A level Biology: Post your doubts here!

[Mstudent]

darks and SohaibButt You guys are welcome any time!! If you have any questions ask me anytime and good luck for your exams

 

[SohaibButt]

darks and SohaibButt You guys are welcome any time!! If you have any questions ask me anytime and good luck for your exams

Thanks a lot bro

 

[janedoe]

Can someone please explain this question?

 

[Mstudent]

Can someone please explain this question?

The atrio ventricular valves and the semilunar valves are both closed only there is a high pressure in the ventricles (during ventricular systole) but not high enough to open the semilunar valves and pump blood through the aorta (Between point 1 and 2) AND when the pressure in the ventricle decreases (Ventricular diastole) but the pressure is. still high enough to keep the semilunar valves closed (between point 3 and 4) . just find the time between these points and add them up!

Even I couldnt solve this ques, this video helped me A LOT! http://highered.mheducation.com/sit...22/animation__the_cardiac_cycle__quiz_2_.html

Hope that helps

 

[janedoe]

The atrio ventricular valves and the semilunar valves are both closed only there is a high pressure in the ventricles (during ventricular systole) but not high enough to open the semilunar valves and pump blood through the aorta (Between point 1 and 2) AND when the pressure in the ventricle decreases (Ventricular diastole) but the pressure is. still high enough to keep the semilunar valves closed (between point 3 and 4) . just find the time between these points and add them up!

Even I couldnt solve this ques, this video helped me A LOT! http://highered.mheducation.com/sit...22/animation__the_cardiac_cycle__quiz_2_.html

Hope that helps

Got it. Thank you so much.

 

[shahzaib ihsan]

guys i need some help regarding these questions:

1. What does not help to maximise uptake of oxygen as blood lows through capillaries in the lungs?
a. dissociation of carbon dioxide from carboxyhaemoglobin allows more haemoglobin to available for oxygen binding.
b. each haemoglobin molecule can temporarily bind to eight oxygen atoms.
c. oxyhaemoglobin formation increases the capacity of red blood cells to transport oxygen.
d. the binding of the first oxygen molecule to haemoglobin increases the molecule's affinity for binding other oxygen molecules.
may/june 2015, variant 12
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Q 15 and 31 from may/june 2016, variant 11
Q 07 from october/november, variant 12 and like this on Q 12 may/june 2015, variant 12
Q 23 from may/june 2015, variant 12

 

[mohmed ahmed soliman]

c. oxyhaemoglobin formation increases the capacity of red blood cells to transport oxygen.

both b and d will help in maximise uptake of oxygen as blood lows through capillaries in the lungs so they are wrong
i think it could be either a or c
oxy hemoglobin formation does not increase Capacity of RBCs to transport o2 but it only increase Affinity of Hb to o2 /cooperative binding so it could be the answer

 

[mohmed ahmed soliman]

ber, varia

guys i need some help regarding these questions:

1. What does not help to maximise uptake of oxygen as blood lows through capillaries in the lungs?
a. dissociation of carbon dioxide from carboxyhaemoglobin allows more haemoglobin to available for oxygen binding.
b. each haemoglobin molecule can temporarily bind to eight oxygen atoms.
c. oxyhaemoglobin formation increases the capacity of red blood cells to transport oxygen.
d. the binding of the first oxygen molecule to haemoglobin increases the molecule's affinity for binding other oxygen molecules.
may/june 2015, variant 12
------------------------------------------------------------------------------------------------------------------------------------------------------------
Q 15 and 31 from may/june 2016, variant 11
Q 07 from october/november, variant 12 and like this on Q 12 may/june 2015, variant 12
Q 23 from may/june 2015, variant 12

does this answer make sense

 

[janedoe]

Can someone please explain this question?
I am confused between the last two options.

 

[janedoe]

Why is option A incorrect? When they have specifically mentioned cell may be 'unable to produce' an enzyme..?
I understand that build up of lipids suggests that this is a hydrolytic enzyme and so lysosomes is the answer.
But I don't get why golgi apparatus is invalid?

 

[shahzaib ihsan]

both b and d will help in maximise uptake of oxygen as blood lows through capillaries in the lungs so they are wrong
i think it could be either a or c
oxy hemoglobin formation does not increase Capacity of RBCs to transport o2 but it only increase Affinity of Hb to o2 /cooperative binding so it could be the answer

i chose c which was wrong i don't know why, but how a is the answer? and can you explain me answers to other questions as well? these: Q 15 and 31 from may/june 2016, variant 11
Q 07 from october/november, variant 12 and like this on Q 12 may/june 2015, variant 12
Q 23 from may/june 2015, variant 12

 

[Mstudent]

Guys help me here plz

which statement is incorrect for mitotic cell division
a.DNA is replicated Semi conservatively during Mitosis
b.DNA is normally unchanged from one generation of cells to the next
c.the daughter cells have the potential to produce the same enzymes as the parent cell
d.the same quantity of DNA is distributed to the nuclei of two new cells

 

[mohmed ahmed soliman]

i chose c which was wrong i don't know why, but how a is the answer? and can you explain me answers to other questions as well? these: Q 15 and 31 from may/june 2016, variant 11
Q 07 from october/november, variant 12 and like this on Q 12 may/june 2015, variant 12
Q 23 from may/june 2015, variant 12

there is a phenomenon known as Haldane effect which explains the answer
google it

 

[Metallic9896]

Guys, I think you all are misreading the statement. Took me long enough but we're really dumb if none of us noticed this (I'm referring to shahzaib ihsan's question above).

