Exchange Surfaces Flashcards
Why do single-celled organisms not need exchange surfaces?
- Metabolic activity is low - low demand for oxygen for respiration
- Large surface area to volume ratio
Why are exchange surfaces necessary for larger organisms?
- High metabolic activity
- Smaller surface area to volume ratio
- Larger distances between cells where oxygen is needed and the supply of oxygen
How is the surface area to volume ratio calculated?
Ratio = surface area / volume
How does the size of an organism correlate it its SA:V?
The bigger the organism, the smaller its SA:V
Describe and explain the features of efficient exchange surfaces
Large surface area
- Provides more surface for diffusion to take place through
- e.g. root hair cells
Thin
- Short diffusion pathway
- e.g. epithelial cells of alveoli
Good blood supply
- Maintains steep concentration gradient
- e.g. dense capillary network around alveoli
Good ventilation
- Maintains steep concentration gradient
- e.g. fish gills maintain steady flow of water over exchange surfaces
Define gas exchange in mammals
Process whereby oxygen enters the blood capillaries in the alveoli and carbon dioxide
leaves
Outline the structure and function of the nasal cavity
- Good blood supply - warms air to body temperature
- Hairy lining - traps dust and bacteria
- Moist surfaces - increases humidity of oncoming air
Outline the structure and function of the trachea
- Carries clean, warm air from nose to chest
- Supported by C-shaped rings of cartilage - stop trachea from collapsing but
allow food to move down neighbouring oesophagus - Smooth muscle contracts to narrow lumen
- Elastic fibres allow lumen to dilate
- Lined with goblet cells and ciliated epithelium - produce mucus to trap
pathogens and move it to throat
Outline the structure and function of the bronchus
- Lead to left and right lungs
- Supported by smaller C-shaped rings of cartilage
- Smooth muscle contracts to narrow lumen
- Elastic fibres allow lumen to dilate
Outline the structure and function of the bronchioles
- Narrow tubes leading from bronchi to alveoli - Made from smooth muscle and elastic fibres - can contract and relax to
control air flow
Outline the structure and function of the alveoli
- Site of gas exchange
- Elastic fibres allow alveoli to stretch and recoil to return to original shape
Describe what happens in alveoli
- Gas exchange
- Oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air
- Oxygen binds to haemoglobin in red blood cells
- Volume of alveoli increases during inspiration
- Concentration gradients of gases maintained
How are the alveoli adapted for gas exchange?
- Very large surface area
- Large surface area to volume ratio
- Thin walls (single cell thick) - short diffusion distance
- Moist - lined with lung surfactant - allows gases to dissolve and keeps alveoli inflated
- Good blood supply from capillaries - maintains steep concentration gradient
- Good ventilation - breathing maintains steep diffusion gradient
Define ventilation
Inhalation and exhalation of air between the lungs and the outside
What is the role of ventilation?
- Maintains concentration gradients of oxygen and carbon dioxide
- Concentration of oxygen remains higher in alveoli than in blood
- Concentration of carbon dioxide remains higher in blood than alveoli
Outline the mechanism of ventilation in the lungs during inhalation
During inhalation:
- External intercostal muscles contract moving rib cage up and out
- Diaphragm contracts and becomes flatter
- Increase in volume in thorax
- Decrease in pressure in thorax
- Air flows into lungs as atmospheric pressure is higher than pressure in thorax
Outline the mechanism of ventilation in the lungs during exhalation
During exhalation:
- Internal intercostal muscles contract so ribs move in and down
- Diaphragm relaxes and becomes domed in shape
- Decrease in volume in thorax
- Increase in pressure in thorax
- Air moves out until pressure in lungs falls
- Abdominal muscles can be used to make a stronger exhalation
Outline the mechanism of ventilation in the lungs during exhalation
During exhalation:
- Internal intercostal muscles contract so ribs move in and down
- Diaphragm relaxes and becomes domed in shape
- Decrease in volume in thorax
- Increase in pressure in thorax
- Air moves out until pressure in lungs falls
- Abdominal muscles can be used to make a stronger exhalation
Define antagonistic muscles
- Muscles that oppose the action of each other
- e.g. internal and external intercostal muscles
Define breathing rate
Number of inhalations or exhalations per minute
Define ventilation rate
Total volume of air inhaled per minute
Define tidal volume
Volume of air taken in or out with each inhalation or exhalation
Define vital capacity
Maximum volume of air that can be breathed in
Define inspiratory reserve volume
Maximum volume of air that can be breathed in over and above normal inhalation
Define expiratory reserve volume
Maximum volume of air that can be breathed out over and above normal tidal volume
Define residual volume
Volume of air left in lungs after largest possible exhale
How is total lung capacity calculated?
Vital capacity + residual volume
How is ventilation rate calculated?
Ventilation rate = tidal volume x breathing rate (per minute)
How is ventilation rate monitored?
- Simple observation
- Data logging with a spirometer
How is tidal volume determined?
