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OCR Biology F212 Revision [3rd June 2013] (Now Closed)

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Why do vaccines need to be continually updated? Apart from mutations... (for a 3 mark question say? )

I think probably its because new strains of bacteria develop, and resistance to antibiotic occurs..something like that...different antigens?
Haha Im not confident...

(edited 10 years ago)

Reply 1101

Juliajuliajulia

Argh T lymphocytes.
Part of the humoral response, secondary defence.
Pathogens that invade the human body display antigens.
Phagocytes that engulf pathogens and infected cells become antigen displaying cells.
T lymphocytes have receptors that are specific and complementary to antigens
T lymphocytes bind to antigens on cell surface.
This triggers colonal expansion, T lymphocytes multiply by mitosis.
T lymphocytes then differenentiate into T killer cells and T helper cells.
T killer cells cause pathogen death; receptors complementary to antigens bind to the pathogen. Kill by secreting toxic substances such as hydrogen peroxide into pathogenic cells.
T helper cells secrete interleukins (or cytokines the two seem to be used interchangeably) which trigger the colonial expansion of B lymphocytes.

Has that come up in a paper?

Does anyone know the average raw mark for full ums conversion? Me and the ocr website aren't friends.

Reply 1102

MrMeep2580

Original post by mastermdc

Huh? In my book, it says that only phagocytes (Macrophages and Neutrophils) engulf cells. It says that T-killer cells secrete toxic substances such as hydrogen peroxide to kill the cell. Is this wrong?

yes sorryy being silly :biggrin:

yeah phagocytes engluf pathogens. T killer cells are what destroyes the infected cells that stimulated the humoral response.

Reply 1103

the A* guy

Outline the Roles of DNA in living organisms. (6 marks)

Any Help appreciated!

Reply 1104

samiwami

Original post by SheriB

Did the january 2013 paper..just got a D..feeling very confident for the exam..not
similarities and difference between Starch and cellulose?

Don't worry about the D...just make sure you concentrate really hard and the knowledge will come to you

Starch -
Made up of alpha glucose
Coiled
Made of straigh chain amylose
Branched
(starch is energy store in plants)

Cellulose -
Beta glucose
Straight chains
Has microfibrils (cross linked)
(forms plants cell wall - gives structure)

Reply 1105

greatwhiteshark

Original post by Ambitions

Why do vaccines need to be continually updated? Apart from mutations... (for a 3 mark question say? :s-smilie:

)

Say if the vaccine is for malaria....
1) There are many different strains/species of malaria
2) The antigens on the malarial virus continue to change shape due to mutation
*3) There is more than one stage in the life cycle of malaria within the human (and different stages have different antigens)
4) Therefore a different vaccine is needed for each strain/stage

*This is specifically for malaria, but the other 3 points should be the same basic foundations for any other virus :smile:

Reply 1106

MrMeep2580

Original post by YouKnowMyName

Question:

Explain the link between classification and phylogeny

We use phylogeny (studing evolutionary relationships) to put different animals into groups, a way of classifying them. we use Cytochrome c, DNA and RNA to find common ancestors and the phylogeny of a animal and can therefore place them into a group according to the base sequence of nucleotides when comparing two animals of the same kingdom or phylum. Or the sequence of amino acids in the polypeptide

Reply 1107

Beni24

What does B lymphocytes do? :smile:

Reply 1108

Gotzz

Original post by Beni24

During Semi-conservative replication does the DNA polymerase help break the hydrogen bonds between the bases apart? Or does it help during Proteinsynthesis? Or is it used for both?

It joins the sugar-phosphate backbone. This is from a mark scheme :smile:

Reply 1109

Juliajuliajulia

The answer in a past paper for induced fit hypothesis was something like:
The substrate binds to the active site forming an enzyme substrate complex. Active site changes shape creating a closer fit between substrate and active sit. Pressure applied destabilises bonds in the substrate which reduces the activation energy. Products are formed which no longer are complementary to the active site, products leave the active site. x

Reply 1110

Ambitions

Original post by Saif95

I think probably its because new strains of bacteria develop, and resistance to antibiotic occurs..something like that...different antigens?
Haha Im not confident...

ahaha, thats sometimes how I structure my answers in exam papers :P
and ooo, thats true, but I was thinking more in the lines of viral infections like influenza vaccinations... do they develop resistance? :s-smilie:

Reply 1111

samiwami

Original post by the A* guy

Outline the Roles of DNA in living organisms. (6 marks)

Any Help appreciated!

DNA is used for coding for a sequence of amino acids...which form the primary structure. This coils to form the secondary structure (alpha helix and beta pleated sheets) held together by Hydrogen bonds. Tertiary structure can be formed

It stores genetic information
dna codes for mRNA , tRNA and rRNA
making new cells
long term store

Are you sure they didn't also ask you for RNA? In which case you talk about protein synthesis

Because I am curious now as to why this is 6 marks!

(edited 10 years ago)

Reply 1112

samiwami

Original post by Beni24

What does B lymphocytes do? :smile:

B lymphocytes differentiate to become memory cells or plasma cells

Plasma cells produce antibodies :smile:

Reply 1113

kited4

What is the chance we could get a long question (8) marks comparing the action of B and T lymphocytes?

- that would give us the chance to talk about T mature in thymus, B have antibodies on the surface but T have receptors, T action kills other cells but B doesnt, both produce memory cells
and stuff like that?

that would be a fab question :wink:

Reply 1114

Ambitions

Original post by Juliajuliajulia

OCR doesn't have a UMS converter on their website annoyingly (unlike Edxexcel and AQA). But I heard that 86 has been the highest for 150 UMS?

So quite decent!!

Reply 1115

HeyMickey6

Original post by samiwami

i would say starch is made from amylose and amylopectin which both form alpha helix structures, not just starch is coiled.

You may not get the mark for saying coiled cause you can have a left handed helix which is the structure collagen

Reply 1116

HeyMickey6

What makes Structure relevant for its function ?

Reply 1117

coco_madem0iselle

Do we have to relate structure to function for DNA? e.g. hydrogen bonds, sugar phosphate backbone, double helix and how these relate to the function of DNA

Reply 1118

fluker6696

Quick query, in the Jan 2013 paper there was a question on the number of species in the world. I put that speciation is an ongoing process and so the number of species is constantly increasing, yet the mark scheme specifically said 'IGNORE refs to speciation' and accepted 'concept of species, difficult to define' (BS). Anyone know why this was the case? Ignoring the quality of OCR's exam writers :rolleyes:

...

Reply 1119

morvenrkr

A low Simpsons index gerally means the habitat has a low species richness which means it is very unstable and even a small change (or a massive one eg the development) would damage the species there either killing them or reducing their numbers substancially :smile:

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