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Download Page of 12 A2 U4 Biology Notes – HM Ecology 5.10 – 5.12
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Page 1 of 12 Disclaimer: These notes are to be taken as a guide only. They are from when I personally did A-level, and there’s some additional things I added. Essentially the information is taken from the Edexcel A-level books mentioned on page 8, and I’ve tried to make it as concise and as complete as possible; it should have the essential bits anyway. But it’s vital that you make sure to edit these with your own notes / Mrs Crouch’s notes, which are more important. If you want me to talk you through any of this, I am at school on a weekly basis for now, let me know on my new site www.qegshm.webs.com and go to the ‘Forums’ or ’Contact Me’ section. (or use QEGS HM on facebook or [email protected]) 5.10. Explain that the numbers and distribution of organisms in a habitat are controlled by biotic and abiotic factors. Difficulty ** 5.11. Describe how to carry out a study on the ecology of a habitat to produce valid and reliable data (including the use of quadrats and transects to assess abundance and distribution of organisms and the measurement of abiotic factors, eg solar energy input, climate, topography, oxygen availability and edaphic factors). Difficulty *** 5.12. Explain how the concept of niche accounts for distribution and abundance of organisms in a habitat. Difficulty ** Background information During AS, we look at biodiversity and the variety of genotypes and phenotypes that exist between and within species, as well as the basic principles of evolutionary biology. Here are introductory terms to be familiar with: Abundance (population size) - the number of individuals of one species in a particular area Distribution - where a species is within a particular area (proportional abundance relative to geographical location) Habitat – the place where an organism lives Page 2 of 12 Population – all the selected organisms of one species in a habitat Community – all the populations of the different species in a habitat at any one time Ecosystem – the set of all biotic and abiotic factors in one or more particular location(s) Biomes – large ecosystems For A2 Topic 5, we take this further by showing that biotic and abiotic factors define the niche of a species and these factors also affect the: Abundance and distribution of organisms 5.10-5.12 Stages of succession and climax communities 5.13 Developmental and physiological adaptations 5.15-5.17 (and behavioural) Evolved adaptations by means of natural selection 5.22 (there are also other selection processes like sexual selection) Speciation (evolutionary event) by reproductive isolation (a process and consequence of natural selection) 5.21 The factors are also relevant when we look at forensics and factors affecting the decay of bodies of dead mammals, and the stages of succession and colonisation by numerous organisms of dead bodies; and how this can be used for estimating time of death. Finally, we must come to appreciate the subtleties of A-level Biology. Throughout topics 5, 6, 7 and 8, we come to consider the biochemical mechanisms underpinning all of the above events, and that all of Biology can be reduced purely to physicochemical interactions. We try to understand: how cells function by looking at their structure (eg. microbial life forms and their adaptations; sliding filaments in muscle cells of higher eukaryotes) how cells harness and store energy (eg. photosynthesis, respiration…) how hereditary information is passed on, from cell to cell, from generation to generation (vertical transfer)… how cells control gene expression (via transcription factors incl. hormones) and how they communicate information with each other (eg. immune system cell responses; endocrine (hormonal) chemical messaging; electric impulses in neural networks, etc), and how these can be affected by drugs. We break down all bodily processes to metabolic sequences (sequences of chemical reactions) that exist to maintain homeostasis. They occur as a consequence of external and internal stimuli, which in turn affects the organism’s physiology and behaviour, and hence also affects the environment of this organism and other organisms too. So one must come to appreciate the complexity of biological interrelationships at all levels of biological organisation (from the molecule, the cell, the organism, the population/ecosystem). This is actually very simple: We understand the multi-factorial nature of biological events and how these are regulated by the interaction between both biotic and abiotic factors. Abiotic factors provide a framework for biotic factors, all of which is then dependent on the changing environment and changing organisms; so if a specific feature of an organism changes (eg. one or more genes mutate and therefore a makes a lion’s legs slightly longer) or the climate gets slightly warmer by a few degrees, it becomes relatively indeterminate to model precisely what will happen further down the line to a group of organisms, as the ecosystem as a whole and all the species within it will need to change, not just a particular feature of the ecosystem. Page 3 of 12 5.10. Explain that the numbers and distribution of