A level Biology: Post your doubts here!

[qwertypoiu]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w04_qp_1.pdf
question
7.answer is A.I had marked B.In which conditions do we add HCl before the Bendicts test or in all?
20.Answer is D.
30.Answer is A.

20: be careful. It says number of DNA molecules. In the prophase, each chromosome has two chromatids, and each chromatid contains one DNA molecule so 46*2=92. After division, each chromosome consists of only one chromatid each. So 46.
30: fungi growing in xylem cannot affect development of root pressure, as this is done by the root hair cells moving ions by active transport, not xylem. They certainly cannot affect stomata, and uptake of water by root hair cells also has nothing to do with xylem.
If fungus = affecting xylem, then, we should look for functions of xylems, as THOSE will be affected.

Fungi growing in xylem can affect water passing through it, just like putting our hand in a lake affects the hydrogen bonds the water molecules had before our hand interfered. I think the fungal cell wall or membrane may have hydrophobic or hydrophilic properties that affect the water

 

[My Name]

Guyss,, I have got some AS Biology notes!!! If you want them inbox me!

Any notes for P1?
Why don't you post them here?

 

[The Godfather]

guys big doubt .................
summer 2006 paper 1 and question 30
asap

 

[phanttasy]

guys big doubt .................
summer 2006 paper 1 and question 30
asap

see the picture for the working.

the question ask the total time when both atrio-ventricular(AV valve) and semi-lunar valve(SL valve) closed at same time
so the time is basically the time between closing of (AV valve / SL valve) and the time just before the opening of (SL valve / AV valve)
the time between closing of AV valve and opening of SL valve is 0.03s, and the time between the closing of SL valve and opening of AV valve is 0.04s

hope you can understand my explanation ><

 

[liiiiting]

Can anyone help me with this question?
Which events occur in the nitrogen cycle?
1.Inorganic nitrogen in the atmosphere undergoes denitrification by specific prokaryotes
2.Nitrate concentrations in the soil are increased by nitrifying bacteria in waterlogged soil
3. Organic nitrogen in the legumes passes through soil where deamination and ammonification occurs
4. Saprotrophic fungi living in the soil decompose organic nitrogen in the faeces.

Why is the answer 3. and 4. and why is 2 wrong?
I really appreciate if anyone could help me!

 

[My Name]

Can anyone help me with this question?
Which events occur in the nitrogen cycle?
1.Inorganic nitrogen in the atmosphere undergoes denitrification by specific prokaryotes
2.Nitrate concentrations in the soil are increased by nitrifying bacteria in waterlogged soil
3. Organic nitrogen in the legumes passes through soil where deamination and ammonification occurs
4. Saprotrophic fungi living in the soil decompose organic nitrogen in the faeces.

Why is the answer 3. and 4. and why is 2 wrong?
I really appreciate if anyone could help me!

Point 2 says:
Nitrate concentrations in the soil are increased by nitrifying bacteria in waterlogged soil.

Nitrifying bacteria carries out nitrification,which is an aerobic process.
Denitrification happens in waterlogged soils.Waterlogged soils are anaerobic.

 

[My Name]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_11.pdf
question
5
17
23
25 point 2 so umm the smooth muscles reduce friction right?

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_w11_qp_12.pdf
question
30
23 I really need help solving these type of questions!
24
20 DNA containing 12 × 10^3 nucleotides so one strand would be used to form the mRNA so now the nucleotides used would be 12 × 10^3/2 nucleotides right? Then...?
17 Diploid cell are cannot divide by mitosis to repair itself.Why? By mitosis repair and replacement take place.
15 so They are all random.What do they mean by random here?

 

[phanttasy]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_11.pdf
question
5
17
23
25 point 2 so umm the smooth muscles reduce friction right?

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_12.pdf
question
30
23 I really need help solving these type of questions!
24
20 DNA containing 12 × 10^3 nucleotides so one strand would be used to form the mRNA so now the nucleotides used would be 12 × 10^3/2 nucleotides right? Then...?
17 Diploid cell are cannot divide by mitosis to repair itself.Why? By mitosis repair and replacement take place.
15 so They are all random.What do they mean by random here?

Not sure about number 5 too.. from my calculation my answer is not accurate but it is quite close to the answer..

See the attachment for questions 17 and 23

for Q25, the overcome the friction, the blood is pumped at a high pressure. Smooth muscle only vasodilate and vasoconstrict.

 

[My Name]

Not sure about number 5 too.. from my calculation my answer is not accurate but it is quite close to the answer..

