KNEC KCSE BIOLOGY TOPICAL QUESTIONS AND ANSWERS

Below is a diagram of a poorly planned town showing some building and facilities

8/1/2023

Comments

Below is a diagram of a poorly planned town showing some building and facilities

a) Giving evidence from the diagram, state two likely sources of water pollution. (2mks)

Industrial effluents because the factory is close to the river.
Domestic effluents since some houses are next to the river and the marsh.

b) State three ways that the positioning of the refuse pit and sewage works pose danger to the residence of the town. (3mks)

Drinking water contamination since the water works is close to the sewage works;
Spread of diseases to residents nearby because many pathogens and diseases vectors are found in the sewage works and refuse pit near the houses;
Air pollution because the prevailing wind carries unpleasant smell over the town;

c) Residents living close to the marsh are likely to suffer from malaria. Explain. (1mk)

The swamp is the breeding site for mosquito larva hence adult mosquitos may spread malaria to residents living nearby.

d) Suggest two control measures to overcome water pollution in the area. (2mks)

Treating industrial and domestic effluents before releases it into the water.
Cooling the water from the factories to avoid raising water temperature in the river and swamp.
Carry out environmental impact assessment before establishing factories/industries;etc

Comments

A group of students carried out a study of the population growth of flour weevils.

4/11/2021

Comments

A group of students carried out a study of the population growth of flour weevils. They put 16 grams of maize flour into two equal boxes K and L respective . They then introduced equal numbers of weevils into the boxes. The boxes were kept under similar environmental conditions. The weevils were counted at intervals and the results recorded in the table below.

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table.
Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks)
Number in K: ..
Number in L:......

K - 555
L - 1020

(c) (i) On what day was the population of weevils in K 580. (1mk)

86th Day

(ii) Between which days was the population difference greatest . (1mk)

100 - 120

(d) Account for the shape of graph L between day 5 and day 100. (4 mks)

Increase in population; because there is adequate food; the number of reproducing individuals is increasing; wastes products have not accumulated to toxic levels.

(e) State factors that would make the human species assume the graph curve above in K. (4mks)

Diseases
Lack of food
Death rate equal to birth rate.

Comments

What are the effects of releasing excess nutrients into lake Naivasha by the nearby flowers farms?

1/11/2021

Comments

What are the effects of releasing excess nutrients into lake Naivasha by the nearby flowers farms? (3mks)

Oxygen depletion due to excessive growth of aquatic plants leading to suffocation and death of aquatic animals;
Entrophication hinder light penetration affecting photosynthesis in submerged hydrophytes;
Cause water surface blockage affecting navigation/fishing.

Comments

What is meant by ecosystem, carrying capacity?

31/10/2021

Comments

(a) What is meant by the following terms; (2mks)

(i) Ecosystem

A natural unit composed of abiotic and biotic factors whose instruction lead to a self sustaining system;

(ii) Carrying capacity

The maximum population of a species that a particular habitat can support;

Total no. of organisms a particular habitat/area/ecosystem/region/environment can support without depleting the resources;
Total no. of population of a species in a given habitat/area/ecosystem/environment can support without depleting the resources.

(b) Give two ways on how hydrophytes are adapted to the process of gaseous exchange (2mks)

Floating hydrophytes have numerous and large stomata on the upper epidermis;
Have aerenchyma tissues in their stems/leaves/roots to store air and for gaseous exchange;
Those in swampy environments have pneumatophods breathing roots;

Comments

The diagram below represents a pyramid of biomass derived from a certain ecosystem

7/9/2021

Comments

The diagram below represents a pyramid of biomass derived from a certain ecosystem

The diagram above represents a pyramid of biomass derived from a certain ecosystem

(a) Suggest the type of ecosystem from which the pyramid was derived (1mk)

Aquatic ecosystem

(b)State the significance of short food chains in an ecosystem (1mk)

The shorter the fluid chain, the more energy can be derived from it, hence the larger the population it can support

Comments

A small boy remarked that his dog looks larger on cold days than on hot days. Give a biological explanation for this

6/9/2021

Comments

A small boy remarked that his dog looks larger on cold days than on hot days. Give a biological explanation for this (2mks)

Cold days

Contraction of erector pilli muscles; hair raised hence the dog appears larger/vasoconstriction

Hot days

Relaxation of erector pilli muscles, hair lies flat hence the dog appears smaller;/ vasodilation

Comments

The graph below represents a population growth of a certain herbivore in grassland ecosystem over a period of time.

