Launch practical
About 90 minutes
- Set up the bench with the 7 items of apparatus.
- Take the readings yourself, into the results table you draw first.
- Process your results and plot the graph.
- Answer exam questions on your own results, which you mark against the mark scheme.
Runs in your browser: a 3D bench with 2D close-ups of each instrument for exact readings. Nothing to install and no account.
What you measure, and how
One run takes 24 readings. You take every one yourself, the way you would in class.
- On the 3D bench (Fig. 1) you set out the apparatus and read each instrument where it stands.
- In the 2D close-up (Fig. 2) the same instrument is drawn large, from the same run, for an exact reading. It is also how the practical runs on a device that cannot show 3D.
- In your table you write what you read, to the instrument’s resolution, and the notebook checks it against the instrument.
How to read it. The light meter lying flat in the middle of the quadrat, sensor up. It reads to the nearest 10 lux.
What it shows
population = mean number per m² × area of the habitat
You cannot count every daisy in a field, so you count them in a sample of small areas (quadrats) and scale up. Placing the quadrats at random makes the sample represent the whole plot. To see how a factor such as light affects where a species grows, you sample along a line across the change (a transect) and measure the factor at each quadrat.
The graph to expect. Few or no daisies in the shade under the tree; the number rises where the tree’s shadow ends and stays about the same (with patchy ups and downs) in the open.
Key equation for the exam: population = mean number per m² × total area in m².
Recall: learn it. Place quadrats at random for an estimate; along a transect for a change.
Apparatus
| Item | What it is for | Resolution |
|---|---|---|
| Quadrat, 50 cm × 50 cm (0.25 m²), strung into 25 squares | Marks out the same area to count in each time. | 0.25 m² |
| Two 30 m tape measures | Laid at right angles along two sides of the plot as the axes of a grid. | 1 cm |
| A third 30 m tape measure | The transect line from the tree out into the open. | 1 cm |
| Calculator with a random number key | Gives the random coordinates. | — |
| Digital light meter (lux meter) | Measures the light intensity at each quadrat on the transect. | 10 lux |
| Identification card | Shows a daisy plant, so it is not confused with dandelion or plantain. | — |
| Clipboard, pencil and results table | Records each count and reading at once. | — |
Method
In our own words, as the Lab runs it. Your school's method sheet may differ in detail.
Which version are you doing?
Boards set this practical slightly differently. Your course setting picks one; you can change it before you start.
Why: The field, the plot and the random quadrats are the same; the transect and the exam questions follow your board.
Walk over the site firstSafety
Before anyone kneels down, walk slowly over the plot and along the transect line. Look for broken glass, sharp litter, dog mess and holes.
Why: You will kneel and put your hands in the grass. Anything sharp or dirty needs to be found and reported first.
Choose where each quadrat goes
You will place quadrats in the 10 m × 8 m plot, count the daisy plants in each, and scale up to the whole plot.
Do: Two tapes at right angles along two sides of the plot, and a random number generator to give the coordinates.
Why: The quadrats are a sample. They must represent the whole plot, so where they go must not depend on what you can see.
Lay out the tapes
Lay one 30 m tape along the front edge of the plot (0 to 10 m) and a second at right angles along the left edge (0 to 8 m), both starting from the same corner peg. Lock both reels.
Why: The two tapes are the axes of a grid: a pair of random numbers is then a place in the plot that anyone could find again.
Choose how many quadrats to use
Each quadrat is 50 cm × 50 cm (0.25 m²).
Do: Ten quadrats.
Why: Daisies grow in patches, so one quadrat can hold none and the next fifteen. More quadrats give a mean that is closer to the true mean.
Lay the transect line
Fix the end of a third tape at the trunk of the tree. Run it out in a straight line into the open field to 13 m and lock it.
Why: A transect samples along a line across a change in the habitat: here from deep shade under the tree into full light.
Choose where along the tape to place the quadrats
Seven quadrats will go along the tape, each with one corner on the tape, on the same side of it.
Do: At regular intervals: every 2 m from 0 m to 12 m.
Why: To see how the number of daisies changes with distance (and light), the quadrats must cover the whole line evenly.
Take the readings
Population: ten random 0.25 m² quadrats in a 10 m × 8 m plot. Distribution: a quadrat and a light reading every 2 m along a transect from a tree, 0 m to 12 m.
Repeats: For the population, the quadrats are the repeats: use about 10 or more, placed at random, and take a mean. More quadrats reduce the effect of chance (random error) from the patchy daisies; they do not remove a bias such as throwing the quadrat. Along a transect, repeat the whole line in other places (round the tree, at other trees) and calculate a mean at each distance; “repeat it” alone is not enough.
