Eukaryotic & prokaryotic cells

Name three structures that are found in some prokaryotic cells but are not found in all prokaryotic cells.

Table 3 shows the resolution of three types of microscope.

Table 4 shows information about yeast cells and mitochondria.

Identify the correct microscope to use in each of the following investigations.

Use your knowledge of microscopes and information in Table 3 and Table 4.

Give two reasons for each choice of microscope.

Investigation 1 – to study the living cells in a yeast culture that contains both living cells and dead cells. The living cells remain colourless and the dead cells are stained blue when a dye is added.

Type of microscope

Investigation 2 – to observe the three-dimensional structure of mitochondria.

Type of microscope

Give the three structural features found in all virus particles and describe the function of one of these features.

Function of one named feature

Explain why viruses are described as acellular and non-living.

Give one reason why antibiotics are not effective against viruses.

Below are four statements about the structure of prokaryotic cells.

1. No prokaryotic cell has DNA that is associated with proteins.

2. No prokaryotic cell has membrane-bound organelles.

3. All prokaryotic cells have one or more flagella.

4. All prokaryotic cells have smaller ribosomes than eukaryotic cells.

Which statements about the structure of prokaryotic cells are correct?

Tick () one box.

A student investigated the effect of two antibiotics on the growth of the bacterium Micrococcus luteus.

During the investigation, the student:

• transferred 9 cm³ of a liquid culture of M. luteus into each of three bottles

• added the antibiotic chloramphenicol to the first bottle

• added the antibiotic novobiocin to the second bottle

• added no antibiotic to the third bottle.

After 24 hours, he diluted the contents of each bottle by 1 in 100 000 (10^–5). He then transferred 0.25 cm³ samples from the first bottle onto each of 3 separate agar plates. He repeated this with 0.25 cm³ samples from the second bottle and the third bottle, resulting in 9 agar plates in total.

He incubated the plates for 48 hours.

Table 1 shows the number of colonies of bacteria he counted on each plate after 48 hours’ incubation.

Calculate the mean number of bacteria in the undiluted bottle of liquid culture containing novobiocin.

Give your answer in standard form. Show your working.

Starting with a single bacterium, calculate how many generations it would take to produce at least the number of bacteria you have calculated for your answer in Question 03.2

You can assume no bacteria die.

You could use the ln or log button on your calculator to calculate your answer.

M. luteus is not resistant to chloramphenicol.

Suggest two reasons why the bacteria were able to grow in the culture containing chloramphenicol.

Give two features of all prokaryotic cells that are not features of eukaryotic cells.

Many multicellular organisms produce antimicrobial polypeptides (APs) that protect them against prokaryotes. Figure 3 shows how one type of AP acts on the cell-surface membrane of prokaryotes.

This AP has a secondary structure in a helical shape.

Tick () the box to show which type of bond maintains the helical structure of the polypeptide.

The amino acids on one side of each AP helix have hydrophobic properties. The amino acids on the opposite side of each helix have hydrophilic properties. Figure 4 shows this.

Suggest how these properties of the APs allow them to become positioned across the membrane (as shown in Figure 3) and make a channel through which ions can pass.

Figure 5 shows further information about a channel formed in the cell-surface membrane by the APs.

Use Figure 5 to calculate the cross-sectional area of the channel through which ions can pass. Assume the cross-sectional area is circular. Use π = 3.14 in your calculation. Give your answer in nm² and to 1 decimal place.

The APs damage prokaryotic cells but do not damage the eukaryotic cells in the organisms that produce them. Prokaryotic cell membranes do not contain cholesterol.

Assess why the APs do not damage the eukaryotic cells of the organisms that produce them.

Scientists observed these APs on prokaryotes using a transmission electron microscope. They stained the APs using a monoclonal antibody with gold attached to it.

Suggest how these techniques allowed observation of APs on prokaryotes.

Describe the structure of DNA.

Name and describe five ways substances can move across the cell-surface membrane into a cell.

Figure 14 shows transmission electron micrographs of two cells, one animal cell and one prokaryotic cell.

Contrast the structure of the two cells visible in the electron micrographs shown in Figure 14.

In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group.

Previously, the viruses infected only one species of frog.

Suggest and explain how the viruses became able to infect other species of frog.

Name two techniques the scientists may have used when analysing viral DNA to determine that the viruses were closely related.

Determining the genome of the viruses could allow scientists to develop a vaccine.

Explain how.

Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus.

You can assume that the B lymphocytes of a frog respond in the same way as B lymphocytes of a human.

Do not include details of the cellular response in your answer.

Table 1 shows cell wall components in plants, algae, fungi and prokaryotes. Complete Table 1 by putting a tick (✓) where a cell wall component is present.

Cell walls make up much of the fibre that people eat.

Scientists investigated the relationship between the mass of fibre people ate each day and their risk of cardiovascular disease (CVD).

They gathered data from a large sample of people and used this to calculate a relative risk.

A relative risk of 1 means there is no difference in risk between the sample and the whole population.

A relative risk of < 1 means CVD is less likely to occur in the sample than in the whole population.

A relative risk of > 1 means CVD is more likely to occur in the sample than in the whole population.

Their results are shown in Figure 3. A value of ± 2 standard deviations from the mean includes over 95% of the data.

A student concluded from Figure 3 that eating an extra 10 g of fibre per day would significantly lower his risk of cardiovascular disease.

Evaluate his conclusion.

The scientists estimated the mean mass of fibre eaten per day using a food frequency questionnaire (FFQ).

The FFQ asks each person how often they have eaten many types of food over the past year.

An alternative method to calculate fibre eaten is for a nurse to ask each person detailed questions about what they have eaten in the last 24 hours.

Suggest one advantage of using the FFQ method and one disadvantage of using the FFQ method compared with the alternative method.

Bacteriophages are viruses that kill bacteria.

Figure 2 shows drawings of a bacteriophage and a bacterium.

Using Figure 2 and your own knowledge, put a tick () in the box next to the only correct statement about the structures of the bacteriophage and the bacterium.

Using the scales in Figure 2, calculate how many times longer the bacterium is than the bacteriophage.

Use the distance between the points labelled A and B on each drawing in your calculations. Show your working.

Scientists investigated the use of bacteriophages to treat lung infections caused by bacteria. They infected the lungs of mice with a pathogenic species of bacterium. The mice were then divided into two groups, A and B.

The mice in group A were not treated with bacteriophage.

The mice in group B were treated by breathing in a spray containing bacteriophage particles.

After 3 days, the scientists killed the mice and removed their lungs. They washed out each set of lungs with a set volume of liquid. The scientists determined the number of live bacteria in the liquid.

Figure 3 shows the scientists’ results. Figure 3 shows the mean and the range of the data about the mean for each group. Standard deviations of the means are not shown.

What would the scientists’ null hypothesis be for this investigation?

With some samples, the scientists decided they needed to carry out a series of dilutions of the sample before counting the bacteria.

Use evidence from Figure 3 to explain why dilutions were necessary for some samples but not for others.

Using only Figure 3, what can you conclude from these data about the effectiveness of the bacteriophage in treating this lung infection in mice?

Do not consider statistical analyses in your answer.