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    (Original post by TheTeresaLover)
    That is really thoughtful of you! I think i have found it. Hopefully its been attached (i still dont know how to use tsr properly)
    Haha i knew i didnt attach it. There u go
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  1. File Type: pdf unit 2 notes.pdf (535.6 KB, 669 views)
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    (Original post by TheTeresaLover)
    That is really thoughtful of you! I think i have found it. Hopefully its been attached (i still dont know how to use tsr properly)
    Ah no, it hasn't been attached but don't worry about it.- I appreciate you telling me. I'm sure it'll be in one of the threads by a CT member in the Biology or A-level/Revision study tips forum or something like that so I can definitely look for it later and if not then I'll google it and it'll probably pop up.
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    (Original post by TheTeresaLover)
    Haha i knew i didnt attach it. There u go
    Oh goodness ..this is marvellous.

    Ilysm. :cry2:
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    (Original post by Anon_98)
    Meiosis - Topic 6.

    A meiotic cell division involves two divisions of the nucleus and two division of the cell.

    - Meiosis I separates the chromosomes from each homologous pair into different cells, halving the chromosome number.

    - Meiosis II separates the chromatids in each chromosomes, like mitosis.

    The main stages of Meiosis I

    Early prophase I
    Late prophase I
    Metaphase I
    Anaphase I
    Telophase I
    Cytokinesisssss.

    ~

    Early prophase. - The DNA has already replicated and each chromosome consists of two chromatids. The cell contains two sets of chromosomes.

    Late prophase - The spindle starts to form. Homologous chromosomes pair up forming bivalents and exchange DNA between non sister chromatids.

    Metaphase I - The spindle is complete and the nuclear envelope has disintegrated. The bivalents are arranged around the middle of the spindle.

    Anaphase I - Homologous chromosomes start to seperate from each other.

    Telophase I - There is one complete set of chromosomes at each end of the cell.

    Cytokinesis.- The cytoplasm divides and two identical daughter cells are formed. The two cells resulting from meiosis I are therefore haploid.


    Crossing over. - An event that occurs during prophase I.

    During prophase I, non sister chromatids may break and rejoin to the other chromosome. Now all four chromatids have different combinations of alleles - more variation exists.

    Random segregation. - The way homologous chromosomes are aligned at metaphase determines how they will be segregated into the two new cells.

    Random segregation of homologous chromosomes gives rise to genetic variation.

    ..The diagrams basically explain everything else tbh.


    Meiosis II

    Prophase II - Each cell contains one chromosome from each homologous pair.

    Metaphase II - The chromosomes are aligned on the centre of the spindle

    Anaphase II - The chromatids are separated. (RANDOM SEGREGATION OCCURS HERE TOO)

    Telophase II - Two haploid nuclei in each cell.

    Cytokinesissss- 4 Genetically different haploid cells.


    The key features of a meiotic cell division are that:

    - It involves two nuclear divisions.
    - It forms four daughter cells.
    - The daughter cells are haploid.
    -The daughter cells show genetic variation ( contain the same genes but different combinations of alleless)
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    Genetic diversity. - Topic 7

    I'm so not going to get this done in time. :banghead: :cry:

    Okay, um.

    Mutations create new alleles of genes. Crossing over and random segregation of chromosomes during meiosis, together with random fertilisation of gametes during sexual reproduction, create new combinations of alleles.

    Random fertilisation results in even more genetic diversity if mating is also random. This type of mating is called out-breeding.

    The founder effect, genetic bottlenecks, in-breeding and selective breeding all reduce genetic diversity.


    The founder effect.

    Inthe founder effect, a few individuals colonise a new environment and breed there.

    Only a fraction of the alleles that were present in the original population is present in the few individuals that colonise in the new environment and establish a new population. Therefore the genetic diversity of the new population will be reduced.

    Examples of the founder effect include:

    - The Afrikaner population of South Africa, which is descended from just a few Dutch settlers.

