A level Biology: Post your doubts here!

[osama ahmed ibrahim]

cie 9700 paper 4

november 2014 p42 last q in secton a

 

[kareem22010]

u are missing many ms points like u didnt discuss that target cells of insulin are muscle liver and adipose cells

The semi colon in the markscheme means 'or' not 'and' so, i don't think I need to mention adipose and muscle cells if I mentioned liver cells. Other than that,how many points do you think I have earned?

 

[nadeen64]

Hi, can someone please explain this? The answer is B

 

[nadeen64]

In active transport, when you increase the difference of the gradient. does the rate of active uptake increase? Like in diffusion and osmosis, it's true when you increase the difference.
Like in this question, why is 2 wrong?

 

[kareem22010]

Hi, can someone please explain this? The answer is B
View attachment 60476

well, when two organisms mate, two HAPLOID gametes fuse together,however,the question shows here diploid cells so you have to divide by two in the first generation to have : 7 +7 = 14 chromosome, but due to mutation , chromosome number is doubled to 28 so,it's haploid is doubled too. as the haploid version of this organism(fertile hybrid 1) fuses with another haploid gamate of different haploid number ( notice that fertile hybrid 1's haploid is 14 and the other is 7) .this results in an offspring with diploid number of 21 and due to mutation, it is doubled to 42. so, answer is B.

 

[qwertypoiu]

In active transport, when you increase the difference of the gradient. does the rate of active uptake increase? Like in diffusion and osmosis, it's true when you increase the difference.
Like in this question, why is 2 wrong?
View attachment 60477

In diffusion and osmosis, a greater concentration gradient means a faster diffusion rate.
In active transport, a greater concentration gradient means more energy is required to maintain this gradient. You must understand that in active transport, we're using energy to move ions AGAINST a concentration gradient. So the less steep this gradient, the easier it is to do this.

EDIT: Take this with a grain of salt, see below

 

[techgeek]

In diffusion and osmosis, a greater concentration gradient means a faster diffusion rate.
In active transport, a greater concentration gradient means more energy is required to maintain this gradient. You must understand that in active transport, we're using energy to move ions AGAINST a concentration gradient. So the less steep this gradient, the easier it is to do this.

errmmm....How can ion concentration affect the rate of transport when the ions have to pass through carrier proteins, and not through membrane?

 

[techgeek]

In diffusion and osmosis, a greater concentration gradient means a faster diffusion rate.
In active transport, a greater concentration gradient means more energy is required to maintain this gradient. You must understand that in active transport, we're using energy to move ions AGAINST a concentration gradient. So the less steep this gradient, the easier it is to do this.

Actually, I just read this:


I don't think the steepness of the gradient has any effect on the rate of transport. Don't you think so?

 

[Rizwan Javed]

Actually, I just read this:
View attachment 60506

I don't think the steepness of the gradient has any effect on the rate of transport. Don't you think so?

According to me, steepness of gradient DOES NOT have any effect on the rate of transport. In Active transport the ions/substances are already being moved by the expenditure of energy, and through carrier proteins. So steepness doesnot affect the rate in any way.

 

[techgeek]

According to me, steepness of gradient DOES NOT have any effect on the rate of transport. In Active transport the ions/substances are already being moved by the expenditure of energy, and through carrier proteins. So steepness doesnot affect the rate in any way.

Exactly! I also said the same
what do you say qwertypoiu ?

 

[techgeek]

Could you guys refer me to a site where there is a good explanation of concentrations of substances in equilibrium, like there are such and such at start then what concentration is there during equilibrium. I have across this :http://www.chemguide.co.uk/physical/equilibria/kc.html#top on chemguide but they didn't explain the calculations thing, like we get in MCQs

 

[Rizwan Javed]

Could you guys refer me to a site where there is a good explanation of concentrations of substances in equilibrium, like there are such and such at start then what concentration is there during equilibrium. I have across this :http://www.chemguide.co.uk/physical/equilibria/kc.html#top on chemguide but they didn't explain the calculations thing, like we get in MCQs

It's simple. Give me a question, I'll explain it.

 

[Rizwan Javed]

Could you guys refer me to a site where there is a good explanation of concentrations of substances in equilibrium, like there are such and such at start then what concentration is there during equilibrium. I have across this :http://www.chemguide.co.uk/physical/equilibria/kc.html#top on chemguide but they didn't explain the calculations thing, like we get in MCQs

And post your question in Chemistry thread

 

[princess Anu]

Can someone help with j10/43 Q5b
Why does the ms include this point ' there tends to be less divergence if DNA is part of an important gene'?

