3.3.2 Gas Exchange Flashcards
why do multicellular organisms require specialised gas exchange surfaces?
their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism
name three features of an efficient gas exchange surface.
- Large surface area, e.g. folded membranes in mitochondria
- Thin/ short distance, e.g. wall of capillaries
- steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli
why can’t insects use their bodies as an exchange surface?
they have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water
name and describe the three main features of an insect’s gas transport system.
- spiracles = holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
- tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
- tracheoles = smaller branches dividing off the tracheae
explain the process of gas exchange in insects.
- gases move in and out of the tracheae through the spiracles
- a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.
- contraction of muscles in the tracheae allows mass movement of air in and out
why can’t fish use their bodies as an exchange surface?
they have a waterproof, impermeable outer membrane and a small surface area to volume ratio
name and describe the two main features of a fish’s gas transport system
Gills = located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles.
Lamellae = at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (counter-current exchange system)
explain the process of gas exchange in fish.
- the fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure.
- the water passes over the lamellae, and the oxygen diffuses into the bloodstream
- waste carbon dioxide diffuses into the water and flows back out of the gills
how does the counter-current exchange system maximise oxygen absorbed by the fish?
maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed
name and describe three adaptations of a leaf that allow efficient gas exchange.
- Thin and flat to provide short diffusion pathway and large surface area to volume ratio
- Many minute pores in the underside of the leaf (stomata) allow gases to easily enter
- air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis
how do plants limit their water loss while still allowing gases to be exchanged?
Stomata regulated by guard cells which allows them to open and close as needed.
Most stay closed to prevent water loss while some open to let oxygen in.
describe the pathway taken by air as it enters the mammalian gaseous exchange system.
Nasal cavity –> trachea –> bronchi –> bronchioles –> alveoli
describe the function of the nasal cavity in the mammalian gaseous exchange system.
A good blood supply warms and moistens the air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria
Describe the trachea and its function in the mammalian gaseous exchange system.
- wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes.
- lined by ciliated epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections
- carries air to the bronchi
describe the bronchi and their function in the mammalian gaseous exchange system.
- like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells.
- however they are narrower and there are two of them, one for each lung
- allow passage of air into the bronchioles
