Biology Paper 1 Questions and Answers - KCSE 2020 past papers

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Instructions to candidates

  • Answer all the questions.
  • Candidates should answer the questions in English.

Answer all the questions in the spaces provided.

  1. Name the taxonomic grouping that contains individuals with most similarities.   (1 mark)
  2. Name the characteristic of living organisms shown by each of the following:
    1. budding in yeast; (1 mark) 
    2. enlargement of the eye pupil in dim light.  (1 mark)
  3. Explain why there is no grass in most dense forests. (2 marks)
  4. State one structural difference between a cell wall and a cell membrane. (1 mark)
  5. The diagram below shows an organism in a certain Kingdom.
              mushroom diagram
    1. Name the Kingdom to which the organism belongs. (1 mark)
    2. State the mode of nutrition for the organism. (1 mark)
      1. Name the part labelled E. (1 mark)
      2. State two functions of the part labelled E. (2 marks)
  6. State the importance of a well-developed blood capillary network in the alveoli. (1 mark)
  7. Name the genetic disorder in humans that is characterised by inability of blood to clot. (I mark)
    1. Sketch a graph on the axis below showing how temperature affects the rate of diffusion. (1 mark)
      graph on temperature affecting diffusion rate
    2. Account for the shape of the sketch made in (a) above. (2 marks)
    1. Explain why plants have lower respiratory rates compared to animals. (l mark)
    2. State two situations in plants when the rate of respiration rises more than normal. (2 marks)
  10. Explain why most plants growing in water-logged areas die before attaining maturity. (3 marks)
  11. The diagram below shows the plan of a pentadactyl limb.
     pentadactyl limb diagram
    Name the bones labelled K and L.
    K  (1 mark)
    L  (1 mark)
  12. With reference to germination explain:
    1. the meaning of the term imbibition (1 mark)
    2. why the dry mass of the endosperm decreases while that of the embryo increases. (2 marks)
  13. State two characteristic features used to classify members of Class Coniferales. (2 marks) 
  14. The graph below represents a growth curve in a certain Phylum.
             curve of a phylum
    1. Name the type of growth curve shown. (1 mark)
    2. Name the Phylum where members show the type of growth curve illustrated. (1 mark)
    1. State two limitations of using fossil records in retracing evolutionary history of living organisms.(2 marks)
    2. Describe cell biology as an evidence of organic evolution. (3 marks)
  16. The illustration below shows a summary of the main phases of the human menstrual cycle.
             Huma menstrual cycle
    1. Name the process that takes place around the 14th day. (1 mark))
    2. Name two hormones produced at the follicular phase. (2 marks)
    3. Under which two conditions would the cycle be interrupted? (2 marks)
  17. State two reasons why blood reaching the glomerulus is always under high pressure. (2 marks)
  18. During a clinical laboratory test, some sugar was detected in an individual's sample of urine.
    1. the hormone that was deficient in the patient: (1 mark)
    2. the gland that produces the hormone named in (a) above; (1 mark) 
    3. the disease the individual was likely to be suffering from. (1 mark) 
  19. The graph below illustrates the effect of pH on certain protein-digesting enzymes, S and T.
             graph on effects of PH on enzymes
    1. Name enzymes S and T.
      S (1 mark)
      T (1 mark)
      1. Name the part of the alimentary canal where enzyme T is likely to be found. (1 mark)
      2. Explain your answer in b(i) above. (2 marks)
  20. Explain the biological significance of completing a dose of antibiotics. (3 marks)
  21. State two reasons why females with Turners' Syndrome are infertile. (2 marks)) 
    1. Define the term "field of view" as used in microscopy. (1 mark)
    2. State two functions of the body tube of a light microscope. (2 marks)
    3. Give a reason why it is not advisable to use water in cleaning a microscope. (1 mark) 
  23. Explain the role of blood capillaries in thermoregulation. (2 marks)
  24. The illustration below shows the effect of hormones on insect growth and development.
             diagram on effects of hormones on insects
    1. Name:
      1. the hormone K (1 mark)
      2. gland L that produces ecdysone hormone (1 mark)
    2. State the role of ecdysone hormone in the growth and development of insects. (1 mark)
      1. Name process M (1 mark)
      2. Account for the rapid increase in size of organisms immediately after moulting. (2 marks)
    1. Complete the table below on the adaptations and functioning of some structures in a dicotyledonous stem. (2 marks)
        Part  Adaptation   
    2. Explain why the leaf of a sisal plant has a thick and shiny cuticle. (2 marks)
  26. Explain why an individual with blood group AB can only donate blood to an individual with the same blood group. (2 marks)
  27. The diagram below illustrates a set of biological processes in a green plant. 
    biological process in a green plant      
    1. Name:
      1. process N (1 mark)
      2. polysaccharide p (1 mark)
    2. State two conditions necessary for the formation of compound Q. (2 marks)
    3. State two environmental conditions necessary for process N to take place. (2 marks)


    • Species.
    1. Budding in yeast;
      • (Asexual) reproduction; Rej sexual
    2. enlargement of the eye pupil in dim light.
      • Irritability/ Response (to stimulus) /Sensitivity

    • Form canopies/shadows/shade; which prevent light from reaching grass; grass die/fail to flourish due to their inability to photosynthesis; 

