Replication & Division of Nuclei & Cells (CIE A Level Biology)

Explain why this is not a suitable description for cells in interphase.

The length of the cell cycle can vary considerably between different tissues within the same organism and is carefully controlled by chemical signals such as cyclins. Suggest the importance of such control in mammals.

Fig. 1 represents an animal cell in the process of dividing.

Fig. 1

Other than reasons relating to cell structure, state two features of Fig. 1 that show that this is an animal cell and not a plant cell.

The genetic differences that occur within populations allow them to be more resilient to change in their environment. Suggest why organisms that reproduce asexually will be more susceptible to extinction if there is a change in their environment.

Describe the role of telomeres in chromosomes.

Telomerase is an enzyme that adds bases to the ends of telomeres. The antibiotic β-Rubromycin has a range of medical uses, one of which is as an inhibitor of human telomerase. Suggest how β-Rubromycin could be utilised as a cancer treatment drug

Skin cells complete the cell cycle in a very short amount of time. Suggest the advantage of this.

The average time required for a human skin cell to complete the cell cycle is 2 hours 50 minutes. Calculate the time required for one skin cell to multiply to produce 16 cells. Give your answer in minutes.

[1]

State the importance of stem cells in the human body.

[1]

Fig. 1 shows stem cells from different stages of human development.

Fig. 1

Contrast the stem cells of the zygote and the foetal/adult stem cells.

Embryonic stem cells taken from blastocysts are highly sought after in stem cell research and therapy.

Explain the potential use of these embryonic stem cells in stem cell therapy.

Specialised cells lose the ability to divide by mitosis.

Suggest how the activity of telomerase differs between stem cells and specialised cells

[1]

Explain your answer to part (i).

The risk of developing breast cancer was investigated in woman of different ages in the US.

Fig. 1 shows the results of this investigation.

Fig. 1

Describe the results of the investigation shown in Fig. 1.

Suggest two possible explanations for the results seen in Fig. 1.

Tumours can be either benign or malignant.

Contrast benign and malignant tumours.

Describe the stages in the development of cancer.

The response of the human body to tissue damage depends on the types of tissues involved. Epithelial tissue, liver tissue and cardiac muscle tissue each respond differently to damage.

• Epithelial tissue of the gas exchange system contains stem cells.
• Liver tissue contains cells in a non‐dividing state that can enter a cell cycle when stimulated.
• Cardiac muscle tissue contains cells that cannot divide at all. Damage is permanent and is associated with scar tissue formation.

Explain the importance of mitosis in the repair of damaged tissue.

Explain why stem cells are important in tissue repair.

Following liver tissue damage, chemicals are produced and released into the circulation. These chemicals are able to stimulate the liver cells to help tissue repair.

Explain how this is an example of cell signalling.

Fig. 1 is a diagram of a monomer of the nucleic acid, messenger RNA.

Telomerase is not present in prokaryotic cells.

Suggest why prokaryotes do not have telomerase.

One of the ways to diagnose lung cancer is to determine the concentration of telomerase in cells from the lining of the bronchus.

Explain why determining the activity of telomerase may be useful in the diagnosis of lung cancer.

Bowel cancer can result from adenoma polyps. Adenoma polyps form as a result of mutations occurring in dividing cells of the colon lining.

Suggest the differences in the cell cycle of a cancer cell compared with that of a normal intestinal cell.

Compare and contrast the process of cytokinesis in plants and animals.

Before the cell progresses from G₁ into S phase, it needs to pass through a checkpoint, which prevents the cell cycle from proceeding if certain conditions are not met. Suggest one reason why a cell might not progress through the checkpoint.

Fig. 1 below shows data produced from a flow cytometer. This measures the number of cells that are labelled with DNA bound to a fluorescent dye, as this is proportional to DNA content. The stages of the cell cycle are indicated.

Fig. 1

Suggest why, during the S phase, that the amount of DNA per cell is between 2n and 4n.

A team of biologists estimated the number of cells in different phases of the cell cycle in Saccharomyces cerevisiae (brewer's yeast). They took two samples, A and B, from different environmental conditions. One sample came from a nutrient-rich environment, the other from a nutrient-poor environment.

Their results are shown in Table 1.

In sample A, a full cell cycle took 1 hour and 35 minutes, whereas, in sample B, a full cell cycle took 60 minutes. 

Calculate the time, in minutes, that the cells in sample A were in S phase during one cycle. Show your working.

The biologists studying the Saccharomyces cerevisiae (brewer's yeast) from part (a) hypothesised that when the yeast was exposed to stressful conditions, the growth rates were low. 

Suggest, with a reason, which sample came from the nutrient-rich conditions.

The availability of nutrients is also a key factor in regulating the cell cycle of Schizosaccharomyces pombe (fission yeast).  Below is Table 2 containing data scientists collected for two sites which were deficient in nitrogen and phosphate. 

Table 2

Deduce, giving a reason, the point at which a nutrient-poor environment would stop the cell cycle of the Schizosaccharomyces pombe.

The Saccharomyces cerevisiae (brewer's yeast) nuclei are, on average, 2 µm in diameter, but the DNA molecules packed into them have been measured up to 355 µm in length. 

Describe the process that enables the DNA molecules, that comprise the 16 chromosomes of yeast, to be packed into the nuclei.