[Answerkey] CSAT 2013 GS: Science: Physics, Biology Questions solved with explanation, reference, all four sets (A,B,C,D)

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Mrunal's Economy Course
  1. Prologue
  2. Internal breakup
  3. Biology Health related
    1. Tattoo
    2. Muscle contractions
    3. Virus
    4. Genetic Engineering
  4. Biology: Botany/Agro related
    1. Aflatoxin
    2. Fruits, Cold storage
    3. Seedlings
    4. Desert Leaf
  5. Physics
    1. Ball bearings
    2. Optical illusions
    3. Rainbow
    4. Forces of Nature
    5. Higgs Boson


  • In UPSC CSAT 2013, General studies (GS) paper, 13 out of 100 questions were from Science.
2012 2013
9 13
Majority from physics Majority from biology.
  • Current affairs based question: only one =from Higgs boson.
  • Few of them can be directly solved from NCERT Science, General Studies manual.
  • Anyways, UPSC did ask plenty of “direct from the routine books” type questions in Economy, polity and Modern History: so can’t expect picnic everywhere hahaha.

Internal breakup

chart CSAT 2013 GS science

Biology: Health related 4
Biology: botany related 4
Physics 5
Total 13

*bio fertilizer, sea-horse etc Questions classified under EnB.

Biology Health related


1. Which of the following diseases can be transmitted from one person to another through tattooing?

  1. Chikungunya
  2. Hepatitis B

Select the correct answer using the codes given below.

  1. 1 only

  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Hepatitis B and HIV are spread via Tattoing hence Indian Army had made rule that disqualified youngsters with tattoos on medical ground.

Chikungunya is not spread via tattooing.

Hence answer (B) 2 and 3 only.

Muscle contractions

2. Consider the following minerals

  1. Calcium
  2. Iron
  3. Sodium

Which of the minerals given above is/are required by human body for the contraction of muscles?

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Calcium=necessary for muscle contraction (NIOS Science Lesson 25, Page9)

Sodium helps nerve cells send electrical signals to muscles for contraction. (Britannica)

Hence answer (D) 1 and 3 only. Or (A) only 1 (depending on the interpretation of UPSC examiner.)


3. Which of the following statements is / are correct?

  1. Viruses lack enzymes necessary for the generation of energy.
  2. Viruses can be cultured in any synthetic medium.
  3. Viruses are transmitted from one organism to another by biological vectors only.

Select the correct answer using the codes given below.

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Statement#2 is wrong because

As per page 109-110 of Analytic techniques in Biotechnology TMH

…Since Viruses lack organelles and are totally dependent on the host cells metabolic machinery for replication, (hence) they cannot be grown in synthetic media. In laboratory, animal viruses are grown in Animals…plant viruses are grown in plants or plant cell culture.

Statement #3 is wrong because

As per page26 Studies in Viral Ecology: Animal Host Systems by Christon J. Hurst

  • There are two categories of Vectors: biological and mechanical. As was stated earlier, if virus increases its number while in association with a vector, then that vector is termed as being biological.
  • Conversely, the vector is termed to be mechanical, if virus doesn’t increase its number while in association with that vector…
  • Arthropods such as wasps, which repeatedly can sting multiple animals, could serve as mechanical vectors by transporting viruses on the surface of their stingers.

Thus, #2 and #3 are wrong, eliminate choices accordingly

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

and we are left with answer (A) only 1.

Genetic Engineering

4. Recombinant DNA technology (Genetic Engineering) allows genes to be transferred

  1. across different species of plants
  2. from animals to plants
  3. from microorganisms to higher organisms

Select the correct answer using the codes given below.

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

#1 is correct

as per BBC article on Genetic Engineering

Golden rice is developed by transferring carrot genes to rice. the new variety of rice contains Vitamin “A”. Hence Statement #1 correct (across different species of plants)

#2 is correct

as per http://news.ucdavis.edu/search/news_detail.lasso?id=4812

In 1953, scientists discovered the structure of DNA, and in 1972, researchers developed a method for cutting and splicing DNA. That method became known as recombinant DNA, or rDNA. Since then, researchers have learned how to move genetic material in the form of DNA from one plant or animal to another. They can also take DNA from an animal and place it in a plant, and vice versa.