Make safe and clear upSafety
Pick up the quadrat. Rewind the tapes slowly, keeping fingers clear of the tape as it goes in. Switch off the light meter and put the kit back in the box. Wash your hands with soap and water.
While you take readings
What do you count?
Kneel by the quadrat and part the grass with your fingers.
Do: Whole plants: each rosette of leaves counts once.
Why: A population is a number of organisms, so you count whole plants. A daisy plant is one flat rosette of leaves; it can have one, two or three flowers.
Plants on the edge
Some rosettes lie across the frame of the quadrat. Decide your rule before you count, and keep to it.
Do: Count plants touching the top and left sides; leave out those touching the bottom and right sides.
Why: A plant across the edge is partly in this quadrat and partly outside it.
When to take the light readings
Hold the light meter flat on the ground in the middle of each quadrat, with the sensor facing up and your shadow off it.
Do: Take all seven readings quickly, one after another, on the same day.
Why: The light reaching the ground changes when a cloud crosses the sun, so readings taken at different times are not a fair comparison.
Hazards and control measures
| Hazard | What could happen | Control measure |
|---|---|---|
| Throwing a metal quadrat | It can hit someone and cut or bruise them, or injure an eye | Never throw a quadrat. Carry it and place it at the coordinates. |
| Broken glass, sharp litter or dog mess in the grass | Cuts to knees and hands; infection | Walk over the site and check it before you start; report anything you find and keep away from it. |
| Wet grass and uneven ground | Slipping, twisting an ankle | Walk, do not run; do not work outside in very wet conditions. |
| A long tape springing back into its case | The metal end or edge can cut a hand | Lock the tape while it is laid out and rewind it slowly with your fingers clear. |
| Soil on your hands; bees and wasps on flowers | Infection through a cut; stings (and an allergic reaction) | Cover cuts, wash your hands after; tell the teacher about any sting allergy and leave insects alone. |
Variables
- Independent: you change
- Distance from the tree (and so the light intensity) in m
- Dependent: you measure
- Number of daisy plants in each quadrat
- Control: you keep the same
- Size of quadrat. The same 0.25 m² quadrat for every count.
- Counting rule. Whole plants; plants touching the top and left sides only.
- Time of the light readings. All taken quickly, one after another, on the same day.
- Same person counting. One person counts, so everyone’s idea of a daisy plant is the same.
Results from a specimen run
| Quadrat | x coordinate in m | y coordinate in m | Number of daisy plants |
|---|---|---|---|
| 1 | 7.5 | 7.5 | 9 |
| 2 | 5.0 | 1.5 | 0 |
| 3 | 7.5 | 3.0 | 7 |
| 4 | 1.5 | 0.5 | 10 |
| 5 | 5.5 | 4.0 | 6 |
| 6 | 3.5 | 0.5 | 2 |
| 7 | 2.5 | 6.0 | 5 |
| 8 | 4.5 | 3.0 | 5 |
| 9 | 5.5 | 7.5 | 8 |
| 10 | 1.0 | 6.5 | 12 |
| Distance from the tree in m | Number of daisy plants | Light intensity in lux |
|---|---|---|
| 0 | 1 | 11090 |
| 2 | 0 | 7640 |
| 4 | 4 | 9570 |
| 6 | 1 | 15280 |
| 8 | 15 | 35500 |
| 10 | 8 | 43610 |
| 12 | 4 | 42960 |
Processing the data
- Mean per quadrat
- 6.4 plants
- Median
- 6.50 plants
- A quadrat with few daisies
- Keep it in the mean: that part of the plot really has few daisies, so it is real data.
- Mean per m²
- 25.6 plants per m²
- Estimated population
- 2048 plants
- Chance and the number of quadrats
- 2 of 2 right first time
- Shape of the graph
- Low under the tree, rising steeply where its shadow ends, then levelling off in the open.
- Light and daisies
- Where the light intensity is higher, there are more daisy plants.
- Does it prove light is the cause?
- No: other factors also change along the line (soil water, the tree’s roots, how trampled it is), so light may not be the only cause.
| Quantity | Specimen run | Accepted |
|---|---|---|
| Daisy plants in the plot (drone photo: every plant counted) | 2050 plants | 1820 plants |
| Mean daisy plants per 0.25 m² (the whole plot) | 6.4 plants | 5.7 plants |
Common mistakes and the fix
Mistakes to check in this practical, and what to do instead. In a write-up or an exam answer, the mark goes to naming the step and saying what it does to the readings.
Method: Start straight away
No effect on your results, but you could kneel on broken glass or put your hand in dog mess (cuts, infection).
