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March 29, 2024, 04:07:59 am

Author Topic: VCE Biology Question Thread  (Read 3570737 times)  Share 

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paper-back

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Re: VCE Biology Question Thread
« Reply #5595 on: July 26, 2015, 02:33:18 pm »
+5
These are copy+paste from my notes on PCR and Gel Electrophoresis

The process of Polymerase chain reaction (PCR) allows for the production of mass quantities of genetic material from a minute starting quantity. PCR can be used for medical applications (testing for genetic mutations) and in forensics.
The process of PCR revolves around the repetition of 3 main parts;
- Denaturation 
- Annealing and
- Elongation
During the denaturation stage; the DNA is heated to temperatures of around 90C in order to break hydrogen bonds between the adjacent DNA strands
During the annealing stage; Primer's (composed of short synthetic DNA strands) with nucleic acid sequences complementary to a portion of the DNA strand hybridize to their corresponding segments of DNA. Temperatures of around 55C are used during this stage
During the elongation stage; DNA polymerase (TAQ polymerase) binds to a forward/reverse primer and begins to synthesis a new strand of DNA using nucleotides found in solution, with a base sequence that is complementary to the template DNA strand. Temperature of 65C are used for optimal enzyme activity.
 
These three stages are repeated consecutively with the quantity of genetic material increasing in accordance with the exponential function 2^n, where n= number of times process is completed
 
Electrophoresis is used to obtain a genetic profile and has many applications such as in paternity testing, and forensics
Electrophoresis separates DNA strands on the basis of length(size/mass)
Electrophoresis is usually performed after PCR has been completed
 
Genetic material is first subject to restriction enzymes which cuts the DNA sequence in accordance to their recognition sequences (I'm not sure if this step is performed before or after PCR has been completed)
DNA samples from the subjects alongside a control/standard (for size measurement) are suspended inside holes (made by a comb) within an agarose gel plate
A negative terminal is placed adjacent to a positive terminal on either side of the agarose gel plate. The DNA samples are located at the negative terminal
Current is switched on, and segments of DNA from each subject proceed to move towards the opposing pole at a pace in accordance with their size and charge
After a suitable period of time, current is switched off and a DNA profile from each subject can be obtained, and matched if required

cosine

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Re: VCE Biology Question Thread
« Reply #5596 on: July 26, 2015, 02:42:48 pm »
+5
Im pretty fucked i have a sac wednesday morning on Unit 4 Aos 1 and i know jack shit.
Teacher told us to know the proccess of PCR, purposes of gel electrophoresis, how DNA and the gel work together.
Also what is two independant assorting loci ?
If someone could explain all that for me thatd be super helpful.
 thanks in advance:)

PCR is an abbreviation for Polymerase Chain Reaction. This reaction is used for DNA amplification; so we have a small sample of DNA and want to make, literally, millions of copies of this sample. PCR is the way to go. This method involves three stages:

Denaturation: The double helix DNA strand is denature, that is, the hydrogen bonds between the bases are broken as the sample is exposed to ~94 degrees Celsius. The bonds are broken and this will leave us with two single stranded DNA molecules with complementary bases.

Annealing: The temperature is dropped significantly and DNA primers are added to the solution so that they can bind to their complementary bases at either end of the single stranded DNA molecules. These primers act as 'starting points' for the synthesis of the new DNA. The primers bind at the 3' end of each single stranded DNA.

Extension: The enzyme DNA polymerase synthesises new DNA strands on each single stranded DNA (that was earlier broken into two) by attaching nucleotides to the exposed complementary bases. The DNA polymerase bases off the primers, and so synthesises the new strands of DNA in the 5'-3' direction. 

Gel electrophoresis:
This is a technique that is used to separate and identify molecules of DNA or proteins. In your example, it would be DNA observation. Basically, electrophoresis separates different sized molecules of DNA, based on their amounts of base pairs (hence their sizes). This is done by pouring an agarous solution in the container, and inserting a comb into one end of the container. Once the gel has solidified, the comb is removed and a number of wells are created. An electric current is switched on and the positive end is at the far end of the wells, whereas the negative end is at the origin (or starting point, where the DNA molecules are placed in the wells). Now you should know that DNA has an overall negative charge due to the negative phosphate group in the sugar-phosphate backbone. This overall negative charge will allow the DNA molecules to move from the negative end, in which where they are initially placed, and move/migrate towards the positive end, as positive attracts negative. The DNA molecules all move at the same time, however, the smaller the DNA molecule (less base pairs/nucleotides), the farther it will move. The larger the DNA (the more base pairs/nucleotides), the slower it will move towards the positive end. At the end of a certain time period, the relative positions of the DNA molecules in each well can be used to determine the size of it.

Edit: Beaten by paper-back's wonderful explanation.
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Jay.C

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Re: VCE Biology Question Thread
« Reply #5597 on: July 26, 2015, 07:48:36 pm »
0
Hey could someone explain to me the factors effecting why variations in typical phenotypic ratios occur and why?

