Questions and Answers
How would you test a liquid sample for the presence of lipid and how would you recognize a positive result?
Mix with ethanol, then water; a white or milky emulsion indicates a positive result.
Explain why the student used only the first 5 mm from the tip of an onion root.
This area is where dividing cells are found, and mitosis occurs.
What should the student have done when counting cells to ensure an accurate mitotic index?
Examine a large number of fields of view; repeat the count.
Describe how to make a 1 in 10 dilution and then a 1 in 1000 dilution of a liquid culture of bacteria.
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Describe the method used to obtain results in a graph from experiments on osmosis with potato cubes.
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What ethical considerations were taken into account when collecting bees?
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Suggest two improvements to the data collection method for the investigation.
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Why was it important to leave the apparatus for one hour after the yeast culture reached a constant temperature?
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Explain why a log scale is used to record the number of cells.
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What is the purpose of boiling the agar in experiments?
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How would you use cell fractionation to obtain chloroplasts from leaf tissue?
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Why was it important for the student to control the volume of water in each tube during the experiment?
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Describe a method to monitor the temperature of the water in each tube.
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How could scientists obtain data to produce a calibration curve for protein concentration?
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How would the student measure the mean diameter of stomata using an eyepiece graticule?
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Why was maintaining a constant temperature important during the incubation of leaf discs?
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Explain the importance of having the same water potential in the chloroplast suspension solution.
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Outline a method to determine plant species richness at one site.
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What measurements should the student have taken to determine the rate of photosynthesis?
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Describe how the students would return the air bubble to the start of a capillary tube.
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What precautions should students take when setting up a potometer?
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Give two reasons why a potometer does not measure the rate of transpiration directly.
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How would you demonstrate that reducing sugars are present in a solution?
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Why did the level of colored liquid in the manometer go down during the experiment?
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Why were pea seedlings kept in the dark after treatments?
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What is the advantage of providing results as ratios?
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Describe how to use the mark-release-recapture method to estimate fish populations.
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Why might the mark-release-recapture technique give unreliable estimates during the breeding season?
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What is the purpose of the strip of filter paper in potassium hydroxide solution?
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How would you measure the dry biomass of herbaceous plants in a 1 m² area?
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How can researchers ensure reliable data for total biomass?
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What are two limitations in measuring plant biomass increases?
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What is the advantage of using the same plant in each treatment?
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Why is it important to keep environmental conditions constant?
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How could you detect protein presence in a solution?
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How would you investigate the optimum temperature for urease activity?
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What is the advantage of measuring dry mass rather than total mass?
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Why was cold isotonic buffer solution used in tissue homogenisation?
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Why is liver tissue homogenized?
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Give two variables that need to be controlled to ensure similar root growth.
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Why was sterilization important at the start of the investigation?
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What conditions are necessary for valid results from mark-release-recapture investigations?
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Explain the advantages of collecting a large number of results.
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How should the students cut cylinders for a fair test?
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Why did the scientist not use glucose as the respiratory substrate?
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How does the reservoir allow repeat measurements in an experiment?
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Why did she make repeat measurements?
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Why did the student blot dry the outside of each cylinder before reweighing?
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Study Notes
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.
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Description
This quiz covers common practical questions in A Level Biology, focusing on the testing for lipids and the specifics of onion root experiments. Each question is accompanied by mark-schemed answers to help deepen your understanding of the topic.