AQA Biology Unit 2 Tuesday 12th May 2015

Reply 40

vd12345

11

Just me doing like the previous 10 past papers for every science exam? :0

Reply 41

SampleX

11

I think enzymes, if it's cell division I'm screwdd

Reply 42

Natalie15

2

Original post by NatalieBlundell

Is P2 the life cycle of a star and stuff like that?

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Do you understand the whole topic of cell division and inheritance? I can't seem to get my brain around it, help would be so appreciated :smile:

P2 also contains the cycle of a star, I think.

Reply 43

NatalieBlundell

9

Original post by Natalie15

Do you understand the whole topic of cell division and inheritance? I can't seem to get my brain around it, help would be so appreciated :smile:

P2 also contains the cycle of a star, I think.

Okay so do you mean cell division as in mitosis and meiosis?

Mitosis -
Okay so this is a process which happens in 'normal' cells within your body. Mitosis starts with one single parent cell. The chromosomes within the cell then double and forms an identical copy of itself. The cell membrane dissolves. The chromosomes then move into the centre of the cell. From here two new membranes are created, one around each set of chromosomes.The cell splits apart forming two daughter cells. Both of these cells are genetically identical. Cells created by a parent cell are called a daughter cell. Don't get confused though, this has nothing to do with reproduction or gender! It is just the name for it.

In simpler terms:

1.

Parent cell

2.

Chromosomes 'double' or 'copy' themselves to create an identical pair

3.

They line up at the centre

4.

The cell splits as the chromosomes move apart

5.

Two daughter cells are formed which are genetically identical to one another and the parent cell.

Meiosis -
Some people have trouble spelling this and it can sacrifice a mark or too. If that is the case I remembered how to spell it by thinking me then ios , as the iPhone/Apple software then is.

Me-ios-is :smile:

Meiosis only takes place in reproductive cells, known as 'gametes' or sex cells. Here a cell will double its chromosomes. It will then mix up it's genes, this process is known as 'recombination'. The cell then divides into two. Leaving two cells with a full set of chromosomes each. The cells will then divide again. You will now have 4 cells.These are sometimes known as Haploid cells.Each with only half the genetic material. If another gamete (egg or sperm) come along and they meet, two of these Haploid cells can join together and form a Diploid cell (one with all of the genetic information required).

In simpler terms:

1.

A cell doubles it's chromosomes

2.

The chromosomes are mixed through 'recombination'

3.

The cell splits into two.

4.

The cell splits a further time, this creates all together 4 Haploid cells

5.

Haploids only have half the genetic information required - 23 chromosomes

6.

Another gamete may meet it, they will join together and result in a cell with full genetic information - 46 chromosomes

7.

This cell will turn into an embryo if fertilisation is successful.

A way to remember Haploid, could be that it has half the genetic information. Haploid - Half. They sound similar sort of.

This video may be helpful too. If helps you compare them which you may be asked to do in the exam. https://www.youtube.com/watch?v=FODmSmG5z2Y

Inheritance -

Inheritance is all down to these little things called Alleles. These word is vital so please learn it! Alleles are either dominant or they are recessive. If an allele is dominant, it will overpower a recessive one. If an allele is recessive it will be overpowered by a dominant one.

You may be wondering what is an allele? An allele is essentially a form of a gene. Or a version. For example there are many different genes which control eye colour. There is an allele for blue eyes, an allele for brown eyes.

Check this out below -Alleles are dominant or recessive:

•

the characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair

•

the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair

Hopefully this makes sense. The allele for brown eyes is dominant, whereas the allele for blue eyes is recessive. This means you would have to inherit 2 recessive alleles in order to get blue eyes.

When you have two alleles that are the same (dominant + dominant or recessive + recessive. You call these homozygous. If it is recessive + recessive you may call it homozygous recessive too.

If two different alleles are present (dominant + recessive or recessive + dominant) you call this heterozygous.

A way I remembered this was that two people of the same sex are called homosexual. Two alleles of the same kind are homozygous. As for couples with one partner who is a female, and one who is a male (different genders) these are called heterosexual. Different alleles when together are called heterozygous.