See the attachment for questions 17 and 23

for Q25, the overcome the friction, the blood is pumped at a high pressure. Smooth muscle only vasodilate and vasoconstrict.

Thank your for your help!

Can you help me with these also:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_12.pdf
question
30
23 I really need help solving these type of questions!
24
20 DNA containing 12 × 10^3 nucleotides so one strand would be used to form the mRNA so now the nucleotides used would be 12 × 10^3/2 nucleotides right? Then...?
15 so They are all random.What do they mean by random here?

Please and Thank you!

 

[ashcull14]

 

[My Name]

View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535 View attachment 57535

answer is B right?

 

[My Name]

How can I attach them sorry for the stupid question, am just new in here!

When you click the reply button there will be a an upload file button on the left side.Then attach the needed file. No not stupid question.
Try it.

 

[My Name]

 

[My Name]

 

[My Name]

 

[qwertypoiu]

View attachment 57539

INSIDE CELL: Low Na+, high K+
OUTSIDE CELL: high Na+, low K+

How could a cell maintain such concentrations? Something like this cannot exist since we would expect diffusion to balance out everything. The answer is ACTIVE TRANSPORT.

Inside the cell, there is a low concentration of Na+, so by diffusion, Na+ moves from outside to inside. (arrow 1)
Since the cell wants to MAINTAIN the low concentration of Na+ inside, it will actively transport Na+ from inside to outside (arrow 3)

The reverse argument applies for K+, so the answer should be A.

 

[qwertypoiu]

View attachment 57538

The water potential of X is LOWER than Y, since it is more concentrated. This makes water move into X at a greater pressure than Y, so that the sucrose solution moves from X to Y. Hope that makes sense.

 

[qwertypoiu]

View attachment 57536

When a cell is placed in a solution that has low water potential, the cell's water content is lost to the surroundings. So the cell shrinks. Should be A.
Perhaps you were confused by D. A cell would actually burst when placed in high water potential solution, since water would move into the cell and make it expand, till it bursts (if it doesn't have a cell wall Eg animal cell)

 

[qwertypoiu]

Thank your for your help!

Can you help me with these also:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_12.pdf
question
30
23 I really need help solving these type of questions!
24
20 DNA containing 12 × 10^3 nucleotides so one strand would be used to form the mRNA so now the nucleotides used would be 12 × 10^3/2 nucleotides right? Then...?
15 so They are all random.What do they mean by random here?

Please and Thank you!

Q30: Plants can transport water up through the xylem by two mechanisms: transpiration pull, and root pressure. So to prove root pressure, we must show that a plant can still pull water up even if transpirational pull doesn't exist. Let's look at the options :
1. This one talks about transpiration, which we want to avoid
2. This statement confuses many people, because the word "sap" is associated with transport of phloem only. However, the water solution transported by xylem can also be called sap, since it does have ions and other molecules dissolved in it. Now, if you cut the shoot of a plant near the bottom, all the leaves requires for transportation pull are gone. But if the water is still leaking out of it, it could only be due to root pressure.
3. Again, this is used to prove transpiration, not root pressure
4. If a plant is placed in very humid conditions, it would not be able to transpire. However, if the plant supplied with water in the soil uses root pressure, it can bring the water up to the leaves. The water droplets formed on the leaves prove that water has moved up.

 

[phanttasy]

Thank your for your help!

Can you help me with these also:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_w11_qp_12.pdf
question
30
23 I really need help solving these type of questions!
24
20 DNA containing 12 × 10^3 nucleotides so one strand would be used to form the mRNA so now the nucleotides used would be 12 × 10^3/2 nucleotides right? Then...?
15 so They are all random.What do they mean by random here?

Please and Thank you!

20: nitrogenous bases are read as 3. Meaning 3 nitrogenous bases codes for one amino acid. Therefore 12/2 = 6, 6/3= 2. Ans is 2 x 10^3
23: Divide first time you get 100% hybrid DNA (as mentioned in the question). Divide twice you get 50% hybrid and 50% containing only 14N. Divide 3 times, you will get 25% of hybrid and 75% containing only 14N. What about 4th times? there will be about 12.5% of hybrid DNA and about 82.5% DNA containing of 14N. You can try to draw the nuclear division diagram like i attached to you earlier so you can have an image about it.
24: I think the volume does not change is because the contraction is very fast, so the volume of ventricle is somehow remain the same ... (sorry I am not sure with this )
30: 1 is caused by the tension of water, forming a negative pressure in the xylem vessel. 3 is somehow relates to the statement 1.
15: Not sure about this too...

Anybody please help out with question 15!! and question 24 as well

Hope you can understand my explanation and correct me if i have made any mistake.