Salinity

Question 1

Salinity

Answer 1

• a measure of how much salt is dissolved in the ocean
• Average salinity in ocean is 35 parts per thousand (PPT)
• High salt means low amount of freshwater (FW)
• Low salt means high amount of freshwater (FW)
• Organisms want to reach homeostasis (constant condition)
• diffusion: movement of molecules from area of high conc to area of low conc until equilibrium is reached
• osmosis: diffusion of water from area of high conc to low concentration
• Salt particles do not move across membrane

Question 2

FW fish in seawater

Answer 2

• FW fish has an internal salinity of 14 ppt, far less than that of seawater (SW) (35 ppt) so more salt outside of the fish body
• FW fish has more FW inside its body than there is in SW
• The FW wants to move from high to low conc (osmosis), therefore, FW diffuses out of the fish, it dehydrates and dies

Question 3

SW fish in freshwater

Answer 3

• SW fish has an internal salt conc (35 ppt) greater than the external environment (0 ppt)
• SW fish has less FW inside of it than there is in the outer environment
• Therefore FW flows, or diffuses, into the SW fish (osmosis), causing the SW fish to swell and expand, die

Question 4

Salmon going from FW to SW

Answer 4

• drinks SW and filters out the salt, keeping the FW left over
• Excess salt is excreted by chloride cells in gills
• Produces concentrated urine (lots of salt)- conserves FW

Question 5

Salmon going from SW to FW

Answer 5

• produce lots of dilute urine (lots of FW)
• absorb salts through chloride cells in gills (more salt in their bodies means less FW)
• get salts from fish