VCE Biology Question Thread

[shivaji]

When tissue rejection occurs, do only NK cells attack the 'non-self' tissue? Can it also be Cytotoxic T cells? Thanks.

Also can vectors include needles?

Yes. I'm not sure, but I believe Tc Cells are in fact used more to attack "non-self" cells (if specific immunity)

[Reus]

What temperature is a PCR mix raised to? There are several degrees so does anyone have a definite? Thanks.

[shivaji]

What temperature is a PCR mix raised to? There are several degrees so does anyone have a definite? Thanks.

I would say 95 degrees for denaturing, 55 degrees for extending, and 72 degrees for extension.

But to be safe, you should probably say something like:

~95 degrees Celsius

[kk.08]

Can secondary structures contain disulphide bridges or are they only limited to tertiary structures?

As I came across a question in a practise exam and am not sure of the answer-

The secondary structure of spider wed proteins, which provides a combination of elasticity and strength to the web, is the result of:
a) The Fluid Mosaic structure
b) Beta pleated sheets
c)Disulfide bridges
d) Peptide Bonds

Thanks!

[Reus]

Can secondary structures contain disulphide bridges or are they only limited to tertiary structures?

As I came across a question in a practise exam and am not sure of the answer-

The secondary structure of spider wed proteins, which provides a combination of elasticity and strength to the web, is the result of:
a) The Fluid Mosaic structure
b) Beta pleated sheets
c)Disulfide bridges
d) Peptide Bonds

Thanks!

The answer should be B. Disulphide bonds are a characteristic of tertiary protein structures.

[kk.08]

Oh okay, yeah I thought so. But since it mentioned elasticity it got me wondering.

Anyhow, thanks!

[simpak]

When tissue rejection occurs, do only NK cells attack the 'non-self' tissue? Can it also be Cytotoxic T cells? Thanks.

Also can vectors include needles?

CTL can definitely attack non-self tissues.  NK cells can't technically differentiate between self and non-self in a specific sense because they are innate cells.  CTL are the ones that will recognise specific non-self proteins on the surface of the cells.

Needles can't be vectors - vectors need to be living things that can carry an infectious organism from one host to another.  A needle is closer to a fomite.

[kk.08]

Aphids are small insects which feed on the sap of plants. While feeding, aphids secrete chemicals which attract other members of their species to the food site. In this instance, aphids would be:

a)Feeding from the xylem and releasing pheromones to attract other aphids
b) Feeding from the phloem and releasing pheromones to attract other aphids
c) Feeding from the xylem and releasing auxins to attract other aphids
d)Feeding from the phloem and releasing auxins to attract other aphids

Thanks!

[Tyleralp1]

It's definitely A or B due to the fact the chemical is a pheromone as it attracts members of the other species. However, I'm not 100% sure if it feeds from the xylem or phloem. The reason being is they both contain sap of some sort, and water solutions with hormones, sugars and minerals. Can you circle two haha?

Though, my gut feeling would be Phloem due to it generally being known for its soluble food substances, so B.

[Reus]

Aphids are small insects which feed on the sap of plants. While feeding, aphids secrete chemicals which attract other members of their species to the food site. In this instance, aphids would be:

a)Feeding from the xylem and releasing pheromones to attract other aphids
b) Feeding from the phloem and releasing pheromones to attract other aphids
c) Feeding from the xylem and releasing auxins to attract other aphids
d)Feeding from the phloem and releasing auxins to attract other aphids

Thanks!

B once again. If they're feeding of a plant, this should be off the phloem since the nutrients/sugars go through it. Secondly pheromones are chemicals that are secreted by organisms to attract/stimulate other organisms of their species.

[anat0my]

CTL can definitely attack non-self tissues.  NK cells can't technically differentiate between self and non-self in a specific sense because they are innate cells.  CTL are the ones that will recognise specific non-self proteins on the surface of the cells.

Needles can't be vectors - vectors need to be living things that can carry an infectious organism from one host to another.  A needle is closer to a fomite.

Thanks simpak!

[shivaji]

How do nerves get excited? what are the steps involved to create a nerve impluse?

Thanks

[vox nihili]

How do nerves get excited? what are the steps involved to create a nerve impluse?

Thanks

Perhaps you'd like to offer what you know first and then get someone to have a look at it.

[Reus]

Perhaps you'd like to offer what you know first and then get someone to have a look at it.

I love the way you do that!

[Scrono13]

Do we need to know specific functions of all plant hormones?