organisms in a habitat are controlled by biotic and abiotic factors. This is very straightforward and self-explanatory: organisms are adapted to specific conditions and need to adapt to new conditions if they change. What you need to know for 5.10: Abiotic factors (non-living, physical, chemical) They take three forms, the physical states of matter: Liquid, gas, solid The list below is not exhaustive. Square brackets indicate how to measure this factor (this is for 5.11) I also include mnemonics at the end. Climatic factors Solar energy input / Light (duration of exposure, intensity) [light sensor] Temperature [thermometer; digital sensor and data logger] Rainfall [rain gauge; beaker for volume over time] (Air) Humidity – this is actually just ‘humidity’ (water vapour in air) [electronic/whirling hygrometer] Wind (ie. speed) Atmospheric CO2/O2 levels Exposure to air Pollution – water, air, land Topography – shape/features of Earth’s surface Slope (the angle/steepness) [clinometer – a string with a weight, attached to a protractor centre] Aspect (direction slope faces) [compass] Relief/Altitude (how land height changes) [GPS; maps with contour lines] (Height above sea level) (Drainage) Environmental Space Water availability; Water (quantity, submersion time, etc) Chemical composition of surroundings Nature of rock (see edaphic) (Wave action) Ground/edaphic Salinity pH [indicator liquid & chart; pH probe/monitor; soil test kit] Organic matter [burnt in crucible] Minerals [gardener’s test kit] Moisture content of soil [dried sample at 80-100oC until constant mass - get %age change] Soil texture [hand assessment, charts] (Toxicity) Substrata Page 4 of 12 Aquatic Water flow/supply [observation; seasonal changes in water levels] Oxygen availability - O2 dissolved in water [oxygen centre/probe] (Natural disturbances) (Earthquakes, floods, volcanic eruptions, fires, etc) Examples of mnemomics: Note: I tend to use a lot of acronym mnemonics for my own learning. I found it particularly useful transferring large amounts of information from paper and uploading it into my brain. Do not underestimate how powerful they are. I’m sure you use them yourselves. Clearly, not only do you need to condense whole textbooks into short notes, but you must further condense these to really make sure you can memorise and remember everything you need to learn. And so in the exam, when prompted with a question, you should be able recall these mnemonics quickly and expand them at will to score as many marks as possible. I didn’t actually use mnemonics for 5.10 – 5.12 back then, but there’s an attempt below, but please be creative and produce some which may be more meaningful to you. CATEGA (climatic, atmospheric, topography, environment, ground, aquatic) STRAW (sunlight, temp, rainfall, (air) humidity, windspeed) Or visual imagery: think of the sun and a cloud: the light and heat of the sun, clouds pouring rain and ‘wetness’ of the air, and blowing wind. Biotic (living, biochemical, other organisms) Competitors (Inter or intraspecific) – competition for resources like food, space, water Predators (Interspecific) Disease: Pathogenic microbes and other parasites (one benefits at the other’s expense) Plant activity Food (Grazing) (Symbiotic relationships; mutualism where both benefit) (eg. bee pollinating flowering plants; natural skin bacteria outcompeting pathogenic bacteria for human host’s welfare in exchange for nutrients and a place to live (the skin), etc.) (Anthropogenic factors) – biotic factor affecting many other biotic factors via abiotic factors (eg. ecological footprint, pollution, global warming, hunting, farming, building, urban areas, wildlife conservation, deforestation, etc.). This can be detrimental for Page 5 of 12 many existing species and ways of life but it also opens there the way for new ways of life to thrive. Population size Abiotic factors: The most suitable conditions mean organisms can grow faster and reproduce successfully, and thereby increasing the overall population faster (eg. an ideal temperature of the surrounding for mammals entails an optimal for metabolic reactions as less energy is used to maintain body temperature by processes of homeostasis) Distribution Organisms can only exist where they can survive Eg. Plants grow on southfacing slopes in northern hemisphere. Inter-specific competition: different species compete for the same resources (eg. red and grey squirrels in the UK) Biotic: Intra-specific: Resources are plentiful, the population grows, but soon resources become limiting (space/food) so the pop. declines (the maximum stable population is the carrying capacity) Predation: We can look at the pattern of snowshoe hare and lynx populations. (see below) One species will need to adapt to another environment due to interspecific competition Page 6 of 12 5.11. Describe how to carry out a study on the ecology of a habitat to produce valid and reliable data (including the use of quadrats and transects to assess abundance and distribution of organisms and the measurement of abiotic factors, eg solar energy input, climate, topography, oxygen availability and edaphic factors). This is slightly more advanced than 5.10, but is based on a sequential understating of the processes of ecological investigation, where each stage is clearly defined and purposeful: A study on ecology of a habitat: An exam question may ask you to describe a study to investigate ecology (for 4-8 marks), in which case you can efficiently touch upon the main points: 1) Named organism and named habitat Method 2) Sampling: Using random sampling (sampling to save time, and random to avoid bias). This is obtained by dividing a uniform field into a grid and using a random number generator on a calculator to select coordinates. 