Turn on thread page Beta
    • Thread Starter
    Offline

    4
    ReputationRep:
    Hey guys! I'm creating this thread for discussions about the AQA unit 2 biology as exam on 1st June so you can talk about any and all of the topics and help each other out! I'm also present to answer any questions !
    Offline

    2
    ReputationRep:
    Posted from TSR Mobile
    Will be on this heavily after unit 1 😃.
    Offline

    4
    ReputationRep:
    can someone explain to me meiosis coz the book really sucks :/
    Offline

    2
    ReputationRep:
    Need to sweat out the BIOL2 after my BIOL1 performance :/
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by edward090)
    can someone explain to me meiosis coz the book really sucks :/
    Sorry for the late reply! Meiosis is a process by which cells divide to produce 4 genetically dissimilar haploid daughter cells called gametes, which are sex cells (sperm and egg cells)- haploid because having only half the genetic information means when the gametes combine with gametes from another sexual partner, the cell will be a diploid cell containing chromosomes from both parents.
    PROCESS-
    (meiosis 1)= first division. the homologous (same structural features) chromosomes pair up and their chromatids, the "legs" of DNA coming out from the centromere, wrap around each other and exchange DNA sections by crossing over- (swapping particular sections of DNA- this is what causes the genetic variation in gametes) The homologous chromosomes then separate, going each into a different daughter cell.
    (meiosis 2)= the chromatids move apart, and each daughter cell of 4 produced each contains one chromatid.

    i think that's all you need to know about that, apart from details about crossing over, and variety from new genetic combinations, but this part is explained nicely in the book with examples

    good luck
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by bishopdon123)
    Need to sweat out the BIOL2 after my BIOL1 performance :/
    I'm sure you did fine i made loads of silly mistakes too, including saying changing small intestine to large intestine as where maltose is produced in the last minute..
    Offline

    2
    ReputationRep:
    (Original post by buckeybarnes)
    I'm sure you did fine i made loads of silly mistakes too, including saying changing small intestine to large intestine as where maltose is produced in the last minute..
    Thanks, I hope we both did well.
    How are you feeling about BIOL2? I'm looking to go through the content again today then start past papers.
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by bishopdon123)
    Thanks, I hope we both did well.
    How are you feeling about BIOL2? I'm looking to go through the content again today then start past papers.
    Sorry was doing past paper! i just got 68/85 in a past paper and im a little bit of a generous marker but it was 8 marks into an A so im pretty happy. I'm a little scared but only because i'm not as familiar with the course, so i'm thinking about going through the entire book content and then past papers, same as you. we could help each other out without any questions, could be very useful to both of us and anyone else who wants to!
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by bishopdon123)
    Thanks, I hope we both did well.
    How are you feeling about BIOL2? I'm looking to go through the content again today then start past papers.
    my plan is that i will take my notebook and read through the whole unit 2 course and make notes on things i think are important, i did about 12 A4 sides of notes for unit 1 and it really helped everything to stay fresh, also bc its in a week i have a while to look over the notes. then im gonna practise alot for data handling and analysis questions bc i know theyre bad and do some practise with 6 markers and stuff, but i also have chemistry physics and further maths to revise for lol..
    Offline

    2
    ReputationRep:
    (Original post by buckeybarnes)
    Sorry was doing past paper! i just got 68/85 in a past paper and im a little bit of a generous marker but it was 8 marks into an A so im pretty happy. I'm a little scared but only because i'm not as familiar with the course, so i'm thinking about going through the entire book content and then past papers, same as you. we could help each other out without any questions, could be very useful to both of us and anyone else who wants to!
    Well done! Yeah i wouldn't mind that, would be very helpful!
    (Your other post) yeah I did the same for Unit 1 where I literally summed up each topic on one side of A4, or two sides of A4.
    Offline

    15
    ReputationRep:
    Resitting BIOL2 after bombing and getting a B in this last year which cost me my A grade event though i got 90% in unit 1
    Offline

    3
    ReputationRep:
    whats the definition of a taxonomy? Is it the 'hierarchical order of taxonomic ranks, based upon the evolutionary relationship between organisms'?
    Offline

    2
    ReputationRep:
    (Original post by awesomewarsome)
    whats the definition of a taxonomy? Is it the 'hierarchical order of taxonomic ranks, based upon the evolutionary relationship between organisms'?


    Posted from TSR Mobile
    Taxonomy is simply the science of classification.
    Offline

    15
    ReputationRep:
    QUESTION: In Meiosis is there replication of DNA or is that only in Mitosis, because currently a simple run down of my idea of meiosis is that a diploid cell undergoes cell division without replicating dna at interphase to produce 2 haploid cells.


    I am aware in mitosis dna replicates undergoes cell division to produce 2 diploid cells then these cells dna replicate in like Mitosis II to produce 4 diploid cells with the same dna. Also there is no chiasmata with mitosis right?
    Offline

    2
    ReputationRep:
    The entire plant related section of chapter 13 is giving me grief! Does anybody have a source which can explain this whole section in a clear and concise manner?


    Posted from TSR Mobile
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by Hudl)
    Resitting BIOL2 after bombing and getting a B in this last year which cost me my A grade event though i got 90% in unit 1
    I bet you can get an A this year! I'll keep this thread updated and help anyone I can! anything you find particularly difficult?
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by Melissaalb)
    The entire plant related section of chapter 13 is giving me grief! Does anybody have a source which can explain this whole section in a clear and concise manner?