#3 is correct

TMH General studies manual, General science, Page 129, Topic #14.14

…..e.g. transfer of gene/s from bacteria to man or vice versa or from bacteria to a flowering plant.=>Statement #3 correct (from microorganism to higher organism)

Hence answer (D) 1,2 and 3 correct.

Biology: Botany/Agro related


1. Improper handling and storage of cereal grains and oilseeds result in the production of toxins known as aflatoxins which are not generally destroyed by normal cooking process. Aflatoxins are produced by

  1. bacteria
  2. protozoa
  3. moulds
  4. viruses

Aflatoxin is a mould produced by fungus that are toxic and carcinogenic. (IndianExpress)


Fruits, Cold storage

2.Fruits stored in a cold chamber exhibit longer storage life because

  1. exposure to sunlight is prevented
  2. concentration dioxide in the is increased of carbon environment
  3. rate of respiration is decreased
  4. there is an increase in humidity

Fruits and vegetables continue their metabolic activity after harvest…Metabolic Activity is manifested by respiration….Reduction of temperature is an effective means of reducing the rate of respiration. (Fundamentals of food process engineering, Page 402)

Hence Answer (C)


3. Many transplanted seedlings do not grow because

  1. the new soil does not contain favorable minerals
  2. most of the root hairs grip the new soil too hard
  3. most of the root hairs are lost during transplantation
  4. leaves get damaged during transplantation

Root hairs are extremely delicate, whether on a tree or a seedling. When transplanting young trees from a nursery to a woodland, damage to the roots and root hairs often leads to death of a tree. (Advanced Biology, Michael Kent, Page 279)

Hence Answer (C) (or debatable)

Desert Leaf

4. Which of the following leaf modifications occurs/occur in desert areas to inhibit water loss?

  1. Hard and waxy leaves
  2. Tiny leaves or no leaves
  3. Thorns instead of leaves

Select the correct answer using the codes given below.

  1. 1 and 2 only
  2. 2 only
  3. 1 and 3 only
  4. 1, 2 and 3
  • Page 530 of Physical Geography by Savindra Singh – “The vegetation of hot desert climate is xerophytic type which has special characteristics to withstand very high rate of evaporation. They have long roots, thick barks, waxy leaves, thorns and little leaves.”
  • Also in Ch. 5 of NCERT 9th Std. Geo book (Page 46)

Hence Ans (D) all of above.


Ball bearings

1. Ball bearings are used in bicycles, cars, etc., because

  1. The actual area of contact between the wheel and axle is increased
  2. The effective area of contact between the wheel and axle is increased
  3. The effective area of contact between the wheel and axle is reduced
  4. None of the statements is correct
  • Friction is independent of surface area of contact. (Pearson Objective Physics For AIEEE page 77)
  • Rolling friction is smaller than the sliding friction, (therefore) sliding is replaced in most machines by rolling by the use of ball bearings. (NCERT Science, Class 8, Chapter 12, Page 153)
  • Therefore, answer (D) none of the statements is correct (or may be the debatable.)

Optical illusions

2. Consider the following phenomena:

  1. Size of the sun at dusk
  2. Colour of the sun at dawn
  3. Moon being visible at dawn
  4. Twinkle of stars in the sky
  5. Polestar being visible in the sky

Which of the above are optical illusions?

  1. 1, 2 and 3
  2. 3, 4 and 5
  3. 1, 2 and 4
  4. 2, 3 and 5

TMH General Studies Manual, General Science > Physics, Page 25. Following things happen due to Atmospheric refraction

  1. When the sun or moon is near horizon, it appears elliptical i.e. with vertical diameter less than the horizontal diameter =>Statement #1 is correct.
  2. Twinkling of stars =>statement #4 is correct.

Hence answer must contain both #1 and #4. Eliminate the choices accordingly

  1. 1, 2 and 3
  2. 3, 4 and 5
  3. 1, 2 and 4
  4. 2, 3 and 5

Thus we are left with answer C.


3. Rainbow is produced when sunlight falls on drops of rain.

Which of the following physical phenomena are responsible for this?

