Photosynthesis Experiment: Light Intensity Effects

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Questions and Answers

What is a suitable preliminary method to measure the volume of gas released during photosynthesis?

Using a photosynth meter with capillary tubing to capture oxygen bubbles.

Why is sodium hydrogen carbonate added to the beaker in the preliminary setup?

It provides an excess of carbon dioxide essential for photosynthesis.

What is the significance of allowing the pondweed to acclimatise before starting the experiment?

It ensures that the plant is stable and can adapt to the light conditions, leading to more reliable data.

Identify one key limitation in controlling environmental factors during the initial phases of photosynthesis experiments.

Temperature control can be difficult to manage effectively. Signup and view all the answers

Describe a method to determine the light intensity range suitable for the preliminary photosynthesis experiment.

Using a lamp positioned at distances ranging from 10 cm to 30 cm from the beaker. Signup and view all the answers

What is a suitable method to measure the zone of inhibition in antibacterial studies?

Using a ruler to measure the diameter of the clear zone surrounding the discs. Signup and view all the answers

In studying the growth of bacteria, why is it difficult to count them in fresh pineapple juice?

The uneven distribution of bacteria makes them difficult to count accurately. Signup and view all the answers

What control measures are necessary for maintaining pH and temperature in antibacterial experiments?

Using a buffer for pH and an incubator to control temperature. Signup and view all the answers

What preliminary factors should be considered when investigating the respiration quotient (RQ) of mung beans?

A suitable age of mung beans and a suitable pH for respiration. Signup and view all the answers

What initial step is crucial to ensure aseptic conditions during the antibacterial compound investigation?

Performing aseptic techniques such as disinfecting the work surface and sterilizing equipment. Signup and view all the answers

What is an important preliminary step when preparing to measure gas volume in mung beans?

Finding a suitable method to measure gas displacement, such as using a manometer. Signup and view all the answers

Why is the use of different masses of leaves important in antibacterial studies?

To assess the impact of varying concentrations of antibacterial compounds on bacterial growth. Signup and view all the answers

What is the first step in the method for extracting pineapple juice?

Cut the pineapple into pieces and blend it to obtain the juice. Signup and view all the answers

How can you control the pH for the growth of bacteria in an experiment?

Use buffer solutions to maintain a stable pH environment. Signup and view all the answers

What method can be used to count the number of bacteria in a sample?

Use a dilution method followed by plating on agar and counting colonies. Signup and view all the answers

Why is it important to label the beakers with different concentrations in the brine shrimp experiment?

Labeling ensures accurate identification of the calcium ion concentration for each test. Signup and view all the answers

What is the role of the thermostatically controlled water bath in the brine shrimp experiment?

It maintains a consistent temperature necessary for optimal hatching conditions. Signup and view all the answers

How do you determine if the quadrat is more than half-filled in the grasshopper counting method?

Visually assess the area filled with grasshoppers to confirm it exceeds half the quadrat's volume. Signup and view all the answers

How is the percentage of full quadrats calculated after counting the grasshoppers?

Divide the number of full quadrats by the total number of quadrats, then multiply by 100. Signup and view all the answers

What is meant by the dependent variable in the calcium concentration experiment on brine shrimp?

The dependent variable is the number of brine shrimp hatched per unit time. Signup and view all the answers

What does 'control variable' refer to in an experimental context?

Control variables are factors kept constant to ensure fair testing, such as temperature and pH. Signup and view all the answers

Why is it necessary to repeat the brine shrimp hatching experiment multiple times?

Repeating the experiment increases reliability and allows for mean calculations of hatching success. Signup and view all the answers

Study Notes

Photosynthesis with Light Intensity

The dependent variable is the number of oxygen released per unit time.
The control variables are temperature (using a thermostatically controlled water bath) and pH (using a buffer).
Use five different distances from the lamp to the beaker (10-30 cm).
Place pondweed (10 cm long) in a beaker of water, remove bubbles.
Cover half the beaker with foil, allowing light from one side.
Add sodium hydrogen carbonate to provide excess carbon dioxide, leave for 5 minutes.
Position the lamp 10 cm away from the beaker, allow the plant to acclimatize.
Fill the capillary tubing of the Photosynth meter with water.
Place the funnel, with plant inside, in the beaker of water and weight with a paperclip.
Start a stopwatch when oxygen bubbles start entering the capillary tubing.
After 10 minutes, use a syringe to collect oxygen, refill the tubing.
Record the number of bubbles/time to calculate the rate.
Repeat for other distances and find the mean and standard deviation.

Limitations of Photosynthesis with Light Intensity

Difficulty controlling temperature.
Possible errors measuring gas volume.
Surface area can't be controlled.

