Exchange Surfaces

OCR A Level Bio

why is diffusion alone sufficient to supply the needs of single-celled organisms?

• low metabolic activity

• large SA:V ratio

characteristics of effective exchange surfaces?

• increased SA to overcome SA:V ratio of larger organisms

• thin layers for short diffusion distances

• good blood supply to maintain a steep concentration gradient

• ventilation to maintain the diffusion gradient

journey of mammalian gas exchange system?

nasal cavity - trachea - bronchus - bronchioles - alveoli

why do mammals need a gaseous exchange system?

• high metabolic rate

• lots of oxygen for cellular respiration

• carbon dioxide to be expelled

nasal cavity

• large surface area

• good blood supply

• hairy lining which secretes mucus to trap dust and bacteria

• moist surface to increase the humidity and reduce evaporation

trachea

• wide tube with incomplete rings of cartilages which stop trachea from collapsing

• lined with ciliated epithelium and goblet cels between and below them

• secrete mucus into the lining of the trachea to trap dirt and microorganisms

bronchus

similar to trachea but smaller

bronchioles

• smaller diameter

• no cartilage

• smooth muscle

• can control amount of air reaching lungs

• lined with a thin layer of flattened epithelium

alveoli

• consist of thin, flattened epithelial cells

• consist of collagen and elastic fibres

adaptations of the alveoli

• large surface area: provides area big enough for oxygen to diffuse into the body

• thin layers: only one epithelial cell thick providing short diffusion distance

• good blood supply: constant flow of blood from capillaries maintains a steep concentration gradient

• good ventilation: breathing in and out maintains steep ventilation gradients

• lung surfactant: prevents the alveoli from collapsing

inspiration?

• active process

• diaphragm muscle contracts

• external intercostal muscles contract

• ribs move upwards and ouwards

• thorax volume increases, pressure decreases, so air is drawn in

expiration?

• passive process

• diaphram muscle relaxes

• internal intercostal muscles contract

• ribs move downwards and inwards

• thorax pressure is increased, so air moves out of lung so thorax volume is decreased

what does a peak flow meter do?

• measures rate at which air can be expelled from the lungs

what does a spirometer do?

• measures different aspects of the lung volume or to investigate breathing patterns

what do vitalographs do?

• measure the forced expiratory volume in 1 second

tidal volume

volume of air that moves into and out of the lungs with each resting breath

vital capacity

volume of air that can be exhaled when the deepest possible intake of breath is followed by the strongest possible exhalation

inspiratory reserve volume

the maximum volume of air you can breathe in and above a normal inhalation

expiratory reserve volume

the maximum volume of air you can breathe out and above a normal exhalation

residual volume

volume of air that is left in your lungs when exhaled as hard as possible

total lung capacity

vital capacity + residual volume

breathing rate

measured in bpm

ventilation rate

breathing rate x tidal volume

journey of gas exchange in insects

spiracles - tracheae - tracheoles - muscle

spiracles

open when oxygen demand is raised or carbon dioxide levels build up

tracheae

• lined by spirals of chitin

tracheoles

• give a large surface area for gaseous exchange

• oxygen dissolves in moisture on the walls of the tracheoles and diffuses into the surrounding cells

what happens when oxygen demands in insects increase?

There is a lactic acid build up in tissues, water moves out of tracheoles through osmosis, this means there is more surface area for gas exchange

adaptations of the gills

• many lamellae and overlapping gill filaments provide large surface are for high rate of diffusion

• gill filaments are thin providing a short diffusion distance

• good blood supply from surrounding blood vessels to maintain a steep concentration gradient

• diffusion occurs in a counter current system also maintaining a steep concentration gradient

cardiac output

beats per minute x stroke volume