ECOLOGY - Form 3 Biology Notes

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  • Ecology is the study of organisms and their environment.
  • All organisms show interdependence on one another.
  • Organisms are affected by their environment, and they in turn affect the environment.
  • Green plants manufacture food by photosynthesis which other organisms obtain directly or indirectly.
  • Growth of plants is mainly affected by environmental factors such as soil and climatic factors.
  • On the other hand, organisms modify the environment through various activities.
  • This interrelationship comprises the study of ecology.
  • The study of ecology is important in several fields of study such as agriculture and environmental studies.

Concepts and Terms Used in Ecology


  • This is the place or "home" that an organism lives or is found, ➢ e.g., forest or grassland.


  • A niche is the functional unit in the habitat.
  • It includes not only the specific place in which an organism lives but also how the organism functions.
  • To avoid or reduce competition, organisms are separated or segregated by their niches, for example, different species of birds make their nest on one tree, some at tips of terminal branches, and others feed on leaves, some on flowers and yet others on fruits of the same tree, i.e., food niche.
  • Yet others feed on same food, e.g., worms in the same place but at different times - time niche.


  • The term population refers to the total number of individuals of a species living in a given area at a particular time.
  • Density is the number of individuals of a population found in a unit area , i.e.,

    Density = Number of individuals/Area


  • This is the distribution of individuals in the available space.
  • Dispersion may be uniform as in maize plants in a plantation;
  • random as in cactus plants in the savannah ecosystem or clumped together as in human population in cities.


  • This is the term used to describe all the organisms living together in an area.
  • During the development of an ecosystem, the species composition of a community changes progressively through stages.
  • Finally a steady state is reached and this is described as the climax community.
  • This development of an ecosystem is termed succession.
  • Each stage in development of an ecosystem is a sere.
  • Succession is primary when it starts with bare ground, and secondary when it starts in a previously inhabited area e.g. after clearing a forest.

The Ecosystem

  • The community and the abiotic or non-living environment together make up an ecosystem or ecological system.
  • In this system energy flow is clearly defined from producers to consumers and nutrient cycling takes place in paths that links all the organisms and the non-living environment.


  • This is the mass of all the organisms in a given area.
  • Ideally, it is the dry mass that should be compared.

Carrying Capacity

  • This is the maximum sustainable density in a given area e.g. the number of herbivores a given area can support without overgrazing.

Factors in an Ecosystem

Abiotic Factors (Environmental Factors)


  • Is the hotness or coldness of an area or habitat.
  • It directly affects the distribution and productivity (yield) of populations and communities.
  • Most organisms are found in areas where temperature is moderate.
  • However, certain plants and animals have adaptations that enable them to live in areas where temperatures are in the extremes such as the hot deserts and the cold polar regions.
  • Temperatures not only influence distribution of organisms but also determine the activities of animals.
  • High temperature usually accelerates the rates of photosynthesis, transpiration, evaporation and the decomposition and recycling of organic matter in the ecosystem.


  • Light is required by green plants for photosynthesis.
  • Light intensity, duration and quality affect organisms in one way or another.

Atmospheric Pressure

  • The force per unit area of atmospheric air that is exerted on organisms at different altitudes.
  • Growth of plants and activity of animals is affected by atmospheric pressure e.g., rate of transpiration in plants and breathing in animals.


  • This is the salt content of soil or water.
  • Animals and plants living in saline conditions have special adaptations.


  • This describes the amount of moisture (water vapour) in the air.
  • Humidity affects the rate of transpiration in plants and evaporation in animals.


  • Is the measure of acidity or alkalinity of soil solution or water.
  • pH is very important to organisms living in water and soil.
  • Most prefer a neutral pH.


  • Is moving air currents and it influences the dispersion of certain plants by effecting the dispersal of spores, seeds and fruits.
  • Air currents also modify the temperature and humidity of the surroundings.


  • These are surface features of a place.
  • The topographical factors considered include altitudes, gradient (slope), depressions and hills.
  • All these characteristics affect the distribution of organisms in an area e.g., the leeward and windward sides of a hill.

