KCSE 2017 General Science Paper 2 with Marking scheme

SECTION A: BIOLOGY (34 marks)

Answer all the questions in this section in the spaces provided.

1. The photographs below show two types of parasites.
            
   1.  
      1. Identify the parasite labelled E and F. (2 marks)
      2. Name one living organism which can host the two parasites.  (1 mark)
   2. Give three adaptations of the parasite labelled E to its mode of life.  (3 marks)
2. Explain how cell biology is an evidence of organic evolution  (3 marks)
3. The diagram below shows a bone found in a mammalian skeleton.
              
   1.  
      1. Identify the bone.   (1 mark)
      2. Which bone articulates at point G?   (1 mark)
   2. What type of joint is formed at point H?  (1 mark)
4. The figure below shows a tissue from a male human being.
             
   1. Name the structures labelled J and K. (2 marks)
   2. Give the functions of structure J and K. (2 marks)
5. Give three adaptations of the sperm cell to its function.   (3 marks)
6. In a breeding experiment, plants with red flowers were crossed. The produced plants included 246 red and 82 white flowered plants.
   1.  
      1. Identify the recessive character.  (1 mark)
      2. Give a reason for your answer in (a) (i) above.   (1 mark)
   2. What were the genotypes of the parent plants that gave rise to the plants with red and white flowers?  (1 mark)
   3. Determine the genotypes of the plants that were produced from the cross. Show your working  (3 marks)
7. The graph below illustrates intermittent growth in insects.
   
   Account for the shape of the graph between Account fort
   1. L and M  (2 marks)
   2. M and N (2 marks)
8. The following structure represents a part of the ear responsible for hearing.
            
   1. Name the structure   (1 mark)
   2. Which structure in the ear detects changes in posture?   (1 mark)
   3. Give three causes of deafness in human beings.   (3 marks)

SECTION B: CHEMISTRY (33 marks)

Answer all the questions in this section in the spaces provided.

9.  
   1. State Boyle's Law.   (1 mark)
   2. A fixed mass of a gas occupies a volume of 225 cm³ at 330°C and 740 mmHg. Calculate the volume the gas will occupy at 13°C and 780 mmHg.   (2 marks)
10.  
    1. What is meant by a molar solution?  (1 mark)
    2. Determine the amount of water that should be added to 15cm of 3M hydrochloric acid to dilute the acid to 1 molar solution.   (2 marks)
11. The molecular formula of an organic compound is C₅H₁₂
    
    1. Draw the structure of the compound.  (1 mark)
    2. Name the structure in (a).  (1 mark)
12.  
    1. What is meant by an endothermic reaction?   (1 mark)
    2. Hydrogen gas burns in air to form water vapour, releasing 286kJ of energy per mole. Draw an energy level diagram for the reaction.   (2 marks)
13. Polymers are large organic molecules formed by combining small molecules.
    
    1. Name two natural polymers.   (1 mark)
    2. State one use of each polymer named in (a) above.   (1 mark)
14. Firewood is used as a source of energy. State two disadvantages of this fuel.   (2 marks)
15. Calculate the mass of 0.35 moles of calcium hydrogen carbonate.    (2 marks)
    (Ca = 40; H=1.0 ; C = 12.0;0= 16.0)
16. The diagram in Figure 1 shows curves obtained when equal amounts of zinc granules were reacted with different concentrations of hydrochloric acid. Study it and answer the questions that follow.
             
    
    1. Identify the curve that represents the most concentrated acid. Explain.  (2 marks)
    2. State two factors that affect rate of a chemical reaction.   (2 marks)
17. Sodium metal is extracted from molten rock salt
    1. Name the ions present in the molten liquid.  (1 mark)
    2. Reduction method is not used in the extraction of sodium.  (1 mark)
    3. Explain. State two uses of sodium.  (1 mark)
18. In the manufacture of sulphuric(VI) acid, sulphur(VI) oxide is absorbed in concentrated sulphuric acid and the product diluted with soft water.
    1. Name the product that is diluted. (1 mark)
    2. Write an equation for the reaction between sulphur(VI) oxide and concentrated sulphuric(VI) acid. (1 mark)
    3. Concentrated sulphuric(VI) acid was added to a beaker containing sugar crystals. Explain the observations made.    (1 mark)
19.  
    1. State the impurities present in the aluminium ore.  (1 mark)
    2. Aluminium is preferred to iron in making utensils. Explain.  (1 mark)
20. The set-up in Figure 2 was used in the preparation of gas B. Study it and answer the questions that follow.
             
    1. Identify:
       1. Solution A   (1 mark)
       2. Gas B   (1 mark)
    2. State the property that enables the gas to be collected as shown.  (1 mark)
    3. State two uses of gas B.  (1 mark)

SECTION C: PHYSICS (33 marks)

Answer all the questions in this section in the spaces provided.

