VCE Biology Question Thread

[nerdmmb]

Can someone please check if the following explanation of defence against bacteria is correct?

If bacteria has entered through a cut on the skin, then mast cells lining the blood vessel will release histamine which will dilate nearby blood vessels and also make the blood vessel more permeable to leukocytes including macrophages, neutrophils, eosinophils and basophils.

The phagocytic leukocytes which include macrophages, neutrophils and eosinophils will engulf the bacteria and the neutrophils will perish due to their inability to form new lysosomes hence resulting in pus. Basophils release more histamine and also heparin to prevent blood from clotting in the blood vessels. This leads to inflammation. Finally, platelets will release chemicals or clotting factors which will eventually lead to the formation of fibrin which will form a clot with its fibres over the wound.

I was also wondering, how do the blood vessels return to their original state (from dilation)- in other words, what happens to the histamine once it has performed its function and is no longer needed?

Thanks!

[RazzMeTazz]

This was a question in my NOB book that I was unsure of..

" Explain why immunity involving T cells is called cellular immunity?"

[rhinwarr]

The cells (namely the cytotoxic T cells) act directly on the infected cells whereas in the humoral immunity, it is the antibodies not the cells themselves which act on the infectious particles.

[Jason12]

explain why the primary immune response is weaker and slower than the secondary immune response?

[militarisation]

why does dna replication start from 5' to 3'? why cant it be the other way around?

[Jason12]

what are some examples of physical and mechanical plant defense?

[vox nihili]

why does dna replication start from 5' to 3'? why cant it be the other way around?

Shape of the enzyme. It only binds the 3' end of DNA.

[auds]

Could someone please explain what interleukins do?? Thank you

[vox nihili]

Could someone please explain what interleukins do?? Thank you

They're signalling molecules of the immune system

[Jason12]

Could someone please explain what interleukins do?? Thank you

Interleukin-1 activates T helper cells and interleukin-2 stimulates growth/multiplication of B & T lymphocytes

[RazzMeTazz]

Do identical twins have the same MHC marker proteins on the surface of their body cells?

But fraternal twins do not?

[vox nihili]

Do identical twins have the same MHC marker proteins on the surface of their body cells?

But fraternal twins do not?

Yes and with fraternal it depends on what markers they inherit from their parents. They technically could be the same, but they don't necessarily have to be the same.

[Reus]

Do identical twins have the same MHC marker proteins on the surface of their body cells?

But fraternal twins do not?

Was this a particular question? If so, from where? 

[RazzMeTazz]

Was this a particular question? If so, from where? 

No, it wasn't a particular question
I was just wondering because my NOB textbook says: " perfect matching of tissues occurs only if identical twins are involved in organ donation"

[RazzMeTazz]

Yes and with fraternal it depends on what markers they inherit from their parents. They technically could be the same, but they don't necessarily have to be the same.

Oh okay, thanks so much!