practicals Flashcards
What is phenolphthalein used for in the diffusion experiment?
Phenolphthalein is a pH indicator that turns pink in alkaline solutions and colourless in acidic solutions. It is used to observe the diffusion of acid into the agar jelly.
Why is phenolphthalein used in the agar jelly diffusion experiment?
It helps visually indicate when the acid has diffused into the agar jelly and neutralised the sodium hydroxide, causing the jelly to turn colourless.
How does the agar jelly in the experiment represent cells?
The agar jelly cubes represent cells in the experiment, where the acid diffuses into the jelly, similar to how substances diffuse into a cell.
What is the first step in the diffusion experiment using agar jelly?
The first step is to prepare the agar jelly with phenolphthalein and dilute sodium hydroxide, which makes the jelly pink.
What should you do after cutting out the agar jelly cubes?
Place the cubes into a beaker containing dilute hydrochloric acid and observe as they turn colourless due to diffusion of the acid.
How can you investigate the effect of surface area on diffusion in this experiment?
By cutting the agar jelly into cubes of different sizes, calculating their surface area to volume ratio, and timing how long it takes each cube to go colourless.
What is the expected result for cubes with a large surface area to volume ratio?
Cubes with the largest surface area to volume ratio will go colourless the fastest because the acid diffuses into them more quickly.
How can you investigate the effect of concentration gradient on diffusion in this experiment?
By using test tubes with different concentrations of hydrochloric acid, placing equal-sized agar cubes in each, and timing how long it takes each to turn colourless.
What is the expected result for cubes in higher concentrations of hydrochloric acid?
The cubes in higher concentrations of hydrochloric acid will go colourless the fastest due to a steeper concentration gradient.
How can you investigate the effect of temperature on diffusion in this experiment?
By placing test tubes with the same concentration of hydrochloric acid in water baths of varying temperatures, adding equal-sized cubes, and timing how long it takes each to go colourless.
What is the expected result for cubes in higher temperatures?
The cubes in higher temperatures will go colourless the fastest due to the increased kinetic energy of the molecules, which speeds up diffusion.
Why shouldn’t the temperature be increased above 65°C?
If the temperature exceeds 65°C, the agar jelly will start to melt, interfering with the experiment.
How do you prepare solutions to investigate water potential?
Prepare sucrose solutions of varying concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M.
What equipment do you need to carry out the potato cylinder experiment?
You need a cork borer or chip maker to cut the potato into uniform cylinders, a mass balance, and a series of sucrose solutions.
How do you conduct the potato cylinder water potential experiment?
Cut potato cylinders into 1 cm pieces, weigh them, place them in sucrose solutions, leave them for at least 20 minutes, remove and dry them, then reweigh and calculate the % change in mass.
What is the purpose of plotting results on a graph in this experiment?
The graph helps to visualize the relationship between sucrose concentration and the % change in mass, showing where the water potential of the sucrose solution equals that of the potato cells.
How do the potato cells change in different sucrose solutions?
In pure water (0.0 M), potato cells become turgid (gain mass), while in higher concentrations of sucrose, they lose mass and become plasmolysed (cells shrink).
What is the point at which the water potential of the solution equals the potato cells’ water potential?
The point where the % change in mass is zero, indicating that the water potential of the sucrose solution is the same as that of the potato cells.
What is a similar experiment to investigate osmosis in animal cells?
A similar experiment can be carried out using eggs with their shells dissolved, where the remaining membrane is partially permeable, acting as a model for osmosis in animal cells.