Biotic Factors

  • These are the living components in an ecosystem,
    • competition
    • predation,
    • symbiosis,
    • parasitism,
    • human activities.

Inter-relationships Between Organisms

  • The relationships between organisms in a given ecosystem is primarily a feeding one.
  • Organisms in a particular habitat have different feeding levels referred to as trophic levels.
  • There are two main trophic levels:


  • These organisms that occupy the first trophic level.
  • They manufacture their own food hence are autotrophic.


  • These are the organisms that feed on organic substances manufactured by green plants.
  • They occupy different trophic levels as follows:

Primary consumers:

  • These are herbivores and feed on green plants.

Secondary consumers:

  • These are carnivores and feed on flesh.
  • First order carnivores feed on herbivores while second order carnivores feed on other carnivores, i.e., tertiary consumers.


  • These are animals that feed on both plant and animal material.
  • They can be primary, secondary or tertiary consumers.


  • This describes the situation where two or more organisms in the same habitat require or depend on the same resources.
  • Organisms in an ecosystem compete for resources like food, space, light, water and mineral nutrients.
  • Competition takes place when the environmental resource is not adequate for all.

Intraspecific competition.

  • This is competition between organisms of the same species.
  • For example, maize plants in a field compete for water and nutrients among themselves.

Interspecific competition

  • This refers to competition between organisms of different species, e.g., different species of predators can compete for water and prey among themselves.


  • It is a relationship whereby one animal (the predator) feeds on another (the prey).


  • Saprophytism is the mode of nutrition common in certain species of fungi and bacteria.
  • Such organisms feed on dead organic material and release nutrients through the process of decomposition or decay.
  • Saprophytes produce enzymes, which digest the substrates externally.
  • The simpler substances are then absorbed.
  • Saprophytes help in reducing the accumulation of dead bodies of plants and animals.
  • Harmful saprophytes cause rapid decay of foods such as fruits, vegetables, milk and meat.
  • Others damage buildings by causing wood rot.
  • Some fungi produce poisonous substances called aflatoxins.
  • These substances are associated with cereal crops which are stored under warm, moist conditions.
  • If the infected grain is eaten, it may cause serious illness, and death.


  • This is an association between members of different species.
  • The parasite lives on or in the body of another organism, the host.
  • The parasite derives benefits such as food and shelter from the host but the host suffers harm as a result.


  • This is an association in which organisms of different species derive mutual benefit from one another.
  • Some symbiotic associations are loose and the two partners gain very little from each other.
  • Other symbiotic associations are more intimate and the organisms show a high degree of interdependence.

Nitrogen Cycle

  • Is the interdependence of organisms on one another and the physical environment as nitrogen is traced from and back into the atmosphere
  • Although nitrogen is abundant in the atmosphere, most organisms are not able to utilise it directly.
  • Some bacteria are capable of converting atmospheric nitrogen into forms which can be used by other living organisms.
  • These bacteria are referred to as nitrogen fIxing bacteria.
  • Symbiotic nitrogen fixing bacteria live in the root nodules of leguminous plants such as beans and peas.
  • Non-symbiotic nitrogen fixing bacteria live in the soil.
  • Nitrifying' bacteria convert ammonia into nitrites and nitrates.
  • Denitrifying bacteria convert nitrates into atmospheric nitrogen.

    nitrogen cycle
    Fig 1: Nitrogen Cycle

Energy Flow in an Ecosystem

  • Most of the energy used in an ecosystem is derived from the sun.
  • Solar energy is trapped by photosynthetic plants.
  • It flows through different trophic levels.
  • At each level energy is lost as heat to space and also through respiration.
  • Besides animals lose energy through excretion and defecation.
  • The amount of energy passed on as food from one trophic level to another decreases progressively.
  • The energy in the organisms is recycled back to plants through the various nutrient or material cycles.

Food Chains

  • A food chain is a linear relationship between producers and consumers.
  • It represents the transfer of food energy from green plants through repeated stages of eating and being eaten.

