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AQA BIOL4 ~ 11th June 2013 ~ A2 Biology

Hi could anyone tell me what I need to know about predator-prey relationships please?
Thanks

This was posted from The Student Room's iPhone/iPad App

Reply 641

master y

12

Original post by billybobs

.

thanks. can i ask what is ur generic answer for why we use a control?

Reply 642

ynm1

Original post by totw

Hi could anyone tell me what I need to know about predator-prey relationships please?
Thanks

This was posted from The Student Room's iPhone/iPad App

1. When the prey population is high, there is a lot of food available for predator.
2. As a result, predator population increases after a time lag as more are likely to survive.
3. More predators -> more predation of prey and therefore prey population reduces.
4. Few prey -> predators in greater competition for remaining prey. Predator population reduces after a time lag of the decrease in prey population as some predators are unable to survive.
5. Few predators -> fewer prey eaten.
6. Prey population rises.

Reply 643

billybobs

5

Original post by totw

Hi could anyone tell me what I need to know about predator-prey relationships please?
Thanks

Not a huge deal, but when it comes up its usually a describe and explain question when interpreting a graph or data about a predator/prey relationship that shows cyclic fluctuations in each population.

Possibly a question or two about how predators are useful for biological control within an agricultural ecosystem.

Reply 644

Shb117

Original post by totw

Hi could anyone tell me what I need to know about predator-prey relationships please?
Thanks

This was posted from The Student Room's iPhone/iPad App

In addition to the answer above just remember that the predator-prey populations are in like an equilibrium and prey population never hits 0. This is also the reason why biological control never eliminates pest completely.

Reply 645

lifeisgood2012

Could someone please help me with what occurs in nitrogen fixation?

Reply 646

billybobs

5

Original post by master y

thanks. can i ask what is ur generic answer for why we use a control?

We'll take the example of testing a drug that relaxes headaches as a clinical trial.

The control group will be treated the same, but with an injection of a liquid (water) that doesnt contain the drug. This is so that the scientists can see that the only factor that causes the changes in an experiment is the drug, and no other factors.

Reply 647

posting

Biol4 in Jan 13 was quite an easy straight-forward paper, Im expecting a hard one this time! Better fasten your belts! goodluck to everyone! x

Reply 648

kitkat95

3

Original post by master y

thanks. can i ask what is ur generic answer for why we use a control?

To allow comparison
To ensure the results are due to the independent variable
Increase reliability?

Reply 649

kdk

question 6b-ii
why is it directional and not stabilising? :confused:

question paper
http://sciencemathsmaster.weebly.com/uploads/6/3/2/4/6324568/aqa-biol4-w-qp-jun11.pdf
ms
http://sciencemathsmaster.weebly.com/uploads/6/3/2/4/6324568/aqa-biol4-w-ms-jun11.pdf
thanks :smile:

Reply 650

kitkat95

3

Original post by lifeisgood2012

Could someone please help me with what occurs in nitrogen fixation?

Nitrogen is converted to ammonia by nitrogen fixing bacteria using the enzyme nitrogenase. This is a reduction reaction.

Reply 651

DELETED ACCOUNT

15

Original post by billybobs

x.

Wold have given you a +1, but I already used up all my ratings on you! :tongue:

Reply 652

Nessie133

Original post by lifeisgood2012

Could someone please help me with what occurs in nitrogen fixation?

Nitrogen fixation is the conversion of gaseous nitrogen in the atmosphere to ammonium ions by nitrogen fixing bacteria.

Reply 653

Tikara

Original post by totw

Hi could anyone tell me what I need to know about predator-prey relationships please?
Thanks

This was posted from The Student Room's iPhone/iPad App

basically, an increase in prey means an increase in predator as more food is available. means a decrease in prey (as they get eaten) - because of less prey, less food for the predators means that the predator population decreases <-- Intraspecific competition.

because of less predation, the prey population increases and so on :P

Just be aware that graphically there is a small time lag between one population increasing and the other increasing

Always be aware of interspecific competition or disease and abiotic factors such as season/temp that may affect the numbers of either population though!

also, just did the jan 13 and what poor tadpoles! surely thats some form of torture haha

mainly losing a few marks on every question overall and messing up the speciation question.
Everyone make sure you say allele!! they love that word, it would have picked me up 3 marks if I had said it grrr

(edited 10 years ago)

Reply 654

Scienceisgood

21

Respiration and Photosynthesis brief.

