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    Head of Biology from Birmingham Tuition Centre

    I will be available all day to answer any questions regarding AQA Biology Unit 2 - just post the questions in this forum

    Find the Revision Notes for Unit 2 attached

    oak12
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  1. File Type: doc AQA U2 Revision Notes.doc (171.0 KB, 510 views)
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    What questions do you predict to come up as you were right last time? Thanks
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    (Original post by Charlie999112)
    What questions do you predict to come up as you were right last time? Thanks
    again, i can mention topics that are overdue:

    - variation (intraspecific/interspecific & discontinuous/continuous)
    - triplet code properties (degenerate/non-overlapping/stop)
    - stages mitosis/meiosis
    - fetal haemoglobin
    - surface area to volume ratio calculation
    - gas exchange in insects/fish
    - structure of capillaries
    - properties of a stable ecosystem
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    (Original post by oak12)
    again, i can mention topics that are overdue:

    - variation (intraspecific/interspecific & discontinuous/continuous)
    - triplet code properties (degenerate/non-overlapping/stop)
    - stages mitosis/meiosis
    - fetal haemoglobin
    - surface area to volume ratio calculation
    - gas exchange in insects/fish
    - structure of capillaries
    - properties of a stable ecosystem


    variation (intraspecific/interspecific & discontinuous/continuous)
    - triplet code properties (degenerate/non-overlapping/stop)
    - stages mitosis/meiosis
    - gas exchange in insects
    - structure of capillaries
    - properties of a stable ecosystem

    do you mind going through these ones?
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    (Original post by Tplox)
    variation (intraspecific/interspecific & discontinuous/continuous)
    - triplet code properties (degenerate/non-overlapping/stop)
    - stages mitosis/meiosis
    - gas exchange in insects
    - structure of capillaries
    - properties of a stable ecosystem

    do you mind going through these ones?
    from the revision notes above:

    What is Variation? difference in characteristics between organisms

    Types of Variation?

    intraspecific= differences between organisms of the same species
    interspecific= differences between organisms of different species

    Causes of Intraspecific Variation?

    Genetic Factors = same genes but different alleles (allele are different type/forms of genes)
    Environmental Factors

    Causes of Interspecific Variation?

    GeneticFactors = different genes and different alleles
    EnvironmentalFactors

    Types of Characteristics? Discontinuous and Continuous

    Properties of Discontinuous Characteristics?

    characteristics fall into certain groups with no overlap (e.g. blood group) – determined by genetics only (a single gene)

    Properties of Continuous Characteristics?

    characteristics show a range (e.g. height) – determined by genetics (a few genes,polygenes) and environment
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    Propertiesof triplet code?
    • degenerate = each AA has more than one triplet code
    • non-overlapping = each base is read only once
    • stop codes = occur at end of sequence – do not code for an AA
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    Mitosis:

    Prophase = nucleus breaksdown, chromosomes coil, spindle fibres form
    Metaphase = chromosomes line up in middle of cell and attach to spindle fibres
    Anaphase = spindle fibres pull, chromatids move to opposite poles
    Telophase = nucleus reforms, chromatids uncoil

    Meiosis:

    (Prophase 1/Metaphase 1/Anaphase 1/Telophase 1,
    Prophase 2/Metaphase 2/Anaphase 2/Telophase 2)

    Prophase 1 = crossing over occurs
    Metaphase 1 = homologous pairs of chromosomes line up in middle of cell
    Anaphase 1 = homologous pairs of chromosomes separate
    Anaphase 2 = chromatids separate
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    How does a Fetus receive oxygen? from mother's blood, oxygen dissociates from mother's haemoglobin and associates with fetal haemoglobin in the placenta – fetal haemoglobin has a higher affinity compared to mother's haemoglobin

    Benefit of fetal haemoglobin having high affinity? fetal haemoglobin's ODC will be to the left, it has high affinity –so the oxygen will dissociate from the mother's haemoglobin and associate with the fetal haemoglobin at the low partial pressures of oxygen in the placenta, so it has enough oxygen for its needs

