A Level Biology: Lipids and Onion Root Experiments

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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.

Add 1 part culture to 9 parts sterile liquid to make 10^-1 dilution, then repeat using 1 part of 10^-1 and 9 parts of sterile liquid for 10^-3 dilution. Signup and view all the answers

Describe the method used to obtain results in a graph from experiments on osmosis with potato cubes.

Ensure all cut surfaces of cubes are exposed to sucrose solution; control temperature and dry cubes before measuring. Signup and view all the answers

What ethical considerations were taken into account when collecting bees?

The method must not harm the bees and must allow accurate identification of species. Signup and view all the answers

Suggest two improvements to the data collection method for the investigation.

Collect data at more times of the year; count number of individuals for diversity index. Signup and view all the answers

Why was it important to leave the apparatus for one hour after the yeast culture reached a constant temperature?

So the oxygen is used or absorbed. Signup and view all the answers

Explain why a log scale is used to record the number of cells.

There is a large range of differences in cell numbers. Signup and view all the answers

What is the purpose of boiling the agar in experiments?

To prevent contamination from other bacteria. Signup and view all the answers

How would you use cell fractionation to obtain chloroplasts from leaf tissue?

Macerate or blend tissues, then centrifuge at increasing speeds to obtain chloroplasts. Signup and view all the answers

Why was it important for the student to control the volume of water in each tube during the experiment?

To ensure results are comparable by keeping pigment concentration consistent. Signup and view all the answers

Describe a method to monitor the temperature of the water in each tube.

Take readings using a digital thermometer or temperature sensor during the experiment. Signup and view all the answers

How could scientists obtain data to produce a calibration curve for protein concentration?

Produce known concentrations of protein, measure absorbance, plot a graph, and use it to find sample concentrations. Signup and view all the answers

How would the student measure the mean diameter of stomata using an eyepiece graticule?

Measure each stoma using the eyepiece graticule, calibrate it against a stage micrometer, and take multiple measurements. Signup and view all the answers

Why was maintaining a constant temperature important during the incubation of leaf discs?

To maintain a constant rate of diffusion of ions out of cells. Signup and view all the answers

Explain the importance of having the same water potential in the chloroplast suspension solution.

So osmosis does not occur and the chloroplasts do not burst or shrivel. Signup and view all the answers

Outline a method to determine plant species richness at one site.

Select sampling sites randomly and use a quadrat to identify species. Signup and view all the answers

What measurements should the student have taken to determine the rate of photosynthesis?

Oxygen production or concentration and time. Signup and view all the answers

Describe how the students would return the air bubble to the start of a capillary tube.

Open or use a tap to add water from the reservoir. Signup and view all the answers

What precautions should students take when setting up a potometer?

Dry off leaves and ensure no air bubbles are present. Signup and view all the answers

Give two reasons why a potometer does not measure the rate of transpiration directly.

Water is used for support and in photosynthesis; apparatus may leak. Signup and view all the answers

How would you demonstrate that reducing sugars are present in a solution?

Add Benedict's solution and heat; a red, orange, or yellow color indicates a positive result. Signup and view all the answers

Why did the level of colored liquid in the manometer go down during the experiment?

Oxygen was taken up by the seeds, leading to a decrease in volume or pressure in the flask. Signup and view all the answers

Why were pea seedlings kept in the dark after treatments?

To prevent phototropic responses. Signup and view all the answers

What is the advantage of providing results as ratios?

Allows comparison across different amounts or sizes. Signup and view all the answers

Describe how to use the mark-release-recapture method to estimate fish populations.

Capture a sample, mark, and release; then take a second sample to count marked organisms. Signup and view all the answers

Why might the mark-release-recapture technique give unreliable estimates during the breeding season?

Population may increase during breeding. Signup and view all the answers

What is the purpose of the strip of filter paper in potassium hydroxide solution?

To increase surface area for carbon dioxide absorption. Signup and view all the answers

How would you measure the dry biomass of herbaceous plants in a 1 m² area?

Collect and dry all above-ground material in an oven at around 100°C until constant mass. Signup and view all the answers

How can researchers ensure reliable data for total biomass?

By taking a large number of sample areas and repeats. Signup and view all the answers

What are two limitations in measuring plant biomass increases?

Drying destroys plant samples, making it hard to get representative samples. Signup and view all the answers

What is the advantage of using the same plant in each treatment?

Ensures that leaf surface area, number of leaves, and other biological factors remain consistent. Signup and view all the answers

Why is it important to keep environmental conditions constant?

Environmental conditions affect the rate of transpiration or evaporation. Signup and view all the answers

How could you detect protein presence in a solution?

Add Biuret solution and look for a violet or lilac color. Signup and view all the answers

How would you investigate the optimum temperature for urease activity?

Maintain a range of temperatures using water baths and measure activity by timing color changes. Signup and view all the answers

What is the advantage of measuring dry mass rather than total mass?

Total mass may vary due to water content. Signup and view all the answers

Why was cold isotonic buffer solution used in tissue homogenisation?

Cold - to reduce enzyme action; isotonic - to prevent osmotic effects; buffer - to prevent enzyme damage. Signup and view all the answers

Why is liver tissue homogenized?

To release the cell contents or to break open the cells. Signup and view all the answers

Give two variables that need to be controlled to ensure similar root growth.

Light conditions need to be the same for consistent photosynthesis; temperature must be constant for optimal enzyme activity. Signup and view all the answers

Why was sterilization important at the start of the investigation?

To ensure that no unwanted bacteria will be present. Signup and view all the answers

What conditions are necessary for valid results from mark-release-recapture investigations?

There should be no immigration or migration and no reproduction during the experiment. Signup and view all the answers

Explain the advantages of collecting a large number of results.

It allows anomalies to be identified and increases reliability of averages. Signup and view all the answers

How should the students cut cylinders for a fair test?

Cut lengthways or down the root through one tissue only. Signup and view all the answers

Why did the scientist not use glucose as the respiratory substrate?

Glucose is broken down during glycolysis in cytoplasm and cannot cross the mitochondrial membrane. Signup and view all the answers

How does the reservoir allow repeat measurements in an experiment?

It returns the bubble to the start position. Signup and view all the answers

Why did she make repeat measurements?

To identify anomalous results. Signup and view all the answers

Why did the student blot dry the outside of each cylinder before reweighing?

To ensure that only the mass of the cylinder contents is measured. Signup and view all the answers

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.