Exchange between organisms and their environment Condensed Notes

Exchange between organisms and their environment
● Exchange
○ Digestive system
○ Human lungs and gas exchange
○ Plant gas exchange
○ Single celled/insects gas exchange
○ Fish gills
● Exchange surfaces
● Mass transport in animals
○ Haemoglobin
○ Circulatory system
○ Heart and cardiac cycle
● Mass transport in plants
○ Xylem - transpiration
■ Xerophytes
○ Phloem - translocation


● External vs internal environment
○ To survive, organisms transfer materials across plasma membranes between the
two environments
○ As animals increase in size, the ratio of their surface area to volume ratio
decreases e.g a baby has a larger SA to V ratio
○ For effective transfer
■ Larger surface area
■ Very thin - short diffusion distance
■ Selectively permeable
● Fick’s law




● Gas exchange
○ Single celled organisms
■ Diffusion over a large surface area
○ Insects
■ Trachea and tracheoles
■ Spiracles
■ Respiration gases move in and out of the tracheal system in 3 ways
● Along a diffusion gradient
● Mass transport
● The ends of the tracheoles are filled with water

, ○ Fish




■ Gills
■ Gill filaments
■ Gill lamellae
■ Countercurrent flow
● The countercurrent exchange principle