3) Technique used: Quadrats are for defining samples. Frame quadrats (square frame with strings or tape to create a grid) – for measuring abundance. Point quadrats (horizontal bar on two legs with holes at set length interval; pins are dropped through holes and the touched plants are recorded). Transects are for distribution and only for when there are changes along an environmental gradient. Belt Transect - they are for selecting samples, for linear habitats; frame quadrats are placed along a transect line, to obtain more data, and it is used for abundance. Page 7 of 12 Line transect – a tape measure touches species and these are recorded, which saves time Interrupted transect – measurements are taken at intervals with a point quadrat at right angle to the transect line Mention of other apparatus/equipment 4) DV – Abundance and/or Distribution IV – Abiotic factor Example of investigation: are there more plants where there is more light? 5) Control variables to take into account!!! – all the other relevant abiotic factors. 6) Quantifying data: The number of individuals is counted in each quadrat, divided by the total area sampled to give mean density State measurements for distribution/abundance Reference to abiotic measurements 7) Reference to safety 8) Increasing accuracy and precision of instrumental data and methods allows for more efficient data collection, but mainly a more reliable set of results and therefore a valid conclusion. Make a reference to taking many samples and readings, as so getting a more reliable est. of whole area. The typical experiment often requires repeats: usually 3 trials (repeats) for 5/8 IV values (subject to context). Talk about this when you talk about the method and data collection. Standardisation is also important: the investigation and trend obtained must be replicable. Also bear in mind: 9) Specific details and precision must go into describing/explaining steps eg, names, temperature values, time periods, etc. 10) All of this must be done in a logical sequence for the examiner to follow. Mnemonic for pts 1-8: NSTVQSR eg. “Name some things very quiet since racing” Name Sampling Technique Variables Quantifying Safety Reliability Coursework: Obviously you have coursework and whether it’s for U4 experimental investigations or the big U6 dissertation, as you know, the main steps of the criteria are as follows: (in bold is for the exam) Page 8 of 12 A well-researched rationale, defining the investigation clearly, a structured and detailed methodology with evidence of preliminary testing, controlling of variables (very important!!), conscientious safety practices; and then the collection, processing and presenting of data, analysing the pattern, looking at anomalies, interpreting with inferential statistics, putting together a conclusion, evaluation and feedback. I have lots of exemplars including my own if you need any help with this. 5.12. Explain how the concept of niche accounts for distribution and abundance of organisms in a habitat. Finally, we have the niche, which is even more straightforward than 5.10, and we need a good understanding of the terminology, which you have already gone through in U2. What is a niche? The lifestyle and relative position of a species within an ecosystem (the habitat it lives in, how it exploits the abiotic components of its environment, and its interactions with other organisms). Every species has its own unique niche. 2 species may live in the same habitat (habitat niche), but there may be variation in what they eat (nutrition niche). If they both occupy the same niche, they will compete until the more successful one is left. “Explain the concept” means being able to say that the idea of niche means they need to live in specific places. Draw on biological knowledge to give reasons and don’t merely restate the information given. It accounts for: Distribution, because there are specific habitat types – eg. bats live in woodland/farmland but not deserts Abundance – eg. inter-specific competition for food reduces numbers in each population. Bear in mind that if the environment changes too much too quickly for extended periods of time, the group of organisms may not be able to adapt, and either they will die or relocate to a different viable niche, to which they can adapt. Book references: 5.10 5.11 5.12 Green CGP revision guide p12-13 p14 p15-17 Purple/green p13,15 p14-15 p13 Page 9 of 12 Edexcel A2 Biology revision guide Green concept-led Edexcel A2 Biology Orange context-led Edexcel A2 Biology p18-19,24-33 p22,24-27 p18-19,30-33 p4-8 p4-5 p6-8 Mapping to How science works: 5.11 only maps to HSW (2, 3, 4, 5 & 8), which tells you to use scientific knowledge to pose questions and using appropriate experimental skills, all explained above. (see specification for more