practice exam questions thread

[Smiley_]

A DNA sequence that is 100 nucleotide pairs long has 200 bases, because the nucleotides come in pairs.

There are 25 adenine bases, which means there must also be 25 thymine bases, making a total of 50 bases.

There must be 150 more bases of cytosine and guanine, and since they will appear in equal numbers, there will be 75 bases of guanine.

also im confused on question 12
and
16

[Stevensmay]

Question 12 is best tackled with a process of elimination.

We have
A. ethylene stimulates cell elongation which enables fruit to grow
B. the scratching of the surfaces of harvested figs speeds up ripening.
C. changes triggered by ethylene would discourage animals from consuming fruit.
D. ethylene receptors are located on the external surfaces of the plasma membrane.

A: The information given tells us that ethylene causes ripening not cell elongation, therefore this is wrong.
B: As injury is one reason ethylene is released, it makes sense that damaging the fig would cause release and thus ripening. This makes sense but we need to make sure there isn't a better answer.
C: Information given makes no mention of animals and whether they like ripe or unripe fruit. This answer is out.
D: Not enough information given to be able to substantiate this answer, and we already have B which makes a lot more sense.

Thus we get answer B.

Question 16.

Spoiler

Agglutination is the clumping of blood cells when they get come into contact with their respective antibody.
Type A blood will clump when presented with type A antigens.
Type B blood will clump when presented with type B antigens.
So on.

Option D is the only one that makes sense here. In all the other options they are presenting the red blood cells with a different antigen to the one they will react with.

[Smiley_]

thanks could someone please clarify the difference between NK and cytoxic t cells

[Yacoubb]

thanks could someone please clarify the difference between NK and cytoxic t cells

Natural killer cells are involved in the innate (non-specific) immune response as part of the second line of defence, inducing cells infected by any pathogen (irrespective of what type it is) to die. Cytotoxic T-cells on the other hand are part of the adaptive immune response, and kill only cells infected by specific pathogenic agent. This specificity is a result of cytotoxic T-cells only releasing cytotoxins on cells whose MHC Class I markers present epitopes (antigen fragments) that the specific immune response by the immune system has been coordinated to attack and destroy.

Hope this helped!

[Smiley_]

Natural killer cells are involved in the innate (non-specific) immune response as part of the second line of defence, inducing cells infected by any pathogen (irrespective of what type it is) to die. Cytotoxic T-cells on the other hand are part of the adaptive immune response, and kill only cells infected by specific pathogenic agent. This specificity is a result of cytotoxic T-cells only releasing cytotoxins on cells whose MHC Class I markers present epitopes (antigen fragments) that the specific immune response by the immune system has been coordinated to attack and destroy.

Hope this helped!

Cytotoxic T cells will attack cancer don't they

[Yacoubb]

Cytotoxic T cells will attack cancer don't they

Yeah, cytotoxic t-cells detect and destroy cancer cells as part of the immune response.

[swagsxcboi]

Natural killer cells are involved in the innate (non-specific) immune response as part of the second line of defence, inducing cells infected by any pathogen (irrespective of what type it is) viruses to die. Cytotoxic T-cells on the other hand are part of the adaptive immune response, and kill only cells infected by specific pathogenic agent. This specificity is a result of cytotoxic T-cells only releasing cytotoxins on cells whose MHC Class I markers present epitopes (antigen fragments) that the specific immune response by the immune system has been coordinated to attack and destroy.

Hope this helped!

I don't think a cell can be 'infected' by anything other than a virus?

[SocialRhubarb]

Some species of bacteria can invade cells. I imagine prions would also be able to 'infect' cells.

[swagsxcboi]

Some species of bacteria can invade cells. I imagine prions would also be able to 'infect' cells.

okay fair enough.
Prions are undetectable though

[slothpomba]

Some species of bacteria can invade cells. I imagine prions would also be able to 'infect' cells.

Prions are infectious but in a very different way to anything else science has previously encountered (viruses, bacteria, you name it).

okay fair enough.
Prions are undetectable though

They're not undetectable actually. You can see them in the brain of an infected organism once the disease progresses to its late state (obviously not much use by then!). I did my biochemistry project on them, there are emerging ways to detect them but they're not of huge clinical use just yet.

In terms of VCE correct though, both those statements in the quotes are what you need to know.

[swagsxcboi]

Prions are infectious but in a very different way to anything else science has previously encountered (viruses, bacteria, you name it).

They're not undetectable actually. You can see them in the brain of an infected organism once the disease progresses to its late state (obviously not much use by then!). I did my biochemistry project on them, there are emerging ways to detect them but they're not of huge clinical use just yet.

In terms of VCE correct though, both those statements in the quotes are what you need to know.

ah right, I see haha yeah I meant they're undetectable by the immune system

[Smiley_]

how much info should we know about apoptosis
I sort of know the stuff in the tsfx notes
but if we were asked to describe the process of apoptosis would you say the inside or outside one

obv if it is 1 mark i will say programmed cell death but how much more should i know considering it is barely in any of the textbooks

thanks

[Yacoubb]

how much info should we know about apoptosis
I sort of know the stuff in the tsfx notes
but if we were asked to describe the process of apoptosis would you say the inside or outside one

obv if it is 1 mark i will say programmed cell death but how much more should i know considering it is barely in any of the textbooks

thanks

The emphasis on the study design in regards to apoptosis, is knowing apoptosis as an example of a signal transduction pathway (involving reception, transduction and response). If you were asked about apoptosis, where you needed to describe the signal transduction pathway of apoptosis, you need to mention it in terms of the extrinsic pathway. This involves the receipt of a death signal by a specific type of cell, which triggers the cascade of events (including the activation of caspases, blebbing of the cell, rupturing of mitochondria), leading to the response that involves the cell self-destructing under this controlled, programmed mechanism [apoptosis].

[Smiley_]

The emphasis on the study design in regards to apoptosis, is knowing apoptosis as an example of a signal transduction pathway (involving reception, transduction and response). If you were asked about apoptosis, where you needed to describe the signal transduction pathway of apoptosis, you need to mention it in terms of the extrinsic pathway. This involves the receipt of a death signal by a specific type of cell, which triggers the cascade of events (including the activation of caspases, blebbing of the cell, rupturing of mitochondria), leading to the response that involves the cell self-destructing under this controlled, programmed mechanism [apoptosis].

thanks did you get this idea from the sample exam ?

[Yacoubb]

thanks did you get this idea from the sample exam ?

Yeah. Just note that apoptosis has its own point on the study design. Personally that means apoptosis is probably going to be assessed extensively in the exam. But who knows!