Thanks!!
Don't worry about scores that you can't change  because there are so many more productive things you could do

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warya

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Re: VCE Biology Question Thread
« Reply #5598 on: July 27, 2015, 12:37:05 pm »
0
Can someone explain the whole chromosome vs chromatid vs chromatin thing
http://i.imgur.com/VK9S9ET.gif

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cosine

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Re: VCE Biology Question Thread
« Reply #5599 on: July 27, 2015, 01:21:51 pm »
+3
Can someone explain the whole chromosome vs chromatid vs chromatin thing

Difference between chromosome and chromatin:
Alright, so DNA in our cells is always situated in the nucleus of the cell. Within the parameters of the nucleus, the DNA exists as a thin thread-like structure known as chromatin. This chromatin is the collection the all the DNA in your cells. You can imagine molecules upon molecules of chromatin, it is like a network of fibres. So, what is mitosis? The division of the nucleus, and hence how can you divide it if there is a whole structure of fibres? Exactly, these fibres, chromatin, condense (become thicker) into chromosomes during prophase of mitosis. This is done so that the nucleus can divide more readily and easily, otherwise how can you separate the network chromatin evenly into two daughter cells? So the DNA in our nucleus is only visible as chromosomes during mitosis, when it's not undergoing nuclear division, that is, not needed to divide, it exists the thread-like network, chromatin.

Difference between chromosome and chromatid:
You must understand that during the S phase of the cell cycle, the DNA in the nucleus replicates and hence the chromosomes appear as sister chromatids held together by a centromere. Each 'arm' of the chromosomal structure is known as a sister chromatid, or just simply a chromatid. The whole structure together, both the sister chromatids, is known as the chromosome. However, when the sister chromatids are separated, they are known as chromosomes and are no longer sister chromatids because they are no longer held together by that centromere.

I hope this helps xD
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@#035;3

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Re: VCE Biology Question Thread
« Reply #5600 on: July 27, 2015, 05:44:35 pm »
0
How are each of the outputs of both cellular respiration and photosynthesis produced?

Thanks in advance:)

pra96

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Re: VCE Biology Question Thread
« Reply #5601 on: July 27, 2015, 05:57:06 pm »
0
Hey I have this unit 4 SAC on Thursday to do with DNA manipulation etc.
We have an excursion to GTAC for the SAC but I have no idea what to expect.

Do you guys know what it's like? I am unsure at the moment...
2015- Biology [41]  2016 goals- [45+] PCSME

cosine

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Re: VCE Biology Question Thread
« Reply #5602 on: July 27, 2015, 06:07:34 pm »
+5
How are each of the outputs of both cellular respiration and photosynthesis produced?

Thanks in advance:)

Photosynthesis:

So you can see that glucose, oxygen gas and water are all products of photosynthesis. Firstly, water is absorbed by the plant and the chlorophyl pigments located on the thylakoid membranes (grana) of the chloroplasts of photosynthetic leaves absorb sunlight, this sunlight is then used to split molecules into it's constituent particles: Hydrogen, oxygen and electrons. The oxygen binds with another oxygen molecule that undergoes the same pathway, and forms oxygen gas. This oxygen gas is released into the atmosphere. The hydrogen ions and electrons are then carried by carrier molecules called NADP+ forming NADPH, ATP is also formed as a result. The NADPH and ATP leave the thylakoid membranes and now are surrounded by the stroma of the chloroplast. Here they will undergo the light-independent reactions of photosynthesis, where they are used to break down carbon dioxide obtained from the atmosphere into glucose. Note that the unused hydrogen ions of the light-independent reactions that are not used to make this conversion, are joined with oxygen and produce water, as a by product and this is why sometimes you do not see water a part of the outputs os photosynthesis, because it will basically be reused. Same goes with ADP + Pi and NADP+ after they 'deliver' the electrons and hydrogen ions to the light-independent stage, they will be reused again in the light-dependent stage and hence are not represented in the equation.

Cellular respiration:

In cellular respiration, glucose is broken down into 2 molecules of pyruvate in the cytosol of cells and the process is known as glycolysis. This process does not require oxygen to proceed. Once the glucose is broken down, 4ATP molecules are produced and 2 molecules are reused for the reaction, and so 2 molecules are transferred to the next stage of cellular respiration, where oxygen is a necessity. The two molecules of pyruvate enter the mitochondrion, where they react with CoA to produce Acetyl CoA. This reaction produces one molecule of NADH, and so two molecules of pyruvate will produce two NADH. The Acetyl CoA molecules will now undergo the krebs cycle, where they will undergo several reactions to produce 1 molecule of ATP each, 3 molecules of each as well as 1 and 3 molecules of NADH. This will result in 8 molecules of NADH and 2 molecules of ,   and 2ATP per molecule of glucose. The carbon dioxide is released at this stage and this whole process of reactions was accomplished in the mitochondrial matrix. The 'carriers' transfer to the cristae (the inner membrane of they mitochondria) where the electron transport chain occurs. The final acceptor here will by oxygen, to accept the hydrogen ions that are left unused and will form water as a result. There will also be a production of 32-34 molecules of ATP during the ETC. So we previously had a production of 2ATP (in glycolysis), 2ATP (in krebs cycle) and now 32-34 ATP. In total: 36-38 ATP.