Types of Food Chains

  • Grazing food chain - starts with green plants.
  • Detritus food chain - starts with dead organic material (debris or detritus).


  • Detritivores feed on organic wastes and dead matter derived from the grazing food chain.
  • Many different types of organisms feed on detritus.
  • They include fungi, protozoa, insects, mites, annelids and nematodes.

Examples of Food Chains

Green plants → aphids → lady-bird beetle
Green plants → antelope → lion
Algae → Tilapia → kingfisher
Plant debris → bacteria → eprotozoa → mosquito larva
Phytoplankron → Zooplankton → Tilapia → Nile perch → Human

Food Web

  • In a natural community, several food chains are interlinked to form a food web.
  • Several herbivores may feed on one plant.
  • Similarly, a given herbivore may feed on different plants and may in turn be eaten by different carnivores.
    food web
    Fig 2: Food Web



  • These are mainly bacteria and fungi.
  • These organisms feed on dead organic matter thereby causing decomposition and decay and releasing nutrients for plants.
  • They form a link between the biotic and the abiotic components.

Pyramid of Numbers

  • Refers to the number of organisms in each trophic level presented in a graphic form and a pyramid shape is obtained.
  • The length of each bar is drawn proportional to the number of organisms represented at that level.
  • This is because a herbivore feeds on many green plants.
  • One carnivore also feeds on many herbivores.
  • In a forest the shape of the pyramid is not perfect.
  • This is because very many small animals such as insects, rodents and birds feed on one tree.
  • It is always upright but in a tree ecosystem, pyramid of number is inverted.
    pyramid of numbers
    Fig 3: Pyramid of Numbers

Pyramid of Biomass

  • This is the mass of the producers and consumers at each trophic level drawn graphically.
  • It can be:
    • Upright, e.g., in grasslands.
    • Inverted, e.g., in pond ecosystem.
      pyramid of biomass
      Fig 4: Pyramid of Biomass in Pond Ecosystem

Population Estimation Methods

  • It is important to find or estimate the sizes of the different populations in a habitat.
  • Direct counting or head count which involves the counting of every individual, is not always applicable for all organisms.
  • e.g., it is impossible to count directly the numbers of grasshoppers in an area.
  • Different sampling methods are thus used.
  • A sample acts as a representative of the whole population.
  • Some of the sampling methods used are as explained below

Quadrat Method

  • A Quadrat is a square, made of woos metal/hard plastic.
  • It can also be established on the ground using pegs, rope/permanent coloured ink, using metre rule or measuring tape.
  • The size is usually one square metre (1m2 ), in grassland.
  • In wooded or forest habitat it is usually larger, and can reach upto 20 m2 depending on particular species under investigation.
  • The number of each species found within the quadrat is counted and recorded.
  • Total number of organisms is then calculated by, finding the average quadrats and multiplying it with the total area of the whole habitat.
  • The number of quadrats and their positions is determined by the type of vegetation studied.
  • In a grassland, the quadrat frame can be thrown at random.
  • In other habitats of forest, random numbers that determine the locus at which to establish a quadrat are used.
    quadrat method

Line Transect

  • A line transect is a string or rope that is stretched along across the area in which all the plants that are touched are counted.
  • It is tied on to a pole or tent peg.
  • It is particularly useful where there is change of populations traversing through grassland, to woodland to forest land.
  • This method can also be used in studying the changes in growth patterns in plants over a period of time.

Belt Transect

  • Two line transects are set parallel to each other to enclose a strip through the habitat to be studied.
  • The width is determined by the type of habitat, i.e., grass or forest and by the nature of investigation.
  • In grassland it can be 0.5 m or 1 m.
  • Sometimes it can be 20 metres or more especially when counting large herbivores.
  • The number of organisms within the belt is counted and recorded.

Capture-recapture Method

  • This is used for animals such as fish, rodents, arthropods and birds.
  • The animals are caught, marked, counted and released.
  • For example, grasshoppers can be caught with a net and marked using permanent ink.
  • After sometime, the same area is sampled again, i.e., the grasshoppers are caught again.
  • The total number caught during the second catch is recorded.
  • The number of marked ones is also recorded.
  • Let the number caught and marked be a.
  • The total number in the second catch be b.
  • The number of marked ones in the second catch be c.
  • The total number of grasshoppers in the area be T.
    capture recapture

The total number T can be estimated using the following formula:

Total Number = Number caught during the first catch × Number caught in the second catch/number marked in the second catch


T = a × b/c

The following assumptions are made:

  • No migration, i.e., no movement in and out of the study area.
  • There is even distribution of the organisms in the study area.
  • There is random distribution of the organisms after the first capture.
  • No births or deaths during the activity.
  • After the estimation, the results can be used to show anyone of the following population characteristics:



  • Density is calculated by dividing the number of organisms by the size of the area studied.


  • Frequency is the number of times that a species occurs in the area being studied.

Percentage Cover:

  • This is the proportion of the area covered by a particular species.
  • For example, a given plant species may cover the whole of a given area.
  • In this case the plant is said to have 100% cover.


  • This is the term used to describe a species that exerts the most effect on others.
  • The dominance may be in terms of high frequency or high density.

Adaptations of Plants to Various Habitats

  • Organisms have developed structural features that enable them to live successfully in their particular habitats.
  • Plants found beneath the canopies of trees are adapted to low light intensities by having broad leaves.


  • These are plants that grow in dry habitats, i.e., in deserts and semi-deserts.
  • They have adaptations to reduce the rate of transpiration in order to save on water consumption.
  • Others have water storage structures.

Adaptations include:

  • Reduction of leaf surface area by having needle-like leaves, rolling up of leaves and shedding of leaves during drought to reduce water loss or transpiration.
  • Thick cuticle; epidermis consisting of several layers of cells;
  • leaves covered with wax or resin to reduce evaporation.
  • Sunken stomata, creating spaces with humid still air to reduce water holes.
  • Few, small stomata, on lower epidermis to reduce water loss.
  • Stomata open at night (reversed stomatal rhythm) to reduce water loss.
  • Deep and extensive root systems for absorption of water.
  • Development of flattened shoots and succulent tissue for water storage e.g. Opuntia.
    structure of xerophy HF88A
    structure of xerophy Bww68


  • These are the ordinary land plants which grow in well-watered habitats.
  • They have no special adaptations.
  • Stomata are found on both upper and lower leaf surfaces for efficient gaseous exchange and transpiration.
  • However, those found in constantly wet places e.g. tropical rain forests, have features that increase transpiration.
  • These plants are called hygrophytes.
  • The leaves are broad to increase surface areas for transpiration and thin to ensure short distance for carbon (IV) oxide to reach photosynthetic cells and for light penetration.
  • The stomata are raised above the epidermis to increase the rate of transpiration.
  • They have grandular hairs or hydathode that expel water into the saturated atmosphere.
  • This phenomenon is called guttation.

Hydrophytes (Water Plants)

  • Water plants are either submerged, emergent or floating.

Submerged Plants

  • The leaves have an epidermis with very thin walls and a delicate cuticle.
  • They have no stomata.
  • Water is excreted from special glands and pores at the tips.
  • Presence of large air spaces and canals (aerenchyma) for gaseous exchange and buoyancy.
  • Some plants have filamentous leaves In order to increase the surface area for absorption of light, gases and mineral salts.
  • Some plants are rootless, hence support provided by water.
  • Mineral salts and water absorbed by all plant surfaces.
  • In some plants, the stem and leaves are covered with a waxy substance to reduce absorption of water. e.g. Ceratophyllum and Elodea sp.
    submerged hydrophyte QH5Be

Floating Plants

  • Their structure is similar to that of mesophytes.
  • The leaves are broad to increase the surface area for water loss.
  • They have more stomata on the upper surface than on the lower surface to increase rate of water loss.
  • Examples are Pistia sp. (water lettuce), Salvinia and Nymphea.

