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Edexcel igcse biology may 2012 exam discussion

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"fish are selectively bred to produce large numbers of off-spring" would probably get you one or two marks depending on how many marks are available although in reality fish in fish farms are, as you say, bred to be of high quality and it is the conditions within the farm that ultimately affect the number of offspring. You would, however, be correct in so far as some farms breed their fish so that they grow at a much faster rate and thus their sexual organs mature earlier. I would probably say something about how conditions such as heat and water quality are kept at optimum levels and fish in the farms are protected from natural predators in the sea which leads to an increase in the relative amount of offspring produced.

Haha don't worry, I was only looking for one mark over there! (The mark scheme had "selective breeding" down as one point alone, but I was worried I would get 0 for the wrong qualifier). My complete answer covered 9 or 10 points that were on the mark scheme, but unfortunately it may be the case that perhaps half of the qualifiers were wrong. If that doesn't matter, great! :smile:

I didn't talk about heat; of course, I did include the cages that protect the fish from natural predators, and I managed to make two points out of water quality (water is kept oxygenated and the fish's waste products (faeces) are removed regularly).

Are you taking it this year?

Reply 41

Umackjiggles

Virus - HIV
HIV is a retrovirus (it uses reverse transcriptase (rna-dependent dna polymerase)) to replicate its rna within a host cell. It causes acquired immuno deficiency syndrome which weakens the immune system and makes the body more vulnerable to pathogens.

Reply 42

Umackjiggles

Yeah my first exam is on Tuesday :s-smilie:

Reply 43

Big-Daddy

Original post by Umackjiggles

Wow, that knowledge about HIV's exact actions - including enzymes (!) - is pretty exceptional. I was expecting something like:

"Virus:
HIV - causes AIDS (a deficiency in the immune system that makes the body vulnerable to pathogens)"

Reply 44

Umackjiggles

Original post by Big-Daddy

Thanks

, I have to admit I am a bit of a genetics nerd so I enjoy learning about replication enzymes / DNA. If you have any questions about DNA or genetic modification feel free to ask me, I would be more than willing to help if it means I can procrastinate revising ~~geography~~ "Human Influences on the Environment" :wink:

Reply 45

Big-Daddy

Original post by Umackjiggles

Thanks

Sorry to have to force this on you, but what does "Human Influences on the Environment" mean? I certainly wouldn't claim to be a genetics nerd (I'm much more into chemistry and physics than biological realms of genetics), but I do feel fine when it comes to genetics for the IGCSE Biology exam.

What do we have to know for "Human Influences on the Environment"? Global warming and that stuff?

Reply 46

Umackjiggles

it consists of : Global Warming, Acid Rain, Fish Farming, Modern Agriculture, hydroponics and greenhouses, cycling nutrients on a farm, fertilisers, pests, pollutoin, eutrophication stuff, pesticide pollution and how to reduce the effects of pollution

Reply 47

Big-Daddy

Original post by Umackjiggles

How do we reduce the effects of pollution?

I've seen lots of questions in past papers like: "why might humans be causing xx to die out?" They're always worth three marks; what reasons would you give? And, if they ask for 4 effects of global warming, what will you put down?

Thanks for the help. :smile:

Reply 48

Umackjiggles

Original post by Big-Daddy

For the first question I would talk about government policies to lower global CO2 emissions, reduce deforestation and introduction of legislation to limit levels of nitrates in water. You can probably see how this could easily be confused with geography.

For the second part, I would say the main effects of global warming are : the ice caps melting thus causing sea levels to rise, the subsequent effect on rainfall (it would increase as per the water cycle), the change that would take place in many ecosystems and subsequent extinction of asexually reproducing organisms such as plants as they would be unable to adapt to a change in their environment.

Reply 49

member963009

Original post by Big-Daddy

Effect of global warming:
-melting ice caps so sea level rise thus increased flooding
-change in major ocean currents so warm water redirected to cooler areas meaning diseases carrying diseases such as mosquitos might migrate north bringing malaria
-nature of ecosystems would be changed and if species cannot migrate or adapt quickly enough, they could become extinct
-higher temperatures mean that pests can complete life cycles more quickly so they become more of a problem thus change in agricultural practices would be needed :smile:

Reply 50

member963009

Original post by Umackjiggles

we posted at the same time! haha

Reply 51

Umackjiggles

Original post by sahajkaur

we posted at the same time! haha

haha thats pretty cool :smile:

Reply 52

Tazxx_xx

Original post by sahajkaur

you guys are freaking me out! are you guys doing the same syllabus? because igcse Edexcel has nothing about enzymes in industry!!! what!!!

even the specification / nor student book has it?

I'm freaking out about that too! I don't remember having to learn that? :confused:

Reply 53

mynameisgrace

WAIT...- SO FOR PAPER 1, (on tuesday) .. WE DONT NEED TO KNOW ABOUT NITROGEN CYCLE OR NITROGEN FIXATION BACTERIA STUFF OR ANYTHING??!

Reply 54

member963009

Original post by Tazxx_xx

I'm freaking out about that too! I don't remember having to learn that? :confused:

its a subpoint on page 238 of the student book , but its not on the specification so dont worry :smile:

Original post by mynameisgrace

WAIT...- SO FOR PAPER 1, (on tuesday) .. WE DONT NEED TO KNOW ABOUT NITROGEN CYCLE OR NITROGEN FIXATION BACTERIA STUFF OR ANYTHING??!

Reply 55

Umackjiggles

Original post by Tazxx_xx

I'm freaking out about that too! I don't remember having to learn that? :confused:

Don't worry the only "enzyme in industry" you need to know for this exam is insulin in so far as it is produced through gm bacteria and the digestive enzymes of yeast during fermentation in the manufacture of beer (you don't need to know their names though).

Reply 56

mynameisgrace

ahh phew! cant believe i left revision so much to the last minute! ah did you see last summers paper? it was basically nearly all on plants.. so i bet this one will have lots about maybe the heart.. or the nephron.. or lungs or something like that ! and i bet the yoghurt thing will come up

Reply 57

member963009

Original post by mynameisgrace

Maybe but nothing is guaranteed. Revise everything. Using microorganisms will most probably come up though :smile:

Reply 58

mynameisgrace

Original post by sahajkaur

Maybe but nothing is guaranteed. Revise everything. Using microorganisms will most probably come up though :smile:

using them for what?!

Reply 59

RoyalBlue7

Original post by Umackjiggles

Thanks

, I have to admit I am a bit of a genetics nerd so I enjoy learning about replication enzymes / DNA. If you have any questions about DNA or genetic modification feel free to ask me

Well in the production of insulin(human --> Bacteria) I know there's a vector involved (Plasmid). But what about in transferring gene from plant to plant? Is there a vector involved? When must you transfer the gene? When its a zygote?Should we directly put gene into plant cell? And what is a transgenic organism? One who has received a gene from any another organism or from an organism of a different species? What is genetic modification - is it modifying genetic material and therefor producing a trangenic organism? It really confuses me! Thanks if you help!