Gas exchange and SA:V Flashcards
Why are gas exchange systems necessary?
SA:V ratio too low, simple diffusion across outer surface only meets needs for inactive organism and also substances take too long to reach middle.
Fick’s law
(SA * difference in concentration) / length of diffusion pathway
General features of gas exchange surfaces
High SA:V
Thin for short diffusion distance.
Selectively permeable.
Movement of environment to maintain diffusion gradient or transport system.
Gas exchange in single organism
Large SA:V ratio.
Oxygen enters and CO2 leaves via diffusion.
Structure of gas exchange system in insects
Air enters through spiracles.
Tracheae supported by rings of chitin.
Divide into tracheoles that supply short diffusion pathways to any cell.
How is a diffusion gradient used in the tracheoles
Respiring cells use oxygen so concentration falls in ends of tracheoles -> oxygen from atmosphere diffuses along tracheae and tracheoles to cells.
Respiring cells produce CO2 so conc. increases in ends of tracheoles -> CO2 diffuses along tracheoles and tracheae to atmosphere.
How is mass transport used in gas exchange in insects
Contraction of muscles means tracheae can be squeezed so mass movements of air in and out speeds up exchange of respiratory gases.
How does the fluid in the end of tracheoles increase gas exchange
Lactate produced during major activity in cells, which lowers water potential of cells. Water moves in from tracheoles into cells by osmosis. Decreased volume of water means air is drawn in. Final diffusion pathway is in gas phase so diffusion is more rapid. Increases rate of gas exchange but more water evaporation.
How do insects reduce water loss
Spiracles at opening of tracheae can close to reduce water loss.
Waterproof cuticle that covers exoskeleton.
Small SA:V.
Why are insects small
Tracheal system relies on diffusion. Short diffusion pathway required so insects need to be small.
Adaptations of leaves for gas exchange
Many stomata so no cell is far from stoma (short diffusion pathway).
Many air spaces in mesophyll so gas can come in contact with cells.
Large surface area of mesophyll for rapid diffusion.
Gas exchange in a leaf in the day vs the night
In day when photosynthesis is taking place, CO2 and oxygen out.
In night when no photosynthesis, O2 in, CO2 out.
Structure of stomata and opening and closing function
Two guard cells surround stoma. Turgid guard cells open stoma and flaccid closes.
How to limit water loss in insects
Small SA:V ratio - minimise surface water is lost on.
Waterproof cuticle on exoskeleton.
Spiracles can open and close to limit water loss when insect is resting.
How to limit water loss in plants
Thick waxy cuticle.
Leaves roll up so high water potential area outside lower epidermis (stomata) = less water potential gradient.
Hairy leaves to reduce water potential gradient.
Stomata in pits to reduce water potential gradient.
Reduced SA:V ratio on leaves (pines).
Why do mammals have need for gas exchange system
Large organisms, high volume of living cells.
High body temp and high metabolic/respiratory rates.
Tracheae structure
Flexible airway with rings of cartilage to prevent low air pressure causing airway to collapse.
Walls made of muscle, lined with ciliated epithelium and goblet cells.
Bronchi structure
Smaller divisions of tracheae, produce mucus and use cilia to waft mucus up. Supported by cartilage.
Bronchioles structure
Walls made of muscle lined with epithelial cells. Muscles can contract to control movement of air in and out of alveoli.
Alveoli structure
Tiny air sacks at end of bronchioles connected by collagen and elastic fibres so they can stretch when filled with air. Spring back to expel CO2.
Site of gas exchange.
Alveoli epithelium flat against capillary epithelium.
Inspiration
External intercostal muscles contract and internal relax.
Diaphragm contracts, flattening.
Volume of thorax increases, reducing pressure in lungs.
Air flows from atmosphere to lungs due to lower pressure.
Expiration
Internal intercostal muscles contract and external relax.
Diaphragm relaxes, arching.
Volume of thorax decreases, increasing pressure in lungs.
Air flows from lungs to atmosphere as pressure is higher in lungs.
How is diffusion of gases maximised in alveoli
Red blood cells slowed as passing through capillaries to allow more time for diffusion.
RBCs flattened against capillary walls to reduce diffusion distance.
Walls of alveoli and capillaries are thin to reduce diffusion distance.
Alveoli and capillaries have large total SA.
Breathing movements ventilate lungs and heart circulates blood so steep conc gradient maintained.
Structure of gills
Gill filaments that have gill lamellae to increase SA of gills.
Countercurrent flow principle
Flow of water over gill lamellae is opposite direction of flow of blood.
Oxygenated blood meets water with max O2 conc first so diffusion happens. Water flow continues over to deoxygenated blood where water has lower O2 conc. Blood has even lower O2 conc so diffusion happens still.
