Biology Paper 2 Questions and Answers - Form 3 End Term 2 Exams 2022

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QUESTIONS

  1. A student observed feeding relationship while on a tour in a coastal Island.
    Eagles feed on small fish, Small fish feed on sea grass, Insect larvae and molluscs feed on sea grass, Insect larvae fed on by small fish, while crabs feed on insect larvae and molluscs.
    1. From the above information, construct a food web.(3mks)
    2. In which trophic level is small fish found. (1mk)
    3. Extract a food chain where the Eagle is a tertiary consumer. (1mk)
    4. Suppose all the crabs were poisoned, what would be the immediate effect in the ecosystem. Give a reason. (1mk)
    5. Give a reason why pyramid of biomass is a better representation of energy flow in an eco system than pyramid of numbers. (1mk)
  2. An experiment was set up as shown below.
    4
    1. A student blew air in and out through point X. Using arrows indicate on the diagram how air gets in and out of the set up(2mks)
    2.      
      1. In which of the test tube would lime water turn milky first. (1mk)
      2. Give a reason. (1mk)
    3. What is the effect of lactic acid in the thigh muscles of an athlete after a short fast race.(2mks)
    4. Identify the type of muscle in human being where formation and effect of lactic acid is not felt. (1mk)
    5. What is the biological significance of boiling milk /ultra heat treated milk. (1mk)
  3. The diagram below is a longitudinal section of an organ in mammals
    5
    1. Name the organ (1mk)
    2. Identify the parts R and S (2mks)
    3.      
      1. State two differences in the structure above found  in the deserted- rat  and fish  (3mks)
      2. Account for the difference stated above. (2mks)
    4. Name the gland associated with the secretion of aldorsterone hormone. (1mk)
  4. The diagram below represents a circulatory system found in a certain class of chordates.
    6
    1. Identify the type of circulatory system shown above. (1mk)
    2. Name one class of animals having this type of circulatory system. (1mk)
    3. Identify parts labelled M, N and P.(3mks)
    4. What disadvantages is faced by having the types of circulatory system shown above?(2mks)
    5. Between blood vessels Q and T, which one carries oxygenated blood? (1mk)
  5. In an experiment to investigate the rate of reaction indicated by the equation.
    C12H22O11 → C6H12O6 + C6H12O6
      Sucrose        Fructose     Glucose
    It was found out that for products fructose and glucose to form, substance “K” was needed. Temperature  was maintained at 37ºC.When substance “L” was added, reaction slowed and then stopped.
    1. Suggest identity of the substances (2mks)
    2. Other than temperature, state three factures that increase the rate of reaction.  (3mks)
    3. Explain how substance “L” slowed the rate of reaction.  (2mks)
    4. What type of reaction is represented by the equation above? (1mk)

SECTION B (40 MARKS)
Answer questions 6 (compulsory) and either questions 7 or 8 in the spaces provided questions 

  1. The glucose level in mg per 100cm3 of blood was determined in two person Y and Z. Both had stayed for six hours without taking food. They were fed on equal amount of glucose at the start of the experiment .The amount of glucose in their blood was determined at intervals .The results are shown in the table below.
    Times in minutes
     
    Glucose level in blood in mg /100cm3
    Y Z
    0 85 78
    20 105 110
    30 105 110
    45 130 170
    60 100 195
    80 93 190
    100 90 140
    120 90 130
    140 88 120
    1. On the grid provided, plot graphs of glucose levels in blood against time on the same axes. (7mks)
    2. What was the concentration of glucose in the blood of Y and Z at the 50th minute? (2mks)
    3. Account for the level of glucose in present Y 
      1. During the first 45 minutes.  (2mks)
      2. After 45th minute to the end. (4mks)
    4. Account for the decrease in glucose level person Z after 60 minutes. (2mks)
    5. Low blood sugar level in harmful to the body .Explain (3mks)
  2. Discuss the adaptations of seeds and fruits to dispersal.(20mks)
  3. Describe the structure and functions of various organelles in a mature animal cell.        (20mks)

 

 

 

 

 

 

 

 

 

 

 



MARKING SCHEME

Question 1

  1.        
    1
  2. Second / Third (1mk)
  3. Sea grass → insect → small → Eagle → Larvae → Fish
  4. The population of molluscs / insect larvae would increase; due to decreased predation; (2mks)
  5. Shows the actual amount of energy flow of a food chain; (1mark)

Question 2

  1.      
    2
  2.    
    1. A; (1 mark)
    2. Exhaled air has more carbon (iv) dioxide; (than B); (1 mark)
  3.      
    • Poisonous if it accumulates;
    • Muscle clump;
    • Fatigue Mark any two correct
  4. Cardiac muscles; (1 mark)
  5. Kill microorganisms (lactobacillus) bacteria R; germs;
  6. High temperature denature bacteria enzymes / stops anaerobic respiration; Rj Respiration alone or aerobic respiration; Rj germs (1 mark)

Question 3

  1. Kidneys rej any other
  2. R –Medulla ; rej any other
    S – Pelvis ; rej pyramids
  3.    

    1. Desert rat Fish
      Large medulla Small medulla surface
      Long loop of henles Short loop of Henles
      Small cortex surface Large cortex surface
    2. Large medulla ----- surface for maximum reabsorption of water ; due to extensive/ long loop of Henles 
      Small medulla -------surface smaller ; surface for reabsorption due to short loop of Henles;

