5.3.1 Ecosystems

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:

5. Biotic vs. Abiotic Factors Create a table and list the factors below as either biotic or abiotic:

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 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

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, Nitrobacterand 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. 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, Nitrobacterand 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. 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 coverin the area being sampled Percentage cover

33. 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 Point quadtats

34. 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. Transects -Measuring changes

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, Nitrobacterand 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 reductaseto 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