21. Figure 3 shows an opaque object placed between the screen and a point source of light in the form of a small hole in a cardboard placed in front of the source of light.
                
    1. Complete the ray diagram to show the shadow formed on the screen.   (2 marks)
    2. State what would be the effect on the shadow if the hole is enlarged.   (1 mark)
22.  
    1. Draw a simple circuit showing two cells in series with a bulb and a switch.   (1 mark)
    2. Indicate on the diagram the direction of current in (a).   (1 mark)
23. Define the following:
    
    1. A wave pulse .......  (1 mark)
    2. Wavelength ...  (1 mark)
24. Explain why repulsion is the only sure test for the polarity of a magnet.  (2 marks)
25. Explain how a glass rod acquires a positive charge when rubbed with silk cloth.(2 marks)
26. Explain how an echo is formed.   (2 marks)
27. Figure 4 shows the scale of an electrical device used to measure a current.
              
    1. Name the device  (1 mark)
    2. Record the current shown by the device.  (1 mark)
28. Figure 5 shows a pin lying at the bottom of a beaker full of water and an observer above the surface of water.
    
    Draw a ray diagram to show how the observer sees the head of the pin.  (3 marks)
29. State the energy changes that take place as the electrons travel to the anode for the production of X-rays in an X-ray tube.   (3 marks)
30. A house has four 75 W lamps. Determine the cost of using the lamps for 6 hours each day for 30 days if the cost of electricity is ksh.9.30 per kWh.  (3 marks)
31. State two properties of an alpha particle.  (2 marks)
32. State three advantages of using a Cathode Ray Oscilloscope as a voltmeter instead of a moving coil meter.  (3 marks)
33. State how the electrical conductivity of a semiconductor can be increased.   (1 mark)
34. State two properties of images formed by diverging lenses.  (2 marks)
35. Name one device that functions by using the heating effect of an electrical current. (1 mark)

MARKING SCHEME

SECTION A: BIOLOGY

1.  
   1.  
      1. E-Roundworms/Ascaris spp;  (1 mark)
         F-Plasmodium ovale/Plasmodium vivax,   (1 mark)
      2. Human beings;  (1 mark)
   2.  
      • Thick and hard protective covering/pellicle to resist digestion by enzymes;
      • Covered by mucus to resist digestion by the host enzymes;
      • Can respire anaerobically to survive in the oxygen-deficient intestines;
      • Eggs are enclosed/covered by hard shells to resist digestion in the intestines and harsh external environment;
      • Has two hosts to increase survival chances;
        3x1 = 3 marks
2. Similar cell organelles/and (some) biological molecules; are found in the cells of almost all living organisms; suggesting that the organisms had a common ancestry/phylogenically related;
   3x1 =3 marks
3.  
   1.  
      1. Femur; (1 mark)
      2. Tibia;  (1 mark)
   2. Hinge joint; (1 mark)
4.   
   1. J-Vas deferens/sperm duct; (1 mark)
      K-Epididymis; (1 mark)
   2. J-Conveys sperms from the epididymis to the urethra during ejaculation;  (1 mark)
      K - Storage of mature sperms;  (1 mark)
5.  
   • Head has acrosome which produces hydrolytic enzyme that digests the vitelline wall of the ovum during fertilization;
   • Head has a nucleus which contains genetic materials that determine the characteristics/traits of the offspring:
   • Middle part has numerous mitochondria to provide sufficient energy required for swimming; towards the ovum;
   • Has a long tail for propulsion/swimming towards the ovum;
     3x1=(3 marks)
6.  
   1.  
      1. White flower gene;  (1 mark)
      2.  Red and white flowered plants are produced in the ratio of 3:1   (1 mark)
   2. Red-Rr, Rr;  (1 mark)
   3.  
       (3 marks)
7.  
   1. Slow growth rate; because the exoskeleton has hardened and is limiting growth;  (2 marks)
   2. Rapid growth occurs after moulting; before the exoskeleton hardens;  (2 marks)
8.  
   1. Cochlea;  (1 mark)
   2. Vestibular apparatus;
   3.  
      • Hereditary abnormalities in the ear; 
      • Injury todhe brain/auditory nerve/cochlea;
      • Damage (mechanical/physical) of the eardrum;
      • Ear infections;
        3x1(3 marks)

SECTION B: CHEMISTRY

9.  
   1. Boyle's Law -A volume of a fixed mass of a gas is inversely proportional to its pressure provided the temperature remains constant  (1 mark)
   2.  
      
