A Level Biology: Lipids and Onion Root Experiments

Lipid Testing

• Mix liquid sample with ethanol followed by water to test for lipids.
• A positive result is indicated by the formation of a white or milky emulsion.

Onion Root Examination

• The first 5 mm of the onion root contains dividing cells where mitosis occurs.
• Firm pressure is applied to the cover slip to create a thin layer of cells and ensure visibility of light and nuclei.

Mitotic Index Accuracy

• Count a large number of fields and cells (20 or more) for a reliable sample.
• Repeat counts to verify accuracy and establish standard counting methods, avoiding partial cell counts.

Bacterial Dilution

• Create a 1:10 dilution by mixing one part bacterial culture with nine parts sterile liquid.
• To achieve a 1:1000 dilution, mix one part of the 1:10 dilution with 99 parts sterile liquid.

Investigating Osmosis

• Ensure all cut surfaces of potato cubes are exposed to sucrose solution.
• Control temperature, dry cubes before mass measurement, and regularly measure mass at specified time intervals.

Ethical Bee Collection

• Collect bees without causing harm to ensure ethical practices.
• Use photographs or specimens for accurate species identification.

Data Collection Improvement

• Expand data collection to various seasonal times for better graph representation.
• Count individuals of each species for diversity index calculation and gather data from multiple sites for accuracy.

Yeast Culture Observation

• Leaving the apparatus for one hour allows oxygen to be absorbed by the yeast culture.

Log Scale Usage

• A logarithmic scale is utilized to accommodate a large range of cell counts.

Agar Plate Preparation

• Boil the agar to prevent contamination by unwanted bacteria.
• Use the same volume of liquid culture for consistency across agar plates to enable comparison.

Chloroplast Isolation

• Macerate or homogenize leaf tissue in a solution before centrifuging at increasing speeds to isolate chloroplasts.

Controlling Water Volume in Experiments

• Controlling water volume ensures consistent pigment concentration, allowing for valid comparisons in results.

Temperature Monitoring Method

• Use a digital thermometer or temperature sensor to monitor water temperature in experiments.

Calibration Curve for Protein Concentration

• Create known protein concentrations and measure their absorbance, plotting results to create a calibration curve for future sample comparisons.

Eyepiece Graticule Usage

• Measure stomata using an eyepiece graticule, calibrating it against a stage micrometer for accurate mean diameter calculations.

Temperature Control in Experiments

• Maintain a constant temperature to ensure consistent diffusion rates and other biochemical processes.

Importance of Equal Water Potential

• Having matching water potentials between solution and chloroplasts prevents osmosis that could damage the organelles.

Plant Species Richness Assessment

• Use random sampling methods with quadrats to identify and count plant species within a defined area.

Measuring Leaf Area

• Calculate leaf area by tracing leaves on graph paper and counting squares, then correlate water loss to total surface area.

Controlled Biochemical Variables

• Maintain initial substrate concentration, enzyme concentration, and pH to ensure reliable experimental conditions.

Aseptic Transfer Techniques

• Keep lid on Petri dish to prevent contamination and ensure hand hygiene to avoid transferring external bacteria.

Counting Capillaries in Heart Muscle

• Calculate mean capillary numbers by measuring field diameter, counting capillaries in random fields of view for accuracy.

Processed Data Explanation

• Processed results come from calculations derived from raw data collected during experiments.

Water Potential of Potato Tissue

• Create a graph of sucrose concentration vs. percentage mass change to determine water potential at the point of zero change.

Stomata Counting Necessity

• Counting in multiple areas ensures a representative sample and reliability of mean results.

Filter Paper Variables

• Control size and absorbency of filter paper discs to standardize experimental conditions.

pH Meter Advantage

• pH meters provide precise numerical data, improving measurement accuracy compared to subjective color changing indicators.

Temporary Mount Preparation

• Create thin slices of tissue, place them in solution on slides, and cover with a slip for examination.

Photosynthesis Measurement

• Measure oxygen production over a set period to assess the rate of photosynthesis.

