7 - Exchange surfaces and breathing Flashcards
Why are specialised exchange surfaces not needed in single-celled organisms?
- diffusion alone is enough to supply needs.
- low metabolic activity.
- large surface area : volume ratio
- short diffusion distance (cell surface membrane)
Why do large multicellular organisms require specialised exchange surfaces?
- small surface area : volume ratio
- higher metabolic rate
- distance between supply of oxygen and cells that require oxygen is too great.
How does SA:V ratio affect rate of diffusion?
- the larger the organism
- smaller SA:V ratio
- distance the substances need to travel from outside to reach the cells at centre of body increases.
- impossible to absorb enough oxygen through available surface area to meet needs of the body.
What are the features of an efficient exchange surface.
- increased surface area: provides for area for diffusion to occur (root hair cells)
- thin layers: provides a short diffusion distance so process is fast and efficient (alveoli)
- good blood supply and ventilation: to maintain a steep concentration gradient
features of the nasal cavity
- large surface area
- good blood supply
- which warms air to body temperature.
- moist surfaces: increases humidity of incoming air.
- hairy lining
- mucus is secreted to trap dust, microorganisms.
c shaped and incomplete rings of cartilage in trachea and bronchus
- for structure and support
- prevents airways from collapsing
Why are the rings of cartilage in trachea incomplete?
- too allow easy movement of food through oesophagus behind trachea.
role of ciliated epithelium in trachea and branches?
- have cilia which waft and beat mucus with trapped dust and microorganisms to back of throat.
- goblet cells secrete a sticky substance called mucus which trap dust and microorganisms.
effect of cigarettes on gaseous exchange system?
- stops the cilia from beating.
smooth muscle
- controls the diameter of the airways (trachea, bronchus, bronchioles).
- during exercise, smooth muscle relaxes, making airways wider.
- resistance to airflow decreases.
elastic fibres
- aids expiration
- during inspiration, elastic fibres are stretched.
- during expiration, the elastic fibres recoil to help push air out during expiration.
features of trachea
- incomplete rings of cartilage: prevents trachea from collapsing.
- ciliated epithelium
- goblet cells between and below ciliated epithelial cells.
- smooth muscle
- elastic fibres
features of bronchus
- rings of cartilage: prevents bronchus from collapsing.
- ciliated epithelium
- goblet cells between and below ciliated epithelial cells.
- smooth muscle
- elastic fibres
features of bronchioles
- smaller bronchioles (1mm diameter or less) do not have rings of cartilage.
- smooth muscle (contract → bronchioles constrict, relax → bronchioles dilate.
- thin layer of flattened epithelium, for some gaseous exchange.
FEATURES OF ALVEOLI
- squamous epithelial cells (1 cell thick) (thin layers) provides a short diffusion distance.
- moist lining of lung surfactant. Helps to dissolve oxygen so it can be easily diffused into the capillaries.
- lots of them provide a large surface area for efficient diffusion.
- rich network of capillaries means good blood supply. Maintains steep concentration gradient.
- good ventilation. Maintains steep concentration gradient.
mechanism of INSPIRATION
- diaphragm contracts and flattens.
- external intercostal muscles contract
- ribcage moves up and outwards
- thoracic volume increases
- pressure decreases
- air rushes in to lungs to equalise the pressure.
mechanism of EXPIRATION
- diaphragm relaxes and moves up, curves.
- external intercostal muscles relax.
- ribcage moves down and inwards.
- thoracic volume decreases.
- pressure increases
- air rushes out of lungs to equalise the pressure.
mechanism of FORCED EXPIRATION
- internal intercostal muscles contract
- ribcage moves further down and inwards.
- thoracic volume decreases further.
- pressure increases
- air is forced out of the lungs.
Tidal volume
- the volume of air in each resting breath. around 500cm3.
vital capacity
- maximum volume of air that can be breathed in or out.
inspiratory reserve volume
- maximum volume of air that can be breathed in above a normal inhalation.
expiratory reserve volume
- extra amount of air you can force out of your lungs after a normal exhalation.
residual volume
- the volume of air left in your lungs after exhaling as hard as possible.
- cannot be measured directly.
total lung capacity
- sum of the vital capacity and the residual volume
breathing rate
number of breaths taken in a minute.
- breaths are the peaks in a spirometry graph.
oxygen uptake
the rate at which an organism uses up oxygen.
spirometry when exercising?
- tidal volume increases 15 to 50%
- breathing rate increases
- ventilation of lungs increases
- oxygen uptake increases.
- to meet metabolic demands of tissues.
why is a canister of soda lime used in a spirometer?
- to remove carbon dioxide produced.
- to prevent carbon dioxide poisoning.
What are spiracles?
- small openings along the thorax and abdomen of an insect.
- air enters and leaves the gaseous exchange system through them.
