A2 Biology OCR June 2015 Revision Thread

Its a nerve connecting the medulla oblongata to the sinoatrial node, it can send and action potential down to the heart causing an increase in the frequency of heart beats. This happens in various situations, e.g. when chemoreceptors detect a low pH in the blood

Ahhh tysm again!!! So helpful

Edit: how is there water in the ascending limb if the water is lost by osmosis in the descending limb?

Does anyone think beta oxidation will come up? If so where is the info on what we need to know because I can't find much in the book about it

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I thought so, but then i saw this ppq http://www.ocr.org.uk/Images/63306-question-paper-unit-f214-communication-homeostasis-and-energy.pdf (question 2b), where we would need to know it in more detail

Pretty sure you have to know the physiological and behavioural adaptations they do whether they are trying to cool down or to conserve heat.

So in endotherms(practically warm blooded animals but don't use that term in the exam - quoted by OCR):

- Sweat glands in skin: If temp is too high endotherms ( an example is us humans), secrete more sweat onto skin, water in sweat eaporates. If tempt too low, less sweat is secreted and les water is evaporated.
- Lungs, mouth and nose: Panting(in dogs for example) increases evaporation of water from lungs, tongue and other moist surfaces. Temp too low, animal does not pant, less water evaporated.
- Hairs on skin: Temp too high hair lies flat providing little insulation and thus more heat is lost. If tempt too low, hairs are raised to trap a layer of insulating air, reducing loss of heat from skin.
- Arterioles leading to capillaries in skin: Temp too high, vasodilation allows more blood into capillaries near the skin surface which allows more heat to be radiated from the skin. Tempt too low, vasoconstriction reduces flow of blood through capillaries near surface of skin, which allows less heat to be radiated.


Behavioural:

- IF too hot, move into shade, hide or burrow, if too cold move into sunlight.
- If too hot orientate body to decrease surface area exposed to sun. if too cold orientate body to increase surface area exposed to sun.
-If too hot remain inactive and spread out limbs to increase surface area. If too cold move about to generate heat in muscles ( except in extreme cold where it is better to keep still and roll into a ball to reduce surface area).


Ectotherms are practically similar (behavioural wise).
It can be found in the OCR biology book pages 8-11.

Anyone tell me how PCR works???

-Heat mixture to 95 degrees c
This breaks the hydrogen bonds between the dna strands to form two single stranded dna molecules

-add primers and reduce to 55 degrees c
This allows primers to anneal to either ends of the single stranded dna fragments. Primers are needed cos dna polymerase cannot bind directly to single stranded dna

-Increase to 75 degrees c
Dna polymerase completes the rest of the fragment
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Thank you so much!!! hope this comes up tomorrow!

it comes up in f215 not f214

Anyone tell me how PCR works???

Omfg you're joking..... including stuff like gene therapy and electrophoresis??

Omfg you're joking..... including stuff like gene therapy and electrophoresis??