Biology Paper 1 Questions and Answers - Form 4 Term 3 Opener Exams 2023

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

1. Give a reason why using a sharp blade is necessary when sectioning during preparation of specimens for observation under the microscope.                                                          (1mk)
2. The following reaction may occur in a forward and backward direction
   Water + Carbon (IV) Oxide  Glucose + Oxygen + Energy
   1. Name the organelle where the above reaction occurs.
      1. Forward direction                                                                     (1mk)
      2. Backward direction                                                              (1mk)
   2. Give one difference for the two organelles named in (a) above    (1mk)
      

      Chloroplast	Mitochondrion

3. The chart below represents how respiratory gases are transported in the human blood.
   
   1. Identify gas Y. (1mk)
   2. Name the advantages that oxyhaemoglobin has over carboxyhaemoglobin.    (2mks)
4. The paddles of whales and the fins of fish adapt these organisms to aquatic habitats.
   1. Name the evolutionary process that may have given rise to these structures.        (1mk)
   2. What is the name given to such structures?                     (1mk)
   3. Give two examples of vestigial organs in man.         (2mks)
5. State one physiological and one structural difference between a cell wall and cell membrane.              (2mks)
   

   	Cell wall	Cell membrane
   Physiological
   Structural

6. Name the organelles that carry out the following functions                                              (2mks)
   1. Formation of spindle fibres
   2. Osmoregulation
7. The diagram below shows part of alimentary canal of a mammal 
   
   1. Name the parts labeled A and C                                              (2mks)
   2. State the function of the part labeled B.                                               (1mk)
8. Name the part of the chloroplast where the following reactions occur.
   1. Carbon (IV) oxide fixation. (1mk)
   2. Photolysis. (1mk)
9. Polydactyl is a genetic disorder in which people inherit an extra digit. Polydactyl is caused by a dominant allele (B). The table below describes the different genotypes for polydactyl.
   1. Complete the table below by giving the correct genotype, alleles of each genotype and the expected number of fingers per hand.   (4mks)
      

      Genotype	Alleles	Expected number of digits per hand
      Homozygous dominant		Six
      	bb
      Heterozygous	Bb

   2. The table below shows results of marriages between various parents. Complete the table by writing the probability of each marriage producing a child with polydactyl. One has been done for you. (2mks)
      

      Parental genotypes.	Probability of child with polydactyl
      Bb X BB	1
      Bb X bb
      Bb X Bb

10.  What are the end-products of respiration in animals when there is sufficient oxygen supply?  (1mks)
11. State two characteristic of visking tubing used in osmosis process?                          (2mks)
12. Explain the physiological process responsible for keeping the seedlings upright.            (3mks)
13. List down substances that depend on diffusion, to be exchanged across the placenta of a female Human being.              (3mks)
14.  
    1. What is meant by the term seed dormancy?                           (1mk)
    2. State any two external causes of seed dormancy             (2mks)
15. Explain what is meant by the following terms?
    1. Plasmolysed cell                     (2mks)
    2. A crenated cell                      (2mks)
16. List down any two domestic applications of anaerobic respiration                              (2mks)
17. State two processes through which heat energy produced by respiration lost from human body?(2mks)
18. Account for the absence of glucose and proteins in the glomerular filtrate.
    1. Glucose                (1mk)
    2. Proteins                                       (1mk)
19. Plants relatively have less waste to excrete than animals. Give two reasons to explain this observation.             (2marks)
20. Homeostasis is defined as the maintenance of a stable internal environment in the body. What is meant by expression ‘internal environment’? (1 mk)
21. Name one factor that is maintained at a relatively constant level in the body by the following organs.             (2mks)
    1. Liver 
    2. Kidneys
22. Explain two ways in which the trachea is adapted to perform its functions.          (2mks)
23. The diagram below represent the reflex arc in human 
    
    1.  Name the parts labelled P and S                                                                  (2mks)
    2. State the function of the part labelled Q                                                    (1mk)
    3. Name the fluid contained in part labelled R.                                               (1mk)
24. State two classes of the classes of the phylum Arthropoda in which the body is divided into cephalothorax and abdomen.   (2mks)
25. Briefly explain two adaptive features present in animal respiratory surfaces that are absent in plant respiratory surfaces.      (2mks)
26. State two external characteristics that distinguish mammals from other vertebrata     (2mks)
27. State two functions of the choroids in the human eye.         (2mks)
28. Explain the effect of temperature above 40°C to the germinating seed.                        (4mks)
29. Examine the diagrams below and answer the questions that follow.
    
