Biology Paper 2 Questions and Answers - Kassu Jet Joint Exams 2020/2021

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÷INSTRUCTIONS TO CANDIDATE:

  • Answer all questions in section A in the spaces provided
  • In section B answer questions 6 ( compulsory) and either question 7 or 8 in the spaces provided

QUESTIONS

SECTION A (40 MARKS)

  1.  
    1. Study the diagram of a cell organelle shown below and answer the questions that follow
      biopaper2a
      1. Identify the organelle (1mark)
      2. State the function (1mark)
      3. Name the parts labelled A and B (2marks)
    2. When preparing plant sections to be observed under the microscope:
      Water is used to mount the tissue
      Very thin sections of plant should be cut
      Give a reason why each of the steps are carried out (2marks)
    3. Naomi observed an object using a microscope with eye piece lens of magnification X5 and an objective lens of magnification X20.What was the magnification of the object? (2marks)
  2. During an experiment a group of students took equal volumes of blood from the same person containing 50 red blood cells and were suspended salt solutions A, B and C.
    After an hour the cells in each solution were counted and their sizes determined and results tabulated as shown below. Study the table and answer the questions that follow
    Solution 
    SIZE  Large  Normal  Small 
    NUMBER  20  50 50
    1. State the nature of solutions
      B (1mark)
      C (1mark)
    2. Account for the number of red blood cells in solution A after one hour (3marks)
    3. Explain how the above physiological process facilitates the following actions in living organisms
      1. Gaseous exchange (1mark)
      2. Osmoregulation (2marks)
  3. A cross between a red flowered and a white flowered Mirabilis plant produced pink flowered F1 plants
    1. Suggest a reason to explain why there were no red or white flowered F1 plants (1mark)
    2. The F1 offsprings were selved to get F2 generation. Using appropriate letter symbols work out the following for the generation: (4marks)
      1. The genotypic ratio
      2. The phenotypic ratio
      3. What would be the result of crossing one of the F1 offspring producing pink flowers with a true breeding plant producing white flowers? (3marks)
  4. Examine the diagram of a synapse below and answer the questions that follow
    biopaper2b
    1. Name the parts labelled A and C (2marks)
    2. Name the enzyme that exerts its effects on the structure above (1mark)
    3. Name the neurotransmitter substance in impulse transmission (1mark)
    4. State the function of B (1mark)
    5. Identify the two synaptic inhibitors that may poison to interfere with a transmission of an impulse across the synapse (2marks)
    6. State the possible causes of hypermetropia (1mark)
  5.  
    1. Define natural selection (2marks)
    2. Explain the following
      Survival for the fittest (3marks)
      Struggle for existence (3marks)

SECTION B

  1. Two sets of a pea seeds were germinated, set A was placed in normal daylight conditions in the laboratory while set B was placed in a dark cupboard. Starting a few days later the shoots lengths were measured twice daily and their means lengths recorded as shown in the table below.
    Time in hours  12  24  36  48  60  72  84
    Set A length(mm)  12 14  20  23  28  31  47  54
    Set B length (mm)  17 23  28  35  48  62 80 94

    1. Using suitable scale draw the graphs of the mean lengths in set A and B against time on the grid provided (8marks)
      biopaper2c
    2. From the graph state the mean shoot length of each of seedling at the 66th hour (2marks)
    3. Account for the difference of curve B and A (3marks)
    4. Explain what would happen to set up B if it were allowed to continue to grow under conditions of darkness (4marks)
    5. State three external conditions which should be constant for both set ups (3marks)
  2. Describe the role of the following parts in human reproduction
    1. Testes (4marks)
    2. Ovary (6marks)
    3. Sperm and ovum (6marks)
    4. Uterus wall/endometrium (4marks)
  3. State the adaptations of the following tissues for support in plants
    1. Parenchyma tissues (4marks)
    2. Collenchyma tissues (4marks)
    3. Sclerenchyma tissues (2marks)
    4. Tracheids (6marks)
    5. Xylem vessels (4marks)

