KCSE 2015 General Science Paper 2 with Marking Scheme

SECTION A: BIOLOGY (34 marks)
Answer all the questions in this section in the spaces provided.

1.      
   1. What is meant by the following terms: (1 mark)
      1. habitat;
      2. population?
   2. Explain one effect for each of the following air pollutants to the environment:
      1. sulphur (IV) oxide; (2 marks)
      2. smoke. (2 marks)
2.    
   1. Explain the significance of the position of testis in humans. (2 marks)
   2. State two reasons why reproduction is important. (2 marks)
3.    
   1. Figure 1 illustrates a longitudinal section of a bean seed.
      
      Name the parts labelled A and B.
      A ......... (1 mark)
      B ........... (1 mark)
   2.    
      1. Distinguish between the terms epicotyl and hypocotyl. (1 mark)
      2. Name a plant hormone that promotes apical dominance. (1 mark)
4.    
   1. State the meaning of the following terms:
      1. genetics; (1 mark)
      2. genes. (1 mark)
   2. What is meant by:
      1. complete dominance; (1 mark)
      2. phenotype? (1 mark)
5.    
   1. Explain why Lamarck's evolution theory was discredited. (2 marks)
   2. What is meant by complete metamorphosis in insects? (1 mark)
6. State two similarities between the endocrine and the nervous system. (2 marks)
7.    
   1. How are the vascular bundles arranged in young:
      1. monocotyledonous stem; (1 mark)
      2. dicotyledonous stem? (1 mark)
   2. Figure 2 illustrates the human arm.
      
      Describe how the muscles work to move the forearm from point C to D. (1 mark)
8.    
   1. Name the causative agent of syphilis. (1 mark)
   2. Which hormone brings about ovulation in humans? (1 mark)
9.      
   1. State two ways in which genetic counselling is used in the community. (2 marks)
   2. State how the following eye defects can be corrected:
      1. short sightedness; (1 mark)
      2. astigmatism. (1 mark)
10. State two differences between simple reflex action and conditioned reflex action. (2 marks)

SECTION B: CHEMISTRY (33 marks)
Answer all the questions in this section in the spaces provided.

11.    
    1. State the two conditions under which Graham's Law of diffusion operates. (1 mark)
    2. Figure 3 shows a set-up in which the porous pot contained air.
       
       
       1. State the observation made in the U-tube if air was replaced with carbon (IV) oxide. (1 mark)
       2. Explain the observation made in (b) (i) above. (1 mark)
12.    
    1. What is meant by the term molarity of a solution? (1 mark)
    2. 100 cm³ of 0.1 M sodium hydroxide solution was mixed with 100 cm hydroxide solution.
       1. calculate the number of moles contained in the mixture; (2 marks)
       2. Determine the molarity of the mixture. (2 marks)
13.    
    1. Complete the following table:
       

       Polymer	Use
       Cellulose	............
       .........	Plastic water pipes

       (2 marks)
    2. State two pollution effects of detergents to the environment. (2 marks)
14. Explain the following statements:
    1. sulphur (IV) oxide is a bleaching agent in wet conditions; (2 marks)
    2. newspapers turn yellow-brown after exposure to sunlight over a period of time. (1 mark)
15. Figure 4 is a representation of Down's cell used in the extraction of sodium metal. Study it and answer the questions that follow.
    
    
    1. Name the materials that are introduced at X. (1 mark)
    2. Write an equation for the reaction that occurs at the anode. (1 mark)
    3. What material is the cathode made of? (1 mark)
    4. Give two industrial uses of sodium metal. (1 mark)
16.      
    1. What is meant by “enthalpy of combustion”? (1 mark)
    2. The table below shows heating values of some fuels. Use it to answer the questions that follow.
       

       Fuel	State at room temperature	Heating value in kJg-1
       Ethanol	Liquid	30
       Kerosene	Liquid	48
       Charcoal	Solid	33
       Propane	Gas	50

       1. Identify the best fuel for use in jet engines. (1 mark)
       2. Give two reasons for the answer in b(i) above. (1 mark)
       3. Which fuel has the greatest pollution effect? Explain. (2 marks)
17. Explain how each of the following affects rate of chemical reaction.
    1. Increase in surface area; (2 marks)
    2. Decrease in concentration. (2 marks)
18.      
    1. When chlorine gas is passed through a solution of potassium iodide, the following reaction takes place.
       CI_2(ag) + 2KI_(aq) → 2KCl_(aq) + 1_2(s)
       Identify the oxidising agent in the reaction. (1 mark)
    2. Explain the pollution effects of chloroflourocarbons (CFCs) to the environment. (2 marks)
19. When a green solid is heated, it forms a black residue and produces a colourless gas which forms a white precipitate with a solution of calcium hydroxide.
    1. Identify the green solid. (1 mark)
    2. Write an equation for the reaction that produces the white precipitate. (1 mark)

SECTION C: PHYSICS (33 marks)
Answer all the questions in this section in the spaces provided.