Observing Grasshoppers

The dependent variable is the number of grasshoppers per unit area.
Control variables are pH and temperature (controlled via slope of rode and gravel area).
Create a coordinate grid over the area to be sampled.
Use a random number generator for 20 coordinates.
Place quadrats at the coordinates and count grasshoppers.
If a quadrat is more than half full, count it as a full quadrat.
Calculate the percentage of full squares.
Record the abundance in a table.
Repeat for one sample area.
Repeat the entire investigation at different times throughout the year.
Calculate population density by dividing the number of grasshoppers by the area.

Limitations of Observing Grasshoppers

Difficulty controlling pH.
Difficulty identifying the species.
Difficulty observing the movement of the species.

Calcium Concentration on Brine Shrimp

The dependent variable is the number of brine shrimp hatched per unit time.
Control variables are temperature and pH (using a thermostatically controlled water bath and a buffer).
Use five different salt concentrations.
Make a salt solution by adding 2 grams of salt to 100 cm³ of de-chlorinated water with the calcium concentration.
Carefully sprinkle brine shrimp eggs onto slightly damp graph paper (count 40).
Carefully place the eggs into the salt solution, graph paper facing down.
Repeat for every concentration, calculate the mean.
Place the beaker in an incubator.
Make another salt solution using the same method as above for counting the hatched shrimp.
Use a light source next to the beaker to observe/count the hatched shrimp swimming towards the light source.
Repeat the counting for two more days.

Fresh Pineapple Juice Affecting Bacterial Growth

The dependent variable is the number of bacteria in 24 hours.
Control variables are pH and temperature (using a buffer and incubator).
Use aseptic techniques (disinfecting the table, using a Bunsen burner, upward flame).
Prepare different concentrations of pineapple juice (0.5%-1.5%).
Use a pestle and mortar to crush pineapple and a 500 cm³ conical flask.
Mix yeast suspension (1.25g) into different concentrations of pineapple juice.
Measure the absorbance every 20-30 minutes for 2 hours.
Repeat the experiment with different concentrations of pineapple juice.
Repeat with and without pineapple juice for comparison.

Yeast Respiration

The dependent variable is the time taken for TTC to change colour.
Control variables for pH and TTC concentration (using a buffer).
Use a range of temperatures from 10-30°C.
Set up a water bath at 30°C. Add 10 cm³ of yeast suspension into a test tube.
Add 1 cm³ of TTC to the test tube, and leave to reach the same temperature as the water bath. Place test tube into the water bath, then start the stop clock.
Stop the clock when the colour of the solution changes to red.
Calculate the rate by dividing the number 1 by the time it took for the colour to change.
Repeat for other temperatures.
Repeat the whole investigation and calculate the mean and standard deviation.

Limitations of Yeast Respiration

Difficult to see the end point.
Difficulty preventing contamination of the yeast culture.

Antimicrobial Compounds Reducing Bacterial Growth

The dependent variable is the zone of inhibition.
Control variables are temperature and pH (controlled by incubator for 48 hours and a buffer).
Aseptic technique (disinfect table, use Bunsen burner, sterile equipment).
Use a range of leaf masses (e.g., 2-4 grams).
Crush leaves with water and alcohol in a pestle and mortar.
Place discs into the agar plate.
Place inoculated agar plate, and put into the incubator at 25°C for 48 hours.
Measure the zone of inhibition using a ruler.
Repeat for different masses.
Repeat the entire investigation and calculate the mean.

Limitations of Antimicrobial Compounds Reducing Bacterial Growth

Difficult to measure distances.
Contamination may occur.

Mung Beans and Their RQ (Respiratory Quotient)

The dependent variable is the distance moved by the meniscus.
The control variables are pH, and temperature (using a buffer and water bath).
Use seedlings of different ages.
Measure 5 g of soda lime, wrap in muslin, in a test tube, and make another tube without soda lime; place a gauze on top.
Sterilize seeds, weigh and place in test tube, and replace the bung.
Carefully place coloured liquid into the tube using a pipette (furthest from the spirometer).
Record initial and final distances every minute for 5 minutes.
Calculate RQ by dividing CO2 released by O2 consumed.
Repeat the entire investigation for various ages and find the mean and standard deviation.

Limitations of Mung Beans and Their RQ

Seedlings may change from aerobic to anaerobic respiration.
Difficult to measure distance.

Gibberellin Solution

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Description

Explore the effects of light intensity on the rate of photosynthesis in pondweed. This quiz covers experimental design, variables, and procedures for measuring oxygen production under varying light conditions. Test your understanding of key concepts and processes involved in photosynthesis.