A2 Biology | Post your doubts here

[usmiunique]

ITS NOT REALLY A CIE QUESTION BT.....a doubt in my mind.....how FSH can cause superovulation when it normally leads to one oocyte per cycle only ,......any idea

Actually FSH only causes the follicles to mature.. Under normal conditions, with the release of FSH, many follicles start to mature but one of them takes the lead and starts to produce oestrogen and progesterone. In superovulation, the follicles are directly taken from the ovary and are not allowed to degenerate.

 

[hassam]

brother one more question......in THE ms of question why its i important to mantain biodiversity:MS alwas mentions ecological role I.E nutrient cycling and climate stability.......but i do not understand how this climate stability and nutrient cycling is acheived

 

[hassam]

what are disadvantages of captive breeding programmes
If the captive breeding population is too small, inbreeding may occur due to reduced gene pool, which may lead to the population lacking immunity to diseases and other problems
Impacts of captive breeding include behavioral problems in released animals e.g they cannot socialise with other animals
Behavioral problems include not being able to hunt or forage for food leading to starvation because they were previousle kept in an environment where they had not to search for food
Released animals often do not avoid predators and are not able to find ample shelter for themselves and may die as a result.

 

[hassam]

what has biodiversity to do with nutrient cycling and climate stability

 

[usmiunique]

what has biodiversity to do with nutrient cycling and climate stability

Biodiversity refers to maintaining all the species of organisms whether they be plants, animals, bacteria, protists etc.
now plants and bacteria have a large role to play in the nitrogenous cycle and in recycling of nitrates, nitrification, denitrification etc.
while all organisms have a role to play in the carbon and water cycle because they all respire and use water!
As for climate stability, greenhousee effect which causes a rise in temperature can be seen, CO2 is a greenhouse gas given out by organisms which warms the earth, if animals are removed, Co2 levels and consequently the temperature will fall,
if a plant species becomes extinct,PARTICULARLY a species which uses up high amount of CO2 then Co2 levels and consequently the temperature levels will increase!

 

[hassam]

can somebody tell me the idea of polygenes and why is it that environment has more effect on polygenes

 

[usmiunique]

can somebody tell me the idea of polygenes and why is it that environment has more effect on polygenes

Polygenic characteristics are those which are controlled by many genes and each of them can have an effect on the phenotype.
For eg. Skin colour is an example of polygenic characteristic because it is controlled by many genes, and thus if the environment suppresses the effect of one or more gene, it can result in a n entirely new skin color which is why the environment has a greater effect on polygenes because many genes increases the chances of one or more genes bein affected by the environment!

 

[hassam]

Explain how the structure of the leaves of maize plants enables them to
photosynthesise more effectively at high temperatures than wheat plants.
ms of this question says
plasmodesmata between bundle sheath cells and mesophyll cells
relevant comment on stomata
what these two points have to do wid the question

 

[XPFMember]

Assalamoalaikum wr wb!
I’d like to share some answers I’ve made according to the marking schemes. They’re some syllabus statements, and I hope it’s gonna be helpful. Although I’m kinda late to do this but I hope inshaAllah I’m able to cover up until the exams..

 

[XPFMember]

Respiration:


Describe the process of oxidative phosphorylation in the mitochondria.
1. reduced, NAD / FAD ;
2. passed to ETC ;
3. inner membrane / cristae ;
4. hydrogen released (from reduced, NAD / FAD) ; R H2
5. split into electrons and protons ;
6. protons in matrix ;
7. electrons pass along, carriers / cytochromes ;
8. ref. redox reactions ;
9. ref. energy gradient ;
10. energy released ; R produced
11. protons (pumped) into intermembrane space ;
12. proton gradient ;
13. protons pass through (protein) channels ;
14. ATP synthase / stalked particles ;
15. ATP produced ;
16. chemiosmosis ;
17. electron transferred to oxygen ;
18. addition of proton (to oxygen) to form water / (oxygen) reduced to water ;

The hydrogens picked up but the NAD and FAD are now split into electrons and protons. The electrons are passed along the electron transport chain, on the inner membrane of the mitochondrion. As they move along the chain, they lose energy which is then used to actively transport the hydrogen ions from the matrix of the mitochondrion, across the inner membrane and into the inter-membrane space. This builds up a high concentration of hydrogen ions in this space. They are allowed to diffuse back into the matrix through special channel proteins that work as ATPases. Associated with each channel is the enzyme ATPsynthase. The movement of hydrogen ions through the ATPases provide enough energy to make ADP combine with the inorganic phosphate to produce ATP. At the end of the chain, the electrons reunite with the protons from which they were originally split. They combine with oxygen to produce water.

Describe ways in which the structure of the mitochondrion is adapted for oxidative phosphorylation.

· folded inner membrane / cristae ;
increases surface area available ;
· intermembrane space ;
allows accumulation of H+ ;
· impermeability of inner membrane to H+ ;
maintains H+ gradient / H+ only go through channels ;
· stalked particles / ATPase ;
channel for H+ / ATP synthesis ;
· linear arrangement of ETC on inner membrane ;
greater efficiency ;

Define the term respiratory quotient (RQ).