    1. Give the identity of bone shown in the diagram above (1mks)
    2. Give two reasons for your answer in a(i) above              ( 2mks)
30.  
    1. State two effects of dumping untreated sewage into a river.              (2 mks)
    2. Name the causative agents of amoebic dysentery disease in human.              (1 mk)
31. What is the importance of the following in external fertilization?
    1. Laying of many eggs (1 mark)
    2. Mention two adaptations of human sperm to its function ( 2 mks)

MARKING SCHEME

1. Give a reason why using a sharp blade is necessary when sectioning during preparation of specimens for observation under the microscope. (1mk)
   • Avoid distortion of the specimen;
2. The following reaction may occur in a forward and backward direction
   1. Name the organelle where the above reaction occurs.
      1. Forward direction                                                                           (1mk)
         • Chloroplast;
      2. Backward direction                                                                         (1mk)
         • Mitochondrion;
   2. Give one difference and one similarity for the two organelles named in (a) above      (2mks)
      
      1. Similarity
         • Both have a double membrane;
         • Both have fluid filled cavity;
      2. Differences
         

         Chloroplast	Mitochondrion
         Has Grana Has fluid Stroma	has Cristae; Has fluid Matrix;

3. The chart below represents how respiratory gasses are transported in the human blood.
   1. Identify gas Y. (1mk)
      • Carbon (II) oxide; 
   2. Name the advantages that oxyhaemoglobin has over carboxyhaemoglobin. (2mks)
      

      Oxyhaemoglobin	Carboxyhaemoglobin
      Unstable hence dissociates releasing oxygen to the tissues	Stable hence does not easily dissociate;

4. The paddles of whales and the fins of fish adapt these organisms to aquatic habitats.
   1. Name the evolutionary process that may have given rise to these structures.         (1mk)
      • Convergent evolution;
   2. What is the name given to such structures?                     (1mk)
      • Analogous structures;
   3. Give two examples of vestigial organs in man.         (2mks)
      • Coccyx; appendix; reduced ear muscles/nictating membrane/reduced body hair;
5. State one physiological and one structural difference between a cell wall and cell membrane. (2mks)

   	Cell wall	Cell membrane
   Physiological	Fully permeable	Semipermeable;
   Structural	Made of cellulose	Made of lipoprotein;

6. Name the organelles that carry out the following functions                                              (2mks)
   1. Formation of spindle fibres
      • Centrioles
   2. Osmoregulation
      • Contractile vacuole
7. The diagram below shows part of alimentary canal of a mammal
   1. Name the parts labeled A and C                                              (2mks)
      • A - oesophagus /gullet  (reject food pipe)
      • C - duodenum         
   2. State the function of the part labeled B.                                               (1mk)
      • Temporally storage of feaces / undigested /indigestible materials /Absorption of water;
8. Name the part of the chloroplast where the following reactions occur.
   1. Carbon (IV) oxide fixation. (1mk)
      • Stroma;
   2. Photolysis. (1mk)
      • Grana;
9. Polydactyl is a genetic disorder in which people inherit an extra digit. Polydactyl is caused by a dominant allele (B). The table below describes the different genotypes for polydactyl.
   1. Complete the table below by giving the correct genotype, alleles of each genotype and the expected number of fingers per hand. (4mks)

      Genotype	Alleles	Expected number of digits per hand
      Homozygous dominant	BB	Six
      Homozygous recessive	bb	Five
      Heterozygous	Bb	Six

   2. The table below shows results of marriages between various parents. Complete the table by writing the probability of each marriage producing a child with polydactyl. One has been done for you. (2mks)

      Parental genotypes.	Probability of child with polydactyl
      Bb X BB	1
      Bb X bb	0.5/ 50%/ ½;
      Bb X Bb	0.75/ 75%/ ¾;