MARKING SCHEME

QUESTIONS

SECTION A (40 MARKS)

  1.  
    1. Study the diagram of a cell organelle shown below and answer the questions that follow
      biopaper2a
      1. Identify the organelle (1mark)
        Mitochondrion;
      2. State the function (1mark)
        Provide site for respiration;
      3. Name the parts labelled A and B (2marks)
        A - Matrix;
        B - Cristae;
    2. When preparing plant sections to be observed under the microscope:
      Water is used to mount the tissue 
      Very thin sections of plant should be cut
      Give a reason why each of the steps are carried out (2marks)
      Water is used - To enhance turgidity of the cells hence easily seen;
      Thin sections - to allow light to pass through;
    3. Naomi observed an object using a microscope with eye piece lens of magnification X5 and an objective lens of magnification X20.What was the magnification of the object? (2marks)
      Magnification = Eye piece lens Magnification X Objective lens Magnification;
                          = x5 X x20;
                          = x100;
  2. During an experiment a group of students took equal volumes of blood from the same person containing 50 red blood cells and were suspended salt solutions A, B and C.
    After an hour the cells in each solution were counted and their sizes determined and results tabulated as shown below. Study the table and answer the questions that follow
    Solution 
    SIZE  Large  Normal  Small 
    NUMBER  20  50 50
    1. State the nature of solutions
      B Isotonic;(1mark)
      C Hypertonic; (1mark)
    2. Account for the number of red blood cells in solution A after one hour (3marks)
      The red blood cells in solution A reduced in number, the solution was hypotonic to the cells Hence the cells gained water molecules through osmosis increased in size and bursted hence the reduction; 
    3. Explain how the above physiological process facilitates the following actions in living organisms
      1. Gaseous exchange (1mark)
        Movement of water in and out of the guardcells facilitate opening and closing of the stomata;
      2. Osmoregulation (2marks)
        In kidney tubules of animals, water is withdrawn from the tubules through the tubular walls through osmosis;
  3. A cross between a red flowered and a white flowered Mirabilis plant produced pink flowered F1 plants
    1. Suggest a reason to explain why there were no red or white flowered F1 plants (1mark)
      Incomplete dominance;
    2. The F1 offsprings were selved to get F2 generation. Using appropriate letter symbols work out the following for the generation: (4marks)
      1. The genotypic ratio
        crossbreedingBioP2a
      2. The phenotypic ratio
        1 Red flowers : 2 Pink flowers : 1 White flowers;
      3. What would be the result of crossing one of the F1 offspring producing pink flowers with a true breeding plant producing white flowers? (3marks)
        biopaper2msb
  4. Examine the diagram of a synapse below and answer the questions that follow
    biopaper2b
    1. Name the parts labelled A and C (2marks)
      A - Synaptic vesicle;
      C - Pre-synaptic membrane;
    2. Name the enzyme that exerts its effects on the structure above (1mark)
      Cholinesterase;
    3. Name the neurotransmitter substance in impulse transmission (1mark)
      acetylcholine;
    4. State the function of B (1mark)
      Supply the energy; necessary for continuous synthesis of neurotransmitter.
    5. Identify the two synaptic inhibitors that may poison to interfere with a transmission of an impulse across the synapse (2marks)
      Atropine;
      Curare;
      Organophosphates;
    6. State the possible causes of hypermetropia (1mark)
      Axial length of eyeball is too short; lens or cornea is flatter than normal; (any 1)

  5.  
    1. Define natural selection (2marks)
      Natural selection is a mechanism by which beneficial variations in a population are perpetuated; while disadvantageous variations are eliminated;
    2. Explain the following
      Survival for the fittest (3marks)
      In struggle for existance individuals with advantageous variations; are well adapted to the environment; since they are suited to the environment they are selected hence survive and reproduce;
      Struggle for existence (3marks)
      Members of the population are constantly competing with each other; in an efforrt to survive and the strong members survive to adulthood and are able to reproduce; This is due to environmental pressure such as predation, diseases and competition for food and breeding sites.

