IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE O - Level => Sciences => Topic started by: iluvme on October 02, 2010, 04:07:50 pm
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There;s this Question,
Which chromosomes are present in an ovum?
A. X only
B. Y only
C. XX
D. XY
Why is C wrong? :-\
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Is the answer A ?
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Yup. Why?
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Yup. Why?
I dont do Biology and whatever you read from now on is due to the knowledge I got from the Discovery Channel ;)
I know that the eggs of a woman have only an X chromosome. Its the male sperm that provides the other chromosome whether it be X or Y.
So in short, a stand alone egg has only an X chromosome and a stand alone male Sperm has either an X or a Y.
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I dont do Biology and whatever you read from now on is due to the knowledge I got from the Discovery Channel ;)
I know that the eggs of a woman have only an X chromosome. Its the male sperm that provides the other chromosome whether it be X or Y.
So in short, a stand alone egg has only an X chromosome and a stand alone male Sperm has either an X or a Y.
Good job Ari..........you know many things for someone who do not do biology.
Indeed the egg is a gamete and it carries only one sex chromosome. In all it will have the number of chromosomes that is only 23.
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Thanks Ari and Deadly King.
I must be mad to do Human Bio. This sucks.
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Thanks Ari and Deadly King.
I must be mad to do Human Bio. This sucks.
Nan......you are wrong. It's not that difficult. Just demands a bit of concentration and understanding.
Don't worry.....you'll get it with time ;)
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Thanks Deadly King.
Whats the difference between gametes and chromosome?
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Thanks Deadly King.
Whats the difference between gametes and chromosome?
I don't think you need to know that for O-level. It's in AS syllabus.
This question does not really arise. Anyway let me get this clear for you.
A gamete is a cell consisting half the number of chromosomes than a normal cell.
Chromosomes are thread-like structures which contain the genes and is found in the nucleus of a cell. A normal human cell consist of 46 chromosomes, while a gamete has only 23 chromosomes.
Don't get too much engrossed in that.......you'll learn it if you take biology for AS in the following years ;)
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I AM doing Bio for AS. Which'll be next May InshaAllah.
Well, what confused me was when drawing crosses, we do this right,
Gametes- X X and X Y
Which means women have XX but when asked about the chromosome in an ovum there's only an X. :-\
I still don't get it.
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I AM doing Bio for AS. Which'll be next May InshaAllah.
Well, what confused me was when drawing crosses, we do this right,
Gametes- X X and X Y
Which means women have XX but when asked about the chromosome in an ovum there's only an X. :-\
I still don't get it.
Ameen :)
Gametes : 1.X 2.X 3.X 4.Y
This means from a woman's normal cell, 2 gametes each having one X chromosome can be formed while a man can provide two gametes, one having an X chromosome while the other contains a Y chromosome.
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Thank you Deadly King. :)
+ rep.
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Thank you Deadly King. :)
+ rep.
hey that's alright. I just hope you understood :)
Seems you returned me my +rep :P
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Lol, yeah maybe. ;D
Though apparently I gotta spread it after 2 hours. :P
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Please explain, the four types of immunity
Active artificial immunity,
Active natural immunity,
Passive artificial immunity,
Passive natural immunity.
Or is there more? These were the four mentioned in the past papers.
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Please explain, the four types of immunity
Active artificial immunity,
Active natural immunity,
Passive artificial immunity,
Passive natural immunity.
Or is there more? These were the four mentioned in the past papers.
Nope these are the only types. I mean there are only 4 types pf immunity.
First you need to differentiate between natural and artificial.
Natural immunity occurs when the body itself produces antibody molecules for immune response.
Artificial immunity take place when we take in drugs and medicines which will lead to a drastic rise in the number of antibody molecules in the body.
Now differences between active and passive.
Active immunity occurs when you have been exposed to a particular disease and your body is preparing itself for defence. In other words it is taking all the appropriate measures to combat this new virus or bacteris.However takes more time as it produces memory cells for future use. Hence if the same virus affects us later on, our immune response will be faster due to the memory cells.
Passive immunity takes place when the body cannot actually do anything against this particular disease which is usually quite dangerous. Hence you take in drugs but this form of immunity is only temporary since the antibodies will be cleared by our immune system as it is foreign.
