[sceptic_medic]

(Original post by M Kh)
Ohkay, I understand the lysozyme action very well. I just don't understand what the interferon is and how it works. I just know that it inhibits (or slows down?) the reproduction of viruses but I just don't understand what is the mechanism involved.

I also don't understand the types of white blood cells - phagocytes, macrophages, types and sub-types of WBCs, lymphocytes etc. I just don't understand the classification. I am googling it now though.

I understand phagocytosis well but not inflammation - how it works and what cells are involved.

Ok cool. They sound pretty much like the same issues I had.

Lysozyme is pretty easy in that breaks the cell walls of bacteria and I know you said you know it but it's also important to know where it's secreted --> in mucus, tears mucosal surfaces, skin.

Interferons are secreted by body cells which are infected by viruses. You don't need to know the mechanism at all, just that it spreads to other cells and stops viral proteins being synthesised from them. It works better under the higher-temperatures experienced during fever.

Types of white blood cell (also called leucocytes): phagocytes and lymphocytes. Essentially there are two types of phagocyte --> macrophages and neutrophils. You don't need to understand the differences between them, other than macrophages are the ones involved during a TB infection. Lymphocytes are involved in the immune response and comprimise T-Helper cells, T-Killer cells, B-Cells and all their associated memory cells.

[avataraang]

(Original post by M Kh)
The Green book does not cover this unfortunately so can you please help me with this:
9. Describe the role of micro-organisms in the decomposition of organic matter and the recycling of carbon?

* Micro-organisms secrete enzymes to help decompose dead organic matter.
* This allows digestion of organic matter, meaning that products released from this is used for aerobic respiration, releasing CO2.
* CO2 released into the atmosphere to be taken up by plants for photosynthesis.

I think thats all the points!

[M Kh]

(Original post by marc_h94)
Ok cool. They sound pretty much like the same issues I had.

Lysozyme is pretty easy in that breaks the cell walls of bacteria and I know you said you know it but it's also important to know where it's secreted --> in mucus, tears mucosal surfaces, skin.

Interferons are secreted by body cells which are infected by viruses. You don't need to know the mechanism at all, just that it spreads to other cells and stops viral proteins being synthesised from them. It works better under the higher-temperatures experienced during fever.

Types of white blood cell (also called leucocytes): phagocytes and lymphocytes. Essentially there are two types of phagocyte --> macrophages and neutrophils. You don't need to understand the differences between them, other than macrophages are the ones involved during a TB infection. Lymphocytes are involved in the immune response and comprimise T-Helper cells, T-Killer cells, B-Cells and all their associated memory cells.

And what type of cells are infected by the HIV?

[tania<3]

I'm entered for this exam as a retake but doubt I will get any revision done - too busy with maths and chemistry! :/

[M Kh]

(Original post by avataraang)
* Micro-organisms secrete enzymes to help decompose dead organic matter.
* This allows digestion of organic matter, meaning that products released from this is used for aerobic respiration, releasing CO2.
* CO2 released into the atmosphere to be taken up by plants for photosynthesis.

I think thats all the points!

I think something is missing.

So you mean that these microorganisms release enzymes.....outside their body onto the dead organic matter (what is this organic matter anyway?).....and the enzymes break down this organic matter (what are the products of this breakdown?).....and then how are these products used for respiration while they are outside the microrganisms' bodies?........and then after they are used in respiration.....carbon dioxide is released into the atmosphere.....which is then used by plants in photosynthesis?

[Jasmine_777]

(Original post by This Honest)
HIV- prevent antigen processing
mutations occur rapidly so different strains are produced; have to launch a new primary response to each strain

TB- prevent antigen processing
form waxy substance outside vacoule to prevent lysosomes from digesting it

I'm missing one more thing but I can't remember

sry, what does 'prevent antigen processing' mean?

[arnab]

(Original post by M Kh)
Bolded part - very, very confused.
T helper cells having complementary receptors to the antigen on the antigen-presenting cell bind their receptors with the antigens. Then how does this stimulate the division of B cells? Does it happen like this that when the T helper cells bind their receptors with the antigens, they become activated and these activated T helper cells then meet B cells and stimulate the division of B cells or what?

Thanks a lot, btw. And what is the difference between the cell-mediated response and humoral response?

wait, i have never heard of these words in bold. Care to explain what they mean?

[M Kh]

(Original post by arnab)
wait, i have never heard of these words in bold. Care to explain what they mean?

Those are two types of the specific response of the human body to infection. If you have the Green-coloured Edexcel A2 Biology book, you can see on pages 100-103 and it explains everything very well.

And I hope this helps you understand further what the differences are:

(Original post by marc_h94)
Oh, and the difference between the cell-mediated and humoral responses:

The humoral response is just as I outlined above, with the plasma cells secreting huge amounts of the right antibody that disables and destroys the antigens/toxins/pathogen. Note that the plasma cells are adapted to secrete huge amounts of protein in this way by having extensive endoplasmic reticulum and lots of ribosomes.