20. Figure 5 is a diagram of a periscope.
    
    Complete the ray diagram to show the image of object A as seen by the observer. (3 marks)
21. An ebonite rod is charged by rubbing with fur. The rod becomes negatively charged while the fur becomes positively charged. Explain how this happens. (2 marks)
22. Draw and label a simple electric circuit diagram having a cell, a bulb, a switch and an ammeter. (Use circuit symbols) (2 marks)
23. State two factors that affect the speed of sound in air. (2 marks)
24. Describe a:
    1. transverse wave; (1 mark)
    2. longitudinal wave. (1 mark)
25. A student placed two iron nails in contact with one end of a bar magnet. The student ob served that the free ends of nails moved apart from each other. Explain this observation. (3 marks)
26. Define electrical resistance and state its SI unit. (2 marks)
27. Figure 6 shows a set-up used to study the effect of placing a triangular glass prism in the path of white light.
    
    
    1. State what will be observed on the screen. (1 mark)
    2. Name the phenomenon being studied. (1 mark)
28. A student made two heating coils using two different wires and used the coils to heat equal amounts of water in identical containers for the same length of time. At the end of heating, water in one of the containers was at a higher temperature than the other. State two factors that would have led to the difference in temperatures. (2 marks)
29. Figure 7 shows an object O placed infront of a converging lens which has the principle focus at F. (3 marks)
    
    On the figure, construct a ray diagram to locate the image formed.
30. A shopkeeper pays an electricity bill of ksh. 180.90 for using four identical bulbs for 3 hours per day for 30 days. If the cost of electricity is ksh. 6.70 per kilowatt hour, determine the power of each bulb. (3 marks)
31. State the role of the control grid in a cathode ray oscilloscope (CRO). (1 mark)
32. State any two dangers of exposure to X-rays. (2 marks)
33. Explain how a photographic film is used to detect radiations. (2 marks)
34. Explain how a P-N junction diode can be forward biased. (2 marks)

MARKING SCHEME

SECTION A: BIOLOGY

1.    
   1.      
      1. habitat - specific locality with particular set of conditions where an organism lives;
      2. population - all members of a given species in a particular habitat at a particular time; (2 marks)
   2.    
      1. SO₂ - dissolves in rain water and falls as acid rain which lowers soil pH affecting agricultural productivity/irritation of respiratory system resulting in ailments;
         (any one explained) (2 marks)
      2. Smoke
         • affect visibility;
         • block stoma, hindering photosynthesis;
         • cause eye irritation, headache and breathing difficulties
         • green-house effect;
         • poisoning.
           (any one explained) (2 marks)
2.    
   1. To ensure a cooler; environment for quality sperm production. (2 marks)
   2. Procreation/sustains or perpetuates the species;
      For quality improvements; (2 marks)
3.    
   1.    
      1. plumule;
      2. Radicle; (2 marks)
   2.    
      1. Epicotyl is part of the embryo between the cotyledon and the plumule, while hypocotyl is the part of the embryo between the cotyledon and the radicle; (1 mark)
      2. Auxins/IAA; (1 mark)
4.    
   1.      
      1. Genetics - study of heredity and variation and how they are inherited / passing of traits from parents to offsprings; (1 mark)
      2. Gene - unit of instruction / inheritance located on chromosomes, that produce or influence a specific trait in the offspring; (1 mark)
   2.    
      1. Complete dominance - Attribute of a trait which is expressed when the responsible gene is present in both homozygous and heterozygous states. (1 mark)
      2. Phenotype - observable traits of an organism that arises because of the interaction between genes and the environment. (1 mark)
5.    
   1. Acquired traits / characteristics cannot be inherited; as they do not affect the genotype of an individual; (2 marks)
   2. Is growth and development process in which insects go through four stages (developmental) that are different from each other in term of structure i.e egg - larva - pupa - adult /imago. (1 mark)
6.    
   • Both elicit a response;
   • Both achieve co-ordination;
   • Both provide means of communication within the body;
     (2 marks)
7.      
   1.      
      1. Scattered;
      2. Ring arrangement; (2 marks)
   2. When the biceps muscle contract the triceps muscle relaxes, this pulls the arm upwards in the direction shown; (1 mark)
8.      
   1. Treponema pallidum; (1 mark)
   2. Luteinising hormone; (1 mark)
9.      
   1.      
      • Resolving disputed parentage;
      • Giving professional advice on genetic disorders and diseases; (2 marks)
   2.    
      1. Wearing concave / divergent lenses;
      2. Wearing cylindrical lenses; (2 marks)
10.      
    • Simple reflex is inborn (innate) while conditional reflex is learned;
    • Simple reflex is specific conditioned reflex is related to varied stimulus;
    • Simple reflex is constant while conditioned can be weakened / strengthened;
    • Simple reflex brain is not involved while conditioned reflex brain is involved; (2 marks)

