PAG 8: Transport Flashcards
What factors affect the permeability of cell membranes? (2)
High temperature and extreme pH can denature membrane proteins, increasing permeability
Some solvents (e.g., alcohol) dissolve phospholipids, increasing permeability
Describe the semi-quantitative technique for investigating membrane permeability using beetroot. (6)
- Make a series of colour standards using pure beetroot extract
- Set up water baths at required temperatures (e.g., 20, 30, 40, 50, 60°C)
- Label test tubes and add the same volume of distilled water to each
- Cut equal-sized beetroot discs using a cork borer and scalpel, then rinse with distilled water
- Add the same number of beetroot discs to each test tube and place them in the water baths for a set time, shaking regularly
- Remove discs and compare the solution colour with the prepared colour standards
Describe the quantitative technique using a colorimeter for measuring membrane permeability. (4)
- Zero the colorimeter using a cuvette filled with distilled water
- Transfer liquid from each test tube into a clean cuvette
- Measure the absorbance using the colorimeter
- The higher the pigment concentration, the higher the absorbance reading
What variables need to be controlled in an experiment measuring membrane permeability? (3)
Source of plant tissue
Length of time in solution
Surface area to volume ratio of plant tissue
What is a limitation of using colour standards to measure membrane permeability? (2)
Matching to colour standards is subjective
The obtained colour may not exactly match any of the prepared standards
Explain why ethanol causes pigment to leak out of beetroot discs. (2)
Ethanol dissolves the phospholipids in the membrane
This disrupts membrane integrity, increasing permeability
Why does increased temperature cause ethanol to turn red more quickly? (2)
Increased temperature increases kinetic energy of molecules
This increases the rate of diffusion of pigment across the membrane
Why did the student wash the beetroot discs in distilled water after cutting them? (1)
Washing removes pigment released from damaged cells to ensure results are due to the independent variable
Why were test tubes of distilled water left in the water bath for 5 minutes before adding beetroot? (1)
To allow the water to equilibrate (reach the required temperature)
Why did the student shake the test tubes every 5 minutes? (1)
To maintain the diffusion gradient for pigment to diffuse into the distilled water
Why did the student use fresh beetroot and not cooked beetroot? (2)
Cooking denatures membrane proteins
This allows pigment to leak out, affecting the results
Describe the method for investigating the effect of concentration on diffusion. (6)
- Make agar jelly with phenolphthalein and dilute sodium hydroxide (jelly turns pink)
- Prepare 5 test tubes with increasing HCl concentrations (e.g. 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M)
- Cut out 5 equal-sized cubes from the agar jelly using a scalpel
- Place a cube into the first test tube and time how long it takes to turn colourless
- Repeat with a fresh cube for each concentration
- The highest concentration of HCl will have the fastest colour change as it has the steepest concentration gradient
What is the expected result when investigating the effect of concentration on diffusion? (1)
The highest concentration of HCl will cause the fastest colour change due to the steepest concentration gradient
Describe the method for investigating the effect of surface area on diffusion. (2)
- Use the same method as the concentration experiment but cut cubes into different sizes and calculate their surface area to volume ratio
- The smallest cube with the greatest surface area to volume ratio would go colourless fastest
What is the expected result when investigating the effect of surface area on diffusion? (1)
The smallest cube with the largest surface area to volume ratio will go colourless the fastest
Describe the method for investigating the effect of temperature on diffusion. (4)
- Use the same method as the surface area experiment but cut equal-sized cubes
- Prepare boiling tubes with the same concentration of HCl
- Place the boiling tubes in water baths of different temperatures
- Higher temperatures will make the cubes go colourless faster
What is the expected result when investigating the effect of temperature on diffusion? (2)
Higher temperatures will make the cubes go colourless faster
Because molecules move faster at higher temperatures, increasing the rate of diffusion