You may be confused about the whole number of alleles and stuff as it is a lot to take in so:

•

During meiosis a gamete is left with 1 allele as it only has half of it's genetic information (23 chromosomes) A regular cell will usually have 2 alleles and 46 chromosomes.

•

This allele will either be recessive or dominant

•

When the gamete meets another and they form to create an embryo, there will be 2 alleles present.

•

These will be either homozygous recessive (recessive+recessive) homozygous(dominant+dominant) or heterozygous (recessive+dominant or dominant+recessive).

•

Dominant alleles= if 1 or both alleles or dominant the characteristic will be present.

•

Recessive alleles= if there are 2 recessive alleles the characteristic will be present.

You will be told in an exam if an allele is recessive or dominant so don't stress about that too much, just understand how it works!

Try and work out what eye colour each individual will have based off this diagram. Answers will be below, no cheating :smile:

Individual A= Brown eyes as the brown eye allele is dominant.
Individual B= Brown eyes as 2 brown eye allele's are present and they are both dominant.
Individual C= Blue eyes, as 2 recessive alleles for blue are present.

If asked simple questions like this in exams, put your reasoning if you have time. You don't need to go into detail, just mention alleles if you can.

Genetic Diagrams -

It is worth knowing how to draw one of these too. You can get marks for drawing one of these and they are so simple!

Okay so this is again for eye colour. The small b represent the allele for blue eyes. The big B represents the allele for brown eyes. Working like a normal grid you go along and match them up. So for the grid in the top left B+b= Bb. Top right is also B+b = Bb. The bottom are the same too. As brown is dominant they will all have brown eyes.

You may be given more of a mix of alleles for example person 1 has Bb and person 2 has bb. If this was the case try drawing out a table and see what the results would be.

Put person 1's alleles across the top and person 2's alleles down the side.

Answers:
Top left- b+B =bB so Brown eyes
Top right- b+b= bb so Blue eyes
Bottom left- b+B= bB so Brown eyes
Bottom right- b+b= bb so Blue eyes

Probability -

You may be asked what are odds or chances of somebody getting a disease or a certain characteristic. You will or should be given their parents alleles or told what allele is recessive and which is dominant. To find out the probability or likelihood draw out one of these genetic diagrams as shown above.

From there you can then do basic maths and figure it out. For the example above, the child would have 50% chance of blue eyes and 50% off brown eyes as the odds are 2/4 for both. Which can then be cancelled down to 1/2 which is 50%.

Hope it helped :smile:

Reply 44

Natalie15

2

Original post by NatalieBlundell

Okay so do you mean cell division as in mitosis and meiosis?

Mitosis -
Okay so this is a process which happens in 'normal' cells within your body. Mitosis starts with one single parent cell. The chromosomes within the cell then double and forms an identical copy of itself. The cell membrane dissolves. The chromosomes then move into the centre of the cell. From here two new membranes are created, one around each set of chromosomes.The cell splits apart forming two daughter cells. Both of these cells are genetically identical. Cells created by a parent cell are called a daughter cell. Don't get confused though, this has nothing to do with reproduction or gender! It is just the name for it.

In simpler terms:

1.

Parent cell

2.

Chromosomes 'double' or 'copy' themselves to create an identical pair

3.

They line up at the centre

4.

The cell splits as the chromosomes move apart

5.

Two daughter cells are formed which are genetically identical to one another and the parent cell.

Meiosis -
Some people have trouble spelling this and it can sacrifice a mark or too. If that is the case I remembered how to spell it by thinking me then ios , as the iPhone/Apple software then is.

Me-ios-is :smile:

Meiosis only takes place in reproductive cells, known as 'gametes' or sex cells. Here a cell will double its chromosomes. It will then mix up it's genes, this process is known as 'recombination'. The cell then divides into two. Leaving two cells with a full set of chromosomes each. The cells will then divide again. You will now have 4 cells.These are sometimes known as Haploid cells.Each with only half the genetic material. If another gamete (egg or sperm) come along and they meet, two of these Haploid cells can join together and form a Diploid cell (one with all of the genetic information required).

