3.1 Surface Area to Volume Ratio + 3.2 Gas Exchange Flashcards
How does an organisms size relate to their surface area to volume ratio?
The larger the organism, the lower the surface area to volume ratio
How does an organisms surface area to volume ratio relate to their metabolic rate?
The smaller the surface area to volume ratio, the higher the metabolic rate
How might a large organism adapt to compensate for its small surface area to volume ratio?
Changes that increase surface area e.g. folding; body parts become larger; e.g. elephant ears; elongating shape; developing a specialised gas exchange surface
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 feature 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 insects gas transport system
Spiracles = holes on the body’s surface which may be opened or closed by a valve used for gas exchange or water exchange
Tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
Tracheolus = 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 memebrane 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 direction (countercurrent exchange system)
Explain the process of gas exchange in fish
The fish opens its mouth to enable water to flow in, them 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 countercurrent 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 to 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 moistests 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 tubes supported by C-shapes cartilage to keep the air passage open during pressure changes
Lined by ciliates 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
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 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
Explain the process of inspiration and the changes 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) bring 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
What is tidal volume
The volume of air we breathe in and out during each breath at rest
What is breathing rate?
The number of breathes we take per minute
How do you calculate pulmonary ventilation rate?
Tidal volume X breathing rate. These can be measure using a spirometer, a device which records volume changes onto a graph as a person bresthes
