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ECOLOGY
Definition;
 Is the scientific study of the complex relationships between organisms and their environment
...

 Environment is the immediate surroundings of an organism
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 The biosphere is divided into two major regions namely;
i
...

ii
...

 On land, there are several biogeographical areas, each with specific conditions that support distinct species of plants and animals
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 Some of these areas may possess similar physical conditions, therefore supporting similar plants and animals; these areas are
collectively called Biomes
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 Organisms have developed adaptations to live in each of the biomes e
...
e desert animals are able to feed less often, thus conserving energy both by slowly
metabolizing food and by not frequently hunting or foraging; while marine organisms are adapted to osmo regulate in highly saline
environment
...
g
i
...

ii
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g snakes, snails, those in benthic zone not able to withstand wave action e
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g photosynthetic algae inhabiting surface zone
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Desert biome divide into surface and subterranean zones; with those in surface zone adapted to withstand extreme heat,
while those in subterranean able to survive in low oxygen content
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ECOLOGICAL NICHE:
 Is the role and position any species has within its habitat, and its interactions with living and non-living environment
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Example
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Types of ecological niche
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 Fundamental niche;
Occurs in the absence of predators, competitors, and parasites; allowing the organism experience a larger habitat and
perform a variety of roles
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(i) Water (aquatic) ecosystems may be fresh water bodies (e
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lakes, ponds, rivers) or marine water bodies (e
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sea,
ocean)
...
g
...
g
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(ii) Land (terrestrial) ecosystems include forests, deserts, savanna, etc
THE MAJOR COMPONENTS OF AN ECOSYSTEM
a) Abiotic / non living things: these are physical and chemical factors that influence living organisms on land (terrestrial) ecosystems

and in water (aquatic)
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climatic factors, which include; Temperature, Light, Wind, Humidity, rainfall etc
ii
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g
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Topography
iv
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g fire and wave action etc
Question
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o Ultimate heating and cooling of rocks cause air to break and crack into small pieces and finally form soil
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g birds to avoid over heating or freezing
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o High temperature increase transpiration and sweating
o Low temperatures break dormancy of some plants
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g cabbage (vernalisation)
o Exposure to low temperature(stratification) stimulate germination in some seeds after imbibitions
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(i) adaptations of animals for life in hot and dry deserts
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g ear lobes ; to increase surface area over which heat is lost
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Behavioral adaptations
 Most are nocturnal, i
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g
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g desert snakes
 Salivation of the neck and legs ; increasing heat loss by evaporation e
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adaptations of animals for life in cold environments
Structural adaptations
 Thick layer of fat under the skin; to increase on insulation by avoiding heat loss
 Small body extremities to reduce the surface area over which heat is lost
 Large sized; thus small surface area to volume ratio; reducing amount of heat lost to the surrounding
 Thick fur; to increase on insulation
 Tissues tolerant to extreme changes in temperature; maintaining their normal functions in the body
Physiological adaptations
 Enzymes work under a high optimum temperature range to maintain metabolism during day and night
Behavioral adaptations
 Hibernation( is seasonal response by animals to cold temperature during which they become dormant, body temperature and
metabolic rate fall to the minimum required for maintaining the vital activities of the body) The animals, said to be in ‘deep
sleep’ ably reduce energy needs to survive the winter when food is scarce allowing them survive extreme cold conditions eg
in polar bears
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g penguins
Rain fall;
o Amount of rainfall in a given area determines the abundance, distribution and types of plants in the area
Ecological significances of water
 Habitat for many aquatic organisms e
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g plants during transpiration, some animals
during sweating
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Humidity;
Amount of water in the atmosphere;
o affects the rate at which water evaporates from organisms i
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o
o

Accordingly , organisms within areas of low humidity are adapted to avoid excessive loss of water by;
 Having reduced number of sweat glands e
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Controls other activities of animals like feeding, hunting, and movements e
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Controls opening and closure of stomata; therefore affecting rate of photosynthesis and transpiration
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o Pollination
o Dispersal of seeds and spores; increasing the spread of non-motile organisms e
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o Takes part in rain formation
o Current and wave formation in seas and lakes enables distribution of mineral salts
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o Causes physical damage to vegetation and soils e
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o Increases dissolution of oxygen in aquatic bodies; thereby increasing aerobic activities of organisms
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 Absence of light causes etiolation (elongation of shoot inter nodes)
...
g
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 Phototropism, by redistributing auxins on the darker sides of shoots and roots, with cells on darker side elongating more
than those on illuminated side
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(are negatively photoblastic)
 Stomatal opening and closure; with most plant species opening their stomata during day(when there is light) and closing
during night (in absence of light/darkness)
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 Stimulates synthesis of vitamin D in mammals; where lipids(sterols) in the dermis are converted to vitamin D by uv light
 It enables the mechanisms photoreceptions in eyes
 Absence of light results in failure of chlorophyll formation in plants i
...
plant remains yellow, and leaves fail to expand
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g
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 Necessary for the germination of certain seeds e
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lettuce
(ii) Topography
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o High altitude is associated with, low atmospheric pressure; low average temperatures,; increased wind speed; decreased
partial pressures of oxygen, thus few organisms live permanently here
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Assignment
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(iii)
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Soil Ph
 Influences physical properties of soil and availability of certain minerals to plants, thus affecting their distribution in soil;
i
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g in acidic medium, the rate of decomposition is reduced, subsequently recycling of matter
in an ecosystem reduced
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 Plants like rice, marshes, and sedges have developed air spaces among root tissues , allowing some diffusion of oxygen from
aerial parts to help supply the roots
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Burrowing organisms e
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Earthworms also improve soil fertility by mixing of soil, as they bring leached minerals from lower layers within reach of
plant roots
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Air content;
 Spaces between soil particles is filled with air from which plant roots obtain oxygen by diffusion for aerobic respiration,
 Also essential for aerobic respiration by micro organisms in the soil that decompose the humus
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 Determines the osmotic pressure of water; therefore the organisms have developed structural, behavioral, and physiological
adaptations to osmo regulate in the respective salt concentration, ( read adaptations of fresh water fish, marine water fish
and migratory fish to their osmo regulatory problems)
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 Plants growing in soils deficient of certain salts, e
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Significances of mineral salts to plants
 Mineral salts together with other solutes determine the osmotic pressure of cells and body fluids
 Determinants in anion and cation balance in cells, e
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 Metabolic activators; some ions activate enzymes, e
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 Mineral salts like potassium are involved in formation of cell membrane and opening of stomata;
 Development of stem and root e
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calcium pectate in formation of plant cell wall
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Properties of fire
 Fire intensity;
Is the heat content of the fire,
Depends on environmental factors such as wind, temperature as well as the amount and type of vegetation
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 Fire severity; is measured in terms of major vegetation destroyed by the fire
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 Breaks dormancy (seed dormancy), incase seed coats are hard and impermeable
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 Improves on visibility of organisms such as predators, prey, mates allowing them easily carry out their activities
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 Destroys pests
 Controls undesirable plant species and weeds
Negative effects
 Increase soil erosion; leading soil infertility
 Kills slow moving animals e
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 Reduction in population density and biodiversity
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 Air pollution by products such as carbon monoxide and carbon dioxide, increasing on global warmimg
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Grasses grow in tussocks to protect the young growing buds
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e
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Many plants are annuals to avoid fire severity in form of seeds, which may be underground
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(b)
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THE MAJOR BIOTIC / LIVING COMPONENTS OF ECOSYSTEMS
1
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g carbon
dioxide and water
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g trees, shrubs, grass
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Others are flagellates like euglena, volvox, chlamydomonas etc
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g sulphur bacteria i
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2
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 Are classified as;
(i) Primary consumers(Herbivore):





