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

oh god, i really don't know them much at all! thanks anyway and good luck tomorrow

Thanks a lot really appreciate it!!

btw is the xylem vessel the same as the capillary tube?

Explain why the values for the pressure in the xylem are negative.

They're the worst! Who even cares about plants? I'm starting a Human Biology degree in September and chose it so I never had to work with plants again!

xylem pressure is lower than atmospheric pressure I remember memorising this from a markscheme

Well with haploid cells, all you need to know is that during Meiosis you half the number of chromosomes, which results in these type of cells.

With crossing over which occurs in the division of cells, is basically the chromosomes cross to form bivalents where genetic information is exchanged between them in a process known as genetic recombination. You will have different alleles but the same genes.

With Independent assortment when the homologous chromosomes line up during the first division they segregate randomly, there are millions of possible combinations of chromosomes in each nucleus.

This in all increases genetic diversity

Hope this helped

Good luck


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Haha, LOL. Good riddance, goold luck tomorrow.

no, only cohesion-tension is negative

Right, I think I've got it thanks.

Can anybody explain what root pressure is exactly?

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Right, I think I've got it thanks.

Can anybody explain what root pressure is exactly?

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Right, I think I've got it thanks.

Can anybody explain what root pressure is exactly?

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the endodermis will first actively transport mineral ions into the xylem. This will lower the water potential of the xylem and so water will enter the xylem by osmosis and down a water potential gradient. This water is then pushed up the xylem, which is why it's called root pressure.

Root pressure is a force which pull up water from the xylem to the leaves.

Active transport of ions/salts into the xylem
Lower water poetical
Water moves into xylem by osmosis
This creates a transpiration pull of water to the leaves, where the water is then transpired




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Thank you!

When the water is pushed up the xylem, is this cohesion tension due to the transpiration pull?

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nope, root pressure is just because of root pressure, so root pressure isn't strong enough to push water all the way up the xylem because only cohesion tension (the stronger pull) can do that. At least that's what my teacher said anyway.