1.1 Laboratory Safety

Biological practical work exposes students to glassware, chemicals, biological specimens, heat sources, sharp instruments and electrical equipment. Laboratory safety is the disciplined use of procedures and controls that prevent injury, contamination and damage. Safe practice begins before an experiment: the procedure should be understood, hazards recognised and protective measures prepared.

1.2 Common Laboratory Hazards

1.3 Prevention and Risk Control

A practical worker should ask what can cause harm, how exposure might occur, how serious the consequence could be and what control will reduce the risk. Controls include safer materials, suitable equipment, ventilation, barriers, appropriate procedures and personal protective equipment.

1.4 First Aid

First aid is immediate assistance provided after injury or exposure while appropriate medical attention is obtained. Chemical splashes generally require prompt flushing with plenty of clean water and immediate reporting. Cuts require control of bleeding and protection from contamination. Burns should receive appropriate cooling and reporting. Serious bleeding, breathing difficulty, unconsciousness or suspected poisoning requires urgent professional attention.

2.1 Importance of Measurement

Measurement converts qualitative observation into quantitative evidence. Saying that a seedling is 'tall' is vague; reporting its height as 14.6 cm allows comparison, repetition and analysis. Every measurement must therefore include an appropriate unit and should reflect the resolution of the measuring instrument.

2.2 Common Measurements and Units

2.3 Accuracy and Precision

Accuracy is closeness to an accepted or true value, whereas precision is closeness among repeated measurements. Repeated readings can be highly precise yet inaccurate if a systematic error shifts every result in the same direction. Random errors produce irregular variation and can often be assessed by repetition.

2.4 Correct Reading of Instruments

The observer should first identify the smallest scale division. When reading liquid volume, the eye should be level with the meniscus to reduce parallax error. Results must be recorded with units, and digits beyond the useful resolution of the instrument should not be invented.

2.5 Worked Example

Given: 12.1, 12.3, 12.2, 12.4 and 12.0 cm.
Required: Mean height.
Formula: Mean = sum of observations ÷ number of observations.
Solution: Sum = 61.0 cm; mean = 61.0 ÷ 5 = 12.2 cm.
Answer: Mean height = 12.2 cm.

2.6 Unit Conversion

Unit conversion is essential in practical biology. Since 1 cm = 10 mm, 4.7 cm equals 47 mm. Since 1 mm = 1000 µm, 0.25 mm equals 250 µm. A numerical value must be changed when the unit changes unless the units are equivalent.

3.1 Principle of the Compound Microscope

A compound light microscope uses visible light and two principal lens systems to form a magnified image of a small specimen. It permits observation of cells and structures that cannot be resolved by the unaided eye. Useful microscopy depends not only on magnification but also on resolution and contrast.

3.2 Parts and Functions

3.3 Using the Microscope

1. Place the microscope securely on a stable bench.
2. Place and centre the prepared slide on the stage.
3. Select the lowest-power objective.
4. Bring the specimen into focus using coarse adjustment at low power, then sharpen with fine adjustment.
5. Adjust illumination for useful contrast.
6. Centre the feature of interest before moving to a higher objective.
7. At higher power, use fine focusing carefully.

3.4 Magnification

Total magnification = eyepiece magnification × objective magnification. If a ×10 eyepiece is used with a ×40 objective, total magnification is ×400.

3.5 Magnification and Resolution

Magnification describes how large the image appears relative to the specimen. Resolution describes the ability to distinguish two nearby points as separate. Increasing magnification without improving resolution merely enlarges a blurred image.

3.6 Care and Maintenance

• Carry the microscope securely.
• Clean lenses only with suitable lens-cleaning material.
• Do not force adjustment controls.
• Avoid allowing an objective to strike the slide.
• Keep liquids away from electrical parts.
• Store the microscope clean, dry and covered.

4.1 Dissecting Microscope

The dissecting or stereoscopic microscope is used for relatively large, often opaque specimens. It provides low magnification, a long working distance and a stereoscopic view that is useful when examining external morphology or manipulating specimens.

4.2 Comparison of Microscopes

4.3 Systematic Observation

Observation should proceed from general to specific. Record the specimen's overall form, dimensions, symmetry and visible regions before focusing on smaller structures. Scientific records should describe what is actually observed rather than what the observer expects from a textbook.

