Gas exchange Flashcards
Why exchange materials?
Cells need to take in oxygen (for aerobic respiration) and nutrients
They also need to excrete waste products like carbon dioxide and urea
Most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too.
Relationship between SA:V and metabolic rate
Rate of heat loss increases as SA:V increases and more heat lost per unit body mass in smaller animals with a high SA:V
So they need a higher metabolic rate/faster respiration to generate enough heat to maintain a constant body temperature.
Adaptations to facilitate exchange in larger, multicellular organisms
Larger organisms have specialised exchange organs (eg lungs) because they have a smaller SA:V and a longer diffusion pathway, as well as a high demand for oxygen and the removal of carbon dioxide.
They also need an efficient system to carry substances to and from their individual cells - this is mass transport eg circulatory system
Shape effect on heat exchange
Animals with a compact shape have a small surface area relative to their volume - minimising heat loss from their surface
Animals with a less compact shape have a larger surface area relative to their volume - this increases heat loss from their surface
Whether an animal is compact or not depends on the temperature of its environment
Adaptations of gas exchange surfaces
Thin surface with a large surface area
Short diffusion pathway across the gas exchange surface for rapid diffusion
Organism also maintains a steep concentration gradient of gases across the exchange surface
Adaptations of gas exchange surfaces shown by gas exchange in the tracheal system of an insect
1) Air moves into the tracheae through spiracles (pores) on the surface of the insect
2) Gas exchange occurs at the tracheoles directly to/from cells. Oxygen diffuses down the concentration gradient to respiring cell and carbon dioxide diffuses down concentration gradient from respiring cells towards the spiracles to be released
There are lots of thin, branching tracheoles which have a short diffusion pathway and a high SA:V for rapid diffusion
Insects use rhythmic abdominal movements to increase the efficiency of gas exchange by increasing the amount of oxygen entering, this maintains a greater concentration gradient for diffusion.
Adaptations of gas exchange surfaces shown by gas exchange across the gills of fish
Counter current blood flow where blood flows through lamellae and water flows over lamellae in opposite directions. There is always a higher concentration oxygen of water than in the blood, so a concentration gradient of oxygen between the water and blood is maintained, maximising diffusion of oxygen.
Each gill is made of lots of gill filaments (thin plates) which are covered in many lamellae. These provide an increased surface area.
Vast network of capillaries on lamellae that remove oxygen to maintain a concentration gradient.
Thin/flattened epithelium that provides a shorter diffusion pathway between water and the blood.
Adaptations of gas exchange surfaces shown by gas exchange by the leaves of dicotyledonous plants
Gas exchange in the leaves occurs as carbon dioxide/oxygen diffuse through the stomata, which are opened by guard cells. Carbon dioxide/oxygen diffuse into mesophyll layer into air spaces and carbon dioxide/oxygen then diffuse down a concentration gradient.
There are lots of stomata (small pores) close together which provide a large surface area for gas exchange.
Interconnecting air spaces in mesophyll layers so that gases can come into contact with mesophyll cells.
Mesophyll cells have a large surface area for the rapid diffusion of gases.
Thin surfaces for short diffusion pathways
Structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by xerophytic plants
Thick waxy cuticle that increases diffusion distance, reduces evaporation
Stomata are in pits/grooves and these ‘trap’ water vapour as the water potential gradient is decreased, less evaporation.
Curled leaves and these ‘trap’ water vapour as the water potential gradient is decreased, less evaporation. These also protect stomata from the wind.
Spindles/needles reduce SA:V
A layer of ‘hairs’ on the epidermis to ‘trap’ water vapour as the water potential gradient is decreased, less evaporation.
Structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects
Thick waxy cuticle that increases diffusion distance, reduces evaporation
The spiracles can be opened and closed using muscles to allow oxygen in and to reduce water loss.
Structure of the human gas exchange system
Trachea splits into two bronchi
Each bronchus branches into smaller tubes called bronchioles
Bronchioles end in air sacs called alveoli
Ventilation and exchange of gases in lungs (oxygen)
Oxygen diffuses from the alveoli down its concentration gradient across the alveolar epithelium.
Then across the capillary endothelium
Into the blood (in haemoglobin)
Ventilation and exchange of gases in lungs (carbon dioxide)
Carbon dioxide diffuses from the capillary down its concentration gradient across the capillary endothelium.
Then across the alveolar epithelium
Into the alveoli.
Why is ventilation needed?
Maintains an oxygen concentration gradient
Brings in air containing higher concentration of oxygen
Removes air with a lower concentration of oxygen.
Features of the alveolar epithelium as an effective surface over which gas exchange takes place
Squamous epithelium; they are thin/one cell thick for a short diffusion pathway, fast diffusion
Large surface area to volume ratio for fast diffusion
Permeable
Good blood supply from network of capillaries and maintains concentration gradient.
Elastic tissue allows it to recoil after expansion
Surfactant released lowers surface tension
