BIOLOGY PAPER 2 Marking Scheme - 2019 KCSE Prediction Answers Set 1

1.  
   1.  
      1. Protandry: condition in which stamen/anthers of a flower mature before the carpels/pistils/stigma;(1 mark
      2. Self sterility; pollen grains from anthers of a flower fail to germinate on the stigma of the same flower ; (1 mark)
   2.  
      1. Q- Antipodal cells/embryo sac wall;
         R - Polar nucleus/nuclei;
         S - Egg call/ovum              3 marks
      2.  
         • Secrete enzymes that digest the stigma/style/ovary tissue;
         • Offer passage for male nuclei to the ovum;          2 marks
   3. Award if correctly shown in the diagram;                  1 mark

2.  
   1. Excess amino acids are deaminated/amino group is removed/amino group is converted in to ammonia; ammonia combines with carbon(iv) oxide(in the ornithine cycle) to form urea; carbohydrate group is converted into glucose for respiration/glycogen for storage;
      2NH₃+CO → CO (NH₃)₂ +H₂O                    3 marks
   2. Glomerulus; Bowman’s capsule; proximal convoluted tubule; distal convoluted tubule; 3 marks
   3.  
      1. Production of large amounts of dilute urine/diuresis; 1mark
      2. Diabetes inspidus; 1mark

3.  
   1.  
      1. Using a living organism to regulate/control/reduce/check the population of another organism; 1 mark
      2.  
         • Cats controlling mice;
         • beetles controlling water hyacinth;
         • fish in ponds controlling mosquito larvae;
         • Majimoto ants controlling scales;
         • goats controlling weeds in plantations; any 1 (1mark)
   2.  
      1. eutrophication is enrichment of water bodies with nitrates/phosphates/ammonium ions/sulphates/nutrients; due to discharge of sewage/domestic effluents/kitchen wastes containing detergents/run off water containing fertilizers; leading to rapid growth of surface plants/algae bloom/aquatic plants/phyloplanktons; 
         Acc symbols for ions (aq) must be present. 
         Rej kitchen wastes alone 
         Rej domestic wastes         3 marks
      2. (Proliferation of plants) block light from reaching plants underneath which will not photosynthesise; the plant die and decompose leading to depletion of oxygen/lack of oxygen ;( as a result) animals also die/suffocate (to death); Reg organisms die 3 marks
   3. Nitrogen (IV) oxide; sulphur (IV) oxide;
      Acc Nitrogen Dioxide and sulphur dioxide
      Rej oxides of sulphur and nitrogen

4.  
   1.  
      • Broad and flat to absorb maximum light;
      • Have chloroplasts which contain chlorophyll for trapping light;
      • Transparent cuticle to allow light to pass through;
      • Palisade cells are near the upper surface for optimum absorption of light; 2 marks
   2. X - Carbon (IV) oxide;
      Y – Oxygen;
   3.  
      1. Xylem
      2. Phloem;
   4. Starch is insoluble in water; hence osmotically inactive; this reduces the effect on absorption of water

5.  
   1. Iodine solution was poured on the agar; 1 mark
   2. Millet seeds produced amylase; that converts starch to maltose2 marks
   3. To activate the enzymes; 1 mark
   4. To increase surface area for exposure of enzymes; 1 mark
   5. Starch would not be digested since the enzymes would be denatured by boiling;
   6. Placing millet seeds that have not been soaked; in water on the agar/boiled millet seeds on the agar;

                                                                                                                                    2 marks

6.  
   1.  
      
