2. POPULATIONS KEY WORDS:
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Abiotic – non-biological factor that makes up part of an ecosystem
Biotic – biological factor that makes up part of an ecosystem
Biodiversity – the range and variety of living organisms within a particular area
Biomass – total mass of living material in a specific area at a given time. (usually dry mass as
amount of water varies)
Climax Community – the organisms that make up the final stage of ecological succession
Community – the organisms of all species that live in the same area.
Conservation – method of maintaining ecosystems and the living organisms that occupy
them
Consumer – any organism that obtains energy by ‘eating’ another
Ecological Niche – all conditions and resources required for an organism to
survive, reproduce and maintain a viable population
Ecosystem – self-contained functional unit made up of all the interacting biotic and abiotic
factors in a specific area
Habitat – the place where an organism lives
Limiting Factor – a variable that limits the rate of a chemical reaction
Population – a group of individuals of the same species that occupy the same habitat at the
same time
Producer – an organism that synthesises organic molecules from simple inorganic ones.
(photosynthetic, 1st trophic level etc.)
Species – a group of similar organisms that can breed together to produce fertile offspring
3. • Fill in words to check understanding of key words:
The study of the inter-relationships between
organisms and their environment is called ____.
The layer of land, air and water that surrounds the
Earth is called the ____. An ecosystem is a more or
less self-contained functional unit made up of all
the living or ____ features and non-living or _____
features in a specific area. Within each ecosystem
are groups of different organisms called a
_____, which live and interact in a particular place
at the same time. A group of interbreeding
organisms occupying the same place at the same
time is called a _____, and the place where they
live is know as a _____.
4. ANSWER:
• The study of the inter-relationships between
organisms and their environment is called
ecology. The layer of land, air and water that
surrounds the Earth is called the biosphere. An
ecosystem is a more or less self-contained
functional unit made up of all the living or biotic
features and non-living or abiotic features in a
specific area. Within each ecosystem are groups
of different organisms called a community, which
live and interact in a particular place at the same
time. A group of interbreeding organisms
occupying the same place at the same time is
called a population, and the place where they
live is know as a habitat.
6. Quadrats
• 3 factors to consider when using quadrats:
- size to use. When studying larger species, you will require larger
quadrats and vice versa. Although when the species in bunched in groups
in random places in the area, (ie. the species are not evenly distributed
throughout the area), a large number of small quadrats will give more
representative results than a small number of large quadrats.
- number of sample quadrats to record within area. The more sample
quadrats, the more reliable the results will be. However it can be time
consuming if too many samples are taken, so there must be a balance
between result reliability and time available. The greater the number of
the different species present in the area being studied, the more quadrats
required to produce valid results.
- position of each quadrat within the area. Random sampling is used, in
order to produce statistically significant results.
• Point quadrats
• Frame quadrats
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7. Point Quadrats
• A horizontal bar supported by 2 legs.
• At set intervals along the bar are ten
holes, through each of which a long pin may
be dropped.
• Each species that the pin touches is recorded.
• Frame quadrats
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8. Frame Quadrats
• A square frame divided by string or wire into
equal size subdivisions.
• The quadrat is randomly placed in different
locations within the area being studied.
• The abundance of each species is recorded.
• Point quadrats
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9. Random Sampling
• It is important to sample randomly in order to
avoid bias.
• METHOD:
1. Lay out 2 tap measures at right angles along
two sides of the study area.
2. Obtain a series of coordinates by using random
numbers taken from a table/random number
generator.
3. Place a quadrat at the intersection of these
coordinates and record the species within it.
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10. Transects and Systematic Sampling
• Systematic sampling is when samples are taken at fixed
intervals, usually along a line.
• A line transect uses a tape measure stretched across
the ground in a straight line. Any species that touches
the line are recorded.
• A belt transect uses 2 lines, and all the species present
between the 2 lines are recorded.
• An interrupted belt transect uses quadrats that are
placed at intervals, and species within them are
recorded.
• Transects are used across areas where there are clear
environmental gradients.
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11. Measuring Abundance
• How abundance is measured depends upon the size of
the species being counted and the habitat.
• Frequency – the likelihood of a particular species
occuring in a quadrat. Useful when a species is hard to
count, e.g. Grass. For example, if grass occurs in 15/30
quadrats, the frequency of it’s occurence is 50%.
• Percentage cover – an estimate of the area within a
quadrat that a particular plant species covers. Again
useful if a species is hard to count. This method
enables data to be collected rapidly.
• To ensure reliable results, a large sample size is
necessary. The larger the sample size the more
representative of the community the results will be.
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12. Mark-Release-Recapture
• A known number of animals are
caught, marked in some way, and then
released back into the community. Later, a
number of individuals are collected randomly
and the number of marked individuals is
Total number of individuals in the first sample x
recorded.
Estimated population size =
(
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Total number of individuals in the second sample
Number of marked individuals recaptured
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)
13. Analysing Data
1. Present data in a table/graph. This makes it easier to
compare data (e.g. 2 different locations.)
2. Statistical analysis of data.
3. Check whether results are due to chance.
4. Data analysed for possible correlations and causes.
5. Statistical tests can be used to calculate the strength
of the correlation.
