Size and Surface Area Flashcards
How do single celled organisms obtain nutrients and excrete waist
by diffusion e.g. Bacteria and Amoeba are single celled
Why are single celled organisms able to obtain nutrients and excrete waist simply by diffusion
Because they have a large surface area to volume ratio, so the diffusion path is short
Other than single celled organisms, what other organisms have a high surface area to volume ratio
Flatworms (because they’re flat) and Hydra (because they’re hollow)
What do multi cellular organisms require for the transport of substances
A more specialised transport system than single celled organisms
Why would diffusion of substances not work in larger organisms
The rate of diffusion would occur far too slowly to enable them to survive: the rate of diffusion increases with the square of the distance it has to travel
What do all cells need to survive
A supply of oxygen and nutrients
Why does diffusion of substances work in small organisms
The cells in small organisms are all close to the environment they are in, so diffusion alone allows substances to enter and leave
What affects the need for a transport system
Size, surface area to volume ratio and level of activity
What does a small surface area to volume ratio (found in large organisms) result in
A large diffusion pathway
How does level of activity effect the need for a transport system
Respiration requires oxygen, if an animal is more active, more energy is required, therefore more oxygen is needed
What is large surface area in an exchange surfaces provided by
The body surface in small organisms or by folding of the exchange surface
Are exchange surfaces generally permeable
Yes
Where is diffusion efficient and how are exchange surfaces adapted to this
Diffusion is only efficient over short distances (<1mm). Therefore, exchange surfaces are generally thin
What is the relationship between rate of diffusion and distance
Rate is inversely proportional to square of the distance
What do substances diffuse in and how are exchange surfaces adapted to this
O2, CO2 and nutrients diffuse in solution. Therefore, exchange surfaces are generally moist
What mechanisms to maintain diffusion gradients do exchange systems have
Transport system, ventilation mechanism or creation of currents across surface
List all the general features of exchange surfaces
Large surface area to volume ratio, Permeable, Thin, Moist, Mechanisms to maintain diffusion gradients
