- This paper consists of TWO sections A and B.
- Answer ALL questions in section A in the spaces provided
- In section B answer question 6(compulsory) and either question 7 or 8.
SECTION A
- The following is an illustration of a certain process that occurs in mammals
- Name process P…………………………………………………………… (1mark)
- Name the juice involved in the process P……………………………………………… (1 mark)
- List two Salts found in the juice name in (b) above that aids in process P (2 marks)
- Give a reason why liver damage leads to impaired digestion of fats (1 mark)
- What would be the likely effect on digestion if the small intestine of a human is reduced in an operation? (2 marks)
- State the fate of excess glucose in the human body. (1 mark)
- The diagrams below shows samples of blood obtained from two different persons A and B.
- What genetic disorder is person B suffering from? (1 mark)
- State one advantage and one disadvantage of the disorder in (a) above when its in heterozygous state. (2 marks)
- Work out the genotypes and phenotypes of the resulting offsprings of marriage between person A and person B
(5 marks)
- The diagram below shows three different types of neurons along a reflex arc
- What is a reflex arc? (1mark)
- Identify the neurons labeled 1 and 2 (2 marks)
- Using arrows show, the direction of impulse transmission on the diagram. (1 mark)
- Name the part of the spinal cord where the cell bodies of neurone 1 and 2 are located
- Describe the transmission of impulse across the part labeled P (3 marks)
- During an ecological study of a grassland ecosystem, a group of students recorded the following observations.
- Grasshoppers feed on grass
- Guinea fowls feed on grasshoppers, termites
- Vultures feed on guinea fowls and leopards
- Leopards feed on gazelles
- Termites feed on grass
- Gazelles feed on grass
- From this record of observations construct a food web. (4 marks)
- Write down, the food chains in which the guinea fowls are secondary consumers. (2 marks)
- Name the organisms through which energy from the sun enters the food web. (1 mark)
- Name the organism that has the least biomass in the food web. (1mark)
- Below is a chemical equation, study it and answer the questions that follow:-
A
Carbon (IV) oxide + water Oxygen + glucose
B- Name process A and B (2 marks)
- What is the biological significance of process A (1 mark)
- In which organelle does process A and B take place? (2 marks)
- Name two stages of process B (2 marks)
- Define compensation point ( 1mark)
SECTION B (40 MARKS)
Answer Question 6 (Compulsory) And Either Question 7 Or 8 In The Spaces Provided After Question 8
- The graph below shows changes in pH and oxygen saturation in river water over a 24 hour period
- When is the pH value and dissolved oxygen saturation % highest? (2 marks)
- Account for the pH value recorded
- Between 08.00 and 1.00 p.m (2 marks)
- Between 2100 and 2400 midnight (2 marks)
- Explain the influence of light intensity on % saturation of oxygen dissolved in this study (4 marks)
- State two structural adaptations that the submerged plants in this river have, which enable them to carry out photosynthesis (2 marks)
- Explain the variations that will be recorded if a similar study was carried out in a river near a nitrate fertilizer industry. (4 marks)
- Explain the various ways in which a typical cell is adapted to its functions (20 marks)
- Discuss the causes, effects and control measures for water pollution (20 marks)
MARKING SCHEME
SECTION A
- The following is an illustration of a certain process that occurs in mammals
- Name process P ; (1mark)
- Emulsification
- Name the juice involved in the process P ; (1 mark)
- Bile juice
- List two Salts found in the juice name in (b) above that aids in process P (2 marks)
- sodium taurocholate ;
- sodium glycocholate ;
- Give a reason why liver damage leads to impaired digestion of fats (1 mark)
- Bile is produced in the liver ;
- What would be the likely effect on digestion if the small intestine of a human is reduced in an operation? (2 marks)
- Surface area of digestion would be reduced hence the rate of digestion ;
- Absorption process would be reduced ; (2 x 1)
- State the fate of excess glucose in the human body. (1 mark)
- Stored in the body as fats or stored as glycogen in the liver and muscles
- Name process P ; (1mark)
- The diagrams below shows samples of blood obtained from two different persons A and B.
