required practicals

1. 🔬 Microscopy – Observing Cells

Purpose:

  • Use a light microscope to view plant and animal cells.

Method:

  • Prepare a slide (e.g., onion epidermis for plant cells, cheek cells for animal).

  • Add iodine stain for plant cells (to highlight structures).

  • Place cover slip gently.

  • Start with low power, focus, then switch to high power.

  • Draw what you see, label key parts.

Key points:

  • Calculate magnification:

    Total magnification=Eyepiece×Objective lens\text{Total magnification} = \text{Eyepiece} \times \text{Objective lens}Total magnification=Eyepiece×Objective lens

  • Use rulers to measure size on drawing and calculate actual cell size.

2. 🥔 Osmosis in Potatoes

Purpose:

  • Investigate osmosis (movement of water) through plant cell membranes.

Method:

  • Cut equal-sized potato pieces.

  • Measure initial mass.

  • Place in different sugar solutions (0%, 0.2%, 0.4%, etc.).

  • Leave for 30 minutes.

  • Remove, dry, measure final mass.

  • Calculate % change in mass:

    Percentage change=final mass−initial massinitial mass×100\text{Percentage change} = \frac{\text{final mass} - \text{initial mass}}{\text{initial mass}} \times 100Percentage change=initial massfinal mass−initial mass​×100

Variables:

  • Independent: sugar concentration.

  • Dependent: change in mass.

  • Controlled: size of potato pieces, time, temperature, solution volume.

Conclusion:

  • Water moves from dilute to concentrated solutions across the membrane.

3. 🧪 Enzyme Activity and pH (Amylase)

Purpose:

  • Investigate effect of pH on amylase enzyme breaking down starch.

Method:

  • Mix amylase, starch solution, and buffer solution at a set pH.

  • Incubate at 37°C.

  • Every 30 seconds, test sample with iodine.

  • Note time until iodine no longer turns blue/black (starch fully digested).

Variables:

  • Independent: pH of solution.

  • Dependent: time taken for starch to disappear.

  • Controlled: temperature, enzyme concentration, starch concentration.

Conclusion:

  • Amylase has an optimum pH (~7), with activity dropping at lower or higher pHs.

4. 🧪 Food Tests

Purpose:

  • Test foods for carbohydrates, proteins, and lipids.

Tests:

Nutrient

Test Solution

Positive Result

Starch

Iodine solution

Blue-black colour

Reducing sugars

Benedict's solution

Turns brick red on heating

Proteins

Biuret solution

Turns purple

Lipids (fats)

Ethanol + water (emulsion test)

Milky white emulsion forms

Method:

  • Add test solution to food sample.

  • Heat (if required).

  • Observe colour change.

5. 🌞 Photosynthesis

Purpose:

  • Investigate factors affecting the rate of photosynthesis (e.g., light intensity).

Example practical (using pondweed):

Method:

  • Place pondweed underwater in a test tube.

  • Shine a light at a set distance.

  • Count bubbles of oxygen released in 1 minute.

  • Repeat at different distances (changing light intensity).

Variables:

  • Independent: light intensity (distance from light).

  • Dependent: number of oxygen bubbles.

  • Controlled: temperature, type of pondweed, CO₂ concentration.

Conclusion:

  • Rate of photosynthesis increases with light intensity until another factor becomes limiting.