Question

5) A salmon enters murky water at the mouth of a river; the overall osmolarity in this spot where ocean and fresh water intermingle is about 800 mosm. Its body fluids have an osmolarity of about 300 mosm. As it swims around this stretch of water, what will the osmotic pressure difference be?

a) 1 atm

b) 6 atm

c) 12 atm

d) 18 atm

e) 24 atm

8) When the hormone ADH is present in the blood, the permeability of the collecting duct to water _____ and the measured value of the osmolarity in the lumen of the collecting duct _____.

a) increases; increases

b) increases; decreases

c) decreases; increases

d) decreases; decreases

e) does not change; does not change

12) A genetic abnormality that resulted in constitutive (continuous) overexpression of aquaporins into the plasmamembrane of epithelial cells of the descending limb of the loop of Henle would likely result in

a) large amounts of glucose in the urine

b) a very dilute urine

c) a very concentrated urine

d) an osmolarity of about 300 at the bottom (lower medulla) portion of the loop of Henle

e) an osmolarity of about 1400 at the bottom (lower medulla) portion of the loop of Henle

20) The enzyme phosphofructokinase plays an important role in the glycolytic pathway, converting fructose 6 phosphate to fructose 1,6 bisphosphate. Stimulation of this pathway leads to the production of pyruvic acid, which ultimately produces high levels of ATP. ATP can bind to the enzyme phosphofructokinase and slow down its activity. This type of regulation is likely to result in

a) an increase in Vmax

b) a decrease in Km

c) a decrease in Vmax and Km

d) a decrease in Vmax

e) Vmax and Km are likely to remain the same

Answer 1

Ans 1- option (c) is correct.

Since , osmotic pressure difference = 19.3* osmolarity difference.

So osmotic pressure= 19.3*500 =9650 mmHg

So, osmotic pressure difference in atm = 9650/760= 12.6

Which is approximately equal to 12 atm .

Ans 2-option (a) is correct.

Since ADH binds to receptors on the cells in collecting ducts of the kidney and increases reabsorption of water back into the circulation, which increases osmolarity of urine in the lumen of collecting duct.

Ans 3-option (c) is correct.

Since ADH acts on aquaporins hence increases the water reabsorption making the urine very concentrated.

Ans 4-option (d) is correct.

Since binding of ATP to enzyme phosphofructokinase and it's inhibition is a type of allosteric or non competitive inhibition , in which km remains constant while Vmax decreases.