detail) U4 Past exam questions: 5.10 Question bank pre2008. “C cycle and ecology past questions” Sept 2008 Specimen (Sample Assessment Material) Jan 2010 Jun 2010 Jan 2011 Jun 2011 5.11 5.12 Q2, ~3 Q2 ~Q2, ~3 Q1, 2, 3, 7 Q3 Q2, 6, 7 Q7 Q2, 3, 6, 10, 13 ? Not yet released Access these via: QEGS Moodle / Edexcel website / LC (including the markschemes and examiners’ reports) If you want the questions relevant to topic 6, let me know. Snapshot of U4 Jan10 Q3: Q6 Page 10 of 12 Commentary on examples of exam questions and exam techniques: 5.10: This particular LO, seeing from past Qs, is likely to be woven into more thorough questions which involve a specific organism and habitat. That could be an organism/species from a range of possible organisms/species, but tends to be more like plant species, sometimes algae-type life forms, and also invertebrates. They will deliberately put in Page 11 of 12 something which you may not have met before to get you to think. There is no need to be alarmed, as the basic principles you learnt can always be applied to all these Qs; but be sure to read the question properly, and acknowledge that abiotic factors might differ greatly depending on the organism mentioned. They may quiz on how organisms are distributed and you will be asked to not only deduce how they are distributed but why that is the case, and follow up with the wider implications that has. It may also ask to describe, given specific factors, how the life forms develop and how they evolve, as we look at the specific adaptations that organisms have to their surroundings. But there are some very easy points to gain: eg. Name 3 abiotic factors that would affect that species’ distribution; this should be ‘give-away’ marks and quickly obtained, and likely to be about 3 marks, but the mark scheme may usually have a possible 8. I suggest you learn about 15-20, some will be more relevant than others, and would safely get you the marks if appropriate to the question. Here we just want to get the marks and move on to the longer questions. It seems these questions on abiotic/biotic factors involve a lot of graphs too. And they may ask to describe and explain the graphed data. Here talk about the trend(s): the general pattern, the range of values, then compartmentalise parts of the graph to look for increases and decreases, fluctuations, rates of change, differences which may be or not significant, and finally correlation and causation. Here often mentioning specific values to quantify your point will entail an extra mark, but you need to do something with it (“manipulation of figures”) Most likely though, they will give you data, a graph, or a combination of graphs and tables, to use and say: Using data from the graph/chart/table(s), explain which species of these invertebrates is more apt at living under water, in which case you would need to not only state the right answer, but also give a specific clear reason for it. That is linked to 5.11. For 5.11, previous examples include: Deducing and explaining which factor affects this bird the most and how the distribution of this species can be affected by that abiotic factor. Percentage cover of different species of seaweeds based on distance from the sea along a rocky shore. Reference to graphs. Invertebrates on sea shores. Mussel on a rocky shore and freshwater stream. Species of plants and mammals in woodland areas. They might also ask for you to discuss the validity of different statements based on a graph and data, by asking if statements are valid and why, or even which ones are more valid than others. (see snapshot on page 10) So they may ask to describe how to investigate X and Y, or even explain a specific stage of a specific investigation. But know all the 5 practicals extremely well by the time you finish them, because one or two or three will come up. Each of them being a set of 5-10 main points, in a simple logical order, which I believe are also ‘give-away’ marks and shouldn’t be problem for you. Here, we go back to an efficient and productive revision system, and where the information you learn is consolidated so well that you should be able to retrieve it from your memory store as quickly as possible and write down all the relevant information on the exam paper as quickly and concisely as possible. Page 12 of 12 This is important as they may also have pre-prepared experiment questions, like above; these range from simple lab experiments about a plant with light and CO2 levels, much alike GCSE and AS, or you may need to talk about numerous species of invertebrates in an whole ecosystem and less familiar abiotic factors; broken down into simpler parts, these questions should not be the hardest at all. The understanding of niche for 5.12 usually ties in understanding selection pressures and how that shapes organisms’ characteristics as well as their abundance and distribution, but also stages of succession, as you can see the way that every way of life opens there to be a new way of life, and there is an incremental build up of complexity of the ecosystem. In exams, you occasionally see synoptic elements being introduced, especially looking at mammalian adaptations; but there are also references to plant physiology. Also let me know if you want any more help related to exam work.