A consumer that eats plants
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g
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(ii) Secondary consumers(Carnivore):


A consumer that eats other animals
...
g
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E
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vultures, hyenas, marabou stocks etc


(iv) Omnivore: A consumer that eats both plants and animals
...
g
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Decomposer:


An organism that feeds on dead organic matter
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(dead and waste matter not eaten by consumers)

 Classified into;
(i) Detrivore/ macro decomposers;

 E
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(ii) Saprophyte:

 A microbe (bacterium or fungus) that lives on detritus
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(2) Recycles nutrients to be used by other organisms e
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Mineral salts are released from dead bodies into soil for plant growth
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ENERGY FLOW THROUGH AN ECOSYSTEM
The sun is the primary source of energy in the ecosystem
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It is then transferred from one feeding level to another through feeding relationships like food chains or food webs
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Along the food chain, only a small proportion of the available energy is transferred from one feeding level to another; much
energy is lost as heat during sweating and evaporation, excretion , respiration, egestion, and some remains locked up in
indigestible parts of the plant like cellulose, or bones, hooves, hair, skin etc of animals
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



TROPHIC EFFICIENCY/ ECOLOGICAL EFFICIENCY

 Is the percentage of energy at one trophic level that is converted into organic substances at the next trophic level
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Can be measured using several methods i
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-Amount of carbon dioxide consumed during photosynthesis
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-Rate of consumption or use of raw materials
 Can be divided into;
(i) Gross productivity; is the total amount of energy and organic matter stored in an organism over a period of time
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(iii) Primary productivity; Is the amount of energy and organic material stored in primary producers
...
)

The initial amount of energy incorporated into primary producers during photosynthesis is called Gross primary productivity
(G
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P)
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P
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It can
as well be called dry mass of the harvest crop
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Secondary productivity; Is the amount of energy incorporated into the body of consumers
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Net secondary productivity; is the amount of energy that can successfully be transferred from one consumer to another
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Herbivores their diet mainly consists of plant materials which are not easily digested
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Net secondary productivity is higher in exotherms than in endotherms, because;
 Energy from absorbed food, is used in replace the lost heat to their surrounding, inorder to maintain a constant body
temperature, unlike exotherms that depend mostly on behavioral means to maintain their body temperature
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FOOD CHAIN
 A linear sequence of energy flow from producers through a series of organisms in which there is repeated eating and being
eaten
...
e
(i) Grazing food chain (ii) Detritus food chain
(i)
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 These are grazed upon by herbivores
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It can be in grass land or water body (aquatic)
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g
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 exists in both aquatic and terrestrial habiats
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g Tree log
wood lice toad python
Dead animal maggotbirds python
FOOD WEB
 is a complex nutritional interrelationship that illustrates alternative food sources and predator for each organism
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Examples of food webs in a grassland

EXERCISE
1
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2
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Discuss the interactions between the living and non living components of such an ecosystem
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(a) What is an ecosystem?

