3.1 Exchange Surfaces 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.
How is surface are to volume ratio calculated ?
Ratio = surface area/volume
Name three features of an efficient gas exchange surface
- 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 passage of air into the bronchioles.
Describe the bronchioles and their function in the mammalian gaseous exchange system
• Narrower than the bronchi.
• 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 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.
- large surface area (300 million in each lung)
- thin layers , both the alveoli and capillaries have walls that are one epithelial cell thick , so short diffusion distance
- good blood supply - because of the network of capillaries there is a constant blood flow through these capillaries. Which brings carbon dioxide and carries off oxygen , maintaining a steep concentration gradient
- good ventilation - breathing moves air in and out of the alveoli , helping maintain steep diffusion gradients for oxygen and carbon dioxide between the blood and the air in the lungs
Explain the process of inspiration and the changed that occur throughout the thorax
• External intercostal muscles contract (while internal relax), pulling the ribs up and out.
• Diaphragm contracts and flattens.
• Volume of the 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 take 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 breath 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 the gill filaments, give an
increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system). Rich blood supply
Explain the process of gas exchange in fish
• The mouth is opened and the floor of the buccal cavity is lowered. Buccal cavity (mouth) 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 bloodstream.
• Waste carbon dioxide diffuses into the water and flows back out of the gills.