Sorry for the brief explanation. I'll elaborate more if you want when i get home :P
I hope i've not exceeded what's in YOUR syllabus ;)
If you want a better explanation follow this link :
http://www.biologymad.com/ -----> AS Biology ----> Immunology -----> Immunity
NOTE : Again this is for AS. Do not learn more than your syllabus ;)
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Thank You Deadly King. :)
And yes I'd like a better explanation on Passive immunity.
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Thank You Deadly King. :)
And yes I'd like a better explanation on Passive immunity.
Alright madam :)
But be attentive because this is not going to be as simple as you think it is!
Passive immunity takes place when a person is infected by a very dangerous disease. Hence medical practitioners prefer not to take any risk and inject some anti-toxins into the person's body. The anti-toxins provide immediate protection but this is only temporary because the antibodies have not been produced by own cells. Therefore they are regarded as foreign and will be removed in a matter of time by the mechanism of the person's body. But since the antibodies have come from the exterior it is regarded as artificial passive immunity.
When antibodies pass from mother to baby across the placenta or via breast milk, it is called natural passive immunity.
Hope you get what am trying to say :)
P.S : I modified my previous post. Do take a look. Might be helpful as well ;)
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Righto Thanks.
I'll be back with more doubts after Friday. ;)
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Righto Thanks.
I'll be back with more doubts after Friday. ;)
No problem.............just let me know........and i'll try my best to clear your doubts ;)
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Ahem,
I've got a whole load of doubts from this paper, so, PLEASE HELP ME OUT!!!
November 2006 Paper1
Questions, 3, 10, 14, 16, 24 and 40.
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Ahem,
I've got a whole load of doubts from this paper, so, PLEASE HELP ME OUT!!!
November 2006 Paper1
Questions, 3, 10, 14, 16, 24 and 40.
Sorry but I need to go now.........i've got exams tomorrow. :-[
Will Insha Allah help you in the afternoon after i've done my papers :)
By the way...........is it O-level papers ???
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Sorry but I need to go now.........i've got exams tomorrow. :-[
Will Insha Allah help you in the afternoon after i've done my papers :)
By the way...........is it O-level papers ???
Oh. Its allright. All the best for your examz.
Yupz, its OL.
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Question 10
Amylase is an enzyme that breaks down starch. You should know that enzymes function the BEST at 35 deg C and if the temp is above or below that level they will denature.
The answer, therefore, is C.
Question 14
Blood is pumped under pressure through the arteries.
Therefore, it wouldnt flow as a constant stream. Since it flows under high pressure (it is synchronized with the heart beat) the blood WILL NOT clot.
Answer = C
Question 40
Lead is the primary substance that causes memory loss and hence could affect intelligence. It also damages the CNS is some way.
Lead is given off in the exhaust fumes of vehicles as it USED to be added to petrol to prevent 'knocking' in car engines.
Block B is closest to a busy flyover and car park.
Answer = B
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Question 14
Blood is pumped under pressure through the arteries.
Therefore, it wouldnt flow as a constant stream. Since it flows under high pressure (it is synchronized with the heart beat) the blood WILL NOT clot.
Answer =C
Why wouldn't the clotting process take place? :-\ Since it flows under high pressure?
Thanks Ari.
Um, other questions please.
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Since the blood is quite literally pouring out of the wound like a waterfall the blood doesnt get time to coagulate into a solid which would stop the bleeding.
I dont know the other questions - remember I never took Biology. This is all my general knowledge in use.
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Oh. Its allright. All the best for your examz.
Yupz, its OL.
Hmm.........it seems Ari has already done the job.
Anyway...........I don't have the papers. Can you give me its link ???
I can take a look if you need some explanations ;)
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Since the blood is quite literally pouring out of the wound like a waterfall the blood doesnt get time to coagulate into a solid which would stop the bleeding.
I dont know the other questions - remember I never took Biology. This is all my general knowledge in use.
Oh right. Thank You. :)
Anyway...........I don't have the papers. Can you give me its link ???
Here,
http://www.xtremepapers.net/CIE/Cambridge%20O%20Levels/5096%20-%20Human%20And%20Social%20Biology/5096_w06_qp_1.pdf
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3. We'll proceed by elimination since I don't think you need to know all these by heart ;)
Anopheles ----> It's a type of mosquito, like all mosquitoes, anophelines go through four stages in their life cycle: egg, larva, pupa, and imago. However it does not involve two hosts.