- What genetic disorder is person B suffering from? (1 mark)
- Sickle cell anaemia
- State one advantage and one disadvantage of the disorder in (a) above when its in heterozygous state. (2 marks)
- Advantage – individual having this condition rarely suffer from malaria
- disadvantage – suffocation due to insufficient supply of oxygen to the (respiring) body tissues ;
- Work out the genotypes and phenotypes of the resulting offsprings of marriage between person A and person B (5 marks)
- What genetic disorder is person B suffering from? (1 mark)
- The diagram below shows three different types of neurons along a reflex arc
- What is a reflex arc? (1mark)
- Pathway followed by a nerve impulse that gives rise to a reflex action
- Identify the neurons labeled 1 and 2 (2 marks)
- 1- motor neurone
- 2 – relay neurone/intermediate neurone
- Using arrows show, the direction of impulse transmission on the diagram. (1 mark)
- The arrows point towards neurone 1 from 2 and 3
- Name the part of the spinal cord where the cell bodies of neurone 1 and 2 are located
- Grey matter (1 mark)
- Describe the transmission of impulse across the part labeled P (3 marks)
- Impulse reaching the dendrite end of relay neurone causes the synaptic vesicles to release a acetylcholine/transmitter substance; into the synaptic cleft, the acetylcholine/transmitter chemical diffuses across the synaptic cleft; and causes the depolarization of the motor neurone/post synaptic membrane. Sodium ions from the cleft then flow through the post synaptic membrane causing an action potential which is transmitted as a nerve impulse along the motor neurone
- What is a reflex arc? (1mark)
- During an ecological study of a grassland ecosystem, a group of students recorded the following observations.
- Grasshoppers feed on grass
- Guinea fowls feed on grasshoppers, termites
- Vultures feed on guinea fowls and leopards
- Leopards feed on gazelles
- Termites feed on grass
- Gazelles feed on grass
- From this record of observations construct a food web. (4 marks)
- Write down, the food chains in which the guinea fowls are secondary consumers. (2 marks)
- Grass → Grasshoppers → Guinea fowls;
- Grass → Termites → Guineas Fowls;
- Name the organisms through which energy from the sun enters the food web.
- Grass
- Name the organism that has the least biomass in the food web. (1mark)
- Vultures
- Below is a chemical equation, study it and answer the questions that follow:-
Carbon(IV) oxide + water Oxygen + glucose- Name process A and B (2 Marks)
- A- Photosynthesis ;
- B – Respiration
- What is the biological significance of process A (1 mark)
- Provision of food to plants organisms when convert light energy into chemical energy to make their own food which is later consumed by animals ;
- In which organelle does process A and B take place? (2 marks)
- A – chloroplast ;
- B – Mitochondrion ;
- Name two stages of process B (2 marks)
- Glycolysis ; Kreb’scycle
- Define compensation point ( 1mark)
- This is the point when the rate of photosynthesis is equal to the rate respiration / All the carbon dioxide released in respiration is used up by photosynthesis.