NB
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 Examination of stomach content through dissecting the animals’ stomach
 Faecal method; observation of faecal materials egested by an animal
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Assignment
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Three types exist i
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pyramid of numbers
(ii) pyramid of biomass
(iii) pyramid of energy
NB
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(i) pyramid of numbers
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NB
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In some cases, the consumers may be more than the producers e
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Limitations of pyramid of number
o Drawing the pyramid accurately to scale may be difficult e
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o Pyramids may be inverted
o The trophic level of an organism may be difficult to ascertain
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(ii) pyramid of biomass; is a histogram showing the total dry mass of organisms present at each feeding level
o
o

Advantages
 Reduces the possibility of forming inverted pyramids because its construction depends n biomass of organisms
NB
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Disadvantages/limitations of pyramid of biomass
 Does not allow for changes in biomass at different times of the year e,g deciduous trees have larger biomass in summer than in
winter when they shed off leaves
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g a mature tree has a large biomass which increases over many
years
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 Results may not be accurate, e
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(iii) pyramid of energy flow it is a histogram showing the total amount of energy present at each feeding level
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 More informative than than pyramids of numbers and biomass because it shows the amount of energy required to support each
trophic level
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 explains why the earth can support more people if they eat at lower trophic level (by consuming grains, vegetables and fruits
directly rather than passing such crops through another trophic level and eating grain eaters
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 Biomass may not be equivalent to energy value, e
...
1g of fat has many more kJ than 1g of cellulose or lignin
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 The solar input of energy may be included as an extra rectangle at the base
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MATERIAL CYCLING/BIOGEOCHEMICAL CYCLING (NUTRIENT CYCLING)
 process by which chemical compounds of a particular element that constitutes living matter are transferred between
living organisms (biotic phase) and non-living environment (abiotic phase)
...
CARBON CYCLE
 Based on carbon dioxide gas, making up 0
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 Carbon fixation involves the reduction of carbon dioxide to large organic molecules during photosynthesis and
chemosynthesis
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 Over millions of years, buried deposits of dead plant debris and bacteria are compressed between layers of sediment to form
the carbon-containing fossil fuels e
...
coal, oil and natural gas, which when burnt release carbon dioxide into air
...
As water warms, more dissolved carbon dioxide returns to the atmosphere
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 When the animals with calcium in shells and skeletons die and drift into deep bottom sediments of oceans, immense
pressure causes limestone and chalk to form after a very long period of time
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How human activities affect the carbon cycle
i) Cutting trees and other plants that absorb CO2 through photosynthesis increases carbon dioxide in the atmosphere
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(b) NITROGEN CYCLE

 Nitrogen is the atmosphere’s most abundant element, with chemically unreactive nitrogen gas making up 78% of the volume of the
troposphere
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 Atmospheric electrical discharges in the form of lightning causes nitrogen and oxygen in the atmosphere to react and produce oxides
of nitrogen, which dissolve in rainwater and fall to the ground as weakly acidic solutions
...
g
...
g
...
g
...

 Nitrification occurs when ammonium compounds in soil are converted first to nitrite ions(highly toxic to plants) by Nitrosomonas
bacteria and later to nitrate ions by Nitrobacter bacteria
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g
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 Assimilation occurs when inorganic ammonia, ammonium and nitrate ions are absorbed by plant roots to make nucleic acids, amino
acids and protein
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g
...
Nitrogen gas is released into the atmosphere while oxygen is used for the respiration of these
bacteria
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Burning of fuels forms nitric oxide, which reacts with atmospheric oxygen to form nitrogen dioxide gas that reacts with water
vapour to form acid rain containing nitric acid
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2
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3
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Adding nitrogen compounds to aquatic ecosystems e
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sewage algal blooming, which upon death, their decomposition causes
oxygen shortage resulting into death of aerobic organisms e
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some fish
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The accelerated deposition of acidic nitrogen containing compounds e
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NO2 and HNO3 onto terrestrial ecosystems stimulates
growth of weeds, which outcompsete other plants that cannot take up nitrogen as efficiently
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(a) Describe the flow of energy and the cycling of carbon and nitrogen in any named ecosystem
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Suggest reasons why felling and removal of forest trees result in changes in the levels of nutrients in the soil
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Biotic factors are those that arise in organisms interacting with each other
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(a) Human influence
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(b) Competition
 This is a relationship whereby two individuals of the same species or different species struggle to obtain resources which are in limited
supply
...
g plants competing for light, carbin dioxide, water, minerals, pollinators , and sites for spores and seeds to germinate while
animals compete for food, mates, breeding sites and shelter from predators
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 Intraspecific competition tends to have a stabilising influence on population size
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 If the population gets too small, intraspecific population decreases, so the population increases again
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Competition is very intense when there is significant overlap of niches, and in this case one of the competing species must;
(i) migrate to another area if possible
(ii) shift its feeding habits or behaviour through natural selection and evolution
(iii) suffer a sharp population decline or
(iv) become extinct in that area, otherwise two species can never occupy exactly the same ecological niche
...
g (i)
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confusum were kept in the laboratory in bottles of flour acting as a
habitat and providing food for them, under variable temperature conditions(24-34) and humid condtions(very humid , 70%RH&
30% RH)
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At high temperatures and in veryhumid conditions, Tribolium castenum succeded better , while at low temperatures
and very dry conditions T
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Whatever the conditions, only one of the species eventually survived
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Two species of Paramecium Aurelia and P
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Observation (i)When cultured separately, each specie has maximum population, only coming almost constant with time due to;
-Presence of toxic wastes which can poison paramecium
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-Decrease in food measures
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caudatum and after several days , P
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P
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Competitive advantages of P
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- High growth rate
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- Being small, it requires less food hence can easily survive when food is scarce
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HOW SPECIES REDUCE OR AVOID COMPETITION THROUGH RESOURCE PARTITIONING
Resource partitioning is the dividing up of scarce resources so that species with similar needs use them (i) at different times (ii) in
different ways or (iii) in different places
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 Resource partitioning decreases competition between two species leading to increased niche specialisation
Examples of resource partitioning:
(i)
...

(ii)Hawks and owls feed on similar prey, but hawks hunt during the day and owls hunt at night
...
g
...

(iv)Different species of eagles in a forest feed at different times of the day e
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bald headed eagles are most active early mornings and
evenings while the white-breasted eagles feed vigorously towards noon
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(vi)
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NB:
i) The more that two species in the same habitat differ in their use of resources, the more likely they can coexist
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iii) The tendency for characteristics to be more divergent when populations belong to the same community than when they
are isolated is termed character displacement e
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Question
...
(a)
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(b)
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Its growth can be measured by counting the number of fronds
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Species grown separately
Species grown together
Days
L
...
minor
L
...
minor
0
30
30
30
30
16
63
78
48
105
36
126
142
84
234
46
177
225
84
324
54
165
276
48
360
60
129
219
45
354
(i)
...

