptidases hydrolyse peptide bonds

  • endpeptidases = hydrolyse peptide bonds in centre of amino acid chain e.g. trypsin
  • exopeptidases = hydrolyse peptide bonds between terminal amino acids
  • dipeptidases = hydrolyse dipeptides into individual amino acids
• Ileum exchange surface + absorption of triglycerides

  • One cell thick, rich blood supply & have microvilli

  Absorption of triglycerides

  1. Micelles make fatty acids soluble in water & allow them to diffuse into epithelial cells via faciliated diffusion
  2. in golgi apparatus - triglycerides reformed & combined with proteins & cholestrol to form vesicles called chlyomicrons
  3. chylomicrons moved into lacteals by exocytosis
  4. chylomicrons carried through lymphatic system & enters bloodstream at vena cava
  5. triglycerides hydrolysed by enzymes in endothelium of capillaries & from there diffuse into cells
• haemoglobin structure

  • haemoglobin = protein in red blood cells which transport oxygen
  • globular protein - hydrophilic side out & hydrophobic side in
  • 2 types of polypeptide - 2 of each (4 chains)
  • haem group = oxygen binding site
  • 4 per Hb & each bind to 1 O2 molecule
  • contain Fe2+ ions

  A) haem group

  B) beta polypeptide

  C) alpha polypeptide

  
• Role & mechanism of haemoglobin

  • readily associates (loads) with O2 at gas exchange surface
  • readily disassociates (unloads) from O2 at tissues requiring it for respiration
  • partial pressure of O2 = measure of oxygen concentration
  • affinity (liking) of haemoglobin for oxygen depends on partial pressure of O2
  • Hb unloads O2 at low pO2
  • presence of other sustances can cause slight change in Hb - changes affinity of Hb for O2 (more loosely binded to O2)
  • Hb loads O2 at high pO2
  • saturation of haemoglobin = no. of haem groups bound to O2
• Oxygen dissociation curve = a graph showing the amount of oxygen combining with haemoglobin at different partial pressures

  A) saturation of Hb

  B) partial pressure of O2

  C) difficult for 1st Hb - tightly packed molecule

  D) binding of 1st Hb causes conformational change

  E) conformational change - easier for 2nd & 3rd Hb to bind

  F) 1st bind induces further binding-positive cooperativity

  G) 4th binding- difficult - less likely to find empty site

  
• Factors that affect the oxygen dissociation curve pt 1

  further left -> higher affinity of Hb for O2

  further right -> lower affinity of Hb for O2

  1. The Bohr Shift

  • partial pressure of CO2 increases unloading of O2 from Hb
  • lowers affinity of Hb for O2 by lowering pH causing Hb to change shape
  • Hb moves to active tissue -> more CO2 -> more acidic -> increased unloading

  A) without CO2

  B) with CO2

  
• Factors that affect the oxygen dissociation curve pt 2

  2. Types of haemoglobin

  fetal haemoglobin

  • has higher affinity for O2 than adult Hb -> lower pO2 in mother's blood than in environment
  • different environments cause Hb affinity to vary
  • High affinity Hb for environments with low pO2 & low affinity Hb for environments with high metabolic rate
• Factors that affect the oxygen dissociation curve pt 3

  2. Types of haemoglobin - myoglobin

  • very high affinity for O2
  • only unloads at very low pO2 -> acts as an oxygen reserve

  A) adult Hb

  B) fetal Hb

  C) myoglobin

  
• Double circulation/Double-pump system

  • double circulation/double-pump system = when blood passes through the heart twice in every circulation of the body
  • 2 circuits:
  • pulmonary circuit - heart to lungs
  • systematic circuit - heart to body
  • advantages of double circulation
  • oxgyenated & deoxygenated blood don't mix
  • allows different blood pressures in the systematic & pulmonary circuits
  • allows lung structure to be protected whilst ensuring efficient transport of nutrients to all part of body
• The Circulatory System

  A) pulmonary vein

  B) aorta

  C) hepatic artery

  D) mesenteric artery

  E) renal artery

  F) renal vein

  G) hepatic portal vein

  H) hepatic vein

  I) vena cava

  J) pulmonary artery

  
• Structure of the heart

  A) vena cava

  B) right atrium

  C) right atrioventricular valve

  D) semi-lunar valve

  E) pulmonary artery

  F) pulmonary vein

  G) left atrium

  H) left atrioventricular valve

  I) left ventricle

  J) semi-lunar valve

  K) aorta

  L) septum

  
• structure of the heart

  • walls of heart made from myocardiam
  • myogenic -> able to generate it's own electrical activity
  • muscle never fatigues but very sensitive to lack of O2
  • valves prevent backflow -> controlled by relative pressure in chambers
  • atria - thin-walled, elastic & structures fill with blood
  • ventricles have much thicker muscle walls -> contract more to pump blood further
  • left ventricle is thicker than right ventricle -> has to pump to whole body whereas right only has to pump to lungs
  • coronary arteries branch off aorta to supply myocardium with O2
• cardiac cycle = sequence of events in 1 heartbeat

