BIOLOGY PAPER 3 Questions and Answers - Form 3 End Term 1 Exams 2023

INSTRUCTIONS TO CANDIDATES:

1.  You are provided with food substance labeled solution G. The reagent provided are Iodine solution, Benedicts solution, 2MHCl acid, 10% Sodium hydroxide solution Copper (II) sulphate and 10-% Sodium hydroxide solution.
   1. Perform food tests and fill in the table below. (12 mks)
      
      

      Food substance	Procedure	Observation	Conclusion

   2.  
      1. Name the enzyme responsible for digestion of food substance present in G in two named regions of the human alimentary canal. (2 mks)
      2. Name three deficiency diseases in children that may result from lack of one of the food substances in G. (1 mk)
2. Study the kidney diagrams below.
   
   1. 1. Name the parts labeled A, B, C and D in figure 1. (4 marks)
      2. Name the processes that take place in the parts labeled. V and W (2 marks)
   2. State two adaptations of the part labeled W. (2 marks)
   3. On the diagram name the part where counter current flow occurs. (1 mark)
   4. State two homeostatic functions of the diagram above. (2 marks)
   5. Explain what will happen to the process of urine formation in absence of vasopressin hormone.(4 marks)
3. The photographs on the leaf attached are of animals belonging to the same taxonomic unit (class).
   
   1. 1. Name the class to which the organisms in the photographs belong. (1mk)
      2. State three reasons for your answer in a) (i) above. (3mks)
   2. State three economic importance of organisms in this class. (3mks)
   3. Use the following characteristics to prepare a two step dichotomous key of the animals in the photographs. (4mks)

MARKING SCHEME

1. You are provided with food substance labeled solution G. The reagent provided are Iodine solution, Benedicts solution, 2M HCl acid, 10% Sodium hydroxide solution Copper (II) sulphate and 10-% Sodium hydroxide solution.
   1. Perform food tests and fill in the table below. (12 mks)
      
      

      Food substance	Procedure	Observation	Conclusion
      Starch	To absorb 2cm3 of G, add a few drops of iodine solution	No color change/brown color of iodine remains	Starch absent
      Reducing sugar	To about 2c3 of solution G, add 2cm3 of benedicts solution and heat (to boil)	No colour change blue colour remains	Reducing sugar absent
      Non-Reducing sugar	To about 2cm3 of solution G add 1cm3 if 2m HCl and boil. Cool and NaHCO3 dropwise until fizzing stops add 1cm3 of Benedicts solution and heat	Colour changes to orange/orange precipitate formed	No reducing surgar present
      Proteins	To about 2cm3 of solution G, add 5 drops of 10% NaOH and shake. Then add 0.5% of copper (II) sulplhate solution drop by dropl while shaking.	Mixture turns purple	Protein present

   2.  
      1. Name the enzyme responsible for digestion of food substance present in G in two named regions of the human alimentary canal. (2mks)
         • In the stomach – enzyme pepsin
         • In the duodenum – enzyme trypsin
      2. Name three deficiency diseases in children that may result from lack of one of the food substances in G. (1 mk)
         • Kwashiorkor
2.  
   1. A – Renal vein. B – Ureter. C – Kidney pelvis. D – Cortex.
   2. Has numerous mitochondria to provide energy for active transport. - Has microvilli in the inner lining to increase surface area for reabsorption of substances. - Highly vascularised for transport of reabsorbed substances. - Has a thin epithelium for rapid diffusion of substances.
   3. On the diagram to show loop of henle.
   4. Osmoregulation. - Regulation of pH.
   5. The distal convoluted tubules and collecting duct will be less permeable to water; therefore less reabsorption of water, leading to production of large volume of urine; that is dilute
3.  
   1. 1. Class insecta; rej insects
      2. Presence of one pair of antennae
         Three body parts; head, thorax and abdomen; rej. if parts are not named
         Three pairs of walking legs;
         One pair of compound eyes; (Acc. any three) b) Some are pollinators
         Some can be used as food e.g. termites - Some produce edible substances e.g. honey
         Some destroy buildings
         Some are disease vectors
         Some acts as pests and parasites Any 3 max 3mks
   2. Insects with wings ............................. go 2;
   3. Insects without wings ............................. Termite/ant;
   4. With proboscis..................................... Butterfly
   5. With mandibles ................................. Cockroach