1. Photolysis (Occures in the Grana) - Light dependant reaction.
H20 --> 2H+ + 1/2 O2-
NADP Picks up the H+ ion to become a reduced NADP molecule.

Also, during this process, chlorophyll is absorbing light from the sun which elevates electrons to a higher energy level and as the electrons go down energy levels, the energy is used to convert ADP and Pi into ATP to be used in the Light Independant Reaction.

Light Independent Reaction.
RuBP reacts (5 Carbon molecule) reacts with CO2 to form a 6 Carbon Molecule
2 G3P molecules are produced from this.
ATP is then broken down into ADP and a Pi ion releasing energy, also, NADPH releases its hydrogen to form NADP which gives the energy needed to break convert the 2 G3P molecules into triose phosphate molecules.
This then gets converted into 2 glucose molecules and 10 molecules of RuBP to start the reaction over again.

Respiration:
Glycoloysis:
Glucose produced in the light independent reaction comes along and 2 ATP molecules are broken down into ADP and Pi Molecules.
The phosphate ions attach and the glucose molecule splits into 2 3 carbon molecules called Triosphosphate.
Then NAD and FAD come along and are reduced by the Triosphosphate molecules to NADH and FADH.
4 ATP molecules are produced as a result of this reaction.

Link Reaction:
Pyruvate + NAD + CoA --> 2 Carbon Molecule molecule + NADH + Acetyl CoA
Acetyle CoA used in next reaction.

Krebs Cycle:
Acetyl CoA reacts and binds with a 4 Carbon Molecule which converts into a 6 Carbon molecule.
2 CO2 molecules and 2 Hydrogen molecules are released from the 6 Carbon molecule making a 4 carbon molecule.
The Hydrogens are picked up by NAD and FAD to form NADH and FADH by reducing NAD and FAD respectively.
The 4 carbon molecule that is left over is then recycled and reacted with another Acetyl CoA.
1 Molecule of ATP Produced.

Electron Transport Chain: - Takes place in mitrochondria
The NAD and FAD attached to the Christae of the mitrochondria react with the Hydrogen released in glycolysis and now form NADH and FADH and now release their electrons from their Hydrogen ions and go down the electron transport chain which travel down the electron carriers releasing energy as they go which combines ADP and Pi molecules into ATP.
The Electrons eventually reach oxygen which is the final electron acceptor and then the Hydrogen + ions are actively transported down the electron transport chain and react with the O(2-) charged oxygen atom to form water which is diffused out of the leaf in a gaseous state.

Reply 655

lifeisgood2012

Original post by Nessie133

Nitrogen fixation is the conversion of gaseous nitrogen in the atmosphere to ammonium ions by nitrogen fixing bacteria.

are nitorgen fixing bacteria in the soil?

Reply 656

kitkat95

3

Original post by kdk

question 6b-ii
why is it directional and not stabilising? :confused:

question paper
http://sciencemathsmaster.weebly.com/uploads/6/3/2/4/6324568/aqa-biol4-w-qp-jun11.pdf
ms
http://sciencemathsmaster.weebly.com/uploads/6/3/2/4/6324568/aqa-biol4-w-ms-jun11.pdf
thanks :smile:

Only one genotype is affected/has decreased- the recessive one. If it were stabilising selection, both the recessive and dominant allele frequency would have been affected.

Reply 657

krane

9

Could anyone tell me how decomposers give back carbon dioxide into the atmosphere?
Is it mainly by respiring but also by breaking down things like starch and not absorbing it all?
Plus how do they give back nitrogen, is it by breaking down proteins etc, absorbing them, and then dieing?

And are saprobiotic microorganisms the same as saprophytic bacteria, and which do they prefer? :biggrin: