Biology; Chemistry; Physics: Post your doubts here!

[shaysharyf]

K... let me see what i can do, then ill tell u!!

Thank you so much, you've been a great help.

 

[Zuhsid]

Thank you so much, you've been a great help.

Command words: A glossary
Account... Give reasons for.
Analyse... Break down the topic into parts and give an in-depth account. Comment.
Annotate... Add labels.
Assess... This is an evaluative question - weigh up the importance of the subject. This means there are a number of possible explanations. You need to give the main ones and then say which you tend to go for.
Briefly... Be concise and straightforward. Don’t spend much too much time on this part (but don’t list - sentences still required).
Classify... Use classification in your answer (ie divide into groups or categories).
Compare… What is wanted is a point by point identification of similarities and of differences (‘compare’ includes looking at contrasts, while a command to ‘contrast’ means only looking for differences). Use comparative adjectives eg. larger than, smaller, more steep, less densely.
Comment... Summarise the various points and give an opinion.
Contrast... on its own, means only looking for differences.
Decide … or make a decision … Here you are usually asked to compare different possible solutions to a problem. This means assessing the strengths and weaknesses of the alternatives. In the end, you have to decide which solution is best. Sometimes you may be asked to suggest how alternative solutions can be combined. It is important to make a clear decision. Your decision may not be a perfect solution – but it should be the best from amongst the alternatives.
Define ... Or explain the meaning of ... These words ask for a relatively short answer (check the marks given) – usually two or three sentences – where the precise meaning of the term is identified (usually doesn’t need an example/case study).
Describe ... This is one of the most widely used command words. Unless the question says ‘describe and explain’, don’t be tempted to explain (just avoid writing ‘because’ in your answer).
‘Describe the characteristics of ...’ means what does the feature look like, eg in the case of a landform - shape, dimensions, composition, location in relation to other features; for a population pyramid shape, dimensions, composition of cohorts, relation to other examples of pyramids.
‘Describe the changes in ...’ is often used with a graph or series of graphs (eg DTM). Accurate verbs are required, and using words like rapidly, steeply, gently, gradually. (One word to avoid is ‘steadily’ as any graph shape can be ‘steady’.)
‘Describe the trends in...’ means more of an overall picture is required – not a ‘blow by blow’ account of what the graph shows. Major exceptions to the trend should be included.
‘Describe the differences between ...’ means only differences are required – no credit is given for similarities or for descriptions of one of the items. Might best be done with individual sentences each identifying a difference.
‘Describe the relationship between ...’ means only the links between the two items are required You must identify and establish the link clearly.
‘Describe the distribution of ...’ mostly used with a map or set of maps. Describe the location of high concentrations of a variable together with significant low concentrations or isolated ‘islands’ within the distribution. Remember the idea is to describe the overall pattern.
‘Describe the effects of ...’ means a factual account of what has occurred, after or as a result of whatever the question has identified.
Describe and comment on … This demands a higher level of response than just ‘describe…’. Usually the description is straightforward, with judgements about the description getting most of the marks.
Discuss … Usually you are expected to build up an argument about an issue and to present more than one side of the evidence with supporting examples. This creates a written debate identifying both positive and negative points and then you must reach a conclusion from the debate. You should both describe and explain. Try to create a balanced answer.
‘Discuss the extent to which …’ requires a judgement about the validity of the evidence or outcome.
‘Discuss varying attitudes to …’ there is a variety of viewpoints (eg decision makers and others affected) and priorities to be included in the answer.
Evaluate … or assess … This is similar to the idea of ‘discuss’.
Assess requires a statement of the overall quality or value of the feature/issue being considered. Evaluate asks the candidate to give an overall statement of value.
In both cases you need to state a viewpoint, after consideration of the evidence. In both cases your own judgement/opinion is wanted. Although an opinion cannot be marked incorrect, credit is given for the justification of the position you’ve taken up. It usually best not to adopt an extreme viewpoint (a balanced answer is best).
Examine... Look closely.
Explain … Give reasons or causes. Description is not enough (and may not be needed at all). Show an understanding of why or how something has occurred.
Give an explanatory (or reasoned) account of … or describe and explain... This is a combination of a ‘describe’ question, and a ‘suggest reasons for’ question. The logical way to answer is to describe first and then provide an explanation for the feature, but sometimes it is possible to provide the reasons first and then describe the consequent feature.
How... Describe. What methods are involved?
Identify... State or name... Point out and name. These words ask for a short answer to a simple task such as: a) ‘Identify the landform from the photograph ...’ b) ‘Identify the value of ... from the graph’ c) ‘Name an example of ...’ Don’t just answer with a single word - it is always better to put the answer in a brief sentence.
Interpret... Bring out the meaning of...
In what ways... Describe. Identify a pattern.
Justify… Usually applies to decision-making questions. When you have made your decision you must justify why that course of action was better than the alternatives. Explain why your chosen course is better than the options that you rejected. Also explain how your choice meets the criteria set out for you in the question (or which you had to describe earlier in your answer).
Locate... State where it is.
Outline... Note the main features.
Quote map evidence... Give examples, including grid references, from map provided. Use compass points. Use scale.
Rank... Put in order of size.
Select... Choose.
Study figure 1... If you’re asked to look at a diagram, then you must use that to help you answer the question which follows.
Suggest... Put forward an idea or reason.
To what extent... Agree and disagree (for and against). There are a number of possible explanations - give these. Then say which you tend to favour.
With reference to specific examples/cases... You must refer to a specific place, preferably a case study you know in some detail. Don’t just say something vague like ‘for example Brazil’; much better to say ‘the Tucuruí dam scheme in Amazonia, Brazil, where...’ .

 

[shaysharyf]

Command words: A glossary
Account... Give reasons for.
Analyse... Break down the topic into parts and give an in-depth account. Comment.
Annotate... Add labels.
Assess... This is an evaluative question - weigh up the importance of the subject. This means there are a number of possible explanations. You need to give the main ones and then say which you tend to go for.
Briefly... Be concise and straightforward. Don’t spend much too much time on this part (but don’t list - sentences still required).
Thaaaaankks.
Classify... Use classification in your answer (ie divide into groups or categories).
Compare… What is wanted is a point by point identification of similarities and of differences (‘compare’ includes looking at contrasts, while a command to ‘contrast’ means only looking for differences). Use comparative adjectives eg. larger than, smaller, more steep, less densely.
Comment... Summarise the various points and give an opinion.
Contrast... on its own, means only looking for differences.
Decide … or make a decision … Here you are usually asked to compare different possible solutions to a problem. This means assessing the strengths and weaknesses of the alternatives. In the end, you have to decide which solution is best. Sometimes you may be asked to suggest how alternative solutions can be combined. It is important to make a clear decision. Your decision may not be a perfect solution – but it should be the best from amongst the alternatives.
Define ... Or explain the meaning of ... These words ask for a relatively short answer (check the marks given) – usually two or three sentences – where the precise meaning of the term is identified (usually doesn’t need an example/case study).
Describe ... This is one of the most widely used command words. Unless the question says ‘describe and explain’, don’t be tempted to explain (just avoid writing ‘because’ in your answer).
‘Describe the characteristics of ...’ means what does the feature look like, eg in the case of a landform - shape, dimensions, composition, location in relation to other features; for a population pyramid shape, dimensions, composition of cohorts, relation to other examples of pyramids.
‘Describe the changes in ...’ is often used with a graph or series of graphs (eg DTM). Accurate verbs are required, and using words like rapidly, steeply, gently, gradually. (One word to avoid is ‘steadily’ as any graph shape can be ‘steady’.)
‘Describe the trends in...’ means more of an overall picture is required – not a ‘blow by blow’ account of what the graph shows. Major exceptions to the trend should be included.
‘Describe the differences between ...’ means only differences are required – no credit is given for similarities or for descriptions of one of the items. Might best be done with individual sentences each identifying a difference.
‘Describe the relationship between ...’ means only the links between the two items are required You must identify and establish the link clearly.
‘Describe the distribution of ...’ mostly used with a map or set of maps. Describe the location of high concentrations of a variable together with significant low concentrations or isolated ‘islands’ within the distribution. Remember the idea is to describe the overall pattern.
‘Describe the effects of ...’ means a factual account of what has occurred, after or as a result of whatever the question has identified.
Describe and comment on … This demands a higher level of response than just ‘describe…’. Usually the description is straightforward, with judgements about the description getting most of the marks.
Discuss … Usually you are expected to build up an argument about an issue and to present more than one side of the evidence with supporting examples. This creates a written debate identifying both positive and negative points and then you must reach a conclusion from the debate. You should both describe and explain. Try to create a balanced answer.
‘Discuss the extent to which …’ requires a judgement about the validity of the evidence or outcome.
‘Discuss varying attitudes to …’ there is a variety of viewpoints (eg decision makers and others affected) and priorities to be included in the answer.
Evaluate … or assess … This is similar to the idea of ‘discuss’.
Assess requires a statement of the overall quality or value of the feature/issue being considered. Evaluate asks the candidate to give an overall statement of value.
In both cases you need to state a viewpoint, after consideration of the evidence. In both cases your own judgement/opinion is wanted. Although an opinion cannot be marked incorrect, credit is given for the justification of the position you’ve taken up. It usually best not to adopt an extreme viewpoint (a balanced answer is best).
Examine... Look closely.
Explain … Give reasons or causes. Description is not enough (and may not be needed at all). Show an understanding of why or how something has occurred.
Give an explanatory (or reasoned) account of … or describe and explain... This is a combination of a ‘describe’ question, and a ‘suggest reasons for’ question. The logical way to answer is to describe first and then provide an explanation for the feature, but sometimes it is possible to provide the reasons first and then describe the consequent feature.
How... Describe. What methods are involved?
Identify... State or name... Point out and name. These words ask for a short answer to a simple task such as: a) ‘Identify the landform from the photograph ...’ b) ‘Identify the value of ... from the graph’ c) ‘Name an example of ...’ Don’t just answer with a single word - it is always better to put the answer in a brief sentence.
Interpret... Bring out the meaning of...
In what ways... Describe. Identify a pattern.
Justify… Usually applies to decision-making questions. When you have made your decision you must justify why that course of action was better than the alternatives. Explain why your chosen course is better than the options that you rejected. Also explain how your choice meets the criteria set out for you in the question (or which you had to describe earlier in your answer).
Locate... State where it is.
Outline... Note the main features.
Quote map evidence... Give examples, including grid references, from map provided. Use compass points. Use scale.
Rank... Put in order of size.
Select... Choose.
Study figure 1... If you’re asked to look at a diagram, then you must use that to help you answer the question which follows.
Suggest... Put forward an idea or reason.
To what extent... Agree and disagree (for and against). There are a number of possible explanations - give these. Then say which you tend to favour.
With reference to specific examples/cases... You must refer to a specific place, preferably a case study you know in some detail. Don’t just say something vague like ‘for example Brazil’; much better to say ‘the Tucuruí dam scheme in Amazonia, Brazil, where...’ .

