A level Biology: Post your doubts here!

[IsaacNewton]

Meri post like karne pe maut ati hai begharaton?

 

[ShreeyaBeatz]

Hello there !
Just a little question
Please reply this !
" The daily average intake of vitamin is about 25mg per day"
What does this mean :
A. 50% of the population should intake
B. 95%of popn should intake

The markscheme says that A is correct. I didnt understand.
God be with you Please Reply!

 

[gary221]

Hello there !
Just a little question
Please reply this !
" The daily average intake of vitamin is about 25mg per day"
What does this mean :
A. 50% of the population should intake
B. 95%of popn should intake

The markscheme says that A is correct. I didnt understand.
God be with you Please Reply!

paper link, pls!!

 

[HorsePower]

Meri post like karne pe maut ati hai begharaton?

 

[ShreeyaBeatz]

paper link, pls!!

9700/01/o/n/03 question 28
thank you

 

[PANDA-]

9700/01/o/n/03 question 28
thank you

I think this topic has been removed from the syllabus. As I've never heard of this... EAR.

 

[Irfan1995]

Hello there !
Just a little question
Please reply this !
" The daily average intake of vitamin is about 25mg per day"
What does this mean :
A. 50% of the population should intake
B. 95%of popn should intake

The markscheme says that A is correct. I didnt understand.
God be with you Please Reply!

They're referring to the EAR (Estimated average requirement)

If you have all the numbers, from 1 to 10, the average would be considered 5.
50% of the numbers are below 5 (the average)
and 50% of the numbers are above 5
The choice was, "50% of the population require more than 25 mg of vitamin C per day."
which is just like the second point I mentioned.

 

[Alice123]

Maybe useful for those giving AS

 

[strangerss]

hey everyone , please I have many doubts in oct/nov 2010 p1 variant 2 question 17 and 26 35 and 37 , can some please explain the answers?

 

[Irfan1995]

hey everyone , please I have many doubts in oct/nov 2010 p1 variant 2 question 17 and 26 35 and 37 , can some please explain the answers?

17) Mitosis does not fix a cell, but it replaces damaged cells in a tissue. The damaged cells will enter apoptosis (programmed cell death). Afterwards, they will be engulfed by phagocytes
26) Xylem vessels are thick and found closer to the centre of the stem (D). Cambium cells separate the xylem and phloem (C). Phloem are relatively thinner and found near the edges of the stem (B). Even closer to the edge is the cortex cells (A).
35) Tidal volume is the volume of air exchanged per breath.
So the total volume of air = tidal volume x breathing rate.
A = 14 x 0.6 = 8.4 L
B = 15 x 0.6 = 9.0 L
C = 16 x 0.5 = 8.0 L
D = 17 x 0.5 = 8.5 L
So B absorbs the greatest volume of air per minute
37) Only the two variable regions can bind to antigens.

 

[strangerss]

17) Mitosis does not fix a cell, but it replaces damaged cells in a tissue. The damaged cells will enter apoptosis (programmed cell death). Afterwards, they will be engulfed by phagocytes
26) Xylem vessels are thick and found closer to the centre of the stem (D). Cambium cells separate the xylem and phloem (C). Phloem are relatively thinner and found near the edges of the stem (B). Even closer to the edge is the cortex cells (A).
35) Tidal volume is the volume of air exchanged per breath.
So the total volume of air = tidal volume x breathing rate.
A = 14 x 0.6 = 8.4 L
B = 15 x 0.6 = 9.0 L
C = 16 x 0.5 = 8.0 L
D = 17 x 0.5 = 8.5 L
So B absorbs the greatest volume of air per minute
37) Only the two variable regions can bind to antigens.

In 17 how is growth of cells isn't important? in 26 I have never studies about cambium cells is it AS? in 35 how is the tidal volume the air breathed in AND out in one breath and when I multiply it by the number of breaths in one minute I get the volume of air which ENTERED the lungs ? in 37 they said it was broken into three fragments whats the third fragment? sorry if too many questions but I'm really messed up X_X thanks though that was helpful

 

[Jaf]

Can anyone give me a clear, precise and legit definition of biodiversity? It's an oft-repeated question in paper 4 and I'm unsure how to frame it. The best I've come up with so far is:
Biodiversity is the total number of species living, including the genetic diversity between the different species and the genetic variation between individuals of the same species, in a defined, widespread region, ecosystem or biome.

