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Edexcel GCE Biology Unit 4 6BI04 June 2013

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Reply 200

amber109

is the exam at am or pm?

Reply 201

PakStar28

Original post by amber109

is the exam at am or pm?

it is at AM.

Reply 202

Lgambo

Original post by bubblegummer

i do not understand the difference between homozygosity and heterozygosity, and why is homozygosity caused by inbreeding? could someone pls explain :s-smilie:

I think this is right, somebody correct me if not.
If a cell is homozygous it has two of the same allele at a locus (a location on your DNA), one from each parent eg a-a
If a cell is heterozygous is has two different alleles at a locus eg A-a

The more inbreeding that happens the greater chance there is of keeping those alleles in the family. This can be bad, as -for example- in some cases having two recessive alleles can give you a genetic illness.
So let's say Mum is A-a and Dad is A-a. There kids can take one of the alleles from each parent.
They have a boy1 (A-a) and a girl1 (a-a).
They do the dirty, and the chances of their kids having a-a is greater (as there are more as between them).
So lets say THEY have a boy2 (a-a) and a girl2 (a-a). Now a-a is the only zygous in this family, and every generation after this will have to genetic illness.

Sorry was long winded! Hope that answered your question? :rolleyes:

I don't even think it comes up in this unit does it?

Reply 203

amber109

Original post by PakStar28

it is at AM.

thanks

Reply 204

bubblegummer

Original post by Lgambo

I don't even think it comes up in this unit does it?

i can understand them better now. hmm i don't think this is in our spec, but i saw it somewhere in the old past papers. not sure though. thank you so much btw :smile:

Reply 205

Brad0440

Predictions for the exam tomorrow:
Photosynthesis
-Hydrogen stored as a fuel in glucose
-Photolysis in the L.D. reactions
-ATP as energy
-Usage of the L.I. reaction products
Food chain/habitats etc.
-Trophic levels
-NPP/GPP
-Biotic/abiotic factors in distribution
-Niche within a habitat
Carbon etc.
-Carbon cycle
-Global warming (cause and effect)
-The effect of temperature on enzyme activity (kinetics etc.) and the development of organisms
-Evidence for global warming, and why this might be controversial/not accepted
-The decomposition of organic material by micro-organisms
Immune system etc.
-Antibiotic resistance
-Bacteria vs. viruses
-Non-specific immune system
DNA etc.
-Protein synthesis
-The use of exons in producing multiple types of proteins from one gene
-DNA profiles
A specific TB/HIV question?

Anyone else got any guesses?

Reply 206

Taylor Swift

Can someone name all the experiments? Thanks

Reply 207

Taylor Swift

Original post by Brad0440

You basically summarised the whole specification ...

Reply 208

Brad0440

Also, I don't know how useful this is but I've attached some of my revision posters for this exam...

Unit 4 biology revision.pptx1168.9KB

Reply 209

iwantopas19

can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn :smile:

Reply 210

SKK94

Original post by iwantopas19

difference between sense and antisense strand...

and how do we know which sampling to go for, random or systematic, i guess i asked this before also, but im not sure. :s-smilie:

The antisense is the strand used as a template to make the mRNA. ( The RNA nucleotides are complementary to bases on this strand)
The sense strand is the DNA strand opposite the antisense strand. It is identical to the mRNA that is formed (except thymine is present instead of uracil)
http://www.google.ae/imgres?q=sense+and+antisense+strands&um=1&hl=en&biw=1366&bih=643&tbm=isch&tbnid=ATBocbVUHjvDLM:&imgrefurl=http://click4biology.info/c4b/7/pro7.3.htm&docid=zZtllyU3iysHEM&imgurl=http://click4biology.info/c4b/7/images/7.3/sense.gif&w=523&h=210&ei=0Zq1UaOuB8aCrgf-6oHABw&zoom=1&ved=1t:3588,r:0,s:0,i:76&iact=rc&dur=920&page=1&tbnh=142&tbnw=355&start=0&ndsp=16&tx=215&ty=33
http://www.google.ae/imgres?q=antisense+strands&um=1&hl=en&biw=1366&bih=643&tbm=isch&tbnid=X6BKNCv-iDy3VM:&imgrefurl=http://www.daviddarling.info/encyclopedia/A/antisense.html&docid=5oVIb8ruCwluDM&imgurl=http://www.daviddarling.info/images/antisense.jpg&w=403&h=598&ei=55q1UdqtAobwrQee3YGIAg&zoom=1&ved=1t:3588,r:2,s:0,i:82&iact=rc&dur=239&page=1&tbnh=193&tbnw=138&start=0&ndsp=15&tx=24&ty=62

Systematic sampling is used when you want to find a trend within an area, relating two variables. For example, to find the effect of distance from shore on the number of shrubs. So you will have to place a line transect starting from the shore and up to, say, 200m.
Now, along this 200m line transect, you can place quadrats at fixed distances and count the number shrubs in each.
Next, you might a pattern with number of shrubs and distance from shore ( i.e the number of shrubs increases with increasing distance)

Random sampling may be used when you want to a trend between two different areas. For example, the effect of light intensity on then number of seeds produced by a plant. You have to choose two areas of the same size (but different light intensities, of known values).
Say one area has low intensity and the other has high intensity. Next, use random sampling within each area to count the number of seeds in each. With this you can see the effect of light intensity on number of seeds produced.

Sorry this is really long! I hope this helped :smile:

(edited 10 years ago)

Reply 211

iwantopas19

Original post by Brad0440

Also, I don't know how useful this is but I've attached some of my revision posters for this exam...

its cute

Reply 212

Lgambo

Original post by iwantopas19

can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn :smile:

HEY
An organism is defined as being a different species if can't interbreed to produce fertile offspring.
Reproductive isolation is just that, not being able to produce fertile offspring (due to sex organ differences or mating season differences blalbllalbla)

Reply 213

SKK94

Original post by iwantopas19

can someone or anyone tell me the difference between definition of species and of reprodcutiive isolationnnnnnnnnnn :smile:

A species are a group of individuals that have similar similar characteristics and can breed to produce fertile offspring.

Reproductive isolation is when individuals of a species cannot breed with each other.
This may be due to a change in structure of reproductive organs, not allowing for sexual reproduction.
It could also be because individuals in a population were geographically separated, and with time, developed different reproductive cycles or courtship behaviours that do not let them to breed with each other.
Reproductive isolation is a way that different species are formed. :smile:

(edited 10 years ago)

Reply 214

confusedgirl22

I was going through the January 2010 paper and i came across a question related to reverse transcriptase?
I swear this isn't in the specification and i also checked the CGP book and it isn't there.
I'm worried now? :/

Reply 215

Brad0440

Original post by confusedgirl22

I think that we just need to know that it is used in the conversion of viral RNA to DNA during the infection of a cell by a virus, but not how it works.

Reply 216

confusedgirl22

Original post by Brad0440

I think that we just need to know that it is used in the conversion of viral RNA to DNA during the infection of a cell by a virus, but not how it works.

thank you! don't you think it's weird that they did that though?
i'm worried they'll ask something else that isn't the specification now!
and i still won't know what kind of question will need this answer :/

Reply 217

Sravya

Original post by confusedgirl22

Which question are you on about?

Reply 218

Brad0440

Original post by confusedgirl22

Is this for question 6C ii? If so, I think that for things like reverse transcriptase and other things that we don't need to know in detail, it is more likely that they will just be marking points as opposed to whole questions by themselves (like in 6c ii).