Mitosis and the cell cycle Exam Questions And Answers

Describe the role of the centromere in mitosis - ANS 1. Holds chromatids together 2. Attaches chromatids to the spindle 3. Allows chromatids to be separated Homologous chromosomes carry the same genes but they are not genetically identical. Explain why. - ANS Homologous chromosomes carry different alleles Figure 2 shows three pairs of homologous chromosomes in a cell at the end of cell division. How does the appearance differ to a pair of homologous chromosomes. - ANS 1. Chromatids have not separated/replicated Mitosis is important in the life of an organism. Give two reasons why. - ANS 1. Growth - increase in cell number 2. Replace cells - repairing tissue/organs 3. Asexual reproduction Explain why the biologist chose to examine 200 cells. - ANS 1. Ensures representative sample 2. Maximises chances of seeing cells that are dividing If the DNA of the cell is damaged, a protein called p53 stops the cell cycle. Mutation in the gene for p53 could causes cancer to develop. Explain how. - ANS 1. Cancer cells often have faulty/damaged DNA 2. Protein p53 faulty/not made 3. Cell with faulty/not made DNA divides 4. Uncontrolled division produces cancer Drugs are used to treat cancer. At what phase in the cell cycle would each of the following drugs act? i) A drug that prevents DNA replication ii) A drug that prevents spindle fibres shortening - ANS i) interphase ii) anaphase In prophase of mitosis, the chromosomes become visible. Describe what happens in i) metaphase ii) anaphase - ANS i) Chromosomes line up along equator of cell Chromosome attaches to spindle by centromere ii) Centromere divide Chromatid pairs split in two and pulled to opposite ends of the cell Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time - ANS 1. Lots of friction therefore cells damaged more easily and faster 2. So cells need to be replaced quicker The time required for a cell to complete the cell cycle was 4 hours and 18 minutes. calculate the time required in minutes for this cell to multiply to produce eight cells. Show your working. - ANS 4 x 60 = 240 240 + 18 = 258 258 x 3 = 774 minutes Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer. - ANS 1. Prevents/slows DNA replication 2. New strand isn't going to be formed 3. Nucleotides aren't going to be put together Suggest an explanation for doubling of chromosome number - ANS DNA replications has occurred but no separation of chromatids Suggest one reason for the lower number of cancer cells compared to healthy cells at the end of the first week. - ANS More cancer cells killed and therefore cancer cells divide more often Describe two differences in the effect of the drug on the cancer cells, compared with healthy cells in the following weeks. - ANS 1. cancer cells take longer to recover 2. Slower rate of mitosis 3. Dividing more slowly Describe how HIV is replicated after it has entered a human cell - ANS 1. Reverse transcriptase 2. Responsible for production of complementary DNA 3. Produces DNA that can be inserted into the host cell genome. 4. Protein synthesis causes production of new vital proteins e.g. capsomeres 5. Assembly of new virus particles budding off from membrane of host cell During metaphase of mitosis, the chromosomes become attached to the equator of the spindle. Name the stage of mitosis that follows metaphase and describe the events that occur in this stage - ANS 1. Anaphase occurs 2. centromere divides and sister chromatid pairs are split in two 3. Spindles contract, pulling chromatids to opposite ends of the cell Chlamydomonas lives in fresh water ponds. Use your knowledge of osmosis to suggest an advantage of using starch as a carbohydrate store - ANS 1. Starch is insoluble 2. Therefore stops water entry (water potential unaffected) Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue - ANS 1. Break open cells and remove debris 2. Solution is cold/isotonic/buffered (Stops enzyme reactions from happening and keeps pH balanced 3. The second pellet is chloroplast Name two structures in a eukaryotic cell that cannot be identified using an optical microscope - ANS 1. Lysosomes 2. Ribosomes