Halophytes (Salt Plants)

  • These are plants that grow in salt marshes and on coastlines.
  • They have root cells that concentrate salts and enable them to take in water by osmosis.
  • They have salt glands which excrete salts.
  • Fruits have large aerenchymatous tissues for air storage that makes them float.
  • Some have shiny leaves to reduce water loss.
  • The mangrove plants have roots that spread horizontally, and send some branches into the air.
  • These aerial roots are known as breathing roots or pneumatophores.
  • They have lenticel-Iike openings called pneumatothodes through which gaseous exchange takes place.


  • This is the introduction of foreign material, poisonous compounds and excess nutrients or energy to the environment in harmful proportions.
  • Any such substance is called a pollutant.

Effects and Control of Causes of Pollutants in Air, Water and Soil

  • Industrialisation and urbanisation are the main causes of pollution.
  • As human beings exploit natural resources the delicate balance in the biosphere gets disturbed.
  • The disturbance leads to the creation of conditions that are un-favourable to humans and other organisms.

Sources of Pollutants

  • Motor vehicles release carbon (II) oxide, sulphur (IV) oxide, and nitrogen oxides and hydrocarbons.
  • Agricultural chemicals, fertilisers and pesticides.
  • Factories, manufacturing and metal processing industries.
  • They release toxic substances and gases as well as synthetic compounds that are bio-undegradable.
  • They release solid particles or droplets of poisonous substances e.g. arsenic, beryllium, lead and cadmium.
  • Radioactive waste: Leakages from nuclear power stations and testing sites release radioactive elements like strontium-90 which can eventually reach man through the food chain.
  • Domestic waste and sewage are released raw into water bodies.
  • Oil spills from accidents in the seas and leakage of oil tankers as well as from offshore drilling and storage and processing.



Water Pollution

  • In most cases, toxic chemical wastes from industries are discharged into water.
  • Toxic chemicals such as mercury compounds may be ingested by organisms.
  • Insecticides like DDT, and weedkillers eventually get into the water and contaminate it.
  • Oil and detergents also pollute water.
  • Excess nitrates and phosphates from sewage and fertilisers cause overgrowth of algae and bacteria in water.
  • This is called eutrophication.
  • As a result there is insufficient oxygen which causes the deaths of animals in the water.

Air Pollution

  • Smoke from industries and motor vehicles contains poisonous chemicals like carbon (II) oxide, carbon (IV) oxide, sulphur (IV) oxide and oxides of nitrogen.
  • When sulphur (IV) oxide and oxides of nitrogen dissolve in rain, they fall as acid rain.
  • Accumulation of carbon (IV) oxide in the atmosphere causes the infrared light to be confined within the atmosphere, the earth's temperature rises.
  • This is called the greenhouse effect.
  • Carbon particles in smoke coat the leaves of plants and hinder gaseous exchange and photosynthesis.
  • The particles also form smog in the air.
  • Lead compounds are from vehicle exhaust pipes.
  • All these have negative effects on man and the environment.

Soil/Land pollution

  • Plastics and other man-made materials are biologically non-degradable i.e they are not acted upon by micro-organisms.
  • Scrap metal and slag from mines also pollute land.
  • Failure to rehabilitate mines and quarries also pollute land.

Effects of Pollutants to Humans and Other Organisms

  • Chemical pollutants e.g. nitrogen oxides, fluorides, mercury and lead cause physiological and metabolic disorders to humans and domestic animals.
  • Some hydrocarbons as well as radioactive pollutants acts as mutagens (cause mutations) and carcinogens induce cancer.
  • Radioactive pollutants like strontium, caesium and lithium are absorbed into body surface and cause harm to bone marrow and the thyroid gland.
  • Communicable diseases like cholera are spread through water polluted with sewage.
  • Thermal pollution result in death of some fish due to decreased oxygen in the water.
  • Oil spills disrupt normal functioning of coastal ecosystems.
  • Birds that eat fish die due to inability to fly as feathers get covered by oil.
  • Molluscs and crustaceans on rocky shores also die.