  1. Dispersion
  2. Refraction
  3. Internal reflection

Select the correct answer using the codes given below.

  1. 1 and 2 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

NCERT Science Class 10, Chapter 11, Page 194

A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop Due to the dispersion of light and internal reflection, different colours reach the observer’s eye
Hence all 3 correct=>Answer (D)

Forces of Nature

4. The known forces of nature can be divided into four classes, viz, gravity, electromagnetism, weak nuclear force and strong nuclear force. with reference to them, which one of the following statements is not correct?

  1. Gravity is the strongest of the four
  2. Electromagnetism act only on particles with an electric charge
  3. Weak nuclear force causes radioactivity
  4. Strong nuclear force holds protons and nutrons inside the nuclear of an atom.

Refer to the table given on NCERT Physics Class11, Chapter1, Page 10

Name Relative strength
Gravitational force 10-39
Weak nuclear force 10-13
Electromagnetic force 10-2
Strong nuclear force 1
  • As you can see, Gravity is the weakest of them all. Hence statement #A is definitely incorrect
  • And the question wants us to identify the wrong statement, hence Answer = (A)

Higgs Boson

5. The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is /are the importance/importance of discovering this particle?

  1. It will enable us to understand as to why elementary particles have mass.
  2. It will enables us in the near future to develop the technology to transferring matter from one point to another without traversing the physical space between them.
  3. It will enable us to create better fuels for nuclear fission.

Select the correct answer using the codes given below:

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

The Higgs Boson gives idea on how each particle has mass. It doesn’t give better fuels for nuclear fission or for inter-space travel. (or atleast I did not find it on the internet.)

Ans: (A) (or perhaps C or D hahaha)

Only one topic remains: EnB answerkeys. They’ll be uploaded soon + thanks Mr. Shiva Ram and Mr. Siriyal Patel for inputs.

Indian History Freedom Struggle Pratik Nayak

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152 Comments on “[Answerkey] CSAT 2013 GS: Science: Physics, Biology Questions solved with explanation, reference, all four sets (A,B,C,D)”

  1. sir,
    Please come up with the detailed strategy for mains 2013 soon sir.

  2. Thank you very much.

  3. sir I am a aspirant from a remote village. sir my financial condition is not so good to take any kind of coaching. I am exclusively relying on your website regarding CSE Preparation. SO sir plz provide detail guidance regarding new mains exam pattern and also for compulsory english language paper.

    1. hi. friend, we have manidhaneyam ias center in chennai .they provide free coaching and stay for poor and also for talented. try it…

    2. Hi Nipon,

      Download the notification and go through it multiple times. Analyze the syllabus and sources from which you can read. Use internet to find out sources you do not know readily. My e-mail id is rahulb635@gmail.com . Please mail me in case you need any help in preparing. Not that I am any expert but I can provide my 2 cents of help :)


    3. Hi,

      Please feel free to contact me if you need any help : soldierofthesoil@yahoo.com

      I have double copy of Pub Ad and Psychology notes/few important text books. If you need them, I would be happy to send it.

      Please let me know.


      1. Hi Rahul & Praveen

        I would like to appreciate for your help and u guys deserve for it .

      2. hi Praveen. I would need help on psychology- the books to follow, the strategy etc. N if u can send notes related to it, that would b great! My id is rahul2188@gmail.com

        1. Just saw your comment, will make an arrangement and get in touch with you through mail

    4. me too bro…!!! gud luck!

    5. nipon bhai

      if you can’t find notes for any particular section please feel free to contact me at manojktka@gmail.com

      i have some pub admin and history books (i changed my optional to geography)

      if u want i can send it u

    6. @Rahul, Manu and Praveen!!

      Respect for all three of you for a genuine help to a needy. A true trait of a future civil servant!!!!

  4. Sir,

    I have something to say

    1. “Creating new money”- one can take it as printing new money – so it will be most inflationary.

    2. Can we say that ” council of ministry is not responsible collectively to Parliament ” no we cant say.
    CoM is responsible to parliamnet in general and Lok sabha in perticular.

