BIOLOGY PAPER 3 - 2020 KCSE PREDICTION SET 1 (QUESTIONS AND ANSWERS)

INSTRUCTIONS TO CANDIDATES

• Answer all the questions.
• Spend the first 15 minutes of the 1¾ hours allowed for this paper reading the whole paper carefully before commencing your work
• Candidates should answer the questions in correct English. Incorrect spellings of
  Especially technical terms may be penalized.

1. You are provided with Ethanol, liquids L,K, an Irish potato and Iodine.
   1. Label two test tubes A and B. Place 2cm3 of water into each test tube. Add 8 drops of liquid L into each test tube. To the test tube labelled A, add 8 drops of Ethanol. Shake both test tubes. Allow to stand for 2 minutes.
      1. Record your observations. (2marks)
         Test tube A
         Test tube B
      2. Name the process that has taken place in test tube A. (1mark)
      3. State the significance of the process named in (a) (ii) above. (1mark)
      4. Name; The digestive juice in humans that has the same effect on liquid L as Ethanol. (1mark)
      5. The region of the alimentary canal into which the juice named in (a) (iv) above is secreted (1mark)
   2. Label one test tube C.
      Place 2cm³ of specimen Kinto the test tube. Add a drop of iodine solution into the test tube.
      1. Record your observation (1mark)
      2. Suggest the identity of K (1mark)
   3. Cut out a cube whose sides are about 2 cm from the Irish potato provided. Crush the cube to obtain a paste. Place the paste into the test tube labelled C containing 2cm³of Kand a few drops iodine solution from (b) above. Leave the set up for at least 30 minutes.
      1. Record your observations. (2marks)
      2. Account for the results in (c) (i) above. (3marks)
   4.  
      1. Cut out another cube whose sides are 1cm from the Irish potato provided. Crush the cube to obtain a paste. Use the paste to carry out food test with Benedict`s solution and record the results. (1mark)
      2. Account for the results in (d) (i) above. (2marks)

2. You are provided with a photograph of specimen Z. Examine it and use it to answer the questions that follow.
   
   
   1.  
      1. Identify specimen Z (1mark)
      2. Give a reason for your answer in (a) (i) above. (1mark)
   2. Specimen Z is an organ obtained from mammals. One of its functions is protection. Explain how specimen Z is adapted to provide;
      1. Mechanical protection. (2marks)
      2. Chemical protection. (2marks)
      3. Protection against predators. (1mark)
   3. Other than protection, state two other functions of specimen Z. (2marks)
   4. Explain how sprinkling of common table salt on specimen Z leads to its preservation. (3marks)
      Give a reason for your answer. (1mark)
3. The photograph below is that of a plant seedling. Examine it.
   
   
   1.  
      1. Using observable features only, state the class to which  the plant belongs. (I mark)
      2. Give reason(s) for your answer in (a) (i) above.(2 marks)
   2. State the roles of the structures labeled T during  germination. (2 marks)
   3.  
      1. Name the part of the seedling labelled K and L(2 marks)
      2. State the significance of the curvature on part K ( 1 mark)
   4. Name the type of germination exhibited by the seedling.(1 mark)
   5. As germination progresses, the curvature on part K straightens. Explain how this occurs (3 marks)

MARKING SCHEME

1. You are provided with cooking oil, liquids L and K and an Irish potato.
   1. Label two test tubes A and B. Place 2cm3 of water into each test tube. Add 8 drops of the cooking oil into each test tube. To the test tube labelled A, add 8 drops of liquid L. Shake both test tubes. Allow to stand for 2 minutes.
      1. Record your observations. (2marks)
         Test tube A
         Oil broken into small/tiny droplets/globules; which are dispersed/spread throughout the liquid//Oil became emusified; Rej. White solution/white ppt/suspension alone
         Test tube B
         Two separate/immiscible layers//oil floats on water/no mixing occured;
      2. Name the process that has taken place in test tube A. (1mark)
         Emulsification;
      3. State the significance of the process named in (a) (ii) above. (1mark)
         To increases the surface area of fats/lipids for digestion;

         NB: a(iii) is tied to a(ii)

