susiebe
Badges: 10
Rep:
?
#1
Report Thread starter 5 months ago
#1
Question is

Explain the results shown in the graph.

I was wondering why the answer is in terms of starch and not amylase?



Name:  Screenshot 2021-02-10 212723.png
Views: 21
Size:  112.0 KB
Name:  Screenshot 2021-02-10 212812.png
Views: 16
Size:  52.2 KB
0
reply
_crys_
Badges: 3
Rep:
?
#2
Report 5 months ago
#2
Hi, this is likely because question’s main topic is on the hydrolysis of starch and amylase was only added for the reaction to occur (i.e. amylase breaks down starch into maltose) so it is not the focus of the question
0
reply
phdmed
Badges: 10
Rep:
?
#3
Report 5 months ago
#3
Amylase is an enzyme, so is not used up in the reaction - hence the “ase” ending being underlined in the answer. It just helps the reaction occur. Does it make sense now?
0
reply
susiebe
Badges: 10
Rep:
?
#4
Report Thread starter 5 months ago
#4
Thank you.

Yes i understand that amylase is the enzyme in this reaction but if there was a limited amount of amylase then the reaction wouldnt occur as it has done in the graph.
So i am surprised that there is no reference to the importance of amylase in the mark scheme eg all active sites of amylase been occupied by starch so reaction stops .Without amylase starch wouldnt beable to convert to maltose- its not used up but its active sites are so after 25 minutes it says no starch left- so how do we know its not because all active sites are occupied???

Also why is the ase underlined-is it just to show its an enzyme or another reason?If the point is being rejected by the mark scheme then why underline it?

Very confused by this answer, and so it is very frustrating as i do understand the topic but not how the q is marked.
0
reply
HarisMalik98
Badges: 12
Rep:
?
#5
Report 5 months ago
#5
You are adding amylase into a suspension with a certain concentration of starch and that concentration is not increasing. The starch concentration is actually decreasing since it's being hydrolysed. Therefore the effect cannot be due to enzyme saturation. Enzyme saturation occurs when you increase the substrate concentration to a level whereby all active sites are occupied and the rate of reaction can't proceed any faster.

On top of this, you determine enzyme saturation on a graph of rate against substrate concentration. When the graph plateaus, it doesn't mean that the reaction has stopped - it just means that the rate can't increase any faster. Since the enzyme isn't used up the reaction will continue to proceed and form product, but at a constant rate. In this questions case, this is a graph of increasing product against time. Since there is no increase in the concentration of product after a certain time point - that means the reaction has stopped.

Hope this helps.
Last edited by HarisMalik98; 5 months ago
0
reply
phdmed
Badges: 10
Rep:
?
#6
Report 5 months ago
#6
Once the reaction has occurred at the enzyme active site the products will be released and the enzyme is free to perform another reaction. It’s active sites are not used up. That’s not how enzymes work.

The “ase” is underlined to emphasise that it’s an enzyme and therefore can’t be used up in the reaction.

When there is less substrate left the reaction rate slows down because the enzyme is going to be finding less starch to hydrolyse. It’s not because of the enzyme.

I think you’re maybe over complicating enzymes in your head. You clearly understand how they work but they cannot be used up. Maybe look over your notes again?
0
reply
susiebe
Badges: 10
Rep:
?
#7
Report Thread starter 5 months ago
#7
Thank you.

So when the graph plateaus it means

1.The reaction hasnt stopped but cant increase any faster
or
2.The reaction has stopped

How do i know which one is the case?
Last edited by susiebe; 5 months ago
0
reply
phdmed
Badges: 10
Rep:
?
#8
Report 5 months ago
#8
(Original post by susiebe)
Thank you.

So when the graph plateaus it means

1.The reaction hasnt stopped but cant increase any faster
or
2.The reaction has stopped

How do i know which one is the case?
As it is plateauing the reaction is slowing down, and won't be able to get faster. When it has plateaued then the reaction is finished because the substrate has been used up.

If a reaction exists in equilibrium, then when the graph plateaus there will still be some exchange, but the concentration of substrate and product will remain the same, so the reaction is essentially finished because it won't go any further.

Does that make sense?
0
reply
HarisMalik98
Badges: 12
Rep:
?
#9
Report 5 months ago
#9
(Original post by susiebe)
Thank you.

So when the graph plateaus it means

1.The reaction hasnt stopped but cant increase any faster
or
2.The reaction has stopped

How do i know which one is the case?
You need to look at what the graph is telling you. If its showing product concentration on the y-axis and the graph plateaus then that means it has stopped since theres no product formation.

If the enzyme is saturated, it's important to remember the reaction hasn't stopped. It's just proceeding at a constant rate.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Poll: What factors affect your mental health most right now? Post-lockdown edition

Anxiousness about restrictions easing (30)
5.32%
Uncertainty around my education (65)
11.52%
Uncertainty around my future career prospects (66)
11.7%
Lack of purpose or motivation (75)
13.3%
Lack of support system (eg. teachers, counsellors, delays in care) (32)
5.67%
Impact lockdown had on physical health (28)
4.96%
Social worries (incl. loneliness/making friends) (60)
10.64%
Financial worries (35)
6.21%
Concern about myself or my loves ones getting/having been ill (22)
3.9%
Exposure to negative news/social media (34)
6.03%
Difficulty accessing real life entertainment (15)
2.66%
Lack of confidence in making big life decisions (56)
9.93%
Worry about missed opportunities during the pandemic (46)
8.16%

Watched Threads

View All