    3. When we say, supply of money remain same that means no new money is coming in the market and what ever money is there out of banks is only circulating..when banks are not supplying money there is no sense and no case of increasing the interest rate.
    Then question says that the demand of money is increased….from first part of question we infer that this increased demand can not be met by more money as it is constant, this will lead to increase in the value of money and if value of money is increased the prices of commodity will fall.

    4. Contour bunding is used against the flow of water due to rain….not against the flooding…mere contour bunding can,t stop the erosion due to flooding.

    5. When coal burning can realease NO2 in environment, then why cant the ash of coal add nitrogen to soil.


    One more

    Disguised unemployment: it occurs when more people are working for a job then required.

    ie if 5 people are working in a farm and only 3 are sufficient…..then it is disguised unemployment. Here we can say that the extra two person are working because they don,t have any other option to work, ie no alternative employment.

    What do you say sir.

    1. On Point 5 – Nitrogen is available in gaseous form. To add nitrogen to soil, it needs to be “Fixed”. Burning coal can produce flyash which is either devoid of nitrogen or contain negligible quantities of nitrogen which still needs to be fixed. So it is not possible without action of leguminous bacteria. Now do you mean to say nitrogen can be fixed from flyash? Then why aren’t we using flyash as a fertiliser? UPSC again doesn’t complicate things. In the other two options, bacteria is allowed to work on urea/dead matter to fix nitrogen whereas burning coal per se doesn’t add nitrogen. So it is 1 and 3 only.

      On Point 2 – When you say collectively responsible to Parliament then it means a no-confidence motion can be moved in both houses. But it is not possible. The council of ministers is collectively responsible only to Lok Sabha.

      On Point 4 – I feel you are right. Contour Bunding is used in plains as well and so you cannot rule out that possibility.

      On Point 3 – I totally agree with you though not many will do. If someone who opposes us can give a good explanation, I’ll be happy to learn.

      On Point 1 – All answers keys concur. So no use in debating when everyone agrees.

    2. Point 1 and 3 i thought in ur way…. but all keys refer creatin new money..there r many ways we can create new money…not alone printing… and 3 option..even i marked option A…but still many keys r sayin 2.. which is a monetary control measure… tats no way related to question….lets wait for UPSC answer key…other 3 Vignesh has given good explanation…. wil think tat we will cear and lets all prepare for mains :) tc

  5. sir dont you think your site is too pre centric ?…

  6. desert leaf ques4
    point c states thorns replaces leaves…. but in books its given leaves diminished nd not replaced…..

  7. hello sir,
    I m having science back ground. due to this I do not have basic knowledge and concept related with the subjects like civics, geography, history. it would be immensely helpful for me if you provide some good authors books on these subjects.

  8. Why deflated tyres are hard to roll if friction is independent of surface area.
    it is because it increases the surface area. so we need to decrease effective area even for rolling.

    1. correct, rolling friction is independent of surface area , where as static and kinetic friction is dependent on surface area …..

  9. Ball bearing are used to reduce the effective area so as to reduce the wear and tear…The answer must be C

  10. only static friction is independent of area not the kinetic one……

  11. hello mrunal this is rakesh can u please provide direction for optional economics as you are giving for other optionals please this is request. And i am trying to download for MA BA notes from ignou it has so many links that i don’t know how to download so many can u give direction for that. thank you god bless you

  12. @vignesh
    maine bhi yehi lagaya hai.. thanks.. every answer key say b but i m confident its c. thanks .

  13. Abe Yaaron !Kya chal raha hai ? 225 above hai to Mains ki prepo karo ,Discussion mein kya rakha hai . its not the half yearly Exam which will gonna help u in yearly exam ! Enjoy !

  14. Please can someone tell the answer of the ‘mycorrhizal biotechnology to rehabilatate degraded sites’ wala question..??

  15. Answer is D – all statements r correct

  16. Mrunal,could you tell me how to approach english literature.All the resources and all the strategy and any resources or links,please.

  17. what could be the cut-off marks. 223(Gen)is safe or not.

  18. please post some topics regarding mains exam..end of holidays after pre

  19. @Mrunal

    Sir its been 12 days since prelims are over.Please post your valuable insights and the strategy in detail for the mains so that we can pull ourselves out of the holidays mood and start serious prep for the mains.


    1. also waiting eagirly..

