Gas exchange and SA:V Flashcards
What are examples of things that need to be exchanged?
- respiratory gases eg. oxygen and carbon dioxide
- nutrients eg. glucose, amino acids, fatty acids and glycerol
- excretory products eg. urea, salt
- heat
What are the 2 types of exchange?
active eg. active transport and co-transport
passive eg. diffusion and osmosis
What is fick’s law?
surface area x difference in concentration divided by length of diffusion path
Describe the relationship between size and surface area to volume ratio of organisms
the larger the size of an organism, the smaller the SA:V ratio
How is gas exchange achieved in single-celled organisms eg. amoeba?
- 1 cell therefore very large SA:V ratio
- folds in surface called pseudopods - increase surface area
- thin cell membrane - short diffusion distance
- partially permeable which allows movement of O2 and CO2 by simple diffusion
- engulfs food using pseudopods for nutrients
What are xerophytic plants?
Plants adapted to dry conditions with little water
What are the adaptations of xerophytic plants?
Thick - larger diffusion distance so little water loss
Rolled up leaves - traps air within the roll which becomes saturated with water vapour, so has a very high water potential - no water potential gradient therefore no water loss
Hairy leaves - traps still, moist air on the leaf surface which reduces water potential gradient so less water loss through evaporation
Stomata in grooves - trap still moist air which reduces water potential gradient
Small SA:V ratio - reduced water loss
Root system - deep to penetrate water table and shallow to absorb rainfall
How have insects evolved for gas exchange?
- insects have evolved an internal network of tubes called trachae, which are supported by strengthened rings to prevent them from collapsing
- trachae divide into smaller tubes called tracheoles which extend throughout the body tissues
- oxygen is brought directly into respiring tissues as there is a short diffusion distance from tracheoles to body cells
How do gases move into an insect along a diffusion gradient?
- when cells respire, oxygen is used up so concentration of oxygen at the ends of tracheoles falls
- this creates a diffusion gradient that causes oxygen to diffuse from the atmosphere along the trachae and tracheoles to the cells
- CO2 is produced by cells during respiration
- this creates a diffusion gradient in the opposite direction which causes CO2 to move along tracheoles and trachae from cells to the atmosphere
How do gases move into an insect through mass transport?
rhythmic contraction of abdominal muscles can squeeze the trachea, ‘pumping’ air in and out
How do gases move into an insect due to the ends of tracheoles being filled with water?
- needed because diffusion through tracheal fluid is too slow to provide enough oxygen during periods of rapid respiration
- this is because diffusion occurs much more quickly in air than fluid, so the tracheal fluid is moved into the muscle cells
- fluid is replaced by air in the tracheoles
- this allows for much more rapid exchange of oxygen and carbon dioxide
- lactate produced in muscle cells during anaerobic respiration lowers water potential so tracheal fluid moves into cells by osmosis
How do gases enter and leave the trachae?
Through tiny spores called spiracles on the body surface which are opened and closed by valves. Insects close spiracles to prevent water loss.
Spiracles open to air filled pipes called trachae which branch into trachaeoles and capillaries
How do insects maintain a steep concentration gradient?
Muscle cells rapidly use up oxygen during respiration leading to a low oxygen concentration in muscles. There is always a high concentration of oxygen in the air
How do insects have a large surface area?
- small - large SA:V ratio
- large SA through legs/wings
- lots of trachae and trachaeoles
How do insects have a short diffusion pathway?
There is a direct link between tracheoles and muscle cells
What is the structure of fish gills?
- made up of gill filaments
- gill lamallae which increases the surface area of the gills
How does water move across the gills?
- water enters through the mouth - volume increases and buccal cavity lowers
- this lowers the pressure which allows water to flow in from high to low pressure
- water flows over the gill into the opercular cavity
- mouth closes and buccal cavity raises which increases pressure - operculum opens and water flows out
How do fish gills have a large surface area?
presence of gill filaments and lamellae
How do fish gills have a steep concentration gradient?
- countercurrent flow
- good blood supply - oxygen absorbed by diffusion from water into blood vessels
How do fish gills have a short diffusion path between water and gills?
lamellae and filaments are very thin - 1 cell thick
What is the countercurrent exchange principle?
- blood and water flow over gill lamallae in opposite directions
- blood always passing water with a higher oxygen concentration
- maintains a concentration/diffusion gradient of oxygen
- oxygen uptake is maintained across the entire length of the lamellae
How are leaves adapted for efficient gas exchange?
