AS-Organisms exchange substances with their environment Flashcards
What factors effect the rate an organism can exchange substances? (actively or passively)
-Volume - the space it occupies
-Surface area - how much is exposed to the environment
How does an organism’s size relate to their SA:V ration?
Larger the organism the lower the SA:V ratio
How does an organism’s surface area to volume relate to their metabolic rate?
The smaller the SA:V ratio the higher the metabolic rate
How might a large organism adapt to compensate for it’s small SA:V ratio?
-create changes to increase surface area e.g.
-body parts getting bigger (e.g. elephant ears
-elongating shape
-specialised gas exchange surface
Why do multicellular organisms require specialised gas exchange surfaces?
-Their small SA:V ratio means that their length of diffusion pathway is larger
-substances cannot easily enter the cells
Name 3 features of efficient gas exchange
-Large Surface area e.g. folded membranes
-short diffusion pathway e.g thin capillary walls
-Steep concentration gradient e.g alveoli
Recall Fick’s Law
rate of diffusion (is proportionate to) surface area X concentration difference (divided by) length of diffusion pathway
How do single cell organisms exchange gases/substances?
Diffusion
Why can’t insects use their body as an exchange surface
- they have a waterproof chitin exoskeleton
-they have a reduced SA:V
(ALL TO CONSERVE WATER)
Name the 3 main features of the insect’s gas transport system
-spiracles
-tracheae
-tracheoles
describe the spiracles
holes in the body’s surface which may be opened or closed by valve for gas or water exchange
Describe the Tracheae
large tubes extending through all body tissues, supported by rings to prevent collapse
Describe the tracheoles
smaller branches dividing off the trcgeae
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
How is the insect gas exchange system efficient
-all body cells are close to tracheole end
(diffusion pathway shortened)
-oxygen concentration is low near respiring tissues
(large concentration difference)
What are the problems with the insect gas exchange system?
- relys on passive transport
(limiting the size of insects)
-waterloss
(when spiracles open water is lost through evaporation)
(closing spiracles completely limits oxygen supply)
Why can’t fish use their bodies as an exchange surface?
-they have a waterproof, impermeable outer membrane
-they have a small surface area to volume ratio
Name the two main features of a fish’s gas transport system
-Gills
-Lamellae
Describe of the Gills
- have gill filaments that are stacks on top of each other
Describe the Gill Lamellae
-Right angles to the gill filaments
-give an increases surface area
- blood and water flow in opposite direction
(counter current flow)
How does the counter current flow system lead to efficient gas exchange across the gills of a fish
-water and blood flows in opposite directions
-this increases oxygen and CO2 exchange
-this means there is a constant concentration different all throughout gill
How are plants adapted to allow efficient gas exchange
-Thin and flat leaves = short diffusion pathway and large SA:V ratio
-lots of stomata = gases can easily enter
-air spaces = allow gases to exchnage to all cells
What are the limitations with the plants gas exchange system
water loss through transpiration
How do plants limit their water loss while still allowing gas exchange
-stomata regulated by guard cells
-most stay closed to prevent water loss while some open to let oxygen in
What are Xerophytes
-plants that live & are adapted to live in arid/dry conditions
Name some features of xerophytes
- they have hairs (increases water vapour conc.)
-sunken stomata (increased LODP making it hard for water to escape)
-Leaves curled (increased water vapour outside leaves- conc grad created
-thick stems (reduce water loss)
-water store
