Biology Required Practicals

How do you prepare a microscope slide to view onion cells?

Prepare thin epidermis from onion, place in water on slide, add iodine stain, lower coverslip carefully, and view under light microscope at suitable magnification.

How do you prepare a microscope slide to view cheek cells?

Swab inside of cheek, smear cells on slide, add methylene blue, lower coverslip, soak excess, and observe to see nucleus and cell membrane clearly.

What is the formula for calculating magnification in microscopy?

Magnification = image size ÷ actual size, or total magnification = eyepiece magnification × objective magnification.

How can you improve the validity and reliability of microscopy measurements?

Use thin specimens, good staining, calibrated eyepiece graticule, and repeat observations to improve validity and reliability of measurements.

What are the key rules for producing a biological drawing from a microscope?

Draw with sharp pencil, smooth lines, no shading, include title and labels with ruler lines, and state magnification or scale bar.

What is the definition of osmosis in the context of cell biology?

Osmosis is movement of water from a high to a lower concentration of water through a partially permeable membrane.

How do you carry out the investigation into the effect of sugar solutions on plant tissue?

Place equal-length potato cylinders in sugar or salt solutions of different concentration, leave, then reweigh and remeasure length.

What are the variables in the osmosis potato practical?

Independent variable = solution concentration; dependent variable = change in mass or length of potato; controls include temperature, time, and cylinder size.

How do you calculate percentage change in mass for the osmosis practical?

Percentage change = (final mass − initial mass) ÷ initial mass × 100, used to compare potato pieces with different starting masses.

How do you interpret the mass change results in the osmosis practical?

If potato gains mass solution is hypotonic to cells; if it loses mass solution is hypertonic; point where mass change is zero estimates cell water potential.

What is the aim of the amylase enzyme practical?

Investigate how pH (or temperature) affects the time taken for amylase to break down starch to sugar.

What is the method for investigating the effect of pH on amylase activity?

Mix starch and buffer of set pH, add amylase, take samples every 10 s into iodine on spotting tile, time until iodine stays brown.

What are the variables when investigating the effect of pH on amylase?

Independent variable = pH (or temperature); dependent variable = time for starch to disappear; control variables include enzyme and substrate volumes and concentrations.

How do you process the results to find the rate of reaction in the amylase practical?

Plot 1 ÷ time against pH or temperature to compare enzyme activity; highest point shows optimum conditions.

Why does enzyme activity decrease at extreme pH or high temperatures in the practical?

Extreme pH or high temperature changes active-site shape so substrate no longer fits and reaction rate falls sharply.

How do you test for reducing sugars using Benedict's solution?

Heat food sample with Benedict’s solution in hot water bath; colour change from blue to green, yellow, orange or brick-red shows reducing sugar.

How do you test for the presence of starch in food?

Add iodine solution to food; blue-black colour indicates presence of starch, no change means starch absent.

How do you test for the presence of lipids (fats) in food?

Shake food with ethanol then add water; milky white emulsion in top layer shows lipid present.

How do you test for the presence of proteins in food?

Add Biuret solution to food suspension; colour change from blue to lilac or purple shows protein present.

Are the standard food tests qualitative or quantitative?

These food tests are qualitative or semi-quantitative, indicating presence or approximate amount rather than an exact concentration.

What is the aim of the photosynthesis pondweed practical?

Investigate how light intensity (or colour) affects the rate of photosynthesis using pondweed.

What is the method for measuring the rate of photosynthesis using pondweed?

Place pondweed in sodium hydrogencarbonate solution under funnel, vary lamp distance, count oxygen bubbles per minute at each distance.

What are the variables in the photosynthesis light intensity practical?

Independent variable = light intensity or distance; dependent variable = number of bubbles per minute; control variables include temperature, carbon dioxide concentration, and piece of pondweed.

How does light intensity affect the rate of photosynthesis in the practical?

As light intensity increases, rate of photosynthesis increases then levels off when another factor such as carbon dioxide or temperature becomes limiting.

How can you improve the accuracy of the photosynthesis pondweed practical?

Use gas syringe or measure bubble volume instead of counting bubbles and repeat readings to calculate a mean.

What is the aim of the reaction time practical?

Measure human reaction time using the ruler-drop method and investigate factors that may affect it.

What is the ruler-drop method for measuring reaction time?

Person B drops ruler without warning between person A’s thumb and finger; record distance caught, repeat several times, and use conversion chart to find reaction time.

What are the variables in the reaction time ruler-drop practical?

Independent variable often attempt number or condition tested; dependent variable = distance ruler falls or calculated time; controls include ruler, hand position, and drop height.

How do you reduce random error in the reaction time practical?

Take many repeats, ignore anomalies, and calculate mean reaction time to reduce random error.

What are common sources of error in the reaction time ruler-drop practical?

Inconsistent ruler release, distraction of subject, and parallax when reading scale can all affect accuracy of measured distance.

How do you use quadrats and transects to investigate plant distribution?

Use quadrats placed along a transect line to measure distribution and abundance of plant species across a habitat.

Why is random sampling important in field investigations?

Use random coordinates or random number generator to choose quadrat positions to avoid bias in sampling.

What are the variables when investigating plant distribution along a transect?

Independent variable = position along transect or distance from feature; dependent variable = number or percentage cover of each species.

How do you ensure reliability in a field investigation using quadrats?

Use many quadrats and calculate mean values to obtain more reliable estimates of population distribution.

What are the rules for counting plants within a quadrat?

Count each plant only once, use a grid on the quadrat if needed, and be consistent with borderline plants.