    Posted from TSR Mobile
    I need to revise unit 2 anyway, so I may as well explain

    Leaf adaptations and structure

    Leaves are adapted to gas exchange in multiple ways-
    No living cell is far from external air
    diffusion occurs in the gas phase
    large surface area due to thin, flat shape
    small pores called stomata in abundance for gas exchange
    interconnecting air spaces through mesophyll

    There is a diagram of the structure of a leaf in your book, so I won't explain that, apart from a few key points. The palisade mesophyll layer is where the majority of photosynthesis takes place, so the cells must have adaptations to optimise this. These include the regular arrangement of the cells, so that every cell is in the optimum position for absorption of sunlight, a large vacuole so that all chloroplasts in the palisade cells are forced to the surface of the cell so to be exposed to more sunlight, and an abundance of chloroplasts. The air space in the spongy mesophyll layer is where all of the oxygen and carbon dioxide diffuse through, and gas enters and leaves the leaf through many stomata, usually on the lower epidermis, which can be closed and opened to certain degrees by the guard cells that control them. In order to prevent water loss plants can shut stomata, for example.

    Movement of water through roots

    Root hairs are the exchange surfaces on the roots that are responsible for the absorption of water and mineral ions. Root hairs are long, thin extensions, so provide a large surface area through which gases and ions can diffuse , and have a very thin surface layer so the diffusion pathway is short. They stick out into the soil and are surrounded by soil solution, although that is mostly water, so the water potential of the soil solution is higher than the root hair cell contents because it contains many minerals and ions, so water moves by osmosis into the roots along the water potential gradient. Water can then travel by two means, the first being:-

    The apoplastic pathway

    The simple one I think, this is where as water is drawn into the endodermal cells, more water is pulled in due to the cohesive properties of water, creating a tension that pulls water along the cell walls of the root cortex. The mesh like structure of the cortex cell walls allows for an easy movement with little to no resistance

    the symplastic pathway

    the slightly harder one, I have "sympathy for those who have to learn it". This is where osmosis is involved, and is a little more complex:-
    -> Water that has entered by osmosis increases the water potential of the root hair cells. These now have a higher water potential than first neighbouring cortex cell, so water moves by osmosis into the cortex cell, along the concentration gradient. The first cell now has a higher water potential than the next, so the process repeats itself. The loss of water from the first cell in the cortex to the next lowers its water potential so it draws in even more water by osmosis, and the process continues, think of it like a wave of water potential. It moves this way along the cytoplasm of the cells, and moves between cells along a thin connected bit of cytoplasm called the plasmodesmata.

    Water into the xylem

    When water arrives at the endodermis by the apoplastic pathway, a ring of waterproof tissue called the casparian strip stops the water moving across the cell wall, meaning it is forced into the symplastic pathway, and it is because of this that all water arrives at the xylem in the symplastic pathway. However, the water potential of the xylem is higher than the surrounding cells, so water cannot enter passively by osmosis. This is remedied by the fact that carrier proteins in the endodermal cells actively transport mineral ions into the xylem, lowering its water potential to less than the surrounding cells and allowing water to move into the xylem by osmosis. Because it involved active transport, this process is not passive and requires energy. This process as a whole is called root pressure. Root pressure can be reduced by metabolic inhibitors to prevent energy release required for active transport, or decrease in respiratory substrate availability.

    Movement of water up the stem

    Because water is cohesive, it forms a long, unbroken column of water running the length of the xylem, and adheres/sticks to the xylem walls. Tension is created in this column because water leaves the leaf by transpiration, and since all water molecules are to an extent attracted to each other, the loss of water molecules into the atmosphere drags other water molecules forward, meaning the column of water in the xylem is pulled by the created tension up the xylem constantly, then transported across the leaves via the apoplastic or symplastic pathway. This is referred to as the transpiration stream, or transpiration pull.

    Cohesive properties- Water is a polar molecule, so has poles of different charges, the hydrogen and a partial positive charge, and the oxygen is a partial negative charge. Due to this, nearby water molecules are attracted to the water molecule, with the positive hydrogen being attracted to the negative oxygen and vice versa, so all molecules of water attract each other. (not on the syllabus but may help you understand!)

    I hope you understand when i say i can't be bothered to type up all the factors affecting transpiration and xerophytic adaptations as well, but what i've said here is basically a crash course in movement of water all the way through the plant

    thanks for posting, and good luck in your exam
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by awesomewarsome)
    whats the definition of a taxonomy? Is it the 'hierarchical order of taxonomic ranks, based upon the evolutionary relationship between organisms'?
    i would say that is correct
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by Hudl)
    QUESTION: In Meiosis is there replication of DNA or is that only in Mitosis, because currently a simple run down of my idea of meiosis is that a diploid cell undergoes cell division without replicating dna at interphase to produce 2 haploid cells.


    I am aware in mitosis dna replicates undergoes cell division to produce 2 diploid cells then these cells dna replicate in like Mitosis II to produce 4 diploid cells with the same dna. Also there is no chiasmata with mitosis right?
    there is no DNA replication in meiosis- the homologous pairs line up in the equator of the cell, one chromosome goes to each first stage daughter cell, and one chromatid goes to each of the 4 final daughter cells, which are haploid gametes
    Offline

    3
    ReputationRep:
    what are all the ethical related stuff in unit 2?
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: December 21, 2015

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.