 

[raynalist]

Excretion is the removal of waste products of metabolism and toxic material from living organism.These waste products are formed and absorbed within the cells.
Egestion is the removal of undigested remains(faeces)from the alimentary canal via the anus.These substances are notformed within the cells nor have been absorbed by the cells.

 

[raynalist]

thank you

 

[shaysharyf]

Excretion is the removal of waste products of metabolism and toxic material from living organism.These waste products are formed and absorbed within the cells.
Egestion is the removal of undigested remains(faeces)from the alimentary canal via the anus.These substances are notformed within the cells nor have been absorbed by the cells.

Thank youu.

 

[irfan.kheerdali]

explain why a plant growing in soil deficient in magnesium stores far less energy than one growing in soil rich in magnesium??

 

[Nabeel.Ahmad]

So, I'm new here, and I have this question to ask.
Explain the difference between excretion and egestion. (3 marks).
What's worrying me is the marks. Will I get the full marks just by writing the definitions of both?

Thanks in advance.

You have to write the definitions of both:

Excretion is the removal of Metabolic waste products and toxic materials from the body with the help of special excretory organs.
Egestion is the removal of Un-digested, Un-absorbed material from the digestive track.

They are completely different things. Metabolic reactions take place in cells and in the body. Some of the Products of ''Metabolic Reactions''.. and considered ''waste'' ... and ''harmful''.. and ''toxic''.. if they accumulate in the body. Such metabolic waste products are removed from the body using Excretion.
Examples of Excretory products:

- Carbon Dioxide (Metabolic Waste Product produced in Respiration)
- Urea (Produced by the Deamination of Amino Acids and Proteins in Liver)
- Uric Acid (Produced by the decomposition of Nucleic Acids)
- Creatinine (Produced by the breakdown of muscles)
- Excess Mineral Salts and Water. (Excess mineral salts and water need to be removed in order to maintain a constant water potential in the blood)

So all these Excretory Products are produced within the body by Metabolic Reactions and they are removed using Excretion.

Now Egestion is a completely different process. It has no link to the Chemical Reactions taking place in the body and cells. The Digestive Track/Alimentary Canal is the track through which food passes as it is digested and stuff is absorbed from it. As it reaches the Large Intestine the digestion and absorption are almost complete. By the End of the Large Intestine Water and Mineral Salts are also absorbed. This leaves behind Un-Digested and Un-Absorbed matter that needs to be expelled from the body. This is Egestion. No Chemical Reactions, No Metabolic Products.

In Order to get 3/3 you need to mention the definition and the difference between the products.

 

[Zuhsid]

explain why a plant growing in soil deficient in magnesium stores far less energy than one growing in soil rich in magnesium??

Well magnesium ions are used by the plant to make the chlorophyll pigment, and in turn, chloroplasts (which is used to stores sunlight during photosynthesis)..... so if there is less magnesium, that means less chlorophyll to catch light..... so it actually becomes a limiting factor for photosynthesis and thus less energy(carbohydrates) are formed/stored.....

P.S...this is not the actual answer you should write, this was just to make you understand!!!
Hope it helps!!