Control of Air Pollution

  • Use of lead-free petrol and low sulphur diesel in vehicles.
  • Use of smokeless fuels e.g electricity or solar.
  • Filtration of waste gases to remove harmful gases.
  • Liquid dissolution of waste gases.
  • In Kenya, factories are subjected to thorough audits to ensure that they do not pollute the environment.
  • Factories should be erected far away from residential areas.
  • Reduce volume or intensity of sound.
  • Use of ear muffs.
  • Vehicle exhaust systems should be fitted with catalytic oxidisers.
  • Regular servicing of vehicles to ensure complete combustion of fuel.

Control of Water Pollution

  • Treatment of sewage.
  • Treatment of industrial waste before discharge into water.
  • Use of controlled amounts of agrochemicals.
  • Organic farming and biological control.
  • Avoid spillage of oils and other chemicals into water.
  • Good water management.
  • Stiff penalties for oil spillage.
  • Use of Pseudomonas bacteria that naturally feed on oil and break it up.

Control of Soil Pollution

  • Addition of lime to farms to counteract the effect of agrochemicals.
  • Recycling of solid waste.
  • Compacting and incineration of solid waste.
  • Use of biodegradable materials and chemicals.
  • Good soil management to avoid soil erosion.

Human Diseases

  • The term disease denotes any condition or disorder that disrupts the steady state of well being of the body.
  • Health is a state of physical, mental and emotional well being in the internal environment of the body.
  • Some of the causes of diseases are due to entry of pathogens and parasites.
  • Pathogens include bacteria, viruses, protozoa and fungi.
  • Parasites are organisms which live on or in the body of another organisms.
  • Vectors are animals that carry the pathogen from are person to another.
  • Most are ectoparasites that transmit the disease as they feed.

Bacterial Diseases


  • Causative agent a bacterium Vibrio cholerae.
  • Transmission - It is spread through water and food contaminated by human faeces containing the bacteria.
  • The bacteria produce a powerful toxin, enterotoxin, that causes inflammation of the wall of the intestine leading to:
    • Severe diarrhoea that leads to excessive water loss from body.
    • Abdominal pain
    • Vomiting
    • Dehydration which may lead to death.


Prevention and Control

  • Adequate sanitation such as water purification sewage treatment and proper disposal of humanm faeces.
  • Public and personal hygiene e.g washing hands before meals and washing fruits and vegetables, boiling drinking water.


  • Carriers should be identified, isolated and treated during outbreaks.


  • Use of appropriate antibiotics.
  • Correcting fluid loss by injecting fluids or by administration of oral rehydration solutions.


  • Causative agent.
  • The disease is caused by Salmonella typhi.
  • Transmission is through contaminated water and food.
  • It is also transmitted by certain 'e.g foods, e.g. oysters, mussels and shell fish.


  • Fever
  • Muscle pains
  • Headache
  • Spots on the trunk of the body
  • Diarrhoea
  • In severe cases mental confusion may result and death.


  • Boil drinking water.
  • Proper sewage treatnient.
  • Proper disposal of faeces, if not flushed use deep pit latrines.
  • Observe personal hygiene e.g. washing hands before meals.
  • Washing fruits and vegetables.


  • Use of appropriate antibiotics.

Protozoa Diseases


  • Malaria is caused by the protozoan plasmodium.
  • The most common species of plasmodium are P. falciparum, P. vivax, P. rnalariae and P. ovale with varying degree of severity.


  • Is by female anopheles mosquito as it gets a blood meal.



  • Headache, sweating, shivering, high temperature (40-41 0C) chills and joint pains.
  • The abdomen becomes tender due to destruction of red blood cells by the parasites.


  • Destroy breeding grounds for mosquitoes by clearing bushes and draining stagnant water.
  • Kill mosquito larvae by spraying water surfaces with oil.
  • Use insecticides to kill adult mosquitoes
  • Sleeping under a mosquito net.
  • Take preventive drugs.


