A level Biology: Post your doubts here!

[qwertypoiu]

The cell surface membranes of plants adapted to cold conditions change as the weather gets colder, allowing the plants to carry out exocytosis. Which change occurs?
A a decrease in the ratio of proteins to saturated phospholipids
B a decrease in the ratio of unsaturated phospholipids to saturated phospholipids
C an increase in the ratio of proteins to unsaturated phospholipids
D an increase in the ratio of unsaturated phospholipids to saturated phospholipids

It should be D, since in cold conditions, fluidity of the cell membrane decreases.
Unsaturated phospholipids have unsaturated fatty acid tails, which have a "kink" in their shape, and make the bilayer more fluid.

 

[qwertypoiu]

View attachment 52547

It should be A. All structures are important in keeping the exact 3-D figure of the enzyme.

 

[nehaoscar]

http://www.cie.org.uk/images/157397-november-2012-question-paper-22.pdf

Question 5 part B please explain!
I know that p.d
AC = 4.8V
BC = 7.2V
AD = 8V
BD = 4V

Now it's asking pd between CD so wouldn't CD be either CB + BD
or CA + AD

But the answer is 3.2V which means they are subtracting... why??

 

[My Name]

http://www.cie.org.uk/images/157397-november-2012-question-paper-22.pdf

Question 5 part B please explain!
I know that p.d
AC = 4.8V
BC = 7.2V
AD = 8V
BD = 4V

Now it's asking pd between CD so wouldn't CD be either CB + BD
or CA + AD

But the answer is 3.2V which means they are subtracting... why??

Post your doubt here:
https://www.xtremepapers.com/community/threads/physics-post-your-doubts-here.9860/

 

[nehaoscar]

Post your doubt here:
https://www.xtremepapers.com/community/threads/physics-post-your-doubts-here.9860/

sorry! i accidentally posted it here... do you do physics though?

 

[My Name]

sorry! i accidentally posted it here... do you do physics though?

Its alright. I can't help you at the moment.
But do this might:
http://physics-ref.blogspot.com/2014/06/9702-november-2012-paper-22-worked.html

 

[Mahnoorfatima]

What do I write for this question: Sucrose is one of the assimilates transported in phlowm sieve tubes of plants from source to sick. Sucrase is found in sinks. Suggest the role played by sucrase in the process of unloading of sucrose at sinks? 2 marks??
And there's this other question : Some large animals feed on more than one trophic level. Suggest why? In MS it's written about the energy losses occuring all the way up to such a high trophic level and how large animals spend more energy in catching animals.
Can we write about how large animals are more metabollicaly active and respire more or that would be wrong?

 

[ashcull14]

,

Not really sure but It can't be related to size of chromosomes etc because that takes place in during the S Phase not 'division'. I guess C is incorrect becuz centrioles speed up eukrayotic division coz of the movement of organelles etc, they are saying prokaroytes are faster, so it can't be a reason . But to why D is wrong, the only logical explanation would be becuz as the cells are smaller maybe everything will be relative, for ex small conc of enzymes etc.
But A is correct becuz the eukaryotes still have to break down the nuclear membrane whereas Prokaryotes can just replicate their DNA and divide directly.

got it ty

 

[ashcull14]

It should be D, since in cold conditions, fluidity of the cell membrane decreases.
Unsaturated phospholipids have unsaturated fatty acid tails, which have a "kink" in their shape, and make the bilayer more fluid.
View attachment 52561

ty so nice of u

 

[ashcull14]

What do I write for this question: Sucrose is one of the assimilates transported in phlowm sieve tubes of plants from source to sick. Sucrase is found in sinks. Suggest the role played by sucrase in the process of unloading of sucrose at sinks? 2 marks??
And there's this other question : Some large animals feed on more than one trophic level. Suggest why? In MS it's written about the energy losses occuring all the way up to such a high trophic level and how large animals spend more energy in catching animals.
Can we write about how large animals are more metabollicaly active and respire more or that would be wrong?

i think sucrase like invertase IS responsible for hydrolysis of sucrose . it converts sucrose to glucose and fructose to decrease its concentration to maintain the concentration gradient..

