Biology Paper 2 Questions and Answers - Butere Mock Exams 2021

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  1. The figure below is a pedigree diagram showing the inheritance of phenylketonuria a disease transmitted
    through a recessive gene.
    1. Using the symbols P for the normal gene and p for the phenylketonuric gene, write down the genotypes of the parents 1 and 2. (1mk)
    2. Work out the possible genotypes of the normal child 4. (4mks)
    3. Marriage between closely related individuals is always not advised in many communities. Give the biological explanation for this. (2mks)
  2. Study the diagram below and answer the questions that follow.
    1. Which part(s) marked a-d, when defective after implantation may lead to abortion. Give a reason for your answer. (2mks)
    2. The part labelled b can be removed after 4 months of pregnancy without interfering with the pregnancy. Explain. (2mks)
    3. Under each of the following, state the name of the causative organisms.
      1. Syphilis (1mk)
      2. Candidiasis (1mk)
      3. Gonorrhoea (1mk)
      4. AIDS (1mk)
    4. State 2 disadvantages of external fertilization. (2mks)
  3. The figure below shows the body temperature of a person before, during and after taking a cold bath. The temperature of the bath water is 22ºC
    1. What is homeostatis (1mk)
    2. For how long was the person in the bath? (1mk)
    3. Explain why the person’s body temperature fell. (1mk)
    4. Explain the role played by the following in helping to return the body temperature to normal.
      1. The liver (2mks)
      2. Blood vessels in the skin. (2mks)
      3. muscle of the body (1mk)
  4. Two sets of experiments were carried out to investigate a certain concept of population ecology. In each experiment, two different species of the protozoa paramecium were placed in flasks containing bacteria – rich in broth. The paramecia feed on bacteria
    1. Account for the results in:-
      1. Flask C (3mks)
      2. Flask F (3mks)
    2. Describe briefly the principle that was being investigated in the two experiments (2mks)
  5. An experiment was carried out to determine the rate of transpiration in three plants A, B and C. Plants A and B belonged to different species while plants B and C belonged to the same species. Plant C had all its leaves removed. The three plants were of similar size and were exposed to the same environmental conditions. The results are as shown in the graphs below.
    1. Suggest possible environmental conditions under which the experiment was carried out between 30 and 60 minutes (2mks)
    2. Account for the results obtained for plant C (2mks)
    3. Suggest the habitat for plant A and B. Give reasons for your answer. (4mks)
      Habitat for plant A…………………..
      Reason ………………………………
      Habitat for plant B…………………..

Answer question 6 (compulsory) and either question 7 or 8 in the spaces provided after question 8.

  1. Students investigated a certain physiological process using beans treated as described below
    Set up 1 – Beans soaked in water and introduced into a vacuum flask
    Set up 2 – Boiled beans were introduced into a vacuum flask.
    Set up 3 – Boiled beans washed in antisceptic solution
    Thermometers were used to measure temperature changes. It was observed that there was no temperature change in set up 3. The results of set up 1 and 2 shown in the table below.
    Time (days)

    Temperature (ºc)
    Set up 1 Set up 2
    1. Plot graphs on the same axis of temperature change against time (7mks)
    2. Account for the temperature change observed in set up 1 and 2
      1. From day zero to day two (4mks)
      2. After day five (4mks)
    3. Explain the observation for the physiological process taking place in set up 3 (2mk)
    4. Write a word equation for the physiological process taking place in set up 1 (1mk)
    5. The respiratory quotient of fat is 0.7 and that of carbohydrate is 1
      Explain the difference (2mks)
    1. Describe how a green leaf is adapted for photosynthesis(10mks)
    2. Describe what happens in the nervous system of a person who withdraws a finger from a very hot object (10mks)
  3. Describe locomotion in a finned fish. (20mks)


