โ Surface area to volume ratio - as size increases, surface area to volume ratio decreases,
because surface area increases by a factor of 2, but surface area increases by a factor
of 3. This reduces rate of diffusion, meaning that large organisms require specialised
exchange surfaces in order for sufficient oxygen to be absorbed to meet metabolic
demand
โ Metabolic rate - rate of the sum of all chemical reactions in a cell or organism. Amount of
energy used by an organism in a given time
โ Metabolic demand - amount of oxygen and nutrients to meet metabolic rate.
โ Basal metabolic rate - metabolic rate at rest, so the amount of energy needed for only
vital organs
โ Adaptations to dry environments:
Behavioural - nocturnal so they are most active during cooler temperatures, meaning
they loose less water from sweating or panting.
Physical - specialised kidney structures to reabsorb more water, making urine very
concentrated
โ Adaptations to hot environments:
Behavioural - nocturnal so they are most active at lower temperatures therefore less
water lost and lower chance of overheating. Animals may be semi-aquatic such as
hippos, meaning they spend most of the day in water, which acts as an insulator,
keeping the animals cool
Physical - Large ears and pointed snouts to increase surface area to volume ratio. There
is a greater surface area to lose heat over, so animals do not overheat
โ Adaptations to cold environments:
Behavioural - Small animals such as rodents require a lot of energy to maintain a
constant body temperature as they quickly lose heat. This means they often eat high
energy foods such as seeds or nuts. Animals may hibernate when food is in low supply
in the winter months so the animals do not die of starvation
Physical - compact, streamlined body shape to reduce surface area to volume ratio.
Animals may also have smaller ears and a less pointed snout to further decrease
surface area to volume ratio. Furthermore animals have blubber or a thick double coat of
fur for insulation to keep animal from freezing
โ Xerophytic plants - plant adapted to lose little water in hot or dry environments
General adaptations:
โFew stomata - reduce water loss
โSunken stomata - traps humid air around stomata, reducing concentration
gradient and so rate of osmosis
โStomatal hairs - traps humid air around stomata, reducing concentration gradient
and so rate of osmosis
โExtensive root systems - access wider types of water sources
โRolled leaves - traps humid air around stomata, reducing concentration gradient
and so rate of osmosis
โThick waxy cuticle - reduces water loss and can store water in swollen stems
โ Insect gas exchange structure
Spiracles - opening in the chitin exoskeleton that allows gas to enter tracheae. Valved to
