Biology P2 Questions and Answers - Form 3 Term 3 Opener Exams 2022

INSTRUCTIONS TO CANDIDATES:

• Write your name and Admission number in the spaces provided.
• Answer all the questions in Section A in the spaces provided.
• In section B answer questions 6 (compulsory) and either question 7 or 8 in the spaces provided.

QUESTIONS

SECTION A (40 Marks)
Answer all questions in this section in the spaces provided.

1.                          
   1. The figure below shows the effect of pH on an enzyme catalysed reaction.
      
      
      1. State the pH at which the enzyme is most active……………………………………. (1 mark)
      2. Name one enzyme likely to be the one in the figure above and suggest the part of the alimentary canal where it is found. (2 marks)
         Name...............................................................................................................................
         Location in the alimentary canal......................................................................................
      3. Name the digestive juice that contains the enzyme. (1 mark)
   2. Explain how temperature affects the rate of enzyme controlled reactions (3 marks)
   3. What is enzyme specificity? (1 mark)
2. The figures below represent mammalian tissue as seen under a light microscope.
   
   
   1. Identify the tissue ……………………………………………………… (1 mark)
   2. Name the cells represented by (3 marks)
      R…………………………………………………………………………….
      S…………………………………………………………………………….
      T…………………………………………………………………………….
   3. State the function of structure S and R. (2 marks)
      S ……………………………………………………………………………………………….
      R………………………………………………………………………………………………..
   4. Explain one adaptations of structure T to its function. (1 mark)
   5. Name one defect of the circulatory system. (1 mark)
3.                        
   1. Define the term photosynthesis (1 mark)
   2. State two raw materials of photosynthesis (2 marks)
   3. State two factors that affect the rate of photosynthesis (2 marks)
   4. Describe briefly the light stage of photosynthesis (3 marks)
4. The diagram below represents the nitrogen cycle.
   
   
   1. Identify the processes labelled A and D. (2 marks)
      A ………………………………………………………
      D ………………………………………………………
   2. Name the compound represented by B. ………………………………………………… (1 mark)
   3. Name the group of organisms labelled C. ………………………………………………. (1 mark)
   4.                        
      1. Name the group of plants that promote process A………………………. (1 mark)
      2. In which part of the plant does process A take place? (1 mark)
   5. How would excess pesticides in the soil interfere with process A (2 marks)
5. Below is a diagram of a plant a student collected while carrying out an ecological study.
   
   
   1. With reasons identify the division into which the students classified the plant.
      Division ………………………………………………………………………… (1mark)
      Reasons ……………………………………………………………………….. (2marks)
   2.                          
      1. Name the structure that produces spores in this plant. (1mark)
      2. State two differences between the plant division above and that of the division spermatophyta. (2 marks)
         

         	Spermatophyta

   3. Give two distinguishing features of class Amphibia (2 marks)

SECTION B (40 marks)
Answer question 6 (compulsory) and either question 7 or 8 in the spaces provided.

6. The table below shows how the quantities of sweat and urine vary with external temperature
   

   External temperature °C	0	5	10	15	20	25	30	35
   Urine cm³/hr	100	90	80	70	60	50	40	30
   Sweat cm³/hr	5	6	10	20	30	60	120	200

   1. On the same graph, plot the quantities of urine and sweat produced against the external temperature. (7 marks)
      
   2. At what temperature are the amounts of sweat and urine produced equal? (1 mark)
   3. What happens to the amount of sweat produced as the temperature rises? Explain the observation. (3 marks)
   4. Explain the observation made on the amount of urine produced as the temperature increases. (3 marks)
   5. How does the skin regulate temperature? (6 marks)
7.                        
   1. What is meant by the term digestion (2 marks)
   2. Describe how mammalian small intestine is adapted to its function (18mks)
8.                      
   1. Explain how xerophytes are adapted to their habitats (10 marks)
   2. Describe how insect pollinated flowers are adapted to pollination. (10 marks)

