Transcript A2 5.3.1 Ecosystems

5.3.1 Ecosystems
• define the term ecosystem;
• state that ecosystems are dynamic systems;
• define the terms biotic factor and abiotic factor, using named
examples;
• define the terms producer, consumer decomposer and trophic level;
• describe how energy is transferred though ecosystems;
• outline how energy transfers between trophic levels can be
measured;
• discuss the efficiency of energy transfers between trophic levels;
• explain how human activities can manipulate the flow of energy
through ecosystems (HSW6b);
What is an Ecosystem?
• A self contained system including all the living
organisms and the environment, interacting
with each other
• We say that ecosystems are dynamic, as
changes happen all the time as interactions
are taking place
Biotic vs. Abiotic Factors
• Biotic factors are ones that involve other
living organisms
• Abiotic factors are ones that involve nonliving components of the environment
Biotic vs. Abiotic Factors
Create a table and list the factors below as
either biotic or abiotic:
Atmospheric humidity
Feeding
Water supply
Predation
Carbon dioxide
concentration
Parasitism
Edaphic (soil) factors
pH
Mutualism
Light intensity
Temperature
Wind speed
Organic ion availability
competition
Oxygen concentration
Biotic vs. Abiotic Factors
Create a table and list the factors below as
either biotic or abiotic:
Atmospheric humidity
Feeding
Water supply
Predation
Carbon dioxide
concentration
Parasitism
Edaphic (soil) factors
pH
Mutualism
Light intensity
Temperature
Wind speed
Organic ion availability
competition
Oxygen concentration
5.3.1 Ecosystems
• define the term ecosystem;
• state that ecosystems are dynamic systems;
• define the terms biotic factor and abiotic factor, using named
examples;
• define the terms producer, consumer, decomposer and trophic level;
• describe how energy is transferred though ecosystems;
• outline how energy transfers between trophic levels can be
measured;
• discuss the efficiency of energy transfers between trophic levels;
• explain how human activities can manipulate the flow of energy
through ecosystems (HSW6b);
Task
• Find the definition of the following key terms:
•
•
•
•
Producer
Consumer
Decomposer
Trophic level
Task
• Find the definition of the following key terms:
• Producer: an organism that transfers energy from light or an
inorganic compound to an organic compound e.g. plants
• Consumer: an organism that obtains it’s energy from organic
compounds such as carbohydrates, fats and proteins
• Decomposer: an organism that breaks down organic remains
of other organisms, returning matter from them to the soil
and air
• Trophic level: the stage of a food chain at which an organism
feeds
Questions
1. How is energy transferred through ecosystems?
2. How can energy transfers between trophic levels
be measured?
3. What affects the efficiency of energy transfer
between trophic levels?
4. How can the efficiency of energy transfers be
measured?
5. How can human activities manipulate the flow
of energy in ecosystems?
Past Paper Question 2005
5.3.1 Ecosystems
• define the term ecosystem;
• state that ecosystems are dynamic systems;
• define the terms biotic factor and abiotic factor, using named
examples;
• define the terms producer, consumer, decomposer and trophic level;
• describe how energy is transferred though ecosystems;
• outline how energy transfers between trophic levels can be
measured;
• discuss the efficiency of energy transfers between trophic levels;
• explain how human activities can manipulate the flow of energy
through ecosystems (HSW6b);
Energy Transfer
• Food chains show how energy is transferred
from one organism to another
• Each level is known as a trophic level
• Different food chains join together to make a
food web
Efficiency of Energy Transfers
• Energy is lost at each trophic level and is unavailable to the next
trophic level
• Energy is lost through respiration then converted to heat, stored in
dead organisms and waste material and is therefore only available
to decomposers
• Because of this, there is less living tissue (biomass) at higher levels
of a food chain
• A pyramid of numbers illustrates this. There are always less
consumers due to energy loss at each trophic level
Measuring Energy Efficiency
Pyramids of biomass
• bars are proportional to the dry
mass of all the organisms at that
trophic level
• Organisms are collected and
heated at 80⁰C until the water in
them has evaporated
• As it is very destructive, the wet
mass is used and the dry mass is
calculated using previous data
• Disadvantage: different species
may release different amounts
of energy per unit mass