Question 4

  1. single  circulatory system
  2. Pisces
  3. M-gills
    N- auricle/atrium
    P – Ventricle  
  4. Blood passes through two capillary networks before returning back to the heart hence its under low pressure. This makes the animals less active (sluggish)
  5. Q

Question 5

  1. K – Enzyme
    L – Enzyme inhibitor
  2.        
    • Optimum PH rej PH alone
    • Increases enzyme concentration rej amount of enzyme alone.
  3. It occupied active sites of substances ; No competition with enzymes ; enzyme could not catalyse the reaction.
  4. Hydrolysis.

Question 6


  1. 3S – ½  x 2 = 1
    C – 1 x 2 = 2
    A – ½ x 2 = 1
    P – 1 x 2 = 2
    Total = 6mks
  2. Y – 120mg / 100cm3 
    Z – 178mg / 100cm3  (2mks)
  3.         
    1. Blood sugar level increased to 130 mg / 100cm3; glucose is being absorbed from the intestines;
      Some of it by – passes the liner without entering the cells thus raising blood glucose level;
    2. Glucose concentration declined to normal 90mg / 100cm3 high blood glucose stimulates the pancreas to produce insulin ; which stimulates the liver cells to take up glucose ; and consists it to glycogen;   (4mks)
  4. Some of the glucose is used in respiration to generate energy; some is lost in urine;      (2mks)

Question 7

  • Animal dispersal
    Presence of hooks on ovary walls/ calvx e.g. in Bidens pilosa for attachment on animals hair! fur or clothes of human beings;
    Succulent fruits; brightly coloured and scented fruits that attract animals; Some fruits are eaten together with seeds. The seeds have coats which are resistant to digestive enzyme; hence pass through the gut undigested and passed out through faeces far from the parent plant; e.g. passion, tomato, guava, lantana
  • Water dispersal
    Fruits and seeds dispersed by water are light; hence float on water. Their seed coats are waterproof; This avoids soaking;
    In some fruits e.g. coconut, mesocarp is fibrous and spongy; Air is trapped making the fruit light. Some water plants e.g. the water lily have seeds whose coats trap out bubbles. The bubbles make the seeds float on water; and can be carried away from the parent plant. The pericarp and the testa are waterproof; hence seeds remain afloat without soaking and sinking;
  • Wind dispersal
    Fruits and seeds should be light; and small; to be carried away by air currents.
    Some fruits and seeds have hairy; and feather- like projections; that increase the surface area; for them to be carried away by air currents and dropped far from the parent e.g. sonchus sp and cotton
    Some fruits and seeds have wing-like structures; e.g. jacaranda, sycamore, tridax and nandi flame. Extensions increase the surface area; so that they are easily carried away by air currents;
  • Censor mechanism
    Some fruits are capsule- shaped; Some have pores at the top; e.g. tobacco split along lines of weakness. The capsule is attached to a long stalk; hence when swayed by the wind. The seeds are released and scattered away from the parent plant;
  • Self dispersal
    This method occurs in legumes. When the pod dries up; the seeds break off from the placenta;
    The pod opens along the lines of weakness throwing seeds away from the parent; e.g. beans,
    castor oil, peas, crotalaria
    Any 1 point with explanation 2 mks i.e. 1 point 1 mark. Explanation 1 mark.
    (10 x 2 = 20 mks)

Question 8

  • Mitochondria;
    Has a double membrane surrounding it and inner membrane folded to form cristae which increases the surface area for attachment of respiratory golgi body/apparatus, are stack of membrane bound like sac/is a system of membranes sacs/hollow spaces; that transports glycoproteins/carbohydrates and proteins; They package glycoproteins; secrete mucus/enzymes/synthesized proteins.
  • Lysosomes
    Are spherical in shape and enclosed by a single membrane; contain hydrolytic enzyme which destroy worn out organelles, micro-organism/ingest food/breakdown large molecules.
  • Endoplasmic reticulum
    Are membrane bound cavities in cytoplasm; smooth endoplasmic reticulum site for lipid/sterot transport. Rough endoplasmic reticulum ahs ribosome on its surface; and transport proteins.
  • Centrioles
    Rod shaped; located outside the nuclear membrane, for formation of fibs and cilia 
  • Cytoplasm;
    It’s a fluid medium; where chemical reaction occurs, contains organelles and inclusions (e.g. glycogen granules, fat droplets and dissolved substances).
  • Cell membrane
    Encloses all cell organelles; has phospholipid layer between two protein layers/it’s a lipoprotein layer has pores that selectively allows substances to pass in and out of the cell/its semipermeable.
  • Nucleus
    Has a double membrane/nuclear membrane around it, which has pores to allow substances in and out of the nucleus; Has nucleoplasm, which contain nucleolus/chromatin, nucleus controls all cell activities, Nucleolus manufactures ribosomes and centrioles.
  • Ribosomes
    Are spherical in shape and suspended in cytoplasm and attached on endoplasmic reticulum; synthesis proteins.

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