Gas exchange (6) Flashcards
Why do multicellular organisms need specialised gas exchange surfaces?
their smaller SA:V ratio means the distance that needs to be crossed is larger + substances cannot easily enter the cells like in a single-celled organism
What are 3 features of efficient gas exchange?
1) large surface area e.g. folded membranes in mitochondria
2) thin/short distances e.g. wall of capillaries
3) stop concentration gradient, maintained by blood supply or ventilation e.g. alveoli
Why can’t insects use their bodies as an exchange surface?
- waterproof chitin exoskeleton
- small SA:V ratio in order to conserve water
Describe gas exchange in insects.
- gases move in and out of tracheae through spiracles
- diffusion gradient allows O2 to diffuse into body tissue whilst waste CO2 diffuses out
- contraction of muscles in the tracheae allows mass movement of air in and out
What are the 3 structures in an insect’s transport system?
1) spiracles
2) tracheae
3) tracheoles
What are spiracles?
holes on body’s surface which may be opened or closed by a valve for gas or water exchange
What are tracheae?
large tubes extending through all body tissues, supported by rings to prevent collapse
What are tracheoles?
smaller branches dividing off the tracheae
Why can’t fish use their bodies as an exchange surface?
- waterproof, impermeable outer membrane
- small SA:V ratio
What are the 2 features of fish gas transport systems?
gills
lamellae
What are gills and where are they found?
- located within the body
- supported by arches along which are multiple projections of gill filaments, which are stacked up in piles
What are lamellae?
at right angles to gill filaments
increase surface area
blood + water flow across them in opposite direction
What’s the term used to describe blood + water flowing in opposite directions?
counter-current exchange system
What is the process of gas exchange in fish?
(3 points)
1) fish opens mouth to enable water to flow in, then closes its mouth to increase pressure
2) water passes over lamellae and O2 diffuses into bloodstream
3) waste CO2 diffuses into water and flows back out of the gills
How does the counter-current exchange system maximise O2 absorbed?
maintains steep concentration gradient as water is always next to blood of a lower O2 concentration, which keeps rate of diffusion constant and enables 80% of available O2 to be absorbed
What are 3 adaptations of leaves which allow for efficient gas exchange?
1) think + flat
2) many stomata
3) air spaces in mesophyll
How does being thin + flat allow leaves to have efficient gas exchange?
provide short diffusion pathway and large SA:V ratio
How does having stomata allow leaves to have efficient gas exchange?
allow gases to easily enter
What are stomata?
minute pores on underside of leaf
How does having air spaces in mesophyll allow leaves to have efficient gas exchange?
allow gases to move around the leaf, facilitating photosynthesis
How do plants limit water loss?
- stomata regulated by guard cells which allows them to open and close as needed
- most stomata stay closed while some open to let O2 in
What is the order of the mammalian gaseous exchange system?
1) nasal cavity
2) trachea
3) bronchi
4) bronchioles
5) alveoli
What is the function of the nasal cavity?
- good blood supply warms and moistens air entering the lungs
- goblet cells in membrane secrete mucus which traps dust and bacteria
How do you calculate the pulmonary ventilation rate?
tidal volume x breathing rate
How do you measure tidal volume and breathing rate?
spirometer
What is a spirometer?
device that records volume change onto a graph as a person breathes
What is the structure of the trachea?
wide tube supported by C-shaped cartilage
lined by ciliated epithelium cells
Why is the trachea a wide tube supported by C-shaped cartilage?
to keep air passage open during pressure changes
Why is the trachea lined by ciliated epithelium cells?
moves mucus towards the throat to be swallowed, preventing lung infections
What is the function of the trachea?
carries air to the bronchi
What is the structure of the bronchi?
like trachea, they are supported by rings of cartilage and are lined by epithelium cells, however narrower, 2 of them and 1 for each lung
What is the function of the bronchi?
allow passage of air into the bronchioles
What is the structure of the bronchioles?
narrower than the bronchi
don’t need to be kept open by cartilage, therefore mostly only muscle + elastic fibres so they can contract and relax easily during ventilation
What is the function of the bronchioles?
allow passage of air into the alveoli
What is the structure of alveoli?
- mini air sacs lined with epithelium cells
- walls only 1 cell thick, covered with network of capillaries
- 300 million in each lung
What is the function of alveoli?
facilitate gas exchange
What is tidal volume?
volume of air we breathe in and out during each breath at rest
What is breathing rate?
number of breaths we take per minute
What happens during inspiration?
- external intercostal muscles contract, pulling ribs up and out
- internal intercostal muscles relax
- diaphragm contracts + flattens
- thorax volume increases
- air pressure outside lungs is therefore higher than air pressure inside, so air moves in to rebalance
What happens during expiration?
- external intercostal muscles relax
- internal intercostal muscles contract
- diaphragm relaxes + domes upwards
- thorax volume decreases
- air pressure outside lungs is therefore lower than air pressure inside, so air moves out to rebalance