In simpler terms:

1.

A cell doubles it's chromosomes

2.

The chromosomes are mixed through 'recombination'

3.

The cell splits into two.

4.

The cell splits a further time, this creates all together 4 Haploid cells

5.

Haploids only have half the genetic information required - 23 chromosomes

6.

Another gamete may meet it, they will join together and result in a cell with full genetic information - 46 chromosomes

7.

This cell will turn into an embryo if fertilisation is successful.

A way to remember Haploid, could be that it has half the genetic information. Haploid - Half. They sound similar sort of.

This video may be helpful too. If helps you compare them which you may be asked to do in the exam. https://www.youtube.com/watch?v=FODmSmG5z2Y

Inheritance -

Inheritance is all down to these little things called Alleles. These word is vital so please learn it! Alleles are either dominant or they are recessive. If an allele is dominant, it will overpower a recessive one. If an allele is recessive it will be overpowered by a dominant one.

You may be wondering what is an allele? An allele is essentially a form of a gene. Or a version. For example there are many different genes which control eye colour. There is an allele for blue eyes, an allele for brown eyes.

Check this out below -Alleles are dominant or recessive:

•

the characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair

•

the characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair

Hopefully this makes sense. The allele for brown eyes is dominant, whereas the allele for blue eyes is recessive. This means you would have to inherit 2 recessive alleles in order to get blue eyes.

When you have two alleles that are the same (dominant + dominant or recessive + recessive. You call these homozygous. If it is recessive + recessive you may call it homozygous recessive too.

If two different alleles are present (dominant + recessive or recessive + dominant) you call this heterozygous.

A way I remembered this was that two people of the same sex are called homosexual. Two alleles of the same kind are homozygous. As for couples with one partner who is a female, and one who is a male (different genders) these are called heterosexual. Different alleles when together are called heterozygous.

You may be confused about the whole number of alleles and stuff as it is a lot to take in so:

•

During meiosis a gamete is left with 1 allele as it only has half of it's genetic information (23 chromosomes) A regular cell will usually have 2 alleles and 46 chromosomes.

•

This allele will either be recessive or dominant

•

When the gamete meets another and they form to create an embryo, there will be 2 alleles present.

•

These will be either homozygous recessive (recessive+recessive) homozygous(dominant+dominant) or heterozygous (recessive+dominant or dominant+recessive).

•

Dominant alleles= if 1 or both alleles or dominant the characteristic will be present.

•

Recessive alleles= if there are 2 recessive alleles the characteristic will be present.

You will be told in an exam if an allele is recessive or dominant so don't stress about that too much, just understand how it works!

Try and work out what eye colour each individual will have based off this diagram. Answers will be below, no cheating :smile:

Individual A= Brown eyes as the brown eye allele is dominant.
Individual B= Brown eyes as 2 brown eye allele's are present and they are both dominant.
Individual C= Blue eyes, as 2 recessive alleles for blue are present.

If asked simple questions like this in exams, put your reasoning if you have time. You don't need to go into detail, just mention alleles if you can.

Genetic Diagrams -

It is worth knowing how to draw one of these too. You can get marks for drawing one of these and they are so simple!

Okay so this is again for eye colour. The small b represent the allele for blue eyes. The big B represents the allele for brown eyes. Working like a normal grid you go along and match them up. So for the grid in the top left B+b= Bb. Top right is also B+b = Bb. The bottom are the same too. As brown is dominant they will all have brown eyes.

You may be given more of a mix of alleles for example person 1 has Bb and person 2 has bb. If this was the case try drawing out a table and see what the results would be.

Put person 1's alleles across the top and person 2's alleles down the side.

Answers:
Top left- b+B =bB so Brown eyes
Top right- b+b= bb so Blue eyes
Bottom left- b+B= bB so Brown eyes
Bottom right- b+b= bb so Blue eyes

Probability -

You may be asked what are odds or chances of somebody getting a disease or a certain characteristic. You will or should be given their parents alleles or told what allele is recessive and which is dominant. To find out the probability or likelihood draw out one of these genetic diagrams as shown above.

