OCR AS Biology (F211) - Jan 2013.

Can water pass through the phospholipid bilayer?

Posted from TSR Mobile

There's nothing about water in the text book. Oxygen, carbon dioxide and lipid-based molecules like steroid hormones can just simply diffuse through the bilayer. :smile:

Reply 781

SuperMushroom

9

Can someone help me with calculating things such as:

Magnification
image size
actual size

I know the formulae to use, but dont get how you get the answers like in MM UM stuff like that
any help would be much appreciated thanks!

Reply 782

theworld

Original post by Jrph

Here is a diagram which I hope explains it better than what I can...

That did help me a lot. thank you. But I still think the arrow on the exam paper should be a bit shorter pointing to the outside CLEARLY and not going inside at all.. because tbh i couldnt tell which one was which, dont you think? :frown:

Reply 783

priya8D

9

Original post by Jrph

How do you calculate oxygen consumption?

Is that the same as oxygen uptake?

(amount of oxygen in dm^3 x 60)/seconds

Please correct me if I'm wrong but this is in the specification.

Reply 784

HeyMickey6

Original post by Jrph

What are homologous pairs and what are alleles?

They are chromosomes that have the genes in the same position ,but the gene in the chromosomes are different variations (alleles) of each other.

For EXAMPLE : the position of the gene that determines your hair colour is in the same section for both chromosomes but one gene has coding for blonde colour hair and the other gene has coding for black colour hair.

Reply 785

joef1134

Could someone describe water transport in plants (root,stem etc) please as simple as possible please?

Reply 786

SomePotential

4

Original post by wannabe med doc

Can water pass through the phospholipid bilayer?

Posted from TSR Mobile

A small amount of it can pass through the plasma membrane by Osmosis, as even though it is a polar molecule, they have enough energy to diffuse through occasionally. However, water can pass through much faster (~ 1000 times faster, iirc) when facilitated by the channel protein aquaporins which are found in some plasma membranes.

What is mass flow?

Original post by theworld

That did help me a lot. thank you. But I still think the arrow on the exam paper should be a bit shorter pointing to the outside CLEARLY and not going inside at all.. because tbh i couldnt tell which one was which, dont you think? :frown:

Oh I see what you mean now. Yes, I definitely agree!

Reply 789

Jrph

Original post by Uniiverse

What is mass flow?

Mass flow is when solutes are actively loaded in the sieve tube element. This lowers the water potential inside the sieve tubes at the source end of the phloem, so water enters by osmosis. This creates a high hydrostatic pressure inside the sieve tubes at the source end of the phloem.

At the sink the solutes are removed from the phloem to be used up. This increases the water potential inside the sieve tubes at the sink end of the phloem, so water leaves by osmosis. This lowers the hydrostatic pressure at the sink end of the sieve tube.

This results in a pressure gradient from the source end to the sink end. The gradient pushes solutes along the sieve tubes to where they're needed.

Reply 790

JamesNeedHelp2

5

Does anyone know how to calculate breathing rate, and can anyone please tell me what past paper a breathing rate question has come up?

Reply 791

Jrph

Original post by priya8D

Is that the same as oxygen uptake?

(amount of oxygen in dm^3 x 60)/seconds

Please correct me if I'm wrong but this is in the specification.

Yes it is and yes you are correct... I just found an example of it :smile:

Reply 792

otrivine

14

Original post by JamesNeedHelp2

Does anyone know how to calculate breathing rate, and can anyone please tell me what past paper a breathing rate question has come up?

want to revise?

Reply 793

priya8D

9

Original post by JamesNeedHelp2

Does anyone know how to calculate breathing rate, and can anyone please tell me what past paper a breathing rate question has come up?

On the spec it says,
number of breathes divided by time in mins.
I haven't come across a breathing rate question :s-smilie:

Reply 794

Jrph

Original post by HeyMickey6

They are chromosomes that have the genes in the same position ,but the gene in the chromosomes are different variations (alleles) of each other.

For EXAMPLE : the position of the gene that determines your hair colour is in the same section for both chromosomes but one gene has coding for blonde colour hair and the other gene has coding for black colour hair.