    - The grey squirrel population in the UK, which is descended from a small number of colonising individuals.

    Genetic bottlenecks.

    In a genetic bottleneck, the population is reduced drastically by some environmental effect such as disease.

    Examples of genetic bottlenecks.


    - The population of lions in Tanzania, which crashed from 75 individuals in 1962 to 7 in 1964

    - The cheetah population in Africa.

    The population size may recover after a bottleneck event, but if the population crash is too great then it may lead to extinction.

    Selective breeding.

    A form of in-breeding controlled by humans.

    Examples..

    - Cattle bred for high meat/milk yield.

    - Wheat, descended from grasses and selectively bred to give a high grain yield and be resistant to diseases.
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    Just read through the powerpoints on the topics above + it's explained things pretty well. Um, umumummm.
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    (Original post by Anon_98)
    Just read through the powerpoints on the topics above + it's explained things pretty well. Um, umumummm.
    I'm glad the powerpoints are helping you. How much do you have left? In my opinion, you should do the gas exchange stuff now, as it usually gets asked. And its a biggie as well.
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    (Original post by TheTeresaLover)
    I'm glad the powerpoints are helping you. How much do you have left? In my opinion, you should do the gas exchange stuff now, as it usually gets asked. And its a biggie as well.
    Thanks, yeah- they're quite nice + simplified. I'm currently on haemoglobin..I think you're right- maybe I'll do that next then.

    I have quite a lot left:

    Carbohydrates
    Cells
    Replication of DNA.
    Mitosis.
    Cell cycle
    Cell differentiation
    Size + surface area
    Gas exchange.
    Mass transport
    The blood system
    The passage of water through a plant
    Principles of taxonomy
    Genetic comparisons
    Proteins
    Behaviour/courtship
    Genetic variation in bacteria
    Species diversity.
    Index diversity.
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    I'm taking a break until 11:00pm, bc I feel like I need to remain calm for this to work + I'm struggling to focus atm.

    When I return I'll be continuing with haemoglobin.
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    Good luck on your exam tomorrow! I hope it goes amazingly. :heart:
    Spoiler:
    Show
    You really don't need to worry because I know you'll ace it. :jumphug:
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    I can't do this anymore lol.

    What time do I go to bed. :cry:

    Do I even go to sleep tonight.

    Should I sleep now until 3am then do work until Midday?

    Or maybe work until Midnight then wake up at 5am or something?

    Ohmyg, I can't do this LMAO.

    LOLOLOLLLLLLLLLLLLLLLLLLLLLLLLLL LLLLLLLLLLLLLLLLLLLLLLLL.

    it's not even funny. :nope:

    These are such bad ideas.

    I'M DOING IT AGAIN, WHAT IS WRONG WITH ME. WHY COULDN'T I HAVE JUST READ MY STUPID EXAM TIMETABLE CORRECTLY LIKE A NORMAL HUMAN BEING AND REVISED FOR THE RIGHT EXAM. WHY DO I LACK BASIC SKILLS.

    Who reads their timetable wrong fgs.

    I hate myself so much. :banghead:

    Meh. :'3

    I'm taking another break.
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    Thank you!! Your notes have helped
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    (Original post by haj101)
    Thank you!! Your notes have helped
    yay.
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    (Original post by TheOtherSide.)
    Good luck on your exam tomorrow! I hope it goes amazingly. :heart:
    Spoiler:
    Show
    You really don't need to worry because I know you'll ace it. :jumphug:
    ty, chicken. <3
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    (Original post by Anon_98)
    I can't do this anymore lol.

    What time do I go to bed. :cry:

    Do I even go to sleep tonight.

    Should I sleep now until 3am then do work until Midday?

    Or maybe work until Midnight then wake up at 5am or something?

    Ohmyg, I can't do this LMAO.

