TOPIC 2

A2 Edexcel

ECOLOGY

Dr. Nihal Gabr

28/ 10/ 2024
Part 1 ecology
Succession
Biotic and abiotic factors

Classwork :
1. Define biodiversity , population , community , abiotic factors ,
ecosystem ,habitat , niche, microhabitat
2. State edaphic factors , biotic factors
3. define ecological succession
4. Define primary succession
5. state the steps of primary succession
6. define climax community
7. What happens to reach climax community
8. Compare between primary and secondary succession
9. Role of microorganism in recycling of organic matter in dead animals .
10.Explain how formation of decomposition island is an example of succession
11. State Abiotic factors (read alone )
Some important definitions

Species ( number + abundance )

1. Biodiversity
Genetic diversity
Habitat diversity
A) number of species in a habitat ( species richness ) Genetic variation
B) relative species abundance ( evenness in distribution ) , indicating number of individuals per species and variation of
C) types and number of different alleles in gene pool ( genetic diversity / genetic variation within a species
species )
D) diversity of habitat

Abundance …population size ( number of particular organisms

2. Population Members of same species living in the same place at the same time

3. Community All populations of living organisms of all different species living in one area at the same time

4. Abiotic factors Non living factors ( non living elements of the habitat of an organism,
they include those related to climate , such as amount of sunlight ,
temperature , rain fall .
And those related to soil ( edaphic factors ) Include pH
5. Edaphic factors They include the physical , chemical. , and biological properties of soil .

1. Soil pH
2. Soil mineral ions content
3. soil water / moisture
4. Air spaces ( drainage rate ) …how rapidly excess water leaves the soil
by running off or internal drainage .
Drainage ensure that the soil is well aerated.
5. Soil structure ( size of particles , humus content )
6. Soil temperature .

6. Biotic factors : The living elements of the habitat that affect the ability of a group to survive
Example presence of a suitable prey species will affect number of predators in a habitat
Amount food ….FOOD CHAIN ….
Predation /disease

7. Ecosystem : Organisms interacting with each other and with abiotic factors ( physical / chemical
environment ) ..self sustained unit

8. Habitat : Place that provides food, shelter and breeding sites for Microhabitat
living organisms Is a small area of habitat ( single fig on a
Place where organisms live tree is home to fig wasp )
9.niche

Role of the organism in its habitat and how it interacts with its environment
Example : type of food it eats , where it lives , where it reproduce , relation with other living organisms

10. Abundance vs distribution

Where the organisms are found / located

Number of particular organisms in a species
 Evolution of ecosystem

Ecological succession

A process by which communities of animals and plants colonise an area and then ,
over period of time , are replaced by others , usually more varied communities

Series of changes ( that occur to the composition of species in the community ) of

organisms ( present in an area ) over a period of time .

Primary succession Secondary sucession

Secondary
Soil is already
Occurs when communities develop on ENTIRELY NEW climax
formed and community
LAND without any established soil
contain seeds , differs from the
Starts with empty inorganic surface as bare rocks
roots and soil primary /
After volcanic eruption or sand dune . original climax
organisms.
community.
Continue with primary succession: https://youtu.be/uqEUzgVAF6g

1 . Colonisation 2. Decomposition: 3. Grass and ferns grow 4. Taller plants

1 . Colonisation
2. Decomposition:
First stage of succession
Where the first organisms appear are opportunists or This helps break down the rocks into small grains ( particles )
pioneer species ( adapted to sever conditions so can and trap organic material thatwill break down to humus …to
grow in no soil ) ……..such as algae , mosses and fungi / start forming the soil ( formation of top layer )
lichens …which are simpler organisms . So they change the rocks into soil .