    • Cell wall is (fully) permeable while cell membrane is semi-permeable.
      (cell wall has larger pores while cell membrane has smaller pores)
    • Cell wall is (mainly) made up of cellulose (fibres) while cell membrane has a (double) protein layer sandwiching a lipid layer; Acc. lipoprotein
    • Cell wall is rigid, tougher ( cannot burst) while cell membrane is weaker (bursts)
    1. Fungi; Acc. fungi
    2. Saprophytism/saprophytic/food on dead decaying (organic) matter; Rej. Saprophyte
      1. Hypha/Hyphae; Acc. mycelium Rhizoids
        • Secretes digestive enzymes(for external digestion); 
        • Anchors the organism/mushroom (firmly) onto the substrate. Acc. anchorage.
        • Absorbs digested food materials/Absorbs water and mineral salts/ions.
  3. Increases the surface area for (efficient) exchange/transport of respiratory gases ( oxygen and carbon (IV) oxide)
  4. Haemophilia; Acc. Hemophilia
      1 diagram on temp against diffusion  Diagram 2 on temp against diffusion   Diagram 3 on Temp against diffusion
    2. The rate of diffusion increases with the increase in temperature; Increase in temperature increases the kinetic energy of the (diffusing) molecules (increasing the rate of diffusion).
    1. Plants are less active than animals, hence require lower amount of energy than animals.
      • During germination (to generate energy required for the process.
      • During rapid growth/cell division (at the tips of roots/shoots).
      • During active uptake/transport of substances (through the roots).
    • Waterlogging submerges the plant root system; Cutting off supply of oxygen to the roots/soil surrounding the roots.
    • (Aerobic) respiration in the roots is hampered
    • active uptake/transport of materials is affected (leading to the death of the affected plants).
  8. K- Ulna
    L- Radius
    1. (Rapid) absorption of water by (germinating) seed (through the micropyle/seed coat).
    2. During germination, stored food in the endosperm is broken down/hydrolyzed/oxidized; to provide nutrients for the growing embryo.
    • Presence of cones
    • Naked seeds, seeds not enclosed in fruits
    • Xerophytic characteristics/needle-like leaves/ thick waxy cuticle/sunken stomata.
    1. Intermittent/staircase (growth curve)
    2. arthropoda; correctly spelt
      Acc. arthropoda/Athropoda/athropoda    Rej. Anthropoda/ anthropoda
      • Missing links due to complete decomposition of some organisms. 
        Acc. some parts decomposing
      • Distortion of parts during sedimentation.
      • Destruction of fossils by geological activities (earthquakes/faulting/mass movement of earth surfaces/volcanicity) 
      • Presence of similar cell organelles ( mitochondria, ribosomes,lysosomes);
      • Similar biological chemicals(ATP/proteins/DNA); 
      • Similar blood pigmentation in tissues of some groups of animals show they have a common phytogenetic origin.
    1. Ovulation
      • Follicle stimulating hormone Rej. FSH
      • Oestrogen/Estrogen
      • Luteinizing hormone  Rej. LH
      • Sickness
      • (Drastic) change in weather/environment.
      • Pregnancy/Implantation/Conception   Rej. fertilisation
      • Emotional instability (anger, stress, anxiety).
    • Renal artery branches directly from (dorsal) aorta whose blood under pressure
    • Afferent arteriole/supplying blood is broader than efferent taking out blood.
    1. Insulin
    2. Pancreas
    3. Diabetes mellitus    Rej. Diabetes alone
    1. S - Pepesin; Acc.  Chymosin/Rennin  Rej. Renin
      T- Trypsin
      1. Duodenum
      2. In the duodenum, the medium is alkaline/basic; favouring the optimal working of the enzyme (T) as illustrated
  17. To completely kill/contain the (targeted) pathogens; Since failure to take full dose accords the pathogens an opportunity to develop resistance to the drug; the pathogen mutates(overtime) giving rise to a new strain; finally the drug becomes ineffective.
    • They lack ovaries
    • Have small uterus
    • Less number of chromosomes.
    1. A circular area seen (on the stage) when focusing/viewing through the eyepiece of a microscope.
      • Holds the revolving nose piece/objective lenses in place
      • Holds the ocular/eyepiece (lens) in place
      • To avoid rusting
      • To avoid interference with visibility of the lens.
    • Constrict during cold/low temperatures; to conserve heat
    • Dilate during hot/high temperature; to facilitate heat loss
      1. Juvenile (hormone)
      2. prothoracic (gland)
    2. Ecdysone (hormone) causes metamorphosis; or causes the larval stage (of an insect to change/metamorphosize into pupa and pupa into adult.
      1. Complete Metamorphosis
      2. During moulting (the tough/hard impermeable) exoskeleton is shed; allowing the (soft permeable) larvae to take in air/water leading to rapid growth (which in turn results to increase in size of the organism).
        Part  Adaptation   
        Cambium  (Small) cells with dense cytoplasm to enable rapid mitotic division/giving rise to secondary growth.
       Parenchyma     Have thin walls for faster passage of materials
      have large vacuole/irregular shape for storage/provide space for packing.
      • (Sisal is a xerophyte) the thick cuticle enables it to conserve water; reduce water loss;
      • It is shiny to reflect light,minimizing evaporation by radiation.
  23. The individuals blood has both antigen A and B; which will coagulate/agglutimate with antibodies a and b; found in individuals with blood groups A,B and O; OWTTE
      1. Photosynthesis
      2. Starch
      • Respiratory enzymes
      • Absence/little oxygen
      • Optimum temperature
      • Light
      • Water/Moisture
      • Carbon (IV) oxide
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