A level Biology: Post your doubts here!

[sagystu]

help biology activation energy

could some one help explain this graph
especially why does energy level decrease again
and why energy level in products lower than reactants ( when lower and when higher )

 

[sagystu]

Re: help biology activation energy

the attachment is an image save it on ur pc so u could see it as the back ground is black and the graph is drawen in black too

 

[sagystu]

Re: help biology activation energy

also you may see the 2nd graph diagram in this page http://www.avogadro.co.uk/definitions/hactivation.htm
or this link http://en.wikipedia.org/wiki/File:Activation_energy.svg


same question why energy decrease after reaching topp of graph


HELP PLEASEEE

 

[Dayyanah]

for anyone like me who needs help with synapses

 

[princesszahra]

^great!!

and i think its written very well in mary jones

 

[Dayyanah]

yeah... tried tht lyk a million tyms, i cant download if for some reason evn with the mega upload account... but thnx
i got another pic tht explains it all really well..

 

[VelaneDeBeaute]

What happens to the nucleolus in the late prophase?
In Mary Jones book, it is written that nucleolus disappears and forms part of several chromosomes! What is meant by the bold text?

 

[Nibz]

It 'disassembles' or 'breaks down' in the late prophase. NOR (Nucleolus Organizer Region) is the chromosomal site of nucleolus that remains somehow visible. Maybe 'part of several chromosomes' is referring to that.
You don't need this much detail, though.

 

[VelaneDeBeaute]

^Oh cool! Thanks Nibz!
I have another question though!
They said in the book that there are 23 pairs of homologous chromosomes in the nucleus! Aren't there just 22? B/c the last one could be XX or XY ! I tried but i literally failed to understand this!

 

[Nibz]

Anytime.

 

[Nibz]

I have another question though!
They said in the book that there are 23 pairs of homologous chromosomes in the nucleus! Aren't there just 22? B/c the last one could be XX or XY ! I tried but i literally failed to understand this!

In males, there are 23 pairs of chromosomes - 22 homologous and one non-homologous (allosomes). Whereas in females, the 23rd pair is also homologous which makes all 23 homologous.

 

[VelaneDeBeaute]

^ So when we are talking about the chromosomes in general, it is wrong to say k all pairs are homologous, ryt?

 

[Nibz]

I guess so.

 

[XPFMember]

Assalamoalaikum!!

In June:2010 Paper:41

Q:8 (b) (i) Outline, with reference to CF, what is meant by gene therapy.

Mark scheme says:

1 alters genotype ;
2 insert, dominant/normal, allele ; R gene
3 into, affected/appropriate, cells ;
4 use of vector/named vector ;
5 ref. recombinant DNA ;


In point 2: why does it say 'R gene'
er says: Common errors included references to gene rather than allele.


But the application booklet says: Since it is a recessive condition, such gene therapy does not need to remove or
replace the existing genes in the person’s cells – adding a working copy of the gene
to a cell and having it expressed would be sufficient to permit that cell to transport
chloride ions normally.

The Cambridge Revision guide also refers to inserting the gene. :%)


What's wrong...and whats right????

anyone????

 

[XPFMember]

Assalamoalaikum!!

Another question....it's urgent...have an exam tomorrow

Q:Explain the mechanisms that cause movement of water in xylem vessels. Q:3 (a) (ii) of Nov:2007 Paper:2

If possible, can anyone please give me the complete answer for this...

and the er says
"Some of the better candidates still consider that water in the xylem is under a
positive pressure (rather than tension) with water moving from a region of high hydrostatic pressure
to a low hydrostatic pressure."
If this is not true then what happens actually??

Plz help!

 

[Dayyanah]

hey, am not sure how well my answer will help u coz im not really a pro but it might just give u a gist of how it works

once the water is inside the xylem,it has elongated cell wall which are lignified to allow the water to pass through smoothly down the water potential gradient. the cohesion forces within the molecules and adhesion forces between the molecules of water and the lignified cell walls allow the water to pass though without breaking the water column. together with that, since the xylem is hollow, it works more like a straw. when you suck through a straw, water is flowing out of the top so the water pressure-hydrostatic pressure at the bottom of the straw increases. the same way, because water flows out of the leaves through transpiration, the hydrostatic pressure increases in a xylem so the water is moving from a region of high pressure to a region of low pressure and this is know as mass flow.

well i guess thats it, unless u want to know how the water flows in to the xylem and how it moves thought the leaves. i really hope it helps and good luck with the test

 

[OakMoon!]

Re: help biology activation energy

also you may see the 2nd graph diagram in this page http://www.avogadro.co.uk/definitions/hactivation.htm
or this link http://en.wikipedia.org/wiki/File:Activation_energy.svg


same question why energy decrease after reaching topp of graph


HELP PLEASEEE

You need to know what ENDOTHERMIC and EXOTHERMIC reactions are. In exothermic reactions heat is released and so the energy of the products is less than the energy of reactants (as energy is lost to the surroundings). Whereas in endothermic reactions energy is absorbed/taken in and so the energy of products is higher than the energy level of reactants. If the ENTHALPY (energy) change of reaction is -ve then the reaction is exothermic, whereas if its positive then the reaction is endothermic.
Now coming to the second point: Why the peak is higher than the final energy level? The reason behind this is that the reactants have to undergo a minimum energy level before the reaction can occur, or for the reactant molecules to perform an EFFECTIVE collision. This energy level is called the activation energy and it is more than the energy level of products or reactants.
What an enzyme does? It lowers the activation energy, as shown by the dotted line in the pictures.

 

[Nibz]

Assalamoalaikum!!

In June:2010 Paper:41

Q:8 (b) (i) Outline, with reference to CF, what is meant by gene therapy.

Mark scheme says:

1 alters genotype ;
2 insert, dominant/normal, allele ; R gene
3 into, affected/appropriate, cells ;
4 use of vector/named vector ;
5 ref. recombinant DNA ;


In point 2: why does it say 'R gene'
er says: Common errors included references to gene rather than allele.


But the application booklet says: Since it is a recessive condition, such gene therapy does not need to remove or
replace the existing genes in the person’s cells – adding a working copy of the gene
to a cell and having it expressed would be sufficient to permit that cell to transport
chloride ions normally.

The Cambridge Revision guide also refers to inserting the gene. :%)


What's wrong...and whats right????

anyone????

AOA!

Here's how it's done:

In gene therapy of CF, the genotype of the cells affected by CF is altered by inserting normal alleles of genes into the target cells by using a genetically modified virus as a vector to infect the target cells. The normal form of the gene is transcribed and translated and in this way a normal functioning protein is produced in the target cells.

Hope this helps.

 

[XPFMember]

Wa-alykum-as-salam!

Thank you so much! Jazak Allah Khairen!!!!
It surely helped!

 

[rz123]

energy level needs to be rised up at the beginning so that the reactants can be reacted, energy is released when products are made. they loose energy to the surroundings. exothermic reaction