- water is lost from here as well.
what controls the opening and closing of spiracles?
sphincters
why are spiracle sphincters kept closed as much as possible?
to minimise water loss.
What kind of cartilage does the trachea and bronchi have?
trachea: C-shaped rings of cartilage
bronchi: incomplete rings of cartilage.
When are spiracles closed and opened? How many?
- inactive and low oxygen demands: spiracles will all be closed most the time.
- active, higher oxygen demands, increase in CO2 levels, more spiracles open up.
What are tracheae in insects?
- largest tubes of the insect respiratory system 1mm diameter.
- carries air into the body.
- run into and along the body.
What material is the trachea lined with?
- spirals of chitin
- relatively impermeable to gases so little gaseous exchange occurs in the tracheae.
What are tracheoles?
- branched from tracheae.
- minute tubes
- 0.6-0.8um
- single greatly elongated cell.
- no chitin, freely permeable to gases.
- runs between individual cells.
- where most of gaseous exchange between air and respiring cells take place.
Why do the tracheoles provide a good exchange surface?
- lots of them, provides very large surface area for gaseous exchange.
What is tracheal fluid?
- present towards the ends of tracheoles.
- limits the penetration of air for diffusion.
- oxygen dissolves in the fluid which is then diffused into the respiring cells.
What happens to tracheal fluid when oxygen demands are high?
- lactic acid build-up in tissues
- water (part of the tracheal fluid) moves out of the tracheoles by osmosis.
- exposes more surface area in the tracheoles for gaseous exchange to occur.
What system provides oxygen needed by cells in insects?
tracheal system.
What controls the extent of gas exchange in insects?
opening and closing of spiracles.
what methods do larger insects have to increase levels of gaseous exchange?
- mechanical ventilation of tracheal system
- collapsible enlarged tracheae or air sacs.
mechanical ventilation of the tracheal system (insects)
- air is actively pumped into the system
- muscular pumping movements of the thorax and abdomen.
- the movements change the volume of the body, changes pressure in tracheae and tracheoles.
- air is drawn in or forced out the tracheae and tracheoles as pressure changes.
collapsible enlarged tracheae or air sacs (insects)
- inflated and deflated by the ventilating movements of the thorax and abdomen.
- increases the amount of air moved through the gas exchange system.
- acts as air reservoirs.
roles of lung surfactants in alveoli?
- helps to dissolve oxygen so that it can be easily diffused into the capillaries.
- reduces the surface tension of water, allowing alveoli to expand.
Why do bony fish require special adaptations for gaseous exchange?
- small SA:V ratio
- scaly outer covering does not allow gaseous exchange
- oxygen concentration in water is much lower than in the air.
in how many directions does water flow over the GILLS?
one direction
features of gills for a successful gaseous exchange surface
- bony gill arch supports structure of gills.
- lots of gill filaments provide a large surface area for gaseous exchange.
- gill plates are formed from lots of gill filaments stacked together. Gill plates have thin surfaces to increase rate of diffusion.
- gill filaments contain lots of gill lamellae. Gill lamellae provide a large surface area and have a rich blood supply. Main site of gaseous exchange.
What is operculum
The flap that covers the gills.
stages of fish ventilation
- mouth opens
- volume of buccal cavity increases
- pressure in the buccal cavity decreases
- water moves into the cavity.
- at the same time, opercular valve closes.
- opercular cavity (containing gills) expands.
- pressure of opercular cavity decreases
- floor of buccal cavity moves upwards.
- pressure of buccal cavity increases
- water moves to opercular cavity and water moves over the gills.
- mouth closes
- opercular valves open
- opercular cavity shrinks
- pressure in opercular cavity increases.
- water moves over the gills and out the opercular valves.
- buccal cavity moves up steadily to maintain a flow of water over the gills.
gill characteristics for gaseous exchange
- countercurrent system: maintains an oxygen concentration gradient between water and blood along the entire length of the exchange system.
- lots of gill filaments covered with gill lamellae: provides a very large surface area for gaseous exchange.
- thin layers in lamellae and blood capillaries: provides a short diffusion distance.
- rich blood supply, continual refreshing of oxygenated water: maintains oxygen concentration gradient.
explain the counter current flow system?
- blood and water flow in opposite directions.
- oxygen concentration in water is always greater than in blood.
- oxygen continues to diffuse down concentration gradient from water to blood.
- oxygen concentration gradient is maintained all along the gill.
- a high(er) saturation of oxygen in blood is achieved.
why is a parallel flow system bad?
- blood in gills and water flow in the same direction.
- there is an initial steep oxygen concentration gradient between blood and water.
- oxygen concentration in blood and water eventually reach equilibrium, no net movement of oxygen in blood occurs.
- high oxygen saturation in blood cannot be reached.