The fix: Walk over the site first. You will kneel and put your hands in the grass. Anything sharp or dirty needs to be found and reported first.
Method: Stand in the plot and throw the quadrat over your shoulder
Not random: it only lands as far as you can throw it, from where you chose to stand, and you tend to aim at the flowers. Your estimate usually comes out about half as much again as the true population (biased). Throwing a metal frame can also hurt someone.
The fix: Choose where each quadrat goes. The quadrats are a sample. They must represent the whole plot, so where they go must not depend on what you can see.
Method: Put it down in places that look typical
Your eye is drawn to patches with flowers, so the quadrats sample the best patches: the estimate comes out about 25–90 % too high (biased).
The fix: Choose where each quadrat goes. The quadrats are a sample. They must represent the whole plot, so where they go must not depend on what you can see.
Daisy plants in quadrat 1: Typed 17 plants
The fix: That is the number of flower heads. Count whole plants: one rosette of leaves is one plant, even with two or three flowers.
Daisy plants in quadrat 1: Typed 10 plants
The fix: You counted plants touching the bottom or right side too. Under your rule, count only those touching the top or left side.
Exam answer: Leaving out: Two tapes at right angles (a grid) and random numbers (from a calculator or random number generator) used as coordinates (ignore throwing)
The fix: Say how the places were chosen: tapes at right angles as a grid, and random numbers for the coordinates.
Exam answer: Leaving out: To avoid bias / so the sample is representative of the whole plot / every part of the plot has an equal chance of being sampled
The fix: Explain why: random placement avoids bias, so the quadrats represent the whole plot.
Worked exam-style questions
Written for Study Hack in the style of exam questions, on the specimen run above. They are not taken from any exam board's papers. Try each one before you open the worked answer.
- Question 1Placing quadrats at random · Knowledge[2 marks]
You estimated the population of daisy plants in a 10 m × 8 m plot of the school field using ten quadrats.
Describe how you decided where to place each quadrat, and explain why you did it this way.
Worked answer and how the marks are given
A full-mark answer
I laid two tapes at right angles along two sides of the plot to make a grid, and used a random number generator to give the coordinates of each quadrat. This avoids bias, so the quadrats are representative of the whole plot.
Mark scheme
- Two tapes at right angles (a grid) and random numbers (from a calculator or random number generator) used as coordinates (ignore throwing)
- To avoid bias / so the sample is representative of the whole plot / every part of the plot has an equal chance of being sampled
Where marks are usually lost
- Missing: Two tapes at right angles (a grid) and random numbers (from a calculator or random number generator) used as coordinates (ignore throwing). Say how the places were chosen: tapes at right angles as a grid, and random numbers for the coordinates.
- Missing: To avoid bias / so the sample is representative of the whole plot / every part of the plot has an equal chance of being sampled. Explain why: random placement avoids bias, so the quadrats represent the whole plot.
- Question 2Estimating a population · Applying knowledge[4 marks]
Your counts in your 10 quadrats were: 9, 0, 7, 10, 6, 2, 5, 5, 8, 12.
Your mean was 6.4 daisy plants per quadrat. Each quadrat was 50 cm × 50 cm. The plot was 10 m long and 8 m wide.
Use your mean to estimate the number of daisy plants in the plot.
Give your answer to 2 significant figures.
Number of daisy plants =
Worked answer and how the marks are given
A full-mark answer
mean per m² = 6.4 × 4 = 25.6
area = 10 × 8 = 80 m²
population = 25.6 × 80 = 2048
= 2000 (2 s.f.)Mark scheme
- Mean per m² = 6.4 × 4 (or ÷ 0.25) = 25.6; or 80 ÷ 0.25 = 320 quadrats (method)
- Area of the plot = 10 × 8 = 80 m² (method)
- 2048 daisy plants
- 2000 (2 significant figures) (precision)
- Allow answers from 2000 to 2100 (the marker's tolerance; correct rounding of the student's own working is also accepted).
- One mark for giving the answer to 2 significant figures.
- A correct answer with no working scores full marks.
Where marks are usually lost
- Answer 510 (gains 1 mark). 6.4 is per quadrat, not per m². A 50 cm × 50 cm quadrat is 0.25 m², so there are 25.6 plants per m². Then × 80.
- Answer 130 (gains 1 mark). Multiply by 4 (or divide by 0.25) to go from 0.25 m² to 1 m²: you multiplied by 0.25. 6.4 × 4 = 25.6 per m².
- Answer 1000 (gains 1 mark). 50 cm × 50 cm is 0.5 m × 0.5 m = 0.25 m², not 0.5 m². So the mean per m² is 6.4 × 4 = 25.6.
