Edexcel BIOLOGY Doubts!!!!

[-Cornea]

Captive breeding programs-this is done by keeping animals in zoo or in national parks,keeping a record of their genetic information in the studbooks and allowing them to breed with individuals which is different from the previous mating or with different species increasing genetic diversity and gene pool size the genes are swapped with different zoos to maxmise genetic variation hence increasing allele frequency and providing right conditions for them to mate they sometimes use the cross cloning species after this process they are then re-introduced into the wild to restore their original population and to acclamtize to their original habitat.By keeping them in the zoos they increase the public awareness of the people and keeps them away from the predators and poachers (the reasons of their extinction in the first place )

[-Cornea]

Point 6- one of the most important characteristic of meiosis that it produce tetra(4 cells) which contains haploid number of chromose 23 yes the sperms has a nucleus but it contains only 23 chromosome so during fertilization it can restore the diploid number ,and the gametes are produced by MEIOSIS !

[-Cornea]

I forget to mention this in my last post
If the cell is damaged or repair the new cells must have the same structure and function as the old ones or else the tissue won't function as effective as before MITOSIS ensures this

[-Cornea]

Don't mix up between kingdoms and domains consider them as two separate things  the domains are archae bacteria and eukaryotes you don't need to know much just a couple of differences between each of them and you need to know that ARCHAE AND EUKARYOTES are more closely related than ARCHAE  AND BACTERIA   

[-Cornea]

the last point - you need to obtain the plant material first crush it 10 cm^3 of industralised denatured alcohol to kill any bacteria that might be contaminated with the extract shake the test tube from time to time pippete 0.1 cm^3 of plane extract onto filter paper discs and place it in a petri dish incubate it at 25 degree Celsius for 24 hours tape the petri dish but do not tape it in a way that might lead to the growth of anaerobic bacteria and of course you know that the petri dish contains agar with a microbial lawn growing on it .The plant extract will diffuse from the paper disc and it will inhibit the growth of the bacteria to a certain extent this area which appears to be clear is known as the ZOI(ZONE OF INHIBITION) it can be measured using a ruler if it regular and then repeat the measurements and take the average if it's irregular take the readings from different angles or there is another method in which u use the graph papers and counting the surface area(which i have no idea about it)

and about the manila you don't need to know the name of different fibers you just to need to know how to extract the plant fibers and how to measure the tensile strength !

[Malak]

How do these factors affect the rate of cooling of a body (forensics)

Humidity
Body size

And this spec point --> Discuss the way in which scientific conclusions about controversial issues, such as what actions should be taken to reduce global warming or the degree to which humans are affecting global warming, can sometimes depend on who is reaching the conclusions


Edit: another doubt

What is the difference between extent of decomposition and stages of sucession in terms of forensics.
Isnt it that, as the body decays, insect speices feeding on it change (sucession) :S

Thanks

[MKh]

How do these factors affect the rate of cooling of a body (forensics)

Humidity
Body size

And this spec point --> Discuss the way in which scientific conclusions about controversial issues, such as what actions should be taken to reduce global warming or the degree to which humans are affecting global warming, can sometimes depend on who is reaching the conclusions
Edit: another doubt
What is the difference between extent of decomposition and stages of sucession in terms of forensics.
Isnt it that, as the body decays, insect speices feeding on it change (sucession) :S
Thanks

Ohk so for the spec. point u have mentioned, u have to discuss the ways in which scientific conclusions (what must be done to reduce global warming) about controversial issues (the fact that global warming is rising and its causes including anthropogenic -human!- and natural activities) can sometimes be affected by who (politicians and scientists who are funded by oil companies who are all biased by their own interests) is reaching those conclusions.

In the Edexcel A2 Biology June 2011 Unit 4 examination, we had this question about why some scientists claim that burning fossil fuels is not the main cause of global warming. Do not forget to read the relevant marking scheme as you will get a good idea about what this specification point expects us to know This is a HSW type question.