These organisms penetrate the rock surface in number 3. Grass and ferns grow
0f ways : 3. Grasses and ferns grow establishing short root system .
A) dissolving rocks by acids they secrete . Where they displace the pioneer species ….where their death and decay
B) penetrating ting cracks with root hairs and hyphae . add more nutrients to soil and become avilable for plant roots …( soil
improved by time ) ..so less resistance species can survive ( like small
shrubs / ferns )
 4. Taller plants

4 Gradually larger /taller plants can be supported and the diversity of species increase …..this increase in
plant biodiversity results in an increase in the diversity of animals that can be supported ….reaching a climax
community ( in which biodiversity and range of species are generally constant if no change in the environment )

Pioneer species : First organisms that colonise an area and are adapted to sever conditions
They reproduce asexually / fast life cycle .
They can live in extreme conditions .
They need less amount of nutrients and minerals in soil /They can live in bare rocks .

Decomposition
Where the organic materials are broken down into humus ( top layer of soil )

Grass and ferns replace pioneer species Less resistant species

Decomposition of these pioneer species add extra minerals to soil

Reach to climax community Community of plant and animals , and fungi

Which remain stable and exist in balance with each other and their environments.
Until destroyed by an event such as fire or human interference .

Definition Final stage of succession / final community , community that has

reached to a steady state / remains generally constant over
time / self sustaining stable one
Time taken to move from a bare earth to climax community varies
enormously , According to different factors ……..

1. Temperature
2. Rain fall
3. Fertility of soil
The climax community that is formed will depend on the climatic factors, also plants and animals and microorganisms
that are able to colonise area .

What happens when reaching to Climax community : ( primary / secondary )

Gradually larger plants can be supported and the diversity of species increase
…this increase in plant biodiversity results in an increase in diversity of animals that can be supported.

So high biodiversity of plants and animals is reached

With interaction between species
Dominant / co dominant plants or animal species
Range of species are generally constant if no change in the environment .
 Primary succession Secondary succession

Both results in Climax community

Shrubs and small trees grow
Occurs over long period of time
Decomposition takes place

• Happens relatively faster .

• Happens relatively slower

• Starts with plants and animals ( previous

• Starts on bare rock ( no previous life existing)
existing life but destroyed ) .

• Would occur after lava cools and hardens into rocks

• Would occur after a forest fire / flood…..also
( after volcanos or receding glacier)
would occur after land is cleared by humans

• Soil must be formed before plants grow

• Soil is already present ( previous existing soil)

• Pioneer species include lichens ( break down rocks

• Pioneer species : Grasses and weeds are first
to form soil) and mosses
plants to grow

• no previous life
• Occurs in area where organisms lived
previously
 Proteins
Role of microorganism in recycling of organic matter in dead animals . Glycogen
• Microorganisms such as bacteria and fungi acting as decomposers Starch / cellulose

• Releasing extra cellular enzymes for decomposition

Notice if its a dead
• Such as protease that breaks down proteins into amino acids plant or animal
• Or Carbohydrase that breaks down glycogen ( in case of animals ) into glucose
• Or cellulase that breaks down cellulose into glucose ( in case of dead plants ) .

• Where small soluble molecules such as glucose is being absorbed by microorganism by

diffusion
Being used as respiratory substrate to microorganisms
Example of microorganisms
Release extracellular enzymes
• To carry respiration and release energy Examples
And CO2 ( for carbon cycle ) gas is released into atmosphere to made available for Protease …plant and animals
Cellulase …plants
plants for photosynthesis .
Carbohydrase …plants( starch ) and
animals ( glycogen )
The other broken down products Return back to soil ./ dissolved molecules can soak Definition of chemical digestion
Respiratory substrate …glucose
into the ground Energy …..
For recycling CO2 ….atmosphere..absorbed by plants

Broken down products return back to soil

Explain how formation of decomposition island is an example of succession :

1. Where decomposition takes place in sequence of stages

Breaking down of organic matter by extra cellular enzymes of fungi and bacteria
Followed by formation humus which is a top layer of soil rich in nutrients to provide high fertility of soil .