However, the two factors may correlate very well, but it is
possible that both of them are affected by the same
environmental factor.
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14. Ethics and Fieldwork
• Where possible, the organisms should be studied in situ.
(Where they are found) If it is necessary to remove
them, the numbers taken should be kept to the absolute
minimum.
• Any organisms removed from a site should be returned to
their original habitat as soon as possible. This applies even
if they are dead.
• A sufficient period of time should elapse before a site is
used for future studies.
• Disturbance and damage to the habitat should be avoided.
Trampling, overturning stones, permanently removing
organisms etc. Can all adversely affect a habitat.
• There must be an appropriate balance between the
damage done and the value of the information gained.
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15. Population Size
No population continues to grow indefinitely
because certain factors limit growth, for
example; availability of
food, light, water, oxygen and shelter, the
accumulation of toxic waste, disease and
predators.
16. Population Growth Curves
• The usual pattern of growth for a natural population has 3 phases.
1. Slow growth. Initially small numbers of individuals reproduce.
2. Rapid growth. The ever-increasing number of individuals continue to
reproduce. The population size doubles during each interval of
time.
3. Stable state, no growth. Growth is limited by factors such as
increased predation or food supply. The graph therefore levels
out, some cyclic fluctuations due to variations in factors.
p
17. Abiotic Factors
• The non-living part of the environment conditions that influence
the size of a population:
- Temperature; Each species has a different optimum temperature at
which it is best able to survive.
Cold-blooded animals + plants: temperatures below
optimum, enzymes work more slowly and so their metabolic rate is
reduced. Populations therefore grow at a slower rate. Temperatures
above optimum, enzymes undergo denaturation and therefore they
work less efficiently. Again the population grows more slowly.
Warm-blooded animals: can maintain a relatively constant body
temperature. However, the further the temperature of the external
environment gets from their optimum temperature, the more
energy these organisms expend in trying to maintain their normal
body temperature.
This leaves less energy for growth and so they mature more
slowly, and their reproductive rate slows. The population size
therefore decreases.
18. Abiotic Factors cont.
- Light; is a source of energy for ecosystems. The rate of
photosynthesis increases as light intensity increases. The
greater the rate of photosynthesis, the faster plants grow
and the more seeds they produce. There population size is
therefore potentially greater and in turn the populations
size of the animals that feed on the plants is too greater.
- pH; Enzymes operate most effectively at their optimum pH.
Population size is larger where the appropriate pH exists
and decreases/becomes non-existent where the pH is too
far from optimum.
- Water and humidity; Where water is scarce, populations
are small and consist of species well adapted to living in dry
conditions. Humidity affects the transpiration rates in
plants and the evaporation of water from the bodies of
animals. The population of species adapted to low humidity
will be larger than those without these adaptations.
19. Practice questions
1.
An ecologist was estimating the population of sandhoppers on a beach. 100
sandhoppers were collected, marked and released again. A week later 80
sandhoppers were collected, of which five were marked. Calculate the estimated
size of the sandhopper population on the beach.
2.
When using mark-release-recapture technique, explain how each of the following
might affect the final estimate of a population:
a.) The marks put on the individuals captured in the first sample make them more
noticable to predation and so proportionally more are eaten than unmarked
individuals.
b.) Between the release of marked individuals and the collection of a second sample
an increased ‘birth’ rate leads to a very large increase in the population.
c.) Between the release of marked individuals and the collection of a second
sample, disease kills large numbers of all types of individual.
20. Answers
1.
100 x 80 =1600
5
1.
a.) Population over-estimated as there will be proportionally fewer marked
individuals in the second sample.
b.) Population over-estimated as there will be proportionally fewer marked
individuals in the second sample because all the ‘new’ individuals will be
unmarked.
c.) No difference because the proportion of marked and unmarked individuals
killed should be the same.
21. Application Questions
1.
Suggest a reason why even dead organisms should be returned to the habitat
from which they came.
2.
Suggest why it is beneficial to a habitat that further investigations are not
carried too soon after an initial study.
3.
In the study of a seashore, students turn over large stones to record the
numbers of different organisms on their underside. Suggest reasons why it is
important that these stones are replaced the same way up as they were
originally.
4.
In the case of experienced ecologists obtaining data that enables habitats to be
conserved, the benefits usually outweigh any damage that they cause to the
habitats. This makes their work ethically justifiable. It might be said that the
same is not true of school or college students performing field studies. Give
reasons for and against A-level students carrying out ecological investigations in
this field.
22. Answers
1.
2.
3.
4.
-
They can be eaten by other organisms and so provide energy and nutrients to the
ecosystem.
It allows the habitat to recover from any disturbance/removal of organisms. The
results of a further study carried out too soon after may result in data that are not
typical of the habitat under ‘normal’ conditions.
The organisms live beneath stones so they remain moist when not covered by the
tide. If the stone is left upside down the organism may become desiccated and die.