  • each around 0.8s & consists of contraction (systole) & relaxation (diastole)
  • muscle contraction reduces volume of chamber -> increases pressure
  • blood flows from high to low pressure
  • valves open if there's a high pressure behind them
  • valves close if there's a low pressure behind them

  A) atrial systole

  B) ventricular systole

  C) ventricular diastole

  
• cardiac cycle

  1. atrial systole
  2. most blood moves into ventricles by passive flow
  3. both atria contract to push out last 10% of blood
  4. atrioventricular valves open
  5. pressure behind valves in atria is more than pressure in front of them in ventricles
  6. ventricular systole
  7. atria relax (atrial diastole) & ventricles contract
  8. pressure in ventricles increase
  9. atrioventricular valves close & semi-lunar valves open -> blood flows out of arteries ('lub' sound)
  10. ventricular diastole
  11. ventricles relax & high pressure in arteries closes semi-lunar valves ('dub')
  12. blood flows into atria
• Cardiac cycle graph

  A) aorta

  B) left ventricle

  C) left atrium

  D) atria contract

  E) atria relax

  F) ventricles contract

  G) ventricles relax

  H) AV valves close

  I) semi-lunar valves open

  J) semi-lunar valves closing

  K) AV valves open

  L) blood pressure in arteries increased

  
• cardiac output = amount of blood pumped around the body

  • depends on stroke volume & heart rate
  • stroke volume = volume of blood pumped by ventricle in each heart beat
  • heart rate = no. of heart beats per minute

  cardiac output = stroke volume x heart rate
• Nervous control of the cardiac cycle

  1. Impulse starts in Sino Atrial (SA) node located in right atrium
  2. also called pacemaker
  3. Impulse travels through atria walls causing both atria to contract
  4. cardiac impulse reaches atrioventricular (AV) node
  5. helps delay impulse to allow atria to finish contracting
  6. impulse spreads down the bundle of His
  7. located in septum & carries signal to apex
  8. Bundle of His is insulated
  9. Impulse spread around ventricle walls through purkinje fibres
  10. causes both ventricles to contract
  11. purkinje fibres aren't insulated
• Nervous Control of Cardiac Cycle

  A) Sino Atrial (Sa) node

  B) atrioventricular (AV) node

  C) bundle of His

  D) purkinje fibres

  
• Artery structure

  • thick walls - transports at high pressure
  • consists of collagen & elastic tissue
  • collagen gives strength & ability to maintain high pressure
  • elastic allows walls to stretch as a pulse moves through
  • artery recoils -> pushes blood & maintains pressure
• Arterioles structure

  • lower blood pressure -> pressure distributed
  • thinner walls, less elastic tissue but more smooth muscle
  • smooth muscle under unconscious control
  • allows arterioles to constrict & regulate blood flow to different areas of the body
• vein structure

  • thin walls - less muscle, less elastic & have valves
  • don't need to regulate how much blood goes to each tissue

  capillary structure - gas exchange surface

  • very thin -> short diff. distance
  • many of them & highly branched -> larger surface area
  • narrow diameter -> permeates tissues
  • no cell is too far away
  • narrow lumen -> RBC squished in
  • O2 even closer to cells
• Blood vessels

  A) tunica adventitia

  B) tunica media

  C) tunica intima

  D) tunica intima

  E) lumen

  F) lumen

  G) artery

  H) vein

  I) single layer of endothelial cells

  J) capillary

  
• blood pressure

  • high pressure -> ventricles contract
  • pressure fluctuates -> ventricles relaxing & contracting & elastic fibres stretch & recoil in arteries
  • pressure decreases -> total cross-sectional area increases -> pressure split up

  closed circulatory system = blood confined to vessels

  • allows pressure to be maintained

  
• cardiovascular disease = disease associated with heart & blood vessels


  • atheroma formation
  • damage to endothelium causes WBCs & lipids to clump under lining & form fatty streaks
  • WBCs, lipids & connective tissue build up & harden forming fibrous plaque -> atheroma
  • block artery -> restrict blood flow -> increase pressure
  • risk factors for cardiovascular disease
  • high blood pressure -> increased risk of damage to artery
  • high cholestrol & poor diet (high in salt) -> cholestrol main constitutes of atheromas
  • cigarette smoking -> reduced O2 & decreases antioxidants in blood (protect cells from damage)
• cardiovascular disease pt 2

  • aneurysm = swelling of artery caused by the inner layers being pushed through the outer elastic layer to form an aneurysm
  • thrombosis = formation of a blood clot when atheroma plaque ruptures leaving a rough surface where platelets & fibrin accumulates
  • myocardial infarction (heart attack) = when coronary artery is blocked, cutting off blood supply depriving the muscle of O2 causing damage & death of heart muscle