MARKING SCHEME

1.                
   1.                  
      1. State the pH at which the enzyme is most active. 2.5 (1 mark)
      2. Name one enzyme likely to be the one in the figure above and suggest the part of the alimentary canal where it is found. Name - Pepsin/Rennin; Location in the alimentary canal - Stomach. (2 marks)
      3. Name the digestive juice that contains the enzyme. Gastric juice (1 mark)
   2. Enzymes work best at optimum temperatures; At very low temperature enzymes are inactivated thus the rate of enzyme reaction decreases;at very high temperatures above optimum enzymes are denatured thus the rate of enzyme reaction decreases (3mks)
   3. Enzyme specificity – a particular enzyme only acts on a specific substrate. (1mk)
2.                    
   1. blood
   2. R – Platelets S - White blood cells T - Red blood cells
   3. S – Engulf and destroy foreign micro – organism R – Involved in clotting of blood.
   4.                    
      • Biconcave disc to create a large surface area through which oxygen diffuses into cell.
      • Lack nucleus to create more space for packing of haemoglobin
      • Contain haemoglobin which has high affinity for oxygen.
   5.                        
      • Thrombosis
      • Arteriosclerosis
      • Hypertension
      • Varicose veins
3.                  
   1. Photosythesis is the process by which plants manufacture food substances from carbon (IV)oxide and water using energy from sunlight. (1mk)
   2. Carbon (IV) oxide and water.(2mks)
   3.                        
      • Temperature
      • carbon (IV) oxide
      • light intensity .
      • Availabilty of water (3mks)
   4.                        
      • Occurs in the grana of chloroplasts
      • The light trapped is used to split water molecules into hydrogen atom and oxygen gas i.e photolysis.
      • Some of the light energy is used in the formation of ATP.(3mks)
4.                
   1. A – Nitrogen fixation; D – Absorption; (2mks)
   2. Nitrites; (1mk)
   3. Denitrifying bacteria/Pseudomonas denitrificans/Thiobacillus denitrificans/ Denitrifiers; (1mk)
   4.                    
      1. Leguminous plants/legumes/e.g. beans, peas, covers, cashew nuts, groundnuts, accassia (accept a correct example). (1mk)
      2. Root nodules; rej root Acc. Root tubercles. (1mk)
   5. Reduction/killing of decomposers; Reduction/killing of nitrogen fixing bacteria; Destruction of leguminous plants/killing of leguminous plants; (2mks)
5.              
   1. Division Pteridophyta;
      Reasons: Leaves are compound with leaflets/Pinna/frond; Presence of sori; Presence of horizontal underground stem/Rhizome (2mks)
   2.                  
      1. Sporangia (1mk)
      2.                                        
         

         Pteridophyta	Spermatophyta
         fertilization is dependent on water	fertilization is mainly independent of water
         Does not produce seeds	Seed bearing

         (2mks)
   3. Gaseous occurs through the skin, mouth and lungs /Hind limbs are longer and more muscular than the forelimbs. (2mks)
6.                      
   1. Labeling of axis; (1mk) Scale ; (1mk) Curves; (2mks) Plotting points; (2mks) Curve labelling; (1mk)
      