I hope this helped you xD
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2015: VCE (ATAR: 94.85)

cosine

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Re: VCE Biology Question Thread
« Reply #5603 on: July 27, 2015, 06:11:00 pm »
+2
Hey I have this unit 4 SAC on Thursday to do with DNA manipulation etc.
We have an excursion to GTAC for the SAC but I have no idea what to expect.

Do you guys know what it's like? I am unsure at the moment...

I did this a while back, this is what we were required to know:

- Restriction enzymes:
What are they?
Wy are they used?
What do they do to DNA and how do they do this?

- PCR:
What is it?
What is it used for?
How does it work? List the steps

- DNA probing:
What is it?
List an example of how it is used

- Recombinant plasmids and transformed bacteria:
This one basically involves restriction enzymes, electrophoresis and extensive knowledge about DNA structure
What is it used for?
How can it be used to find a medicinal cure?
2016-2019: Bachelor of Biomedicine
2015: VCE (ATAR: 94.85)

Biology24123

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Re: VCE Biology Question Thread
« Reply #5604 on: July 27, 2015, 09:54:18 pm »
0
What exam score would you need to get a 45 in biology. I know there are several other factors but just want to get a general idea

Thanks

Jay.C

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Re: VCE Biology Question Thread
« Reply #5605 on: July 27, 2015, 10:39:01 pm »
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What exam score would you need to get a 45 in biology. I know there are several other factors but just want to get a general idea

Thanks

Mid-high A+
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Sine

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Re: VCE Biology Question Thread
« Reply #5606 on: July 27, 2015, 10:45:53 pm »
0
Is this relevant to the current study design:

The name of the network that surrounds cells in body tissues: Extracellular Matrix.

The cell which produces this : Fibroblasts.

A few other questions? :)
What companies provide the best practice exams(most similar to VCAA)?

For company practice exams should I stick to 2006+?

When is the best time to start VCAA practice exams?

Should I use practice exams as revision for Unit 3 or should I do something else?

What exam score would you need to get a 45 in biology. I know there are several other factors but just want to get a general idea

Thanks
I would think around 98-100/110
Mid-high A+
What score range do you mean by Mid-high A+? As even the best in the state end up losing marks in Biology.  :)

heids

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Re: VCE Biology Question Thread
« Reply #5607 on: July 28, 2015, 12:06:56 pm »
+5
Is this relevant to the current study design:

The name of the network that surrounds cells in body tissues: Extracellular Matrix.

The cell which produces this : Fibroblasts.
Don't think so.

Quote
What companies provide the best practice exams(most similar to VCAA)?

For company practice exams should I stick to 2006+?

When is the best time to start VCAA practice exams?

Should I use practice exams as revision for Unit 3 or should I do something else?
People seem to recommend STAV (I never had any) and NEAP (often goes beyond the course).

Yes, don't waste your time on pre-2006.

Now. (But that's coz I love VCAA exams - I did ~5-10 commercial U3 exams, but only VCAA for U4 because I thought it was soooo much better preparation).

NEVER use practice exams as your only form of revision; use it instead as a tool to find what you need to revise.  If you get to a question about photosynthesis and you're like, 'What?  I've totally forgotten this!' then stop doing more prac papers until you've totally sorted out your photosynthesis knowledge.  Basically, no matter how many papers you do, if you don't actually learn the stuff, you won't improve.

But how I studied?  First, I went through the study design, figured out the basics I had to know, and asked myself heaps of closed-book questions on all of them, then checked my answers - like 'describe the four levels of protein structure', or 'list the inputs and outputs of each stage of photosynthesis' or 'outline the process of gene expression'.  That ensures that you have all the knowledge, then after that, doing exams (esp VCAA) helps you learn to deal with application and deduction questions.

In fact, I can probably throw together a quick U3 list of questions if anyone wants - basically straight from the study design.
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Jay.C

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Re: VCE Biology Question Thread
« Reply #5608 on: July 28, 2015, 05:11:45 pm »
+1
In fact, I can probably throw together a quick U3 list of questions if anyone wants - basically straight from the study design.

Yes please!!!!!!! This would be a really good resource for many!  :)
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TheAspiringDoc

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Re: VCE Biology Question Thread
« Reply #5609 on: July 28, 2015, 06:30:58 pm »
0
Hey, can someone please 'critique' this definition.

Epigenetics is the study of the expression of genes. Because genes can be expressed in different ways, a particular cell can express its genes in a different way from another cell with an identical nucleotide sequence, and hence display different traits. These variations in expression are due to factors such as age and environmental factors such as diet, exercise, drugs, and chemicals, which may cause changes in the way genes, are ‘switched’ on and ‘off’. Cancer epigenetics is the study of epigenetic modifications to the genome of cancer cells. Epigenetic alterations are as important in genetic alterations in a cell’s transformation to cancer. These changes may be passed from parents to their children.

Thanks!