- many small pores called stomata which reduce diffusion pathway
- large surface area of mesophyll cells for rapid diffusion
How do insects reduce water loss?
- small SA:V ratio - minimises area over which water is lost
- waterproof covering
- spiracles which close to reduce water loss
What is the structure of the respiratory system?
- nasal cavity
- trachea
- bronchus
- bronchiole
- alveoli
What is the location and function of cartilage in the gas exchange system?
- lines trachea and bronchioles
- keeps vessels open to maintain ventilation
What is the location and function of goblet cells in the gas exchange system?
- throughout lungs/bronchioles/alveoli
- secrete mucus which is useful for moisture and diffusion of gases. Also excretes pathogens
What is the location and function of cilia in the gas exchange system?
- trachea, bronchus, bronchioles
- ‘woft’ mucus and pathogens along vessels to be excreted
What is the location and function of muscle tissue in the gas exchange system?
- intercostal muscles, diaphragm and trachea
- contract and relax to control movement - allows for changes in volume
What is the location and function of elastic tissue in the gas exchange system?
- lung tissue in walls of alveoli
- expansion and recoil - allows for increase in size of alveoli when they fill with air
How does air move into and out of the lungs?
when pressure of the atmosphere is greater than air pressure inside the lungs, air is forced into the lungs (inhalation)
when air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs (exhalation)
How are pressure changes of the lungs brought about?
- diaphragm - muscle separating thorax from the abdomen
- internal intercostal muscles, whose contraction leads to expiration
- external intercostal muscles, whose contraction leads to inspiration
What happens during inspiration?
- external intercostal muscles contract, while internal intercostal muscles relax
- ribs are pulled upwards and outwards, increasing the volume of the thorax
- diaphragm muscles contract, causing it to flatten which increases the volume of the thorax
- increased volume of thorax results in reduction of pressure in the lungs
- atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs down a pressure gradient
What happens during expiration?
- internal intercostal muscles contract, while external intercostal muscles relax
- ribs move downwards and inwards, decreasing the volume of the thorax
- diaphragm muscles relax, and so it is pushed up by the contents of the abdomen that were compressed during inspiration, and the volume of the thorax is further decreased
- decreased volume of the thorax increases the pressure in the lungs
- pulmonary pressure is now greater than that of the atmosphere, so air is forced out of the lungs
What is the equation for pulmonary ventilation?
pulmonary ventilation (total volume of air moved into the lungs) =
tidal volume (volume of air taken in during one breath) x ventilation rate (number of breaths per minute)
What are the key features of the human gas exchange surfaces?
- short diffusion distance - capillaries and alveoli made of 1 cell thick epithelial cells
- large SA:V ratio - lungs are big and filled with alveoli - internal surface area
- movement of internal medium - constant movement of blood so constantly oxygenated
- movement of external medium - movement of air into the lungs to allow diffusion of oxygen to capillaries for aerobic respiration
Why is diffusion of gases between the alveoli and blood rapid?
- red blood cells are slowed as they pass through capillaries, allowing more time for diffusion
- alveoli and capillary walls are thin - short diffusion distance
- alveoli and capillaries have a large surface area
- blood flow through capillaries maintains a concentration gradient
What is the structure of an alveolus?
- single cell wall made of epithelial cells
- thin layer of moisture - allows gases to dissolve so they can diffuse quickly
- single cell wall of capillary made of epithelial cells
- low O2 concentration diffuses from blood into and out of the alveolus
- high O2 concentration diffuses from alveolus into the capillaries in blood
What is a disadvantage of an alveolus for gas exchange?
- perfect breeding ground for bacteria because:
- constantly open due to cartilage
- warm - internal + good blood supply
- lots of O2 for growth
- layer of moisture - H2O
What is pulmonary tuberculosis/fibrosis and what effect does it have on gas exchange?
- breathed in bacteria destroy tissue of the lungs. This results in cavities, where the lungs repair themselves leading to scar tissue
- reduces elastic tissue in alveoli, which reduces ventilation
What is asthma and what effect does it have on gas exchange?
- lung condition caused by genetics
- muscles tighten - smaller surface area so less O2 diffusion
- walls of muscle inflame and thicken - larger diffusion distance so slower rate
Describe the pathway taken by an oxygen molecule from an alveolus to the blood
- Across alveolar epithelium
- then endothelium / epithelium of capillary