(ii) What do the graphs suggest about the growth rate of the two species grown separately?
(iii)Account for this difference
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(v)
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(c
...
This is a relationship whereby members of one species (the predator) feed on all or part of a living organism of
another species (the prey)
...
g
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A predator is an animal that feeds on another live organism
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PREDATOR-PREY INTERACTIONS IN ECOSYSTEMS

Description of the changes in population numbers:
Initially, the population of the prey is higher that the
population of the predator
...

The population of the prey reaches a maximum earlier
the predator
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As the predator population continues to decrease, the
prey population starts to increase rapidly, followed by a
rapid increase in predator population
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Explanation for the observed changes in populations:
At the beginning ,there are more prey than predator to provide food to the predators
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The large number of preys provides food to predators, so they reproduce fast and increase in numbers
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The decrease in prey numbers causes the predators to starve and even their reproduction reduces, so the predator numbers crash
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Evolutionary significance of predator –prey
 Predation usually eliminates the unfit (aged, sick, weak)
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How are the predation suited for capturing prey?
 Have keen eyes for locating prey eg wolves, African lions hunt in groups
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 Nocturnal predators eg bats have highly developed sense for detecting sound made by prey
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 Web-spinning spiders use their silky cob webs to catch small sized ground walking or flying insects
...
g sea anemones
 Have long and sharp canines which pierce and kill prey
 Well developed limbs which increase the speed of locomotion to chase and capture prey
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 Possession of highly developed sense of sight or smell alerting the presence of predators
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In some lizards, the tail breaks off when attacked giving the animal (lizard) time to escape
...

In some lizards tails break off when attacked, giving the animal enough time to escape
...
g
...
g
...

NB
...

Exists in various forms;
(i) warning colouration , conspicuous colouring that warns a predator that an animal is unplalable or poisonous e
...
g
...
g
chameleon
...
g
...
g
...
g
...
g
...
g
...

 Some species gain protection to avoid predation by mimicking (looking and acting like) other species that are distasteful to
the predator e
...
the non-poisonous viceroy butterfly mimics the poisonous monarch butterfly
...
g
...
g
...

 Other preys gain some protection by living in large groups e
...
schools of fish, herd of antelope, flocks of birds
...
g
...
g
...

 The flesh of some slow-moving fish is poisonous e
...
porcupine fish
...
g
...

 Other preys employ alarm signals and calls e
...
ants, various fish, small birds and mammals
...
(ii) predators will always be found in places of their potential prey
...

-is a biological control method
...
Insects transfer pollen grains from
anthers to stigma
...

 Both interactions between the flowering plants and animals like insects , birds & bats may be highly elaborate and species
specific
...
e
...

NB
...

Examples include; (i) Many features of flowering plants have evolved as a result of dispersal of plant’s gametes by insects and
insects have in turn evolved special traits for obtaining nectar (ii) Grasses have evolved the ability to deposit silica in their
leaves and stems to reduce their risks of being grazed, large herbivores have in turn evolved complex molars with enamel
ridges for grinding up grass
...
g
...

Two types exist i
...
(ii)interspecific antibiosis secretion by organisms
chemical substances into their surrounding that may be repellant to members of the different species e
...

(f) Parasitism
An organism called parasite obtains part or all its nutrients from the body of another organism of different species called host
...

Parasites do not usually kill their hosts, but the host suffers harm
...


Some parasites are facultative, live on or in the host for some time e
...
Pythium(a fungus) that causes damping off seedlings, on

killing the seedlings, lives as a saprophyte on their dead remains and others are obligate (live on or in the host for their entire lives
...
Is an interspecific association in which both organisms benefit
...
(i) cellulose digesting bacteria in gut of ruminants such as goats, cattle& sheep
...
(ii)leguminous plants e
...
The
plants obtain nitrates while bacteria obtains shelter, sugars, vitamins
...
In
ectotrophic mycorrhiza , the fungus forms a sheath covering lateral roots of forest trees such as oaks, beech , conifers, while
depending on photosynthesis by the tree to provide organic materials
...
(iv)lichens; algae and fungus
...
(v)hermit crab and
sea anemones , with the hermit crab(Eupagurus berhardu)s obtaining defence from the stinging cells of anemones(Adamsia) &
camouflaging from its predators
...

(h) Commensalism Is an association between organisms of different species in which one benefits while the other neither benefits
nor its harmed
...
g (i)cow and white egrets, epiphytes and host plant
...
Explain what is meant by the terms parasitism, mutualism and predation, indicating with the help of suitable
examples how they differ from one another
...

 It is a process by which plants and animal communities in a given area change gradually over time, becoming replaced by
different and usually more complex communities
...

 The process of succession continues through stages known as seral stages and there are a number of sere (complete
succession) according to the environment being colonized
...
g deserts(iv) lithosere; succession on a rocky surface
 The first seral stage has pioneers and the final stage has a climax community, a final stable community at the end of
succession, which a particular environment can sustain
...

Types of succession
a) Primary succession
b) Secondary succession
a) Primary succession
This is the gradual change in species composition of an area that has never had any vegetation growing on it
...

An example of primary succession on land

Description of Primary succession on land
 Lichens and mosses attach to bare rocks and start forming soil by trapping wind- blown soil particles, producing tiny bits of
organic matter and secreting mild acids that slowly breakdown the rock
...

 As patches of soil build up and spread, eventually the pioneer species are replaced by the early successional plants like
small grasses and ferns, whose seeds and spores respectively germinate after arriving by wind or in droppings of birds
...