  20. Regarding the ball bearing question, I referred the site below which says “When the load increases the asperities become flattened by elastic deformation. This increases the effective contact area, and therefore friction.”This implies that the answer is (C).


    1. Bro, isnt it one and the same thing….. :P :P

    2. total internal reflection is associated with double rainbows

  21. friction is independent of surface is wrong bcoz friction is classifed lyk static, kinetic, rolling… static and kinetic friction are independent of surface area… but in this question the friction is rolling friction which is dependent on the surface area …. ALSO consider below statement
    “Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area between the balls and races”

    PLEASE DONT GIVE WRONG ANSWERS AND CONFUSE ASPIRANTS …first get the difference between friction and rolling friction.

    1. Its ok…rather than criticism look at the other ans…if u still dnt lyk ignore my comment….

    2. mrunal should consider blocking people like you.MORON,

  22. hepatit B is not transmittedfrom one person to another.

    1. eliminate the wrong options and you would get the same answer.there is no other way

  23. Friction is indeed independent of the area of contact. In case of ball bearings, the contact with the surface is over a point and thus ideally, no friction develops. Answer to this is C.

    Friction develops when two surfaces come in contact. I hope you get it.

  24. dear all..(specially engineers n mrunal)
    plz tell us if this concept of ball bearing n related frictions are applicable to
    “..CARS & ETC. ” too , in addition to bicycles (as given in the question)…!

    1. @prabhat
      yes cars also have ball bearing but with slight modification ,however they do the same job as in bicycles.
      The question aside , there is nothing as ‘rolling friction’. friction is of two types :either static or kinetic depending on whether the surfaces in contact are static or moving relative to each other.and they depend on the nature of surfaces and the load not on the contact surface area( at least not at the level of upsc). In fact in pure rolling the friction in play is static which is actually assisting in rolling . similarly if rolling with sliding takes place we have kinetic friction. If there was no friction rolling would not take place . for example : on wet roads the tyres skid as there is less friction . skidding is nothing but rolling with sliding.
      So why is the deflated tyre hard to roll than inflated? Nothing to do with increase or decrease in friction . The contact area in deflated tyres has increased so there is an opposing torque due to normal force (due to load) that has started to act. For example try to topple a cuboid instead of sliding it . It is difficult as there is a normal force acting at one of the edge (about which you r trying to topple) is greater than the normal force acting on the toppling edge . hence there is a kind of opposing toppling action that neutralizes your effort. Now try to topple a static top with a pointed end . you dont even need to topple it as it falls due to its own weight itself. the reason is as there is a point contact it is unable to counter the toppling efforts.
      So if you have a point contact it is easier to roll (which is like continuous toppling).
      The key idea is that friction Helps in rolling but opposes sliding! Increase in contact surface area makes it difficult to roll and does not do anything in case of sliding (if of course the load is constant) and the reason is Not friction.
      Just an interesting aside: why do we oil ball bearing if friction helps in rolling? The answer is that even though the ball need friction to roll between the two surface but they are also sliding along each other by being in contact. so oiling decrease friction between the balls but hardly affects the friction between the two surface of the axle and the one connected to wheel as the load is high enough to sufficiently increase the static friction required for rolling.
      If you have any doubts regarding this you can post it in the forum.
      All the best.


  26. 2. Consider the following minerals

    Which of the minerals given above is/are required by human body for the contraction of muscles?

    1 only
    2 and 3 only
    1 and 3 only
    1, 2 and 3

    Answer- Only “Calcium” is required for muscle contraction, thus it is option “1 only”.

  27. recombinant dna technology allows genes to be transferred from plants to animals and not from animals to plants.

    1. absolutely correct ……….. infact transfer of DNA from animal to plant is possible not by Recombinant DNA or rDNA but it is through cDNA technology

  28. ball bearning ans is must B

  29. moon visible at dawn is larger than its usual size..its an optical illusion..so, isnt “moon being visible at dawn” also an optical illusion?

    1. no buddy. visibilty cant be called as optical illusion.optical illusion is the phenomenon where due to refraction or reflction or through other ways of light interference the object appears to look different to our eyes.but it is actually same.i am just expaining it to you.its not the correct definition

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