Mycobacterium tuberculosis ----> It's a bacteria and bacteria proliferates asexually only.
Tinea is a fungus and it reproduces by spores only which is an asexual method.
Schistosoma mansoni ----> never heard about it :P But this is the only plausible answer here.
Upon some research I found out that it has the ability to reproduce both sexually and asexually and it also involves two hosts.
The life cycle is common to all species with a sexual generation in vascular system of the definitive host and an asexual generation in the intermediate hosts (snails).
Answer is C
16. At rest ---> first graph
You must number of cycles in 30s which is 6 cycles. 1 cycle represents 1dm3 of air.
Therefore in one minute, Volume of air = (6/30 x 60) = 12dm3
Apply same principle for the other graph except that in this case 1 cycle represents 2dm3
10 cycles in 30s. ----> In one minute = 2(10/30 x 60) = 40 dm3
Answer is D
24.
Part 1 is the placenta and the latter's functions is to provide the fetus with all its requirements namely nutrients, oxygen and also antibodies from the mother. However it connot prevent nicotine or alcohol from diffusing to the fetus.
Part 2 is the amniotic fluid which indeed spreads pressure evenly all around the fetus protecting it from external damage.
Part 3 is the amniotic wall which prevents the fetus from getting into direct with the internal body structures and the blood of the mother.
Part 4 is the umbilical cord which connects the fetus to the placenta across which nutrients, gases and waste products travels.
Hence answer is B
Hope it helps and am sorry for late reply :-[
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Thank You. :) Really helped. +rep
Anyways,
C02 reacts with lime water when blown through it to form a chalky suspension. Suggest how you could use this information to show that you produce more CO2 when you exercise than when you are at rest.
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Thank You. :) Really helped. +rep
Anyways,
C02 reacts with lime water when blown through it to form a chalky suspension. Suggest how you could use this information to show that you produce more CO2 when you exercise than when you are at rest.
You're welcome ;)
Hmm........the concentration of the chalk suspension will reveal its amount.
Firstly, when you are at rest, expired air is blown into a boiling tube containing lime water for about 10s.
Now take another similar test-tube containing same amount of lime water. After having exercised, expired air is blown into the test-tube for the same lapse of time.
NOTE : Keeping all the above mentioned variables constant is very important so that the results of your experiment are affected only by concentration of carbon dioxide from expired air.
You will note that the suspension is thicker in the second test-tube. This will indicate that more carbon dioxide is present in expired air when you exercise than when at rest. ;)
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Oh okay thanks.
I was thinking about the number of breaths and stuff. :)
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Oh okay thanks.
I was thinking about the number of breaths and stuff. :)
Anytime :)
Yeah ......... you can take the number of breaths instead of 10 seconds. It would turn out to be the same ;)
The key part is to keep it constant for both experiment. So if you took 10 breaths for the first one, you should take 10 breaths for the second one as well :D
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Righto, thanks.
Distinguish between the terms meiosis and mitosis.
For this Q, should we write about the number of daughter cells obtained, the chromosomes and stuff?
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http://www.differencebetween.net/science/difference-between-mitosis-and-meiosis/
http://www.answerbag.com/q_view/278075
I hope i helped :)
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Thanks Muallima ;)
This Question too, Two insects mosquito and housefly spread diseases through their saliva. Explain how this is achieved. This is a two mark Q.
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Actually i don't know but I'll give u smthn that will help :S
http://www.mosquitoworld.net/mosquitodiseases.php
http://www.pitara.com/discover/5wh/online.asp?story=45
:S :S
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The parasites enter their salivary glands. Here they multiply, the saliva contains anti-coagulant which stops the blood from clotting. When the insects bite they inject their saliva into the human's body and human gets infected.
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The parasites enter their salivary glands. Here they multiply, the saliva contains anti-coagulant which stops the blood from clotting. When the insects bite they inject their saliva into the human's body and human gets infected.
That's correct ;)
I confirm master_key's answer :D
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Thanks muallima, master key and deadly king :)
How about the house fly?
Explain why one contact with an infected mosquito can lead to malaria but repeated larval contacts are needed to produce symptoms of schistosomiasis.
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Thanks muallima, master key and deadly king :)
How about the house fly?
Explain why one contact with an infected mosquito can lead to malaria but repeated larval contacts are needed to produce symptoms of schistosomiasis.