From there you can then do basic maths and figure it out. For the example above, the child would have 50% chance of blue eyes and 50% off brown eyes as the odds are 2/4 for both. Which can then be cancelled down to 1/2 which is 50%.

Hope it helped :smile:

You are an absolute life saver! I feel like I understand a bit more now, I'm going to keep going over it. Thank you so much, this has seriously helped me :smile:

Reply 45

NatalieBlundell

9

Original post by Natalie15

You are an absolute life saver! I feel like I understand a bit more now, I'm going to keep going over it. Thank you so much, this has seriously helped me :smile:

You're welcome :smile:

Just make notes and keep going over it in your head and maybe even speak it out loud (it can actually really help!)

Good luck for tomorrow, you will do great :biggrin:

Reply 46

Willnewman234

3

Original post by NatalieBlundell

You're welcome :smile:

Just make notes and keep going over it in your head and maybe even speak it out loud (it can actually really help!)

Good luck for tomorrow, you will do great :biggrin:

Saying out loud is the best. Ask yourself questions related to what you are revising

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Reply 47

Ankit.B

Original post by SuperHuman98

I'm good in everything except for the dreaded topic with Quadrats and Transects :frown:

I agree i hate that so much

Reply 48

Willnewman234

3

Original post by Ankit.B

I agree i hate that so much

They are not that hard. Using quadrat make sure you don't look so it's random. For transept, mention using a measuring tape and saying it's random as you place the transect line randomly

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Reply 49

username1292215

22

I hope the 6 mark is about Leaf tissue,enzymes or speciation.

How can they ask a 6mark about Meiosis and Mitosis though?

Reply 50

SampleX

11

Original post by SuperHuman98

I hope the 6 mark is about Leaf tissue,enzymes or speciation.

How can they ask a 6mark about Meiosis and Mitosis though?

Speciation would be brill.

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Reply 51

username1292215

22

Original post by SampleX

Speciation would be brill.

Posted from TSR Mobile

It was in 2014s paper :frown:

Reply 52

thepurplerain

15

Sorry if this is a stupid question, but is there going to be two 6 mark questions? I only ask this because I think there was last year? :smile:

Reply 53

username1292215

22

Original post by thepurplerain

Sorry if this is a stupid question, but is there going to be two 6 mark questions? I only ask this because I think there was last year? :smile:

yeah its a possibility.

Reply 54

DTonesXD

OP

3

i hope enzymes come up on a 6 marker. I know a lot about them
cell devision could be okay
i chemistry. Phisics isn't bad

thanks for the help, natalie :smile:

Reply 55

Philip3199

1

Biology Unit 2 and 3 is my first exam, and holy moley it's tomorrow, has anyone else felt that exams came by super quickly? I'm guilty of huge procrastination, I only started revising last week, I think I'll be okay since I got an A in my mock from revising the night before (but that was only Units 1 and 2). My method is just making notes from the revision guide, I spent most of the weekend doing that and surprisingly a lot of it has stuck in. I plan on using tonight to go over anything I'm unsure of or have forgotten, and then (with a bit of hope and luck) I'll be well prepared for the exam. Good luck everyone! :smile:

Added: If anyone needs me to explain anything, I'll be happy to do so, as long as I know the topic myself.

Added 2 (sorry I keep thinking of new things to write): Vis-a-vis the six-marker, I wouldn't mind most things, I'm just hoping for something quite broad so I can write lots about it and guarantee getting most (if not all) marks.

(edited 8 years ago)

Reply 56

THEPROLORD98

Original post by SampleX

Speciation would be brill.

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Wont be that as that was from last years paper I think

Reply 57

THEPROLORD98

Original post by DTonesXD

i hope enzymes come up on a 6 marker. I know a lot about them
cell devision could be okay
i chemistry. Phisics isn't bad

thanks for the help, natalie :smile: