Biology Paper 2 Questions and Answers - Form 3 Term 2 Opener Exams 2023

1. Below is a set up that was used to investigate a certain process in plants
   
   1. State the process that was being investigated   (1 mark)
   2.  
      1. Give two precautions that should be taken when preparing the experiment (2marks)         
      2. State a reason for each precautions stated in b (i) above  (2marks)                                     
   3.  List three structural factors that affect the process under investigation (3 marks)                   
2.  
   1. Distinguish between pyramid of numbers and pyramid of biomass.(2marks)
   2. From an ecological study, students formed the following food web
      
      From the food web, construct two food chains with lizard as tertially consumer.(2 marks)
   3.  
      1. Which organism has the least biomass in the ecosystem.(1 mark) 
      2. Give reasons for your answer in c)i) above (3marks)
3. The diagram below represents structure found in the walls of ileum.
          
   1. Identify the structure shown in the diagram. (1 mark)
   2. Name parts labelled S, T and L. (3 marks)
   3. Name products of digestion which are absorbed into; (2 marks)
   4. State how the above structure is adapted to its function. (2 marks)
4.  
   1. Name the gaseous exchange structure in the following organisms.
      1. Amoeba (1 mark)
      2. Grasshopper (1mark)
   2. The diagram below illustrates the structure of a gill from a bony fish.
            
      1. Name the parts labelled A, B, C (3 marks)
      2. State the function of the part labelled C (1 mark)
      3. How is part A adapted to carry its functions (2 marks)
5.  
   1. The diagram below shows an experimental set – up by form two students.
            
      1. State the aim of the experiment. (1mark)
      2. State the expected results at the end of the experiment. (2 marks)
      3. What conclusion can you make from this experiment? (1 mark)
   2. Examine the diagram which shows a set used to demonstrate a certain process.
              
      
      1. State the aim of the experiment. (1 mark)
      2. Why was it necessary to boil the glucose solution before adding the yeast suspension. (1 mark)
      3. Why was it necessary to cool the glucose before adding the yeast suspension?(1mark)
      4. Why was the oil layer added? (1 mark)

SECTION B(40MARKS)

Answer questions 6 (Compulsory) and either question 7 or 8 in the spaces provided.

6. Two herbivorous mammal species were introduced into an ecosystem at the same time and in equal numbers. The graph below represents their populations during the first seven years. Study the graph and answer the questions that follow.
   
   1.  
      1. Which species has a better competitive ability?(mark) 
      2. Give a reason for your answer.(1mark)       
   2. Account for the shape of the curve for species A between;
      1. One year and three years. (3mark)     
      2. 4 years and eight years. (3mark)
   3. A natural predator of species A was introduced into the ecosystem. With a reason, state how the Population of each species would be affected? (4marks)     
   4. State four other biotic factors of the ecosystem which affects organisms distribution in their habitat other than the one illustrated in the above graph.  (4mrks)
   5. Name the instruments used to measure the following;
      1. Light intensity       (1mrk)
      2. Light penetration in water          (1mrk)
      3. Speed of wind         (1mrk)
      4. Atmospheric pressure      (1mrk)
7. Describe the nitrogen cycle ( 20 mks)
8.  
   1. State four characteristics  of gaseous exchange surfaces ( 4 mks)
   2. Describe the mechanism of gaseous exchange in a mammal (16mks)

MARKING SCHEME

1.  
   1. Rate of transpiration;
   2.  
      1.  
         • Cut short under water;
         • Apply petroleum jelly to cork, glass/ bung glass;
         • Open reservoir:
      2.  
         • To ensure no air enters leafy shoot xylem; 
         • To ensure the apparatus is airtight;
         • To remove air bubbles from tube   
   3.  
      • Stomata size and number;
      • Hairy leaf;
      • Leaf size and shape;
      • Leaf fall;
      • Cuticle;     
2.  
   1. Pyramid of numbers is pictorial representation of organisms number at each trophic level  in an ecosystem while pyramid of biomass is pictorial representation of dry weight of organism species at each trophic level  of an ecosystem
   2.  
      • Green plants→ caterpillar→ small insect→ lizard→ hawk
      • Decaying leaves→caterpilar→small insect→ lizard→ hawk
   3.  
      1. Hawk
      2.  
         • Some energy lost during respiration as heat
         • Defecation
         • Source energy from structure / tissues which could not be passed over to the next level. ✔1mk
3.  
   1. Villus
   2.  
      • S – Epithelium
      • T – Lacteal
      • L – Blood capillaries
   3.  
      • L – Amino acids, glucose
      • T – Fatty acids and glycerol
   4.  
      • Supplied with blood capillaries – to transport absorbed products of digestion
      • Presence of lacteals – To transport fatty acids and glycerol
      • Lined with thin epithelium for faster absorption of products of digestion
4.  
   1.  
      1. Cell membrane;
      2. Tracheole system/Tracheoles; ( 2mks)
   2.  
      1.  
         • A. – (Gill) filament, rej. Filaments
         • B. – (Gill) bar;
         • C. – (Gill) racker; Rej: rakers
      2. Prevent solid particles from harming/injuring gill filaments;
      3.  
         • Thin membrane for fast diffusion of gases;
         • Supplied with blood capillaries to transport gases;
         • Spread singly in water to increase surface area for gaseous exchange;   Rej: moist
5.  
   1.  
      1. To find out the products formed when food is burnt/oxidized;
      2. Water vapour accumulates on the walls of test tube; while lime water in test tube B forms white  precipitate;
      3. When burnt /oxidized, food substances produce water and carbon (IV) oxide;
   2.  
      1. To investigate anaerobic respiration in yeast cells/fermentation.
      2. To avoid destroying/killing yeast cells and to remove oxygen; rej air
      3. To avoid denaturing enzymes in yeast cells;
      4. Prevent re-entry of air into yeast solution;
6.  
   1.  
      1. Species A;
      2. The rate of growth (multiplication) of species A is higher than that of  B;
   2.  
      1. Population increased exponentially (rapidly); due to high number of reproducing individuals; and  suitable environmental conditions (such as food , space, resources not limiting e.tc.);
      2. Population becomes constant; because of shortage of resources like food and space; and birth rate  equals death rate;
   3. Species A would decrease; due to predation; while the population of species B would increase; due to less competition for food with species A/  more resources or food  available;
   4.  
      1. Predation;     
      2. Parasitism;     
      3. Symbiosis;     
      4. Saprophytism;
   5.  
      1. Photographic light meter;     
      2. Sacchi disc;     
      3. Anemometer;     
      4. Barometer;     
7.  
   • During thunderstorm/ lightning; nitrogen gas  combines with O₂ to form nitrogen  oxides; nitrogen  oxides dissolve in water to for nitric acid; acid is deposited in the soil by rain, nitric acid combines with chemical substance to  form  nitrates/ nitric acids dissolves to form nitrates which are  absorbed  by plants symbiotic bacteria/ such as rhizobium; which are  found in root nodules of leguminous  plants, fix free nitrogen to  nitrates.
   • Free living bacteria/ clatridium/ azotobacteria fix nitrogen to all rates
   • Nostoc algae/ chlorella/ anaemia/ ix nitrogen to nitrates.
   • Plants use Nitrates to form plant proteins
   • Animals feed on plants and convert  plant proteins into animal proteins
   • Plants/ animals die and decomposed by bacteria/ saprophytes/ fungi decomposing  plants/ animals/ release ammonia which is covered to nitrates/ by nitrosomomes nitrococcus bacteria
   • Nitrates  are converted to nitrates; by  nitrobacteria
   • Nitrates in the soil can be converted to free nitrogen/ denitrification by some  fungi; pseudomonas/ hulobacillus denitrifying bacteria.
8.  
   1.  
      • Highly vascularized/ network  of blood capillaries
      • L.S.A ( for G.E)
      • Thin membrane/ epithelium/ one cell thick wall/ thin lining; rej thin walls moist lining
   2.  
      1. Breathing in
         • External intercostals muscles contract; internal, intercostals muscles relax lifting/ raising the ribcage upwards and outwards; muscles of diaphragm contract. It flattens the volume of the thoracic cavity increases; pressure decrease; higher air pressure in the atmosphere forces air into the lungs
      2. Breathing out
         • External intercostals/ muscles relax; internal intercostals muscles contract moving the ribcage downwards and inwards; the muscles of diaphragm relax, the diaphragm assumes dome shape; volume of thoracic cavity decreases; while pressure increases; higher pressure forces air out of the lungs