SECTION B

  1. Two sets of a pea seeds were germinated, set A was placed in normal daylight conditions in the laboratory while set B was placed in a dark cupboard. Starting a few days later the shoots lengths were measured twice daily and their means lengths recorded as shown in the table below.
    Time in hours  12  24  36  48  60  72  84
    Set A length(mm)  12 14  20  23  28  31  47  54
    Set B length (mm)  17 23  28  35  48  62 80 94

    1. Using suitable scale draw the graphs of the mean lengths in set A and B against time on the grid provided (8marks)
      biopaper2e
    2. From the graph state the mean shoot length of each of seedling at the 66th hour (2marks)
      A - 39±1;
      B - 71±1;
    3. Account for the difference of curve B and A (3marks)
      B Grew tall/longer; the stem/seedling etiolated; cells elongate faster; weak, slender stem; Lengthening faster in search of light ;
      A Shorter,healthy because of normal conditions i.e sufficient light;
    4. Explain what would happen to set up B if it were allowed to continue to grow under conditions of darkness (4marks)
      The seedling will eventually die; this because of insufficient/lack of sunlight which is neccessary for photosynthesis; Increase/continuous increase of etiolants that completely suppress the Chloroplasts hence no chlorophyll for food formation; 
    5. State three external conditions which should be constant for both set ups (3marks)
      Water;
      Oxygen;

      Suitable temperature;
  2. Describe the role of the following parts in human reproduction
    1. Testes (4marks)
      Hang outside the body to provide a cooler environment for sperm production;
      Seminiferous tubules in the site for formation of sperms;
      Final products of meiosis enter the sertoli cells; where they are nourished and undergo differentiation into mature sperms;
      Has interstitial cells that produce male hormones called androgens; i.e testosterone that stimulates testes to produce sperms;
    2. Ovary (6marks)
      Site for formation of ova; potential eggs are enclosed by ovary cells known as primary follicles; which provide nourishment; few egg cells develop into ova during puberty by meiosis; by undergoing growth to become mature graafian follicle; that burst at ovulation to release mature sperms;
      Secretes hormones; Oestrogen -healing and repair of endometrium; progesterone - increased blood supply and thickening of endometrium;
    3. Sperm and ovum (6marks)
      Nucleus of a male gamete fuses with the nucleus of  a female gamete to form a zygote; Sperms are drawn by suction into the uterus where they swim using their tails; Sperms comes into with contents of ovum produced by ovary in the oviduct; acrosome bursts to release lytic enzyme which dissolve membranes of ovum. The acrosome turns inside out forming a fine filament; that penetrate the ovum; Head of sperm enters ovum and bursts to release the male nucleus; that fuses with female nuclues to form a diploid zygote; the vitelline membrane undergoes a change which stops any other from entering the ovum;
    4. Uterus wall/endometrium (4marks)
      Site where attachment of blastocyst occurs; blastocyst develop fingerlike projections called villi which grows into endometrium; and forms the placenta; 
      Stimulated by the hormone to contract to expel foetus from uterus;
      Capable of expanding to allow growth of embryo;
  3. State the adaptations of the following tissues for support in plants
    1. Parenchyma tissues (4marks)
      When cells are turgid they provide mechanical support in herbaceous plants
    2. Collenchyma tissues (4marks)
      Cells when turgid; provide mechanical support; 
      Walls are thickened with cellulose; to provide mechanical support;
    3. Sclerenchyma tissues (2marks)
      Cells are thickened by lignin;
      Consists of dead cells thickened by lignin;
    4. Tracheids (6marks)
      Dead cells with thick unevenly lignified walls that provides strength and support to the stem;
      Long cells with tapering ends.
      Pits on the ends allow lateral water to cells surrounding.
    5. Xylem vessels (4marks)
      Thick  walled tubes with lignin deposited unevenly in rings, spirals or patches on the walls.
      Bordered pits on the xylem vessels permit the passsage of water in and out of the lumen into the neighbouring cells.
      Long and hollow

 


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