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Edexcel A2 Biology SNAB 6BI04 ~ 6BIO5 June 2016

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Original post by tayloryeah
yes, you're correct :smile:
exons = contain genetic code
introns = do not contain genetic code
During post transcriptional changes, Introns are spliced out of the mRNA strand catalysed by splisosome. Exons are recombined in many different ways giving rise to to different combinations of mRNA, therefore many proteins can be produced from one gene as the mRNA acts as the template for the tRNA molecules which carry the specific amino acid to compliment the codons on the mRNA strand (using anticodons). This sequence determines the sequence of amino acids in the primary structure which determines what and where bonds form and as a result how the protein folds (between R groups) including; hydrogen bonding, disulphide bridges and ionic bonding!


Thank you so much!!!!
Can someone share some generic points for the following synoptic topics within the context of a BIO4 paper?

- Cellulose
- Starch (amylopectin and amylose)
- Glucose
- Glycogen
- Globular/fibrous proteins
- Primary, secondary, tertiary protein structures
- Phase 1,2,3 trials
- Cellulose & Lignin

^ Those are often the common synoptic topics that pop up on BIO4. If people could attempt to share a couple of marking points for questions related to them in general, would be great help for everyone and would save people the trouble of having to go through the entire AS syllabus.
Original post by tayloryeah
NPP= the rate at which energy is transferred into organic matter to make up new biomass of a plant (energy stored)

GPP= the rate at which energy is incorporated into organic matter by a plant ( energy used)

GPP> NPP
because energy loss mainly comes from respiration in the form of heat.
NPP= GPP-R
Other sources of energy loss: inedibility of a plant ,urine and faeces, movement and reproduction.
In relation to a plant: photosynthetic inefficiency may include, the wrong wavelength thus the light is reflection, excess light and the light may not be hitting the chlorophyll molecules


So both GPP and NPP are dependent on photosynthesis right? Both increase with temperature and rainfall due to photosynthesis?
Reply 383
Will someone explain insect succession as a means of determining time of death pls
Reply 384
guys what do we need to know about hiv?


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Reply 385
Original post by kxx_
Will someone explain insect succession as a means of determining time of death pls


ImageUploadedByStudent Room1465985076.887598.jpg

pretty useful! gl


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Reply 386
guys whats a macrophage and a lymphocyte ? im so confused


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Original post by ranz
guys whats a macrophage and a lymphocyte ? im so confused


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A lymphocyte is a white blood cell, so there's B-lymphocytes and T-lymphocytes. Macrophage is a type of lymphocyte which is involved in phagocytosis.
Reply 388
Original post by shooting_stars
A lymphocyte is a white blood cell, so there's B-lymphocytes and T-lymphocytes. Macrophage is a type of lymphocyte which is involved in phagocytosis.


oh thanks! when do i use phagocyte and when do i use macrophage?


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Original post by ranz
oh thanks! when do i use phagocyte and when do i use macrophage?


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A machrophage is a phagocyte, so when you talk about phagocytosis you would say the macrophage engulfs the pathogen.
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Can someone explain marking point 3? I'm not sure why the B-cell acts as an APC to itself rather than act as an APC to a T-helper cell as it releases cytokines to help the b-cell divide.
This is the June 2014 reserve paper btw
Original post by noctisff
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Can someone explain marking point 3? I'm not sure why the B-cell acts as an APC to itself rather than act as an APC to a T-helper cell as it releases cytokines to help the b-cell divide.
This is the June 2014 reserve paper btw


Yeah I thought that it acts as an APC to a T helper cell too :/
Reply 392
Can anyone describe the investigations that needs to be carried out to measure the abundance and distribution of a species ? I know one is systematic and one is random sampling, but get confused on the different steps for each. Thankss :h:
Original post by Cakey_101
So both GPP and NPP are dependent on photosynthesis right? Both increase with temperature and rainfall due to photosynthesis?


yes, an increase in temperature would increase photosynthetic reaction rates and therefore more organic matter produced from the light independent stage in the form of glucose can be used to make starch and thus more is able to be stored by a plant (NPP) and used by a plant (GPP).
Original post by kxx_
Will someone explain insect succession as a means of determining time of death pls


The study of insects when determining death is referred to Forensic entomology. Insects successively change from egg to adult over a period of time. Scientists can use the life cycle of the insect and which stage it is at to determine how long the body has been left dead for as insects appear when the body starts to decompose and thrive.A factor that affects the life cycle of the insect is temperature (down to rate of reactions). This information pieced with other factors that help determine death like decomposition, rigor mortis and core temperatures (increases reliability) can be used to workout the TOD.
guys how do u use transects?? (do we need to know this)
Reply 396
Original post by tayloryeah
The study of insects when determining death is referred to Forensic entomology. Insects successively change from egg to adult over a period of time. Scientists can use the life cycle of the insect and which stage it is at to determine how long the body has been left dead for as insects appear when the body starts to decompose and thrive.A factor that affects the life cycle of the insect is temperature (down to rate of reactions). This information pieced with other factors that help determine death like decomposition, rigor mortis and core temperatures (increases reliability) can be used to workout the TOD.


omg thanks this was really helpful x
Original post by ranz
guys what do we need to know about hiv?


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HIV is a retrovirus it contains the nucleic acid - RNA
- Viruses can affect macrophages and T helper cells
GP120 receptors on the virus bind to CD4 receptors on T helper cells
The envelope of the virus fuses with the phospholipid bi layer of the t helper cell and releases its contents by endocytosis.
Viral RNA enters the nucleus of the T helper cell
Viral RNA is converted into Viral DNA, catalysed by Reverse transcriptase
Viruses reproduce within the cell
Virus particles leave the T helper cell, causing the cell to burst
T killer cells release cytotoxins to destroy t helper/ virus infected cells
this intern reduces the CD4 count when tested in the blood
which leads to high susceptibility to opportunistic infections
which increases the risk of death

Anti viral drugs inhibit viral infections by preventing replication
therefore t helper cells are not destroyed when virus droplets are released
the drug inhibits the action of reverse transcriptase and so viral dna is not produced
the drug also inhibits the action integrase which prevents viral DNA from integrating with the hosts DNA
Original post by noctisff
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Can someone explain marking point 3? I'm not sure why the B-cell acts as an APC to itself rather than act as an APC to a T-helper cell as it releases cytokines to help the b-cell divide.
This is the June 2014 reserve paper btw


Someone answer this ^^ plz b0ss
Original post by _H_V
Can anyone describe the investigations that needs to be carried out to measure the abundance and distribution of a species ? I know one is systematic and one is random sampling, but get confused on the different steps for each. Thankss :h:


so generic phrases to be used in these types of questions which usually always get the mark include:
- mentioning quadrat
- Repeat to gather a mean
- record results in a table
- plot a graph
- improvement to be made: to increase accuracy, increase the number of squares in the quadrat

Random sampling
- use a random number generator calculator to generate a set of co- ordinates (hence random) so that you can place the quadrat down
- count the presence of each organism per quadrat
- calculate the total no. of species/ by the total area sampled

Systemic sampling
- involves placing a transect along a distance
- quadrats are placed at regular constant intervals (eg. per metre)
- count the presence of each organism per quadrat - calculate the total no. of species/ by the total area sampled

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