 

[cadburrylover]

can someone give me the answer to this question: Discuss ethical implications of gene technology?

 

[ashcull14]

shudnt it be C.......temp doesnt the increase the product conc ryt?? it only speeds up the product formation then hws A the ans?

 

[ashcull14]

15 Which role of the cell surface membrane is not a result of the properties of the phospholipids?
A to allow cytokinesis to occur in mitotic cell division
B to allow entry and exit of the water-soluble gases, oxygen and carbon dioxide
C to allow phagocytosis of a bacterium into cells
D to allow surface membranes to stabilise by binding with water molecules

 

[qwertypoiu]

View attachment 52562
shudnt it be C.......temp doesnt the increase the product conc ryt?? it only speeds up the product formation then hws A the ans?

Remember the enzyme becomes denatured in the middle!!
(if still not clear ask again i'll explain)

 

[qwertypoiu]

15 Which role of the cell surface membrane is not a result of the properties of the phospholipids?
A to allow cytokinesis to occur in mitotic cell division
B to allow entry and exit of the water-soluble gases, oxygen and carbon dioxide
C to allow phagocytosis of a bacterium into cells
D to allow surface membranes to stabilise by binding with water molecules

This is D.
Allowing the cell to stabilize by binding with it was one of the functions of glycoproteins and glycolipids, not the phospholipid.

 

[qwertypoiu]

What do I write for this question: Sucrose is one of the assimilates transported in phlowm sieve tubes of plants from source to sick. Sucrase is found in sinks. Suggest the role played by sucrase in the process of unloading of sucrose at sinks? 2 marks??
And there's this other question : Some large animals feed on more than one trophic level. Suggest why? In MS it's written about the energy losses occuring all the way up to such a high trophic level and how large animals spend more energy in catching animals.
Can we write about how large animals are more metabollicaly active and respire more or that would be wrong?

As ashcull said sucrase is present at the sink so that the concentration gradient from phloem sieve tube to the sink remains, so that sucrose can move.
As for your second question, you can add that but you really should mention the energy loss down the food chain, since this is in our syllabus.

 

[Mahmood Magdy]

can someone give me the answer to this question: Discuss ethical implications of gene technology?

Is your question about a specific section in the Gene technology? Because it is pretty vague...
Some points may include transfer of genes by conjugation and transduction from from one bacterial cell to the others, super weeds, reduction in bio-diversity, allergic reactions etc
If it is about insulin then Gene tech is on the good side as many ethical issues arise due to the use of 'pig' and 'cow' insulin. There are many other points though

 

[ashcull14]

Remember the enzyme becomes denatured in the middle!!
(if still not clear ask again i'll explain)

but y does product conc increase?

 

[ashcull14]

This is D.
Allowing the cell to stabilize by binding with it was one of the functions of glycoproteins and glycolipids, not the phospholipid.

but isnt this so tht the phospholipid molecules form hydrogen bonds with water?? as they r hydrophilic

 

[oahmed64]

The process of extraction of metals using bacteria is known as Bio-leaching. Chemoautotrophic bacteria, which obtain their energy from oxidation reactions, such as A.ferrooxidans are used to extract the metals of Copper, zinc, gold, silver etc from their low grade ores. The insoluble ore is turned to soluble ore. First of all, the ore is piled up, followed by creating acidic conditions (pH 1.5-3). Different types of bacteria can be used, not just one. The reaction is highly exothermic. The reaction could be direct oxidation from Sulfide to Sulfate , Ferrous to Ferric. Products are washed in pools and the metal is displaced by adding scrap iron.

Mahmood Magdy, thanks for answering, could you PLEASE answer my question again ?

One thing I do not understand is what does it mean when they say in the mark scheme that ferric oxidizes other ores ? does this mean that the bacteria oxidizes ferrous to ferric and then ferric oxidizes sulfide to sulfate ? I dont understand this part at all,please answer me .

Thank you