FOR:
Practical experience aids learning/better than theoretical study
Experienced ecologists have to start somewhere
Students may become ecologists and so aid conservation in the long term
AGAINST:
Students are inexperienced and therefore more likely to damage habitats
Informations could be provided by theory/videos
Large number of A-level students puts pressure on/increase damage on popular
sites
23. Competition
• Intraspecific – individuals of same species compete for the
same resources. (food, water, breeding sites etc.) Lower the
availability, the smaller the population and vice versa.
e.g. Limpets competing for algae
Oak trees competing for resources (some grow larger and
restrict light availability)
Robins competing for breeding territory. (females only
attracted to those who have established breeding
territories)
• Interspecific – individuals of different species compete for
resources such as food, light, water etc. Where 2 species
occupy the same niche, the competitive exclusion principle
applies. This principle states that where 2 species are
competing for limited resources, the one that uses these
resources most effectively will ultimately eliminate the
other.
24. Predation
• A predator is an organism that feeds on
another organism, known as their prey.
• In laboratory, the prey is usually exterminated
by the predator. This is because the situation in
their natural environment is different. In their
own habitat, the area over which the
population can travel is greater and there are
more potential refuges. In these
circumstances, some of the prey can escape
predation.
25. Predator-Prey Relationship +
Population Size
• Predators eat prey, prey population decreases.
• Fewer prey available for predator food and
limits chances of survival for some
predators, predator population decreases.
• Fewer predators, so fewer prey eaten. Prey
population increases.
• More prey available as food, so predator
population increases.
26. Human Populations
• Recent explosion in human population size:
- the development of agriculture.
- the development of manufacturing and trade
that created the industrial revolution.
• We are currently in the exponential phase, in
which our population grows rapidly rather
than gives way to the stationary phase in
which the population stabilises.
27. Factors affecting growth
• Immigration (Individuals join from outside.)
• Emigration (Individuals leave a population.)
Population growth = (births + immigration) – (deaths + emigration)
% Population growth rate = population change during period
-------------------------------------------- x100
population at the start of the period
28. Factors affecting birth rate
• Economic conditions – countries with a low per capita income tend
to have higher birth rates.
• Cultural and religious backgrounds – Some countries encourage
larger families and some religions oppose birth control.
• Social pressures and conditions – In some countries a large family
improves social standing.
• Birth control – The extent to which contraception and abortion are
used markedly influences the birth rate.
• Political factors – Governments influence birth rates through
education and taxation policies.
number of births per year
Birth rate = total population in the same year
x 1000
29. Factors affecting death rate
• Age profile. The greater the proportion of elderly people in a
population, the higher the death rate is likely to be.
• Life expectancy at birth. The residents of economically developed
countries live longer than those of economically less develooped
countries.
• Food supply. (Nutrition.)
• Safe drinking water. Reduces the risk of water-borne diseases such
as cholera.
• Medical care.
• Natural disasters. How prone a region is to drought, famine or
disease.
• War. Deaths during war produces an immediate drop in population
and a longer term fall as a result of fewer fertile adults.
number of deaths per year
Death rate = total population in the same year
x 1000
30. Population Structure
• Demographic transition – A change in population
from those where life expectancy is short and
birth rates are high, to those where life
expectancy is long and birth rates are low.
• Stable population – Birth and death rate are
same, so there is no change in population size.
• Increasing population – High birth rate. Typical of
economically less-developed countries.
• Decreasing population – Low birth rate + low
mortality rate. E.g. Japan.
33. Anaerobic Respiration
-PRODUCES 2 ATP AS AN EMERGENCY
SHORT BURST OF POWER
-ETC ALONE PRODUCES 38 ATP, SO THIS
IS MUCH LONGER LASTING THAN
ANAEROBIC RESPIRATION
Glycolysis
NAD
Pyruvate
CO2
Lactic acid
Ethanal
NAD
NADH
PLANTS
ANIMALS
NADH 2H
2H
Ethanol
ATP + Respiration
Photosynthesis
34. •
•
•
•
ATP Synthesis
ADP + Pi ATP
Photophosphorylation (During photosynthesis)
Oxidative phosphorylation (During respiration)
Substrate-level phosphorylation (When phosphate groups are transferred
from donor molecules to ADP to make ATP.)
Role of ATP:
The instability of its phosphate bonds makes ATP a good energy donor, but also
stops it from being a good long term energy store. ATP is better as an
immediate energy source (than glucose) because ATP can be broken down
to ADP + Pi in a single reaction releasing energy. The breakdown of glucose
is a long series of reactions and therefore the energy release takes longer.
ATP Is the Source of Energy for:
- Metabolic processes
- Movement
- Active transport
- Activation of molecules
- Secretion
ATP + Respiration
Photosynthesis
35. Aerobic Respiration
• C6 H12 O6 + 6O2 energy + 6H20 + 6CO2
• requires oxygen and produces carbon dioxide, water and
lots of ATP. Aerobic Respiration can be summarised into
four stages 1. Glycolysis - splitting of a 6 carbon molecule into two 3
carbon pyruvates
2. Link Reaction - conversion of pyruvate into C02 and 2
carbon molecule Acetyl coA.
3. Krebs Cycle - intro of Acetyl coA into a cycle of oxidationreduction reactions that creates some ATP and a large
number of electrons.
4. Electron Transport Chain - electrons from the Krebs cycle
are used to synthesise ATP with water produced as a by
product.
