A level Biology: Post your doubts here!

[techgeek]

How do we do such types of questions?

We are given that one division is 0.1 mm, which equal to 40 divisions as you can see in the diagram ( starts from 10 and ends at 50)
0.1 mm is 100 μm
so 40 divisions = 100 μm
1 div = 100/40
and radius = 50 div = 100/40 x 50
= 125 μm
Area of the circle (the field of view) = pi r^2
= pi x 125 x 125
so the answer must be C

 

[usef shahin]

Can someone explain why it's option A and not option B?View attachment 61601

they showed in the graph that the concentration of glucose outside the cell will keep increasing and the if it does then glucose will keep entering the cell , and because of that the concentration of glucose will never be equal (as it is increasing outside the cell) , hence if I think of it from an enzyme substrate perspective it will make sense that the answer is A (i hope u understood cuz i suk at explaining)

 

[krishnapatelzz]

Can someone explain why it's option A and not option B?View attachment 61601

because if concentration were equal there wouldnt be any flow of glucose. cause the membrane has work to keep concentration equal inside and out of the cell. if any doubts further , i can explain

 

[alevel_student]

"Explain the roles of cell of Macrophages, B-lymphocytes and T-lymphocytes in an immune system?" Anyine who knws the ans

 

[usef shahin]

"Explain the roles of cell of Macrophages, B-lymphocytes and T-lymphocytes in an immune system?" Anyine who knws the ans

macrophages detect and carries out phagocytosis on the pathogen , it then displays its remains on an APC molecule as an antigen, when the T Helper cells binds to it , T helper cell gets activated and releases cytokinin which furthermore brings about the activation of B cells causing them to divide by clonal selection producing memory cells and plasma cells , the plasma cells synthesises antibodies that are specific to the pathogen and the memory cells stay in the blood for long-term immunity and play a major role in the secondary response.

just wanna warn u that there are different types of T cells , that includes T suppressor cells , T helper cells and memory T cells , each play a different role during an immune response , if u are in doubt about any of the 3 types , feel free to ask <3

cheers

 

[teachyourself]

https://www.youtube.com/channel/UCPE16d0nN5JNt9LQrYsMKDQ/playlists
https://www.youtube.com/channel/UC2yOqKblASJzqMZfRL0DbYA
https://www.youtube.com/channel/UC3U4hZ65iX6VM3JKbg5EoFQ

https://www.khanacademy.org/science/health-and-medicine

 

[drowning-in-studies]

?
How do we do e(i)? How work out the sequence of the DNA template? Which is the 3 end?

 

[student2]

whts pure bred maize? ny1?

 

[krishnapatelzz]

whts pure bred maize? ny1?

Difference Between Hybrid and Purebred. Hybrid: Cross between two species.Hybrid Organisms are the offspring of two heterozygous parents. Purebred: Genes come from one gene of species. Purebred organisms are the offspring of two homozygous parents.

 

[darks]

explain please...

 

[techgeek]

View attachment 61751
explain please...

You need to identify the stage the cell is under and then arrange the stages.
1. Centromeres divide before chromatids move apart, i.e. before Anaphase
2. that's Anaphase so 2 shall come after 1
3. Chromosomes line up along equator during Metaphase
so the sequence must be 3 then 1 then 2
4. Chromosomes coil up during Early Prophase and throughout the process of mitosis, they remain coiled, so it's during telophase or after that, which means 4 should be the last one
5. Sister chromatids join during late prophase since prophase is the first stage so 5 must be first
we have reached the sequence 5 -->3-->1-->2-->4
It's D

 

[darks]

explain...? ans.
C.. how is the cross sectional area increasing?

 

[techgeek]

View attachment 61752
explain...? ans.
C.. how is the cross sectional area increasing?

Nearer the heart, the vessels are wider and farthest they are, the narrowest
As we move from aorta to capillaries, (the oxygenated pathway), the diameter of vessels decrease, the aorta is the largest and capillaries are the tiny vessels with very narrow lumen (for blood to diffuse more quickly in all parts of the body) after capillaries, the blood starts it's way back towards heart, through tiny venules and then back through veins. This diagram might help you remember

 

[darks]

Nearer the heart, the vessels are wider and farthest they are, the narrowest
As we move from aorta to capillaries, (the oxygenated pathway), the diameter of vessels decrease, the aorta is the largest and capillaries are the tiny vessels with very narrow lumen (for blood to diffuse more quickly in all parts of the body) after capillaries, the blood starts it's way back towards heart, through tiny venules and then back through veins. This diagram might help you remember
View attachment 61753

Thanks a lot!!! Got it!

 

[Djlucifer]

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


Any other definition?!

Well I am giving my exams on this May/June session and now I have near about 53 days in my hand how do i exactly utilize this time for biology

 

[techgeek]

Well I am giving my exams on this May/June session and now I have near about 53 days in my hand how do i exactly utilize this time for biology

Revise the book or if you took notes during your classes, review them, get a copy of syllabus, make sure you covered everything.
Then embark on the journey to past papers. The more you do the better, read mark schemes and Examiner Reports. Example Candidate Responses help too. And I just found out, Revision Guides are quite a lot of help as well when you want to revise every little bit but not waste time on things in reading little details, that you already are familiar with.
After every paper you solve, highlight for yourself the topics you need more work on. Expand them in more detail. Make sure you read from multiple sources (like more than one book) as it solidifies the concepts more when you view one particular topic from different angles and point of views.

 

[Djlucifer]

Thanks a bunch and as for practical (PAPER 3) how do I ace it as in get the most of the marks for biology

 

[student2]

electrophoresis helps to separate dna fragments. bt vn sm1 xplain hw do v find out gene sequence of a fragment?

 

[student2]

n y do growers need to by gm seeds every year?

 

[Djlucifer]

Can someone help me with serial sample and series dilution. Please provide me the step by step procedure for doing this