Thank you.

 

[Irfan1995]

In 17 how is growth of cells isn't important? in 26 I have never studies about cambium cells is it AS? in 35 how is the tidal volume the air breathed in AND out in one breath and when I multiply it by the number of breaths in one minute I get the volume of air which ENTERED the lungs ? in 37 they said it was broken into three fragments whats the third fragment? sorry if too many questions but I'm really messed up X_X thanks though that was helpful

17) The cell does not grow by mitosis. It only divides by mitosis. It grows during interphase (when it's not dividing)
26) I really have no idea if cambium cells are included. In my school, we take AP courses, and it's included there. Not sure about the AS syllabus though.
35) Okay, if I breathe in and out 5 times, and in every breath I take in 2 litres of air (exaggerated example). The total volume of air exchanged was 10 litres (every breath = 2 litres. So 5 breaths = 5 x 2 = 10 litres).
EDIT: a full breath is breating in and out once.
37) When an antibody fragments (breaks down), it breaks down into three parts. Remember that it looks like a "Y"
It breaks down into two "fragments antigen-binding" (Fab) and one "fragment crystallizable" (Fc)
The top part of the "Y" breaks down into "\" and "/" (2 fragments, each one can bind to an antigen)
The bottom part of the "Y" breaks down into "|" (the constant region/straight line)
Hope that helped

 

[Irfan1995]

Can anyone give me a clear, precise and legit definition of biodiversity? It's an oft-repeated question in paper 4 and I'm unsure how to frame it. The best I've come up with so far is:
Biodiversity is the total number of species living, including the genetic diversity between the different species and the genetic variation between individuals of the same species, in a defined, widespread region, ecosystem or biome.

Thank you.

Biodiversity is a really hard term to define. There is no exact definition of it.
The closest you can get to the definition is the one provided in the mark schemes.
From Oct/Nov '07:
1 ref. variety of, species / organisms;
2 genetic diversity within species / AW ;
3 genetic diversity between species ;
4 wide range of, habitats / ecosystems;

I'll try to explain each point:
1) Variety of species means the different species that are in an ecosystem. For example, an aquarium with fishes, moss, larvae, daphnia, and algae has more biodiversity than an aquarium with only fish.
2) Genetic diversity within species is the variation within the same species. For example, if all the fish were identical, biodiversity is low. But if you have a mixture of big fish, small fish, colourful fish, large-eyed fish, etc..., then biodiversity is high.
3) Genetic diversity between species is having many fishes from the same genus, but of different species. For example, if you have a fish from the Atlantic ocean and a fish from the Indian ocean, biodiversity is increased.
4) This is pretty much self-explanatory

I hope this makes it a bit clearer

 

[geek101]

Can anyone give me a clear, precise and legit definition of biodiversity? It's an oft-repeated question in paper 4 and I'm unsure how to frame it. The best I've come up with so far is:
Biodiversity is the total number of species living, including the genetic diversity between the different species and the genetic variation between individuals of the same species, in a defined, widespread region, ecosystem or biome.

Thank you.

This is what the mary jones study guide says: Biodiversity can be defined as the range of habitats, communities and species in an area, and the genetic variation that exists within the populations of each species. The greater the ''species richness'' the greater the biodiversity.

 

[Jaf]

Thanks everyone.

 

[knowitall10]

Assalamu alaykum.
I was going through the mark scheme of p4 one day and came across the word "disturbing selection". Is this the same thing as directional selection?

 

[Irfan1995]

Assalamu alaykum.
I was going through the mark scheme of p4 one day and came across the word "disturbing selection". Is this the same thing as directional selection?

I think you mean disruptive selection.
And no, it isn't.
Stabilizing selection = the intermediate is preferred
Directional selection = one extreme is preferred
Disruptive selection = both extremes are preferred

 

[knowitall10]

I think you mean disruptive selection.
And no, it isn't.
Stabilizing selection = the intermediate is preferred
Directional selection = one extreme is preferred
Disruptive selection = both extremes are preferred

Yes, i mean "disruptive selection".. I'm sorry..
Thank u anyway, Jazak Allahu Khair

 

[knowitall10]

I think you mean disruptive selection.
And no, it isn't.
Stabilizing selection = the intermediate is preferred
Directional selection = one extreme is preferred
Disruptive selection = both extremes are preferred

But wait, what's the difference in "intermediate" and "both"?