However, this is isn't particularly effective when body cells have actually been infected by a pathogen. This is where the cell-mediated response comes into play. The infected body host cell acts as an APC as above, presenting the antigens of the pathogen that it has been infected by on its MHC complexes. Then, a T-killer cell (or cytotoxic T cell) comes along and binds to the APC if it has complementary receptors to the presented antigen. Meanwhile, an activated T-helper cell will release cytokines which will activate the T-killer cell. This then finally causes the T-killer cell to do what it was made to do: release chemicals that will cause the body cell to lyse. This will kill the body cell but also kill the pathogen too (or at the very least expose it to the humoral response). Hope that helps!

[arnab]

(Original post by M Kh)
Those are two types of the specific response of the human body to infection. If you have the Green-coloured Edexcel A2 Biology book, you can see on pages 100-103 and it explains everything very well.

And I hope this helps you understand further what the differences are:

ahh thanks but its not in the CGP revision guide

Can you explaining to me the process of splicing?

[arnab]

still dont understand the difference between Forensic entomology and Stage of succession? can someone clarify. I read the post that was made by aqua05 but i still dont get it lol

[d_94]

(Original post by arnab)
still dont understand the difference between Forensic entomology and Stage of succession? can someone clarify. I read the post that was made by aqua05 but i still dont get it lol

Heyy Arnab.

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

Stage of Succession:
As a body decays, the populations of insects found in it change. There is a succession of species. The community of species present when a body is found allows the stage of succession to be determined and the time of death is estimated.

Note~ Putting all of this information together can give the forensic scientist a very good estimate of time of death

[arnab]

(Original post by d_94)
Heyy Arnab.

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

Stage of Succession:
As a body decays, the populations of insects found in it change. There is a succession of species. The community of species present when a body is found allows the stage of succession to be determined and the time of death is estimated.

Note~ Putting all of this information together can give the forensic scientist a very good estimate of time of death

ahh so for Forensic Entomology, you look at the age of the insect and the life cycle of the insect where as for Stage of Succession, you look at the variety of insects that are present in the body? Am i right?
Also care to explain to me the process of splicing? its not really clear in the book....

[d_94]

(Original post by arnab)
ahh so for Forensic Entomology, you look at the age of the insect and the life cycle of the insect where as for Stage of Succession, you look at the variety of insects that are present in the body? Am i right?
Also care to explain to me the process of splicing? its not really clear in the book....

Yess. You're rightt (:

Whats splicing? Never heard of it?

[alexsasg]

(Original post by arnab)
ahh so for Forensic Entomology, you look at the age of the insect and the life cycle of the insect where as for Stage of Succession, you look at the variety of insects that are present in the body? Am i right?
Also care to explain to me the process of splicing? its not really clear in the book....

Sorry to butt in - I don't understand what splicing is either! The textbook isn't clear enough

[d_94]

(Original post by alexsasg)
Sorry to butt in - I don't understand what splicing is either! The textbook isn't clear enough

What is splicing???? I never saw it. Godd. Im freaking out now!
What book?

[SimpleGirl]

(Original post by arnab)
Also care to explain to me the process of splicing? its not really clear in the book....

(Original post by alexsasg)
Sorry to butt in - I don't understand what splicing is either! The textbook isn't clear enough

(Original post by d_94)
Whats splicing? Never heard of it? Godd. Im freaking out now!
What book?

DNA is made up of both introns and exons.
Introns - Non coding regions
Exons - Coding regions.
After transcription takes place, a strand of mRNA is made. This strand is then expressed during translation and proteins are synthesised. Only exons, the coding regions, can be expressed; therefore, the introns (the non coding regions) are removed after transcription as they are not needed. This leaves a strand of mRNA consisting of only exons (only sections of coding regions that can now be expressed).

When mRNA is spliced, all introns are removed and the exons are spliced together. When they are spliced together, there are a number of different combinations in which they can form a sequence. That's why several proteins can be made with just one strand of mRNA. The exons of that one strand can be spliced together in different ways, creating different combinations hence resulting in a different sequence being translated and giving the end protein.

For example (from the textbook, page 120):

pre-mRNA: (just after transcription, and before splicing has taken place)
Exon 1; Intron 1; Exon 2; Intron 2; Exon 3

Introns are removed and the exons can be spliced together to form different sequences:
Exon 1; Exon 2; Exon 3
Exon 1; Exon 3
Exon 2, Exon 3
Exon 1, Exon 2

The original strand of mRNA can produce these 4 different sequences meaning that many different proteins can be synthesised from just a single strand.

[d_94]

Woooww. Thanks sooooooo much @SimpleGirl

[SimpleGirl]

(Original post by d_94)
Woooww. Thanks sooooooo much @SimpleGirl

You're welcome

[VRS]

Can some one explain

Gel Electrophoresis

and

PCR - Polymerase Chain Reaction

Please

[arnab]

(Original post by d_94)
Woooww. Thanks sooooooo much @SimpleGirl

sorry i never answered your question about splicing but i have been on and off ( doing papers in between) but i guess you know it no

Guys what could your answer be to this question :

Foxes are territorial animals. Rural foxes commonly have territories between
two and six km2 (200 to 600 hectares) in size. Urban foxes have a much smaller
territory of less than 0.6 km2. Explain how this could affect the population of
foxes in urban areas.

I thought the answer was this :

- smaller area, hence less food available
- Lower area, hence less "space" to find a good nesting/breeding site
- More competition due to smaller area
- hence population will decrease

Can that be right?