  • Use appropriate anti-malarial drugs.

Amoebic dysentry (Amoebiasis)


  • This disease is caused by Entamoeba histolytica.
  • The parasites live in the intestinal tract but may occasionally spread to the liver.
  • Transmission - They are transmitted through contaminated water and food especially salads.


  • Abdominal pain, nausea and diarrhoea.
  • The parasites cause ulceration of the intestinal tract, which results in diarrhoea.

Prevention and control

  • Proper disposal of human faeces.
  • Boiling water before drinking.
  • Personal hygiene e.g. washing hands before meals.
  • Washing vegetables and steaming particularly salads and fruits before eating.


  • Treatment of infected people with appropriate drugs.

Parasitic Diseases

Ascaris lumbricoides

  • Ascaris lumbricoides lives in the intestines of a man or pig, feeding on the digested food of the host.
  • The body of the worm is tapered at both ends.
  • The female is longer than the male.
    ascaris lubricoides

Mode of transmission

  • The host eats food contaminated with the eggs, the embryo worms hatch out in the intestine.
  • The embryo worms then bore into the blood vessels of the intestine.
  • They are carried in the bloodstream to the heart and then into the lungs.
  • As they travel through the bloodstream, they grow in size.
  • After sometime, the worms are coughed out from the air passages and into the oesophagus.
  • They are then swallowed, eventually finding their way into the intestines where they grow into mature worms.

Effects of Ascaris lumbricoides on the host

  • The parasites feed on the host's digested food.
  • This results in malnutrition especially in children.
  • If the worms are too many, they may block the intestine and interfere with digestion.
  • The worms sometimes wander along the alimentary canal and may pass through the nose or mouth.
  • In this way, they interfere with breathing and may cause serious illness.
  • The larvae may cause severe internal bleeding as they penetrate the wall of the intestine.

Adaptive Characteristics

  • The female lays as many as 25 million eggs.
  • This ensures the continuation of the species.
  • Eggs are covered by a protective cuticle that prevents them from dehydration.
  • The adult worms tolerate low oxygen concentration.
  • Have mouth parts for sucking food and other fluids in the intestines.
  • Has a thick cuticle or pellicle to protect it from digestive enzymes produced by the host.

Control and Prevention

  • Personal hygiene e.g. washing hands before eating.
  • Proper disposal of faeces.
  • Washing of fruits and vegetables.


  • Deworm using appropriate drugs ant-helmintics.


  • Schistosoma or bilharzia worm is a flat worm, parasitic on human beings and fresh water snails. (Biomphalaria and Bulinus.)
  • The snail act as intermediate host.

Mode of Transmission

  • Schistosomiasis also known as a bilharsiasis is caused by several species of the genus schistosoma.
  • Schistosoma haematobium infects the urinary system mainly the bladder
  • S. japonicum and S. mansoni both infect the intestines.
  • Schistosoma haemotobium is common in East Africa where irrigation is practised and where slow moving fresh water streams harbour snails.
  • It is spread through contamination of water by faeces and urine from infected persons.
  • The embryo (miracidium) that hatch in water penetrates into snails of the species Biompharahia and Bulinus.
  • Inside the snail's body, the miracidium undergoes development and multiple fission to produce rediae.
  • The rediae are released into the water and develop to form cercariae which infect humans through:
    • Drinking the water
    • Wading in water;
    • Bathing in snail-infested water.
  • The cercaria burrows through the skin and enters blood vessel.

Effects on the host

  • Inflammation of tissues where egg lodge.
  • Ulceration where eggs calcify.
  • Egg block small arteries in lungs leading to less aeration of blood.
  • The body turns blue - a condition known as cyanosis.
  • If eggs lodge in heart or brain, lesions formed can lead to death.
  • Bleeding occurs as the worms burrow into blood vessels (faeces or urine has blood).
  • Pain and difficulty in passing out urine.
  • Nausea and vomiting.
  • When eggs lodge in liver ulceration results in liver cirrhosis.
  • Death eventually occurs.