2. So soil conditions continue to improve during decomposition stages of animals and plants .

3. So more , longer , different grass start to grow

4. Followed by taller trees ( gradually larger plants can be supported )
Increase diversity of species

5. Allowing more and different animals to arrive where they are provided with food and shelter

6. Greater biodiversity because increase in species richness ( increasing in different types of plants
and animals )
Increase in plant biodiversity ….increase in animal biodiversity that can be supported

7. Reaching to climax community

 Effect of biotic and abiotic factors

Biotic Predation
Competition
Disease / parasitism

Abiotic factors Non living

Edaphic / climate

Can vary a lot within a habitat to produce microhabitats with microclimates

Microhabitat ….small area with distinct climate that is different from the surrounding

So can provide different niches :

• this will reduce competition
• So determine the distribution and abundance of different populations in a habitat

Example :
Logs may be places in an open area
Where they are will be largely dry and well lit .
Except under log it will be damp and shady , allow different organisms
occupying different niche to grow and become strong and healthy
compared with those in open area .
Abiotic factors Light , temperature , water availability , oxygen
Read to understand and have ideas
availability in water and soil , structure and composition
of soil.
Only stress on underlined .

A) light A

• plant need light for photosynthesis ( light dependent stage ) …..

• Amount of light directly affect the number of organisms found
a) Large plants compete with small ones for sunlight and water by shading caused by larger plants
B) yet shaded plants can adapt to survive
1.. have more chlorophyll or different ratios of photosynthetic pigments that are sensitive to lower
light levels .
2. More leaves with larger sized leaves .
3. Grow and reproduce very earlier time in the year before being shaded .

1)Animals are affected by light levels , as a result of food plant distribution.

2) seasonal light changes , affect the reproductive pattern ( as light and dark control much of animal
physiology and behavior)
 B) temperature

Temperature change ( hotter / cooler )

Where any change in temperature affects the enzyme activity + Oxygen concentration

Plants ( RUBISCO )
Animals ( adapt by physiological and behavioral adaptation)
Marine animals ….oxygen levels and water temperature combine to determine which part of
oceans are breathable for different aquatic species

C) water availability

Affected by rain fall ( precipitation ) , that is affected by evaporation and rate of loss of water by drainage
through the soil .
Wetter environment can cause the roots to become water logged
Some animals can’t cope and others can cope with water stress .

D) oxygen availability It can be short supply in both water and soil

Water :

Where when water is cold or fast flowing ….there will be enough oxygen dissolves to support life
If temperature of water rises or water becomes still and no longer flowing ….the oxygen content
will drop .
 Cold water can hold more dissolved oxygen than warm water ,so in winter the dissolved oxygen
concentration is high due to low temp .
In summer, when water temp is high,the dissolved oxygen concentration is lower .

This is due to the fact that warmer water , molecules move faster than in cold water and thereby
allow oxygen to escape from water …so the warmer and the salter the water , the less dissolved
oxygen it will contain ..

Soil : Soil usually need to be well aerated-with spaces between particles with ' plenty of oxygen
If water logged ( extremely wet) …air spaces will be filled with water …so roots can t get oxygen so
plants may die

However some plants have have aerial roots , longer aerial parts above soil surface with accessibility to
oxygen to grow successfully in water logged soil
F) structure of soil and its minerals

The Edaphic factors

They include soil properties that affect diversity of organisms living in the soil environment

Sand…easily drained …leaching minerals ….reducing population density

Clay particles …difficult to drain water …they are more water logged
Loam ….has particles with wide range of size so heavier so less leaching ( sand + clay)
( sand + clay)

Edaphic factors Measure

Soil pH Sample removed , pushing or inserting a Probe into soil and reading the meter
( should be clean )

Soil water / Soil removed . Moisture probe / meter ( inserting a probe in soil at same
moisture depth ) + testing soil around the plant .

