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MegMoo12
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#2161
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#2161
(Original post by ConorP)
Stage one is saying you add the primers to the "mixture" and stage 2 is the attaching of the primers to the single DNA strands


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And the cooling down causes that I guess?
Thank you!!

Why the neg?? " the mixture is cooled to 55degrees, causing the primers to join/anneal to their complementary bases at the end of the DNA fragment."
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master y
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#2162
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(Original post by safis)
Just a heads up: I was told that a future essay question on energy transfer might come up. I was told this last year so might come up on this paper.
how/who told you this?
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marleyxd
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(Original post by ConorP)
Thanks, I think it's when you apply that to the oestrogen cycle.. Everything seems to inhibit and stimulate everything haha


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Yeah, with the Oestrous cycle, the majority of feedback is negative e.g Oestrogen and Progesterone inhibiting FSH and LH from the pituitary gland. However there is Positive feedback involved when Oestrogen levels reach a certain point, which then stimulates the production of FSH an LH.
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HELPIMSTUCK
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Essay plan ideas on biological importance of water (I feel this may come as its quite a broad topic, like bacteria and cycles):

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- Use in plants
- Water uptake in roots - apoplastic (cell wall) /symplastic (cytoplasm)
- minerals build up in root due to low water potential
- causes root pressure, evidenced by guttation

- Transpiration - is the loss of water from plant surface due to evaporation
- dependent on water potential in leaf and in air
- transpiration stream is continous flow of water from root to leaf
- Cohesion-Tension (water pulled up by transpiration replaced by more water

- Photosynthesis - water used in photolysis of water, molecule splits into
- H+ ions reduce NADP
- electrons replace electrons lost from PSII in non-cycli phosphorylation
- oxygen released as waste gas

- Xerophytic adaptions - thick waxy cuticle reduces evaporation
- close stomata in daylight to reduce transpiration
- succulent leaves store water
- smaller leaves, reduced SA:V ratio slows diffusion

Reproduction
- sexually reproducing organisms use water to bring male and female gametes together in fertilisation
- in mammals foetus develops in water filled sac which provides thermal and physical stability

Hydrolysis and condensation
- ATP -> ADP + Pi
- restriction endonucleases use hydrolysis
- hydrolysis/condensation reactions of biopolymers (polysaccharides, polypeptides, nucleic acids)

Osmosis
- movement of water molecules from a high water potential to low water potential through partially permeable membrane
- water potential in cells (if isotonic no net diffusion, if in hypotonic soln cell swells/plant cell turgid, if in hypertonic soln cell crenates/plant cell undergoes plasmolysis)

Blood Glucose

- Blood glucose conc too high - water potential too low
- causes water to leaves surrounding cells to increase water potential, cells my dehydrate/die
- Diabetes - blood has lower water potential, leads to thirst, copious urine produced due to XS water in blood, poor vision due to osmotic loss of water from eye, blood pH falls leading to acidosis

Cholera
- bacterial cell adheres to epithelia and secretes exotoxin, which enters cell and opens chloride ion channels
- chloride ions diffuse out of cells into lumen, lowering lumen's water potential
- water osmotically diffuses into lumen, produces diarrhoea
- treat with ORS salts

Cystic Fibrosis
- in healthy cells CFTP protein carries Cl ions out of cell, increases water potential of cytoplasm
- water leaves cell by osmosis, makes mucus watery
- CFTP protein absent due to genetic mutation
- Cl ions cannot leave cell, water remains in cell
- produces thick sticky mucus which blocks airways, leads to coughing, wheezing, bacterial infection

OTHER TOPICS could be considered
- water as a habitat (oceans, lakes, rivers) for marine life (fish gills, counter-current exchange)
- adaptions of hydrophytic plants
- Role of water in thermoregulation
- Osmoregulation (TBH this is quite complicated)



Obviously I wouldn't write all this. Some topics relate to other titles
- Cholera relates to bacteria, disease
- Cystic Fibrosis relates to genetics, disease, gene therapy
- Osmosis (might be an essay in itself)
- Osmoregulation, Thermoregulation relate to negative feedback
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khalidpatel
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Guys 1 quick question, describe the biological consequences of pollution of water by sewage? 4 marker need help I'm kinda confused


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hannahs14
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#2166
(Original post by samfreak)
yh im stuck on this aswell :-( can someone please help us?

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you are right the textbook is wrong..our strand is the complementary copy. Don't trust the textbook, my teacher says its flooded with mistakes.
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hannahs14
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(Original post by mathsguy)
I think there'll be an essay on controls, practical investigations and statistical tests

Also something to do with proteins
That was tested in our EMPA/ISA how could they do it again? Furthermore how could you relate it to all 4 units?
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hannahs14
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(Original post by Richyp22)
Ok I think homeostasis may come up as an essay title, I'm just wondering if theres any other methods of homeostatsis that people can think of apart from-

- Blood pressure
- Temperature
- glucose
- Ph buffers
- Immune response(Possibly)
- Kidney ultrafilteration
?
Isn't homeostasis too narrow? I would think it would be a broader question? How can you relate homeostasis to units 1 and 2??
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gingerandice
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#2169
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how can thermoreceptors send nerve impulses to the hypothalamus via the autonomic nervous system? I thought the ANM was between the coordinator and the effector?
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SamEastie
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i do not know how to prepare for the essay!? theres no way i can learn all 4 units by monday.. or ever :L
how are other people doing it? :/
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marleyxd
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(Original post by gingerandice)
how can thermoreceptors send nerve impulses to the hypothalamus via the autonomic nervous system? I thought the ANM was between the coordinator and the effector?
No the autonomic nervous system is functions unconsciously (you don't need to control it)
I think you're thinking of a motor neuron....
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Med_me
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(Original post by sienna5)
A fluorescent marker is basically a marker gene that codes for fluorescence. And the point of a marker gene is to identify cells that have been transformed ( the host cells that's actually taken up the vector and Dna)
Ah, thanks!
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F1's Finest
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(Original post by hannahs14)
That was tested in our EMPA/ISA how could they do it again? Furthermore how could you relate it to all 4 units?
Exactly.

The only questions they will ask for the essay are ones where we can bring in topics from all units of the entire A-Level spec.
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ropin1
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hi, just wondering if an essay came up about the biological importance of water could you link in points about eutrophication, and how the contamination of water can have negative impacts on organisms. Ive just retaken unit 4 so thats still fresh in my mind
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JoshL123
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Hey everyone, if an organsims is in a favourable environment, does it turn a lot more often?
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ActaNonVerba
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(Original post by khalidpatel)
Guys 1 quick question, describe the biological consequences of pollution of water by sewage? 4 marker need help I'm kinda confused


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nitrate in faeces.. causes eutrophication (you have to explain it obv)
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Tikara
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(Original post by JoshL123)
Hey everyone, if an organsims is in a favourable environment, does it turn a lot more often?
It'll turn more often - in order to stay in that environment for longer

I think the text book is wrong on that bit
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JoshL123
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(Original post by Tikara)
It'll turn more often - in order to stay in that environment for longer

I think the text book is wrong on that bit
Thought so! I was getting so confused as people were saying the opposite haha! Thanks
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Anjna
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what is the exact definition of a primer?
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ConorP
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#2180
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(Original post by MegMoo12)
And the cooling down causes that I guess?
Thank you!!

Why the neg?? " the mixture is cooled to 55degrees, causing the primers to join/anneal to their complementary bases at the end of the DNA fragment."
Yeah I agree, don't know what you mean why the neg?


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