ATP + Respiration
Photosynthesis
36. Glycolysis
• Occurs in cytoplasm
• 2 ATP go in as activation energy
• 4 ATP produced, net gain of 2 ATP
1. Glucose (6C) is phosphorylated.
2. Breaks down into 2 x triose phosphate (3C).
3. Phosphate donated to ATP.
4. NAD reduced.
5. 3+4 happen twice per glucose molecule, as 2
triose phosphate molecules are produced
6. This creates 2 x pyruvate (3C).
ATP + Respiration
Photosynthesis
37. Link Reaction
• Occurs in mitochondrial matrix
1. Co-enzyme A combines with pyruvate (3C).
2. CO2 is removed.
3. 2H removed, donated to NAD, produces
NADH.
4. Resultant molecule is Acetyl CoA (2C)
ATP + Respiration
Photosynthesis
38. Krebs Cycle
• Occurs in mitochondrial matrix
1. 4C compound combines with Acetyl CoA to
produce 6C compound.
2. CoA is removed and recycled.
3. NAD + FAD are reduced.
4. ATP created.
5. 2 CO2 removed, regenerating 4C compound
ATP + Respiration
Photosynthesis
39. Electron Transport Chain
• Occurs in mitochondria cristae
1. NAD and FAD are reduced.
2. They then donate electrons to the first molecule in the electron
transport chain.
3. This releases protons which are then actively transported across the
inner mitochondrial membrane.
4. Meanwhile, the electrons pass along the chain of electron transport
carrier molecules in a series of oxidation-reduction reactions. The
electrons lose energy as they travel down the chain and some of
this energy is used to combine ADP and Pi to form ATP. The rest is
released as heat.
5. Protons accumulate in intermembrane space before they diffuse
back into the mitochondrial matrix through special channel
proteins.
6. At the end of the chain, the electrons combine with the protons and
oxygen to make water. O2 is the final acceptor of electrons in ETC.
ATP + Respiration
Photosynthesis
40. Photosynthesis
• CHLOROPLAST STRUCTURE:
Photosynthesis takes place in the chloroplast of the plant cell. They
consist of a double membrane, thylakoids which are stacked up
into grana, lamellae which link grana molecules, photosynthetic
pigments, stroma and starch grains.
• Photosynthetic pigments (e.g chlorophyll and carotene) are
coloured substances that absorb light energy for
photosynthesis, they are found in the thylakoid membrane and are
attached to proteins. The protein and pigment are called a
photosystem.
• Plants use two types of photosystems to capture light energy, 1
which absorbs light at 700nm and number 2 which absorbs light at
680nm.
• Stroma is the gel liquid which fills the rest of the chloroplast and
surrounds the thykaloids. It contains some sugars, enzymes and
organic acids.
• Carbs produced by photosynthesis and not used up straight away
are stored as starch grains (round blobs) in the stroma.
41. The equation for Photosynthesis is • 6 CO2 + 6 H2O ------------> C6H12O6 + 6 02
42. Light Dependent Reaction
• Photosynthesis takes place in two stages - light dependant and
light independent.
• The light dependant stage takes place in the thykaloid membranes
of the chloroplast.
• The light energy is used to create ATP (adding another phosphate
to ADP), and to reduce NADP to form Reduced NADP.
• The products of the light dependant stage (ATP, Reduced NADP) are
used in the light independent stage. The ATP is used as energy and
the reduced NADP transfers a hydrogen.
• During the light dependant stage, photolysis of water occurs (use
of light to break water). Water is split into proton (H+), electron (e-)
and oxygen, which is released into the atmosphere. The e- is used
to replace the excited electron emitted from chlorophyll, the H+
goes back to the e- (after it has passed through electron carriers) to
reduce NADP.
43.
44. Light Independent Reaction
• The light independent reaction takes place in the
stroma of the chloroplast. This reaction is also
known as The Calvin Cycle. Carbon fixation takes
place in the Calvin Cycle, this is where carbon is
'fixed' into an organic molecule.
• The products of the light independent stage are
triose phosphate which can be used to make
glucose and other useful organic substances.
45.
46. Limiting Factors
There are optimum conditions for
photosynthesis:
• High light intensity of a certain wavelength
• temperature around 25 degrees
• C02 at 0.4%.
All of these factors can limit photosynthesis, if
one or any of the factors are too high or too
low it will slow down photosynthesis
47. ENERGY AND ECOSYSTEMS KEYWORDS
• Producer – Photosynthetic organisms that manufacture
organic substances.
• Consumer – Organisms that obtain their energy by feeding
on other organisms rather than using the energy of
sunlight directly.
• Decomposer - An organism who recycles nutrients by
performing decomposition as it feeds on dead or decaying
organisms.
• Detritivore - An organism that feeds on detritus or organic
waste.
• Trophic level – The position of an organism in a food
chain.
• Net production = gross production – respiratory losses.
48. Energy transfer between trophic levels
• Plants normally convert 1-3% of the Sun’s
available energy into organic matter. This is
because:
- 90%+ is reflected back into space by clouds and
dust or absorbed into the atmosphere.
- Not all wavelengths can be absorbed and used for
photosynthesis.
- Light may not fall on a chlorophyll molecule.
