AQA BIOL2~3rd June 2013~AS Biology (Now Closed)

might as well answer, as it helps me revise as well as you.

Basically for the transpiration question, water evaporates first from the surface of the leaves which lowers the water potential of the leaves. This causes water to be pulled up the xylem by tension and all the water molecules cohesively stick together due to hydrogen bonding. Also, the water molecules are in adhesion with xylem walls which creates a single water column. This is the cohesion-tension theory.

In regards to the potometer question, it's about the air bubble moving inside the tube. So the shoot is dispensed in water and as it transpires water is pulled up the xylem so the bubble will move towards the xylem, so to calculate the rate of water uptake you'd do calculate the distance and surface area of the leaves. To make sure the potometer investigation is reliable though you have to make sure all the apparatus is sealed, there are no air bubbles and that the shoot is placed in water. All the leaves also need to be dry. The investigation might not be an accurate indicator though of water uptake because the apparatus might not have been sealed, air bubbles might have been present in the xylem vessel and some water is lost during photosynthesis. Hope that helps.

Thanks!!!, http://filestore.aqa.org.uk/subjects/AQA-BIOL2-QP-JAN12.PDF question 3aii?

Thanks!! . http://filestore.aqa.org.uk/subjects/AQA-BIOL2-QP-JAN12.PDF

3aii?

what is the difference between the casparian strip and the endodermis

very much appreciated

Glad I could help
Mochokus niloticus, because it branched off first which means that other catfish evolved from it a long time ago.

How do you ensure that the potometer is air tight - i thought if you are cutting the leaf inside the potometer isn't there going to be some space for air to enter - how do you make sure it is air tight?

is the june 2009 paper the earliest past paper? I can't seem to find the jan 2009....does anyone have it?

Cut leafy shoot under water

Can somebody please just go over what we need to know about cancer for the exam? D:

If you remove leaves - I understand that fewer stomata and smaller surface area reduce transpiration rate - but how is there a less cohesion/tension force?