Biology Paper 2 Questions and Answers - Cekana Mock Exams 2023

INSTRUCTIONS

• Answer ALL questions from Section A, Question 6 and Either Question 7 or 8 from Section B.
• All working must be clearly shown where necessary.
• Answer all questions in English

QUESTIONS 

SECTION A: 40 MARKS

1. The figure below shows the teeth in the lower jaw of an adult human
   
   
   1.  
      1. Name the teeth labelled X and Z (2marks)
      2.  Describe the functions of teeth Y and Z (2marks)
   2. Name one mineral and one vitamin that are essential for the healthy development of teeth (1mark)
   3. The figure below shows a section through a tooth.
      
      
      1. Tooth decay is caused by bacteria getting into the dentine. Explain how bacteria can enter the dentine (2marks)
      2. List one action you could take to reduce the risk of tooth decay (1mark)
2. 1. What are the analogous structure as used in evolution (1mark)
   2. How do disease causing micro-organisms become resistant to drugs (3mark)
   3. The diagram below represents a bone of a mammal
      
      
      1. Identify the bone (1mark)
      2. Name the bone that articulate at the point labelled F (1mark)
      3. Explain two adaptations of the bone identified in (i) above (2marks)
3. Study the flow chart below of a process that takes place in both plants and animals
   
   
   1. Name the above process (1mark)
   2.  
      1. In the above process name the chemical reaction represented by X (1mark)
      2. Name the part of the cell where the enzyme controlled reactions in b(i) above takes place (1mark)
   3. Name the product Z in
      1. Plants (1mark)
      2. Animals (1mark)
   4. What would be the fate of pyruvic Acid if oxygen supply is availed in the mitochondria of an animal cell (2marks)
   5. What is meant by the term oxygen debt (1mark)
4.  
   1. Differentiate between the following terms
      1. Dominant gene and recessive gene (1mark)
      2. Continuous variation and discontinuous variation (1mark)
   2. In Drosophila melanogaster the gene for eye colour is sex linked. The gene for red eye is dominant. A cross was made between homozygous red eyed female and a white eyed male. Work out the phenotypic ration of the F₁ generation.( use R to represent the gene for red eyes) (4marks)
   3. Suggest two reasons to explain why Drosophila melanogaster is most preferred for studies in modern genetics. (2marks)
5. The diagram below represents a feeding relationship in an ecosystem
   
   
   1. Name the type of ecosystem represented by the above food web (1mark)
   2. Name the organism in the food web that:
      1. Are producers (1mark)
      2. Occupies the highest trophic level (1mark)
   3.  
      1. Write a food chain that ends with the hawk as quaternary consumer (1mark)
      2. State two short term effects on the above ecosystem if all the small fish were killed (2marks)
   4. How does oil spills lead to death of fish (1mark)
   5. Name one other cause of water pollution apart from oil spills (1mark)

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

6. Two species of parasitic wasps X (Vespula vulgaris) and Y (Vespula acadica) were introduced in an orchard in order to control the population of aphids. The numbers of each species of wasps were counted at two-month intervals and recorded. The table below shows the population of the two wasps over a 18-month period in the orchard.
   

   Time		0	2	4	6	8	10	12	14	16	18
   Population	Species X	40	100	280	440	540	600	640	640	620	640
   	Species Y	40	180	240	220	180	140	80	60	40	60

   
   
   1. Plot a graph of population of wasp against time (7marks)
   2. State the type of relationship between the two wasps population (1mark)
   3. Account for the differences in population of the two wasp populations:
      1.  0 – 3 years (3marks)
      2. 4 – 14 years (3marks)
         
   4. The experiment was continued for another 8 months. On the 18th month the population of species X increased and surpassed that of Y. Account for this observation (3marks)
   5. Explain how the population of the wasps was determined (3marks)
7. Describe how the structure of mammalian eye is adapted to its function (20marks)
8.  
   1. State four characteristics of gaseous exchange surfaces (4marks)
   2. Describe the mechanism of gaseous exchange in a mammal (16marks)

