Edexcel AS Biology - 6B101 + 6B102 - Unit 1 and Unit 2 Exam Discussion Thread

1. Explain the difference between correlation and causation.
2. Compare cohort studies with case-control studies
3. Name three different types of pairs of molecules that can be joined together in a condensation reaction
4. Give two ways in which the structure of a tRNA molecule differs from the structure of a mRNA molecule
5. Explain how the structure of the aorta relates to its function
6. Describe the structure of starch
7. Describe how amino acids join together to form the three-dimensional structure of a protein

There you are folks, enjoy

1. Correlation is where a change in one variable is reflected by a change in another, causation is where a change in one variable is responsible for a change in another

2. Not too sure

3. Monosaccharides, Amino Acids and Fatty Acids + Glycerol?

4. mRNA is straight chained, tRNA is not. tRNA has an amino acid paired to it, mRNA does not

5. The aorta has thick muscular walls to maintain the blood pressure. The endothelial lining of the artery is smooth to reduce friction whilst blood is travelling. It has collagen and elastic fibres to withstand the high blood pressure. The aorta has valves to prevent the back-flow of blood to the left ventricle.

6. Starch is made of amylose and amylopectin. Amylose is spiralled and compact, amylopectin is branched. Both are made of alpha-glucose. Amylopectin has both 1,4 and 1,6 glycosidic bonds however amylose only has 1,4 glycosidic bonds between molecules.

7. The primary structure of a protein is the sequence of amino acids held together by peptide bonds between the amine group of one amino acid and the carboxyl group of another amino acid. The amino acids have varying R groups as well. The different R groups allow the primary structure to fold into the tertiary structure, Different bonds such as ionic bonds, disulphide bridges, hydrophobic/hydrophillic interactions and London forces occur which allows the protein to fold into a specific structure. Therefore the primary structure determines how the protein folds into the tertiary structure

1. Nice, exactly what I would've said 2. Cohort studies include a large number of people over a long period of time, case-control studies is a comparison between a control group and a group with the condition being investigated. It's quite a challenging question, I can't see it popping up in the exam but you never know. I found it in one of the revision guides, here is the answer: Case-control studies: looks at past history to explain present observations Cohort studies: follows study groups into the future, prospective 3. Correct 4. Yep, I think you could also say that tRNA molecules have hydrogen bonds, mRNA molecules don't 5. Correct 6. Correct 7. Correct Just some questions which I chose from one past paper and a couple from a revision guide I've got.

I've seen quite a few of them from different past papers, guessing you used the CGP revision guide for the cohort/case-control one

1. Nice, exactly what I would've said
2. Cohort studies include a large number of people over a long period of time, case-control studies is a comparison between a control group and a group with the condition being investigated. It's quite a challenging question, I can't see it popping up in the exam but you never know. I found it in one of the revision guides, here is the answer: Case-control studies: looks at past history to explain present observations Cohort studies: follows study groups into the future, prospective
3. Correct
4. Yep, I think you could also say that tRNA molecules have hydrogen bonds, mRNA molecules don't

5. Correct
6. Correct
7. Correct Just some questions which I chose from one past paper and a couple from a revision guide I've got.

Nope! I used the red revision guide made by Pearson themselves, it is SO helpful!

I think for 4, you wouldn't really say that tRNA have hydrogen bonds since mRNA can form hydrogen bonds too. I think though, you can say that tRNA are codons whilst mRNA has anticodons

I'm certain that you can say mRNA has no hydrogen bonds, here's the mark criteria for that question:



Also tRNA has anticodons, not codons? Think you've got it the wrong way around :P

I think for 4, you wouldn't really say that tRNA have hydrogen bonds since mRNA can form hydrogen bonds too. I think though, you can say that tRNA are codons whilst mRNA has anticodons

1. Correlation is where a change in one variable is reflected by a change in another, causation is where a change in one variable is responsible for a change in another

2. Not too sure

3. Monosaccharides, Amino Acids and Fatty Acids + Glycerol?

4. mRNA is straight chained, tRNA is not. tRNA has an amino acid paired to it, mRNA does not

5. The aorta has thick muscular walls to maintain the blood pressure. The endothelial lining of the artery is smooth to reduce friction whilst blood is travelling. It has collagen and elastic fibres to withstand the high blood pressure. The aorta has valves to prevent the back-flow of blood to the left ventricle.

6. Starch is made of amylose and amylopectin. Amylose is spiralled and compact, amylopectin is branched. Both are made of alpha-glucose. Amylopectin has both 1,4 and 1,6 glycosidic bonds however amylose only has 1,4 glycosidic bonds between molecules.

7. The primary structure of a protein is the sequence of amino acids held together by peptide bonds between the amine group of one amino acid and the carboxyl group of another amino acid. The amino acids have varying R groups as well. The different R groups allow the primary structure to fold into the tertiary structure, Different bonds such as ionic bonds, disulphide bridges, hydrophobic/hydrophillic interactions and London forces occur which allows the protein to fold into a specific structure. Therefore the primary structure determines how the protein folds into the tertiary structure

For question5, I thought aorta doesn't have valves...

Aorta does have valves, semi-lunar valve

What practical do you guys reckon will come up tomorrow for unit 3?

hello can we discuss horrible questions that could potentially come up

Sample material? What do you exactly mean?

is there any sample material for this exam?

You can do it Just believe in yourself and you'll pull through I hate when I make those silly mistakes though, they end up costing you like an A Edexcel Chemistry is really harsh

Considering your unis and predicted grades are based .

I've finished all the past papers and the SNAB syllabus past papers too so please can you provide me with some resources I can use.

Like do you know any websites that have practise questions for 6Bi01? I did the past papers so many times that I basically have the mark scheme memorised.

CGP practice questions? Edexcel textbook? We could test you here

Do you reckon the CPJ book is helpful? I might buy it now if it is.

Does anyone have a PDF of the June 2014 paper? The one on Edexcel seems to be packed with "DRAFT" and "EXEMPLAR" when you try to print it.