4.4 Practical Records

A useful record includes specimen identity where known, date, treatment, magnification or scale where relevant, labelled observations and a concise interpretation. Objective terms should replace subjective expressions. For example, leaf length, margin, venation and colour are more informative than saying a leaf is 'beautiful'.

5.1 Meaning and Purpose

A biological drawing is a scientific representation of an observed specimen. It is intended to communicate structure accurately, not to display artistic ability. The drawing should preserve the relative positions and sizes of important structures.

5.2 Rules of Biological Drawing

• Make the drawing large enough for details to be clear.
• Use clean, continuous lines rather than sketchy strokes.
• Avoid decorative shading in standard introductory drawings.
• Maintain correct proportions.
• Use straight label lines that terminate on the intended structures.
• Keep labels neat and horizontal.
• Give the drawing an informative title.
• State magnification or provide scale information when appropriate.

5.3 Accuracy and Proportion

Accuracy means that observable structures are represented faithfully. Proportion means that their relative sizes are preserved. Correct labels cannot compensate for a drawing in which structures are grossly enlarged or reduced relative to one another.

5.4 Low-Power and High-Power Drawings

A low-power plan drawing emphasises the arrangement and distribution of major tissues without unnecessary cellular detail. A high-power drawing records selected cells or structures in greater detail. The amount of detail must therefore match the scale of observation.

6.1 Scale and Magnification

Scale expresses the relationship between a representation and the real specimen. Magnification is calculated using the relationship magnification = image size ÷ actual size. Image and actual measurements must first be expressed in the same unit.

6.2 Worked Example: Magnification

Given: Actual size = 50 µm; image size = 75 mm.
Required: Magnification.
Conversion: 75 mm = 75,000 µm.
Formula: Magnification = image size ÷ actual size.
Solution: 75,000 ÷ 50 = 1,500.
Answer: Magnification = ×1500.

6.3 Worked Example: Actual Size

Formula: Actual size = image size ÷ magnification.
Solution: 32 mm ÷ 400 = 0.08 mm. Since 1 mm = 1000 µm, 0.08 mm = 80 µm.
Answer: 0.08 mm or 80 µm.

6.4 Proportional Enlargement

When a specimen is enlarged in a drawing, every linear dimension should be enlarged by the same factor. If a structure occupies one-quarter of the actual specimen length, it should occupy approximately one-quarter of the drawing length.

7.1 Common Laboratory Apparatus

7.2 Temporary Wet Mount

1. Place a clean slide on a level surface.
2. Add a small drop of suitable mounting liquid.
3. Place a thin specimen in the drop.
4. Lower the coverslip gently at an angle to reduce trapped air.
5. Remove excess liquid carefully if necessary.
6. Observe first at low power and then increase magnification where appropriate.

7.3 Observation of Cells

A basic practical can compare suitable plant and animal cells. Students should identify only structures actually resolved with the preparation and microscope used. Failure to see a structure does not necessarily prove its absence; it may be too small, unstained, transparent or outside the focal plane.

7.4 Osmosis Investigation

Osmosis can be investigated by placing comparable pieces of plant tissue in solutions of different concentrations and measuring a change in mass or length. Solution concentration is the independent variable; change in tissue mass or length is the dependent variable. Tissue dimensions, exposure time and temperature should be controlled as far as practicable.

7.5 Worked Percentage Change

Change: 4.60 − 4.00 = 0.60 g.
Formula: Percentage change = (change ÷ initial mass) × 100.
Solution: (0.60 ÷ 4.00) × 100 = 15%.
Answer: The mass increased by 15%.

7.6 Variation and Ecological Observation

Variation may be investigated by measuring a clearly defined characteristic such as leaf length or seed mass across several specimens. Ecological observations may use quadrats for sessile organisms or transects to investigate change along an environmental gradient. Repeated sampling reduces the chance that a single unrepresentative location determines the conclusion.

7.7 Variables and Results

Results should be entered promptly in tables with clear headings and units. Graph axes must be labelled. A conclusion should answer the investigation question using the evidence obtained, not merely repeat a memorised theoretical statement.

BIO 107 establishes the practical foundation for further biological science courses. By the end of the course, the student should be able to recognise common hazards and precautions, make and record measurements, operate and maintain basic microscopes, produce scientifically acceptable biological drawings, calculate magnification and scale, select common apparatus correctly and conduct introductory experiments that illustrate biological principles.