Cell membrane structure

Use the following information to answer questions 14 and 15.

Beetroot cell vacuoles contain a red pigment.

Some students are investigating the effect of ethanol on the permeability of plant cell membranes.

This is the method that they use:

• Soak identical pieces of beetroot for 30 minutes in different concentrations of ethanol.

• After 30 minutes, measure the redness of the ethanol solution using a colorimeter.

The graph shows the students’ results. Each data point shows the mean ± 2 standard deviations.

One student made the following observations:

1 Ethanol disrupts the cell membranes leading to increased permeability. 2 The permeability of the cell membranes is proportional to concentration of ethanol between 0% and 50% ethanol. 3 The cell membranes are completely disrupted in 60% ethanol.

Which observation(s) is / are correct?

A 1, 2 and 3 are correct

B Only 1 and 2 are correct

C Only 2 and 3 are correct

D Only 1 is correct

Your answer

Use the following information to answer questions 14 and 15.

Beetroot cell vacuoles contain a red pigment.

Some students are investigating the effect of ethanol on the permeability of plant cell membranes.

This is the method that they use:

• Soak identical pieces of beetroot for 30 minutes in different concentrations of ethanol.

• After 30 minutes, measure the redness of the ethanol solution using a colorimeter.

The graph shows the students’ results. Each data point shows the mean ± 2 standard deviations.

The students were asked to decide whether the permeability of the membrane is significantly greater with 50% ethanol compared to 40% ethanol.

Which statistical test should they use?

B Spearman’s rank correlation coefficient

C Standard deviation

D t-test

Your answer

Organisms can be ectotherms or endotherms.

Define the term endotherm.

Suggest one advantage and one disadvantage that ectotherms have compared to endotherms.

* During a class discussion, one student stated:

‘Ectotherms cannot control their body temperature.’

Another student stated:

‘Ectotherms control their body temperature by behavioural responses, but endotherms do not.’

Discuss, using examples, whether these two statements are correct.

Additional answer space if required.

Infection by pathogens such as bacteria and viruses often causes release of pyrogens into the blood.

Pyrogens stimulate the enzyme COX-2 to produce the compound PGE₂.

PGE₂ binds to receptors in the hypothalamus and this results in an increase in the thermogenic set point.

Suggest the consequences of an increase in the thermogenic set point.

PGE₂ receptors are located on the cell surface membrane.

State two functions of the cell surface membrane that are illustrated by the action of PGE₂.

Chromista are photosynthetic protoctists that live in water.

Chromista are different from other photosynthetic organisms because they contain the pigment chlorophyll c.

Chlorophyll c is not found in plants.

Outline the importance of photosynthetic pigments in photosynthesis.

The wavelengths of light absorbed by chlorophyll c are different from those wavelengths absorbed by chlorophyll a and chlorophyll b.

Suggest why Chromista need pigments that are different from those of other photosynthetic organisms.

Fig. 17.1 is a diagram of the chloroplast found in a Chromista cell.

Outline the structural differences between the Chromista chloroplast in Fig. 17.1 and the chloroplasts found in flowering plants.

Fig. 17.2 is a diagram of part of the plasma membrane of a Chromista cell.

State and explain how one property of region A in Fig. 17.2 contributes to the stability of the plasma membrane.

There are differences between the plasma membrane and membranes within cells.

Outline the role of membranes within cells.

A student carried out an investigation into the effect of ethanol on the permeability of cell membranes in beetroot.

The student’s method comprised the following five steps:

Each step in the student’s method relies on certain assumptions.

For each assumption listed below, select the numbered step from the student’s method that relies upon that assumption.

Assumption A

Pigment will only leak into the solution if membranes are disrupted.

Assumption A relates to step ………….

Assumption B

Absorbance is proportional to concentration of pigment.

Assumption B relates to step ………….

Assumption C

Pigment will be released when the beetroot is sliced.

Assumption C relates to step ………….

The student kept the ethanol solutions at a constant temperature. State two other variables which need to be controlled in this investigation to ensure the data collected are valid.

Fig. 20.1 shows the graph plotted by the student.

Make three criticisms of the way the student has displayed these results.

Explain how carrying out replicates would improve this investigation.

Membranes are found within and surrounding cells.

Which of the statements, A to D, is not a role of membranes in cells?

A acts as a barrier between areas

B cell signalling

C provides support for cell

D site of chemical reactions

Your answer

The diagram below shows part of a plasma membrane.

Which of the label lines points to a structure that could contain a sulfur atom?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer