surface area to volume ratio and gas exchange

metabolism

sum of all chemical reactions that take place within cells and organisms

metabolic rate of an organism

amount of energy expended by that organsim within a given period of time, more active animals have a higher metabolic rate than less active animal

basal metabolic rate

metabolic rate of an organism when at rest

what methods can we use to measure metabolic rate

o2 consumption, co2 production, heat production - measured using respirometers, o2 and co2 probes, calorimeters

what materials do all organisms need for respiration and growth

mineral ions, glucose, aas, o2 for aerobic respiration to produce ATP

what metabolic waste products must all organisms remove

co2 because accumulation lowers ph of cells, ammonium, urea

why does less mass mean increased metabolic rate

bmr per unit body mass is higher in smaller organisms because larger sa:v ratio so more heat loss so need to use more energy to maintain temp

features of specialised gas exchange surfaces

large sa:v ratio, thin to reduce diffusion distance, selectively permeable, movement of environmental medium (e.g. air to maintain conc gradient), transport system (e.g. blood to maintain conc gradient), moist (o2,co2,nutrients diffuse in solution)

ficks law: rate of diffusion is directly proportional to…

(sa x diff in conc)/length of diffusion path

diffusion in single celled organisms

ext surface acts as gas exchange surface, has large sa:v ratio, short diffusion distance between surface and centre of organism

trachea

c shaped rings of hard cartilage keep air passage open during pressure changes, rings separated by muscle and elastic tissue - contracts and relaxes to control amount of air in passage, soft tissue allows the trachea to be flexible and stretch to change size of trachea to allow more or less air through

bronchus (first branch of trachea)

lined with cilia that make mechanical movements to waft dirt caught on mucus back up to the mouth to be swallowed where hcl in the stomach destroys it preventing infection of the lungs, has cartilage but is not c-shaped to allow them to stay open

bronchioles

end in clusters of alveoli, smaller bronchioles only have muscle and elastic tissue so can contract and relax easier during ventilation, larger ones have cartilage to keep them open, elastic fibres allow stretch and recoil of bronchioles

gas exchange in alveoli

o2 from air moves down trachea, bronchi, bronchioles into alveoli - movement occurs down a PRESSURE GRADIENT, o2 diffuses across alveolar epithelium & capillary endothelium down conc gradient co2 diffuses from capillaries into alveoli

alveolar adaptations for efficient gas exchange

single layer of cells for fast, short diffusion path, large sa (millions of alveoli), extensive capillary network to maintain steep conc gradient, moist inner layer (gases cannot enter cells unless in solution), lined with cells releasing surfactant (ensures alveoli do not stick together in pressure change so maintains high sa)

surfactant

lowers surface tension of water because sometimes pressure change is not enough to break surface tension so gases cannot enter the water to be diffused into cells

ventilation

movement of air into and out of the lungs by inspiration and expiration, controlled by movement of diaphragm, internal and external intercostal muscles and ribcage, tidal because moves in and out in the same way through the trachea

inspiration (active process requiring energy from atp)

ext icm contract, int icm relax, ribs pulled up and out increasing volume of thorax, pressure in lungs reduced as volume of thorax increases, atmospheric pressure greater than pulmonary pressure, air pulled into lungs due to pressure gradient

expiration (only if forceful otherwise passive and relies on recoil of elastic tissue in the lungs

int icm contract, ext icm relax, ribs pulled down and in decreasing volume of thorax, diaphragm muscles relax so pushed up by contents of abdomen compressed during inspiration, volume of thorax further decreased, pressure in lungs increased as volume of thorax decreases, atmospheric pressure less than pulmonary pressure, air forced out of lungs due to pressure gradient

pulmonary ventilation

tidal volume x ventilation rate

tidal volume

volume of air taken into the lungs at each breath when at rest

ventilation rate

number of breaths taken per minute, tidal volume x breathing rate

residual volume

air in your lungs that is never moved

exoskeleton (insects)

waxy coating impermeable to gases made of chitin

spiracle

opening in exoskeleton with valves, allows air to flow into tracheae, closed most of the time to prevent water loss

tracheae

tubes leading to tracheoles, have reinforcement to keep open as air pressure inside fluctuates

tracheoles

ends are water filled, run between cells and into muscle fibres (site of gas exchange)

generating conc gradient in insects for gas exchange

o2 used by respiring tissues in aerobic respiration, co2 moves out through spiracles down conc gradient

increasing rate of diffusion in insects

opening spiracles, contracting abdominal muscles to force air out of spiracles and maintain ventilation, lactate production in muscle cells lowers water potential so water in spiracles moves into muscle by osmosis

preventing water loss in insects

spiracles closed by muscles and valves, waterproof waxy cuticle to reduce water evaporation, hairs around spiracles reduce water loss by creating humid environment by recondensing of water vapour around the spiracle so no more conc gradient, sunken spiracle

gas exchange in fish

water flows through mouth out of operculum passing over gills, gill arch supplies gills with oxygen poor blood vessels to maintain conc gradient, gill lamellae site of gas exchange so membrane close to capillaries to reduce diffusion distance, flat so high sa:v ratio, many gill filaments covered in gill lamellae to increase sa

countercurrent exchange in fish

water and blood travel in opposite directions, ensures higher conc of oxygen in water compared to blood, higher diffusion rate, maintains large conc gradient

gas exchange in dicotyledonous plants (2 leaves in embryo of seed)

large sa for max diffusion of gases in spongy mesophyll and air spaces, stomata (pores in epidermis) open and close to allow gas exchange, guard cells control the opening and closing of the stomata

controlling water loss in dicotyledonous plants (2 leaves in embryo of seed)

stomata open during day, water enters guard cells making them turgid allowing stomata to open so more water evaporates, if dehydrated, guard cells lose water and become flaccid, stomata closes, water loss prevented, waxy cuticle on upper epidermis prevents water vaporising

special adaptations of xerophytes (specially adapted for warm, dry windy habitats)

sunken stomata and hairs on epidermis trap moist air reducing water potential gradient between leaves and air, curled leaves/ spikes trap area of still air that becomes water saturated so has high water potential and stomata is protected from wind, reduced number of stomata, thick waxy cuticle