B3.1 gas exchange

gas exchange function in plants and mammal

1. obtain gases for metabolism

2. release waste products

1. respiration

2. photosynthesis

gas exchange occurs

diffusion - gases travel from high to low concentration to reach diffusion

structure to facilitate gas exchange (4)

1. large SA:V (branches+foldings)

2. permeability of O2 and CO2

3. thin tissue layer minimise diffusion distance

4. moist layer for gases to dissolve 

how is concentration gradient maintained (3) 

1. Dense capillary network around gas exchange surfaces

2. Continuous blood flow

3. Ventilation 

• With air for lungs

• With water for gills

Lungs

trachea

bronchus 

bronchiole 

alveoli

lungs 

ribs 

intercostal muscle 

diaphragm 

definition for ventilation + gas exchange + cellular respiration

1. Ventilation : exchange of air between atmosphere and lungs - breathing

2. Gas exchange : exchange of O2 and CO2 between alveoli and bloodstream - passive diffusion 

3. Cellular Respiration : release of ATP from organic molecules 

exchange on ventilation rate

increase rate exercise > increase cellular respiration > increases uptake of oxygen > increase ATP - breath in faster

By product of cellular respiration increases: Co2 > blood gets acidified > proteins like RBC denatures > dont carry oxygen > dies.

To avoid Co2 accumulation - breath out faster > ventilation rate faster 

respiratory system (5)

1. air travels from nose&mouth - pharynx - trachea

2. air divides into two bronchi

3. right : 2 lobes, left : 3 lobes

4. bronchi - many bronchiole ( increases SA)

5. bronchiole - airsacs: alveoli ( gas exchange w bloodstream occurs)

structure of alveolus

1. thin epithelial layer ( one cell thick ) > minimuze diffusion distances

2. surrounded by rich capillaries layer > increase capacity for ge with blood 

3. spherical in shape > maximize SA for ge 

4. internal surface - covered with surfactant > dissolved gas better able to diffuse in bloodstream + reduce surface tention 

where is pneumocytes

(alveolar cells) - line the alveoli , comprise the majority of inner surface of lungs

what is alveoli made out of 

• type 1 + type 2 pneumocytes 

type 2 pneumocytes 

• secrete alveolar fluid → contain surfactant

how surfactant works 

Alveoli is moist, water attracts to together due to cohesion , risk of alvelio collasping

Type 2 pneunocytes secret surfactant, reduce surface tension

adaptations for lungs(4)

1. surfactant - decrease pressure

2. short diameter of bronchiole - slow air flow increases efficiency 

3. many alveoli attached at the end - increase SA for gas exchange 

4. extensive capillaries around alveoli - short diffusion distance 

ventilation in antagonistic muscle 

Inhalation  

1. external intercostal muscle contracts → ribcage move out and up

2. diaphagram contracts and flattens

3. volume increase in thorax, decrease pressure

4. air flows into the lungs

exhalation

1. internal intercostal muscle contracts → ribcage moves in and down

2. Abdominals contract. pushes diaphragm up into dome shape

3. volume decrease in thorax, Increase pressure

4. air flows out the lung

measure lung volume

spirometry

spirometry trace

gas exchange in leaf

• stomata 

• guard cells control opening and closing of stomata 

adaptations of leaf 

waxy cuticle - hydrophobic - prevents water loss

palisade layer/mesophyll - photosynthesis, lots of chloroplast

spongy mesophyll - lots of air spaces for gas exchange

xylem&pholem

stoma + guard cells - gas moves in and out

transpiration

• movement of water from roots to leaves

Water vapour diffuse out the leaf via stoma, creating a negative pressure gradient → water drawn out of xylem through cell wall by capillary action, generate tension → draw water up xylem vessel from roots to leaf

Transpiration facilitates:

• Temperature regulation

• Absorption of water and minerals from soil

factors affecting transpiraton

• increase transpiration

  • light - more light, more transpiration

  • temperature- more heat, more evaporation, more transpiration

decrease transpiration

• humidity: more humid, higher concentration of water vapour outside the plant ( low concentration gradient) slower transpiration

hemoglobin (location, function , structure)

Location: RBC

Function : transport O2 to respiring tissue, transport byproduct Co2 to lungs

Structure: quaternary, conjugated protein - 4 polypeptide with heme group

hemoglobin and oxygen

• coorporative binding

• structure changes - affinity for oxygen ^

fetal hemoglobin higher affinity than adult hemoglobin, why?

• more efficient delivery of O2 from placenta to fetus 

Co2 binds xx to hemoglobin 

allosterically 

• change the shape - less affinity for O2  

how does Bohr Shift illustrates when there is ^ in Co2

• increase Co2, increase carbonic acid , decrese pH

• hemoglobin change shape, decrease affinity to oxygen

• O2 dissociation curve shifts right, O2 is released more readily to respiring tissues