A level Biology: Post your doubts here!

[kareem22010]

Ribosomes consist of two subunits, each containing rRNA. An analysis of all the 70S ribosomes
from a single cell of the bacterium, Escherichia coli, showed that there were:
• 38 000 rRNA molecules
• 2 main types of rRNA molecule
• 19 000 copies of each type of rRNA molecule
How many 70S ribosomes were there in the E. coli cell?
A 9500 B 19 000 C 38 000 D 76 000

How do you do this calculation? btw, Answer is B

basically, to prevent confusion, you can just use the first fact as ur only guide as each ribosome contains two rRNA molecules and there is 38000 rRNA so, you can divide by 2 to get 19000 ribosomes. however, if you want to go deeper to use the other two facts, it says that there are 19000 copies of each type of rRNA and there are two types of rRNA so ,multiply that by 2 to get total number of rRNA then divide by 2 because one ribosome contains two rRNA molecules.

 

[drowning-in-studies]

When there's thyamine in the nucleic acid, there's no uracil and if there's uracil, there will be no thyamine.
So from the table it is quite clear that when there's Base C there's no uracil. And when there's Uracil there's no base C. This shows that the Base C is thyamine. You know that thyamine is complementary to Adenine. So from the table look for the Base whose's percentage values are closely equal to that of Base C. And that Base whose values match with those of C is Base B. So the answer is B.

Thank you

 

[drowning-in-studies]

basically, to prevent confusion, you can just use the first fact as ur only guide as each ribosome contains two rRNA molecules and there is 38000 rRNA so, you can divide by 2 to get 19000 ribosomes. however, if you want to go deeper to use the other two facts, it says that there are 19000 copies of each type of rRNA and there are two types of rRNA so ,multiply that by 2 to get total number of rRNA then divide by 2 because one ribosome contains two rRNA molecules.

Thank you

 

[drowning-in-studies]

In question 26, Shouldn't water potential increase since amino acids are taken out, therefore making the solution less negative???
The answer is D.

 

[kareem22010]

In question 26, Shouldn't water potential increase since amino acids are taken out, therefore making the solution less negative???
The answer is D.

actually water potential should decrease because it says water potential in phloem tube not in sink and as you can see,amino acid is removed from sink into the assimilates of phloem tube and anything other than water is added to a substance lowers the water potential.

 

[drowning-in-studies]

actually water potential should decrease because it says water potential in phloem tube not in sink and as you can see,amino acid is removed from sink into the assimilates of phloem tube and anything other than water is added to a substance lowers the water potential.

Oka-ay

 

[mohmed ahmed soliman]

Re: Stuck in Biology?? Post your doubts here!!

WELL SOME BODY CLEAR ME....THAT IN LOOP OF HENLE WATER IS GIVEN OUT TO PERITUBULAR CAPILLARIES OR TISSUE OF MEDULLA?

it is not clear in textbook but i dont think we should know all of this details as i didnt see any marking point for this information anyway we hould know that water is lost from decending limp to tissue fluid in meddula because of high concentration of na and cl ions along with urea

 

[mohmed ahmed soliman]

can anyone help me to get better understanding of countercurrent multiplier

 

[Awesome12]

can anyone help me to get better understanding of countercurrent multiplier

Do you not understand how the counter current multiplier works in the kidneys, or do you just not understand it in general?

 

[mohmed ahmed soliman]

Do you not understand how the counter current multiplier works in the kidneys, or do you just not understand it in general?

well both

 

[mohmed ahmed soliman]

explain how an understanding of limiting factors is used to increase crop yields in protected environments, such as glasshouses
i want notes for this syllabus point

 

[mohmed ahmed soliman]

Do you not understand how the counter current multiplier works in the kidneys, or do you just not understand it in general?

explain how an understanding of limiting factors is used to increase crop yields in protected environments, such as glasshouses
i want notes for this syllabus point

 

[drowning-in-studies]

When cylinders of potato tissue were immersed in a 0.35 mol dm–3 sucrose solution, they showed
no change in mass.
What will happen when cylinders are immersed in a 0.1 mol dm–3 sucrose solution?
A The pressure potential of the cells will become more positive.
B The solute potential of the cell will become more negative.
C The water potential of the cells will become more negative.
D The water potential of the solution will become less negative

 

[drowning-in-studies]

How do you do this? Why isn't it B? The answer is C.

 

[My Name]

How do you do this? Why isn't it B? The answer is C.

The tRNA will be like this > CUUUUAUGGGGA
SO mRNA will be like this > GAAAAAUACCCCU
SO DNA will be like this > CTTTTATGGGGA
This matches only one answer from the options.That is C.

 

[drowning-in-studies]

The tRNA will be like this > CUUUUAUGGGGA
SO mRNA will be like this > GAAAAAUACCCCU
SO DNA will be like this > CTTTTATGGGGA
This matches only one answer from the options.That is C.

Thanks

 

[kareem22010]

explain how an understanding of limiting factors is used to increase crop yields in protected environments, such as glasshouses
i want notes for this syllabus point

Farmers can use their knowledge of factors limiting the rate of photosynthesis to increase crop yields. This is particularly true in greenhouses, where the conditions are more easily controlled than in the open air outside:

• The use of artificial light allows photosynthesis to continue beyond daylight hours. Bright lights also provide a higher-than-normal light intensity.
• The use of artificial heating allows photosynthesis to continue at an increased rate.
• The use of additional CO2 released into the atmosphere inside the greenhouse also allows photosynthesis to continue at an increased rate

 

[kareem22010]

can anybody help me with this question?

I don't understand what the makscheme is saying, can anybody explain how to get to the answer of this question?

any clear explanation would be very helpful

 

[leenz98]

can anybody help me with this question?
View attachment 59594 View attachment 59595 View attachment 59596
I don't understand what the makscheme is saying, can anybody explain how to get to the answer of this question?

any clear explanation would be very helpful

What mark scheme says is that the doubling of the chromosome number is inevitable since the homologus chromosomes have to pair so if the the chromosome number has not doubled during the interphase it would have been possible to get a sterile hybrid just by the combination of two which itself is impossible under normal circumstances. I hope I didn't complicate this further for you.

 

[kareem22010]

What mark scheme says is that the doubling of the chromosome number is inevitable since the homologus chromosomes have to pair so if the the chromosome number has not doubled during the interphase it would have been possible to get a sterile hybrid just by the combination of two which itself is impossible under normal circumstances. I hope I didn't commplicate this further for you.

but i don't get it, why if the chromosome number didn't double during interphase , the hybrid would be sterile?