 After a long period of time, the soil becomes deep, moist and fertile enough to support the growth of mid successional plant
species like herbs, large grasses, low shrubs and small trees that need a lot of sunlight
...

 Unless natural or human processes disturb the area, a complex forest community remains
(b) Secondary succession
...

It occurs on abandoned farmlands, burnt or cut forests, heavily polluted streams, flooded land
...

Seeds and spores can be present in the soil and can be carried from nearby plants by wind, birds and insects
...

Characteristics of the stages of primary succession;
a) Early succession
 Species grow very close to the ground and have low biomass
...

 Species are simple and small sized
...

 Community is open ie allows space for other colonizers
...

 Species are poor competitors and hence get replaced by higher, more demanding plants like grasses ,shrubs and trees
...

 Net productivity is high
...

b) Late succession
 Plants are of large size and complex
...

 Biomass is high
 Net productivity is low
 Community takes a longtime to establish
...

 There is increased soil depth and nutrients
...

 There is little space for new species
 The climax community is stable and is in equilibrium with its environment
...

POPULATION DYNAMICS
These are changes in population in response to environmental stress or environmental conditions
...

TERMS USED IN POPULATION STUDIES:
Population size: Number of individuals in a population
...
Expressed as
the number of individuals born in a given period for every 1000 individuals e
...

Death rate (mortality): Number of individuals dying per unit of time per unit of population (humans: number of deaths per
1000 per year e
...
20 deaths per 1000 people per year)
Environmental resistance: All the environmental factors acting jointly to limit the growth of a population
...

Age structure/distribution; is the proportion of individuals of each age in a population
...






Immigration: Movement of individuals into a population from neighboring populations
...

Rare species: Species with small populations either restricted geographically with localized habitats or with widely scattered
individuals
...

Extinct species: Species, which cannot be found in areas they previously inhabited nor in other likely habitats
Population distribution/dispersion - distribution of organisms in a habitat
...
e (i) uniform
distribution organisms are equidistantly placed due to severe struggle for resources in the environment
...
(iii) clumped distribution organisms aggregate into groups to gain better protection, feeding, reproduction
etc
...

NB
...

POPULATION GROWTH PATTERNS
 Population grows when(i) natality is greater than mortality (ii) immigration is greater than emigration
 Population growth may form a curve which is either (i) exponential population growth curve (J-shaped) (ii) logistic
population growth curve( Sigmoid/S-shaped)
(i) Exponential population growth (J-shaped curve)
It is a theoretical population growth curve in which the population growth rate increases with time indefinitely
...

It occurs when resources are unlimited and the population can grow at its intrinsic rate of growth
...


Population size

C

B

A

Description
Number of individuals(population) is small
...
Later thw
population size increases rapidly/sharply/drastically with time
along CB
Explanation
Initially , the number of individuals increases gradually with
time because the population size is small, thus few reproducing
individuals, ,reproducing individuals are scattered within the
environment, some may not have reached reproductive age,
organisms are still getting used to their environment
...

 Population growth starts out slowly and then proceeds faster to a maximum (carrying capacity) and then levels off
...

 The population stabilises at or near the carrying capacity (K) of its environment due to environmental
resistance(any factors that may prevent a population from increasing as expected eg predation, parasitism, and
accumulation of toxic substances)

The actual factors responsible for the shape of each phase depend on the ecosystem, and this can be illustrated by considering two
contrasting examples: yeast in a flask (reproducing asexually), and rabbits in a field (reproducing sexually)
...

Individuals may rarely meet, so few matings
...

Long gestation so few births
...

Rapid exponential growth
...

density
...
g
...

sugar
...

Stationary phase
and below the carrying capacity)
...
The more
individuals there are in the population, the greater the percentage of population that dies or fails to reproduce
...

(b) Density independent factors, are those whose effectiveness is not related to the density of the population
...
They include; temperature, rainfall, light, floods, soil nutrients, fires,
drought, hurricanes and habitat destruction e
...
clearing a forest or fishing in a wetland, pesticide spraying
...


SURVIVORSHIP

Survivorship per 1000 live births

This is the percentage of an original population that survives to a given age
...


III

II

I

Age in years

(I) Late loss curves
Occurs in Humans, elephants, rhinoceroses, mountain sheep
These are organisms with stable populations close to carrying capacity of the environment (K)
...

(II)Early loss curves
Occurs in annual plants, most invertebrates and most bony fish species; with a high intrinsic rate of increase
...

There is high survivorship once the surviving young reach a certain age and size
...

There is an equal chance of dying at all ages
...

Importance of plotting survivorship curves:
 Enables determination of mortality rates of individuals of different ages and hence to determine at which age they are most
vulnerable
...

 Enables determination of carrying capacity in the area
...
e determine whether existing population are likely to be
sustainable
...

 It enables projection of how population size is likely to change with time for proper planning eg determining the peak
populations of organisms e
...

FACTORS TO CONSIDER BEFORE COUNTING ORGANISMS
 The area of land or volume of water or air under study should be determined
...

 Size of organisms under study
...








Behavior of the organism e
...
their level of hostility and excitement when disturbed
...

Risks involved during the exercise
...


METHODS OF DETERMINING POPULATION SIZE OF ORGANISMS

(a)Total count:
This is the physical counting of every individual of a population in a specified area of ground
...
It includes; (i) Direct counting method (using a low flying
aircraft) (ii)Aerial photography (iii)Drive and count (iv)Strip census (v)Removal method
(i)Direct counting method using a low flying aircraft
Used to determine population of large animals
...
g
...

This is repeated several times
...

Advantages
 It gives a quick estimate of the population size
 Other studies on the population such as feeding habits, reproductive behavior, and predation can be carried out
simultaneously
...
g
...