Measuring Energy Efficiency
Pyramids of Energy
• Involves burning the organism in a calorimeter and work
out how much heat energy is released per gram
• This is calculated from the temperature rise of a known
mass of water
• This is also destructive, only takes a snapshot of an
ecosystem at one moment in time and takes no account of
population fluctuations
Measuring Energy Efficiency
Productivity
• The rate at which energy passes through each trophic level
• Gives an idea of how much energy is available to the
organisms at each trophic level per unit area (m2) in a given
amount of time (one year)
• Primary productivity is the name for the productivity of
plants
• Gross primary productivity is the rate that plants convert
light energy into chemical energy, although as energy is lost
through respiration, less energy is available to the primary
consumer. The energy available is called the net primary
productivity (NPP)
5.3.1 Ecosystems
• define the term ecosystem;
• state that ecosystems are dynamic systems;
• define the terms biotic factor and abiotic factor, using named
examples;
• define the terms producer, consumer, decomposer and trophic level;
• describe how energy is transferred though ecosystems;
• outline how energy transfers between trophic levels can be
measured;
• discuss the efficiency of energy transfers between trophic levels;
• explain how human activities can manipulate the flow of energy
through ecosystems (HSW6b);
Explain how human activities can manipulate
the flow of energy through ecosystems
• Use OCR Biology p196-197 to write about how
humans can manipulate the flow of energy
through ecosystems including:
• How scientists increase NPP
• How energy is manipulated from producer to
consumer
• Complete the questions on p197
5.3.1 Ecosystems
• define the term ecosystem;
• state that ecosystems are dynamic systems;
• define the terms biotic factor and abiotic factor, using named
examples;
• define the terms producer, consumer, decomposer and trophic level;
• describe how energy is transferred though ecosystems;
• outline how energy transfers between trophic levels can be
measured;
• discuss the efficiency of energy transfers between trophic levels;
• explain how human activities can manipulate the flow of energy
through ecosystems (HSW6b);
5.3.1 Ecosystems Continued…
• describe one example of primary succession resulting
in a climax community;
• describe how the distribution and abundance of
organisms can be measured, using line transects, belt
transects, quadrats and point quadrats (HSW3);
• describe the role of decomposers in the decomposition
of organic material;
• describe how microorganisms recycle nitrogen within
ecosystems. (Only Nitrosomonas, Nitrobacter and
Rhizobium need to be identified by name).
Describe one example of primary succession
resulting in a climax community;
• Succession = A change in a habitat causing a change in the make-up
of a community
Primary succession (from bare rock)
• Pioneer community like algae and lichens live on bare rocks
• Rock erodes and build up of dead organisms produces soil
• Mosses and ferns grow and succeed (replace) algae
• Larger plants succeed smaller plants until community is stable
• The stable community is called a climax community
Secondary Succession
• Secondary succession can also take place on a previously colonised
area
Sand Dune Succession
• You have to know one example of succession.
Use OCR Biology to outline succession on sand
dunes
Sand Dune Succession
• Sea rocket and prickly sandwort colonise above the high
water mark
• Mini sand dunes form and accumulate nutrients from
decaying plants
• Sea sandwort and sea couch grass with underground stems
colonise it
• Sea spurge and marram grass grow
• Marram grass traps win blown sand allowing shoots to
grow taller
• Hare’s foot clover and bird’s foot trefoil (legumes) begin to
colonise containing nitrogen-fixing bacteria in their roots
• When nitrates are available, sand fescue and viper’s
bugloss colonise, stabilising the dune further
Week 25
Cross-section of a sand dune showing stages of succession
© Pearson Education Ltd 2009
This document may have been altered from the original
5.3.1 Ecosystems Continued…
• describe one example of primary succession resulting
in a climax community;
• describe how the distribution and abundance of
organisms can be measured, using line transects, belt
transects, quadrats and point quadrats (HSW3);
• describe the role of decomposers in the decomposition
of organic material;
• describe how microorganisms recycle nitrogen within
ecosystems. (Only Nitrosomonas, Nitrobacter and
Rhizobium need to be identified by name).