      V₂ = (740x 225 x 286)
                  (603x 780)
          = 101.24 cm³  (2 marks)
10.  
    1. A solution that contains one mole of a substance in 1dm³ /1000 cm³ of solution. (1 mark)
    2. Dilution formular
       C₁V₁ = C₂V₂   
       V₂ = C₁V₁ = 15 × 3 = 45cm³
                 C₂          1
       =Amount of water added = 45 – 15 = 30cm³  (2 marks)
11.  
    1.  
          (1 mark)
    2. Pentane  (1 mark)
12.  
    1. A reaction where heat is absorbed from the surrounding.   (1 mark)
    2.  
          (2 marks)
13.  
    1. Cellulose, rubber, cotton, carbohydrate, protein, silk  (1 mark)
       (Any 2 correct @ ½ mark)
    2. Manufacture of clothing/fibres
       Manufacture of tyres             (1 mark)
       (Any 2 correct @ ½ mark) 
14.  
    • Deforestation/ cutting down trees.
    • Produces Carbon(IV) oxide which causes global warming.    (2 marks)
15. R. Formula Ca(HCO₃)₂
    R.F.M. =( 40+2+24+96) = 162 
    Mass of Ca(HCO₃)₂ =(0.35 x 162)
    = 56.7g  (2 marks)
16.  
    1. Curve i 
       • The gradient for curve (i) is steeper hence the reaction is faster implying the concentration is higher 
         (2 marks)
    2.  
       • Temperature;
       • Surface area of solid reactants; 
       • Catalyst
       • Concentration.
         (Any 2 correct @ 1 mark)
17.  
    1. Na⁺, Cl⁻ Penalize if written in words (1 mark)
    2. Sodium is more reactive than carbon and the ore is not an oxide  (1 mark)
    3.  
       • Coolant in nuclear reactions;
       • Sodium lamp: 
       • Extraction of gold. 
       • Extraction of titanium  
         (Any 2 correct @ ½ mark)  (1 mark)
18.  
    1. Oleum 
    2. SO_2(g) +H₂SO_4(l) → H₂S₂O_7(l)
    3. The sugar turned brown then a black mass is formed because conc. H2SO, dehydrates /removes the elements of water from sugar.  (1 mark)
19.  
    1. •  Silica;
       • iron(II) oxide.  (1 mark)
    2.  
       • Aluminium is a better conductor of heat.
       • Aluminium does not corrode easily because it forms a layer of insoluble oxide. (1 mark)
20.  
    1.  
       1. Solution A - dilute hydrochloric acid;   (1 mark)
       2. Gas B-sulphur(IV) oxide.   (1 mark)
    2. Gas B is denser/ heavier than air   (1 mark)
    3.  
       • Manufacture of sulphuric(VI) acid;
       • Bleaching agent; 
       • Fumigating houses;
       • Preservative
         (Any 2 correct @ 1 mark)  (1 mark)

SECTION C: PHYSICS

21.   
    1.  
       
       (2 marks)
    2. The shadow formed would have two regions. A full shadow and a partial shadow.  (1 mark)
22.  
    
23.  
    1. A pulse is a single disturbance that moves through a medium from one point to another. (1mark)
    2. The distance between two successive crests (or troughs)   (1 mark)
       Or
       The distance between two successive points in a wave that are in phase.
24. Repulsion takes place only between like poles of a magnet while attraction can occur between unlike poles of magnets or between a magnet and any magnetic material (2 marks)
25. On rubbing the glass loses some electrons to the cloth, it therefore gets a net positive charge. (2 marks)
26. When sound from a source is reflected by a barrier and reverses direction.
    Reflected sound (echo) is received by observer.  (2 marks)
27.  
    1. Ammeter/millimeter/micro ammeter    (1 mark)
    2. Current = 1.7 A   (1 mark)
28.  
     (3 marks)
29. Electrical energy(electric field) → Kinetic energy of electrons) → heat and x-rays   (3 marks)
30. Energy consumed = 4x75x6x30 kWh  (3 marks)
                                      1000
                                = 54 kW
                        Cost = 54 x 9.30 
                                 =Ksh. 502.20 
31.  
    • Carries a positive charge. 
    • Can ionize gas/air strongly 
    • It is equivalent to helium ion 
    • Can be stopped by a thick sheet of paper
    • Is deflected by both electric and magnetic fields
      (Any two correct)  (2 mark)
32.  
    • Can measure both alternating and direct voltages
    • Responds instantaneously unlike ordinary meter
    • Does not affect the circuit due to its high resistance
    • Can measure large voltages without getting damaged.
      (Any three @1 mark)  (3 marks)
33. Raise temperature/by doping   ( 1 mark)
34.  
    • Virtual
    • Diminished   (2marks)
35. Electrical kettle/electric iron/filament lamps/soldering gun/electric heater
    (1 mark for any one correct)  (1 mark)