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K.C.S.E Biology Q & A - MODEL 2016PP1QN12
Other than using the quadrant, give two methods of estimating population of grass.
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN11
Name two benefits that a parasite derives from the host
answers
K.C.S.E Biology Q & A - MODEL 2015PP2QN06
The graph below shows the relative numbers of three main species of organisms in a pond.
​(a) Giving a reason for your answer, which of the species is a
(i) producer? Reason (ii) secondary consumer? Reason (b) State the depths at which each of the populations labelled L, M and N is at its optimum. L M N (c) (i) Which method may have been used to determine the population of organisms labelled N in the pond? (ii) Give a reason for your answer in (c) (j) above. (iii) State the assumptions made when using the method in (c) (i) above. (d) State two reasons why primary productivity in the pond decreases with depth. (e) Explain the ecological importance of fungi to plants. (f) Why is flooding likely to lead to a cholera outbreak?
ANSWERS
​(a) (i) Producer - M
Reason Largest in number hence source of food for the other species Abundant on the water surface to trap light for photosynthesis; (ii) Secondary consumer - N Reason - Smaller in number than L and M (b) L -1.125m; M- 0.75m; N- 2.00m; (c) (i) Capture - Recapture (method) /Capture - mark - release - recapture; (ii) Animals are highly mobile; (iii) No migration during the period of survey/study; No deaths/variation/reproductiori in population during the period; Method of marking does not affect the animal behaviour; Marked/released animals will freely mix with others in the pond; Released/marked animals will have enough time to mix with the others; There is uniform/random distribution of animals within the period. (d) Decrease in light intensity as depth increases; Decrease in temperature as depth increases; (e) Breakdown of organic materials/decompose/rot/decay of materials; to release plant nutrients; (f) Flood water may mix with human waste contaminated with cholera bacteria; The flood water may then contaminate food / water sources; The contaminated water/food causes cholera infection when ingested; K.C.S.E Biology Q & A - MODEL 2015PP1QN12
​(a) What is meant by each of the following:
(i) pyramid of biomass? (ii) pyramid of numbers’? (b) During an ecological visit to the Savanna Grassland, students were able to see lions, antelopes, vultures and pastoralists grazing their cattle. Construct a food chain with four consumer levels to illustrate the energy flow in the ecosystem.
answers
(a) (i) Pyramid of biomas represents total dry mass weight of organisms in each trophic level;
(ii) While pyramid of numbers represents the total number of organisms at each trophic level/feeding levels/nutrition levels; 
K.C.S.E Biology Q & A - MODEL 2014PP2QN06
An experiment was done to determine the uptake of nitrogen from the soil by broad bean seedlings. The experiment was done with one set of seedlings M grown in the atmosphere enriched with carbon (IV) oxide and another set up of seedlings N grown in the normal atmosphere.
The amount of nitrogen in each seedling was measured in milligrams at intervals often days. The table below shows the results obtained. 
​(a) Using the same axis draw line graphs of nitrogen uptake by the two (M and N) sets of broad bean seedlings against time.
(b) Determine the rate of uptake of nitrogen in Set M between 65 and 85 days. (c) (i) What is the relationship between carbon (IV) oxide concentration in the air and nitrogen uptake? (ii) Account for the relationship in (c)(i) above. (d) (i) What would happen to the concentration of nitrogen in the seedlings in set M, if after 75 days the seedlings are transferred to a normal atmosphere. (ii) Explain your answer in (d)(i) above. (e) State three ways in which nitrogen fixation occurs.
answers
(c) (i) The higher the carbon UV) oxide content in air, the higher the nitrogen uptake and vice versa;
(ii) More Carbon (IV) oxide in the air makes the seedlings to photosynthesize more; hence more amino acids/protein; are formed in the dark stage; formation of amino acids/protein requires nitrogen; (d) (i) The concentration of nitrogen would remain constant; (ii) Despite decline in CO,; the nitrogen already absorbed/taken up by the plant will still remain: (iii) Lightning; By free-living bacteria/micro organisms; By Rhizobium (in root nodules of legumes); K.C.S.E Biology Q & A - MODEL 2013PP2QN06
A scientist carried out an investigation to find out the population growth of mice under laboratory conditions. Twenty young mice were placed in a cage. The results obtained from the investigation were as shown in the table below.
​(a) On the grid provided, draw a graph of the number of mice against time.
GRAPH PAPER (b) Account for the changes in mice population between (i) O to 2 months (ii) 2 to 6 months (iii) 6 to 10 months (iv) 10 to 12 months. (c) (i) Between which two months was the population change greatest? (ii) Calculate the rate of population change over the period in (c)(i) above. (d) What change in population would be expected if the investigation was continued to the 19th month? (e) To obtain the observed results state two variables that were kept constant during the investigation.
answers
(b) (i) No change in population/population is constant: mice still maturing/have not given birth:
(ii) Slow/gradual population growth; few mice have reached sexual maturity; (iii) Faster/rapid rate of population growth/exponential; Many mice sexually matured/reproducing/enough food/space/no competition birth rate higher than death/no diseases: (iv) Population decline; Competition is high / food is limiting / space is limiting/accumulation of toxic waste/disease (outbreak) deathrate higher than birth rate. (c) (i) 6 and 8; (ii) 310-115 = 195 mice per month; (d) Population would increase; (e) Food; space ; cage size; water; Describe how environmental factors increase the rate of transpiration in terrestrial plants.26/6/2020
K.C.S.E Biology Q & A - MODEL 2012PP2QN08
Describe how environmental factors increase the rate of transpiration in terrestrial plants.
