A level Biology: Post your doubts here!

[sashaleon]

so there are 3 types of natural selction \
1-directional selection : in which an environmental change causes a change in the gene pool of a population favoring one characterstict over the others e e.g. the peppered mot example
2-stablising selection : in which the environmental factor is stable and so is the characteristics
e.g. the newborn weight its stable since the human being was made because the too heavy or too light babies wont survive
3-disruptive selection in which two extremes characteristic are favored
e.g. malaria and sickle cell anaemia

Thanks <3

 

[comrade]

hey and what are difference between continous and discontinous variation . Can u explain this fully. And my other question: And in section b where we have to answer 1 question. Whenever i answer those questions my answers are not very long but they do contain all the points in the markscheme. Like if they give a space of 3 pages my answer to a come in half page or a little more and the answer to b is also a half page or can be less. So, will my marks be deducted if i write short answers like this?

Continuous variation refers to a variation where there is a complete range of measurements from one extreme to the other, while a discontinuous variation is where distinct features cannot be measured across a complete range. Variations are small differences that exist between individuals. Variations can be caused by either environment or genetics.
Continuous variation or continuous matter is gradual, something that is not so clear cut. For example, height can vary amongst population and there are many different heights.
Discontinuous variation or matter is where you are either in one category or the other, but never in between. Examples of this are: Blood group - you are either O, A, AB, ABO but never anything in between. Another example would be tongue rolling - you can either tongue roll or you can't.
As for the long questions make sure that you have ALL the points according to mark scheme. Marks won't be deducted. But do try to increase the length if you can. Try to make the sentences longer. Although it isn't required but I'll recommend you to increase it. A bigger handwriting and add a bit more of English. Do not deviate from the question. The examiner will not give you marks for that.

 

[LMGD33]

Hey guys i have a question that I came across while solving, and i have no idea how to solve it.. It's question 8 part (b) (i) in http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_qp_41.pdf
and the mark scheme says http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_ms_41.pdf
The examiners report didn't mention any formula, I'm confused.. is there one I'm supposed to know?

 

[knowitall10]

Hey guys i have a question that I came across while solving, and i have no idea how to solve it.. It's question 8 part (b) (i) in http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_qp_41.pdf
and the mark scheme says http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s12_ms_41.pdf
The examiners report didn't mention any formula, I'm confused.. is there one I'm supposed to know?

There's no specific formula. It's the rate of photosynthesis yeah? And it's unit is millimol/s so divide the uptake if CO2 with 20..

 

[LMGD33]

There's no specific formula. It's the rate of photosynthesis yeah? And it's unit is millimol/s so divide the uptake if CO2 with 20..

Of course!! I missed the 20 second thing, thank you so much! god bless you!

 

[knowitall10]

Of course!! I missed the 20 second thing, thank you so much! god bless you!

No problem
May Allah bless u 2..

 

[dornam]

Is this a correct use of monoclonal antibodies in diagnosis?


o locate the position of blood clots in the body a person though to have a deep vein thrombosis

 

[knowitall10]

Is this a correct use of monoclonal antibodies in diagnosis?


o locate the position of blood clots in the body a person though to have a deep vein thrombosis

Yep 100%

 

[Alice123]

Describe a reflex arc and explain why reflex arcs are important...

some1 pls write the answer: markscheme given below

Irfan1995 knowitall10


strong stimulus in receptor / AW ;
action potential / impulses, along sensory neurone ;
dorsal root of spinal nerve ;
into spinal cord ;
synapse with intermediate neurone ;
(then) motor neurone ;
action potential / impulses, to effector ;
action potential / impulses, to brain ;
response ; e.g. knee jerk 5 max can be on diagram
fast / immediate ;
stops / limits, damage / danger ;
automatic / no conscious thought ;
innate / stereotyped / instinctive

 

[hela]

1) We know that along food chains, the biomass decreases (roughly 10% is transferred to the next trophic level)
To find the total biomass of a population, multiply the number of individuals by the biomass of one individual
R: 10,000 x 0.1 = 1,000
S: 5 x 10.0 = 50
T: 500 x 0.002 = 1
U: 3 x 300,000 = 900,000
Just arrange them in decreasing order to get U --> R --> S --> T


2) If animal cells absorb too much water by osmisis, they will go through lysis (they will burst). Plants, on the other hand, have a cell wall which prevents lysis (bursting) and can allow the development of turgor pressures. Once a plant is turgid, no more water can get through.
Animals need the vacuole to remove water to prevent lysis.