Spirometer (tube used to measure the volume of exhaled air)
Describe how a spirometer would be used to measure tidal volume
- Subject breathes evenly into spirometer
- Subject wears nose clip so as not to breathe through nose
- Measure height of waves from the spirometer trace
- Measure at least three waves and calculate mean
Explain the change in tidal volume during exercise
- Exercise increases rate of respiration
- Produces more carbon dioxide
- Requires more oxygen
- Increased tidal volume excretes more carbon dioxide
- Increased tidal volume increases gas exchange
- Concentration gradients of gases is maintained
What features of an insect requires them to have a different gas exchange system to mammals?
- Large surface area : volume
- Tough exoskeleton - no gas exchange can take place through it
- Blood pigments do not carry oxygen
What are spiracles?
- Small openings along thorax and abdomen of insects
- Allow air to enter and leave tracheal system
- Water lost through open spiracles
What are tracheae?
- Network of air filled pipes that run into body of insect
- Spiracles at end control opening and closing
- Supported by rings of chitin
What are tracheoles?
Narrower tubes formed from branching of tracheae
Where does most of the gas exchange occur in an insect?
In the tracheoles
What is the role of tracheal fluid?
- Limits penetration of air for diffusion
- Lactic acid causes tracheal fluid to leave tracheoles by osmosis
- Occurs when oxygen demand is high
- More surface area exposed for gas exchange
How does oxygen reach the cells in an insect?
- Tracheoles run past each cell
- Oxygen diffuses from tracheoles into cells
How is gas exchanged controlled in insects?
- Opening and closing of spiracles
- Sphincters open and close to minimise water loss
- When oxygen demand is low, spiracles are closed
- When oxygen demand is high, spiracles are open
Describe how gas exchange takes place in insects
Oxygen used up by cells during respiration
- O2 concentration towards ends of tracheoles falls
- Diffusion gradient established - O2 diffuses from atmosphere through tracheae and
tracheoles into cells
CO2 produced by cells during respiration
- Diffusion gradient established in opposite direction
CO2 diffuses along tracheoles and tracheae to atmosphere
- Diffuses into atmosphere through open spiracles
How do larger insects increase the level of gas exchange?
Mechanical ventilation - air actively pumped into system by muscular contraction of thorax
and abdomen
- Changes pressure in tracheae, drawing air in and forcing it out
Collapsible air sacs in tracheae - act as air reservoirs
- Increase amount of air moved through gas exchange system
- Inflated and deflated by movements of thorax and abdomen
Give the advantage of the tracheal system
Direct delivery of oxygen to the tissues and direct removal of carbon dioxide
Give the disadvantages of the tracheal system
- System limits size of the organism
- Tracheoles can only successfully deliver enough oxygen if diffusion distance is short
and pumping mechanism of abdomen keeps the air flowing - This can only occur over a relatively short distance
Describe the similarities between the gas exchange of an insect and that of a
mammal
- Large surface area
- Moist gas exchange surface
- Thin gas exchange surface
- Concentration gradient maintained by ventilation
Describe the differences between the gas exchange of an insect and that of a mammal
- Oxygen transported to cells via circulatory system in mammals
- Alveoli are gas exchange surface in mammals, in insects it is the junction between
tracheoles and respiring tissues
What are the issues with carrying out gas exchange in water?
- Water is denser and more viscous than air
- Water has much lower oxygen content than air
What are the issues with carrying out gas exchange in water?
- Water is denser and more viscous than air
- Water has much lower oxygen content than air
Describe the respiratory system of a bony fish
- Buccal cavity - mouth of the fish - floor can lower and raise to change volume
- Operculum - bony flap that covers gills
- Gill filaments - occur in stacks (gill plates) - separated by flowing water to provide large
surface area - Ends overlap to slow down water flow - Gill lamellae - organs of gas exchange - rich blood supply and large surface area
How are the gill filaments adapted for gas exchange?
Covered in lamella
- Increase surface area
Tips overlap
- Increases resistance to flow of water
- Slows water down for more effective gas exchange
How are the gill lamellae adapted for gas exchange?
- Rich blood supply to maintain concentration gradient
- Large surface area
- Very thin - short diffusion pathway
Describe how a constant flow of water is maintained by bony fish
- Mouth opens and floor of buccal cavity lowered
- Volume of buccal cavity increases
- Pressure decreases
- Water moves into buccal cavity
- Mouth closes and floor of buccal cavity raised
- Forces water over gills and out of operculum
What is the countercurrent flow system?
- Blood flows through the lamella in one direction
- Water flows over lamellae in the opposite direction
How does the countercurrent flow system mean that gas exchange is more efficient?
- Water and blood flow in opposite directions
- Maintains constant concentration gradient along length of gill
- Water always next to blood with a lower concentration of oxygen
Explain how the structure of the gas exchange system of bony fish maximises the amount of oxygen than can be absorbed from water
Gills have large stacks of gill filaments carrying gill lamellae
- Gill lamellae adapted for successful gaseous exchange
- Large surface area
- Good blood supply
- Thin layers
Constant flow of water maintained over gills
- Maximises diffusion gradient for respiratory gases
Tips of gill filaments overlap
- Increases resistance to flow of water
- Slows water down for more effective gaseous exchange
Countercurrent exchange system maximises the potential exchange of gases