Sample removed , measure mass flow through soil directly /

Air spaces measure the volume with and with out air / drainage rate ….( dig a
hole 12 inches deep and 8 inches wide ) fill with water ….measure
the time taken for the water to drain …then 12 inches / time in
hours
Soil mineral ions content Sample removed , use mineral testing kit / use extractant.

Soil structure Sample removed , by humus content mea'sured by weighing a dry soil
sample , burning the humus in soil , then weighing the soil left … the
difference between the two figures is the humus content .
Measure size of particle .

Soil temperature Soil in situ measures using

Temperature probe
30/10/2024
Part 2
Biotic factors ( predation )
Natural selection
Speciation

Class work :
1. Define grazing and predation
2.What can cause a decrease in a population of an animal
3.State all biotic factors affecting distribution and abundance
4. state two types of competition
5.Compare between Density dependent and independent factors
6.Explain why some species may become extinct
7. Explain why some plant species population may decrease
8.Explain why habitat destruction affects the biodiversity and population?
9. Steps of natural selection
10. Steps of allopatric speciation
 Biotic factors affecting the population

Predation , disease , food availability , competition , grazing , finding mate

Grazing : too little leads to dominant plants outcompeting other species, too much
reduces species numbers overall. Both decrease biodiversity

Predation …a reduction in predators can lead to an increase in prey. High numbers of prey
can lead to overgrazing, which can reduce biodiversity
 At 1852
Predators decrease ..affected by disease , hunting level,

1. Predation
loss of a prey species , not healthy enough ti mate ……so
the prey took an advantage to increase in birth rate so high
Its impossible to
prey number
consider effect of
Lack of food one biotic factor
They may have an excess of plant food / good on the population
Disease growing season ,alternative prey animals as size with isolating
Hunting food supply ..so both species peaked at the
the factors
same time
Being eaten
Finding mates ( not Prey
Predator
healthy enough to mate ).
Different preys of the
I

3
1. Predation
predator .
2

1. Increase in predators due to 5. There is a time delay / lag between / ( staggered

A) increase in birth rate which is higher than death rate change ) in population of preys and predators as it takes
time for animals to give birth and die . /
B) more prey / more food supply to predators / more preys to hunt
2. An increase in population of predation to the point at which they are eating more preys …./ after an
increase in predator population , there was a decrease in prey population due to more predation , so they are
eaten at a faster rate than they are replaced by reproduction ( death rate > birth rate )
3. So praedator number will fall , due to reduction food supply / not healthy enough to find a mate / hunted , so wont
produce off springs ( lower birth rate than death rate ) .
4. Number of preys increasing as they reproduce faster than they are eaten …..as there are fewer predators to
predate / kill them
Staggered = different staring time
2. Finding mate

Depends
A) abundance of any type of animals that reproduce sexually found in an area affect on availability
of mates / abundance of mates .
B) not healthy to find a mate .

3. Territory
An area held and defended by an animal or group of animals against other
organisms , which may be of same or different species ……… it makes sure that
a breeding pair has suffecient resources to raise young

Territory, in ecology, any area defended by an organism or a group of similar organisms

for such purposes as mating, nesting, roosting, or feeding

Animals marked out and defend their territories in different ways :

Example :
Territorial boundaries may be marked by sounds such as bird song, or scents such as pheromones secreted by the
skin glands of many mammals.
4. Diseases
Diseased organisms will be weakened and often don’t reproduce successfully
Sick predators cant hunt well
Diseased animals are more likely to be caught.
Some diseases can be highly infectious and spread without contact such as avian ( bird) flu .

5. Parasites
Affects their hosts by feeding off the living body of their host and so weakening it ..example parasitic
fungal disease that damaged banana crops .

Both diseases and parasites are widely spread in populations with high density …yet in a community with
greater biodiversity , their effect will be much less .