SECTION B: CHEMISTRY

11.      
    1. Constant pressure
       Constant temperature (1 mark)
    2.      
       1. The level of coloured water at A lowers/goes down while at B rises/goes up. (1 mark)
       2.    
          • Carbon (IV) oxide is heavier than air hence its rate of diffusion is lower than that of air 
          • Air diffuses faster into the porous pot exerting more pressure hence pushing the coloured water level at A downward (1 mark)
12.    
    1. Molarity refers to the number of moles of a substance contained in 1000 cm³ or 1 litre of solution / concentration of a solution in grams in a litre solution/1000 cm³
    2.    
       1. No. of moles in 100 cm³ of 0.1 MNaOH, 100  x 0.1 = 0.01 ✓ (1)
                                                                   1000
          No. of moles 100 cm' of 1 MNaOH, 100 x 1 = 0.10 moles
                                                            1000
          Total No. of moles = 0.01 +0.1 = 0.11 moles
          Total volume = 200 cm³ (2 marks)
       2. Hence  200  x c= 0.11 
                    1000
          C = 0.11 x 1000 (1) 
                            200
          =0.55 M  (2 marks)
13.    
    1. paper/clothing (1 mark)
       polyvinyl chloride / pvc (1 mark)
    2.    
       • Non-biodegradable
       • Most detergents contain phosphates which cause environmental pollution ("Algae growth")
       • Detergents discharged to water cause pollution i.e. foaming of water.
       • Kill aquatic animal (Any two correct) (2 marks)
14.    
    1. Sulphur (IV) oxide combines with moisture/water to form sulphurous acid
       SO_2(g) + H₂O_(l) → H₂SO_3(aq) ; (dye-oxygen)(coloured) + H₂SO_3(aq) → (dye)(white) +H₂SO_4(aq)
    2. The oxygen in the dye combines with the sulphurous acid to form sulphuric (VI) acid and hence the dye becomes decolourised/bleached. (2 marks)
15.      
    1. Oxygen from the air re-oxidises the colourless material in presence of sunlight to restore the dye. (1 mark)
    2. Molten sodium chloride and calcium chloride. (1 mark)
    3. At the Anode: 2CI_(l) → Cl_2(g) + 2e (1 mark)
    4. Steel (1 mark)
    5. Uses of sodium metal
       • coolant in nuclear, anti-nock
       • extraction of titanium metal
       • sodium lamp - street light
       • making alloys Na₂ Pb
       • makes sodium peroxide
       • makes sodium cyanide for gold extraction
         (any two correct) (1 mark)
16.    
    1. Enthalpy of combustion is the energy released when one mole of substance is completely burned in oxygen/ air. (1 mark)
    2.      
       1. kerosene (1 mark) .
       2. It is liquid, room temperature which is easy to carry and store. It has high heat value V., 48kJg^-1 (1 mark)
       3. Charcoal ✓ solid at room temperature and undergoes incomplete combustion to produce pollutants namely carbon (II) oxide, soot, Nitrogen (IV) oxide and sulphur (IV) oxide. ✓(2 marks)
17.      
    1. The greater the surface area of the reactant, the higher the rate of reaction (1) since more particles come into contact hence higher rate of reaction (2 marks)
    2. The decrease in concentration of reactants slows down the rate of reaction because there are fewer particles that collide/react/combine. ✓ (2 marks)
18.    
    1. Oxidizing agent - chlorine
    2. CFCs
       • when burned, they produce gases such as carbon (IV) oxide which accumulate in the atmosphere causing greenhouse effect/global warming
       • when they are released to the atmosphere, they cause depletion of the ozone layer leading to increased UV rays / radiations reaching the earth hence affecting people and living things in general. (2 marks)
19.      
    1. copper (II) carbonate (CuCO₃) (1 mark)
    2. CO_2(g) + Ca(OH)_2(aq) → CaCO₃₍₈₎ + H₂O_(l) (1 mark) 

SECTION C: PHYSICS

20. .
    
21. The rod gains some electrons thus becoming negatively charged while the fur loses electrons thus becoming positively charged. Electrons moved from the fur to the rod.
22.    
    
23.    
    • Temperature of air ✓
    • Humidity ✓
    • Wind
24.    
    1. Vibration of the medium particles is perpendicular to the direction of the travel of the wave. ✓
    2. The vibration of medium particles is in the same direction of travel as the wave.
25. On placing the nails in contact with the magnet they become magnetised. The free ends have identical poles and therefore they repel each other. ✓
26. This is the measure of the opposition offered to the flow of an electric current in a conductor. The SI unit is the Ohm (Ω).
27.      
    1. Distinct colours will be observed/spectrum of colour. ✓
    2. Dispersion of white light/splitting of white light/separation of white light. ✓
28.    
    • The coils had different resistance/x-sectional area length. ✓
    • The coils had different current passing through them. ✓
    • Different electrical conductivity
29.    
    
30. Total cost = Total power x cost per kilowatt hour
    180.90 = x × 4 × 30 × 6.7 × 3
    x = 180.9 
           2412
    = 0.075 kW/75 W
31. Control the brightness of the beam on the screen/control number of electrons reaching the screen. ✓
32.      
    • may damage cells/living tissue/kills cells ✓
    • may cause cancer
    • may cause genetic mutations/damage/unpredictable chemical changes in living cells
    • Produce deep rooted burns
33.      
    • When exposed to radiations it becomes dark. ✓
    • The amount of darkness can be used to detect the presence of radiations.
34. PN junction diode is forward biased when the P-type is connected to the positive terminal and the n-type to the negative terminal.