Biology Paper 2 Questions and Answers - Momaliche Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

• Answer questions 1-6 (compulsory) and either question 7 or 8.

1.  
   1. Arrange the following structures in ascending order (2mks)
      Chromosomes; Alleles; Genes; Chromatid; DNA
   2. The letters below represents nitrogenous organic bases,
      CCG;              ATT;               CGA;                TAG
      1. What term is given to each group (1mk)
      2. Give two functions of the three bases (2mks)
   3. Study the diagram below on chromosomes and answer the questions that follow
      
      1. Identify the type of cell division (1mk)
      2. Name the stage of cell division illustrated by the above diagram (1mk)
      3. Describe what has occurred in the above chromosomes (1mks)
2. The diagram below is of a bean seedling placed horizontally in normal light condition
   
   1. What is the expected observation after five days (2mks)
   2. Name two responses exhibited by above seedling after 5 days (2mks)
   3. Name the chemical substances responsible for inducing observation in (b) above    (1mk)
   4. Name the structure in which the chemical substance in (c) above is conducted in the seedling (1mk)
   5. Explain two survival values of Phototropism in plants (2mk)
3. Describe how each of the following cells are adapted to their functions
   1. Root hair cells (4mks)
   2. Sperm cells (4mks)
4.  
   1.  
      1. What are sex linked genes (1mk)
      2. Give one reason why most sex linked genes are located on X chromosome   (1mk)
   2. A red- green color blindness is a sex linked trait controlled by a sex linked recessive allele (
   3. A normally sighted woman whose father was color blind marries color blind man.
      1. Draw a genetic cross diagram and show phenotypic ratio of their children (5mks)
      2. Calculate the probability that their son will be color blind (1mk)
5. The chart below is a summary of blood clotting mechanism in humans
   
   1. Name
      1. the blood components represented by X (1mk)
      2. Metal ion represented by Y (1mk)
      3. What is the role played by metal ion in (ii) above (1mk)
   2. Name the site where vitamin K is formed in human body (1mk)
   3. Explain why an injured person loses more blood during hot weather when injured   (3mks)
   4. Name one way in which white blood cells defend the body against harmful microorganisms (1mk)

SECTION B( 40 MARKS)

Answer questions 6 (compulsory) and either questions 7 or 8 in the spaces provided questions 8

6. An experiment was carried out using yeast at various temperatures starting at 15 degrees centigrade by immersing boiling tube with glucose yeast mixture in a water bath and results were tabulated as follows
   

   Temperature(°C)	15	20	25	30	35	40	45	50	55	60	65
   Number of bubbles in every 2 minutes	0	1	4	9	18	28	26	20	15	10	0

   1. Using suitable scale plot a graph of number of bubbles every 2 minutes against temperature (6mks)
   2. from the graph determine the rate of bubble production at 27 0C (2mks)
   3. At what temperature was rate of bubbling at maximum (1mk)
   4. Name metabolic process taking place in the boiling tube with Glucose- Yeast mixture   (1mk)
   5. Explain why there was decline in rate of bubbling if temperatures was reduced from 65 0C to 45 0C (3mks)
   6. Name the method of reproduction in yeast  (1mk)
   7. State the economic importance of the above process in Agriculture (3mks)
   8. Draw well diagram of a yeast cell (3mks)
7. Describe the role of the kidney in the following homeostatic processes
   1. Osmoregulation (10mks)
   2. Selective reabsorption of sodium ions (10mks)
8. Explain the factors that affect the following processes in living organisms
   1. Diffusion (10mks)
   2. Active transport (10mks)

MARKING SCHEME

1.   
   1. Alleles; Genes; D.N.A; chromatid; chromosome;
   2.  
      1. codon
      2.  
         • codes for a specific amino acids; 
         • determine sequence of amino acids in a polypeptide chain;
   3.  
      1. Meiosis; Accept Meiosis I;
      2. Prophase I;
      3.  
         • Homologous chromosomes have paired/ synapsis;
         • Crossing over/ chiasma formation
2.  
   1.  
      • Root will curve downwards;
      • Shoot will curve downwards;
   2.  
      • Shoot - Negative geotropism
      • Root - positive geotropism   rej. geotropism alone
   3. Natural auxin/ Indoleacetic acid   Acc. Auxin
   4. Phloem tissue; Acc. phloem
   5.  
      • Positive phototropism; expose the leaves to light energy for photosynthesis
      • Positive geotropism; enables the roots to absorb water and uptake of mineral salts form soil.
      • Positive chemotropism; enable pollen tube to grow towards embryo sac resulting in double fertilisation;
      • Positive thigmotropism; enable plants with weak stems to coil around solid objects hence obtaining mechanical support.
3.  
   1. Root hair cells
      • Elongated/ long; to increase surface area for absorption of water and uptake of mineral ions
      • Have cell sap; with dissolved mineral salts to create steep concentration gradient for absorption of water by osmosis
      • Have numerous mitochondria; to provide energy for uptake of mineral salts by active transport.
      • Have thin flexible cell walls; to facilitate easy penetration between soil particles.  4pts 1mk each
   2. Sperm cells
      • Have abundant mitochondria; in the middle piece; to provide energy(ATP) for swimming towards ova.
      • Have streamlined shape; to reduce resistance hence faster swimming towards mature ovum.
      • Have a long tail; for faster swimming towards ovum.
      • Have acrosome with lytic enzyme; that digest membrane of the ovum. Acc. other correct.
4.  
   1.  
      1. Are genes located on the chromosome that determine sex of an individual and are transmitted together onto same gamete.
      2. x - chromosome is larger hence can accomodate many genes.
   2.  
      1.  
         