High biodiversity
Explain why a disease is likely to have a greater effect on ecosystem with little biodivesity than with More buffer
more diverse community? species ( plant or
animal that
With little biodiversity , if one organism is affected by disease ,it will have a major impact on the small number
become
of other organisms in the ecosystem .
alternative prey
1. They will not get eaten , their predator numbers will fall substantially …with little biodiversity there will
to a predator ) ,
be few other available food resources
less affected by
2. Also , disease is more likely to spread between individuals where there are few buffer species .
disease.
 4;27
6. Competition density dependent

Competition occurs when two organisms compete for a resource that is in limited supply
May be for abiotic resources resources such as sun light , minerals , water
Or biotic factors such territories, nest sites , or mates , food

Intraspecific competition Interspecific competition

Is competition between members
of same species within same Is competition between different species within a community for the same

niche for a limited resources such resources ( food , space) …where the niches of species overlap

as food, territory , mates . ….competition-reduce the abundance of the competing species .

Tends to affect the abundance of a particular species of organism .

Some individuals may not survive ,
Low resources , much competition, less reproduction and more mortality .
or may not reproduce ,
Plenty of resources , little competition , lots of breeding , low mortality …
So population growth slows down
On contrast , large amount of Affect distribution of species in a habitat and also the abundance of species ( biodiversity)
resources …so little / less
If there is a greater density of one species , or it has faster
competition and the number of
reproduction rate than its competitor ( one species competes very
individuals will increase
successfully against the other ) , then one of the species may
become extinct in that area .
 Density dependent and independent factors

Biotic and abiotic factors can be density dependent or density independent

Independent…..abiotic factors ..distribution .( IAD) Dependent ……biotic ……..abundance ( DBA)
Density independent factors Density dependent factors
Factors affecting the number of
Factors affecting the number of
organisms occupying a niche which
organisms occupying a niche which are
are the same regardless of
dependent on the number of organisms
population size
of population in a specific area

Its effect on the population is the same

regardless of the population size
Effect on the population is different

Abiotic factors depending on the population size

A) temperature ( weather ) such as climatic change, rain fall

Examples :
B) pollutant in environment / natural disasters Limit the abundance of species
Competition
Disease / parasitism……as the larger the number of
individuals , the more likely the disease or parasite can
be transmitted between individuals.
Predation
Limit the distribution of species
Breeding / habitat space / food shortage .
1. Explain why some species may become extinct Explain why some plant species population may
1. Habitat destruction …. decrease
Such deforestation which removes vegetation
animals wont find food, shelter and habitat 1. Disease in plant
And less probability of finding mates 2. Introducing new of plants that would
….decrease in population compete with main plant species
3. Introducing new herbivores that feed on
2. Increase in disease specially in larger populations these plants
3. Predation and hunting ( biotic factors ) 4. Habitat destruction such as
deforestation.
4. Increase in competition
May be due to introduction of new species which would increase competition

5. Increase in grazers
6. Pollution such as eutrophication
7. Climatic changes such global warming
Build up of green house gases such CO2 in the atmosphere , trap infrared radiation ,increasing temperature of
Earth’s atmosphere …so some animals migrate towards north areas where there is lower temperature and towards
higher altitude .
Increasing competition with existing communities

8. Decrease in prey population and food resources .

 3. Explain why habitat destruction affects the biodiversity and population?

Species Genetic diversity

Species richness ( number of species) / ( types of alleles in a gene pool)
abundance

Population will decrease as organisms of one species die , they wont find food , shelter, habitat and mates .

While biodiversity , will decrease , as a-result of decrease in genetic diversity ( number of alleles in gene pool ) …due to
loss of habitat
Also decrease in species richness as some species might become extinct as they lose their habitat .