   2. 24ºC;
   3. Sweat production increases with increase in temperature; because high temperatures increase the evaporation rate, hence more sweat is converted to water vapour; This uses latent heat of vapourization from the body causing cooling; (3mks)
   4. An increase in temperature decreases the amount of urine produced; This is due to increased sweating which raises the osmotic pressure of blood; A lot of water is reabsorbed into blood in the kidney tubules resulting in the production of little, concentrated urine; (3mks)
   5. Hair - When hot, the erector pili muscle relax; the hair lies that on the skin surface; to reduce insulation and encourage heat loss; When cold, the erector pili muscles contract; causing hairs to stand and trap a layer of warm air which insulated the body; (3mks)
      Blood vessels - When cold blood vessel; constrict (vasoconstriction); Less blood flows near skin surface; reducing heat loss by radiation and convection; When hot, blood vessels dilate (vasodilatation); more blood flows on the skin surface; increasing heat loss by radiation and convection thus cooling the body; (3mks)
      Sweat glands - When hot, sweat is released; it evaporates, taking latent heat of vapourisation from the body; hence cooling it; When cold, sweat glands release less sweat; there is less evaporation; and hence less heat loss; Total = (9mks; Max = 6mks)
7.                        
   1. Digestion is the breakdown of complex food sustances(by enzymes) to simpler compounds which can be absorbed.
   2.                  
      • The small intestine has two functions i.e final stage of digestion takes place here and so does absorption of soluble products of digestion.
      • Is long to provide a large surface area for absorption of digested food.
      • Is narrow so as to to bring digested food into close contact with the walls of the ileum for easier absorption.
      • Is highly folded/coiled to slow down the movement of food to allow more time for digestion and absorption and also to increase surface area for digestion and absorption.
      • Inner surface of the ileum has alarge number of villi and micro villi which increase surface area for absorptionof end products of digestion.
      • The wall of the ileum is thin/thin epithelium which is one cell thick to reduce distance over which digested foood has to diffuse into the blood.
      • Villus/villi are highly vascularised/have a rich blood supply/rich network of blood capillaries,into which amino acids,glucose,vitamins etc diffuse into and this helps to maintain a steep concentration gradient.
      • Villi have lacteal for absorption of fatty acids and glycerol and channels them to lymphatic system.
      • Cells of the ileum have a large number of mitochondria to release energy that aids in active transport of materials across the epithelium.
      • Have intestinal glands that secretes intestinal juices that complete digestion process since they contain various enzymes e.g.maltase,sucrase,peptidase,lipase to complete digestion of maltose,sucrose,proteins and lipids respectively.(each point 2mrks).
8.                      
   1. Adaptations of xerophytes
      • Some have leaves reduced in size / to spine of reduces the surface area for water loss.
      • Some xerophytes have photosynthetic stems that take the place of leaves; to reduce the surface area for transpiration;
      • Some shed-off leaves during dry season; reduce surface exposed to transpiration;
      • Some have thick wax cuticle; which reduces cuticular transpiration;
      • Some xerophytes have fleshy / succulent /juicy stems / roots for storage of water;
      • Some have sunken stomata; that accumulate moisture / creating low diffusion gradient; thus reducing transpiration rate;
      • Most have reduced number of stomata; mostly on the lower leaf surface to reduce the rate of transpiration; The stomata are also small in size to reduce loss of water by transpiration;
      • Some show reversed stomatal rhythm (open stomata at night and close during the day) to prevent excessive loss of water by transpiration;
      • Some have succulent stem; that stores water; used in dry season;
      • Some have long tap roots that extend deep into the soil to absorb water far below.
      • Some xerophytes have shallow roots that spread widely / extensively in order to trap water from any little shower of rain;
      • Some xerophytes roll their leaves to reduce surface area exposed thus reducing rate of water loss by transpiration;
      • Some xerophytes have thorns on their stems / branches / midribs / leaves to protect the plant from predator / browsers / herbivorous animals;
      • Some xerophytes have a very short life cycle thus grow fast to use the little rain within a very short time; and produce seeds that can survive the drought.
   2. Adaptations of insect pollinated flowers
      • Large; brightly coloured petals/ bracts; to attract insects; scented; to attract insects.
      • Have nectar guides that direct insects into nectaries which secrete nectar;
      • Pollen grains rough/ sticky surface; to stick on insects body;
      • Special shaped corolla tube; to enable insects to land
      • Anthers situated inside the flowers; to ensure that they get into contact with the insect;
      • Sticky stigma; for pollen to stick and adhere; Total 12 marks = max 10 marks