Biology Paper 2 Questions and Answers - Form 3 End Term 3 Exams 2023

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  • This paper consists of sections A and B answer all questions in section A
  • In section B answer question 6 compulsory and either question 7 or 8 
  • Answer all the questions
  1. The figure below represents a set up that was used to investigate a certain process in a plant.
    1. State the aim of the experiment. (1mk)
    2. Why was sodium hydrogen carbonate added to water in this experiment? (1mk)
    3. Explain why the number of bubbles reduced by evening. (2mks)
    4. Explain the use of the following in this experiment
      1. Water plant (2mks)
      2. Wooden block (1mk)
    5. Write a word equation to represent the chemical process being investigated. (1mk)
  2. The figure below represents a diagram of a potometer
    1. What is the potometer used for ? (1mk)
    2. State the precautions which should be taken when setting up a potometer (3mks)
    3. Explain what you will expect if set up was placed under the following environmental conditions;
      1. Dark room (2mks)
      2. Leafy shoot enclosed in polythene bag (1mk)
      3. In a current of air created by a fan (1mk)
  3. In an experiment to investigate on aspect of digestion, two test tubes A and B were set-up as shown in the diagram below;
    The test tubes were left in the bath for 30minutes.The content of each test tube was then tested for starch using iodine solution:-
    1. What was the aim of the experiment? (1mk)
    2. What results were expected in test-tube A and B (2mks)
    3. Account of the results you have given in (b) above in test tube A and B
      Test tube A    (2mks)
      Test tube B   (2mks)
    4. Describe the procedure of testing for starch (1mk)
  4. The diagram below represents a part of thoracic region of a human being;
    1. Name the structures labeled K and L (2mks)
    2.  How does structure R bring about inhalation (4mks)
    3. Give the scientific name of the organism that causes whooping cough (1mk)
    4. Name the main site of gaseous exchange in human being. (1mk)
  5. The diagram below shows the vertical section of a female reproductive system
    1. Name the parts labeled A and B (2mks)
    2. Name the gonadotrophic hormone that affects the part labeled A (1mk)
      1. State a hormone(s) produced by each of the following structures in a female: (2mks)
      2. State one effect of each of the above hormones on uterine wall (2mks)
    4. Name a sub-division in the kingdom plantae that exhibit double fertilization (1mk)
                                                                                  SECTION B (40 MKS)
                      Answer question 6 (Compulsory) and either question 7 or 8 in the spaces provide after question 8
  6. The table below shows the changes observed in the dry weight (in milligrams) of a barley seedling, its embryo and endosperm during the first ten days after the onset of germination.
                                             DRY WEIGHT IN MILLIGRAMS
                   0              2                   41                          45 
                   2              2                   39                          43 
                   4              7                   32                          41 
                   6             15                   21                          38 
                   8             22                   11                          35 
                  10              35                   6                         43

    1. Using a suitable scales on the same axis, plot graphs of dry weight of embryo endosperm and whole seedling against time. (8mks)
    2. State and account for the changes in dry weight shown by:
      1. Embryo (4mks)
      2. Endosperm (4 marks)
    3. Explain the role of water during germination. (4 marks)
    1. Describe the process of fertilization in a flowering plant. (15mks)
    2. State the changes that take place in a flower after fertilization. (5mks)
    1. Describe the dentition of carnivorous mammals and their adaptation to the mode of feeding. (10mks)
    2. Activities of humans are contributing to the pollution of water bodies. Describe the causes and methods of controlling water pollution in Kenya. (10marks)