4. Effect of habitat fragmentation

less genetic diversity ,

Because of reduction in gene flow
Where there is less choice of mates …..leading to inbreeding ,
 1. Variation
Steps of natural selection and evolution 2. Mutation
3. Selection pressure
4. Advantageous allele
5. Passing allele to offsprings
6. Change in allele frequency
1. Genetic variation within the population ( intraspecific variation )
2. Caused by Random / spontaneous mutation introducing new favorable allele coding for a desirable
trait ( which is X) ….(mutation was present in gametes of…. )

3. Presence of selection pressure ( predation / poison / cold temperature / competition/ food

availability / space)……should be described.
Mention : Those with large bills have selective advantage in finding food .
4. Individuals with the advantageous allele ( showing desirable trait ) survive as they are better / more
adapted tp survive ..selection of the fittest….mention how adapted / ………has a selective advantage
where better able to feed on small shrubs , better camouflaged ).
5. Surviving individuals with selective advantage will reproduce / breed passing on their advantageous
allele to coming generations
6 Change in allele frequency over generations … showing an increase in advantageous allele
7. Due to natural selection some species become markedly different to extend that they cant reproduce
with original members of this species( reproductive isolation) …..
11. New species of iguana can evolve (leading to speciation ) by natural selection .
 Species X occupies a forest area. Individuals within the
Allopatric speciation
forest form a single gene pool and freely interbreed

Imp
Species X lives and
1. Geographical isolation breed in the forest
2. Reproductive isolation
3. Where original population become divided by a geographical 2. Climatic changes to drier conditions reduce the size of the forest to

barrier such as rivers , oceans , mountains , deserts .

two isolated regions . The distance between the two regions is too
great for the two groups of species X to cross to each other
4. The separated population become isolated where:
Forest B
A) no gene flow between population
Forest A
Group X 1 Arid grassland Group X 2
B) different mutation occur …new alleles
C) they are exposed to different environmental conditions / 3 .further climatic changes results in the one region ( forest A)
becoming colder and wetter . Group X1 adapts to these new
different selection pressures . conditions . Physiological and anatomical changes in this group

D) selection / survival of the fittest with advantageous allele , Forest B

Forest A
being better adapted . Group X 1 Arid grassland Group X 2

E) breed and pass on the advantageous allele

4 .continued adaptation leads to evolution of a
F) resulting in change in allele frequency new group Y in forest A .

G) . Over time , the morphological , physiological and behavioral Forest A Forest B

features of the island population became so different from the main Group Y Group X

land population , that the two populations can no longer interbreed

5.a return to the original climatic conditions results in regrowth of forest ,
so forest A and B are merged and groups X and Y are reunited , yet 2
5. Genetic drift where there is a change in the allele frequency /
groups are no longer capable of interbreeding
There are now 2 species , each with its own gene pool.
founder effect ) Species
Forest A
Species Y
4/11/ 2024
Part 3
Sympatric speciation
Sampling technique

Class work :
1. explain how Sympatric speciation takes place
2.Explain how random sampling technique using quadrat can be done
3.Explain how systematic sampling technique using quadrat can be done
Geographical isolation ….leading to reproductive isolation due to envi factors change

1. the are separated population become isolated geographically

2. They are exposed to different environmental conditions such as Temperature
3. So different selection pressures
4. No gene flow between populations
5. Resulting in reproductive isolation

Geographical isolation ….leading to gene mutation

1. Different mutation occurs leading to production of new allele .

2. Leading to New phenotype
3. Selection / survival of the fittest with advantageous allele , being better adapted
4. Breed and pass the advantageous allele
5. Resulting in change in allele frequency
6, over time , the morphological , physiological and behavioral features of the both
populations become so different that the two populations could no longer interbreed .
 Sympatric speciation
Court ship display …behavior to attract / win
Definition mates
Court ship ritual …period of getting to know
Formation of one new species from a pre existing one .
each other / getting to know one another
Where both species continue to inhabit the same location

Steps

• involves the formation of new species from an existing one

• Where the two populations become reproductively isolated due to
A) mechanical mechanism ….genital organs not compatible so unable to mate
B) behavioral mechanism …..changes in court ship rituals/ display ….so can’t recognise each other as potential mates .
C) seasonal mechanism …..mating / fertile season is different .

