surface area to volume ratio

Question 1

what does the requirement to exchange substances and energy depend upon ?

Answer 1

it depends upon the size of an organism

Question 2

the bigger an organism is….

Answer 2

the smaller the SA: vol ratio is

Question 3

what are 2 examples of successful single celled organisms ?

Answer 3

• amoeba
• Euglina

Question 4

what are the features of a euglina that allow it to be so successful ?

Answer 4

• single celled therefore low requirements (not many mitochondria )
• single celled so its size is microscopic and has a large SA:vol ratio
• short pathway
• steep conc gradient

Question 5

state Ficks law in terms of diffusion

Answer 5

rate of diffusion is proportional to (SA x diff in conc) / size of pathway

Question 6

however in what environment can single celled organisms only exist in ?

Answer 6

water
- because the rate of evaporation is high due to their large surface area to vol ratio

Question 7

what must large multicellular organisms have to increase their rate of exchange ?

Answer 7

adaptations

Question 8

multicellular organisms that have layers of cells must have adaptations like organs to: (3)

Answer 8

• increase surface area
  -decrease size of exchange pathways
• increase the diff in conc / heat

Question 9

what do large multicellular organisms often need and what for ?

Answer 9

these organisms often need a circulator system to transport materials and energy through layers of cells

Question 10

example of adaptations
human tapeworm

Answer 10

-it meets all of its low requirements through simple diffusion
- its long and thin so it has a large sa:vol ratio

Question 11

examples of adaptations (cold environment )
arctic fox

Answer 11

-large sized organisms = small SA:vol ratio
-radiates less heat into the environment as it needs to use that energy for processes such as respiration
- the fur traps warm air next to the skin
- thick layer of fat increases pathway for heat exchange
- small features e.g small ears further reduces the surface area for heat exchange

Question 12

adaptations (warm environment)
e.g fennec fox

Answer 12

-large features e.g large ears increase surface area for heat exchange
- small size = large SA:vol ratio
-thin layer of fat provides a short pathway for exchange

Question 13

hat special feature do elephants have ?

Answer 13

• they have large ears for heat exchange
  their ears constantly move to waft the layer of hot air away in order to provide a conc gradient