BIOLOGY PAPER 1 PRACTICALS

Aim of Microscopy Required Practical

To prepare a slide and use a microscope to observe cells.

Equipment for Microscopy

Light microscope, glass slide, coverslip, iodine solution (stain), sample (e.g., onion epidermis, cheek cells), tweezers, pipette.

Method for Preparing a Slide

Peel a thin layer of onion epidermis or scrape inside of the mouth for cheek cells, place on slide, add iodine stain, lower coverslip at an angle, and secure on microscope stage.

What does iodine do?

A stain that colours cell structures, making them distinct and easier to observe under the microscope.

Magnification Equation

Magnification = image size / real size.

Units of Measurement in Microscopy

Millimeters (mm), micrometres (μm), nanometres (nm); conversions: 1 mm = 1000 μm, 1 μm = 1000 nm.

Variables in Microscopy

Independent: magnification setting; Dependent: appearance or level of detail observed; Control: type and amount of stain, specific microscope, lighting conditions.

Common Errors in Microscopy

Using a sample too thick, coverslip movement during observation, improper focusing.

Aim of Osmosis Required Practical

To investigate the effect of different sugar or salt concentrations on the mass of potato cylinders.

Method for Osmosis Experiment

Cut uniform potato cylinders, measure initial mass, place in solutions of varying concentrations, measure final mass after a set time, calculate percentage change in mass.

Osmosis Definition

The net movement of water molecules from higher water potential (dilute) to lower water potential (concentrated) across a partially permeable membrane.

Percentage Change Formula for Osmosis

Percentage change = (final mass - initial mass) / initial mass × 100.

Expected Results of Osmosis

In dilute solutions, mass increases; in concentrated solutions, mass decreases. Concentration at which there is no net change indicates equal water potential.

Common Errors in Osmosis Experiment

Non-uniform potato sizes, inconsistent drying, different timing in solutions.

Aim of Food Tests Required Practical

To test for the presence of biological molecules (sugars, starch, protein, lipids) in food samples.

Controls in Food Tests

Test samples to ensure reagents do not give false positives.

Benedict's Test Method

Add Benedict's solution to sample, heat in water bath, observe color change for reducing sugars.

Results of Benedict's Test

Blue: no sugar; green: small; yellow: moderate; orange/red: large amount of reducing sugar.

Iodine Test Method

Add a few drops of iodine to the sample and observe color change to test for starch.

Results of Iodine Test

Orange-brown: no starch; blue-black: starch present.

Biuret Test Method

Add Biuret A and Biuret B to thaw food solution, shake, observe color change for protein.

Results of Biuret Test

Blue: no protein; purple/lilac: protein present.

Ethanol Emulsion Test Method

Shake food sample with ethanol, pour into water, observe appearance for lipid presence.

Results of Ethanol Emulsion Test

Clear: no lipid; cloudy white emulsion: lipid present.

Aim of Enzymes Required Practical

To investigate the effect of pH on the activity of the enzyme amylase.

Method for Enzyme Activity Investigation

Mix amylase with buffer at varied pH, add starch, observe color change with iodine to indicate starch breakdown.

Variables in Enzyme Activity Investigation

Independent: pH; Dependent: time for starch to digest; Control: temperature, concentration of solutions.

What is Optimum pH?

The pH at which an enzyme is most effective; extreme pH can denature the enzyme.

Aim of Photosynthesis Required Practical

To investigate the effect of light intensity on the rate of photosynthesis in pondweed (Elodea).

Method for Photosynthesis Investigation

Place pondweed in water, create carbon dioxide source (sodium hydrogencarbonate), measure oxygen bubbles produced at varying lamp distances.

Expected Results of Photosynthesis Experiment

Closer lamp (higher light intensity) generates more oxygen bubbles, indicating a faster rate of photosynthesis.

Inverse Square Law in Photosynthesis

Light intensity is inversely proportional to the square of the distance from the light source.

Common Errors in Photosynthesis Experiment

Varying bubble sizes, inconsistent counting, warming effects from lamp.