                                                                                           MARKING SCHEME

    1. The aim of the experiment is to test the plant for photosynthesis.
    2. Adds carbon (IV) oxide to the water;
    3. At evening the light intensity has reduced; hence reduction in the rate of photosynthesis;
        • Water plants are able to extract dissolved carbon(IV)oxide in water;
        • Water plants are able to use low light intensity under water;
      2. Facilitate air circulation/ movement in water;
    1. Measure rate of transpiration;
      • Assemble apparatus under water;
      • Apply vasectomy between cork shoot contacts;
      • Open the reservoir tap;
      1. The air bubble will not move, no photosynthesis in absence of light/ dark place;
      2. Water droplets will be seen in the polythene because of trapped and condensed water vapour;
      3. Air bubble will move faster due to increased rate of transpiration. Air current drive away water moisture around the leaves of plants and increase the saturation deficit
    1. To investigate the effect of boiled saliva on starch/to show the effect boiled/denatured enzyme amylase has on starch;
      • A - brown colour/ colour of iodine persists;
      • B - blue black/ blue colouration;
      • A - starch has been digested/ starch has been broken down/ amylase hydrolyses starch; hence no colour changes;
      • B - enzymes/amylase denatured; hence no starch digested;
    4. Put the 2cm3 of food substance into a test tube add 2/3/4 drops of iodine solution;
    5. Note: a known volume mentioned eg Rj if the volume is presented as 2cm. A definite number of drops mentioned Rj. A range eg 2-3 drops
      • K - pleural membrane ;
      • L – intercostal muscles; acc external and internal muscles
        rej intercostal muscle 2mks
    2. R (diaphragm) muscles contract; causing it lie flat / flatten; This increases volume of the thoracic cavity / lungs; (hence lowering the pressure inside) and air is forced in; 4mks
    3. Bordetella pertussis scientific rules to be followed 1mk
    4. Alveolus/ alveoli 1mk
      • A...........ovary
      • B...........cervix acc uterine wall 2mks
    2. FSH (Follicle Stimulating Hormone) rej F.S . H 1 mk
        • Ovary --- oestrogen / progesterone
        • Placenta – progesterone 2 mks
        • Oestrogen – causes repair and healing of endometrium 1mk
        • Progesterone----- 
          1. causes thickening of endometrium
          2. Causes increased blood flow any 1 = 1mk
          3. (vascularisation ) to the endometrium
    3. Angiospermaphyta
        • The  weight of the embryo is steadily increasing; cells of the embryo undergo mitotic cell division; and synthesis new protoplasm; hence the increase in weight;
        • 1st to 2nd days, the dry weight remains the same; because the enzymes breaking down the food reserve in the endosperm are being activated;
        • From 3rd day up to the end of the dry weight increases; because the products of hydrolysis in the endosperm are translocated to the embryo, and used in synthesis of new cellular components;
      2. Decrease in weight; stored food is hydrolysed; and transported to growing regions; for respirations and synthesis of new
        • 1st and 2nd days, dry weight decreases gradually; due to the hydrolysis of food reserve in the endosperm;
        • From the 3rd day, dry weight decreases rapidly until the decreases rapidly until the 8th day after which the decrease is slow; due to further hydrolysis of food reserve, the products are translocated to the embryo during germination; cellular materials;
    3. Hydrolysis of stored food;
      • Activation of enzymes and germination hormones;
      • Medium for chemical reactions;
      • Medium for transport for hydrolysed nutrients to growing regions.
      • Pollen grains a stick in the stigma surface; that surface of stigma produces a chemical substance ; which stimulates the pollen grain to produce a pollen tube/germinate. The pollen tube grows down ( into the tissue of the style) from where it derives nutrient; the generative nucleus divides to give rise to two male nuclei and the embryo sac contains eight nuclei, 2 synergids, ovum two polar nuclei, and three antipodal cells, when pollen tube reaches the micropyle the vegetative nucleus/ pollen tube nucleus in the pollen tube disintegrates and male nucleus fuses with the egg cell and form the triploid nucleus/ zygote.
      • The other male nucleus fuse with the two polar nuclei to form a triploid nucleus/ primary endosperm.
      • The process involves double fertilization.
      • Intergument changes into seed coat/ testa
      • Zygote into embryo
      • Ovary wall into pericarp
      • Ovary into fruit
      • Petals dry and fall off
      • Intergument and embroyonic mother cell form the seed
      • Flower stalk into fruit stalk
      • Have sharp pointed incisors ; for tearing and stripping flesh from bones
      • Have canines that are long / curved / pointed; for piercing , grasping and holding the prey;
      • Have got the carnassial teeth (upper fourth premolar and lower first molar) with smooth sides; sharp edges to shear and slice flesh from tendons and crush the bones;.
      • Have powerful jaw bones for powerful muscle attached; This prevents dislocation of jaws for cutting and shearing of flesh;
      • Have sharp and curved claws; for holding and grasping prey; ( 10mks)
    2. Causes of pollution/water pollutants.
      • Domestic effluents/garbage/animal bones/broken glasses/plastics/polythene;
      • Human waste/sewage;
      • Phosphate detergents;
      • Industrial wastes e.g heavy metals such as lead/copper/mercury/chromium;
      • Hot water;
      • Oil spillage;
      • Agro chemicals ;eg inorganic fertilizers;
      • Herbicides/insecticides/fungicides/pesticides;
      • Silting/soil erosion;
        Methods of control:
      • Treating domestic water; utilizing human waste in biogas production;
      • Using biotechnology;
      • Recycling of plastic/glass/polythene;
      • Banning the use of phosphate detergents;
      • Treating industrial effluents /cooling hot water before discharging;
      • Establishing industries away from water bodies;
      • Cleaning spilt oil using biotechnology/bacteria eg pseudomonas;
      • Penalizing the companies/industries/individuals that cause oil spills/water pollution;
      • Use mechanical/biological methods to control pests/weeds;
      • Use biodegradable/manure/organic fertilizers/pesticides.;
      • Use appropriate farming methods/contour farming/re aforestation/building of gabions/terracing/avoid farming on steep grounds; Total : max 10mk
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