    1. Both PP; 1 mk
      Explanation: Both parents are phenotypically normal but produced a phenylketonuric child. This means that both must be heterozygous for the phenylketonuria gene; 1 mk
    2. Parental phenotypes normal normal ;
      7Possible genotype of normal child 4 is PP; or PP;
    3. Marriage between closely related individuals leads to unmasking of harmful mutations; (1 mk) that were hidden in the heterozygous state; (1 mk)
    1. C; (1 mk) it is the uterine wall where implantation occurs; (1 mk)
    2. Part b secretes the hormones oestrogen and progesterone before 4 months of pregnancy; (1 mk). This role is taken over by the placenta hence they have no active role; (1 mk). Progesterone and oestrogen maintain pregnancy
      1. Treponema pallidum; 1 mk
      2. Candida albicans; 1 mk
      3. Neisseria gonorrhoea; 1 mk
      4. Human Immuno Deficiency virus Rej. HIV 1 mk
        Note: Reject names that are not underlined (i- iii)
      • lack of protection; 1 mk
      • Low chances of fertilization; 1 mk
    1. Homeostasis is the process of maintaining a constant internal environment; eg. Body temperature, osmotic pressure;
    2. 20 minutes;
    3. In a cold bath, the body tends to lose much more heat through convection and conduction, causing the body temperature to fall;
      1. The liver (2mks)
        In the liver, heat is produced as a result of numerous chemical activities occurring there;
        The heat is distributed by blood to other parts of the body;
      2. Blood vessels in the skin. (2mks
        The low external temperature brings about a reflex constriction of the skin arterioles; less heat flows through the skin and less heat is lost;
      3. Muscle of the body. (2mks)
        Tissue respiration is very active in muscles setting free large amounts of heat; which is distributed to different parts of the body;
      1. The two paramecia share the same niche/ competes for same resources/ seeds on same food; P.Aurelia is
        faster growing/ better adapted; so it outcompetes p. caudatum
      2. The two paramecia have slightly adjustment niches so they do not compete for resources and can co – exist.
    2. Two species cannot co – exist in the same habitat; if they share the same niches; (competitive exclusion principle)
    1. Strong air currents / winds;
      High temperatures;
      Low humidity/dry conditions any 2 pts = 2mks
      Light / Bright light;
    2. Absence of leaves/stomata absent;
      Transpiration is reduced/ little transpiration; (2mks)
    3. Habitat for A: Arid/dry/desert/semi-desert; little amount of water loss/ low rate water loss
      Habitat for B: Areas of adequate water / high rainfall/ plenty of water;
      Reason: High rate of water loss / more water lost / A lot of water loss; (2mks)
    1. Scale (s) 1mk
      Axis (A) 1mk
      Identify (I) 1mk
      Curve (C) 2mks
      All points correct (P) 2mks
      Temperature 0c ½ A Time (Days) ½ A
      0 10 20 30 40 0 1 2 3 4 5 6 7 8 9
      Set up1: identify set up 2: identify ½ ½ S ½ S P√ P √C √C√ A √½
    2. Day zero to day 2
      Set up 1 – Temperature increased with time; seeds were germinating and respiring to produce energy;
      Set up 2 – Temperature remained constant within this period; since seeds were boiled. No respiration occurred;
      After day 5
      Set up 1 – Temperature reduced slightly; After germination the seedlings respired moderately;
      Set up 2 – Temperature increased with time; decomposition led to increase in heat production;
    3. Seeds in set up 3 were washed in antiseptic which killed the micro-organisms. No decomposition occurred; 2mks
    4. Glucose + Oxygen water + carbon (iv) oxide + energy; 1mk
      Rej. Chemical equation.
    5. Fat – 0.7, high amounts of oxygen is used /consumed while carbohydrate 1.0 less oxygen is consumed / substrate is completely oxidised.
      • broad leaf lamina which provides a large surface area for the absorption of carbon (iv) oxide and light energy.
      • thin leaf lamina reduces diffusion distance for light and CO2 to reach the photosynthetic cells.
      • presence of stomata ensures efficient diffusion of carbon (IV) oxide into the leaf.
      • the cuticle and epidermis are transparent to allow penetration of light to the palisade cells.
      • palisade cells contain large number of chloroplasts and their arrangement and location next to the upper epidermis enables them to receive maximum sunlight.
      • existence of extensive veins that contain vascular bundles which conduct water and mineral salts to the photosynthetic cells and removes the products of photosynthesis.
      • spongy mesophyll cells are loosely arranged , leaving large intercellular air spaces that are interconnected for rapid diffusion of carbon (iv) into the cells and oxygen out into the atmosphere.
        Max 10mks
    2. When the finger touches a very hot object; pain receptors; in the skin of the finger are stimulated; Nerve impulses are triggered off; and transmitted through the sensory neurone; to grey matter of the spinal cord; The impulse is then transmitted to the relay neurone; through the synapse; then to the motor neurone; through another synapse; Through the ventral root, the impulse is transmitted to the effector organ (bicep of the arm); which contracts; and the forearm is withdrawn; and thus the finger is raised from the hot object;
      max 10mks
  8. Locomotion in a finned fish.
    • The fish has a streamlined body shape; to reduce resistance against movement / and enable it to cut through water easily;
    • Inflexible head; that enables it to maintain forward thrush;
    • Scales overlap backwards; to allow water to pass over the fish easily;
    • Secretes mucus; which covers the body to reduce friction during movements;
    • Flexible backbone onto which segments of myotomes are attached; The muscles contract and relax to bring about undulating movements;
    • Swim bladder provides the fish with buoyancy; and help the fish adjust it vertical position in relation to depth in water;
    • Lateral line; enables the fish to detect vibrations and change of pressure;
    • Well developed fins; help the fish to move in water and maintain balance;
    • Unpaired fish / dorsal, anal and caudal reduce rolling and yawing;
    • Caudal fin propels the fish forward and steers; the fish while in motion;
    • Paired/ pectoral fins are used for maintaining balance, braking and changing direction; they also control pitching of the fish; (20mks)
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