Exchange between organisms and their environment

Question 1

what two ways can exchange take place?

Answer 1

• actively (active transport)

- passively (diffusion, osmosis)

Question 2

what things need to be exchanged between an organism and its environment?

Answer 2

• respiratory gases (oxygen, carbon dioxide)
• nutrients (amino acids, glucose)
• excretory products (urea, carbon dioxide)
• heat

Question 3

what is needed for exchange to be effective?

Answer 3

the surface area of the organism must be large compared with it’s volume

Question 4

why is it as an organism gets bigger the gas exchange becomes less efficient?

Answer 4

as they become larger, their volume increases at a faster rate than their surface area, simple diffusion can’t meet all their needs
it would take too long to reach the middle of the organism

Question 5

how have organisms evolved to overcome gas exchange becoming less efficient?

Answer 5

• a FLATTENED SHAPE so no cell is ever far from the surface eg flatworm
• SPECIALISED EXCHANGE SURFACES with large areas to increase the surface area to volume ratio eg gills in fish

Question 6

what are the features of specialised exchange surfaces?

Answer 6

• A large SA:V ratio
• Very thin diffusion distance
• Partially permeable
• Movement external medium
• Movement internal medium

Question 7

what is diffusion proportional to?

Answer 7

     length of diffusion pathway

Question 8

why are specialised exchange surfaces often located inside an organism?

Answer 8

they are easily damaged

Question 9

how do large organisms increase their SA:V ratio?

Answer 9

• many alveoli
• many filament e.g. fish
• elongated/ flattened shape
• many TRACHAE in insects
• leaves- gas exchange spongy mesophyll, air spaces

Question 10

what is the calculation for volume?

Answer 10

length x width x height

Question 11

what is the calculation for ratio of surface area to volume?

Answer 11

surface area DIVIDED BY volume