Presbyterian Prelim 2018, q.14 [multiple choice] (1 Viewer)

[jane1820]

can someone please explain this graph? i dont get it, i thought the answer mightve been 600 cm^3 because 3hrs into adding light oxygen absorbed increased to 600 cm^3 (A) but the answer said 1800 cm^3 (D)

 

[Hehehe22]

Ooh this one's confusing. It's 1800 cm^3 because I think it's talking about the rate of release of oxygen. The total oxygen released would be the area under the curve at that point, which is 600 x 3

 

[Eagle Mum]

Yes, for the last three hours, the plant has been producing 600 cm^3 of oxygen per hour. Therefore, the total amount of oxygen produced by the plant in the last three hours is 3 x 600 = 1800 cm^3.

 

[Eagle Mum]

They made the qualifying statement about respiration because plants can perform simultaneous processes of respiration (which consumes oxygen) and photosynthesis (which produces oxygen), so the net amount of oxygen may be 1800 cm^3 (which they can measure), but the actual amount produced is higher because some of what is produced is consumed. I think they should just have referred to the measured amount of oxygen as the net amount, rather than qualify the question with incorrect ‘if’ statements.