3/8/2020

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Suggest three factors that could have caused the population change between C and D.

Comments

The table below shows a list of five human diseases. Complete the table by naming the causative agent of each.

3/8/2020

Comments

The first one has been completed for you.

The table below shows a list of five human diseases. Complete the table by naming the causative agent of each.

Comments

State how excessive use of pesticides may affect soil fertility.

3/8/2020

Comments

Pesticides may kill soil micro-organisms that decompose humus to release mineral salts. In this
way they interfere with nutrient cycling.

how excessive use of pesticides may affect soil fertility

Overuse of chemical fertilizers and pesticides have effects on the soil organisms that are similar to human overuse of antibiotics. Indiscriminate use of chemicals might work for a few years, but after awhile, there aren't enough beneficial soil organisms to hold onto the nutrients” (Savonen, 1997).

Comments

ECOLOGY: Topical Biology Questions and answers

3/8/2020

Comments

1. 1989 Q4 P1
State how excessive use of pesticides may affect soil fertility
2. 1989 Q8 P1
The table below shows a list of five human diseases. Complete the table by naming the causative agent of each.
The first one has been completed for you.

Human Diseases

Comments

K.C.S.E Biology Q & A - MODEL 2019PP2QN07

2/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2019PP2QN07

Giving examples, describe the following interactions among organisms:
(a) predator-prey
(b) symbiosis
(c) parasitism.

answers

.(a) Predator-Prey

-Predator is an animal that hunts/kills another/ other animals(prey) for food;
-A dog and a hare; (acc. either correct examples)
Preys desire survival mechanism in their habitats not to be eaten/killed; to survive and reproduce/propagate this in linage; to this end (prey)(adaptations)
-They run faster (strong hind muscles);
-Camouflage with environments;
-Mimic the predators; (acc. some have a wider field of view/vision;)
-Some emits some chemical/smell that turn of predators;
-Others like porcupine use quills/ spikes/spines to fight off predators;
-Some have good sense of smell to detect predators; on the other hand, predators also evolve/desire means to be able to survive in such an ecosystem for instance.
-Running faster; strong jaws/long/sharp canine/talons;
-Camouflaging with the environment;
-Mimicking prey
-Sharp eyesight;
-Strong sense of smell
-Produce venom/poison that paralyze/kill prey.

(b) Symbiosis

A close (long term) association between two organisms of different species where the two mutually benefit from each other;
Example; The bacteria in the rumen/gut of herbivores; which help herbivores digest cellulose; as they are sheltered by the herbivores;
-The bacteria found in the human digestive system/gut/colon
-the bacteria are sheltered by humans;
-The bacteria aid human in synthesis of vitamin K/ B12/enzyme microbial balance;
-The nitrogen fixing bacteria on the root nodules of legumes;
-NFB benefits from shelter offered by the plant;
NFB facilitate conversion of free atmospheric Nitrogen into forms that can be readily used by the plants;

(c) Parasitism

A kind of (inter-specific) relationship/Association where one member/organism, the parasite, benefits while the other the host is harmed/loses; Also called antagonistic symbiosis)
Example;
A tick (parasite) sucking blood /Nutrients from a cow (host); making the cow to be anaemiac/skin destroyed/malnourished/transmission of diseases;
Parasite can be external/Exo-Parasite; or internal/ endo-parasite; e.g. liver fluke
Example- Liver fluke sucks blood/Nutrients from host and cause death/bodily harm on the internal Organs of the host including blocking blood vessels

Comments

State two limitations of using a quadrat to estimate the population of organisms.

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2018PP1QN13

State two limitations of using a quadrat to estimate the population of organisms.

