AS (Biology) P1 MCQs Preparation Thread.

[vivilow]

q29 - water potential is most negative when it has the most sucrose concentration. Since sucrose is produced at the leaf, B would be the correct choice. A cannot be correct because if the mesophyll cell was indeed the most negative, water would pass into the cell which is not what the cell needs. For mass translocation to occur, B needs to be more negative, so that the sucrose travels downwards towards the roots to relieve the hydrostatic pressure.

q30 - When cutting the stem near base, the pressure difference would become different, which forces sap out of the stem. For the fourth statement - Although there is a high humidity, transpiration is still occurring because pressure at the roots is higher, so water would pass upwards.

thank you!! all understood

 

[SalmaXXXX]

Can anyone explain me question 25?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_1.pdf

The answer is D. Why would the circumference increase if no water flows through the xylem? Circumference is directly proportional to diameter, so I can't figure out why would diameter increase when no water flows

I've been trying to figure that out, too. So, I think that since since the transpiration rate is minimum, water is not sucked up by transpiration pull force that fast so more water liger in the xylem vessel with the adhesive forces so pressure is applied on the walls of the xylem and the diameter increases. Water should be sucked as a continuous column that can't be broken, water is always present in the xylem. so I think that that since no transpiration occurs, no difference in pressure is maintained and water stays in the xylem.
Hope I helped.

 

[vivilow]

Can anyone explain me question 25?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s09_qp_1.pdf

The answer is D. Why would the circumference increase if no water flows through the xylem? Circumference is directly proportional to diameter, so I can't figure out why would diameter increase when no water flows

I've been trying to figure that out, too. So, I think that since since the transpiration rate is minimum, water is not sucked up by transpiration pull force that fast so more water liger in the xylem vessel with the adhesive forces so pressure is applied on the walls of the xylem and the diameter increases. Water should be sucked as a continuous column that can't be broken, water is always present in the xylem. so I think that that since no transpiration occurs, no difference in pressure is maintained and water stays in the xylem.
Hope I helped.

when transpiration occurs, the cohesive and adhesive forces pull the xylem vessels in thus decreasing the diameter of the trunk. when transpiration is minimum this tension is released so diameter increases.

 

[1357911]

o/n 2012 varient 11 q-33,36,and 40......... SOMEBODY PLZZ HELP

 

[mushu.jr]

How to solve this

 

[potatocorn12]

How to solve this View attachment 63050

most prolly its A because the water potential of cell sap must be less than the one in soil to maintain a gradient so that ions and minerals can easily move into cell sap.Hence -60 would be ideal. But just recheck the answer i m kinda confused because it can be C too but-20kpa means water would move out of cell to soil