A level Biology: Post your doubts here!

[ABC12348]

can somebody please explain the epidemiological and experimental evidences linking cigarette smoking to disease and early death?

 

[manutd96]

Thanks! But I would also like to know, what are the cells next to the sieve tube element? Those which dont have any contents. Are they the companion cells or something else? Because I have also seen before sieve tube elements with no contents

Yes!

 

[jungly krinsky]

Hi, I have some questions to ask about the AS past papers for biology and specifically where they seem to contradict the book i am working from ( which is the biology coursebook by Mary Jones Richard Fosbery Jennifer Gregory and Dennis Taylor. ) firstly in this book the antibiotic penicillin is referred to as a non-competitive inhibitor ( on page 62) ( as it bonds permanently to the active site of enzymes used in cell wall synthesis ) but in the past paper 2012 October November specimen paper 23, question 2, c (ii) it is stated that "Penicillin acts as a competitive inhibitor" . also the second point on which i am somewhat uncertain is, when referring to normal cells, that is cells not currently undergoing mitosis or meiosis, is it not incorrect to refer to the cells as containing chromosomes? ( because the genetic material of the cell is contained in chromatids in the nucleus, which are in the form of loosely coiled chromatin, and so cannot contain chromatin, )

 

[DeViL gURl B)]

Can someone please explain me .. That as the pathogen or the antigen develops resistance against an antibiotic .. How is it related to the change in DNA structure .. Or like mutation .. Of that pathogen ?

Help would be really appreciated .. Detail answer please .. Thank you

Anyone ? Please ..

 

[RoOkaYya G]

Manage your time!
Revise the structures of the plant and how to draw a plan diagram
Beside each label put a small note
and good luck

You are of precious help dear. Thank you again

putting a lil note means annotation.
if the question doesnt ask for annotation then DO NOT annotate. only label.
for labelling...even if theydint ask to label..u shld label.

 

[Tasneeem]

putting a lil note means annotation.
if the question doesnt ask for annotation then DO NOT annotate. only label.
for labelling...even if theydint ask to label..u shld label.

But if you annotate even if the question DOESN'T say so, you will gain extra marks.

 

[RoOkaYya G]

But if you annotate even if the question DOESN'T say so, you will gain extra marks.

well, ill confirm ths with my teacher today. n btw do read examiners report. it helps a lot.
btw NEVER shade ur drawings. until n unless its told in the question like shade the chromosome

 

[Gorgeous doll]

I need the mark schemes of oct/nov 2001 and may/june 2002.. Can anyone help me please .. i need these mark schemes today

 

[f.mohamed]

Whats the difference between elastic and collagen fibers ?

 

[Gorgeous doll]

Whats the difference between elastic and collagen fibers ?

Elastic fibres are present in alveoli and they recoil durind expiration to fore air out and constrict diring inspiration to provide surface area for air to get in. Collagen fibres are present in collages which is a finrous protein and play a part in structural support

 

[Gorgeous doll]

Elastic fibres are present in alveoli and they recoil durind expiration to fore air out and constrict diring inspiration to provide surface area for air to get in. Collagen fibres are present in collages which is a finrous protein and play a part in structural support

During* Collagen*

 

[f.mohamed]

Elastic fibres are present in alveoli and they recoil durind expiration to fore air out and constrict diring inspiration to provide surface area for air to get in. Collagen fibres are present in collages which is a finrous protein and play a part in structural support

Thaankk Youu <3

 

[Tasneeem]

Is prevention same as control of disease?

 

[Gorgeous doll]

Yes

Is prevention same as control of disease?

yes almost same

 

[Gorgeous doll]

I need mark schemes of bio paper 2 may june 2002 and oct/ nov 2001

 

[ABC12348]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w12_qp_21.pdf
Q2 part a(i) can somebody please explain this? isn't this facilitated diffusion as it is being carried out through a protein channel? whereas the ms states it as 'diffusion through fully permeable cell wall'

 

[Bba321]

Hey .Can anyone please answer this question.Thanks a lot

How the structure of DNA makes it suitable for replication

 

[Tasneeem]

Hey .Can anyone please answer this question.Thanks a lot

How the structure of DNA makes it suitable for replication

its double stranded joined by hydrogen bonds between complementary base pairing. Therefore each DNA strand can act as a template for formation of complementary strand by being paired with complementary neucleoutides to produce two identical molecules of DNA.

 

[Bba321]

Thank

its double stranded joined by hydrogen bonds between complementary base pairing. Therefore each DNA strand can act as a template for formation of complementary strand by being paired with complementary neucleoutides to produce two identical molecules of DNA.

Thankyou

 

[princess Anu]

14 Some inhibitors of enzyme reactions bind to the enzyme / substrate complex.
Which statements about this type of inhibition are correct?
1 The active site changes shape
2 The inhibitor is non-competitive.
3 The initial rate of reaction is reduced.
4 maximum rate of reaction (Vmax) is increased.

A 1 and 2 only B 1and3only C 2and3only D 2,3and4only

How is the answer C?
I don't understand that if the active site is not changing shape then how is the non competitive inhibitor causing the rate of reaction to decline?