6.Exchange between organisms and their environment Flashcards
For an effective exchange…
the exchange surface of the organism must be large compared with their volume.
Name features of specialised exchange surfaces
- large SA:V ratio
- short diffusion pathway
- selectively permeable (to allow selected materials across)
- a transport system to maintain a diffusion gradient
What is Fick’s Law
Rate of diffusion α (surface area x concentration) / distance
Describe gas exchange in single-celled organisms
They have large SA:V meaning oxygen can just diffuses across their body surface
What are tracheae (i)
Internal network of tubes inside an insect
What are tracheoles
Smaller dead end tubes that are sub branches of tracheae
Name three ways gases move in and out the tracheal system
- along a diffusion gradient
- mass transport (abdominal pumping)
- through water or gas phase at end of tracheoles
Describe how gases move in and out the tracheal system along a diffusion gradient
- when cells are respiring oxygen is used up so concentration gradient is created
- causes oxygen to diffuse from atmosphere into and along the tracheal system
- when cells are respiring carbon dioxide is produces so concentration gradient is created
- carbon dioxide diffuses along and out the tracheal system
Describe how gases move in and out the tracheal system via mass transport
- abdominal pumping is the contraction of muscles in insects
- squeezes the trachea enabling mass movements of air in and out
- speeds up gas exchange
Describe how gases move in and out the tracheal system at the end of the tracheoles
- during periods of high activity muscles cells around the tracheoles respire anaerobically
- this produces lactate which is soluble and lowers the water potential of the muscle cells
- the water therefore moves via osmosis into the cells
- this causes air to be drawn in as it decreases the pressure
- also means the final diffusion pathway is gas rather than liquid phase and therefore more rapid
What are spiracles
Tiny pores that gases enter and leave the tracheal system. Mainly stay closed to reduce water loss
What is a limit of the tracheal system
Relies on diffusion meaning for it to be effective the diffusion pathway needs to be short. This limits the size the insects can attain.
Describe the structure of gills
- made up of gill filaments, stacked
- gill lamellae are at right angles to the gill filaments
What is a countercurrent system
a mechanism by which the efficiency of exchange between two substances is increased by having them flow in opposite directions
Countercurrent flow means that…
- blood already well loaded with oxygen meets water with max concentration so diffusion still takes place
- blood with little oxygen meets water with little oxygen but diffusion can still take place
Name 2 ways gas exchange in plants is similar to that of insects
- no living cell is far from external air and therefore a source of Co2 and oxygen
- diffusion takes place in a gas phase which makes it more rapid (compared to a liquid phase)
What adaptations for gas exchange do leaves show
- many stomata, no cell is far from stomata and therefore diffusion pathway is short
- numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
- large SA:V ratio means rapid diffusion
What are stomata
- minute pores that occur mainly on leaves
- each stoma is surrounded by a pair of guard cells
- they control rate of gas exchange as they can open and close the stomatal pore
- they are important in controlling water loss
- close at times when water loss would be excessive
What problem do plants and insects have
The opposing needs of an efficient gas-exchange system and the requirement to conserve water
Describe the ways insects are adapted to reduce water loss
- small SA:V ratio to minimise the area over which water can be lost
- waterproof coverings over their body surfaces, insects have outer skeleton of waterproof chitin
- spiracles are the opening of the tracheae at the body surface which can be closed to reduce water loss
Describe the ways plants are adapted to reduce water loss
- waterproof covering
- ability to close stomata
What are xerophytes
Plants that are adapted to living in areas where water is in short supply
Name the ways xerophytes have evolved to reduce water loss
- a thick cuticle
- rolling up of leaves
- hairy leaves
- stomata in grooves or pits
- reduced SA:V of leaves
Describe how rolling of leaves reduces water loss
- causes air to be trapped in a region around the lower epidermis (where most stoma are found)
- this region becomes saturated with water vapour causing a high water potential
- there is no water potential gradient
- no water is lost from the leaf.
Describe how hairy leaves reduces water loss
- traps moist air near leaf surface
- water potential gradient between inside and outside is reduced
- less water is lost by evaporation
What is inspiration
- inhaling
- when air pressure is greater than the air pressure inside the lungs
What is expiration
- exhaling
- when air pressure in the lungs is greater than that of the atmosphere
What are the three muscles that cause pressure changes within the lungs
- diaphragm
- internal intercostal muscles
- external intercostal muscles
Which intercostal muscle is responsible for expiration
Internal intercostal muscles