ANSWERS

Cannot be used for most animals/plants;
Assumes organisms are evenly distributed;
Inaccuracy (over/under-estimation);

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN07

1/7/2020

Comments

K.C.S.E Biology Q & A - MODEL 2017PP2QN07

Explain the importance of protecting the forest ecosystem with reference to the following:
(a) climate change
(b) biodiversity
(c) biotechnology
(d) water conservation
(e) pollution.

answers

a) Climate change

Promote(regular) rainfall/precipitation/prevent desertification;
Act as wind breakers;
Keep earth temperatures cool/reduce global warming;
Keeps biogeochemical cycles going e.g. hydrological, carbon,nitrogen, phosphorous, sulphur cycles;

b) Biodiversity

Conserve diverse flora/ fauna;
Conserve genetic variety;
Prevent extinction of rare species;
Source of research/employment;
Aesthetic/attracting tourism in foreign exchange;
Have impact on culture/religion/politics; ‘
Food and shelter for other organisms and man;
Source of oxygen;

c) Biotechnology

Manufacture of medicines/directly used as medicinal;
Source of food/food products;
Provide fuel (when regulated);
Provide paper and related by-products (when regulated);
Provide timber (when regulated);
Products used in other industries e.g. tannin, wax, rubber, oil, honey;

d) Water conservation

Increased ground water/high water tables;
Adds into rivers/lakes/permanency ¡n existing water bodies/reservoirs;
Water towers/water catchment;

e) Pollution .

Minimize soil pollution/ensuring cover against surface run-off/wind erosion/denudation;
Trees/vegetation clean the soil surface by absorbing nutrients from decomposed matter e.g. sewage;
Large scale clean-up of polluted air/dust;
Muffle noise pollution;

Comments

K.C.S.E Biology Q & A - MODEL 2016PP1QN21

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2016PP1QN21

The figure below illustrates a food web in a certain ecosystem.

From the food web:
(a) Draw the shortest food chain
(b) Identify the organism with the highest:
(i) number of predators
(ii) biomass

answers

Comments

State three factors that contribute to the deceleration phase in the population curve of an organism.

30/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2016PP1QN20

State three factors that contribute to the deceleration phase in the population curve of an organism.

answers

Overcrowding
Accumulation of toxic wastes
Limited resources such as nutrients

Comments

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​Below is a diagram of a poorly planned town showing some building and facilities

​a) Giving evidence from the diagram, state two likely sources of water pollution. (2mks)

​b) State three ways that the positioning of the refuse pit and sewage works pose danger to the residence of the town. (3mks)

​c) Residents living close to the marsh are likely to suffer from malaria. Explain. (1mk)

​d) Suggest two control measures to overcome water pollution in the area. (2mks)

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table. Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks) Number in K: .. Number in L:......

​(c) (i) On what day was the population of weevils in K 580. (1mk)

​(ii) Between which days was the population difference greatest . (1mk)

​(d) Account for the shape of graph L between day 5 and day 100. (4 mks)

(e) State factors that would make the human species assume the graph curve above in K. (4mks)

What are the effects of releasing excess nutrients into lake Naivasha by the nearby flowers farms? (3mks)

​(a) What is meant by the following terms; (2mks)

​(i) Ecosystem

(ii) Carrying capacity

​(b) Give two ways on how hydrophytes are adapted to the process of gaseous exchange (2mks)

(a) Suggest the type of ecosystem from which the pyramid was derived (1mk)

(b)State the significance of short food chains in an ecosystem (1mk)

​A small boy remarked that his dog looks larger on cold days than on hot days. Give a biological explanation for this (2mks)

Cold days

Hot days

K.C.S.E Biology Q & A - MODEL 2019PP2QN07

State two limitations of using a quadrat to estimate the population of organisms.

K.C.S.E Biology Q & A - MODEL 2017PP2QN07

K.C.S.E Biology Q & A - MODEL 2016PP1QN21

State three factors that contribute to the deceleration phase in the population curve of an organism.

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Below is a diagram of a poorly planned town showing some building and facilities

a) Giving evidence from the diagram, state two likely sources of water pollution. (2mks)

b) State three ways that the positioning of the refuse pit and sewage works pose danger to the residence of the town. (3mks)

c) Residents living close to the marsh are likely to suffer from malaria. Explain. (1mk)

d) Suggest two control measures to overcome water pollution in the area. (2mks)

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table.
Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks)
Number in K: ..
Number in L:......

(c) (i) On what day was the population of weevils in K 580. (1mk)

(ii) Between which days was the population difference greatest . (1mk)

(d) Account for the shape of graph L between day 5 and day 100. (4 mks)

(a) What is meant by the following terms; (2mks)

(i) Ecosystem

(b) Give two ways on how hydrophytes are adapted to the process of gaseous exchange (2mks)

A small boy remarked that his dog looks larger on cold days than on hot days. Give a biological explanation for this (2mks)