Am not 100% confident about this..............but my answer is quite reasonable :-[
Both the house fly and the mosquito operate by sucking blood from a person. In doing so, their saliva get into direct contact with the person's blood ,hence infecting him.
Larva however have not yet developed structures with which they'll be sucking blood. Hence it will take some time for them to grow into adults. Only then will they be harmful to us.
Hope it helps ;)
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My book dsn't explain clearly too. :(
By the way, those were 2 dffrnt questions.
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My book dsn't explain clearly too. :(
By the way, those were 2 dffrnt questions.
I'll try to get more info and will let you know :)
Yeah..........I know they are two different questions ;)
But house flies and mosquitoes operate the same way :D
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OKiez thank You. :)
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Since when do common house flys suck blood from a person ? They dont have the hypodermic needle like thing that mosquitoes have....
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Thanks muallima, master key and deadly king :)
How about the house fly?
Explain why one contact with an infected mosquito can lead to malaria but repeated larval contacts are needed to produce symptoms of schistosomiasis.
I think i got it now.
Schistosomiasis is caused by larval forms of the parasite which penetrates the body. However our body and defensive system is highly beneficial against these parasites. Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely ;)
Therefore malaria is more dangerous to humans than schistosomiasis since the latter is transmitted more easily and the body's defence mechanism cannot prevent it from entering the body. Our immune system will only respond to it when the parasite is already in the body.
For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria :D
Ref : http://www.who.int/topics/schistosomiasis/en/
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Since when do common house flys suck blood from a person ? They dont have the hypodermic needle like thing that mosquitoes have....
Oops..........i have been mistaken......My bad :-\
You have a point there :)
Indeed houseflies do not suck blood. Sorry for the confusion :-[
House flies can become a vector of certain diseases since they are always attracted to sites of bacteria such as feaces or vomit.
Hence the bacteria may get attached to its hairs or other parts of the body. When the fly lands up on a person, the bacteria has a chance to penetrate the latter's body through the nose, ears, mouth and other parts.
One likely disease transmitted in this way is cholera.
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I think i got it now.
Schistosomiasis is caused by larval forms of the parasite which penetrates the body. However our body and defensive system is highly beneficial against these parasites. Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely ;)
Therefore malaria is more dangerous to humans than schistosomiasis since the latter is transmitted more easily and the body's defence mechanism cannot prevent it from entering the body. Our immune system will only respond to it when the parasite is already in the body.
For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria :D
Ref : http://www.who.int/topics/schistosomiasis/en/
I'm confused.
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I'm confused.
Would you mind telling me what's confusing you ???
I'll try my best to clear your doubt ;)
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This schistosomiasis thing, is spread by the larval forms of a parasite. From what I've read in Google, it is spread through water like cholera.
Our skin for example is almost impenetrable except if we have been cut or some kind of injuries. Only then will the larva be successful to attack us. which is not very likely ;)
Where does the skin come into this? Did you mean like when the skin is cut and when water enters?
I think i got it now.
For schistosomiasis, however, they have very little chance of even entering the body. So we are more protected from schistosomiasis than from malaria :D
It is spread by water isn't it? So why is there a very little chance of the larval forms entering the body?
It is very similar to cholera isn't it?
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This schistosomiasis thing, is spread by the larval forms of a parasite. From what I've read in Google, it is spread through water like cholera.
Where does the skin come into this? Did you mean like when the skin is cut and when water enters?
It is spread by water isn't it? So why is there a very little chance of the larval forms entering the body?
It is very similar to cholera isn't it?
This disease is most commonly found in Asia, Africa, and South America, especially in areas where the water contains numerous freshwater snails, which may carry the parasite.
So it is the snails or larvae which carry the disease. Water is just a medium which is favourable to the carriers.
I took the skin as an example since the latter is involved in the defence mechanism of the human body.
Penetration of the human skin occurs after the cercaria have attached to and explored the skin. The parasite secretes enzymes that break down the skin's protein to enable penetration of the cercarial head through the skin. As the cercaria penetrates the skin it transforms into a migrating schistosomulum stage.
So it's not really spread by water.
Ref : http://en.wikipedia.org/wiki/File:Schistosomiasis_Life_Cycle.png
If you have any other questions, feel free to ask. I'll not leave you unless you have understood ;)