 

[nadeen64]

Hiii, can someone please help me with this question ?

 

[qwertypoiu]

Exactly! I also said the same
what do you say qwertypoiu ?

You guys have raised good points and I admit I have made a mistake.
If there is a greater concentration gradient, more energy will be required to maintain that concentration gradient. However, instead of affecting the rate of the transport, the channel proteins will expend more energy to maintain it (so that the rate of active transport remains constant). So assuming there is enough energy, the rate of active transport does not change if concentration gradient changes.
However:

1. If energy is in limiting supply (eg. because there is limited amount of O2 or glucose so that there isn't enough ATP) then the rate of active transport will change based on the change in concentration gradient, because there isn't excess energy available to maintain a high gradient.
2. If not ALL the channel proteins are involved in active transport (ie some are 'free') then increasing concentration gradient will increase rate of active transport until all the proteins are 'occupied', after which the rate remains constant. Have a look at this:
   Spoiler

   

Mediated transport here means active transport. 'Flux' is rate of transport. (Source)

When the solute concentration outside the cell increased, the diffusion rate increased linearly. Active transport rate also did increase. The reason it stopped increasing after a while is because all the membrane proteins were 'fully occupied'.

The reason I'm saying the above is just so if someone had similar confusions to me hopefully this will clear it up.

In our questions unless otherwise stated I believe we are to assume there is both enough energy and that all channel proteins are working so again you're right

 

[Rizwan Javed]

You guys have raised good points and I admit I have made a mistake.
If there is a greater concentration gradient, more energy will be required to maintain that concentration gradient. However, instead of affecting the rate of the transport, the channel proteins will expend more energy to maintain it (so that the rate of active transport remains constant). So assuming there is enough energy, the rate of active transport does not change if concentration gradient changes.
However:

1. If energy is in limiting supply (eg. because there is limited amount of O2 or glucose so that there isn't enough ATP) then the rate of active transport will change based on the change in concentration gradient, because there isn't excess energy available to maintain a high gradient.
2. If not ALL the channel proteins are involved in active transport (ie some are 'free') then increasing concentration gradient will increase rate of active transport until all the proteins are 'occupied', after which the rate remains constant. Have a look at this:
   Spoiler

   

Mediated transport here means active transport. 'Flux' is rate of transport. (Source)

When the solute concentration outside the cell increased, the diffusion rate increased linearly. Active transport rate also did increase. The reason it stopped increasing after a while is because all the membrane proteins were 'fully occupied'.

The reason I'm saying the above is just so if someone had similar confusions to me hopefully this will clear it up.

In our questions unless otherwise stated I believe we are to assume there is both enough energy and that all channel proteins are working so again you're right

This is a very good explanation! Thumbs up.

 

[qwertypoiu]

This is a very good explanation! Thumbs up.

Thanks

 

[Rizwan Javed]

Hiii, can someone please help me with this question ?
View attachment 60516

What's the answer?

 

[techgeek]

You guys have raised good points and I admit I have made a mistake.
If there is a greater concentration gradient, more energy will be required to maintain that concentration gradient. However, instead of affecting the rate of the transport, the channel proteins will expend more energy to maintain it (so that the rate of active transport remains constant). So assuming there is enough energy, the rate of active transport does not change if concentration gradient changes.
However:

1. If energy is in limiting supply (eg. because there is limited amount of O2 or glucose so that there isn't enough ATP) then the rate of active transport will change based on the change in concentration gradient, because there isn't excess energy available to maintain a high gradient.
2. If not ALL the channel proteins are involved in active transport (ie some are 'free') then increasing concentration gradient will increase rate of active transport until all the proteins are 'occupied', after which the rate remains constant. Have a look at this:
   Spoiler

   

Mediated transport here means active transport. 'Flux' is rate of transport. (Source)

When the solute concentration outside the cell increased, the diffusion rate increased linearly. Active transport rate also did increase. The reason it stopped increasing after a while is because all the membrane proteins were 'fully occupied'.

The reason I'm saying the above is just so if someone had similar confusions to me hopefully this will clear it up.

In our questions unless otherwise stated I believe we are to assume there is both enough energy and that all channel proteins are working so again you're right

Yeah...that really was a good explanation. A big round of applause !