Biology IA · A · Unity and diversity · topic 4 of 25
Does mowing change what grows? · IB Biology IA idea: guide, sample graph and step-by-step plan
great for a first IA. sampling is everythingA lawn looks boring until you count it. How often it is cut decides who survives, and you can measure that.
- ✓ you like being outdoors
- ✓ you can get permission for a site
- ✓ you want a clear idea like disturbance to test
The big idea
← this is your RQ hook!Cutting is a disturbance, and disturbance shapes who wins. Rarely cut, tall plants shade out the rest. Cut constantly, few species can cope. One idea to test is that diversity peaks in between, but your data may say otherwise. You sample areas with different mowing, count species in quadrats, and calculate a diversity index. The strength of this IA is the sampling design: where you put quadrats, how many, and how you stop your own choices from biasing the result.
Make it yours: pick one twist
Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.
Swipe for more twists →
Include intermediate regimes, such as every two weeks or every two months, if your site has them.
→ With only three levels you cannot see the shape of the pattern. More levels give a curve instead of three bars.Survey the same plots a few days and a few weeks after cutting.
→ Adds recovery as a second question. Your graphs have time on one axis and you need to repeat surveys.Count grasses and broad-leaved herbs separately.
→ Asks who wins and who loses. Your analysis compares groups of species, not just totals.Record soil moisture or light at each quadrat.
→ Checks whether mowing or something else drives the pattern. Your analysis needs a second variable.Estimate percentage cover for each species in each quadrat.
→ Gives a different diversity picture, especially when plants are hard to count. You need to explain how you estimate cover.Sample along a line from a mown area into an unmown edge.
→ Turns a three-group comparison into a gradient with distance as the variable.Your Biology IA research question: run the check
Write your own question first. Then make sure it ticks every box:
- Names the independent variable (the mowing regimes, with their frequency) and the dependent variable (species richness and the diversity index you will use).
- Names the site and says how you know the mowing history.
- Says how quadrats are placed (random coordinates), how many in each area and why.
- Says what is held constant (soil, sunlight, slope, time of year, quadrat size) and how you check.
- Is narrow enough for about 10 hours, with a sampling plan you can finish in one or two visits.
The set-up
how will you stop yourself cheating?One way to set it up. Draw your own plan, with your real plot sizes and quadrat positions, for the Method section.
How your Biology IA could be laid out
The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.
Your question; the site and its mowing; what you expect to see and why.
Disturbance, competition and species diversity; the index you chose and what a high or low value means (cite the formula); your prediction.
Independent, dependent and controlled variables, each with how you measure or check it and why it matters.
Site map; the plot sizes; how random coordinates were generated; quadrat size and number; how plants were identified; enough detail to repeat.
Specific: permission to survey, ticks and insect bites, avoiding trampling, no picking of rare or protected plants.
Species counts for every quadrat in every area, with units and a note on how unknown plants were handled.
Richness and index for each quadrat; mean and spread per area; one worked example of each calculation.
A graph that compares areas with error bars as SD; ANOVA (or Kruskal-Wallis if the counts are skewed) across three or more regimes, with sample size, or Spearman's rank if you treat mowing frequency as a scale.
Answer with values and the test result; compare with published work on disturbance; keep your claim to the plots you surveyed.
Weaknesses ranked by effect (quadrat placement, plot independence, identification, one visit); linked improvements.
Every source for theory, the index formula and plant identification.
What your Biology IA graph could look like
Made-up data, to show you the form of a strong graph, not the answer. Yours will look different. example only
- Error bars are the standard deviation of the quadrats, with the number of quadrats stated.
- Two ideas drawn, so the reader can see which pattern your data follow.
- With only three mowing levels there are only three points, and the shape stays hidden. Say so if that is your design.
- Use the same axis scale for richness and the index if you plot both, or show them on two graphs.
- Another graph to consider: plot the Simpson's index against mowing frequency, or show the individual quadrat values as dots beside each mean.
Your game plan
permission first!Tick steps off as you go. We'll remember on this device.
0 of 10 done
- Read and predictFind the theory on disturbance and plant diversity and the formula for the index you will use. Decide what a high value means. Write down what you predict.
- Get permission and choose the siteAsk the school or landowner. Check the mowing history so you know the regimes are real, and check soil, slope and light are similar.
- Trial run (1 lesson)Place a few quadrats and identify everything in them. How long does one take? Which plants are hard to name? Fix your quadrat size and method now.
- Decide quadrat number and placementChoose how many quadrats per area and how to place them at random. Write down why for each choice.
- Collect the dataRecord every species in every quadrat straight into the table, and note photos of unknown plants. Keep the same observer where possible.
- Calculate the indexWork out richness and your index for each quadrat. Do one worked example by hand and check your spreadsheet formula against it.
- Choose the testDecide how to compare three or more areas, and what the test assumes about your data. Note how many independent areas you really have.
- Graph and interpretPlot means with SD error bars, and state the test result and its sample size. Decide how far your conclusion can reach.
- EvaluateWhich weakness in your sampling mattered most? Make every improvement specific.
- Check before your teacher's draftRun the checklist below, then get your RQ or draft checked. Your teacher reads one draft only, so make it count.
Biology you'll need
- Uncertainties and error bars (physics examples, same ideas) →
- Biology past-paper analysis (HL) →
- IB command terms explained →
Traps to avoid in this Biology IA
- Placing quadrats where it looks interesting: that biases the result towards species-rich spots.
- Different numbers of quadrats in each area.
- Treating every quadrat as an independent replicate when each mowing regime has only one patch.
- Using the wrong form of Simpson's index, or not knowing whether a high value means more diversity.
- Misidentifying plants, and not saying how unknowns were handled.
- Surveying once and claiming it holds for the whole year.
More Biology IA ideas like this
- Species–area on a school field●●○
- Capillary rise: can xylem lift a tree by itself?●●○
- Does heat-loving mean GC-rich?●●●
This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.