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AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

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Reply 3860

WesleyT

Original post by rommy123

your welcome :smile:

can someone explain the oestrous cycle please in bullet points
thanks

Oestrous Cycle

-FSH, secreted from pituitary gland, stimulates follicle development

-Oestrogen is released from the follicle and the ovaries

-Oestrogen stimulates the uterus lining to thicken and inhibits FSH

-As Oestrogen concentration increases, it stops inhibiting and stimulates the pituitary gland to secrete LH and FSH (LH surge)

-LH surge causes ovulation where the follicle ruptures and an egg is released

-LH stimulates the follicle to become the corpus luteum

-Progesterone secreted by corpus luteum

-Progesterone maintains the uterus lining and inhibits LH and FSH

If no embryo implants

-Corpus luteum breaks down

-Progesterone no longer released

-FSH concentration increases because it is no longer inhibited by progesterone

-Cycle starts again

Remember you're not a flop at Biology, you're a F.O.L.P.!

Hope this helps! :biggrin:

Reply 3861

DoeADeer

Hey, could someone just give me a quick overview of t cells, b cells, lymphocytes, antigens ans antibodies please?

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Reply 3862

ropin1

Original post by JasminC

If they were to ask the biological importance of water what would you include? apart from osmosis i cant really think of much x

Someone else posted there plan to that question, there you are
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)

Reply 3863

ahmmm

anybody got an off spec addition for the atp essay!? only essay im gonna bother with !!!

Reply 3864

JasminC

also what would you include if hey asked about the importance of hydrogen bonds?

Reply 3865

ropin1

Anyone know any out of spec points for Ions, If so could you please help? thanks

Reply 3866

giselle1994

can anyone help me with this question- 'Describe and explain how expression of the target gene is affected by siRNA.'

Reply 3867

KaranbirBandesha

Original post by master y

For the essay about shapes in 2012 how is haemoglbin, DNA replcation, restriction enzymes, Vaccines got to do with it? PLLLLEEASE someone help me

Haemoglobin - because haeomoglobin associates with oxygen it needs to have the right quatenery structure to pick up the 4 molecules of oxygen and it changes shape when it releases it in tissues with high levels of co2

DNA replication - complementary base pairs, free nucleotides need to attach to the base pairs need to be complementary but remember when refering to bases remember their specific shapes, C is curved at the end i think and T is pointy

Restriction enzymes - they cut at complementary places

Vaccines - antibodies and that they have to bind to stuff with complementary shapes

Sorry bout the spelling

Reply 3868

angel2

Original post by LegendX

What's the chance of a previously featured essay title coming up again? By previously featured I mean in the last 3 years?

low I'm afraid....there are so many possibilities so they decide to be mean and choose different ones

Reply 3869

ropin1

Original post by ahmmm

anybody got an off spec addition for the atp essay!? only essay im gonna bother with !!!

• Eg of ATP use - In animals, kidneys use ATP for active transport of sodium chloride out of the ascending limb of the loop of Henle, lowers water potential in the surrounding tissues.
• Creates water potential gradient, causes reabsorption of water through the permeable descending limb of the loop of Henle, leading to the production of more concentrated urine. Other uses of ATP and muscle contraction, Energy from ATP to move myosin heads
• Plants require the translocation of glucose (as sucrose) from source cells to sinks (roots, fruits and shoots)
• Provides energy for non-photosynthetic tissues.
• Achieved through active transport of sucrose (using energy from ATP) into phloem which lowers water potential. Causes water to enter by osmosis, creates hydrostatic pressure which forces the sugar solution up and down the phloem towards the sink regions.

Just copied and pasted that from my essay plan, reading through it its more about water but should still be okay if you emphasize the points about ATP

(edited 10 years ago)

Reply 3870

LitGeek94

Original post by master y

For the essay about shapes in 2012 how is haemoglbin, DNA replcation, restriction enzymes, Vaccines got to do with it? PLLLLEEASE someone help me

Restriction enzymes need specific palindromic sequence to bind to and cut, which can then be used in in vivo cloning/ recombinant DNA with plasmids... all about enzyme active site/ substrate complex really

Reply 3871

stoppy123

So sorry to keep repeating myself

but, what have you got for ATP essay plan? Is this enough?

- Produced in Aerobic and Anaerobic respiration.
- Produced in light dependent and independent reactions
- Produced by phosphocreatine ssytem
- Used for Muscle contraction
- Used for active transport
- Used to create second messenger when adrenaline binds
- Used for sodium potassium pump
- Good as it's simple one step reaction
- Can be regenerated
- Does not affect osmotic potential of cell like glucose would.
- Produces energy in managable amounts.

Reply 3872

helpme456

Are the exampro questions any good or are they mostly irrelavant?

Ive done all past papers and essay practice, should I do exam style questions or exampro questions?

Reply 3873

DrewYouTwo

For the water essay, think of bodily fluids. In the spec:

Lymph
Blood
Tissue fluid
Water in xylem
Cytoplasm
Bile saliva stomach acid and digtive juices

And think of other tenuous ones you can put in as well - cerebrospinal fluid, menstrual flow,

Then hydrolysis and photolysis - two mechanism that involve water

And rock it all off with some ecology ( my favourite topic)

Reply 3874

TauMuon

Original post by LitGeek94

So then is teh potassium gated channel open during depolarisation?

Potassium voltage-gated channels are closed during depolarisation, and open during repolarisation (at around +40 mV).

I THINK; can anyone clarify?

Reply 3875

ropin1

Original post by stoppy123

I would say that its used up in photosynthesis to create glucose or other products, Dont know if im right on that tho

Reply 3876

LitGeek94

How much depth does out of spec part of essay need to be?

Reply 3877

rm.xo

Original post by helpme456

Are the exampro questions any good or are they mostly irrelavant?

Ive done all past papers and essay practice, should I do exam style questions or exampro questions?

Aqa human biology 4 have a similar spec, I've done some of those questions.

Reply 3878

TauMuon

Original post by giselle1994

can anyone help me with this question- 'Describe and explain how expression of the target gene is affected by siRNA.'

siRNA guides an enzyme associated with it to a specific mRNA molecule with complementary bases to the siRNA. The enzyme then breaks the mRNA strand into smaller pieces, so the polypeptide for which it codes for cannot be translated.

Reply 3879

rm.xo

Original post by LitGeek94

How much depth does out of spec part of essay need to be?

You don't need any. This isn't required. That's just extra. I did this exam last year and got 23/25 on the essay without including any off spec topics.