[MKh]

For the specification point i explained above, from the Edexcel A2 Biology Revision Guide, I quote:

There is little doubt that global warming is happening, but there are still big questions over what is causing it and what we should do about it. It is quite normal for scientists to disagree but this topic is also a matter for public debate. Non-scientists may not understand the uncertainty and naturally want a clear answer. The people who will give them this are often not the scientists but politicians, economists and other policy makers. Quickly the debate becomes politicised and then the usual impassionate methodology of science becomes sidelined.

It soon becomes clear that data are being interpreted with various hidden agendas and then this becomes the news rather than the science itself. So, scientists are being accused of being funded by oil companies if they argue against the established political view, or politicised if they argue for it.

What conclusions people reach are often coloured by who funded the research they are doing, and pressures of economics and politics.

Regarding your question about how humdity and body size affects the rate of cooling:

Humidity: Actually, body temperature is usually 37 degrees celcius but the body begins to cool straight after death. If the environment of a dead body is more humid than normal than then, as far as i think, the rate of cooling of the body will be higher.

Body size: the rate of cooling of a dead body with a larger body size, the surface area:volume ratio will be lower so the rate of cooling will be lower.

I am sorry i m not that sure about the effect that the above two factors have on the rate of cooling, but it is all that i can deduce from what i already know, so it is better that you try googling it.


In forensic terms, extent of decomposition is the extent to which the dead body has decayed. It is actually one of the main indicators of the time of death of a body. And how does a forensic scientist use this information? Bodies usually follow a standard pattern of decay. Enzymes in the gut start to break down the wall of the gut and then the surrounding area. As cells die they release enzymes which help to break down tissues. The signs of decomposition, such as discoloration of the skin and gas formation, combined with information about environmental conditions allow time of death to be estimated.
 
What about the stage of succession? It is also one of the five main indicators of the time of death of a body that a forensic scientist uses. And how is this information used by a forensic scientist? As a body decays, the populations of insects found on it change. There is a succession of species. The community of species present when the body is found allows the stage of succession to be determined and time of death estimated.

In addition to the extent of decomposition and stage of succession, the other three indicators of the time of death of a body used by a forensic scientist includes: body temperature, degree of muscle contraction and forensic entomology.

Body temprature: As I mentioned before, the body temperature is usually 37 degress celcius but the body begins to cool straight after death. During the first 24 hours after death the temperature of the body when it is found can be used to work out how long ago the person died.

Degree of muscle contraction: After death, muscles usually totally relax and then stiffen. This stiffening is called rigor mortis. This happens within about 6-9 hours (depending upon temperature). The stiffness occurs because muscle contraction relies on ATP, which cannot be made once respiration has stopped. So the muscles become fixed. The stiffness wears off again after about 36 hours in cooler conditions as the muscle tissue starts to break down.

Forensic entomology: Determining the age of any insect maggots in the body allows the time the eggs were laid to be determined. This provides an estimate of time of death assuming any eggs were lad soon after death.

Putting all this information together can give the forensic scientist a very good estimate of the time of death.
Please do not confuse stage of succession and forensic entomology - they are two different indicators of the time of death.

I know you did not ask for all this but i hope it helps your understanding.

[Malak]

Thanks a lot for the detailed reply.

About the extent of decomposition and sucession, I understand what they both are but my confusion is that they both are linked right? I mean that one of the reasons the body decays is because of the insects right? And then sucession is the change in the speices of these insects.

So they are sort of linked ? 

[MKh]

^
You are welcome.
Yes both these processes are linked.

What attracts these insects so strongly to a dead body?? The answer is this body decay. Like I mentioned before, Enzymes in the gut start to break down the wall of the gut and then the surrounding area. As cells die they release enzymes which help to break down tissues. This is called body decay and it produces gas that attracts these insects.

