A lab report example in biology is most useful when it shows both (1) the standard writing structure and (2) the way real measurements become tables, calculations, and a figure that supports the conclusion.
Standard structure for a biology lab report
| Section | Purpose | What to include (typical) |
|---|---|---|
| Title | State the experiment clearly and specifically. | Independent variable + dependent variable + organism/system (when relevant). |
| Abstract | Provide a brief, complete summary. | Question, method (1–2 lines), key result (numbers), conclusion. |
| Introduction | Explain the biological concept and justify the hypothesis. | Background, definitions, hypothesis/prediction, rationale. |
| Methods | Allow replication of the work. | Materials, procedure, controls, sample size, how measurements were taken. |
| Results | Present data without interpretation. | Tables, calculations, summary statistics, graphs with captions. |
| Discussion | Interpret results and connect to biology. | Meaning of results, sources of error, limitations, improvements, comparison to expectations. |
| References | Credit sources and enable verification. | Textbook/primary sources in a consistent citation style. |
A frequent grading rule: results must be understandable without reading the methods. That requires clear units, labeled tables/figures, and at least one worked calculation that shows how raw measurements become the reported values.
Lab report example: osmosis in potato tissue
The example below models a common biology investigation: how sucrose concentration affects water movement across cell membranes. The dependent variable is percent mass change of potato cores after soaking in sucrose solutions of different molarity.
Title
Effect of Sucrose Concentration on Percent Mass Change of Potato Cores (Osmosis)
Abstract
Potato cores were incubated for 30 minutes in sucrose solutions (0.0–0.8 M), then reweighed to quantify osmosis as percent mass change. Average percent mass change decreased with increasing molarity, from a gain at low sucrose to a loss at high sucrose. A trendline between the nearest points around zero suggested an isotonic concentration of approximately \(0.33\ \mathrm{M}\), consistent with net water movement approaching zero when external solute concentration matches internal solute concentration.
Introduction
Osmosis is the net diffusion of water across a selectively permeable membrane driven by differences in solute concentration. When plant tissue is placed in a hypotonic solution (lower solute outside), water tends to enter cells; in a hypertonic solution (higher solute outside), water tends to leave cells. The isotonic point is the external concentration at which net water movement is approximately zero, producing minimal mass change.
Prediction: increasing sucrose molarity will decrease percent mass change of potato cores, crossing zero near the isotonic concentration.
Methods
- Prepared sucrose solutions at 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M (equal volumes).
- Cut potato cores to similar size; blotted dry and recorded initial mass for each replicate.
- Soaked cores for 30 minutes, removed, blotted consistently, and recorded final mass.
- Computed percent mass change for each replicate and the average for each molarity.
Results
Percent mass change calculation (used for each replicate):
\[ \%\ \Delta m = \frac{m_{\text{final}} - m_{\text{initial}}}{m_{\text{initial}}} \cdot 100 \]
| Sucrose (M) | Replicate | Initial mass (g) | Final mass (g) | \(\%\ \Delta m\) |
|---|---|---|---|---|
