VCE Biology Question Thread

[RazzMeTazz]

Why is that when a harmless microorganism gains access to some part of the body where it does not normally exist, there is potential for it to become a pathogenic parasite?

[katiesaliba]

How are vaccines and antibody serums present in nature? Aren't they both artificially induced?

Also, what are some examples of chemical barriers in plants?

[sparked]

Why is that when a harmless microorganism gains access to some part of the body where it does not normally exist, there is potential for it to become a pathogenic parasite?

This is because different regions of the body do not secrete the same kinds of defensive enzymes/have the same competing forms of microflora that regulate 'safe' population sizes of these otherwise harmless microorganisms. They become harmless when they occur in drastically greater numbers, where their byproducts of cellular metabolism and/or nutrient demand exceedes the capacity for the body to not be adversely affected by this.

How are vaccines and antibody serums present in nature? Aren't they both artificially induced?

Also, what are some examples of chemical barriers in plants?

Antibody serums such as 'anti-venom' for example, sometimes naturally exist via natural selection in organisms that have become immune to snake bites of a certain predator. Nature's "vaccines" are just pathogen infection, where the response to the infection gains immunity. The difference between this and artificial vaccinations is that artificial vaccinations do not lead to an actual infection by an agent able to reproduce within the body (attenuated viruses, only sub-components etc.) and a natural immunity runs the risk of severe symptoms/death if the body cannot produce antibodies quickly enough.

[RazzMeTazz]

Why does the allergic response increase in its severity, with consecutive exposure to the allergen?

Are there more mast cells present each time?

[RazzMeTazz]

This is because different regions of the body do not secrete the same kinds of defensive enzymes/have the same competing forms of microflora that regulate 'safe' population sizes of these otherwise harmless microorganisms. They become harmless when they occur in drastically greater numbers, where their byproducts of cellular metabolism and/or nutrient demand exceedes the capacity for the body to not be adversely affected by this.

Antibody serums such as 'anti-venom' for example, sometimes naturally exist via natural selection in organisms that have become immune to snake bites of a certain predator. Nature's "vaccines" are just pathogen infection, where the response to the infection gains immunity. The difference between this and artificial vaccinations is that artificial vaccinations do not lead to an actual infection by an agent able to reproduce within the body (attenuated viruses, only sub-components etc.) and a natural immunity runs the risk of severe symptoms/death if the body cannot produce antibodies quickly enough.

Thankyou!!!

[sparked]

Why does the allergic response increase in its severity, with consecutive exposure to the allergen?

Are there more mast cells present each time?

Yes.

So the way an anaphylaxis response works is like so:

Mast cells contain vesicles of histamine waiting to be released.

Upon the 1st exposure of the allergen, antibodies are formed. These then sit on mast-cells with the two variable regions reaching into the extracellular fluid surrounding the cells. These antibodies link with the allergen spread across the two separate antibodies (think   Y-Y) essentially linking them together in a chain.

When they are re-exposed BAM. These antibodies trigger a cascade response, the vesicles are exocytosed and the reaction occurs.

Subsequent exposures may or may not trigger the creation of more mast cells hence increased severity.

[Scooby]

How are vaccines and antibody serums present in nature? Aren't they both artificially induced?

Both confer artificially-acquired immunity. The difference is that immunity acquired by vaccination is active, whereas an antibody serum would confer passive immunity. Vaccination triggers an immune response within an organism, resulting in production of antigen-specific memory cells and antibodies. This doesn't occur when an antibody serum is used, so the the resulting immunity remains for a much shorter time frame. Antibody serums are produced by infecting some animal with a particular pathogen and then extracting antibodies from its blood which are specific to the antigens of that pathogen. Antibody serums are often used to prevent infection (rather than treat it) in high-risk circumstances (eg. if you're living in a house with your family and all your family members are infected, and the infection is quite nasty and highly communicable, etc)

[Scooby]

Subsequent exposures may or may not trigger the creation of more mast cells hence increased severity.

The antibody response to the allergen will be greater, but there shouldn't be increased production of mast cells

[RazzMeTazz]

are mast cells involved in the inflammatory response as well as, the allergic response?

:)

[Reus]

are mast cells involved in the inflammatory response as well as, the allergic response?

Yes. They are the granulated cells that produce histamines.

[RazzMeTazz]

What would be an example of a systemic immune response ?

[grannysmith]

How could we account for the fact that a different flu vaccine is needed every year?

Is it due to mutations and hence the change of receptors which bind to a host cell? If receptors mutate, among other things, then can host specificity/ regions of infection change as well?

Someone please tell me if I'm understanding it correctly

[vox nihili]

How could we account for the fact that a different flu vaccine is needed every year?

Is it due to mutations and hence the change of receptors which bind to a host cell? If receptors mutate, among other things, then can host specificity/ regions of infection change as well?

Someone please tell me if I'm understanding it correctly

Yeah it's just really small mutations in the receptor. They actually don't tend to change the binding site but other sites around it so antibodies find it tougher to bind.

[grannysmith]

Why do subsequent exposures to a pathogen generate a greater and faster production of antibodies specific to the antigen? I know that this is primarily due to memory cells, but how/why exactly do they produce a greater and faster amount of antibodies? Wouldn't they have to go through the same process of clonal selection and expansion?

[katiesaliba]

Equally make sure you understand that viruses that invade lymphocytes express on the MHC I molecule!

Considering lymphocytes are antigen presenting, couldn't they express viral antigen fragments on both MHC I and MHC II molecules?
Also, are T- and B-lymphocytes phagocytic, considering that they're APCs?