- A factor e.g. Low CO2 levels, may limit the rate of
photosynthesis.
49. Energy transfer between trophic levels
• The total quantity of energy that the plants in
a community convert to organic matter is
called the gross production.
• However plants use 20-50% of this in
respiration.
• The rate at which they store the remaining
energy is called net production.
• Net production = gross production –
respiratory losses.
50. Energy transfer between trophic levels
• 10% of energy stored in plants is used by primary
consumers for growth.
• Secondary and tertiary consumers are slightly more
efficient (transferring 20%). Low % energy transfer is due
to:
- Some of organism is not eaten.
- Some parts are eaten but not digested and therefore lost in
faeces.
- Some of energy is lost in urine.
- Some energy losses are due to heat from the body to the
environment and heat loss during respiration. These losses
are high in mammals and birds because they require more
energy to maintain their high body temperature.
51. Energy transfer between trophic levels
• Because energy transfer between trophic
levels is inefficient. It explains why:
- Most food chains have only 4/5 trophic levels.
Insufficient energy to support a large enough
breeding population at trophic levels higher
than these.
- The biomass is less at higher trophic levels.
- Total amount of energy stored is less at each
level as you go up the food chain.
52. Calculating the efficiency of energy
transfer
• Energy transfer = energy available after the transfer
----------------------------------------------energy available before the transfer
X 100
54. Ecological
Pyramids
Pyramids of Number
Agricultural
Ecosystems
• An ecological pyramid of numbers shows graphically the population
of each trophic level in a food chain.
• No account is taken of size – this sometimes results in an inverted
shape, or a shape that does not resemble a pyramid at all.
• The number of individuals is so great that it is not possible to
represent them accurately on the same scale as other species in the
food chain. E.g. 1 tree may accommodate for millions of greenfly.
57. Ecological
Pyramids
Agricultural
Ecosystems
Comparison
Number
Biomass
Energy
Doesn’t take into account size of
organisms.
Does take into account size of
organisms.
Collecting the data can be
difficult and complex.
Number of individuals are so
great that it is impossible to
represent them accurately.
Fresh mass easy to access and
measure, however varying
amounts of water make it
unreliable.
More reliable data than
biomass, because 2 organisms
of the same dry mass may store
different amounts of energy.
Dry mass is harder to
access, organisms must be killed
and so it is usually only made on
a small sample – which may be
unrepresentative of the
population.
Seasonal differences not taken
into account, as only organisms
at a particular are shown.
Seasonal differences not taken
into account, as only organisms
at a particular are shown.
Data collected for a year and so
can take into account seasonal
differences.
58. Agricultural Ecosystems
• Net productivity = gross productivity – respiratory losses
Natural Ecosystem
Agricultural Ecosystem
Solar energy only – no additional energy
input
Solar energy + energy from food (labour)
and fossil fuels (machinery and transport)
Lower productivity
Higher productivity
More species diversity
Less species diversity
More genetic diversity
Less genetic diversity
Nutrients recycled naturally within the
ecosystem with little addition from outside
Natural recycling is more limited and
supplemented by the addition of artificial
fertilisers
Populations are controlled by natural means, Population are controlled naturally and by
e.g. Competition and climate
use of pesticides and cultivation
A natural climax community
An artificial community prevented from
reaching its natural climax community.
59. Pest and Pesticides
• A pest is an organism that competes with humans
for food/space/could be a danger to health.
An effective pesticide must be:
- Specific (toxic to the pest only.)
- Biodegradable (once applied, it will break down
into harmless substances in the soil.)
- Cost-effective (development costs are high and
new pesticides remain useful only for a limited
time as pests can develop genetic resistance.)
- Not accumulate (so that it does not build up in an
organism or as it passes along food chains.)
60. Biological control
• Controlling pests using organisms that are
either predators or parasites of the pest
organism.
• The aim is to control, not eradicate. If the
pests were eradicated, the predators would
die out from lack of food and therefore the
pests could reinstate themselves. The pest and
control agent should exist in a balance at a
level where the pest causes little damage.
61. Pesticides vs. Biological control
Biological Control
Pesticides
Very specific
Not as specific – often have an effect on
non-target species.
Once introduced the control organism
reproduces itself.
Must be reapplied at regular intervals,
this means they are expensive.
Pests do not become resistant.
Pests develop genetic resistance and new
pesticides have to be developed.
Does not leave chemical in environment /
on crop / no bioaccumulation.
Can bioaccumulate.
May become a pest itself.
Does not become a pest itself.
Does not get rid of pest completely.
Aim is to eradicate pest completely.
Takes time to reduce pest population.
Fast effect.
62. Integrated pest-control systems
• Integrates all forms of pest control rather than being reliant on one type.
• Aim is to reduce pest population to an acceptable level. Eradication is
costly, counterproductive and almost impossible to achieve.
• Integrated control involves:
- Choose animal/plant varieties suitable for the area and as pest-resistant as
possible
- Managing the environment to provide suitable habitats close to the crops
for natural predators
- Regularly monitor crop for signs of pests and take early action if need be
- Removing the pests mechanically (hand-picking/erecting barriers...) if pest
exceeds acceptable population level
- Use biological agents if necessary and available
- Pesticides are to be used as a last resort, when pest population is starting
to get out of control
63. Pest control and productivity
• Pests reduce productivity, any resources taken by the
pest means less is available for crop.