MARKING SCHEME

SECTION A: 40 MARKS

1. The figure below shows the teeth in the lower jaw of an adult human
   1.  
      1. Name the teeth labelled X and Z (2marks)
         X – Pre-molar
         Z – Incisor
      2. Describe the functions of teeth Y and Z (2marks)
         Y (canine)
         • Seizing prey and rearing flesh
         • Hold, kill and tear the prey
           Z (incisor)
         •  For gripping and stripping flesh ( from the bones)
         •  For cutting and biting
   2. Name one mineral and one vitamin that are essential for the healthy development of teeth (1mark)
      Mineral – Calcium, Phosphorus
      Vitamin – (Vitamin) A, C and D
   3. The figure below shows a section through a tooth.
      1. Tooth decay is caused by bacteria getting into the dentine. Explain how bacteria can enter the dentine (2marks)
         • The sugar and starch mix with micro-organisms forming plaque which get lodged between the teeth.
         • The micro-organisms break down the sugar in the plaque producing acids as waste products
         •  Acids react with enamel and dentine causing them to solve.
         • A hollow area of those decayed parts is formed.
         •  (Bacteria enters the teeth through this hollow area.)
      2. List one action you could take to reduce the risk of tooth decay (1mark)
         • Regular brushing of teeth after every meal
         • Avoid eating too much sugary food
         • Take diet rich in calcium/phosphate/vitamin A/ C/ D
         • Regular visit to a dentist at least twice a year
2.  
   1. What are the analogous structure as used in evolution (1mark)
      • Are structures having different embryonic origin but are modified to perform similar functions (wings of birds as those of insects)
   2. How do disease causing micro-organisms become resistant to drugs (3mark)
      • Through mutation and selection
      • Long exposure to drugs make organisms to mutate and develop new strain whose protein coat cannot be destroyed.
      • Through reproduction, the population of the new strain increases
   3. The diagram below represents a bone of a mammal
      1.  Identify the bone (1mark)
         • Scapula rej. Shoulder bone
      2. Name the bone that articulate at the point labelled F (1mark)
         • (Head of the) Humerous
      3. Explain two adaptations of the bone identified in (i) above (2marks)
         • Glenoid cavity to articulate with the head of humerous
         • Long (scapula) spine to increase surface area for muscles attachment
         • Broad blade to increase surface area for attachment of muscles
         • Has coracoid process to increase surface area for muscle attachment
3. Study the flow chart below of a process that takes place in both plants and animals
   1. Name the above process (1mark)
      • Anaerobic respiration rej. Respiration
   2.  
      1. In the above process name the chemical reaction represented by X (1mark)
         • Glycolysis
      2. Name the part of the cell where the enzyme controlled reactions in b(i) above takes place (1mark)
         • Cytoplasm
   3. Name the product Z in
      1. Plants (1mark)
         • Ethanol; Energy
      2. Animals (1mark)
         • Lactic Acids; Energy
   4. What would be the fate of pyruvic Acid if oxygen supply is availed in the mitochondria of an animal cell (2marks)
      • Pyruvic acid is (decarboxylated forming Acetyl Co-enzyme which gets to the Krebs cycles which is) further oxidised by oxygen in a series of enzymatic reaction into carbon (IV) oxide energy and water
   5. What is meant by the term oxygen debt (1mark)
      • Extra amount of oxygen required to get rid of the lactic acid that accumulate in the body tissues when the supply of oxygen is less than demand
4.  
   1. Differentiate between the following terms
      1. Dominant gene and recessive gene (1mark)
         • Dominant gene expresses itself in both its homozygous and heterozygous states while recessive gene can only express itself in the homozygous state
      2. Continuous variation and discontinuous variation (1mark)
         • Continuous variation is a characteristic for which there is a range with many intermediaries while discontinuous is a characteristic for which there are discrete/distinct categories or units or clear out differences
   2. In Drosophila melanogaster the gene for eye colour is sex linked. The gene for red eye is dominant. A cross was made between homozygous red eyed female and a white eyed male. Work out the phenotypic ration of the F1 generation.( use R to represent the gene for red eyes) (4marks)
      
      
   3. Suggest two reasons to explain why Drosophila melanogaster is most preferred for studies in modern genetics. (2marks)
      • It produces a larger number of offspring and allows sufficient data to be collected.
      •  It has a shorter life cycle/ lifespan
      • It has fewer pairs of chromosomes that are easier to study
      • They share upto 75% of genes that causes diseases in humans
5. The diagram below represents a feeding relationship in an ecosystem
   1. Name the type of ecosystem represented by the above food web (1mark)
      • Aquatic
   2. Name the organism in the food web that:
      1. Are producers (1mark)
         • Phytoplanktons
      2. Occupies the highest trophic level (1mark)
         • Hawks
   3.  
      1. Write a food chain that ends with the hawk as quaternary consumer (1mark)
         • Phytoplanktons →Zooplanktons→ Frogs →Snakes→ Hawks
      2. State two short term effects on the above ecosystem if all the small fish were killed (2marks)
         • Snakes would decrease due to less food
         • Phytoplanktons would increase
   4.  How does oil spills lead to death of fish (1mark)
      • Oil clogs fish gills hence reducing surface area for gaseous exchange
      • Oil cuts off dissolved oxygen in water leading to suffocation
   5. Name one other cause of water pollution apart from oil spills (1mark)
      • Domestic waste and sewage
      • Silting
      • Industrial effluents
      • Agro-chemicals

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

6. Two species of parasitic wasps X (Vespula vulgaris) and Y (Vespula acadica) were introduced in an orchard in order to control the population of aphids. The numbers of each species o wasps were counted at two-month intervals and recorded. The table below shows the population of the two wasps over a 18-month period in the orchard.
   

