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