3) It is the time between 1 and 2 plus the time between 3 and 4.

4) Goblet cells make a lot of vesicles which secrete mucus by exocytosis.

5) The first column shows how much reducing sugars are present.
After hydrolysis, you break down the non-reducing sugars into reducing sugars.
So the second column is the reducing sugars + non-reducing sugars
To find the amount of non-reducing sugars, subtract the corresponding values
A: 55 - 35 = 25
B: 55 - 55 = 0
C: 85 - 65 = 20
D: 80 - 70 = 10
So A has the most non-reducing sugars

6) When an inhibitor binds to the active site, this is known as competitive inhibition. The active site does not change shape, and the initial rate decreases
When an inhibit binds to a different site (allosteric site), then this is known as non-competitive inhibition.

thanks a lot very helpful
can you explain
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w11_qp_11.pdf Q39
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w11_qp_12.pdf Q16
http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w10_qp_12.pdf Q2

 

[knowitall10]

Describe a reflex arc and explain why reflex arcs are important...

some1 pls write the answer: markscheme given below

Irfan1995 knowitall10


strong stimulus in receptor / AW ;
action potential / impulses, along sensory neurone ;
dorsal root of spinal nerve ;
into spinal cord ;
synapse with intermediate neurone ;
(then) motor neurone ;
action potential / impulses, to effector ;
action potential / impulses, to brain ;
response ; e.g. knee jerk 5 max can be on diagram
fast / immediate ;
stops / limits, damage / danger ;
automatic / no conscious thought ;
innate / stereotyped / instinctive

A reflex arc is a pathway taken to bring about a reflex action without including the conscious regions of the brain. It includes the passing of the nerve impulse from the receptor, to the sensory neurons, through the synapse, to the intermediate neurons, through the synapse, to the motor neurone and finally to the effector.
When touching a hot object, the skin cells are the receptors, and an action potential is generated in the sensory neurone. The impulse travels through the dorsal root of the spinal nerve and reaches the gray matter, where the sensory neurone synapses with the intermediate neurone. Neurotransmitter e are released and the nerve impulse passes from the sensory to theintermediste neuron which again synapses with the motor neurone. Once the nerve impulse reaches the motor neurone in the ventral root of the spinal nerve, an action potential is generated and passes through the neurone and to the effector, which are the muscles at the arm: causing them to contract and remove the hand away from the hot object.within the spinal cord, the impulse will be passed onto other neurons that will take the impulse up the cord to the brain. This reaction stimulus is the reflex action: a fast, automatic, response to a stimulus.


I hope I answered ur question

 

[geek101]

Is this a correct use of monoclonal antibodies in diagnosis?


o locate the position of blood clots in the body a person though to have a deep vein thrombosis

absolutely. You can insert human fibrinogen molecules into the mice and obtain antibodies complementary to them from its spleen. you can then follow the monoclonal antibody procedure and prepare monoclonal antibodies complementary to the human fibrinogen. when these antibodies are injected into the person having the clot, they will attach to the fibrinogen molecules, which are present at the site of the clot that way its position can be identified!

 

[knowitall10]

absolutely. You can insert human fibrinogen molecules into the mice and obtain antibodies complementary to them. you can then follow the monoclonal antibody procedure and prepare monoclonal antibodies complementary to the human fibrinogen. when these antibodies are injected into the person having the clot, they will attach to the fibrinogen molecules, which are present at the site of the clot that way its position can be identified!

Someone seems excited

 

[knowitall10]

And IMPORTANT:

The impulse is passed to the brain AT THE SAME TIME AS THE MESSAGE IS TRAVELLING THROUGH THE MOTOR NEURONE TO THE EFFECTOR. The effector therefore responds to the stimulus before there is any voluntary response, involving conscious regions of e brain.

 

[geek101]

Someone seems excited

oi hehe excitement nahee, exam anxiety

 

[knowitall10]

oi hehe excitement nahee, exam anxiety

Haan bilkul!

 

[mariyam95]

SERIOUSLY??!?? THATS AWESOME.

yeh its really awesome that means the 15 marks gonna be really easy

 

[mariyam95]

Thanks <3

welcome

 

[Oceanic]

Please post a guess, important topics or anything important
Please help !!!!!
I'm very nervous for the exam tomorrow

 

[mariyam95]

Please post a guess, important topics or anything important
Please help !!!!!
I'm very nervous for the exam tomorrow

dude this wont help
no one can guess it's a THEORY PAPER!