 

[Deadly Orchid]

Hey folks. I am in grade 10 and have selected biology. I wanted to know the successful method to study it, not just Cie preparation but general school exams. Do I just read the chapter and solve pastpapers? Please help me out

P.s: i am using cambridge igcse biology coursebook by jones and jones

 

[Zuhsid]

Hey folks. I am in grade 10 and have selected biology. I wanted to know the successful method to study it, not just Cie preparation but general school exams. Do I just read the chapter and solve pastpapers? Please help me out

P.s: i am using cambridge igcse biology coursebook by jones and jones

Well learn the definitions by heart... n the thing with past papers is that, there is no negative side to it... he more you do, the more you prosper!!! Especially MCQs.....
Try to be explicit in your answers!!!
The best way is to interlink the chapters, makes em easy to learn!!!

 

[Deadly Orchid]

Well learn the definitions by heart... n the thing with past papers is that, there is no negative side to it... he more you do, the more you prosper!!! Especially MCQs.....
Try to be explicit in your answers!!!
The best way is to interlink the chapters, makes em easy to learn!!!

Ok. So do i need any notes?

 

[Zuhsid]

Ok. So do i need any notes?

i got an A* without any notes or tuition..... so i hope that answers your question!!!

 

[princess Anu]

PHYSICS QUESTION
can someone please tell me that is the object at C accelerating or de accelerating?
and whats the way to determine this?
ALso, whats the difference between de acceleration and negative acceleration?
JazakAllah.

 

[Zuhsid]

PHYSICS QUESTION
can someone please tell me that is the object at C accelerating or de accelerating?
and whats the way to determine this?
ALso, whats the difference between de acceleration and negative acceleration?
JazakAllah.

Well i think that.....as the on the y-axis, its velocity, therefor, the plus and minus denote the direction..... so C is accelerating...
Let me interpret the whole graph, at A, the object was moving at constant speed in a specified direction, then at B, the car started to slow down(decelerate)(but the car was moving in the same direction, just slowly with time).... then as it reached a speed of zero, it turned around and starred accelerating in the opposite direction(C).....

Deceleration is simply when the car's speed is decreasing.....
"Negative acceleration" is when the cars speed IS increasing(accelerating) but the acceleration is decreasing with time(its speed is increasing but at a lesser pace than before!!))so the speed is not decreasing like before)....
To make it more clear:
http://www.cyberphysics.co.uk/graphics/graphs/terminal_velocity.gif
In the pic, from 0-10, the car is accelerating..... from 10-20, although the car's speed is increasing, but at a lesser rate than before(negative acceleration)..... n as u can see where "decelerates is written", the cars speed is simply decreasing!!!

Hope it helps!!!

 

[princess Anu]

"Negative acceleration" is when the cars speed IS increasing(accelerating) but the acceleration is decreasing with time(its speed is increasing but at a lesser pace than before!!))so the speed is not decreasing like before)....
I thought it meant acceleration in a negative direction :/?

and yeah it helped, JazakAllah.

 

[AAAYY***]

ppl plzz help me with mcq 37 ,38 and 39 i could not understand it .

 

[Kamihus]

ppl plzz help me with mcq 37 ,38 and 39 i could not understand it .

37. Just remember every carbon atom will result in 1 mole of products and every 2 hydrogen atoms 1 mole of products. So C is correct as in propane (C3H8) carbon will produce 3 moles and hydrogen will produce 4 moles so total 7 moles of products.
38. Check all the options. In option C, 3 carbon atoms have a total of 36 mass, and if we add 8 of hydrogen and 16 of oxygen we have a molecular mass of 60. So 36/60 is 60%.
39. The oxidation of an alcohol involves the loss of hydrogen and the gain of oxygen with the number carbon atoms remaining unchanged. Thus the acid containing four carbon atoms, B, was the answer to the question.

From the next time remember to post a link to the question paper rather than uploading it.

 

[princess Anu]

37. Just remember every carbon atom will result in 1 mole of products and every 2 hydrogen atoms 1 mole of products. So C is correct as in propane (C3H8) carbon will produce 3 moles and hydrogen will produce 4 moles so total 7 moles of products.
38. Check all the options. In option C, 3 carbon atoms have a total of 36 mass, and if we add 8 of hydrogen and 16 of oxygen we have a molecular mass of 60. So 36/60 is 60%.
39. The oxidation of an alcohol involves the loss of hydrogen and the gain of oxygen with the number carbon atoms remaining unchanged. Thus the acid containing four carbon atoms, B, was the answer to the question.

From the next time remember to post a link to the question paper rather than uploading it.

^
how do u know that 3 carbon atoms= 36 mass? `nd there are only 7 of hydrogen :S please make me understand it ?

 

[Kamihus]

^
how do u know that 3 carbon atoms= 36 mass? `nd there are only 7 of hydrogen :S please make me understand it ?

1 carbon atom has atomic mass of 12 so 3 will make 36. There are 7 first and one in the end too.