    LOLOLOLLLLLLLLLLLLLLLLLLLLLLLLLL LLLLLLLLLLLLLLLLLLLLLLLL.

    it's not even funny. :nope:

    These are such bad ideas.

    I'M DOING IT AGAIN, WHAT IS WRONG WITH ME. WHY COULDN'T I HAVE JUST READ MY STUPID EXAM TIMETABLE CORRECTLY LIKE A NORMAL HUMAN BEING AND REVISED FOR THE RIGHT EXAM. WHY DO I LACK BASIC SKILLS.

    Who reads their timetable wrong fgs.

    I hate myself so much. :banghead:

    Meh. :'3

    I'm taking another break.
    :hugs: I've been following your thread since it started and I'm very impressed at the progress you've made so far, and that your handwriting is quite good (compared to mine, anyway :awesome:)
    One of my flatmates misread his timetable this semester and had 1 day to revise for an exam that he thought was some way away, but he kept working, sacrificed a bit of sleep (but still got enough) and worked right up to the exam and reckons he did okay.

    I've also been working right up to an exam, trying to learn stuff, so I know just how stressful it is :hugs:

    Whatever you do with regards to sleep, just try to get as much done as you reasonably can and get stuff done, and have a look at past papers if you get the time. But at the same time, you have your other units which you've also worked for to average things out if this doesn't go as good as you'd hoped. Okay, that might not be particularly reassuring, but this is the situation that you're in and you have to make the most of it. You can do it.
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    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    CALM DOWN FFS :fuhrer:

    Stop. You knew it was gonna be tough before you sat down and started, but you just have to get it done. Take your break, do whatever needs to be done, then get right back to work.

    Your first mistake was reading your timetable wrong but that's done now, don't let being overwhelmed by what's in front of you be your second.

    Relax. Breathe. And just do your best with the time you have left, you don't have a choice. You either work or you complain and we both know which one you much rather be doing (don't let hindsight tell you which one you should've done). Complaining is fine tbh, so long as you get a grip and get back to work after it.

    Relax Anon.

    Smile & just do what you can, if that means giving up sleep (& Ik you're capable of doing that + learning this stuff) then so be it.
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    (Original post by SeanFM)
    :hugs: I've been following your thread since it started and I'm very impressed at the progress you've made so far, and that your handwriting is quite good (compared to mine, anyway :awesome:)
    One of my flatmates misread his timetable this semester and had 1 day to revise for an exam that he thought was some way away, but he kept working, sacrificed a bit of sleep (but still got enough) and worked right up to the exam and reckons he did okay.

    I've also been working right up to an exam, trying to learn stuff, so I know just how stressful it is :hugs:

    Whatever you do with regards to sleep, just try to get as much done as you reasonably can and get stuff done, and have a look at past papers if you get the time. But at the same time, you have your other units which you've also worked for to average things out if this doesn't go as good as you'd hoped. Okay, that might not be particularly reassuring, but this is the situation that you're in and you have to make the most of it. You can do it.
    tysm for the reassurance.<3 I kinda needed that. :cry:
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    (Original post by Fiduciam)
    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    Calm down.

    CALM DOWN FFS :fuhrer:

    Stop. You knew it was gonna be tough before you sat down and started, but you just have to get it done. Take your break, do whatever needs to be done, then get right back to work.

    Your first mistake was reading your timetable wrong but that's done now, don't let being overwhelmed by what's in front of you be your second.

    Relax. Breathe. And just do your best with the time you have left, you don't have a choice. You either work or you complain and we both know which one you much rather be doing (don't let hindsight tell you which one you should've done). Complaining is fine tbh, so long as you get a grip and get back to work after it.

    Relax Anon.

    Smile & just do what you can, if that means giving up sleep (& Ik you're capable of doing that + learning this stuff) then so be it.
    tysm tysm tysm tysm. :cube:
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    OKAY. :lockstock:
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    Keep trucking, breh. You're on the way.
 
 
 
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