10. What are the end-products of respiration in animals when there is sufficient oxygen supply?   (3mks)
    • Energy/heat;
    • Carbon (iv) oxide;
    • Water;
11. state two characteristics of visking tubing used in osmosis process?                          (2mks)
    • Its semi-permeable;
    • It’s a thin membrane;
    • Its synthetic;
12. Explain the physiological process responsible for keeping the seedlings upright            (3mks)
    • Its due to osmosis; water is drawn into the cells; becoming turgid providing mechanical support;
13. List down substances that depend on diffusion, to be exchanged across the placenta of a female Human being.          (3mks)
    • O₂  gas (from the maternal blood to foetal blood)
    • CO₂  gas (from the foetal blood to maternal blood)’
    • Some digested foods;   
14.  
    1. What is meant by the term seed dormancy?                                                                    (1mk)
       • A period (of rest) in which a seed performs its physiological processes slowly (and utilize little food);
    2. State any two external causes of seed dormancy                                                                         (2mks)
       • Low/freezing temperatures;
       • Lack of appropriate light wavelength
15. Explain what is meant by the following terms?
    1. Plasmolysed cell                                                                                       (2mks)
       • A plant cell that has lost water by osmosis; and has become flabby/ shrunk;
    2. A crenated cell                                                                                                 (2mks)
       • an animal cell  that has lost water by osmosis; anad shrunk;
16. List down any two domestic applications of anaerobic respiration                              (2mks)
    • Fermentation of dairy products yoghurt, sour milk etc
    • Fermentation of porridge;
    • Production of biogas;
    • Preparation of sillage;
    • Baking of cakes/bread;
17. State two processes is heat energy produced by respiration lost from human body?   (2mks)
    • Conduction
    • Convection/sweating/perspiration;
    • Radiation;
    • urination
    • Defaecation;
18. Account for the absence of glucose and proteins in the glomerular filtrate.
    1. Glucose                (1mk)
       • All glucose reabsorbed at proximal convoluted tubule;
    2. Proteins                               (1mk)
       • Proteins not filtered into glomerular filtrate as molecules too large to pass through capillary pores;
19. Plants relatively have less waste to excrete than animals. Give two reasons to explain this observation.   (2marks)
    • Plants reuse some of their waste products; Plants produce their waste products slowly compared to animals that produce slowly;
20. Homeostasis is defined as the maintenance of a stable internal environment in the body. What is meant by expression ‘internal environment’? (1 mark)
    • Tissue fluid/ Intercellular fluid/ Interstitial fluid;] Acc. Surrounding of the body cells
21. Name one factor that is maintained at a relatively constant level in the body by the following organs.  (2mks)
    1. Liver 
       • Blood glucose (Reject: sugar) level;
    2. Kidneys
       • Osmotic pressure/ Water content/ Osmolarity of body fluids (Accept: blood and tissue fluid) Accept: pH of body fluids (Accept: blood and tissue fluid);
          Reject: Osmoregulation
22. Explain two ways in which the trachea is adapted to perform its functions.  (2marks)
    • Made up of rings of cartilage to ensure it does not collapse (or to keep it open always) during breathing. Also they enable the tubes   to be stretched e.g. during coughing;
    • Hollow tube to allow passage of air into the lungs.
    • The incomplete rings (c-shaped) have gaps on the side facing the oesophagus which allow smooth swallowing;
    • The inner lining of the trachea has mucus to trap and filter   micro-organisms and dust particles preventing them from entering the lungs;
    • The trachea is lined with cilia which beat in waves and move mucus and other foreign particles upwards into the pharynx;
23. The diagram below represent the reflex arc in human
    1. Name the parts labelled P and S                                                                  (2mks)
       • P-Dorsal root ganglion
       • S-grey matter
    2. State the function of the part labelled Q                                                   (1mk)
       • Part through which motor neuron leaves the spinal cord
    3. Name the fluid contained in part labelled R.                                              (1mk)
       • Cerebrospinal fluid
24. state two classes of the classes of the phylum Arthropoda in which the body is divided into cephalothorax and abdomen.     (2mks)
    • Arachnida
    • Crustacea
25. Briefly explain two adaptive features present in animal respiratory surfaces that are absent in plant respiratory surfaces.      (2mks)
    • Highly vascularized for transport of respiratory gases;
    • thin epithelial lining to reduce diffusion distance;
26. State two external characteristics that distinguish mammals from other vertebrates     (2mks)
    • Body covered with fur/hairs;
    • Has external ear/pinna;
27. State two functions of the choroids in the human eye. (2 marks)
    • Has numerous blood vessels to supply nourishment of the eye cells;
    • Has dark pigment to absorb stray light;
28. Explain the effect of temperature above 40°C to the germinating seed.                             (4mks)
    • The temperature would denature the respiratory enzymes; the stored food would
    • Not be hydrolysed/broken down; leading no germination;
    • Higher temperature would kill the embryo;
29. Examine the diagrams below and answer the questions that follow.
    1. Give the identity of bone shown in the diagram above (2marks)
       • Cervical vertebra;
    2. Give two reasons for your answer in a(i) above         ( 2marks)
       • Presence of branched transverse processes;
       • Presence of vertebrarterial canals;
30.  
    1. State two effects of dumping untreated sewage into a river. (2 marks)
       • leads to eutrophication, kills organisms in water;
       • Changes the water PH, reduces amount of oxygen in water;
       • Causes water borne diseases eg cholera;
       • Reduces the quality of water for consuming;
    2. Name the causative agents of amoebic dysentery disease in human.    (1 mk) 
       • Entamoeba histolytica
31. What is the importance of the following in external fertilization?
    1. Laying of many eggs (1 mark)
       • to increase chances of survival since the fertilized eggs could be attacked by predators or micro-organisms;
    2. Mention two adaptations of human sperm to its function ( 2 marks)
       • have large nucleus which contains haploid genetic material;
       • Has an acrosome which contains lytic enzymes which dissolves the membrane of an ovum for 
       • Penetration;
       • Has a long tail which propel the sperm towards the ovum by its side-to-side movement;
       • Has numerous mitochondria to provide the energy necessary for propulsion of the sperm towards the ovum;