• One may become a limiting factor in
photosynthesis, reducing the rate and subsequently
productivity.
• Pests also eat leaves of crops, limiting photosynthesis
and leaving less crop for harvest.
• Many crops are grown in MONOCULTURE. This means
insect and fungal pests as well as diseases can spread
rapidly. Animals may not grow as rapidly, die, be unfit
for human consumption – due to pests and therefore
would lead to reduced productivity.
64. Intensive Rearing of Domestic
Livestock
• Aim: to convert the smallest amount of food energy into
the greatest quantity of animal mass.
• How to increase energy-conversion rate:
- Restrict movement, less energy used by muscle contraction
- Environment kept warm in order to reduce heat loss as
most livestock are warm-blooded
- Feeding can be controlled so that the animals receive
optimum amount and type of food for maximum growth
- Predators are excluded
- Selective breeding to produce varieties that are more
efficient at converting the food they eat into body mass
- Use hormones to increase growth rates
65. Features of Intensive Rearing of
Domestic Livestock
•
•
•
•
•
•
•
•
•
•
Efficient energy conversion
Low cost products
Less space used
Safety, smaller concentrated units are easier to regulate
Disease, living in close proximity results in easily spread
infection
Use of drugs (over use of antibiotics has led to antibiotic
resistance)
Animal welfare, better healthcare but confined space can
cause distress
Pollution, large concentration of waste in small area
Use of fossil fuels to heat buildings
Reduced genetic diversity due to selective breeding, resulting
in the loss of genes that may have been beneficial
67. Basic Nutrient Cycle Sequence
Inorganic
molecule
or ion
Absorption
Organic
molecules in
Producers
Feeding and
digestion
Organic
molecules in
Consumers
Death
Decomposition
Nutrient Cycles
Organic
molecules in
Decomposers
Succession
68. Carbon Cycle
CO2 in
atmosphere
Photosynthesis
C containing
compounds in
Producers
Combustion
Fossil
Fuels
Respiration
Feeding
Organic
molecules in
Consumers
Death
Decomposition
Nutrient Cycles
Organic
molecules in
Decomposers
Decay Prevented
Succession
69. Nitrogen Cycle
Nitrogen fixation by free-living bacteria
Denitrification
Ammonium
Ions
Nitrification
Nitrate
Ions
Nitrification
Nitrate
Ions
Nitrate in
atmosphere
Absorption
Feeding and
digestion
Ammonium
containing
molecules in
Producers
Death
Ammonification
Nutrient Cycles
Organic
molecules in
Decomposers
Succession
Ammonium
containing
molecules in
Consumers
Death
and
excretion
70. Ammonification
• The product of ammonia from organic
ammonium containing compounds
• These compounds include
urea, proteins, nucleic acids and vitamins
• Saprobiotic microorganisms feed on these
materials, releasing ammonia, forming
ammonium ions in the soil.
Nutrient Cycles
Nitrogen Cycle
Succession
71. Nitrification
• The conversion of ammonium ions to nitrate ions. The
conversion occurs in 2 stages:
1. Oxidation of ammonium ions to nitrite ions (NO2-)
2. Oxidation of nitrite ions to nitrate ions (NO3-)
• This is an oxidation reaction, and so releases energy
• It is carried out by free-living soil microorganisms
called nitrifying bacteria
• The bacteria require oxygen to carry out this
conversion and so they need soil with many air spaces
• To raise productivity, it is important for farmers to keep
soil structure light and well aerated by ploughing.
• Good drainage prevents air spaces from being filled
with water
Nutrient Cycles
Nitrogen Cycle
Succession
72. Nitrogen Fixation
• Nitrogen gas is converted into nitrogen-containing
compounds.
• It is carried out by 2 different microorganisms:
1. Free-living Nitrogen-fixing bacteria – these reduce
gaseous nitrogen to ammonia, which they then use to
manufacture amino acids. When they die and
decay, they release nitrogen-rich compounds.
2. Mutualistic Nitrogen-fixing bacteria – these live in
nodules on the roots of plants such as peas and
beans. They obtain carbohydrates from the plant, and
the plant acquires amino acids from the bacteria.
Nutrient Cycles
Nitrogen Cycle
Succession
73. Denitrification
• When soils become waterlogged, the conditions
become anaerobic.
• Therefore fewer aerobic nitrifying and nitrogen-fixing
bacteria are found, and more anaerobic denitrifying
bacteria.
• These convert soil nitrates into gaseous nitrogen.
• As this process reduces the availability of nitrogencontaining compounds for plants.
• This reduces productivity. To increase productivity, the
soils on which crops grow must therefore be kept well
aerated to prevent the build-up of denitrifying bacteria
Nutrient Cycles
Nitrogen Cycle
Succession
74. Fill in the blanks to complete the passage below in order to
check your understanding of the nitrogen cycle.