 It’s greatly hampered by some weather conditions e
...

 Can only be used on large animals and those in open grass lands
 Not easy in very hilly areas
...

Requirements
(i) Low flying air craft (ii) Good camera
Procedure
Photographs are taken from a low flying air craft over the whole study area
...

Advantages
i
...
g
...

ii
...

Disadvantages
-It cannot be applied to aggressive animals e
...
lions, tigers, etc
-Limited to slow moving animals
-Restricted to animals moving in herds
(iv) Stripe census
Requirements
(i) Map of the area (ii) Vehicle
Procedure
 While driving , animals are counted in a given strip /besides the road
...

 Such is repeated for several strips and the average population density for the strips is calculated
...

Advantages
 It’s quick
 It’s cheap compared to aerial means
Disadvantages
 Moving vehicles scare away animals that may run into hiding
 Some animals avoid roads and paths commonly used by man in the park
...


 Very many counts have to be made so as to come out with a reliable number
...

(i) Capture mark Release recapture method (Lincoln Index)
...
g
...

Requirements
(i) Suitable traps (ii) Suitable tags/label e
...
aluminum discs for fish, permanent ink for rats/mice
Procedure
 Traps are set up randomly over study area
...
, noted as N1
...
g
...

 These animals are then released back to their natural environment
...

 A count is made of all animals captured on the second catch noted as N2
...
e
...

Noted as N3
...

N2- number of individuals captured on the second catch
...

Assumptions made when using the capture mark Release recapture method
- That organisms mix randomly within the population
...

- That changes in population size due to immigration, emigration, death and birth are negligible
...

- That there is even dispersing of organisms within the study area
...

Disadvantages/limitations
- It’s only reliable when the organisms’ range of movement is relatively restricted and defined
...

- Many animals have particular localities where they confine, so the marked animals may not spread widely
...

The label may psychologically or physically disturb the organism
...
One week later, 873
were netted of which 129 tilapia had been marked
...
In an investigation of a fresh water pond, 35 water bugs(Notonecta) were caught, marked and released
...

(a) What is the approximate size of population of water bugs in the pond? Show your working
...

(ii) Use of quadrat
This is suitable for slow moving animals and grass
...
g
...

All individual within a quadrat are counted each time
...

Total population is got by multiplying the average with the total area under investigation
...
(iii) It provides an absolute measure of abundance
...
(ii) It’s not suitable for first moving animals
...
(iv) some plants
e
...
grass species are indistinguishable and may disturb
...

After sweeping with a heavy net, counting and recording of the animals captured is done without replacement
...

A graph of number of animals captured per sample against the previous cumulative number of animals captured is plotted and
extrapolation of the line of the graph is made to the point at which no further animals would be captured, from which the population
is estimated
...
g
...
Give reasons for your choice of each
method and outline the associated limitations
...
These populations are
controlled by homeostatic means depending on the density controlled factors e
...
food, pests, diseases, predators etc
...
e an increase in population stimulates environmental resistance which brings the
population back to normal, and a decrease in population below carrying capacity, environmental resistance decreases, thus causing an increase
in the number of organisms e
...
predator –prey relationship
...
g
...
E
...
(i) Using cats to eat rats, (ii) using beetles to feed on the water hyacinth on Lake Victoria, (iii) placing fish in ponds to eat
mosquito larvae
...

Biological control method can be used to; (i) control of vector population (ii) control of parasites (iii) control of pathogens (bacteria& virus)
(iv)control of some plants e
...
weeds (v) control of pests
...
e
...

 Investigating the original site of the pest and identifying natural predators, parasites or pathogens of the pest
...

 Mass culturing of the control agent
...

NB
...

(b) Chemical method
...
g
...

Properties of an ideal pesticide:
 Should be biodegradable / non-persistent so that toxic products are not left in or on crop plants
...


 Should not accumulate either in specific parts of an organism or as it passes along food chains
...

Problems of using insecticides:
 Accidental misuse of toxic chemicals results in death of humans and domestic animal
...

 Pest resistance occurs i
...
genetic variation enables a few individuals in the pest population to survive and may quickly reproduce
...
e
...

 Pest resurgence may occur i
...
non-specific pesticides may kill natural predators as well as pests, and so a small residual pest
population may multiply quickly without being checked
...
E
...
If Dichlorodiphenyl trichloroethane, DDT is sprayed on plants, to kill green flies, some survive, and absorb the chemical
into their bodies
...
g birds of prey, the
accumulation of DDT reaches a level which burns up and kills the final consumer
...
(a)What is a biological pest control?
(b)
...
) State two ways in which the chemical control method can upset an ecosystem
(d) Suggest three characteristics of a good pesticide
...
The table shows the amount of DDT in plants per million found in a variety of organisms associated with fresh water lake
...
Calculate how many times DDT is more concentrated in
million
carnivorous fish compared with its concentration in water
water
0
...
002
(b)Explain why the concentration of DDT changes from water to
zooplankton
0
...
39
c) Explain how a pest sprayed with a pesticide may flourish
Carnivorous fish
0
...

Fish eating birds
14
...
In an aquatic ecosystem which was affected by an insecticide, analysis of energy flow and concentration of the insecticide in each trophic
level in a food chain was made
...

Energy flow
pesticide
(a)Explain why from producers to consumers,(i) level of insectide increases(ii) the
Producers
0
...
(b) Give three ecological problems that may arise from
Herbivores
10
the use of pesticides
...
g
...
g
...


CLASSIFICATION OF NATURAL RESOURCES
Type of natural resource & its definition
(i) Perpetual resources
...

(ii) Renewable resources
Resources that are replenished (replaced) fairly rapidly (hours to decades)
through natural processes as long as the usage is not faster than the
replacement
...

