3.1.1 Exchange Surfaces Flashcards
Why do larger more active organisms require specialised gas exchange surfaces?
- higher demand for oxygen
- greater need to remove carbon dioxide
- have a smaller SA:VOL ratio
- diffusion distance too great to just use SA
- diffusion alone wouldn’t meet needs of organism
Why don’t smaller more active organisms require specialised gas exchange surfaces?
- lower demand for oxygen
- lesser need to remove carbon dioxide
- have a larger SA:VOL ratio
- diffusion distance small enough to just use SA
- diffusion alone meets needs of organism
What factors affect rate of diffusion?
- temperature
- concentration gradient
- stirring movement
- surface area
- diffusion distance
- size of molecule
Explain the structure of trachea
- supported by cartilage c-ring - prevents collapse during low air pressure
- elastic fibers allow stretch, preventing bursting
- smooth muscle fibres can contract to reduce the diameter of the trachea
- goblet cells release mucus - trapping pollen/bacteria
Explain the structure of bronchi
- similar structure to trachea - smaller diameter + thinner walls
- complete rings of cartilage - doesn’t lie against the oesophagus
- larger bronchioles have muscle cells
- smaller bronchioles have no muscle cells
Explain the structure of alveoli
- arranged in groups at end of small bronchioles
- walls consist of squamous epithelium cells - short diffusion distance
- elastic fibres allow for stretching - prevents bursting
- water fluid lining - produces surface tension
Explain the structure of ciliated epithelial tissue
- columnar
- have cilia
- line the trachea, bronchi and larger bronchioles
What is the rib cage?
Provides a semi-rigid case within which pressure can be lowered with respect to the air outside
Explain the different muscles used for ventilation
External Intercostal Muscle
- when these contract, the ribcage moves up + out - opposite when relaxed
Internal Intercostal Muscle
- when you exhale forcibly using energy these contract, pulling ribs down hard and fast
Diaphragm
- broad, doamed sheet of muscle which forms the floor of the thorax
Explain the mechanism of inspiration
- external intercostal muscles contract
- ribcage moves up + out
- diaphragm contracts + moves down
- thorax volume increases
- pressure in thorax decreases below atmospheric pressure - air flows in
Explain the mechanism of expiration
- external intercostal muscles relaxes
- ribcage moves down + in
- diaphragm relaxes + moves up
- thorax volume decreases
- pressure in thorax increases above atmospheric pressure - air flows out
What is pulmonary ventilation and how is it calculated?
The volume of air breathed in during 1 minute
Pulmonary ventilation = ventilation rate x tidal volume
What is tidal volume?
The volume of air inhaled or exhaled in one breath during steady/regular breathing
What is inspiratory + expiratory volume?
The additional volume of air that can be inhaled/exhaled after normal inspiration/expiration.
What is vital capacity?
The maximum volume of air inhaled or exhaled in one breath - reserve + tidal capacity = vital capacity
What is total lung capacity
The maximum volume of air that can fill the lungs
What is residual volume?
Air stuck in the lungs - thorax/ribcage cannot be completely flattened
Explain key aspects of using a spirometer
- person attached via tube to air chamber
- chamber contains oxygen, sits on top of water
- moves up during expiration, down during inspiration
- traced on graph
- contains soda lime - removes CO2
- nose clip ensures all air goes through chamber - no invalid result due to breathing out through nose
List safety precautions when using a spirometer
- use medical grade oxygen
- disinfect mouthpiece
- person is healthy/ not asthmatic
- ensure chamber can move
List features of an efficient exchange system and how they are achieved
- increased surface area (e.g. root hair cells)
- thin layer (e.g. alveoli)
- good blood supply to maintain steep concentration (e.g. gills/alveolus)
How does air enter into insects?
Through spiracles in the thorax + abdomen
How can spiracles be opened and closed?
Sphincters
Where does air flow after entering spiracles, and give key aspects
- leads into tracheae (1mm diameter)
- run into and along the insect body
- supported by circular bands of chitin (NOT C-shaped)
- impermeable to gases
Where does air flow after entering trachea, and give key aspects
- leads into tracheoles (0.6-0.8 μm diameter)
- single, greatly elongated cells
- no chitin lining
- freely permeable to gases
- run between individual cells
How does air move along the tracheal system?
- mostly diffusion alone
- due to vast number of tracheoles giving a large SA for gaseous exchange
How does oxygen get into surrouding cells from the system?
- dissolves into the moisture of the walls
- then diffuses into cells
What prevents pentration of air at the end of tracheoles
Tracheal fluid
How do insects decrease ther amount of fluid limiting diffusion of air?
- lactic acid builds in tissue during movement (e.g. flying)
- water moves from high ψ in tracheoles to low ψ in tissues (osmosis)
- more surface area exposed for gaseous exchange
Explain how insects move more air into + around the tracheal system
- mechanical ventilation
- muscular pumping of thorax + abdomen
- changes volume of body, subsequently changing pressure of tracheae + tracheoles
- breathing in = volume increases - lower pressre inside than out - air drawn in
- breathing out = volume decreases - higher pressre inside than out - air forced out
How else can insects store air?
- air sacs
- inflated + deflated by ventilating movements
What is fluttering and why could insects do it?
- pattern of opening + closing spiracles
- may reduice water loss by evaporation
Why do bony fish require specialised exhange surfaces?
- large organisms so have a small SA:VOL ratio
- concentration of oxygen in water much lower than air
- water much more viscous than air so lungs not appropriate
Describe the movement of water through the gills of a fish
- water moves from outside of fish through open mouth
- into buccal cavity
- into opercular cavity
- over gills
- out of fish through open opercular valve
Explain the alternative system fish uses to ventilate
- mouth and operculum open alternativley
Explain what happens when the mouth is open
Mouth Open
- buccal cavity lowered
- volume of buccal cavity increases
- pressure of buccal cavity decreases
- water moves into cavity
- opercular valve shut
- opercular cavity containg gills expands - lowers pressure
- floor of bucal cavity moves up, increasing pressure
- water moves over gills due to pressure difference
Explain what happens when the mouth is closed
Mouth Closed
- sides of opercular cavity move inwards - decreasing pressure
- increase pressure in opercular cavity forces water over gills + out operculum
- floor of buccal cavity moved up, maintaining flow over gills
- when buccal cavity is lowered, operculum sucked shut
List features of bony fish that allow for efficient gaseous exchange
- gills have larger SA - large area for diffusion to occur
- gills have rich blood supply - steep concentration gradient
- gills have thin layers - short diffusion distance
Explain the structure of gills
- each gill made of 4 bony arches
- arches lined with gill filaments (thin + flat)
- gill filaments occur in stacks called gill plates
- filaments have lamellae - increased SA
How do neighbouring gill filaments interact to increase gaseous exhange?
- overlap at their tips
- provides resistance to water flow
- water slowed down
- more time for gaseous exchange
What is counter current and how does it work?
- water moves over gills + blolod flows in gill filaments in opposite directions
Compare concurrent and counter-current systems
Concurrent/ Parrallel Flow
- water + blood flow together
- equilibirum quickly reached
- no further diffusion
Counter-Current
- blood flowing past water of higher oxygen concentration
- diffusion occurs all along gill
- equilibrium never reached
Compare bony fish and cartilaginous fish
Bony Fish
- e.g. trout/cod
- skeleton made from bone
- counter-current exchange system
- remove ~80% of oxyegn from water flowing over gills
Cartilaginous Fish
- e.g. sharks/rays
- skeleton made from cartilage
- parrallel exhange system
- remove ~50% of oxygen from water flowing over gills