A few organisms can convert nitrogen gas into
compounds useful to other organisms is a process
known as (1). These organisms can be free-living or live
in a relationship with certain (2). Most plants obtain
their nitrogen by absorbing (3) from soil through their
(4) by active transport. They then convert this to
(5), which is passed to animals when they eat plants.
On death, (6) break down these organisms, releasing
(7), which can then be oxidised to form nitrates by (8)
bacteria. Further oxidation by the same type of
bacteria forms (9) ions. These ions may be converted
back to the atmospheric nitrogen by the activities of
(10) bacteria.
Answers
75. Answers:
A few organisms can convert nitrogen gas into compounds
useful to other organisms is a process known as (1 –
Nitrogen fixation). These organisms can be free-living or
live in a relationship with certain (2 - Plants). Most plants
obtain their nitrogen by absorbing (3 – Nitrate ions) from
soil through their (4 – Root hairs) by active transport. They
then convert this to (5 – Proteins/Amino acids/Nucleic
acids), which is passed to animals when they eat plants. On
death, (6 - Decomposers) break down these
organisms, releasing (7 – Ammonium ions), which can then
be oxidised to form nitrates by (8 - Nitrifying) bacteria.
Further oxidation by the same type of bacteria forms (9 Nitrate) ions. These ions may be converted back to the
atmospheric nitrogen by the activities of (10 - Denitrifying)
bacteria.
Nutrient Cycles
Succession
76. Fertilisers
• In natural ecosystems, the minerals that are removed from
the soil by plants are returned when the plant is broken
down by microorganisms on its death.
• In agricultural ecosystems, the crop is harvested and the
dead remains are rarely returned to the same area of land.
Therefore the levels of mineral ions in agricultural land
falls, and in order to be replenished, fertiliser must be
added to the soil.
2 types of fertiliser:
1. Natural (organic) fertilisers – dead and decaying remains
of plants and animals, as well as animal waste.
2. Artificial (inorganic) fertilisers – mined from rock and
deposits and converted into compounds containing
nitrogen, phosphorous, potassium.
Nutrient Cycles
Succession
77. Consequences of nitrogen fertilisers
• Reduced species diversity (nitrogen-rich soils
favour the species grown, which outcompetes
other species.
• Leaching – Rain dissolves soluble nutrients such
as nitrates, carrying them deep into soil beyond
the reach of plant roots. The leached nitrates can
then find their way into watercourses, such as
streams and rivers. They may then pollute the
source of human drinking water.
• Eutrophication – the process by which nutrients
build up into bodies of water.
Nutrient Cycles
Succession
78. Nutrient Cycles
Succession
Eutrophication
1.
In most lakes and rivers there is naturally very little nitrate (a limiting factor for plant and
algal growth).
2. As nitrate concentration increases as a result of leaching, it is no longer a limiting factor for
the growth of plants and algae.
3. As algae mostly grow at the surface, the upper layers of water become densely populated.
This is an ‘algal bloom’.
4. This dense surface layer of algae absorbs light and prevents it from reaching lower depths.
5. Light becomes a limiting factor for the growth of plants and algae at lower depths so they
eventually die.
6. There are more dead plants and algae for the growth of saprobiotic algae which grow
exponentially.
7. The saprobiotic bacteria require oxygen of respiration, creating a demand for it.
8. The concentration of oxygen in the water is reduced and nitrates are released from
decaying organisms.
9. Oxygen then becomes the limiting factor for the population of aerobic organisms. These
organisms ultimately die as the oxygen is used up.
10. Without the aerobic organisms, there is less competition for the anaerobic organisms
whose population rises exponentially.
11. The anaerobic organisms further decompose dead material, releasing more nitrates and
some toxic waste, which make the water putrid.
Animal slurry, organic manures, human sewage and natural leaching can all contribute to
eutrophication, but the main cause is leaching of artificial fertilisers.
79. Succession Key Words
KEY WORDS:
• Biodiversity – the range and variety of living organisms within a
particular area
• Biomass – total mass of living material in a specific area at a given
time. (usually dry mass as amount of water varies)
• Climax Community – the organisms that make up the final stage of
ecological succession
• Community – the organisms of all species that live in the same
area.
• Conservation –
• Ecosystem – self-contained functional unit made up of all the
interacting biotic and abiotic factors in a specific area
• Pioneer species –
• Succession –
80. Succession
• Succession is
e.g. When bare rock/barren land is colonised
This may occur as a result of:
- a glacier retreating and depositing rock
- sand being piled into dunes by wind or sea
- volcanoes erupting and depositing lava
- lakes or ponds being creating by land subsiding
- silt and mud being deposited at river estuaries
81. Primary Succession
1. The hostile environment that inhospitable to other
species, is colonised a pioneer species.
2. The pioneer species dies, decomposes and adds
nutrients to the environment. This change in the
abiotic environment caused by the pioneer species...
3. Enables other species to colonise/survive the area.
4. This results in a change in diversity/biodiversity.
5. Therefore stability increases, the environment
becomes less hostile.
6. A climax community is established.
82. Example of ecological succession:
- Area of bare rock
- Pioneer species are Lichens as they can survive
considerable drying out
- Over time, weathering of the rock produces sand/soil
- The lichens die and decompose releasing nutrients
- These two stages change the abiotic environment and
enable it to support a community of small plants
- Next typical stages in succession are mosses and ferns.