ANSWERS
In bright light; stomata are fully/wide open; increasing contact between the atmosphere and air spaces in the leaf; This in turn increases water loss by evaporation through the
open stomata High environmental temperatures; increase the rate of evaporation from the leaf surface thus more water leaves cells due to the increased diffusion gradient; Iii a windy day; air around the leaf is carried away reducing water vapour around the leaf; more water moves into the atmosphere from the leaf air spaces; In low humidity/when the atmosphere is less saturated with water vapour; more water will move from leaf air spaces into the atmosphere; leading to increased rate of transpiration; . Low atmosphere pressure; increases diffusion gradient between atmospheric and leaf increased rate of evaporation;Availability of water; causes turgidity of guard cells hence stomata open; increasing rate of transpiration. K.C.S.E Biology Q & A - MODEL 2012PP2QN06
The data provided below represent populations of a predator and its prey over a fifty years’period.
​(a) (i) Using the same axes, draw graphs of the relative populations of P and Q against time.
(ii) With a reason, identify the curve that represents the prey. (iii) Account for the two populations between 25 arid 32 years. (iv) Which years were the two populations equal? (v) A part from predation, state three biotic factors that may have led to the decline of the prey population. (b) Describe the hazards of air pollution by Sulphur (IV) Oxide.
answers
(a) (i) title - Graph of Prey-predator relationship; (OWTE)
Scales X axis; Graph should cover more than half of the grid provided. Y axis; Graph should cover more than half of the grid provided. correct plotting P; Q; smooth curves P; Q; labelling axes; 
(ii) P represents the prey;
Prey population is initially higher prey population usually starts falling earlier; (iii) Both populations decrease; because prey is not enough to sustain predator/population environmental stress limit population of prey; (iv) at 23±0.5 years; and at 39±0.5; (v) less food for the prey/intra specific competition; emigration of the prey; diseases causing death of the prey; parasitism; human activities b)sulphur dioxide in the air - causes respiratory diseases; poisons plants; forms acid rain which increase soil pi-J; corrodes metals in buildings;
K.C.S.E Biology Q & A - MODEL 2012PP1QN21
Name the process through which free atmospheric nitrogen is converted into nitrates.
answer
K.C.S.E Biology Q & A - MODEL 2012PP1QN05
The table below shows results of a study of three plants C, D and E growing in different habitats.
(a) Which one of the plants C, D and E grows in an area of relatively low water availability?
(b) Explain your answer in (i) above.
answers
​(a) Plant C;
(b) Thick cuticle reduces water loss; Low number of stomata reduces water loss; Large root-surface area enhances water absorption; K.C.S.E Biology Q & A - MODEL 2011PP2QN06
An experiment was carried out to investigate the population of a certain micro-organism. Two petri-dishes were used. Into the petri-dish label led M, 60cm3 of a culture medium was placed while 30cm3 of the same culture medium was placed in petri-dish labelled N. Equal numbers of the micro-organisms were introduced in both petri-dishes. The set-ups were then incubated at 35°C. The number of micro-organisms in each petri-dish was determined at irregular intervals for a period of 60 hours. The results were as shown in the table below.
(i)On the same axes, draw the graphs of relative number of micro-organisms against time on the grid provided.
(ii) After how many hours was the difference between the two populations greatest? (iii) Work out the difference between the two populations at 50 hours. (iv) With a reason state the effect on the population of micro-organisms in petri-dish M if the temperature was raised to 60°C after 20 hours. (v) Account for the shape of the curve for population in petri-dish N between 46 hours and 59 hours.
answers
​(ii) 42 hours;
(iii) Graph M at 50 hrs is 1220 ± 20. Graph N at 50 hrs is 540 ± 20 (2 m 1220-540=680±4; (iv) Population growth stops; . High temperatures kill the microorganisms/denature enzymes; (v) 46 hours to 59 hours death rate of the microorganisms is higher, than their population growth rate; due to exhaustion of nutrients; and accumulation of toxic wastes; K.C.S.E Biology Q & A - MODEL 2011PP1QN14
The diagram below represents a certain plant.
​(a) What is the likely habitat for the plant?
(b) Give two reasons for your answer in (a) above.
answers
​(a) Dry/Arid/Semi-arid/Desert;
(b) Succulent/ fleshy stem; reduced leaves/leaves reduced into thorns/leaves modified into spines/spikes; K.C.S.E Biology Q & A - MODEL 2011PP1QN06
What is meant by the following terms?
(a) Ecology. (b) Carrying capacity.
answers
​(a) This is the study of the inter-relationship between organisms and their environment;
(b) The maximum population of a species than a particular habitat can support; without depletion of resources. K.C.S.E Biology Q & A - MODEL 2011PP1QN05
The figure below illustrates a food web in a certain ecosystem.
From the food web:
(a) draw the shortest food chain; (b) identify the organisms with the highest (i) number of predators; (ii) biomass.
answers
(a) Grass > Grasshopper >- Lizards;
(b) (i) Chicken; (ii) Grass; K.C.S.E Biology Q & A - MODEL 2010PP2QN03
The diagram below represents a food web in a certain ecosystem.
(a) Name the trophic level occupied by each of the following:
(î) caterpillars; (ii) small insects. (b) From the food web, construct two food chains which end with lizards as a tertiary consumer. (e) (i) Which organisms have the least biomass in this ecosystem? (ii) Explain the answer in (c) (1) above.
ANSWERS
​(a) (i) Primary consumers;
(ii) Primary/secondary consumers; (b) Green plants — Caterpillars — Lizards; Decaying leaves —Caterpillars — small insects — Lizards; (e) (i) Hawks; (ii) At each trophic level energy is lost as heat in respiration; and during decomposition; lost in defecation/faeces/ waste products or metabolism/excretion; some parts of organism not eaten e.g. feathers; |
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