30 What does not help to maximise uptake of oxygen as blood flows through capillaries in the
lungs?

A Dissociation of carbon dioxide from carboxyhaemoglobin allows more haemoglobin to be
available for oxygen binding.
B Each haemoglobin molecule can temporarily bind to eight oxygen atoms.
C Oxyhaemoglobin formation increases the capacity of red blood cells to transport oxygen.
D The binding of the first oxygen molecule to haemoglobin increases the molecule’s affinity for
binding other oxygen molecules.

It's A because.......

CARBOXYhaemoglobin.

*facepalm*

Carbon dioxide doesn't form carboxyhaemoglobin, carbon MONOXIDE does. Carbon dioxide forms CARBAMINOhaemoglobin. That's why the option is incorrect.

I think being such little geniuses here on xtremepapers (no sarcasm) sometimes we all end up overthinking.

 

[Metallic9896]

Why is option A incorrect? When they have specifically mentioned cell may be 'unable to produce' an enzyme..?
I understand that build up of lipids suggests that this is a hydrolytic enzyme and so lysosomes is the answer.
But I don't get why golgi apparatus is invalid?

Question 4
The majority of candidates answered this incorrectly. A build-up of lipids in cells means that the excess lipids
are not being broken down. Excess lipids are normally broken down by hydrolytic enzymes found in the
lysosomes.

This is what the examiner report says. This is one of the reasons I really dislike Biology paper 1s. Some questions are simply too vague with overlapping correct options. Their emphasis is the 'build up' part and not the enzyme not being produced part. My first instinct was that Golgi apparatus is not part of 'producing' the enzyme, as we read and are expected to learn that it is involved in 'packing' the enzyme or adding non-protein elements to it, but that's something too trivial to be reason enough. More importantly, I guess what they mean to say is that in the production process, anything could be at fault, from the gene sequence of the enzyme to the ribosomes to the endoplasmic reticulum and the Golgi apparatus - all of these could be or one of these could be faulty. However, something that for CERTAIN won't function is the lysozomes because they are what the enzymes eventually should end up and if the enzymes aren't produced then for certain they won't end up there. These 2 arguments are what I could think of in favor of option A, but I do understand why anyone would have an issue with this question, including myself. They should have written something like, 'Which cell structure MUST not function correctly.." writing must in bold etc.

 

[shahzaib ihsan]

Guys, I think you all are misreading the statement. Took me long enough but we're really dumb if none of us noticed this (I'm referring to shahzaib ihsan's question above).

30 What does not help to maximise uptake of oxygen as blood flows through capillaries in the
lungs?

A Dissociation of carbon dioxide from carboxyhaemoglobin allows more haemoglobin to be
available for oxygen binding.
B Each haemoglobin molecule can temporarily bind to eight oxygen atoms.
C Oxyhaemoglobin formation increases the capacity of red blood cells to transport oxygen.
D The binding of the first oxygen molecule to haemoglobin increases the molecule’s affinity for
binding other oxygen molecules.

It's A because.......

CARBOXYhaemoglobin.

*facepalm*

Carbon dioxide doesn't form carboxyhaemoglobin, carbon MONOXIDE does. Carbon dioxide forms CARBAMINOhaemoglobin. That's why the option is incorrect.

I think being such little geniuses here on xtremepapers (no sarcasm) sometimes we all end up overthinking.

shoot i didn't see that coming! lol thanks by the way it is solved..
can you help with these?
Q 15 and 31 from may/june 2016, variant 11
Q 07 from october/november, variant 12 and like this on Q 12 may/june 2015, variant 12
Q 23 from may/june 2015, variant 12

 

[techgeek]

Answer in ms is B.
But shouldn't the answer be A?
ER also says: T-lymphocytes can secrete cytokines. Cytotoxins are released by certain pathogens.
which means C is incorrect but A is correct, right? I never heard of T-lymphocytes leaving blood

 

[Mstudent]

Could anyone help me out here?
B looks correct, and D looks correct,
So why is D the answer? And not B?

 

[Brisingr]

Could anyone help me out here?
B looks correct, and D looks correct,
So why is D the answer? And not B?

in prophase chromosomes recoil and condense and the centriole divide to reach at the oppsite pole of the cell. hope this helps

 

[Mstudent]

in prophase chromosomes recoil and condense and the centriole divide to reach at the oppsite pole of the cell. hope this helps

So in that case B is correct? So why in the marking scheme did they chose seperation of centrioles not the formation of chromosomes (Condensation of chromosomes)?