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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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Original post by al_habib
thanx for that, i'll do the paper tomorrow and i'll let you knw any problems that will crop up.have you finished ol bio Past papers..:smile:


onlii the 4 available
Reply 321
Original post by aa_6
Can someone please explain how water is transferred up from the xylem? I believe there are two ways. Can you also make your answer specific to what the markscheme answer for such a question would be.

:smile:


Well, the water can be transferred up by two methods: cohesion-tension, and root pressure.

The first method involves the evaporation of water from the mesophyll cells of the leaf by transpiration. This lowers the water potential in the cells of the leaf to a level lower than in the xylem. Water than flows out of the xylem by osmosis into the leaf. As water is a cohesive molecule due to H+ bonding, a tension is applied to the water and the entire column is pulled up. This is the main way in which plants transport water through the xylem.

The second method is root pressure. This is caused when ions are actively transported out of the endodermis of the root and into the xylem. This causes the water potential in the xylem to decrease, which then causes water to flow into the xylem by osmosis, which exerts a pressure on the water column, causing it to be pushed up. This is the main method of water transport in seedlings and new plants, but in older and larger plants who have a much longer water column, root pressure is in inadequate to provide the force required to transport water to the top of the plant.
Reply 322
Some questions for you all:

Describe the structure of haemoglobin and how it is involved in the absorption of oxygen and transporting it to respiring tissues. [8 Marks]

Describe cellulose and how it is adapted for it's presence in cell walls [4 marks]

Explain how genetic diversity can be reduced [6 marks]

Explain why diversity of species in natural woodland is higher than on farmland [4 marks]

Explain how courtship behaviour can be used to identify species.

Explain the adaptations of arteries, veins and capillaries and how this makes them suited for their function [8 marks]

Explain the process of meisos, and how it leads to genetic variation in gametes.

Explain the process of mitosis, and how it leads to genetically identical daughter cells.
(edited 12 years ago)
'Suggest why antibiotics may be used successfully to treat viral diseases.' :confused:

This question stumps me.

Also, what is the different haemoglobins about? I thought all haemoglobin change their shape and affinity under certain conditions e.g. in the presence of carbon dioxide............but the book says there are 2 different types i.e. those with a high affinity for oxygen and those with a low affinity for oxygen........seems a bit of a contradiction?
Original post by xkate1019x
Haemoglobin

Are my Facts correct? I'm a bit unsure on my termonology...

- Haemoglobin is a protein
- It is made up of 4 polypeptide chains (quartenary structure)
- Each polypeptide has a haem group (non protein ), which contains iron
- It is hard for oxygen to bind with haemoglobin but when the first haem binds to oxygen, the structure of the polypeptides change to make the haemoglobin have a high affinity for oxygen.
- A haemoglobin with a high affinity for oxygen takes up oxygen more easily, but released it more readily. (e.g. in the lungs)
- when one oxygen molecule is released from the haem group, it changes the shape of the haemoglobin structure, and makes it easier for the other 3 to be released, giving it a low affinity for oxygen
- a low affinity for oxygen means the haemoglobin takes oxygen up less easily but released it more readily easily (e.g. in a quickly respiring muscle)

Thanks in advance :smile:


I think you mixed up with the words readily and easily. The both have the same meaning.

So...:ms:

Haemoglobin with high affinity loads oxygen more readily/easily and unloads less readily/easily.

Haemoglobin with low affinity loads oxygen less readily/easily and unloads more readily/easily.
Original post by Introverted moron
'Suggest why antibiotics may be used successfully to treat viral diseases.' :confused:

This question stumps me.

Also, what is the different haemoglobins about? I thought all haemoglobin change their shape and affinity under certain conditions e.g. in the presence of carbon dioxide............but the book says there are 2 different types i.e. those with a high affinity for oxygen and those with a low affinity for oxygen........seems a bit of a contradiction?


Antibiotics will kill bacteria. Bacteria is sometimes the site of which viruses can be taken in and modified to form new strands of viruses or reproduce the orignal virus. (I can't explain the theory as it is 'suggest'). Therefore in killing these bacteria would avoid production of viruses hence treating the viral disease. This is little from HSW from NT text book and most from my mind and not entirely sure..:frown:

There are many types of haemoglobin (Hb), this depends on on the DNA that has coded for it. Each Hb organism contains Hb best suited to the environment they live in and can only have that one structure of Hb through out all the RBC.
Example: People in high altitude have Hb with higher affinity for oxygen than people living in lower altitude, due to lack of abundant oxygen.