      2. ¼ × 100 = 25%
5.  
   1.  
      1. Platelets/ Thrombocytes
      2. calcium ion;
      3. Serves as a cofactor; activating enzyme  thrombokinase, enhancing enzyme reaction;
   2. Colon. Acc. large intestine
   3.  
      • Blood clotting is at optimum at 37°C; During hot weather blood vessels near skin surface vasodilate, increasing blood supply to the skin surface, hence more blood is lost during bleeding.
      • At temperature above optimum; platelets fail to clump together, hence failing to seal the wound hence loosing more blood
   4.  Through phagocytosis; production of antibodies which attack harmful micro organisms
6.  
   1.   
      
   2.  Rate = Gradient of tangent
      ΔY =   7 − 2     = 5 = 1.3333 bubbles/ minute
      ΔX.    30 − 27      3
   3. 40°C
   4. Fermentation, Anaerobic respiration
   5. All enzyme molecules in yeast are denatured at 65°C, hence reducing temperature to 45°C; there was no chemical breakdown of glucose, hence no bubbles produced.
   6. budding
   7.  
      • Compost manure making
      • Silage making
      • biogas production
   8.  
      
7.  
   1. Osmoregulation
      
      • When osmotic pressure of blood plasma rises; e.g due to dehydration; Osmoreceptors cells in hypothalammus are stimulated ; and send impulses to the (posterior) pituitary gland;
        Pituitary gland release (more) ADH into the blood stream; ADH stimulates Distal convoluted tubule and blood capillaries to become (more) permeable to water; more water is (reabsorbed) back into blood stream;
        The osmotic pressure is consequently reduced to the normal; leading to low volume of concentrated urine;
      • When osmotic pressure of blood falls; due to drinking a large volume of water; the hypothalamus sends impulses to posterior pituitary gland to release less vasopressin; ADH into blood stream; the DCT and blood capillaries become (less) permeable to water; less water reabsorbed into blood stream; The Osmotic pressure of (blood plasma) rises to the normal; large volume of dilute urine is produced; i.e diuresis.
   2.  
      • Kidney regulates Na⁺ under influence of hormone Aldosterone produced by Adrenal glands. 
      • When concentration of Na+ in the blood is low; Adrenal glands are stimulated to release (more) Aldosterone into blood stream. Aldosterone stimulates ascending loop of Henle to reabsorb Na+ actively into the blood; The level of Na+ increases, bringing concetration of Na+ to normal.
      • When the concentration of Na+ in the blood is above normal, Adrenal glands are less stimulated hence secrete (less) Aldosterone into blood stream; Ascending loop of Henle are less stimulated; hence less Na+ are selectively reabsorbed actively into blood stream. The level of Na+ in blood plasma decreases; thus lowering concentration to the norm;
8.  
   1. Diffusion
      • Diffusion gradient; the greater the concentration gradient the nfaster the rate of diffusion. Acc. converse
      • Surface area to volume ratio; The higher the surface area to volume ratio the faster the rate of diffusion; and the lower the surface area to volume ratio the slower the rate of diffusion.
      • Thickness of membrane; The thicker the membrane; the lower the rate of diffusion because molecules take longer time to pass across thicker membrane mmthan across thiner membrane.
      • Temperature; Increase in temperature increases kinetic energy of the molecules; increasing the rate of diffusion. Acc. converse
      • Size of the molelcules; The smaller the molecule; the faster the rate of diffusion; the larger the molecule the slower the rate of diffusion; because the molecule experience more resistance in diffusion medium.
   2. Active transport
      • Oxygen concentration; Active transport requires energy. Energy production is by respiration and respiration in the cells require oxygen; An increase in oxygen concentration increases the rate of energy production and hence active transport. Acc. Vice versa.
      • Change in pH; Energy production is influenced by respiratory enzymes; respiratory enzymes work best at specific pH values; Extreme pH denatures enzymes decreasing rate of respiration  ( energy production) and hence active transport.
      • Glucose concentration; Glucose is the main substrate during respiration; An increase in glucose concentration increases the rate of respiration and hence active transport; up to a certain point; beyond which further increase in glucose concentration does not affect it.
      • Temperature; Respiratory enzymes work best at temperature of 35 − 40°C, which is the optimum temperature; at this temperature respiratory enzymes are activated and active tramnsport is at optimum.
        Acc. converse. Very low temp. inactivates enzymes decreasing the rate of respiration and active transport. Temperature above optimum ,above 40°C denature enzymes; reducing the rate of respiration and energy production and active transport; finally stops enzyme inhibitors; slow down or completely to enzyme activitiy which in turn slow down/ stop respiration hence active transport e.g cyanide poison.