- More soil is built up from continuing rock erosion and
more organic matter available from death of the plants
- This again changes the abiotic environment, more suitable
for organisms that follow e.g. Shrubs, trees
- Climax community establishes
84. Common features during a succession
- Non-living environment becomes less hostile (Soil
forms, more nutrients, shelter provided)
- A greater number/variety of habitats (Due to less
hostile environment)
- Increased biodiversity (Evident in early stages, peaks at
mid-succession, decreasing when climax community is
reached due to dominant species out-competing other
species.)
- More complex food webs (Due to increased
biodiversity)
- Increased biomass (Due to the more complex food
web)
85. Secondary Succession
• Another type of succession is when land that already
supports life is suddenly altered.
• This could be due to a forest fire or agriculture.
• In this case, the stages are the same but they occur and
reach the climax community much more rapidly
^ This is because...
Spores and seeds often remain alive in the soil and there is
an influx of animals and plants through dispersal and
migration in the surrounding area
*This succession does not have a pioneer species as the
organisms are from subsequent successional stages.
BUT as the land has been altered, the climax community will
be different.
86. Conservation of Habitats
• Conservation is the management of the Earth’s natural
resources so that use of them in the future is
maximised.
Reasons for conservation:
• Ethical (Respect for living things. Other species have
occupied the Earth far longer than us, therefore should
be allowed to coexist with us.)
• Economic (Many species have the capacity to make
substances, many of which may prove valuable in the
future.)
• Cultural and Aesthetic (Variety adds interest to
everyday lives and inspires writers etc.)
87. Inheritance and Selection
KEYWORDS
•
Phenotype - The observable characteristics of an organism. (Appearance.)
•
Genotype - The genetic composition of an organism.
•
Gene - A section of DNA, a sequence of nucleotide bases that usually determines a single characteristic of an organism.
•
Allele - Different forms of a gene.
•
Homologous chromosomes - A pair of chromosomes that have the same gene loci and therefore determine the same
features.
•
Homozygous - Two of the same alleles present.
•
Heterozygous - One of each allele present.
•
Dominant - The allele that is expressed even when present with the recessive allele.
•
Recessive - The allele that is not expressed. Expressed only in the presence of another identical allele.
•
Homozygous dominant - Two dominant alleles.
•
Homozygous recessive - Two recessive alleles.
•
Diploid - 2 copies of each allele in cells.
•
Co-dominant - Two alleles that both contribute to the phenotype.
•
Multiple alleles - A gene that has more than 2 allelic forms e.g. blood type.
•
Gene pool - All the alleles of all the genes of all the individuals in a population at any one time.
•
Allelic frequency - The number of times an allele occurs within the gene pool is referred to as the allelic frequency,
•
Hardy-Weinberg Principle - p + q = 1
p2 + 2pq + q2 = 1
•
Directional selection - Selection may favour individuals that vary in one direction from the mean of the population. It
changes the characteristics of the population.
•
Stabilising selection - Selection may favour average individuals. It preserves the characteristics of a population.
•
Speciation - The evolution of a new species from existing species.
•
Geographical isolation - Occurs when a physical barrier prevents two populations from breeding with one another.
88. Monohydrid Inheritance – Genetic
cross diagram example
Parental Phenotype:
Green pods
Parental Genotype:
GG
Gametes:
G+G
Yellow pods
gg
g+g
Male gametes
Female gametes
G
G
g
Gg
Gg
g
Gg
Gg
100% green
89. Sex Inheritance/Linkage
• Any gene that is carried on either the X or Y
chromosomes is said to be sex linked.
• However, the X chromosome is longer than the Y
chromosome, meaning for most of the X chromosome
there is no homologous equivalent portion of the Y
chromosome.
• Those characteristics that are controlled by recessive
alleles on this non-homologous portion of the X
chromosome will appear more frequently in the male.
• This is because there is no homologous portion on the
Y chromosome that could possess the dominant
allele, in which circumstances the recessive allele
would not present itself.
92. Directional selection
• If environmental conditions change, so will the
phenotypes needed for survival. Some
individuals, which fall to the left or right of the
mean, will possess a phenotype more suited to
the new conditions. These individuals will be
more likely to survive and breed. Over time, the
mean will then move in the direction of these
individuals.
93. Stabilising selection
• If environmental conditions remain stable, it is
the individuals with phenotypes closest to the
mean that are favoured. These individuals are
more likely to pass their alleles on to the next
generation. The individuals with extreme
phenotypes are less likely to pass on their
alleles. Therefore stabilising selection tends to
eliminate the extremes
94. Speciation
1. Geographical isolation occurs. A physical barrier splitting
the species into two groups, and preventing them from
mixing.
2. This also prevents interbreeding and forms 2 separate gene
pools.
3. Variation is created between both due to mutation.
4. In each group, there are different
environmental/abiotic/biotic conditions creating selection
pressures.
5. Selection favours the advantageous
features/characteristics/mutation/ allele.
6. This results in only selected organisms surviving to
reproduce.
7. This leads to a change in allele frequency in the groups.
This process occurs over a long period of time.