These insects feed on the dead body and lay eggs as well. The hatched insects also feed on the body and so the body changes in a way that is unsuitable for them and so the species of insects that can now feed on the inner parts of the body replace them. The early colonisers of a dead body also release various body fluids as a result of their metabolism which attracts other species of insects that colonise the dead body and feed on it. This is called succession. And these insects feed on the body causing further decay of the dead body. So yes, they are linked.

The decay of a body after death caused by its natural processes attracts the insects that feed on it causing further decay and attracting other species which is called Succession.

Also note that our own body has a variety of good bacteria that also contribute to the decay of our body after we die. They are the earliest corpse fauna that contribute to the decay of a dead body as they can respire anaerobically.

Also read the following:
Decomposition - Succession
The environment provided by a dead body changes with time. This change is a result of drying, and the activities and by-products of the corpse fauna. Different groups of animals find the corpse attractive at different stages of decomposition and the resultant change in the animal community is called a succession.
 
Source: http://australianmuseum.net.au/Decomposition-Succession  --> check it out.

Hope it is clear. If not, feel free to ask again. And read the A2 Biology Textbook.

[Malak]

Yeah, I understand now :d

Thanks

[Malak]

Another doubt.

What actually is the acute phase of HIV.

I am confused, does it happen after HIV virus has binded with the host cell and all the viral dna thing has taken place? :S

[MKh]

Another doubt.
What actually is the acute phase of HIV.
I am confused, does it happen after HIV virus has binded with the host cell and all the viral dna thing has taken place? :S

The acute phase of HIV infection is when the Human Immunodeficiency Virus has infected the host cell. Actually viruses need to bond to a host cell inorder to reproduce; before this they cannot reproduce - all viruses depend on a host cell inorder to replicate themselves.
The acute phase of HIV infection is the first phase of HIV infection which is called the primary HIV infection phase

1. The primary HIV infection phase (or acute sero-conversion illness)Graphic, Phase 1.

The acute phase of HIV infection (also called acute sero-conversion illness) begins as soon as sero-conversion has taken place. Sero-conversion means the point in time when a person’s HIV status converts or changes from being HIV negative to HIV positive. This also usually coincides with the time when an HIV antibody test will show that a person is HIV positive.

Sero-conversion usually occurs four to eight weeks after an individual has been infected with the HI virus. About 30%-60% of people infected with HIV develop flu-like symptoms such as sore throat, headache, mild fever, fatigue, muscle and joint pains, swelling of the lymph nodes, rash, and (occasionally) oral ulcers. These symptoms usually last from between one and two weeks.

Because of the rapid replication of the virus, the HIV viral load is usually very high during the acute phase. Immediate and aggressive treatment with anti-retroviral therapy (ART) at this stage may be effective in reducing the viral load to undetectable levels, or even in eradicating the virus.

Source: http://www.health.am/aids/more/symptoms_and_phases_of_hiv_infection_aids/

Hope this helps.

[Malak]

^Thanks.

Sometimes in questions, they ask us to give an example of an organism and its habitat.

Can someone name some for me with their habitat.

Thanks. *i think i will fail* >_<

[MKh]

^Ohh don't be put off by the amount of information i have linked you to, it's simply to help your understanding. I wish i had the opportunity to look onto these sites before my exam to help my understanding, even if it was a day before, because you see the book doesn't tell us the whole thing.

But keep to the specification only. Have you referred to those notes i once uploaded here?

Tips: -Learn the common definitions like gene mutation, allele frequency and some other commonly asked ones - you must have noticed that they are even mentioned in the Edexcel A2 Revision guide. Also see the marking schemes for exact definitions.

-Revise the core practicals very well - the one for measuring the effectiveness of an antibiotic, the PCR and the DNA profiling one --- check the marking schemes. For the other two core practicals - the investigation of ecology and measuring the effect of temperature on growth of seedlings, they might ask some random questions so be prepared by practicing past papers. Also understand their underlying biological principles.

-Check out the Quick questions on your revision guide

-Learn the whole immune system response and evolution topics very well.

And about your question, can you give me a few examples of such questions that you have come across?