-In the other hand that single type of Hb can change its shape slightly in response to CO2 levels. (will not go through the process).

Hope you understand now.:wink:
(edited 12 years ago)
Original post by Introverted moron
'Suggest why antibiotics may be used successfully to treat viral diseases.' :confused:


Are you sure the question is not, suggest why antibiotics cannot be used to treat viral diseases ?
Original post by ChessMister
Are you sure the question is not, suggest why antibiotics cannot be used to treat viral diseases ?


Yeah, viruses can't be treated with antibiotics only bacteria can.
why cant antibiotics treat viral infections? is it because viruses have no cell wall so will not be made permeable?
Original post by jessplease
why cant antibiotics treat viral infections? is it because viruses have no cell wall so will not be made permeable?


they have a different type of cell wall
Hellooo :smile:

I know this is a really simple question but my teacher managed to confuse me! :tongue:

What is the definition of transpiration??

In the textbook, it says it the evaporation of water from the surface of a plant... but apparently this doesnt get you the marks?? You have to say something to do with the movement of water through a plant??

Does anyone have a defintion that is sure to get you marks??
(even with AQA being very pedantic with their keywords :rolleyes: )
Reply 331
Evapouration of water moving out the surface of the leaf by osmosis?
Tricky!!
Original post by Sockhead
Evapouration of water moving out the surface of the leaf by osmosis?
Tricky!!


Thats what I thought, but apparently that doesnt get you any marks...

(although my teacher may have been talking rubbish...:rolleyes: )
Original post by spoinkytheduck
Hellooo :smile:

I know this is a really simple question but my teacher managed to confuse me! :tongue:

What is the definition of transpiration??

In the textbook, it says it the evaporation of water from the surface of a plant... but apparently this doesnt get you the marks?? You have to say something to do with the movement of water through a plant??

Does anyone have a defintion that is sure to get you marks??
(even with AQA being very pedantic with their keywords :rolleyes: )


Transpiration is just the uptake of water through the plant. :tongue:
Original post by awais590
Transpiration is just the uptake of water through the plant. :tongue:


So it is the definition is talking about the uptake of water rather than the water leaving the plant...?

Okey doke :smile:

Ha, I feel so simple :tongue:
I have two questions :smile:
What is meant by the term 'hierarchy'? and how do you work out the image size, as in whats the formula and do you convert micrometers in mm, I am rather confused :L thanks in advance
Original post by spoinkytheduck
So it is the definition is talking about the uptake of water rather than the water leaving the plant...?

Okey doke :smile:

Ha, I feel so simple :tongue:


Lol,


Definition of Transpiration:

Uptake of water through the plant. :wink:
Original post by PumbaWiggles
I have two questions :smile:
What is meant by the term 'hierarchy'? and how do you work out the image size, as in whats the formula and do you convert micrometers in mm, I am rather confused :L thanks in advance


Heirachy is just 'a group within groups', it represents the classification groups of 'Kingdom, Phylum, Class etc'.

'A big group containing smaller groups'

Hope that made sense? :confused: :tongue:
Original post by Insanity514
Could someone explain answer of question 5dii in the June 2010 paper please?

Also what does the term degenerate mean for DNA base sequences?


There are three chromosomes in the question. On lining up during meiosis metaphase 1, any chromosome in given particular position could either be one of two: paternal or maternal. The number of combinations possible therefore is 2 to the power of 3, which is 8.
Similarly you can apply combinations to why DNA is a triplet code. There are 4 possible bases to choose from, if we want a code of 3 out the 4 we can have 4^3=64 combinations. This gives a surplus of codes which can accommodate all 20 amino acids known to exist.
Basically, take your base as what a thing can be, e.g. maternal or paternal = 2, A C G or T = 4 and have your index as how many things there are.
Original post by awais590
Heirachy is just 'a group within groups', it represents the classification groups of 'Kingdom, Phylum, Class etc'.

'A big group containing smaller groups'

Hope that made sense? :confused: :tongue:


haha it made sense, thank you :smile:

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