Task: Answer the following question
• describe how the distribution and abundance
of organisms can be measured, using line
transects, belt transects, quadrats and point
quadrats
Random Sampling
• The best way to get information about a particular ecosystem would be to
count every individual of every species. This would take too long so we
sample a small part of the ecosystem we are studying
• Throwing is not random
• Measure out an area using tape measures
as axes
• Use random number tables to select coordinates
at which to place quadrats
• Sample (using a quadrat or transect) the population and repeat the
process to make the results more reliable
• Estimate the number of individuals for the whole area by taking an
average and multiplying it by the size of the whole area
Frame Quadrats
• A square of known size divided into a grid of 100
squares(increases accuracy) -used to sample the groundliving (sessile) organisms in an ecosystem. (for larger
plants large quadrats are used)
• Placed on the ground at random points
• Estimating:
• Number of individuals of each species is recorded in each
quadrat and find average or species density
• Percentage cover can also be measured. It is a quick
method
• Species frequency – proportion of quadrats with a
particular species in them
• Subjective rating – ACFOR scale
Subjective rating
• ACFOR
• Look at whole quadrat and decide
if species is
–
–
–
–
–
Abundant
Common
Frequent
Occasional
Rare
• If you want to be a bit
quantitative you can assign each
a score (A=5, R=1)
• Quick and easy
• Subject to innaccuracy due to
subjectivity
• May lack reliability between
samples/samplers
Percentage cover
• Estimate, to nearest 5% how
much of the quadrat is covered
by each species
• Still open to problems of
subjectivity
• Data is more quantitative which is
useful for analysis
• The average percentage cover of
a particular species in all quadrats
is called the species cover in the
area being sampled
Point quadtats
• Most objective of quick
techniques – increases
reliability
• Frame placed on ground at
random points
• Pins dropped into holes in
frame
• Every plant that each pin
touches is counted.
• Useful in areas of dense
vegetation
Transects -Measuring changes
• Studying how the environment
changes over a distance is done using
a transect
• A tape measure is placed in a line
• Quadrats are placed at standardized
distances along the line
• Quadrats laid adjacent to each other
along the line is called a belt transect
• Quadrats at intervals (e.g. 5 m) is
called an interrupted transect
• Again, placement of the quadrat in
relation to the measurement on the
tape needs to be standardized
beforehand, e.g. bottom left corner of
quadrat on tape.
5.3.1 Ecosystems Continued…
• describe one example of primary succession resulting
in a climax community;
• describe how the distribution and abundance of
organisms can be measured, using line transects, belt
transects, quadrats and point quadrats (HSW3);
• describe the role of decomposers in the decomposition
of organic material;
• describe how microorganisms recycle nitrogen within
ecosystems. (Only Nitrosomonas, Nitrobacter and
Rhizobium need to be identified by name).
Role of Decomposers
• Break down dead and waste organic material
• Bacteria and fungi feed saprotrophically and are called
saprophytes
• They secrete enzymes onto dead material
• The enzyme digests the material into small molecules
• Molecules then absorbed into organism
If bacteria and fungi did not do this then energy and
nutrients would remain trapped within dead organisms.
Microbes get a supply of energy this way and also recycle
these trapped nutrients for other organisms
Recycling Nitrogen
• Nitrogen is needed to make proteins and
nucleic acids
• Bacteria are involved in this process
Nitrogen Fixation
• Nitrogen gas is very unreactive
• Plants need fixed nitrogen as ammonium ions (NH4+) or
nitrate ions (NO3-)
• Nitrogen fixing bacteria such as rhizobium live inside
root nodules
• They have mutualistic relationship with the plant, fixing
nitrogen and gaining glucose
• Proteins like leghaemoglobin in the nodules absorb
oxygen to keep conditions anaerobic
• The bacteria use the enzyme nitrogen reductase to
reduce nitrogen gas to ammonium ions
Nitrification
• Chemoautotrophic bacteria in soil absorb ammonium
ions
• Ammonium ions released by bacteria breaking animal
proteins down from dead animals (putrefaction)
• Chemoautotrophic bacteria obtain energy by oxidising
ammonium ions NH4+ to nitrites NO2- (nitrosomonas
bacteria) or by oxidising nitrites NO2- to nitrates NO3(nitrobacter bacteria)
• Only happens in well aerated soils as it requires oxygen
• Nitrates then absorbed by plants
Denitrification
• Bacteria convert nitrates back to nitrogen gas
• When bacteria grow in waterlogged soils
without oxygen they use nitrates NO3- as a
source of oxygen and produce nitrogen gas N2
and nitrous oxide N2O
Summary
Process
Bacteria
Reactant
Product
Nitrogen Fixing
Rhizobium
Nitrogen N2
Nitrates NO3-
Nitrification
Nitrosomonas
Nitrobacter
Ammonium NH4+
Nitrites NO2-
Nitrites NO2Nitrates NO3-
Denitrification
Bacteria
Nitrates NO3-
Nitrogen N2
Nitrous Oxide N2O