   2.  
      1. 26 kgs± 0.5;
      2. Girls 15 yrs − Girls 13 yrs  = 39 − 33 = 6
         6 ÷ 2; = 3.0 kg/year;
   3. Girls at adolescence grow faster; there is an increase in the size of hips and breasts;
   4. Girls generally grow faster than boys /boys grow slowly compared to girls; but later after puberty they grow more steadily.
   5. Girls above ten years begin the menstruation cycle; they need more iron to replace the blood lost during menstruation;
   6. Height of the body; volume of the body;

7. Mouth;
   • With teeth for chewing to increase the surface area for digestion and easy swallowing
   • Has salivary gland which secrete saliva to soften and lubricate food for easy swallowing
   • Has muscular tongue to turn food sideways for proper mixing with saliva and chewing
   • Rolls food in to boluses and pushes them down the gullet
   • Saliva has saliva amylase to initiate digestion of starch;
     
     
   Oesophagus; 
   • Has circular and longitudinal muscles to propel food in to the stomach by peristalsis
     
     
   Stomach; 
   • Has circular and longitudinal muscles to propel food in to the stomach by peristalsis
   • Has cardiac sphincter muscles to allow/regulate food into the stomach
   • Pyloric sphincter to retain food for digestion in the stomach
   • With gastric glands that secrete mucus to protect wall of the stomach from digestive enzymes; enzymes pepsin and rennin to digest proteins;hydrochloric acid to kill bacteria in food;and provide optmum PH for protein digestion,activation of pepsnogen
   • With muscular walls whose contaction churn/mix chyne with digestive enzymes.  
     
     
   Duodenum 
   • With brunners glands in its walls to produce alkaline fluid and mucus
   • Has crypts of lieberkuhnwhose cells produce digestive enzymes
   • Is connected to the pancrease and the liver which supply pancreatic juice and bile respectively
   • Bile emulsifies fats and neutralizes the acid from the stomach. Pancreatic juice contains digestive enzymes/pancreatic lipase, pancreatic amylase and Trypsin that acts on lipids, starch/amylase and proteins respectively. 
     
     
   Ileum
   • Long to allow complete digestion and absorption of food
   • With villi and microvilli to increase surface area for digestion and absorption
   • Folded to increase surface area for digestion and absorption
   • Narrow to keep digested food in contact with epithelium to reduce distance over which food diffuses
   • With moist inner surface to enhance absorption of nutrients
   • With epithelical cells continuously replaced
   • Has lacteals for fat transportation
   • Has muscular walls for peristaltic movement of food 
     
     
   Colon 
   • Folded to increase surface area for absorption of water and mineral salts
   • With muscular walls for peristaltic movement of undigested food 
   
   Rectum;   
   • Secretes large amounts of mucus for lubrication to aid defecation
     
     
   Anus
   • With muscular sphincter to control defecation

8. Causes of air pollution 
   • Sulphur and nitrogen dioxide ;; from industries
   • Carbon (iv) oxide ( from combustion of fuels in industries and motor vehicles);
   • Dust and smoke (from quarries and factories)
   • Radio active radiations(from atomic and nuclear plants)
   • Agricultural chemicals used as sprays;
   • Noise from factories and vehicles; mark any five
     
     
   Effects on organisms 
   • Sulphur dioxide/nitrogen dioxide/dust/smoke/carbon iv oxide and agricultural sprays cause respiratory diseases; and irritate respiratory systems;
   • Nitrogen dioxide /sulphur dioxide combine with atmospheric moisture to form acidic rainfall which is corrosive; poisonsplants; lower metabolic activities/photosynthesis; acidic soils destroy vegetation.
   • Dust/ smoke reduce amount of light reaching on the plant lowering photosynthesis;
   • Carbon II oxide is a respiratory poison/combine with haemoglobin reducing oxygen carrying capacity of red blood cells;
   • Carbon iv oxide causes green house effect by forming a layer around the earth’s atmosphere/insulate the earth causing global warming/ change of climatic patterns;
   • Radioactive radiation causes mutation and cancer;
     
     
   Control methods
   
   • Erect factories and power generating station from residential areas;
   • Build factories with chimneys to discharge waste gases up the ground;
   • Educate people on dangers of air pollution;
   • Filtration of waste gases to remove poisonous pollutants before being discharged into the air;
   • Use of alternative less polluting fuels like hydroelectric power/lead free fuels;
   • Use smokeless fuels in houses and factories;
   • Banning manufacture and use of chemical weapons;
   • Impose heavy fines on air pollutors; (like factories)