Organisms Exchange Substances with their Environment Flashcards
How does an organism’s size relate to their surface area to volume ratio?
The larger the organism, the lower the surface area to volume ratio
How does an organism’s 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’s 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 features of an efficient gas exchange surface
- Large SA 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 y 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 (countercurrent exchange system)
Explain the process of gas exchange in fish
The fish opens its mouth to enable water to flow in, the 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 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 y 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 change system
Nasal cavity –> trachea –> bronchi –> bronchioles –> alveoli
Describe the function of the nasal cavity in the mammalian gaseous changes 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 bronchi.
Describe the bronchi and their functions 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), 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.
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 breaths we take per minute
How do you calculate pulmonary ventilation rate?
Tidal volume x breathing rate
These can be measured using a spirometer, a device which records volume changes onto a gram as a person breathes
