Edexcel BIOLOGY Doubts!!!!

[Blizz_rb93]

umm y dont i remember any such practical :S

seen in any past paper ??

check out the file I uploaded,  it has that practical no the structure of the membrane and the effect of temperature on it etc.

[~ Miss Relina ~]

how many marks is the q for ??

the concentration of the solution shud be known and controlled..
the roots shud be of the same variety of plant..
the mass of root taken shud be same..

3 points for 3 marks

4

[~ Miss Relina ~]

SAQ 29 in the file uploaded plz

[Blizz_rb93]

can someone complete the remaining blanks for me please

Heart wall muscle is a special type of muscle called Cardiac muscle. This muscle can contract or relax without nervous stimulation and is thus described as _____________. To ensure that the cardiac cycle stays in sequence there is an in-built control mechanism. The wall of the right atrium contains a special region of muscle called the ______________ which sets up a wave of electrical activity causing the atrial walls to contract almost simultaneously. There is a band of fibres between the atria and ventricles which _______________ the wave of activity passing to the ventricle walls. The wave of activity is picked up by the ____________ situated in the septum at the junction of the atria and ventricles. The wave of activity then passes down the septum in the _________________ causing the ventricles to contract.


Thank you

[guMnam]

wat is an initial rate of a reaction ?? :S

[guMnam]

can someone complete the remaining blanks for me please

Heart wall muscle is a special type of muscle called Cardiac muscle. This muscle can contract or relax without nervous stimulation and is thus described as _____________. To ensure that the cardiac cycle stays in sequence there is an in-built control mechanism. The wall of the right atrium contains a special region of muscle called the ______________ which sets up a wave of electrical activity causing the atrial walls to contract almost simultaneously. There is a band of fibres between the atria and ventricles which _______________ the wave of activity passing to the ventricle walls. The wave of activity is picked up by the ____________ situated in the septum at the junction of the atria and ventricles. The wave of activity then passes down the septum in the _________________ causing the ventricles to contract.


Thank you

this is A2 stuff .. didnt study tht yet =\

[Blizz_rb93]

this is A2 stuff .. didnt study tht yet =\

are u sure? :s i mean i got this from some worksheets i have from school so maybe it would help with anything relating to the AS material

[guMnam]

yes i m sure all tht Synoatrial nerve and stuff is in A2

[MKh]

Heyyy actually the core prac i waz talking about is --describe how to investigate the effect of temperature on seedling growth rates. It is from the Edexcel A2 Biology specification so u might not have studied it "gumnam" because i assume u r doing AS ryt?...anywayz Thanks for helping...lets wait for someone else to reply...anyone else doing A2 Biology??.....i need to know the procedure for this core prac as it is from the specification.....i have all the Edexcel A2 biology core prac procedures but not this one actually it is a 'part' of a specification point....the spec point of which it is a part of is --- Describe how to investigate the effects of temperature on the development of organisms (eg seedling growth rate, brine shrimp hatch rates). i know how to investigate the effect of temp. on brine shrimp hatch rates but not the seedling growth rates....these both appear to have a similar procedure but not exactly the same....if anyone of u studies in a school and ur teachers have provided u with the procedure of this part of the core prac plz do tell me....many Thanks to all....and good luck with ur exams...

[MKh]

ok so gumnam....an initial rate of a reaction is the rate of a reaction at its beginning-just after the reactants are mixed together. It is measured to give an indication of the reaction rate. It is measured to avoid monitoring the reaction rate throughout the reaction till the end. It is also measured so that variables other than the dependent variable do not have time to change and affect the reliabilty of the results so that the initial rate of reaction is purely the result of the independent variable(s). If anybody finds this wrong or has a better definition of the initial rate of a reaction plz do say...good luck!!

[guMnam]

Heyyy actually the core prac i waz talking about is --describe how to investigate the effect of temperature on seedling growth rates. It is from the Edexcel A2 Biology specification so u might not have studied it "gumnam" because i assume u r doing AS ryt?...anywayz Thanks for helping...lets wait for someone else to reply...anyone else doing A2 Biology??.....i need to know the procedure for this core prac as it is from the specification.....i have all the Edexcel A2 biology core prac procedures but not this one actually it is a 'part' of a specification point....the spec point of which it is a part of is --- Describe how to investigate the effects of temperature on the development of organisms (eg seedling growth rate, brine shrimp hatch rates). i know how to investigate the effect of temp. on brine shrimp hatch rates but not the seedling growth rates....these both appear to have a similar procedure but not exactly the same....if anyone of u studies in a school and ur teachers have provided u with the procedure of this part of the core prac plz do tell me....many Thanks to all....and good luck with ur exams...

actually i m doing AS and A2.. i just havnt studied A2 well yet.. and yea.. i didnt go thru the specification so i think thts y never saw this practical caz i dont have it any notes either but ill let u noe as soon as possible

[MKh]

no probz...Thanks anyway...and i hav replied to ur question above....