• resulting into two reproductively isolated population within same area

• By time they cant interbreed together
• So no gene flow between parents
• Hybrid gene pool maintained by natural selection
 Species
Population

Ready
Living in same place
Geographical isolation
Sympatric speciation
Allopatric speciation

Reproductively isolated

HOT COLd Seasonal isolation

Mechanical
Mutation Behavioral
isolation
Different selection pressure isolation

aucation
Advantageous allele Not recognised as
Survival of the fittest potential mate
Cant interbreed Different court ships

Reproductively isolated
Cant breed together
Species 1 Species 2

Santa No gene flow

 Abundance and distribution Read

• Uniform dispersion. In uniform dispersion, individuals of a population are spaced more or less
evenly. ...
• Random dispersion. In random dispersion, individuals are distributed randomly, without a predictable
pattern. ...
• Clumped dispersion. In a clumped dispersion, individuals are clustered in groups.

Seen with herds of animals

Resources are thinly but
or groups of plants and evenly distributed or
when individuals of
animals that have specific
species are hostile to
resource requirement and each other

therefore grouped together

( clump) in areas where
those resources are found .

Plentiful resources
and no hostility
example weeds in
grass land
https://youtu.be/UDp3I07Wcrg?
Assessing species diversity
si=5TOWfAIWkS6w-Xms
Small part taken to be representative of larger area

A Random sampling Quantitative sampling technique. Why use a smaller divide quadrat
Easier to measure / calculate
1) by frame quadrat More precise

1. Random sampling
2. Lay out two long measuring tape at right angle to one another along the side of the study
3. Using random numbers from a table or using a generator ( mobile application ) , these numbers represent
the coordinates
4. Place the square at the intersection of each pair of coordinates
5. Then measure the ABUNDANCE in several ways :

A) species density ( individual count )

number of individuals per unit area ….number of organisms / total area of quadrates

B) estimating the percentage cover (grid quadrates ) area covered by the above the ground parts of a particular
species ..finding % of the quadrat occupied by each species
Covered squares
Total number of squares 100
Use a tally chart , table for counting
B Systematic sampling ( non random )

Used when investigation the effect of an environmental factor ( such soil moisture, soil pH , light
intensity ,height …) on the distribution of species

Distribution
Quadrat place 2
Distribution and abundance.
meters apart from
each other

1. Random select a starting point in the field , lay out a measuring tape in a straight line
2. Sample the organisms along the line ( transect )
A transect is tape placed across an area so samples are taken at a set distance / at regular intervals

3. Use a line transect ..where the organisms that touch the transect are recorded to show species distribution

4. Use belt transect : where the quadrates are places at intervals along the side of the transect and used
to record the abundance of organisms ( number of individual’s per species )
Then data from belt transect may be represented on kite diagram .
 Unit 4 Edexcel

(i) Describe how the oxygen concentration of water could be measured.

(2)
By collecting a sample of water and dipping an
……………………………………………………………………………………………...
oxygen probe into water
……………………………………………………………………………………………...
……………………………………………………………………………………………...
……………………………………………………………………………………………...
……………………………………………………………………………………………...

(ii) Put a cross in the box next to the percentage that completes the following sentence.

The overall percentage decrease in the concentration of dissolved oxygen is

(1)

A 3.3%

r
6-0.2 X100
B 6.2%
6

ab
C 96.7%
X
D 103.4%

(iii) Suggest why the oxygen concentration of the water may increase again
further downstream.
(1)
lg
There will be less pollution / more plants so more photosynthesis / water is cooler so
…………………………………………………………………………………………………..
hold more oxygen
(b) Freshwater shrimps require high oxygen concentrations. Bloodworms can survive
in low oxygen concentrations.