- Name process A and B (2 Marks)
SECTION B (40 MARKS)
Answer Question 6 (Compulsory) And Either Question 7 Or 8 In The Spaces Provided After Question 8
- The graph below shows changes in pH and oxygen saturation in river water over a 24 hour period
- When is the pH value and dissolved oxygen saturated % highest? (2 marks)
- pH -3.00 p.m or 1500
- dissolved oxygen -3.00 p.m of 1500 –
- Account for the pH value recorded
- Between 06.00 and 9.00 a.m (2 marks)
- pH increased between 06.00 to 09.00; because of increased rate of photosynthesis ; in aquatic plants, which consumed more carbon(IV) oxide gas dissolved in water;
- Between 2100 and 2400 midnight (2 marks)
- pH decreased between 2100 to 2400; of carbon (IV) oxide which was being produced; by the respiring; water plants, but was not being used for photosynthesis;
- Between 06.00 and 9.00 a.m (2 marks)
- Explain the influence of light intensity on % saturation of oxygen dissolved in this study (4 marks)
- Increasing light intensity increases the rate of photolysis/photosynthesis hence increased production of oxygen gas while decreasing light intensity decreases the rate of photolysis; hence reduce production of oxygen gas;
Acc. Photosynthesis instead of photolysis
- Increasing light intensity increases the rate of photolysis/photosynthesis hence increased production of oxygen gas while decreasing light intensity decreases the rate of photolysis; hence reduce production of oxygen gas;
- State two structural adaptations that the submerged plants in this river have, which enable them to carry out photosynthesis (2 marks)
- Have dissected/branched leaves which provide a large surface area of light absorption and gaseous exchange;
- Leaves have chlorophyll which is very sensitive to light;
- Explain the variations that will be recorded if a similar study was carried out in a river near a nitrate fertilizer industry. (4 marks)
- Some nitrate fertilizer would get into the river water; thus causing rapid growth of many water plants;
- Many water plants, photosynthesize food under high light intensity using a lot of carbon (IV) oxide gas thus raising pH value; and produce a lot of Oxygen, increasing the concentration of oxygen;
- The very many water plants also respire rapidly under low light intensity thus producing large volume of carbon (IV) oxide gas which greatly lowers the pH of water ;
- When is the pH value and dissolved oxygen saturated % highest? (2 marks)
- Explain the various ways in which a typical cell is adapted to its functions (20 marks)
- Has a cell membrane; with pores; that regulates substances entering and leaving the cell; cytoplasm; contain sugars and salts; for maintaining its osmotic pressure; also has a liquid medium; for all biochemical reactions; nucleus; contain chromosomes having hereditary material; and controls all the activities of the cell; ribosomes; are sites for protein synthesis; golgi bodies/apparatus; for secretion of hormones and enzymes; formation of lysosomes; lysosomes; contain lytic enzymes for breaking down worn-out organelles; secretory vesicles; formed from golgi apparatus for secreting substances; smooth endoplasmic reticulum; synthesizes and transports lipids; rough endoplasmic reticulum; transport proteins; nucleolus; controls the activities of the nucleus; produces ribosomes; mitochondria; form sites for energy production; centrioles; formation of cilia and flagella; forms spindle fibres used in cell division; plant sap vacuoles; store salts and other dissolved substances; controls osmotic pressure and turgidity of cells; food vacuoles involved in digestion of engulfed food; chloroplasts; form sites for photosynthesis in plant cells; Max. 20 mks
- Discuss the causes, effects and control measures for water pollution (20 marks)
- Causes of water pollution are varied: industrial effluents; have heavy metals that poison aquatic organisms; untreated organic matter has phosphates/sulphates/nitrates/salts; that cause eutrophication; causing algal bloom that deprives the water of nutrients; when the algae die, they lead to an increase in putrefying bacteria whose decomposition activities lead to the release of awful smells/odours; oil effluents clog respiratory surfaces of aquatic organisms/death due to suffocation; domestic effluents/sewage; form a habitat of pathogens that spread water borne diseases; decomposing sewage promotes eutrophication leading to algal bloom; death promotes/attracts saprophytic bacteria that use up oxygen in water; causing suffocation/death to aquatic organisms; agrochemicals/fertilizers; phosphates/nitrates; cause eutrophication; heavy metals in agrochemicals (herbicides/pesticides); affect respiratory surfaces/cause breathing problems; Hot water; raise temperature of water; killing organisms; dissolves less oxygen; reducing its content in water; Oil spillage; in oceans from tanks/refineries; soak feathers of marine birds preventing flight; clogs respiratory surfaces leading to death; coats photosynthetic phytoplanktons; reduces light penetration hampering photosynthesis; Sediments; from soil erosion makes water dirty; making it unfit for consumption; clogs respiratory surfaces hindering gaseous exchange; reduces light penetration hindering photosynthesis; Control methods: Enforcement of environmental laws; Use of unleaded fuel/petroleum products; Proper treatment and disposal of sewage wastes; Treatment of industrial effluents before release; Public education on correct use of inorganic fertilizers and agrochemicals; and use of alternatives such as biological control of weeds/pests/organic manure; Use of undersea pipelines instead of tankers to transport oil products; Cooling hot water before release to water bodies; Max. 20 mks
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