    Why do adults not keep with fetal haemoglobin?the high affinity will mean less oxygen will be unloaded at the respiring tissues
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    surface area to volume calculation:

    surface area / volume
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    Why do Insects have Specialised Gas Exchange Systems?
    • multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand & body surface made of exoskeleton (impermeable barrier to reduce water loss)
    • therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a specialised gas exchange system called Tracheal System
    Structure of Tracheal System in Insects?
    • starts with openings on body surface called Spiracles
    • spiracles contain valves, open = gas exchange, closed = prevent water loss
    • spiracles connect to Trachea
    • trachea connect to Tracheoles
    • tracheoles connect directly to Respiring Cells (delivering oxygen, removing carbon dioxide)
    How does Gas Exchange occur in Tracheal System of Insects?
    • at rest = down a concentration gradient, oxygen moves in & carbon dioxide moves out by simple diffusion
    • when active = by ventilation, air inhaled for mass flow of O2 in & air exhaled for mass flow of CO2 out
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    Why do Fish have Specialised Gas Exchange Systems?
    • multicellular organism so has a small surface area to volume ratio, large diffusion distance, high demand & body surface impermeable
    • therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they require a specialised gas exchange system called Gills
    Structure of Gills in Fish?
    • many gill filaments and gill lamellae = large surface area
    • gill lamellae have a thin wall (short diffusion distance) and are permeable
    • ventilation brings in pure water (high oxygen, low carbon dioxide) and circulation brings in deoxygenated blood (low oxygen, high carbon dioxide), the water and blood pass over in opposite directions (countercurrent flow), which maintains concentration gradient all the way along the gill lamellae
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    Adaptation of Capillaries?
    • many small capillaries = large surface area
    • thin wall, one cell thick, squamous epithelial cells = short diffusion distance
    • pores between cells = allows fluid to move in and out
    • narrow lumen = increase diffusion time and decrease diffusion distance
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    Benefit of high species diversity?
    • Stable ecosystem
    • each species is less likely to become extinct (due to high genetic diversity)
    • & if a species does become extinct it will not affect the food chain as there are other species available
    How to measure Species Diversity for an area?
    • Species Diversity Index
    • takes into account the number of different species and how many individuals there are for each species
    • the larger the species diversity index, the larger the species diversity
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    Please may you go through Tissue fluid formation and reabsorbtion?
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    Hello, apologies if this proves to be inconvenient but is it possible please to note the equations for common mathematical questions (such as percentage increase/decrease, calculating the duration of anaphase etc.) which appear in the biology exams? I am OK with the content but the calculations are my weakness!
    Thank you very much!
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    (Original post by jakemonk17)
    Please may you go through Tissue fluid formation and reabsorbtion?
    from revision notes:

    How is tissue fluid formed and returned to circulatory system?
    • at the start of the capillary (arterial end) there is a build up hydrostatic pressure
    • this pushes fluid out of the capillary via the pores
    • the fluid carries the nutrients with it
    • the fluid surrounds the cells, this is called tissue fluid
    • at the finish of the capillary (venous end) the fluid moves back in by osmosis
    • the capillary has low water potential due to the presence of proteins (too large to move out of capillaries)
    • any excess tissue fluid is picked up by the lymph system and deposited in the vena cava
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    thanks a lot oak12
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    what exactly is the difference between cohesion and tension?
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    (Original post by oak12)
    from revision notes:

    How is tissue fluid formed and returned to circulatory system?
    • at the start of the capillary (arterial end) there is a build up hydrostatic pressure
    • this pushes fluid out of the capillary via the pores
    • the fluid carries the nutrients with it
    • the fluid surrounds the cells, this is called tissue fluid
    • at the finish of the capillary (venous end) the fluid moves back in by osmosis
    • the capillary has low water potential due to the presence of proteins (too large to move out of capillaries)
    • any excess tissue fluid is picked up by the lymph system and deposited in the vena cava
    wats the difference between cohesion and tension?
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    (Original post by oak12)
    Head of Biology from Birmingham Tuition Centre

    I will be available all day to answer any questions regarding AQA Biology Unit 2 - just post the questions in this forum

    Find the Revision Notes for Unit 2 attached

    oak12
    Thankyou these notes have helped me so much!
 
 
 
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