It is the ratio of volume of carbon dioxide evolved to volume of oxygen absorbed in respiration.

Describe the main structural features of an ATP molecule.

1. a nucleotide ;
2. with three phosphate groups ;
3. an organic / nitrogenous base / adenine ;
4. a pentose sugar / ribose ;
5. ref. ester linkages / covalent bonds ;

ATP is a nucleotide. It consists of adenine (an organic base) and ribose (a pentose sugar). This is combined with three phosphate groups to make ATP.

ATP is described as having a universal role as the energy currency in all living organisms. Explain why it is described in this way.

1. energy is released when it is hydrolysed ; A equation A joules for energy
2. easily hydrolysed ;
3. (energy) used in, processes / reactions ; A named process
4. rapid turnover ;
5. links catabolic and anabolic reactions / AW ;
6. found in, most cells / all organisms ;
7. soluble so easily moved (within cell) ;
8. ATP produced from variety of reactions ; A named reactions

ATP is a small water-soluble molecule. This allows it to be easily transported around the cell. It can be easily hydrolysed to release energy to be used for many reactions.
ATP + H2O <--> ADP + Pi + 30.5 kJ
The rate of turnover is enormous.
The cell’s energy-yielding reactions are linked to ATP synthesis. The ATP is then used by the cell in all forms of work. ATP is the universal intermediary molecule between energy-yielding and energy-requiring reactions used in a cell.

 

[zenyatales]

My question :- What exactly is mycoprotein?​

Myco means fungus. And mycoprotein is the protein obtained when a sample of fungus is cultured and provided suitable conditions (oxygen, temp, and nutrients), the protein is produced by the fungus which is then collected. It is actually a water soluble protein in the protoplasm of the cell.

geek101,​

​

so, when the fungus is taken out of the fermenter, they are taking out the entire fungus, and then LATER removing the protein (which is mycoprotein) from the protoplasm of the cell ?​

​

 

[hassam]

cn smone help me in this one http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_w11_qp_43.pdf aq 2 part b (ii) ms says 'accumulation of product leads to product inhibition '; cant this thing also happen in the case of free enzyme???

 

[hassam]

post A2 biology doubts, usefull facts both in paper 4 and 5......and for god sake ...make it sticky.....i cnt bear the pain of ifinding a2 posts in that combo thread

 

[hassam]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_52.pdf
q1. part d
i dint get the 2nd 6th and 12th point of ms......why we want to concentrate extract....whhat wud hapeen if i do not cover the container.....and why we need same mass.....cos we are only separating pigments here so it shud not make a difference
q2 part a
ms says nutrient concentration.....
whats the purpose of nutrient conc....here......i m not setting up a series of experimentsn so as to use same nutrient conc. in each conc. what he means here by nutrient conc.....it cn only be controlled if we are adding nutrients continuously

 

[hassam]

http://www.xtremepapers.com/papers/...nd AS Level/Biology (9700)/9700_s10_qp_42.pdf
q8 part a ii
last ms point no ill effect on gm organism....
what he means here that bacteria will not get affected due to flourescent protiesn??

 

[hassam]

cn u explain effects of gm crops like one markscme says.....reduction in biodiversity.....development of superweeds....cn u explain reasons for this.
http://www.xtremepapers.com/papers/...and AS Level/Biology (9700)/9700_s09_qp_4.pdf
q 6 c i

 

[omg]

pls pls pls can i get a note on the hazards and benfits of gene technology with specific examples??????????

 

[XPFMember]

Assalamoalaikum wr wb!

Can someone plz help me frame the answer to this question...plz

Explain why variation is important in selection;

1. ref. continuous / discontinuous variation ;
2. genetic / inherited variation ;
3. variation in phenotype / characteristics / AW ;
4. (can be due to) interaction of genotype and environment ;
5. e.g. of characteristic that influences survival ;
6. ref. intraspecific competition / struggle for existence ;
7. those with favourable characteristics survive / AW ;
8. pass on favourable characteristics to offspring ;
9. those with disadvantageous characteristics die ;

 

[XPFMember]

<The two A2 biology threads merged>

 

[XPFMember]

And this one also..plz..


Explain the role of isolating mechanisms in the evolution of new species;
n08
1. allopatric speciation ;
2. geographical isolation / spatial separation ;
3. e.g. of barrier ;
4. e.g. of organism ; must relate to 3
5. sympatric speciation ;
6. example ;
7. meiosis problems ;
8. polyploidy ;
9. behavioural / temporal / ecological / structural, isolation ;
10. (isolated) populations, prevented from interbreeding / can only breed
11. amongst themselves ;
12. no, gene flow / gene mixing, (between populations) ;
13. different selection pressures operate ;
14. natural selection ;
15. change in allele frequencies ;
16. different gene pool ;
17. over time (differences prevent interbreeding) ;
18. reproductively isolated ;