exchange Flashcards
Equation to work out SA:V ratio
Surafe area/volume
What does a low SA:V ratio mean
A low SA:V ratio means that there are parts of an object that are a long way from the edge. Means there is a longer diffusion distance.
What happens to SA:V as size increases
As size increases, surface area:volume ratio decreases
What is an organisms metabolic rate
Metabolic rate is the amount of energy expended by that organism in a time period
What is the general rule for metabolism
The greater the mass of an organism, the higher the organisms metabolic rate. This is because organisms with high metabolic rate requires more efficient delivery of oxygen to cells as more respiration is needed
How to increase rate of exchange when it’s a big organism
Larger organisms come up with specialised surface area
Unicellular organisms
They have a large SA:V ratio. Diffusion distance is short to get from outside the cell to the centre. They can exchange materials directly with their environment. They lose water and heat very easily so cant live in very hot or cold climates.
Multicellular organisms
They have a small SA:V. Diffusion distance is large. Heat is maintained better so can survive more easily in cold climates. Some cells arent exposed to outside at all so need internal mass transport systems.
Adaptation for cold climate
Challenge- heat loss
Behavioural- small mammals with large SA:V. They may also hibernate in the coldest months.
Physical- adapted animals with have a streamlined, compacted body shape to give a smaller SA:V. May also have thick fur e.g. arctic foxes
Adaption for hot climate
Challenge- overheating
Behavioural- spending lots of time in the water. Nocturnal as to avoid hot daytime.
Physical- animals with a low SA:V often have larger ears to increase surface area
Adaption for dry climates
Challenge: water loss
Behavioural- may be nocturnal so most active in cooler temperatures
Physical- small animals with high SA:V have kidney structures to produce less urine
Structure of insects
Evolved to live on land and have microscopic air filled pipes. Trachae divides into tracheoles. Divides until they penetrate into individual body cells. Gases are directly exchanged between cells and the atmosphere- there is no need to transport them. Air enters the trachea through pores on the surface of the exoskeleton called spiracles. CO² and O² will diffuse in/out of spiracles down there concentration gradient for gases. Spiracles can be closed/not open all the time, this is to prevent water loss a d to keep the organism waterproof
Structure of fish
Each gill is made of lots of gill filaments which are attached to a bony arch which creates a large surface area for water or flow over. Gill filaments have tiny folds called lamellae which increase surface area. Lamellae have lots of blood capillaries and a thin layer of cells.
What is countercurrect flow
Countercurrent flow is where blood and water flow over and through the lamellae in opposite directions to each other. Blood flows next to water that has higher oxygen concentration, so diffusion happens along the full length of the lamellae. Blood absorbs more and more oxygen as it moves along. Even when blood is highly saturated there is still a concentration gradient so more oxygen can flow in
Adapted structure for fish
Thin walls for lamellae- shortens diffusion distance
Lots of gill filaments and lamellae- increases surface area
Countercurrent flow of blood to water- maintains concentration gradient
Large number of capillaries and lamellae- circulation constantly removes oxygenated blood to maintain steep concentration gradient
Ventilation by operculum- ensures fresh water always goes over gills to replace lost oxygen.
How does ventilation work in fish
The mouth opens, so the operculum shut. Water enters cavity due to a decrease in pressure. The mouth then closes which opens the operculum. This increases pressure which forces the water out of the gills.
Where does co² enter and oxygen leave
Happens in the stomata normally on the lower epidermis
What is right above the lower epidermis
The spongy mesophyll
Adaption of spongy mesophyll
Lots of air gaps which means there is more air space to allow diffusion through the gas phase and increase SA:V formexchnage into photosynthesising cells
What tissue is above the spongy mesophyll
The palisades mesophyll tissue
Adaptions for palisade mesophyll layer
It is more compact to increase light absorption by chlorophyll. High rate of photosynthesis which maintains a steep concentration gradient.