      4. Name;
         The digestive juice in humans that has the same effect on oil as liquid L. (1mark)
         Bile (juice); Rej. Pancreatic juice
         The region of the alimentary canal into which the juice named in (a) (iv) above is secreted (1mark)
         Duodenum;
   2. Label one test tube C. Place 2cm3of liquid K into the test tube. Add a drop of iodine solution into the test tube.
      1. Record your observation (1mark)
         Blue black; Acc. Black
      2. Suggest the identity of K (1mark)
         Starch solution;
   3. Cut out a cube whose sides are about 2cm from the Irish potato provided. Crush the cube to obtain a paste. Place the paste into the test tube labelled C containing K and iodine solution from (b) above. Leave the set up for at least 30 minutes.
      1. Record your observations. (1mark)
         Blue black colour in C fades/disappeared; Acc. Colour change to light orange/yellow/orange/ brown/purple
      2. Account for the results in (c) (i) above. (3marks)
         Enzyme/amylase; in the potato tissue breaks down/hydrolysed starch; into sugars/maltose; which do not give blue black colour with iodine;
   4.  
      1. Cut out another cube whose sides are 1cm from the Irish potato provided. Crush the cube to obtain a paste. Use the paste to carry out food test with Benedict`s solution and record the results. (1mark)
         Turns from blue to green/yellow/orange/brown colour;
      2. Account for the results in (d) (i) above. (2marks)
         Starch in potato is converted/changed; to maltose/reducing sugar/simple sugar; by enzyme/amylase/maltase; OWTTE

2. You are provided with a photograph of specimen Z. Examine it and use it to answer the questions that follow.
   1.  
      1. Identify specimen Z (1mark)
         skin;
      2. Give a reason for your answer in (a) (i) above. (1mark)
         has fur;

         NB: a(ii) is tied to a(i)

   2. Specimen Z is an organ obtained from mammals. One of its functions is protection. Explain how specimen Z is adapted to provide;
      1. Mechanical protection. (2marks)
         Cornified layer made up of keratin; to offer protection against mechanical injury; 
         Cornified layer made up of dead cells;
      2. Chemical protection. (2marks)
         Sebaceous glands secrete sebum; which is antiseptic;
      3. Protection against predators. (1mark)
         (Malpighian layer secretes melanin that enables) the skin camouflage/blend with the surrounding; / the fur/skin is distasteful to keep off the predators;
   3. Other than protection, state two other functions of specimen Z. (2marks)
      Thermoregulation;
      Excretion;
      Storage of fats;
      Synthesis of vitamin D;
   4. Explain how sprinkling of common table salt on specimen Z leads to its preservation. (3marks)
      The salt absorbs water from the cells of Z/ skin; forms a hypertonic solution to the Ncytoplasm of bacteria/pathogens/organisms that cause decay; dehydrating them/making them lose water to the salt solution by osmosis
3. The photograph below is that of a plant seedling. Examine it. 
   1.  
      1. Using observable features only, state the class to which the plant belongs. (I mark)
         Dicotyledonae
      2. Give reason(s) for your answer in (a) (i) above.(2 marks)
         Has two cotyledons
         Has a tap root system
         
         NB: a(ii) is tied to a(i)
   2. State the roles of the structures labeled T during germination. (2 marks)
      Storage of food which is used by the seedling before photosynthesis begins
      Site of hydrolysis of food for onward transmission to the growing points
   3.  
      1. Name the part of the seedling labelled K and L(2 marks)
         K – Epicotyl                           
         L - Hypocotyl
      2. State the significance of the curvature on part K ( 1 mark)
         It protects the delicate plumule roots and the shoot tip from mechanical damage from soil particles as they emerge from the ground
   4. Name the type of germination exhibited by the seedling.(1 mark)
      Hypogeal germination
   5. As germination progresses, the curvature on part K straightens. Explain how this occurs (3 marks)
      Once part K is exposed to sunlight, more light on the upper side causes the auxins to migrate to the lower side. The increased auxin concentration on the lower side stimulates faster elongation of cells on the lower side leading to the straightening of the seedling
      
      NB: Reject wrong spellings for technical term