(6) Exchange Flashcards
why do smaller animals have a larger surface area : volume ratio than bigger animals
because as organisms become larger their volume increases at a faster rate than their surface area
what are 2 reasons why diffusion across the outer membrane is slower in multicellular organisms
1) some cells are deep within the body- long distance
2) large animals have a large sa:v ratio- it’s difficult to exchange enough substances for a large animal over a small SA
how does size influence heat exchange
rate of heat loss depends on SA- a large animal has a smaller SA so it’s hard for it to lose heat
A small organism has a large SA so loses heat more easily so they need a relatively high metabolic rate in order to generate enough heat
how does shape affect heat exchange
a more compact shape means a small SA relative to volume so less heat lost
less compact shape have larger sa which increases heat loss
how do small desert animals compensate for having high sa:v ratio
tend to lose more water as it evaporates from surface. so some have kidney structure adaptations so they produce less urine
how do small animals in cold regions support their high metabolic rates
they eat large amounts of high energy food eg seeds and nuts may also have thick layers of fur or hibernate when it gets really cold
how do large animals in hot areas keep cool
their heat loss is slow so elephants have large flat ears to increase sa
hippos spend most of the day in the water
what is the formula for calculating diffusion
SA x DIC / LODP
what are 5 features of specialised exchange surfaces
1) large SA relative to the volume of the organism which increases the exchange rate
2) thin- short diffusion pathway
3) selectively permeable to allow selected materials across
4) movement of the environmental medium eg air to maintain diffusion gradient
5) transport system eg blood to ensure movement of internal medium and maintain diffusion gradient
how is a fish adapted to absorb enough oxygen
water containing oxygen enters in the mouth and exits through gills
each gill has gill filaments to increase sa these are covered in lamellae which further increase sa.
the lamellae contain blood capillaries
blood flows over the lamellae in one direction and water in the other which creates a counter-current system and maintains a large conc gradient which allows oxygen to diffuse from water into blood
how do insects use tracheae to exchange gases
air moves into tracheae through spiracles (surface pores)
oxygen travels down conc gradient to cells
the tracheae branch into tracheoles which have thin permeable walls and go to individual cells
CO2 from cells moves down its own conc gradient to spiracles to be released into atmosphere
what is the main gas exchange surface in a leaf
the mesophyll cells (inside the cells) so gases move in and out through special cells in the epidermis called stomata
how do insects control water loss
they can close their spiracles using muscles and they have a waterproof waxy cuticle all over their body and tiny hairs around their spiracles
how do plants control water loss
their stomata are kept open to allow gas exchange
water enters making the guard cells turgid which opens the stomatal pore but if the plant becomes dehydrated the guard cells become flaccid which closes the pore
what is a xerophyte
a plant specially adapted for life in warm, dry or windy habitats