On the shorter human time scale, they are depleted much faster than they are
formed
...

(i) Fresh water (ii) fresh air (iii) fertile soil (iv) animals
and plants (Forests, grasslands)

(i) Fossil fuels (e
...
coal, oil, natural gas) (ii) metallic
minerals (e
...
copper, iron, aluminium) (iii) non-metallic
minerals (e
...
salt, clay, sand, phosphates)
...


Term and definition

Examples and/or comments

(i) Sustainable yield
The highest rate at which a renewable resource can be used
indefinitely without reducing its availability supply
...


In spite of the renewability, renewable resources can be depleted or
degraded
...

(v) Wild life
This includes plants and animals that occur in their natural
environment

Old aluminum saucepans and copper items can be recycled
Glass bottles of alcoholic and soft drinks can be collected washed and
refilled many times
Forests and wild animals

POLLUTION
 It is the release of substances or energy into the external environment in such quantities and for such duration that may cause harm to
living organisms or their environment
...

 The parts of external environment affected include air, water and land
...

- Disruption of life support systems for living organisms
...

- Nuisances such as noise and unpleasant smells, tastes and sights
...

Biodegradation: is the breakdown of complex chemical pollutants into simpler chemicals by living organisms (usually specialised bacteria)
e
...
sewage is a biodegradable pollutant
...
g
...
g
...

c) Non-degradable pollutants: these cannot be broken down by natural processes e
...
the toxic elements lead, mercury, arsenic, selenium
TYPES OF POLLUTION
(a) AIR POLLUTION
Pollutant
Source(s)
Effects/ consequences
Control measures
(i)Motor vehicle exhausts
(i) Prevents oxygen usage by blood by
(i)Efficient combustion of fuels in
(i) Carbonmonoxide
ii) Incomplete combustion of
forming carboxy-haemoglobin, which
industry an homes(ii) Avoid
fossil fuels
may cause death
...
(iii) Vehicle exhausts gas
( iii) tobacco smoking
cause dizziness and headache
control e
...
in USA
...
g
...
(ii) Installation of
in high concentrations
...
(iii) Reduces
in industrial fluels and
growth of plants and kills lichens
...

NB
...

The presence of many lichen species
indicates low level of sulphurdioxide
pollution in that area
...
g
...
(ii)Eye,
throat
to form nitrogen dioxide
and lung irritation which may result into
which decomposes to form
death
...

with oxygen molecules to
(iv) Green house effect by absorbing and
form ozone
...

High level (stratospheric) ozone offers
protection against excessive solar heat by
absorbing solar ultraviolet radiation
which would reach the earth’s surface
...
(iii)Stunted growth of
iii)No smoking
iii) tobacco smocking
plants
iv) Vehicle exhausts gas control
iv) Incomplete combustion of
(iv) Stomatal blockage hence reducing
refuse in incinerators and
photosynthesis
bonfires
...
(iv) Smog –

i)Installation of dust precipitators
in industrial chimneys
...


ii) Efficient combustion
...


(i) Car exhaust control

(i)Planting more green plants, (ii0
reduction in combustion of fossil
fuels by relying on alternative
sources of energy e
...
solar energy
...


Ban on the use of CFCs

(i) Hearing impairment,(ii) total deafness
(iii) nervous disorders

(i) Effect laws against excessive
noise(ii)put on ear muffs and
plugs while in industry

Ionizing radiation causes cancer

Nuclear power controls

(ix) Noise

(x) Radioactive

fallout from
explosion

refrigerator (iii) air conditioner
coolants (iv) expanded
plastics
...
g
...


GREENHOUSE EFFECT AND GLOBAL WARMING
Greenhouse effect
 This is a description of the condition which results when greenhouse gases i
...
gases in the troposphere (atmosphere’s inner most
layer extending about 17km above sea level) like carbon dioxide, water vapor, methane and nitrous oxide allow mostly visible light,
some infrared radiation and ultraviolent radiation from the sun to pass through the troposphere to the earth, which transforms this
solar energy to longer-wave lengths-infrared radiation (heat) which then rises into the atmosphere
...

The tropospheric gases act like a glass of large green house surrounding the earth
...
8oC since 1900 as result of the enhanced natural greenhouse effect
...

 Deforestation and clearing of grasslands reduces the uptake of carbon dioxide in photosynthesis
...

 Use of aerosol propellants, which contain CFCs that are 105 times worse than carbon dioxide as greenhouse gases
 Cultivation of rice in swamps and paddy fields causes anaerobic fermentation, which produces methane
...

Effects of global warming
...

 Altered temperature gradients cause cyclones and heavy rains as water evaporates quicker
...

 Reduced cropped fields due to drier weather
...

 Flooding low-lying islands and coastal cities
...

 Increased death of human population
...

ACID RAIN
Formation
Combustion of fossil fuels releases sulphur dioxide and nitrogen oxides into the atmosphere
...

Effects
2 Hydrogen ions bound to soil particles are displaced into runoff water by the SO4 ions from sulphuric acid, causing
formation of soft exoskeletons, which results into death of invertebrates
...

2 Aluminum ions are displaced from soil by SO4 ions into water are toxic when absorbed by plants
...

 Contributes to humans respiratory diseases such as bronchitis and asthma
...

 Damages statues and buildings
...

 Promotes the growth of acid-loving mosses that can kill trees
...
5
Prevention
 Installation of SO2 extraction units (wet scrubbers) in chimneys of industries
...

 Reduce coal use
...

 Tax emissions of sulphur dioxide, “polluter pays principle” should be adopted everywhere
...

(b) WATER POLLUTION
MAJOR CATEGORIES OF WATER POLLUTION
(A) SEWAGE DISCHARGE INTO RIVERS
Sewage is liquid waste (composed of faeces, urine, water, detergents and other substances) from industries and/ or homes carried
through pipes called sewers
...

