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A level Biology: Post your doubts here!

Soldier313

Soldier313

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Am reposting my question....someone please answer urgently.....tx
Soldier313 said:
can someone please provide a detailed explanation which we can write for: Describe the pathway taken by water as it passes from the root hair cells into the cells which are specialized for transport of water and mineral ions(xylem vessels) and then from the xylem vessels out of the plant (by transpiration). Btw these are two qns combined. The marking scheme gives very short points...so please elaborate....tx a lot! and please answer asap as my xam is just in a few hours....tx agan.....God bless.
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Soldier313

Soldier313

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eyamwir said:
can anyone explain to me in a simplified version the action of B and T lymphocyte thank you. please do hurry
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This qn was answered previously by geek101:

Primary response
1) the pathogen invades the body
2) it damages or weakens body cells
3) the weakened body cells produce proteins called histamines
4) the phagocytes in the blood are attracted to these proteins...(chemotaxis)
5) the phagocytes (macrophages) engulf the pathogen by phagocytosis and display the non self antigens on its surface
6) the T helper cells with the complementary receptors goes and recognizes the antigens of the pathogen, and secretes chemicals which cause the bone marrow to form T Killer cells, and secretes cytokines (hormone-like)
7) B lymphocytes with the complementary surface receptors are activated due to these cytokines and divide by mitosis to produce B-memory cells and Plasma cells.
8) The B memory cells further divide to produce more memory cells and plasma cells.
9) the plasma cells release anitbodies with the variable region (antigen binding site) complementary to the antigens of the pathogen. These antibodies destroy the pathogens.
10) The T killer cells (cytotoxic T cells) with the specific complementary receptors release chemicals such as hydrogen peroxide or punch holes in the infected body cells to remove and kill any remaining weakened body cells, and the remaining debris.
11) The memory B and memory T cells remain circulating in the blood.
Secondary response:
The memory cells which are in the blood on the encounter of the pathogen with the antigens complementary to their receptors, divide rapidly producing plasma cells which secrete antibodies (more than the primary response) and the pathogens are destroyed in a short time.

Correct me if im wrong :)​
 
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eyamwir

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Soldier313 said:
This qn was answered previously by geek101:


Primary response ​
1) the pathogen invades the body​
2) it damages or weakens body cells​
3) the weakened body cells produce proteins called histamines​
4) the phagocytes in the blood are attracted to these proteins...(chemotaxis)​
5) the phagocytes (macrophages) engulf the pathogen by phagocytosis and display the non self antigens on its surface​
6) the T helper cells with the complementary receptors goes and recognizes the antigens of the pathogen, and secretes chemicals which cause the bone marrow to form T Killer cells, and secretes cytokines (hormone-like)​
7) B lymphocytes with the complementary surface receptors are activated due to these cytokines and divide by mitosis to produce B-memory cells and Plasma cells.​
8) The B memory cells further divide to produce more memory cells and plasma cells.​
9) the plasma cells release anitbodies with the variable region (antigen binding site) complementary to the antigens of the pathogen. These antibodies destroy the pathogens.​
10) The T killer cells (cytotoxic T cells) with the specific complementary receptors release chemicals such as hydrogen peroxide or punch holes in the infected body cells to remove and kill any remaining weakened body cells, and the remaining debris.​
11) The memory B and memory T cells remain circulating in the blood.​
Secondary response:​
The memory cells which are in the blood on the encounter of the pathogen with the antigens complementary to their receptors, divide rapidly producing plasma cells which secrete antibodies (more than the primary response) and the pathogens are destroyed in a short time. ​
​
Correct me if im wrong :)​
Click to expand...

i thought this was for the action of primary and secondary response..are they the same? :eek:
 
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eyamwir

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:eek: best of luck to everybody! i hope you all pass and thank you for teaching me a whole lot of stuff. (i'm talking as if i'm dying) hahaha :s exam panic
 
Soldier313

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eyamwir said:
:eek: best of luck to everybody! i hope you all pass and thank you for teaching me a whole lot of stuff. (i'm talking as if i'm dying) hahaha :s exam panic
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hey chill, every1s panicking.....dnt take it hard on urself...just do ur best and leave the rest to God!:) G'luck!
 
angelgirl288

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hi! so how was the exam?? i hope everyone did well. i personally have no clue what i wrote in that paper but i just hope i got something right o_O'
so... i have a question..paper 1.. 01/M/J/06 - question 22. i don't get it. can sm1 plz explain the question :s
thanx :)
 
Gémeaux

Gémeaux

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autumnsakura said:
Can I ask about question 6, 15, 18, 22,24, 37?
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s11_qp_11.pdf

Hope this thread is still active!
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6) A. The greatest mass of *non-reducing* sugar would be in the juice that gives less ppt when tested before hydrolysis, and a considerably greater amount of ppt after hydrolysis. Hydrolysis would break down non-reducing ones into reducing sugars.

15)C. Studying structure of membranes show that they have specific sites for enzyme attachment.
A is wrong because *cell* mb. also allows transport of substances into and out of the cell.
B because stability is provided by cholesterol molecules.
D is obvious. Lysosomes are within the cells and themselves are mb. bound.

18)C. Cytokinesis is a process that occurs during telophase. It is the cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells. Cell organelles replicate before this and nuclear envelope reforms after this.

22)A. Bonds are broken once when DNA unzips, and the next time when the mRNA has been formed and is separated from the DNA strand.
Bonds form the first time when free nucleotides join the strand to form mRNA, and the second time when mRNA is formed and DNA strands zip-up to coil. Sugar phosphate bone forms only once for mRNA. Pairing of *free nucleotides* occurs once too.

24)C. Hormones are detected by the chains of glycoproteins present on the cell surface mb, larger the area more of those receptors would be present.
 
autumnsakura

autumnsakura

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Gémeaux said:
6) A. The greatest mass of *non-reducing* sugar would be in the juice that gives less ppt when tested before hydrolysis, and a considerably greater amount of ppt after hydrolysis. Hydrolysis would break down non-reducing ones into reducing sugars.

15)C. Studying structure of membranes show that they have specific sites for enzyme attachment.
A is wrong because *cell* mb. also allows transport of substances into and out of the cell.
B because stability is provided by cholesterol molecules.
D is obvious. Lysosomes are within the cells and themselves are mb. bound.

18)C. Cytokinesis is a process that occurs during telophase. It is the cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells. Cell organelles replicate before this and nuclear envelope reforms after this.

22)A. Bonds are broken once when DNA unzips, and the next time when the mRNA has been formed and is separated from the DNA strand.
Bonds form the first time when free nucleotides join the strand to form mRNA, and the second time when mRNA is formed and DNA strands zip-up to coil. Sugar phosphate bone forms only once for mRNA. Pairing of *free nucleotides* occurs once too.

24)C. Hormones are detected by the chains of glycoproteins present on the cell surface mb, larger the area more of those receptors would be present.
Click to expand...

Thanks!!! :D
 
A

athaan

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Which process occurs during prophase of the mitotic cell cycle in an animal cell?
A. division of centromeres
B. formation of chromosomes
C. replication of DNA
D. separation of centriole

I don't get why B is wrong too, despite knowing the fact that D is right too. Isn't the condensation of the chromosome is the same as the formation of chromosomes?
 
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