- Question 3Planning a transect investigation · Knowledge[6 marks]
A student wants to investigate how light intensity affects the distribution of daisy plants near a tree in the school field.
Describe a method the student could use. You should include how they would collect and use their results.
Worked answer and how the marks are given
A full-mark answer
1. Fix a tape measure at the trunk of the tree and lay it in a straight line out into the open field (a transect).
2. Place a quadrat (0.25 m²) against the tape at 0 m, then at regular intervals, for example every 2 m, to 12 m.
3. In each quadrat count the number of daisy plants (whole plants, using a rule for plants on the edge).
4. At each quadrat measure the light intensity with a light meter held at ground level.
5. Take all the light readings quickly, at the same time of day.
6. Repeat with more transects in other directions round the tree (or at other trees) and calculate the mean number of daisies at each distance.
7. Plot the mean number of daisies and the light intensity against distance and compare them.Mark scheme
Indicative content:
- Lay a tape (transect line) from the tree out into the open
- Place quadrats at regular intervals along the line (do not accept random intervals) Do not accept “random interval… / distance…”.
- Use a quadrat of stated size (0.25 m² or 1 m²)
- Count the number of daisy plants in each quadrat
- Measure light intensity at each quadrat with a light meter
- Take the light readings at the same time / quickly / same day
- Repeat with more transects (other directions or trees) and calculate a mean at each distance
- Plot or compare the number of daisies with the light intensity (or the distance)
Levels of response Level Marks What the answer does 3 5–6 A coherent method that would give valid results: all the important steps are there, in a sensible order. 2 3–4 A method that might not give valid results: most of the important steps are there, but some are missing or out of order. 1 1–2 A method that would not give valid results: some relevant steps are given, but they are not linked into a workable method. In Study Hack a six-mark answer is not given an automatic level: you tick the points your answer makes, then choose the level that fits it.
- No relevant content: 0 marks.
Evaluate
| Source of error | Type | Effect | Improvement |
|---|---|---|---|
| Placing the quadrats by throwing them or by choosing places | Systematic | Quadrats land in the patches of flowers more often than chance would put them there, so the mean and the population are too high (biased). | Use two tapes at right angles and random numbers as coordinates. |
| Too few quadrats in a patchy field | Random | The mean depends on whether the few quadrats happened to land on patches or on bare ground, so the estimate could be far too high or too low. | Use more quadrats (10 or more) and calculate the mean. |
| Counting every plant that touches the frame | Systematic | Plants on the edge are counted in every quadrat they touch, so every count and the population are too high. | Count plants touching only two sides (top and left), and leave out those touching the other two. |
| Counting flower heads instead of whole plants | Systematic | Each plant has one to three flowers, so the counts are about double the number of plants. | Count each rosette of leaves once, whatever the number of flowers. |
| The daisies grow in patches (sampling error) | Random | Even random quadrats give a mean a little different from the true mean, so the population is an estimate. | Use more quadrats, or larger ones, so more of the plot is sampled. |
| Light readings taken at different times | Random | Clouds change the light from minute to minute, so readings differ for reasons that have nothing to do with the tree. | Take all the light readings quickly, one after the other, on the same day. |
| Quadrats at random distances along the transect | Random | Parts of the line are missed and others sampled twice, so the change from shade to light is unclear. | Place the quadrats at regular intervals (every 2 m, or every 1 m). |
| One transect from one tree | Random | One line can pass a patch or a bare area by chance, and other factors change along it too (soil water, trampling), so one line cannot show that light is the cause. | Repeat the transect in other directions round the tree and at other trees, take a mean at each distance, and measure soil moisture too. |
Repeatable. You repeat the transect in the same place with the same method and get similar counts and light readings at each distance.
Reproducible. Another group, or a different method (a 1 m² quadrat every 5 m, or a different tree), finds the same pattern: more daisies where there is more light.
Other exam boards
How this practical lines up with other GCSE boards' required or core practicals. Codes only; check your own specification for the exact activity.
| Board | Practical | Match | What is different |
|---|---|---|---|
| AQA | Required practical 9 | This page | — |
| Edexcel | 9.5 | Similar, with differences | Belt transect along a gradient such as shade to open. |
Print it
- Blank write-up: the nine-step lab book with the correct table headings, ready to print for a real lesson.
- Specimen lab book: this page's run written up in full, with its exam answers ticked against the mark scheme.
- Printable method card: the practical on one index card. Practise with the cards in Study Hack.
- Practical workbook: a full simulated data set to process on paper, with exam questions and answers.
- Teacher and technician pack: apparatus lists, technician notes and marking points.