   Time		0	2	4	6	8	10	12	14	16	18
   Population	Species X	40	100	280	440	540	600	640	640	620	640
   	Species Y	40	180	240	220	180	140	80	60	40	60

   
   
   1. Plot a graph of population of wasp against time (7marks)
      
   2. State the type of relationship between the two wasps species (1mark)
      • Competition. Accept Parasitism
   3. Account for the differences in population of the two wasp populations:
      1. 0 – 3 years (3marks)
         • Both population increases; due to more food and hence less (inter-specific) competition for space and food
         • The increase in population of species Y is higher /faster than that of X
         • Y has a shorter life cycle than X
         • Y has faster growth and maturity rate than X
         • Y lays more eggs // has faster reproduction rate than X
      2. 4 – 14 years (3marks)
         • Population of X is higher than that of Y
         • Population of X increases with increase in time
         • Population of Y decreases with increase in time
         • X is better competitor for food
         • X has a longer life expectancy// span than Y
         • X could be parasitic on Y
         • A disease infestation that only affects Y
   4. The experiment was continued for another 8 months. On the 18th month the population of species X increased and surpassed that of Y. Account for this observation (3marks)
      • Another organism predatory to X migrated or were introduced into the orchard
      • X migrated out of the habitat
      • Spraying of the orchard with a pesticide // chemical that kills X
      • High explosion on the number of aphids so no competition for food
   5. Explain how the population of the wasps was determined (3marks)
      • Capture recapture method; as many wasp as possible were caught; marked and counted; the number was recorded as first marked; the exercise was repeated 24 hours later; as many wasps as possible were caught; their number counted and recorded as second capture; the number of wasps in the second capture that has the original mark was determined and recorded as marked recaptured; the population was calculated as:
        
        
7. Describe how the structure of mammalian eye is adapted to its function (20marks)
   • The sclerotic layer, which contains tough connective tissue fibres, it supports and protect the other parts of the eyeball
   • The choroids, which contains many blood capillaries, supply oxygen and nutrients to the retina and remove metabolic wastes from the eye
   • Its highly pigmented, to prevent reflection of light within the posterior chamber of the eyeball
   • The retina, which contains photoreceptor cells called cones and rods. It is said to be the light-sensitive part of the eye. Cones are adapted for light and colour vision, while rods are adapted for dim light vision
   • The vitreous humour, which is under turgor pressure. It maintains the shape of the posterior chamber of the eyeball. It also plays an important part in the refraction of light rays, enabling them to be focused on the retina
   • The cornea, transparent and curved, it plays an important role in focusing of the image on the retina. It accounts for the largest refraction of light rays
   • The aqueous humour, contains oxygen and nutrients, which nourish the cornea and the lens. It is under pressure, thus maintaining the shape of the anterior chambers of the eye. It also plays a part in the refraction of light rays, enabling them to be focused on the retina
   • The iris is heavily pigmented, to prevent entry of light into the eye except through its central aperture called the pupil. It contains circular and radial muscles which constrict or dilate the pupil depending on the intensity of light.
   • The lens is elastic, therefore allows changes in its shape depending on the tension exerted through the suspensory ligaments. This enables it to bring light rays coming from either near or far objects into sharp focus on the retina
   • The ciliary body contains the ciliary muscles whose contraction and relaxation alter the tension exerted on the suspensory ligaments. This, in turn, alters the shape of the lens enabling it to focus for both near and distant objects
   • The eyelids, which are movable and opaque structures, can be closed through a reflex action to protect the eye from too much light or from foreign objects.
   • The eye muscles help to move the eyeball within the orbit. The lateral rectus muscles move the eye up and down, while the oblique muscles move the eyeball in its up and down movement
   • The lacrimal gland continuously secretes a watery, saline and antiseptic fluid called tears. The tears moisten the cornea and wash foreign particles out of the eye.
   • The eyelashes, which are many hairs, protect the eye from the entry of small foreign particles.
   • The eyebrows, raised portion of the skin above the eye, thickly covered with hair, whose functions are to prevent sweat and dust from entering the eye.
8.  
   1. State four characteristics of gaseous exchange surfaces (4marks)
      • They are densely supplied with blood capillaries, (highly vascularized) for transportation of gases
      • They are thin walled to facilitate easy diffusion of gases and also to reduce the distance covered by the diffusing gases
      • They are moist to dissolve gas
      • They have a large surface area for effective gaseous exchange
   2. Describe the mechanism of gaseous exchange in a mammal (16marks)
      During inhalation/inspiration, the external intercostal muscles contract, while the internal intercostal muscles relax, raising the rib cage upwards and outwards. Muscles of the diaphragm contract, making it flatten. The volume of the thoracic cavity increases as pressure decreases. The higher pressure in the atmosphere forces air into the lungs, inflating them.
      During exhalation, the external intercostal muscles relax while the internal intercostal muscles contract, moving the rib cage downwards and inwards. The diaphragm muscles relax, and the diaphragm retains its dome shape. The volume of the thoracic cavity reduces, increasing pressure. Higher pressure forces air out of the lungs.