[guMnam]

@ MKh... all the reactants are mixed.. i mean for eg the enzyme experiment. so we measure it before adding the enymes or aftr adding......(i gues aftr adding.. just want to clear it)

and u said tht it is meaured so tht we dont have to meausre the rate hruout the reaction.. y exactly wont we measure the rate thru out the reaction ??

Thanks

[MKh]

ohh yes ofcourse we measure the initial rate of a particular reaction a short time after mixing the reactants together.

These are the details that i have collected from the AS Core Practical notes. They will help u understand all this very well

Measuring the rate of enzyme reactions:

1. Firstly you need a signal to measure that shows the progress of the reaction. The signal should change with either substrate (S) or product (P) concentration, and it should preferably be something that can be measured continuously. Typical signals include colour changes, pH changes, mass changes, gas production, volume changes or turbidity changes. If the reaction has none of these properties, it can sometimes be linked to a second reaction, which does generate one of these changes.

2. If you mix your substrate with enzyme and measure your signal, you will obtain a time-course. If the signal is proportional to substrate concentration it will start high and decrease, while if the signal is proportional to product it will start low and increase. In both cases the time-course will be curved (actually an exponential curve).

3. How do you obtain a rate from this time-course? One thing that is not a good idea is to measure the time taken for the reaction, for as the time-course shows it is very difficult to say when the reaction ends: it just gradually approaches the end-point. A better method is to measure the initial rate - that is the initial slope of the time-course. This also means you don't need to record the whole time-course, but simply take one measurement a short time after mixing.

4. Repeat this initial rate measurement under different conditions (such as different substrate concentrations) and then plot a graph of rate vs. the factor. Each point on this second graph is taken from a separate initial rate measurement (or better still is an average of several initial rate measurements under the same conditions). Draw a smooth curve through the points.

Be careful not to confuse the two kinds of graph (the time-course and rate graphs) when interpreting your data.

I think we do not measure the rate throughut the whole reaction because it is better to simply measure the initial rate of a reaction than to monitor the whole reaction because the initial rate measurement gives just as accurate a result and saves time ofcourse....this is all i know..hope i helped...

[guMnam]

ohh yes ofcourse we measure the initial rate of a particular reaction a short time after mixing the reactants together.

These are the details that i have collected from the AS Core Practical notes. They will help u understand all this very well

Measuring the rate of enzyme reactions:

1. Firstly you need a signal to measure that shows the progress of the reaction. The signal should change with either substrate (S) or product (P) concentration, and it should preferably be something that can be measured continuously. Typical signals include colour changes, pH changes, mass changes, gas production, volume changes or turbidity changes. If the reaction has none of these properties, it can sometimes be linked to a second reaction, which does generate one of these changes.

2. If you mix your substrate with enzyme and measure your signal, you will obtain a time-course. If the signal is proportional to substrate concentration it will start high and decrease, while if the signal is proportional to product it will start low and increase. In both cases the time-course will be curved (actually an exponential curve).

3. How do you obtain a rate from this time-course? One thing that is not a good idea is to measure the time taken for the reaction, for as the time-course shows it is very difficult to say when the reaction ends: it just gradually approaches the end-point. A better method is to measure the initial rate - that is the initial slope of the time-course. This also means you don't need to record the whole time-course, but simply take one measurement a short time after mixing.

4. Repeat this initial rate measurement under different conditions (such as different substrate concentrations) and then plot a graph of rate vs. the factor. Each point on this second graph is taken from a separate initial rate measurement (or better still is an average of several initial rate measurements under the same conditions). Draw a smooth curve through the points.

Be careful not to confuse the two kinds of graph (the time-course and rate graphs) when interpreting your data.

I think we do not measure the rate throughut the whole reaction because it is better to simply measure the initial rate of a reaction than to monitor the whole reaction because the initial rate measurement gives just as accurate a result and saves time ofcourse....this is all i know..hope i helped...

Thanks alot mate
+rep