Cell structure

Scientists investigated chloroplasts taken from leaf cells of the species Nicotiana tabacum.

The scientists took chloroplasts from leaf cells of a healthy plant and from leaf cells of a mutant plant.

Chloroplasts are contained in several different types of specialised cells in N. tabacum leaves.

What terms are used to describe an organisation of specialised cells in an organism when:

• all the cells are of one type

• the cells are of more than one type?

Cells of more than one type

Figure 12 shows images of chloroplasts from N. tabacum cells observed with an electron microscope.

Identify the parts labelled Q and R.

Use the images in Figure 12 to predict how photosynthesis could be affected in the mutant plants.

Justify your answer.

Scientists investigated the rate of photosynthesis in healthy plants and in mutant plants.

Table 6 shows the scientists’ results.

Chlorophyll a and chlorophyll b are two types of chlorophyll molecules used in photosynthesis.

The scientists’ results did not support what they predicted from Figure 12 (on page 28) would be the effect of the mutation on photosynthesis.

Use information in Table 6 to describe and explain the effect of the mutation.

Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue.

Describe the role of organelles in the production and release of enzymes by animal cells.

Do not include details of transcription in your answer.

Describe the structure of ATP.

Outline how named enzymes break down and resynthesise ATP.

The human disease, malaria, is caused by infection with a single-celled eukaryotic organism.

Figure 2 shows a diagram of Plasmodium vivax, one of the species that can cause malaria.

Other than the Golgi apparatus, name one structure in Figure 2 which shows that P. vivax is a eukaryote.

Describe two functions of the Golgi apparatus in a eukaryotic cell.

P. vivax evolved from a common ancestor in Africa. As humans migrated around the world, new strains of P. vivax evolved.

P. vivax is now extremely rare in Africa but there are several different strains of P. vivax in other parts of the world.

Figure 3 shows a phylogenetic diagram of the evolution of these different strains.

What does Figure 3 suggest is the order of human migration out of Africa?

Tick (✓) one box.

There are an estimated 229 million cases of human malaria worldwide per year. 94% of these cases are found in Africa, but are not caused by P. vivax. P. vivax does cause 61% of the cases of human malaria outside Africa.

Use this information to calculate the number of cases worldwide caused by P. vivax each year.

In Africa today, most of the human population are resistant to malaria caused by P. vivax.

Use your knowledge of natural selection to explain why this resistance is so common in Africa.

Following a body injury, bone marrow stem cells move to the site of damage and undergo cell differentiation.

Figure 5 shows how this differentiation occurs.

Suggest how SCFR is destroyed by a lysosome.

After a heart attack, cardiomyocytes (cardiac muscle cells) die, and become infarcted tissue. Infarcted tissue cannot contract.

Stem cells in bone marrow cannot move to the infarcted tissue and differentiate into cardiomyocytes. Scientists used laboratory rats to investigate if bone marrow stem cell transplants could be used to repair infarcted tissue resulting from a heart attack.

They split the rats into three groups.

• Control group did not get a transplant of bone marrow stem cells.

• c-KIT+ group got a transplant of bone marrow stem cells with a functioning c-KIT gene.

• c-KIT– group got a transplant of bone marrow stem cells with no functioning c-KIT gene.

After 9 days, the scientists measured the mean ventricular blood pressure of each of the three groups.

Figure 6 shows their results.

The differences between the groups were all statistically significant.

Using all of the information, suggest explanations for the results for the Control group and the c-KIT– group shown in Figure 6.

Nine days after transplantation, the c-KIT+ group showed that 68% of infarcted tissue was made up of new cardiomyocytes. The control group had no new cardiomyocytes.

Assuming that mean ventricular blood pressure is directly proportional to the number of cardiomyocytes, calculate the percentage of infarcted tissue that was made up of new cardiomyocytes in the c-KIT– group.

All new cardiomyocytes produced:

• Connexin-43, a channel protein that allows electrical impulses to pass between cardiomyocytes

• GATA-4, a transcriptional factor that stimulates the expression of genes for actin and myosin.

Suggest how production of Connexin-43 and GATA-4 could give the result seen in the c-KIT+ group in Figure 6 (on page 13).

Do not include details of transcription or translation in your answer.

Describe the structure and function of the nucleus.

Name the main polymer that forms the following cell walls.

Scientists investigated the effect of the number of fungal species in soil on the diversity of plant species.

Table 1 shows their raw data for soil containing 14 fungal species.

Suggest one reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity.

The scientists used this equation to calculate the plant species index of diversity.

where n = shoot biomass of each plant species and N = total shoot biomass of all plant species

Use this equation to calculate the index of diversity for the data in Table 1.

Index of diversity

Figure 1 shows the plant species index of diversity the scientists calculated when the soil contained 0, 1, 2, 4 and 8 fungal species.

Figure 1

Figure 1 not reproduced here due to third-party copyright restrictions

Sometimes farmers stop growing crops on an area of land to allow the natural ecosystem to recover. The plant species index of diversity of these areas previously used to grow crops is different from nearby land that has never been used to grow crops.

Suggest and explain how the plant species index of diversity would be different in these areas previously used to grow crops.

Use Figure 1 and your knowledge of the effect of farming on biodiversity in your answer.

Complete Table 3 to give three differences between DNA molecules and tRNA molecules.

Scientists investigated ribosomal RNA in liver cells.

Figure 10 shows the method they used to isolate the ribosomes from the liver cells. The detergent dissolves lipids.

The scientists broke open the cells to produce a suspension of cell contents.

Describe how the scientists would remove large organelles from this suspension of cell contents.

Explain the position of the bands of ribosomes in tubes A and B in Figure 10.

Describe how a sample of chloroplasts could be isolated from leaves.

Scientists grew two groups of plants:

control plants with all the inorganic ions needed

iron-deficient plants with all the inorganic ions needed but without iron ions.

After 1 week, the scientists measured the mass of protein and the mass of chlorophyll in the chloroplasts isolated from samples of leaves of these two groups of plants.

Table 4 shows the scientists’ results.

Some proteins found inside the chloroplast are synthesised inside the chloroplast.

Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell.

Structural difference

The ratio of protein to chlorophyll in control plants is 9:1

Use the information in Table 4 to calculate the ratio of protein to chlorophyll in iron-deficient plants.

The scientists also observed the chloroplasts from the samples of leaves using an electron microscope.

Figure 6 shows a chloroplast from a control plant (image A) and a chloroplast from an iron-deficient plant (image B).

Figure 6

This source has been removed due to third-party copyright restrictions.

Use Figure 6 to suggest why iron-deficient plants have a reduced growth rate.

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.

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.

Compare and contrast the structure and properties of triglycerides and phospholipids.

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.