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;

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 non-living components of the environment


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


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


examples; • define the terms producer, consumer, decomposer and trophic




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






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


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


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)






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 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

© Pearson Education Ltd 2009This document may have been altered from the original

Week 25

Cross-section of a sand dune showing stages of succession






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 ground-living (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.






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

SummaryProcess Bacteria Reactant Product

Nitrogen Fixing Rhizobium Nitrogen N2 Nitrates NO3-

Nitrification NitrosomonasNitrobacter

Ammonium NH4+Nitrites NO2-

Nitrites NO2-Nitrates NO3-

Denitrification Bacteria Nitrates NO3- Nitrogen N2

Nitrous Oxide N2O

Documents

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;