1. 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);

2. 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

3. 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

4. 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. 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

6. 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);

7. Task Find the definition of the following key terms: Producer Consumer
Decomposer
Trophic level

8. 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

9. Questions How is energy transferred through ecosystems?
How can energy transfers between trophic levels be measured?
What affects the efficiency of energy transfer between trophic levels?
How can the efficiency of energy transfers be measured?
How can human activities manipulate the flow of energy in ecosystems?

10. Past Paper Question 2005

12. 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);

13. 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

14. 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

15. 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

16. 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

18. 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)

19. 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);

20. Explain how human activities can manipulate the flow of energy through ecosystems
Use OCR Biology p 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

21. 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);

22. 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).

23. 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

24. Sand Dune Succession
You have to know one example of succession. Use OCR Biology to outline succession on sand dunes

25. 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

26. Cross-section of a sand dune showing stages of succession
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

27. 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).

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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.

35. 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).

36. 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

37. Recycling Nitrogen
Nitrogen is needed to make proteins and nucleic acids
Bacteria are involved in this process

38. 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

39. 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

40. 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

41. Summary Process Bacteria Reactant Product Nitrogen Fixing Rhizobium
Nitrogen N2
Nitrates NO3-
Nitrification
Nitrosomonas
Nitrobacter
Ammonium NH4+
Nitrites NO2-
Denitrification
Nitrous Oxide N2O