(i) Suggest how the distribution of the freshwater shrimps and bloodworms, in
this shallow river, could be investigated practically.
ha
(4)
① Systematic sampling technique
……………………………………………………………………………………………...
By sampling at regular intervals along the river .
……………………………………………………………………………………………...

Where sample of water is collected using nets / kick sampling .

……………………………………………………………………………………………...
……………………………………………………………………………………………...
Ni

placing a……………………………………………………………………………………………...
net in the direction of water flow, with open net mouth facing
……………………………………………………………………………………………...

upstream…
……………………………………………………………………………………………...
Using the toe or heel of the foot, the area in front of the net is disturbed,
……………………………………………………………………………………………...
the upper layer of gravel and scraping the underlying bed , where sampling time
……………………………………………………………………………………………...
dislodging……………………………………………………………………………………………...
should be……………………………………………………………………………………………...
controlled …mean sampling for same length of time …and also stones
……………………………………………………………………………………………...

can washed to collect the invertebrate animals.

……………………………………………………………………………………………...
……………………………………………………………………………………………...
Then count number of shrimps and blood worms in a tray
……………………………………………………………………………………………...

Use a tally chart or plot a graph to record data

105
Dr Nihal Gabr Compiled By Ali Kamel
 Investigation to determine how close can farmer grow plants near parents

Systematic Sampling ( non random)

1.Planting several plants of same species

2.Planting several different species
3.Planting at different distances (measuring distances that plants
are growing from pre existing bushes)….measuring tape in a straight
line to the marshy area / line ( transect) .
3.Leave the plants to grow for a period of time
4. Then measure the growth using height Marshy area =Wet
5. So that the closest distance that plants grow , is the closest area
distance that they can be planted

2000m

Using a transect to measure at 6 different altitudes.

A transect is tape placed across an area so sample are taken at a set

distance / at regular intervals nor-
2000m

Randomly select a starting point from sea level , and lay out a measuring
-

Sea level
tape in a straight line to above 2000m.

2. Sample the organisms along the line ( transect ) at 0, 500m ,1000m,

1500m , 2000m, 2500m (systematic sampling ).

Measure the height of as many Binara plants as possible .

A process by which communities of animals and plants colonise an
area and then , over period of time , are replaced by others , usually
more varied communities
Or

Series of changes ( that occur to the composition of species in

the community ) of organisms ( present in an area ) over a period
of time .
 Same as notes
empty inorganic surface as bare Rock after volcanic eruption ,
presence of more pioneer species ( adapted to sever conditions ) such
as algae , mosses and fungi/lichens. Less H pebloides present .
More H . Pebloides present.
Grasses and ferns grow , Where they displace the pioneer species
….where their death and decay add more nutrients to soil and become available
for plant roots …( soil improved by time ) ..so less resistance species can survive
( like small shrubs / ferns )

1. Random sampling using a frame quadrat Systematic sampling is a

wrong answer …caused its
2. Lay out two long tape measure at right angle Used when investigation
to one another along the side of a study area the effect of an
environmental factor
3. Using random numbers from a table or using ( such soil moisture, soil
a generator ( mobile application) …these pH , light intensity ,…) on
the distribution of species
random number represents the coordinates
4. Place the square at the intersection of each
pair of coordinates
5. Then measure the abundance by percentage
cover . (estimating percentage covering : ( grid
Use a tally chart for
quadrates ) area covered by the above ground
counting
parts of the plant )

Applysing same steps for another area of same

size .
 So scientist they are proposing new recclassification
(Ualidation
1.New evidence should be written in3na specific paper
2. Science paper is peer reviewed for molecular evidence

8 For ( validity of method, reliability of results , plagiarism exclusion)

Reproducible 3. Critical evaluation ( repeating the experiment with other scientists ) and extend analysis looking
Reliability for similarities and differences in more genes
4. Statistical analysis
5. Publishing in scientific journal .