Module 2 PAGS

Question 1

Describe the method for the practical investigating cell membrane permeability ?

Answer 1

• Using a scalpel, cut five equal-sized cubes of beetroot
• Rinse the beetroot pieces to remove any pigment released during cutting
• Add the beetroot pieces to five different test tubes, each containing the same volume of water (e.g. 5cm3)
• Put each test tube in a water bath at a different temperature (e.g. 10℃, 20℃, 30℃, 40℃, 50℃) for the same length of time
• Remove the beetroot pieces, leaving just the coloured liquid in the five test tubes
• Use a colorimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid

Question 2

What variables must be kept the same during the practical investigating cell membrane permeability ?

Answer 2

• ## The surface area to volume ratio of the beetroot pieces

Question 3

What are the limitations of the practical investigating cell membrane permeability ?

Answer 3

• Cuvettes may differ in thickness : A thicker (or scratched) cuvette will absorb slightly more light than a thinner unscratched cuvette
• The beetroot pieces may not be identical in size and shape, meaning some test tubes could contain slightly more beetroot tissue than others
• Some parts of beetroot tissue have more pigment in their cells than others

Question 4

What is the solution to the cuvette being varying thicknesses ?

Answer 4

Use the same cuvette for every reading, or repeat the investigation many times and find a mean

Question 5

What is the solution to the beetroot pieces not being the same size ?

Answer 5

Cut the discs as accurately as possible using a scalpel and ruler, and repeat each investigation several times to find a mean

Question 6

What is the solution to the beetroot tissue having more pigment in their cells than others ?

Answer 6

Conduct several repeats, using different parts of the beetroot and find a mean

Question 7

What is the trend of results for the practical investigating cell membrane permeability ?

Answer 7

As temperature increases, membrane permeability also increases

Question 8

Describe the method for the practical investigating the glucose concentration of a potato ?

Answer 8

• The required number of potato cylinders are cut (one for each of the solutions you are testing – or more than one per solution if you require repeats)
• They are all cut to the same length and, once blotted dry to remove any excess moisture, their initial mass is measured and recorded before placing into the solutions
• They are left in the solutions for a set amount of time (eg. 30 minutes), usually in a water bath (set at around 30o)
• They are then removed and dried to remove excess liquid
• The final length and mass of each potato cylinder is then measured and recorded

Question 9

Describe and explain the results of the practical investigating glucose concentration in potatoes ?

Answer 9

• A positive percentage change in mass indicates that the potato has gained water by osmosis meaning the solution has a higher water potential than potato
• A negative percentage change suggests the opposite, that is, the solution had a lower water potential than the potato
• If there is a potato cylinder that has neither increased nor decreased in mass, it means there was no overall net movement of water into or out of the potato cells

Question 10

What does the point crossing the x-axis represent in the practical investigating glucose concentration in potatoes ?

Answer 10

The point at which the line of best fit crosses the x-axis is the concentration of sucrose inside the potato cylinders