Air Bubble Management in Potometer

• Use a tap to return the air bubble in the capillary tube for consistent measurements.

Potometer Setup Precautions

• Ensure leaves are dry, no air bubbles are present, and the setup is airtight to secure accurate water uptake readings.

Transpiration Rate Measurement Limitations

• Water used in plant support and respiration lowers accuracy as it does not solely indicate transpiration.

Reducing Sugars Detection

• Add Benedict's solution and heat; a red/orange/yellow coloration indicates the presence of reducing sugars.

Manometer Liquid Levels Changes

• A decrease in liquid level indicates oxygen consumption by seeds and carbon dioxide being absorbed by potassium hydroxide.

Phototropism in Seedlings

• Keeping seedlings in the dark reduces their light response, allowing controlled experimental conditions.

Result Ratios Advantage

• Presenting data as ratios facilitates comparisons across varying experimental conditions and sizes.

Mark-Release-Recapture Method

• Capture, mark, and release fish; then take a second sample to estimate population size based on marked proportions.

Population Estimate Reliability

• Breeding seasons can skew population estimates due to increased numbers from reproduction.

Potassium Hydroxide Solution Filter Paper Role

• The filter paper enhances surface area for more effective carbon dioxide absorption.

Herbaceous Plant Biomass Measurement

• Collect above-ground plant material, dry in an oven at a consistent temperature, weigh, then repeat until constant mass is achieved.

Biomass Data Reliability

• Increasing sample area size and random selection improves the overall reliability of data collected.

Plant Biomass Measurement Accuracy Limitations

• Drying samples can disrupt biomass comparisons, and large plant sizes can complicate obtaining accurate measurements.

Consistency in Plant Treatments

• Using the same plant in experiments ensures uniformity in leaf area, age, and thickness for reliable results.

Importance of Constant Environmental Conditions

• Maintaining a stable environment ensures consistent transpiration rates, minimizing external variability in experiments.

Protein Detection in Solutions

• Add biuret solution for protein testing; a violet/lilac color confirms presence.

Investigating Urease Optimum Temperature

• Maintain a range of temperatures, measure reaction rates, and keep conditions constant to find the optimal urease activity.

Dry vs Total Biomass Measurement

• Measuring dry mass provides consistent results, as water content can fluctuate.

Reasons for Cold, Isotonic Buffer in Tissue Homogenization

• Cold buffer minimizes enzyme activity, isotonic prevents osmotic damage, and buffer maintains pH stability.

Liver Tissue Homogenization Purpose

• Homogenization is necessary to break open cells and release cellular contents for analysis.

Environmental Factors for Root Growth

• Control light and temperature to ensure all plants experience optimal conditions for root development.

Aseptic Technique Importance

• Sterilization of agar plates prevents contamination, ensuring only intended organisms grow in the culture.

Mark-Release-Recapture Validity Conditions

• Criteria for valid mark-release-recapture include no population migration, no reproduction, and effective mixing without behavior alteration from marking.

Advantages of Pooled Results

• Collecting extensive results increases reliability, allows for anomaly identification, and enables statistical analysis.

Leaf Tissue Cutting Techniques

• Cut cylinders lengthwise through uniform tissue sections to ensure fairness and consistency in results.

Respiratory Substrate Selection Reasoning

• Glucose is unsuitable as a respiratory substrate because it undergoes glycolysis outside mitochondria, affecting mitochondrial respiration studies.

Repeat Measurements Benefit

• Repeat measurements help to identify and exclude anomalies, enhancing overall data reliability.

Monitoring Water on Cylinder Surfaces

• Drying cylinders before reweighing eliminates water mass influence, ensuring accuracy in measurements of absorbed water.

Percentage Change in Mass Calculation Benefit

• Calculating percentage change allows for easier comparison among cylinders with varying initial masses, highlighting proportional differences.

Importance of Multiple Stomata Counts

• Counting stomata in several regions provides a more accurate representation of their distribution across leaf tissue, ensuring reliable results.