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ANSWERS TO BIOLOGY TOPICAL QUESTIONS-Growth and Development in Plants and Animals


1.         a) Moulting hormone/ ecdysone                                                                                            

b) It allows growth to take place; since growth can not take place in the presences of the

2.         a) Long sightedness/ hypermetropia   ;                                                                                  

            b) Convex/ converging lenses;

3.         (a) – Excretion;                                                                                                                      

             – Osmo-regulation;    

            (b) – Glucose

           – Amino acids;

            (c) – Nephritis;

          – kidney stones /Gall stones;

         – Hepatitis A and B;       (mark first 2 pts (2mks)

4.         (a) Intermittent growth curve;                                                                                               

            (b) Moulting;

            (c) Ecdysone;

5.         Natural immunity is inherited /transmitted from parent to offspring; Acquired immunity

 is developed after suffering from a disease or through vaccination;

6.         A – Cell elongation/expansion ;                                                                                            

B – Cell division/multiplication ;

C – Cell différentiation/maturation ;

7.         Continuous variation shows gradation in characteristic with intermediate; discontinuous shows distinct characteristics between organisms with no intermediate groupings;                        

8.         a) to investigate the effect of the force of gravity on the growth of a seedling                     

  (shoot and root);

            b) Force of gravity cause accumulation of auxins on the lower side of the seedling

                 – Higher concentration of auxin will promote growth in the shoot but inhibit growth in the


             – There will be more/ faster growth on the upper side of the root than on the lower side hence

    the downward bending;

-There will be more/ faster growth on the lower side of the shoot than on the upper part hence

 the upward curvature;

9.         i) Between xylem and phloem;                                                                                              

10.       Growth – Increase in size of an organism or its parts due to synthesis of protoplasm         

            Development – Differentiation and formation of various tissues to perform specialized                   


11.       – Reduce competition between the young ones (larvae) ;                                                      

            – Avoid predation of the young ones as they are different ;

            – The pupa stage can withstand harsh environment by being inactive;

12.       Disadvantages of exoskeleton;                                                                                              

            – Limits growth

             – heavy to the insect;

13.       Primary growth results form the activity of primary/embryonic tissues/apical meristems and    

lead to increase in height, while secondary growth result from activities of secondary meristems; /cambium and leads to increase of girth/diameter /circumference;               

14.       i) — Oxidizes food to release energy needed for germination;                                            

            ii) — Stores food for the seed;

                         – Stores enzymes;

15.         .- Selective weeding                                                                                                            

            – Ripening of fruits

            – Parthenocorpy

                        Reject Prunning of coffee and tea

16.       – -Contraction of muscles                                                                                                       

            – Formation of bones

17.       allow growth to the place;                                                                                          

               (ii) Grain/cotyledon remains underground below the soil level: (I mark)

18.       (a)(i) Hypogeal;                                                                                                         

            (b) Photosynthesis; OWTTE

              -Gaseous exchange; accept. Transpiration.

19.       (a) Effect of unilateral/unidirectional light on shoots:                                  

            (b) Seedling/shoots growth towards light’ growth curvature towards light;

20.       (a) Intermittent growth;

            (b) Moulting /ecdysis;

            (c) Ecdysone rej. Moulting hormones;

21.       (a) Divide giving rise to more vascular tissues – phloem and xylem; hence leading to secondary

     growth/thickening of the stem; 

           (b) They lack vascular cambium;                                

22.       – It has chondrionic villis to increase surface area for excahgne of materials

             – Has thin epithelium for rapid exchange of exchanged substances

              – Has counter current flow of foetal and maternal blood to enhance speed diffusion gradient.

             – Highly vascularised (dense network of capillaries) for faster transport of exchanged material

23.       (a) For oxidation of stored food;

            (b) Breakdown and oxidation of food

24.       (a) (i) osmotaxi/cremotaxis                                                                                                    

            (ii) phototaxis

(i)Sensory neuron

            (ii)   Direction of nerve impulse                                                                                                                                                                                                            

            (iii) Schwarn cell

            (iv) insulate the axon/Speed up transmission of impulses                                                     


Reflex actionConditioned reflex action
Single stimulus to bring about response. Simplest form of behaviouir and is  independent of experience Sensory and mother  component are the same at all timesRepeatal stimulus to bring about response Involves modifications of behaviour and dependent experience . Primary sensory  component is repeat by a sensory component bat the motor. Component remains unchanged.


            (a) To absorb carbon (IV) oxide;                                                                                           

            (b) to provide moisture to germinating seeds;

            (c) (i) (Left – right direction                    );

                (ii) Oxygen in the tube is taken up by the seeds for germination; the Carbon (IV Oxide

                      Produced during respiration and the one in the tube reacts with potassium hydroxide

                      pellets; lowering the pressure inside the set-up; the higher pressure from outside  the tube

                       forces the dye in the direction shown;

26.       (i) Lag phases; Dry mass increases slowly; became in plant has not developed                  

leaves; for photosynthesis hence is depending on stored food;

(ii) Expontial phase; Rapid growth /increase in dry mass, leaves developed; photosynthesis taking place leading to accumulation of food and rapid cell division / plant adapted to the environment

(iii) Death phase/ senescence; Negative growth/decrease in dry mass as some tissues die after reaching maximum maturity; Fall in photosynthesis activity; toxic wastes poison tissues;

(c) (i) When dry mass was first recorded/at germination

     (ii) Dry mass would decrease first because food is oxidized to produces energy; water and   

        carbon  dioxide/utilized in respiration;

(d) (i) Harvest every week about five seedlings; dry in oven to a constant dry mass; Calculate the average mass for one seedling and record the results.