Some of these changes are due to specific chemical pollutants (e
...
heavy metals such as cadmium from industrial processes, and
pesticides from agriculture, with the effects varying according to the chemicals present in the discharge
...
Explain the changes in BOD shown in the diagram
(c
...

(ii)
...

(d)
...
(Your answer should include practical details of
your method)
(e) Suppose that the chemical works also discharged
thermal pollution
...


Component(s)

(i) Dissolved oxygen and B
...
D
(Biological or biochemical oxygen
demand)
NB
...

B
...
D indicates the oxygen not
available to more advanced organisms
...
O
...


Variation down stream
-Dissolved oxygen level is high in unpolluted
water; decreases rapidly at sewage discharge
to the minimum; and then increases gradually
downstream, returning to a normal level
further downstream
...
O
...


Explanation
-Decomposition of organic components of
sewage by aerobic bacteria coupled with
reduced photosynthesis because of low
illumination caused by suspended solids in
sewage rapidly reduce oxygen (cause
oxygen sag) and create a high BOD at
outfall
...

-The death of aerobic bacteria due to
reduction in organic substances decreases
BOD down stream
...


-Sewage discharge adds decomposable
organic matter into the water at the point of
discharge, the progressive decrease
downstream is due to bacterial consumption
and dilution by water
...
g Aerobic
bacteria, sewage fungus((filamentous
bacteria), algae(cladophora) and higher
plants
...

-Sewage fungus is contained in sewage
population; increases to a maximum
immediately after outfall, but decreases
rapidly downstream to very low level
...


(iv) Ammonium, nitrate and phosphate
ions
...

-NH4+ ions increase rapidly at discharge;
more rapidly to a maximum just after outfall;
then decreases first rapidly and later
gradually to a very low level downstream
...

-PO43- ion concentration increases (1)
rapidly at discharge, (2) gradually just after
outfall to a maximum, then decreases
gradually to a very low level downstream
...
g
...

-Population increases at outfall because the
sewage fungus thrives in anaerobic
conditions and is very tolerant at high
ammonia concentrations
...

-Sewage contains NH4+ ions
...
Downstream,
NH4+ ions are converted to NO3- by
nitrifying bacteria and further downstream
there is dilution by water
...

Sewage contains PO43- ions from (1)
detergents and (2) decomposition of organic
matter, yet the consumption by autotrophs
is very low at outfall, accounting for the
high PO43- ion concentration
...

-Clean water species cannot tolerate
anaerobic conditions at outfall, populations

increase downstream because oxygen and
food become available
...

-The increase in population of Tubifex, and
Chironomus is because they are (i)
relatively inactive to reduce oxygen demand
and (ii) have haemoglobin with very high
affinity for oxygen enabling them to be
tolerant to anaerobic conditions
...

Tubifex, is the most tolerant to anaerobic
conditions, followed by rat tailed maggots
and Chironomus
...

NB
...
(5)existing population of microorganisms
...
g
...

larvae) Asellus (fresh water louse),
Chironomus(bloodworm), Tubifex and
rat –tailed maggots(not indicated on the
graph but it can be sketched basing on
tolerance to pollution)
NB- organisms above are indicator
species of un polluted, well oxygenated
water
...

-Asellus population decreases rapidly to zero
at outfall, only appearing and increasing
rapidly to a maximum a short distance
downstream after which it decreases rapidly
...

- Chironomus population increases rapidly to
a maximum at a slightly longer distance from
outfall and then decreases rapidly
downstream
...

Pollutant
(i) Plant
nutrients

Examples
(i)Nitrate (NO3-) (ii) phosphate
(PO43-) and (iii) ammonium
(NH4+) ions
...
g
...


(ii) Sediment

(i) soil

Land erosion

(ii) silt

(iii) Inorganic
chemicals

(i) acids, (ii) compounds of toxic
metals like lead (Pb), mercury
(Hg), arsenic (As) and selenium
(Se) and (iii) salts e
...
NaCl in
ocean water

Surface runoff, industrial
effluents and household
cleaners

Harmful effects
(i)Rapid growth of algae and green protists
(algal blooming/dramatic first growth of algae)
(ii) reduces light penetration in water leading to
(iii) Death and decay of algae, which depletes
water of dissolved oxygen, killing fish and other
aerobic animals
...

Can (i) cause turbidity / cloudiness in water;
light penetration is reduced therefore reduce
photosynthesis, (ii) settle and destroy feeding
and spawning grounds of fish, (iii) clog and fill
water bodies, shortening their lifespan (iv)
disrupt aquatic ecosystems (v) carry pesticides,
bacteria and other harmful substances into
water
...


C
...
g
...

Harmful effects
1) Lowers dissolved oxygen levels since solubility of most gases reduces with temperature
...

3) When a power plant shuts down for repair or opens, fish and other aquatic organisms adopted to a particular
temperature range can be killed by the abrupt change in water temperature
...

4) Some aquatic animals may migrate to water with favorable temperature
...

2) Reduced dissolved oxygen levels in water
...
What are advantages and disadvantages of biological rather than chemical control of eutrophication?
Organisms live in their environment all the time; their presence (or absence) reflects the suitability of that environment for their living
requirements at all times
...
Biological indicators can therefore be a more
sensitive and representative reflection of environmental conditions
...
g small rivers , streams and remote areas
...

2
...

(b) Give two ways of reducing domestic waste in urban communities
(c
...


(i) Explain the trend in the lichen

Number of lichen species

species with distance from the urban
centre
...


Distance from the urban centre
3
...
Describe the factors which influence the concentration of dissolved oxygen in a river
...
Explain the presence nor absence of those organisms may be used as indicators of the concentration of dissolved oxygen



---