Biology Paper 3 Questions and Answers With Confidential - Form 3 End Term 1 Exams

INSTRUCTIONS TO CANDIDATES:

• Answer ALL the questions
• Answers should be written in the spaces provided

1. Below are diagrams P, Q, R and S. Examine them.
            
   
   1. Using observable features in the photographs, complete the dichotomous key given below. (2mks)
      1.  
         1. Animals with legs………………………………................go to 2
         2. Animals without legs…………………………………………....snake
      2.  
         1. Animals with two body parts .......................spider
         2. …………………………………………………………..........……go to 3
      3.  
         1. ………………………………………………………...… locust
         2. Animals without wings…………..............Ant
   2. In each case show steps followed to arrived at the identity. (4mks)
      

      Organism	Steps followed	Identity
      P		Locust
      Q		Ant
      R		Snake
      S		Spider

   3. Name the main characteristics used to classify members of the phylum Arthropoda. (3mks)
   4. State five economic importance of insect. (5mks)
   5. Using observable features only show how specimen P adapted for locomotion. (2mks)
2. You are provided with a specimen Q.
   Obtain two equal cubes about 1cm in length from specimen Q. Crush one of the cubes and place it in test tube labeled B. Place the other cube as a whole in test tube labeled A. In to each of the test tubes add 10cm³ of hydrogen peroxide.
   1. State the observations made in test tube B. (1mk)
   2. Explain the results in a (i) above. (1mk)
   3. Write an equation for the breakdown of hydrogen peroxide. (1mk)
   4. Peel the remaining half of specimen Q and crush it in a motar. Using the reagents provided test for the various food substances in the extract obtained from crushed material. Record the procedures, observations and conclusions in the table below.
      

      Food substance	procedure	Observations	Conclusions

3. The following set-up was used by students to demonstrate a certain process.
            
   
   1. Identify the process being investigated. (1mk)
   2. Name solution C (1mk)
   3. State the observations expected at the end of the experiment in:-
      Tube A.......................................(1mk)
      Tube B...................................(1mk)
   4. Account for the observations made in:- (2mks)
      Tube A
      Tube B            (2mks)
   5. If the animal was replaced by a potted plant.
      1. What modification would you make in the set-up above? (2mks)
      2. Give a reason for your answer in d (i) above. (2mks)

Marking Scheme

1. Below are diagrams P, Q, R and S. Examine them.
   1. Using observable features in the photographs, complete the dichotomous key given below.
      1.  
         1. Animals with legs……………………………………………….go to 2
         2. Animals without legs…………………………………………..snake
      2.  
         1. Animals with two body parts ……………………………..spider
         2. …animals with three body parts………………………..go to 3 (1mk)
      3.  
         1. …animals with wings………………………………………….. locust (1mk)
         2. Animals without wings………………………………………Ant
   2. In each case show steps followed to arrived at the identity. (4mks)
      

      Organism	Steps followed	Identity
      P	...1a, 2b, 3a...	Locust
      Q	...1a, 2b, 3b...	Ant
      R	...1b...	Snake
      S	...1a, 2a...	Spider

   3. Name the main characteristics used to classify members of the phylum Arthropoda. (3mks)
      • Number of body parts
      • Number of limbs
      • Presence and number of antennae
   4. State five economic importance of insect. (5mks)
      • Some produce delicious food e.g honey
      • Act as pollinators for plants e.g. bees
      • Vectors for hyme and animals diseases e.g tsetsefly, mosquito, housefly.
      • Destroy timber/building e.g. timber
      • Pests feedings on crops in the field or store
      • Aerate soil hence improve soil fertility e.g ants, termites.
   5. Using observable features only show how specimen P adapted for locomotion.  (2mks)
      • P has wings for flight
      • 3 pairs of legs for walking and hoping for long distance i.e. legs for walking / strong hind legs for hopping.
2. You are provided with a specimen Q.
   Obtain 2 equal cubes about 1cm in length from specimen Q. crush one of the cubes and place it in test tube labeled B. place the other cube as a whole in test tube labeled A. in to each of the test tubes add 10cm³ of hydrogen peroxide.
   1. State the observations made in test tube B.                                             (1mk)
      • Boiling tube B – many/more bubbles/rapid effervescence due to enzymatic activity.
   2. Explain the results in a (i) above. (1mk)
      • Crushing increased the surface area more in B than in A for enzymatic activity.
   3. Write an equation for the breakdown of hydrogen peroxide. (1mk)
      
   4. Peel the remaining half of specimen Q and crush it in a motar. Using the reagents provided test for the various food substances in the extract obtained from crushed material. Record the procedures, observations and conclusions in the table below
      

      Food substance	Procedure	Observations	Conclusions
      Starch	Add 3 drops of iodine solution to the extract on a white tile	brown colour of iodine solution changes to blueblack	Starch present
      Reducing sugar	To 2cm3/ml of test substance add equal amount of Benedict solution and heat to boil	Blue colour of Benedicts solution changes to green then yellow	Reducing sugar present
      Protein	To 2ml of test tube add 2ml of sodium hydroxide then copper II sulphate solution dropwise while shaking	Blue colour of copper II sulphate solution persist	Proteins absent

3. The following set-up was used by students to demonstrate a certain process. 
   1. Identify the process being investigated. (1mk)
      • Respiration
   2. Name solution C.                         (1mk)
      • Calcium hydroxide / lime water
   3. State the observations expected at the end of the experiment in:-
      1. Tube A     (1mk)
         • Remains colourless / no change in colour
           Rej no change / observation
      2. Tube B     (1mk)
         • White precipitate formed.
   4. Account for the observations made in:-                                   
      1. Tube A   (1mk)
         • Carbon IV Oxide in air is observed by sodium hydroxide therefore solution C/Calcium hydroxide solution / lime water does not change in colour.
      2. Tube B   (2mks)
         • The animal / rat respires producing carbon (IV) Oxide which passes to tube B and reacts with solution C to form a white precipitate
   5. If the animal was replaced by a potted plant.
      1. What modification would you make in the set-up above? (2mks)
         • The bell jar would be covered with a black cloth/paper / alluminium foil.
      2. Give a reason for your answer in d (i) above. (2mks)
         • The black cloth/paper/alluminium foil prevents light from reaching the plant; therefore preventing photosynthesis from taking place/the plant carries out respiration only.

CONFIDENTIAL

• IRISH POTATO (A PIECE PER STUDENT)
• RULER
• SCAPEL
• LABELS (A AND B)
• IODINE SOLUTION
• BENEDICTS SOLUTION
• SODIUM HYDROXIDE SOLUTION
• COPPER II SULPAHATE SOLUTION
• TEST TUBES (5 PER STUDENTS )
• MEANS OF HEATING
• HYDROGEN PEROXIDE 20ML PER STUDENT
• MORTAR AND PESTLE