AQA BIOL1 Biology Unit 1 Exam - 16th May 2011

Original post by liviaaa

Describe the structure of an antibody.

Made out of 4 polypeptide chains, 2 heavy chains and 2 light chains. It has a variable region which has a specific tertiary structure and a constant region that does not change. Ugh I can't do this. :frown:

Reply 162

Original post by liviaaa

Magnification and resolution are different though. :smile:

Magnification is about enlarging, and resolution is about the ability to distinguish between 2 points.

Hmm yeah I guess lol. :redface:

Reply 163

Original post by liviaaa

What's in an oral reyhdration solution, and how does it help diahorea?

Water to rehydrate the tissues.
Potassium, sodium and citrate ions to replace lost ions.
Potassium to boost appetite.

Reply 164

Original post by Sparkly-Star

Yeah I don't really know what else.. I don'tunderstand, why does it need a variable region if it's specific to one antigen?

Reply 165

Original post by Sparkly-Star

What is cell fractionation?
Why is there a need to filter the solution?
Why was the solution placed in a cold, isotonic and buffered solution?
What is homogenization?
Describe the process of ultracentrifugation.

Describe the differences between TEM and SEM.

Cell Fractionation: The process of separating organelles from the rest of the cell.

Filtration isrequired to separate the organelles from the connective tissue of the cell

Homogenization is required to break open the plasma membranes and release organelles into solution.

Solution is cold to prevent enzyme activity, isotonic to prevent osmotic activity (which may shrink/make cells turgid) and bugger tio required to keep PH constant.

In ultracentrifugation, the solution containing a mixture of organelles is spun in a centrifuge, first at low speed. Sediment forms at bottom = a pellet, firstly the pellet is the nuclei. The solution of lighter organelles at the top is known as supernatant and this is drained off and poured into another tube, put into centrifuge again and spun at a higher speed. This continues untill all organelles are separate. Order = nuclei, mitocondria, lysosomes, ER and ribosomes.

SEM: Scannig beam of elextrons across specimen, knocks electrons of specimen, gathered in cathode ray tuve to form an image. Lower res and mag than TEM, can be used on thick specimens, can form 3D image. Yet only shows surface of specimen. Long prep time (often needs to be coated in gold), yet specimen can be alive.

TEM: Electromagnets focus a beam of electrons through specimen, denser parts of specimen absorb more electrons and so show up darker. Higher res and mag than SEM. Yet only used on thin specimens and do not show 3D image. Specimen needs to be dead too.

Reply 166

Original post by Sparkly-Star

Water to rehydrate the tissues.
Potassium, sodium and citrate ions to replace lost ions.
Potassium to boost appetite.

I would also talk about how the ions are reabsored into cells out of lumen, lowering water potention, so water moves from l. intestine into cells by osmosis. :smile:

Reply 167

Original post by liviaaa

Yeah I don't really know what else.. I don'tunderstand, why does it need a variable region if it's specific to one antigen?

Its exactly the same as an enzymes active site, specific, complementary to one antigen. Needs variable region to make it specific.

Reply 168

Original post by Tericon

SEM: Scannig beam of elextrons across specimen, knocks electrons of specimen, gathered in cathode ray tuve to form an image. Lower res and mag than TEM, can be used on thick specimens, can form 3D image. Yet only shows surface of specimen. Long prep time (often needs to be coated in gold), yet specimen can be alive.

It's not alive - it's in a vacuum. :smile:

Reply 169

Original post by liviaaa

I would also talk about how the ions are reabsored into cells out of lumen, lowering water potention, so water moves from l. intestine into cells by osmosis. :smile:

Haha I was gonna write that and thought nahh I can't be bothered right now. :redface:

Reply 170

username459260

Original post by jsmith6131

does anyone know if we need to know about how virus / fungi cause disease SPECIFICALLY

or is it just

toxin production
damaging host cells

Reply 171

Original post by Tericon

Its exactly the same as an enzymes active site, specific, complementary to one antigen. Needs variable region to make it specific.

Ohh so it means the variable region changes shape on the different antibodies! I thought it meant on 1 antibody it kept changing shape. :tongue:

Thanks!

Reply 172

RoadRunner

Original post by liviaaa

I would also talk about how the ions are reabsored into cells out of lumen, lowering water potention, so water moves from l. intestine into cells by osmosis. :smile:

You can also mention use of amino acids to increase co transport of sodium ions

Reply 173

Rahul.S

any1 has an idea whatt the two 5 markers will be....i know the paper will have 7 questions....got it from the aqa website...since its a 16 page booklet.

Reply 174

Original post by jsmith6131

or is it just

toxin production
damaging host cells

Those 2 are on the spec, so I'd just learn them. :smile:

Reply 175

Original post by jsmith6131

or is it just

toxin production
damaging host cells

Ive got the above two, only more specific as to damage to host cells:

1. Rupturing host cell to release nutrients
2. Breaking down nutrients in host cell for own use
3. Replicating inside host cell, thus bursting it.

Reply 176

Original post by liviaaa

Ohh so it means the variable region changes shape on the different antibodies! I thought it meant on 1 antibody it kept changing shape. :tongue:

Thanks!

Also always think of proteins because antibodies are made out of them, so talk about the primary and tertiary structure etc. and how this changes the variable region.

Reply 177

Describe the structure of the cell - surface membrane.

Reply 178

Define diffusion.
Is it passive or active transport?
What is diffusion proportional to?
Describe facilitated diffusion.

Reply 179