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AQA AS Unit 1 Biology Exam 21st May 2015

Reply 1980

Monoclonal antibodies... As bacteria and other pathogens have hundreds of different antigens on its surface, which all induce a different B cell to multiply and clone itself. Each clone will produce an antibody (collectively known as polyclonal antibodies). An monoclonal antibody is when doctors or scientists etc are able to produce these antibodies outside the body, so one type of bcell can be isolated and cloned. :smile:

Reply 1981

samwillettsxxx

3

Original post by Kill3er

5 points for comparing SEM to TEM.
TEM is 2D, SEM is 3D
Sample has to be thin for TEM, not for SEM
TEM has higher resolution and magnification?

What else?

Non-living specimens have to be used
SEM thick specimens

Reply 1982

Windowswind123

2

Original post by samwillettsxxx

Non-living specimens have to be used
SEM thick specimens

All electron microscopes require non living specimens as it is done in a vacuum.

I don't think they could ask you a long question based on TEM vs SEM
Only on optical vs electron (I'm not positive though).

Reply 1983

Januu Dolly

1

Original post by Kill3er

5 points for comparing SEM to TEM.
TEM is 2D, SEM is 3D
Sample has to be thin for TEM, not for SEM
TEM has higher resolution and magnification?

What else?

TE

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Reply 1984

Anon_98

19

Original post by Kill3er

5 points for comparing SEM to TEM.
TEM is 2D, SEM is 3D
Sample has to be thin for TEM, not for SEM
TEM has higher resolution and magnification?

What else?

Specimen preparation- TEM: specimen is fixed with salts of heavy metals.
Whereas SEM: specimen is chemically treated and coated with thin film of gold.

I think that's everything..

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Reply 1985

97Lily.P

3

any predictions for the 5 markers?

Reply 1986

Samera97

1

Original post by edward090

how would u answer the question if it was??

I'd first say that a living organim e.g. a rat is radiated with cancer cells. And another rat is injected with non self antigens. This rat will produce polyclonal antibodies.

The cancer cells from the original rat and the rat with non self antigens are fused together by adding detergent which breaks the plasma membrane.

Since we now have polyclonal antibody cellsm the fused cells are separated and each cell is tested to see whether it is producing the required antibody.

once the monoclonal antibody has been detected it needs to be humanised because rats antibodies are foreign and will be rejected by humans.

(Also it has to be cancer cells because plasma B cells are shortlived ) hope that makes sense?

Reply 1987

MedioCentro97

9

Original post by StarStruckShield

Monoclonal antibodies... As bacteria and other pathogens have hundreds of different antigens on its surface, which all induce a different B cell to multiply and clone itself. Each clone will produce an antibody (collectively known as polyclonal antibodies). An monoclonal antibody is when doctors or scientists etc are able to produce these antibodies outside the body, so one type of bcell can be isolated and cloned. :smile:

My man

Reply 1988

Anon_98

19

Original post by 97Lily.P

any
predictions for the 5 markers?

Maybe...

-Microscopes
-Lung diseases

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Reply 1989

Windowswind123

2

What is a good answer to write for the question regarding microscope pictures misleading.
It is to do with the perspective and how it is a cross section I think but I'm not sure how to phrase it.

Reply 1990

Tigernater

1

Original post by buckeybarnes

EMULSION- add ethanol to sample, shake with water
RESULT- cloudy, white precipitate indicates the presence of a lipid
REDUCING SUGAR- crush the solution with water, and add Benedict's reagent, then heat for 5 minutes (gentle boil
RESULT- Colour change from blue to orange indicates a reducing sugar
NON-REDUCING SUGAR- Same start process as reducing sugar, but no colour change is observed. Add dilute Hydrochloric acid to hydrolyse the disaccharides in to constituent monsaccharides and add sodium hydrogencarbonate to neutralise. Boil again with Benedicts reagent.
RESULT- colour change from blue to orange/brown indicates a non-reducing sugar
BIURET TEST- Add sodium hydroxide and copper (II) sulfate then stir gently
RESULT- Colour change to yellow indicates presence of peptide bonds and hence proteins
STARCH TEST- mix a sample with Iodine solution (2 drops)
RESULT- a colour change to blue/black indicates the presence of starch

:smile:

good luck!

For Biuret, isnt the colour change to lilac/purple?

Reply 1991

jameslondon05

2

are vaccines mono-colonial? (other than things than MMR etc)

Reply 1992

MedioCentro97

9

Original post by buckeybarnes

EMULSION- add ethanol to sample, shake with water
RESULT- cloudy, white precipitate indicates the presence of a lipid
REDUCING SUGAR- crush the solution with water, and add Benedict's reagent, then heat for 5 minutes (gentle boil
RESULT- Colour change from blue to orange indicates a reducing sugar
NON-REDUCING SUGAR- Same start process as reducing sugar, but no colour change is observed. Add dilute Hydrochloric acid to hydrolyse the disaccharides in to constituent monsaccharides and add sodium hydrogencarbonate to neutralise. Boil again with Benedicts reagent.
RESULT- colour change from blue to orange/brown indicates a non-reducing sugar
BIURET TEST- Add sodium hydroxide and copper (II) sulfate then stir gently
RESULT- Colour change to yellow indicates presence of peptide bonds and hence proteins
STARCH TEST- mix a sample with Iodine solution (2 drops)
RESULT- a colour change to blue/black indicates the presence of starch

:smile:

good luck!

Biuret test= PURPLE colour indicates proteins, not yellow!

Reply 1993

corpeal

9

God. I came here looking to see if i had any gaps in my knowledge and see all these errors people make. LOOK AT YOUR BOOKS/NOTES, stop trusting random people and their knowledge. They maybe right, they may not be. It probably is much faster to find out yourselves anyway.

/rantover

Reply 1994

CMooreFalcons

2

Good luck everyone! :smile:

Reply 1995