Exchange Surfaces Flashcards
How is surface area to volume ratio calculated
Ratio = Surface area / Volume
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 system
- Large surface area e.g. root hair cells
- Thin / short distance, e.g. alveoli
- Steep concentration gradient, maintained by blood supply or ventilation e.g. gills
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, produced by goblet cells, 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 and goblet cells
However they are narrower and there are two of them, one for each lung
Allow the passage of air into the bronchioles
Describe the bronchioles and their function in the mammalian gaseous exchange system
Narrower than the bronchioles
Do not need to be kept open by cartilage, therefore mostly have only smooth muscle and elastic fibres so that they can contract and relax easily during ventilation
Allow passage of air into the alveoli
Describe the structure of the alveoli and their function in the mammalian gaseous exchange system
Mini air sacs, lined with epithelium cells, site of gas exchange
Walls only one cell thick, covered with a network of capillaries, 300 million in each lung, all of which facilitates gas diffusion
Explain the process of inspiration and the changes that occur throughout the thorax
External intercostal muscles contract (while internal relax), pulling ribs up and out
Diaphragm contracts and flattens
Volume of thorax increases
Air pressure outside the lungs is therefore higher than the air pressure inside so air moves in to rebalance
Explain the process of expiration and the changes that occur throughout the thorax
External intercostal muscles relax (while internal contract), bringing the ribs down and in
Diaphragm relaxes and domes upwards
Volume of the thorax decreases
Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance
Explain how a spirometer works
Used to measure lung volume. A person breathes into an airtight chamber which leaves a trace on a graph which shows the volume of the breaths
Define vital capacity
The maximum volume of air that can be taken in or expelled from the lungs in one breath. Can be calculated from the spirometer graph by finding the maximum amplitude
Define tidal volume
The volume of air we breathe in and out during each breath at rest. Can be calculated from the spirometer graph by finding the amplitude at rest
Define breathing rate
The number of breaths we take per minute. Can be calculated from the spirometer graph by counting the number of peaks in one minute
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 gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system)
Explain the process of gas exchange in a fish
Buccal cavity volume increased to enable water to flow in, reduced to increase pressure
Water is pumped over the lamellae by the operculum, oxygen diffuses into the blood stream
Waste Carbon Dioxide diffuses into the water and flows back out the gills