| 0.0 | 1 | 5.00 | 5.55 | \(\frac{5.55 - 5.00}{5.00} \cdot 100 = 11.0\%\) |
| 2 | 5.02 | 5.55 | \(\frac{5.55 - 5.02}{5.02} \cdot 100 \approx 10.6\%\) | |
| 3 | 4.98 | 5.50 | \(\frac{5.50 - 4.98}{4.98} \cdot 100 \approx 10.4\%\) | |
| 0.2 | 1 | 5.01 | 5.22 | \(\frac{5.22 - 5.01}{5.01} \cdot 100 \approx 4.19\%\) |
| 2 | 5.00 | 5.20 | \(\frac{5.20 - 5.00}{5.00} \cdot 100 = 4.00\%\) | |
| 3 | 5.03 | 5.24 | \(\frac{5.24 - 5.03}{5.03} \cdot 100 \approx 4.17\%\) | |
| 0.4 | 1 | 5.02 | 4.92 | \(\frac{4.92 - 5.02}{5.02} \cdot 100 \approx -1.99\%\) |
| 2 | 5.00 | 4.91 | \(\frac{4.91 - 5.00}{5.00} \cdot 100 = -1.80\%\) | |
| 3 | 5.01 | 4.90 | \(\frac{4.90 - 5.01}{5.01} \cdot 100 \approx -2.20\%\) | |
| 0.6 | 1 | 5.02 | 4.61 | \(\frac{4.61 - 5.02}{5.02} \cdot 100 \approx -8.17\%\) |
| 2 | 5.00 | 4.60 | \(\frac{4.60 - 5.00}{5.00} \cdot 100 = -8.00\%\) | |
| 3 | 5.01 | 4.62 | \(\frac{4.62 - 5.01}{5.01} \cdot 100 \approx -7.78\%\) | |
| 0.8 | 1 | 5.02 | 4.29 | \(\frac{4.29 - 5.02}{5.02} \cdot 100 \approx -14.54\%\) |
| 2 | 5.00 | 4.30 | \(\frac{4.30 - 5.00}{5.00} \cdot 100 = -14.0\%\) | |
| 3 | 5.01 | 4.31 | \(\frac{4.31 - 5.01}{5.01} \cdot 100 \approx -13.97\%\) |
Summary averages (rounded to two decimals):
| Sucrose (M) | Average \(\%\ \Delta m\) |
|---|---|
| 0.0 | 10.67% |
| 0.2 | 4.12% |
| 0.4 | -2.00% |
| 0.6 | -7.98% |
| 0.8 | -14.17% |
Isotonic estimate (worked calculation)
Using the two nearest average points around zero: \((0.2,\ 4.12)\) and \((0.4,\ -2.00)\), with y in percent.
\[ m = \frac{-2.00 - 4.12}{0.4 - 0.2} = \frac{-6.12}{0.2} = -30.6 \]
Line through \((0.2,\ 4.12)\): \(y - 4.12 = -30.6 \cdot (x - 0.2)\). Set \(y = 0\) to find the isotonic concentration:
\[ 0 - 4.12 = -30.6 \cdot (x - 0.2) \quad\Rightarrow\quad x - 0.2 = \frac{4.12}{30.6} \quad\Rightarrow\quad x \approx 0.2 + 0.135 = 0.335\ \mathrm{M} \]
Discussion (model paragraphs)
The data support the prediction that increasing external sucrose concentration reduces percent mass change of potato tissue. At low molarity (0.0–0.2 M), mass increased, consistent with net water entry into cells in a hypotonic environment. At higher molarity (0.4–0.8 M), mass decreased, consistent with water leaving cells under hypertonic conditions. The observed zero-crossing near \(0.33\ \mathrm{M}\) provides an estimate of the isotonic point for the potato tissue under the conditions used.
Key limitations include variability in core size, blotting consistency, and the assumption that equilibrium is reached within 30 minutes. Experimental improvements include increasing soak time to verify equilibrium, standardizing surface drying with a fixed blotting protocol, using more replicates, and measuring temperature to reduce uncontrolled effects on membrane transport rates. A fuller analysis could fit a regression model to all points and report uncertainty (for example, confidence intervals for the zero-crossing).
References (example formatting)
- Introductory Biology textbook section on membrane transport and osmosis.
- Laboratory manual protocol for osmosis in plant tissues (course-provided source).
Checklist for turning this into a strong submission
- Every table and figure includes units and a caption that explains what is shown.
- At least one worked calculation is shown using the same numbers reported in the results.
- Results are presented before interpretation; interpretation is reserved for the discussion.
- Discussion addresses whether the hypothesis is supported and explains the biological mechanism.
- Limitations and sources of error are specific (what they change and in which direction).