Adaptive Characteristics

  • The female has a thin body and fits into small blood vessels to lay eggs.
  • Eggs are able to burrow out of blood vessel into intestine lumen.
  • Many eggs are laid to ensure the survival of the parasite.
  • Large numbers of cercariae are released by snail.
  • The miracidia and cercariae larvae have glands that secrete lytic enzymes which soften the tissue to allow for penetration into host.
  • The male has a gynecophoric canal that carries the female to ensure that eggs are fertilised before being shed.
  • Has suckers for attachment.

Prevention and Control

  • Drain all stagnant water
  • Boil drinking water.
  • Do not wade bare feet in water.
  • Wear long rubber boots and gloves (for those who work in rice fields).
  • Eliminate snails, by spraying with molluscides.
  • Reporting to doctor early when symptoms appear for early treatment.

Practical Activities

  • Ecology is best studied outdoors.
  • Students identify a habitat within or near the school compound, e.g. a flower bed.
  • The quadrat method is used.
  • Observation and recording of the various animals as well as their feeding habits is done.
  • Birds that feed on the plants or arthropods in the area studied are noted through observation of habitat at various times of the day.
  • Food chains are constructed e.g green plants ~ caterpillar ~ lizard and many others involving all organisms in the area.
  • The numbers of animals in 1 m2 is counted directly or estimated e.g small arthropods like black ants.
  • The number of plants is easily counted and recorded and ratio of consumers to producers calculated.
  • It will be noted that in terms of numbers where invertebrates are involved, there are very many consumers of one plant.
  • Several other quadrats are established and studied and averages calculated.

Adaptions to Habitat


  • Specimen of hydrophytes e.g water lily is observed.
  • Students should note the poorly developed root systems and broad leaves.
  • Stomata distribution on leaf surface is studied through microscopy or by emersing a leaf in hot water and counting number of bubbles evolved.


  • Ordinary plants e.g bean hibiscus and zebrina can be studied.
  • Size of leaves is noted and stomata distribution studied.


  • Specimen include Euphorbia, cactus and sisal which are easily available.
  • The root system e.g in sisal is noted as shallow but extensive.
  • It will be noted that sisal has fleshy leaves and stem while cactus and Euphorbia have fleshy stem but leaves are reduced to small hair-like structures.

Comparison of Root Nodules from Fertile and Poor Soils - Root Nodules

  • Are swellings on roots of leguminous plants.
  • Soil fertility determines number of root nodules per plant.
  • Bean plants are best used in this study.
  • One plot can be manured while the other is not.
  • Similar seeds are planted in the two plots.
  • The plants are uprooted when fully mature (vegetatively) i.e any time after flowering and before drying.
  • The number of nodules per plant is counted.
  • An average for each plot is calculated.
  • It is noted that the beans from fertile soil have more and large nodules than those grown in poor soils.

Estimation of Population Using Sampling Methods

  • The number of organisms both producers and the various consumers is recorded in each area studied e.g. using a quadrat.
  • The total area of the habitat studied is measured.
  • The average number of organisms per quadrat (1 m 2 ) is calculated after establishing as many quadrats as are necessary to cover the area adequately.
  • Total population of organisms is calculated from the area.
  • Abiotic environment is studied within the area sampled.
  • Air temperature soil surface temperature are taken and recorded.
  • This is best done at different times of day, i.e., morning afternoon and evening.
  • Any variations are noted.
  • pH of the soil is measured using pH distilled water to make a solution.
  • Litmus papers can be used to indicate if soil is acidic or alkaline, but pH paper or meter gives more precise pH values.
  • Humidity is measured using anhydrous blue cobalt chloride paper which gives a mere indication of level of humidity.
  • A windsock is used to give an indication of direction of wind.
  • As all the abiotic factors are recorded observations are made to find the relationships between behaviour of organism and the environmental factors for example:
    • The temperature affects the behaviour of animals.
    • The direction of wind will affect growth of plants.
    • The level of humidity determines the type, number and distribution of organisms in an area.
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