   (ii) Advantage; Dry mass is not affected by environmental conditions while fresh weight is

        dependent on the amount of water in the plant which fluctuate with environmental factors

       affecting transpiration rate.

27.       a)klinostat/clinostat;                                                                                                  

          b)i)the radicle remains /grow horizontally;                                                                                                 

             ii)rotation  of klinostal causes uniform distribution of auxins/ indoleacetic acid; hence

      uniform growth/clongations (no curvature  formed);                                                                            c)the  experiment repeated but with stationary klinostat;                                                                            

             d)-(tropism)enable plants  to get water-hydrotropism;

                 -chemotropism aids  plants in fertilization  and  nutrients absorption;

                 -thigmotropism enable  weak plants  to obtain support

                 -phototropism enable  plants  to  obtain light for photosynthesis;

                 -geotropism enables the roots grow down the  soil towards the  centre of the earth  thus 

                   providing  support to the plant

28.       a)graph                                                                                                                                               

-axes have to be labelled- ½ mk@-1mk No axes marking  stops there.

-scale-should  be appropriate and workable- ½ mk @-1mk

-plotting  correctly-1mk@*RCH*∗wrong scale stop marking.

-curve-smooth and not extrapolated beyond 3 small  squares- ½ mk@-1mk

-identity- ½ mk each-*RCH*

Note/ -axes reversed-award only for identity

 -no origin-award only for one scale/vertical one.

b) i)bamboo;                                                                                                                                                           

  ii)(bamboo)have  higher average weigh

            c) i)average height of maize  plant between weeks 14  and 18 constant (at 2.1m); maximum 

      height attained;   average weight increased; because there  was slight increased in the girth;                        

   ii) dry weight represents the  actual dry  matter/fresh weight  includes weight of water;                        

               iii)-average height was determined by measuring the  length; of the plants at various intervals;

                 -average dry  weight was determined by heating the plants to exclude all the water;  and then  

                    taking their  dry weights;

            d) both height  and weight are used to  show  rates  of  growth;

e) lacks  cambium(tissue)hence no secondary thickening;

29.       a) Fusion of an egg cell nucleus with sperm cell nucleus; to form a zygote 

            b)         i) Meiosis

                        ii) In the testis/ testes/ ovary/ ovary

            c)         i) There is increased blood supply causing thickening of the uterine walls;

                        ii) Capillaries break up/ endometrium is lost with some blood/ menstruation occurs


  • Large number/ numerous blood vessels to increase surface area for exchange of materials
  • Thin membrane for faster diffusion across it
  • Has villi to increase surface area for diffusion
  • Special cells to produce hormones
  • Membrane selectively allows materials across it

30.       a) Number of seeds that germinate     X 100  = % seed germination                                    

                  Number of seeds planted

            b) Seeds dry mass would have resulted in death of embryo thus no germination

            c)i)  Mean seedling fresh mass include the mass of water that has not resulted from growth

            ii) At regular intervals of time; uproot seedlings (say five each) dry to constant weight,

             and record

            d) Directly proportional / Increase in seed mass results in increase in % seed germination,

                survival and seedling fresh mass

            e) Embryo well developed/ Embryo very mature;

            – Large food reserves for growth and development

30.       a) Directly proportional/ increase in enzyme concentration results in increase in    

reaction rate

            b)         i) Increase in substrate concentration results in increase in reaction rate

                        Increase in concentration results in more active sites occupied by substrate

                         molecules, resulting in higher turn over

                        ii)A rate of reaction constant/ does not change

                                    Active sites fully occupied

                        iii) Sharp decrease in reaction rate

                                    Enzymes denatured

            c) PH/ Enzyme inhibitors/ Enzyme co- factors

31.       a)        


            b) the rotation of the  machines/ klinostat  ensured equal  distribution  of Auxins in the 

seedling (upper & inner) side;

 c) Klinostat;

 d) radicle grow  dominants; plumule  grow upwards;



32. (a) (i) Carbam inohaemoglohin:               

      (weak) Carbonic acid: (2marks)

                 (ii) Oxyhaemoglobin; (I mark)

            (b) Secretes pleural fluid:

                 – Makes lungs air tight:(OWTTE) (2marks)

(c ) Carboxyhaemoglobin doesn’t dissociate readily (OWTTE):

                Hence its formation reduces the capacity of haemoglobin to carry oxygen to time lungs

hence resulting in death: (2marks)

(d) Cuticle: lenticels: (Both to be correct to score I mark) (I mark)

33.       (a) Region of rapid growth / cell elongation in a radicle: root                                              


(c ) Dense cy1oplasms

                 Lack cell vacuoles

                Thin cell walls

(d)  -Presence of germination inhibitors / abscicic acid:

                   – Low concentration of hormones / Enzymes/ gibberclic acid:

                 – Impermeable seed coats to water and oxygen:

                 – Embryo not fully developed:

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