5. The mitotic cell cycle
A section of Biology, 9700
Listing 10 of 324 questions
The photomicrographs in show stages of the mitotic cell cycle occurring in the root tip of the onion, Allium sp. They are all of the same magnification. Stages A to C are in the correct sequence and stages K to N are not in the correct sequence. stages in correct sequence stages not in correct sequence A B C K L N M Name stages A and C. A C Put stages K to N in the correct sequence, starting with the stage that immediately follows stage C. C Explain how the behaviour of the chromosomes and spindle during stage L in ensures that the two daughter cells will be genetically identical.
9700_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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Meristematic tissue is found in the growing region of plants, such as root tips. shows a section through the meristematic region of a root tip of onion, Allium cepa. H G F E magnification ×2200 D C B A Table 2.1 shows the numbers of cells in different stages of the cell cycle that were observed in sections of the meristematic regions of root tips of A. cepa. Table 2.1 stage of cell cycle one example of cell from number of cells counted in each stage replicate 1 replicate 2 replicate 3 mean interphase prophase metaphase anaphase telophase total Complete Table 2.1 by using the letters A to H from to identify one cell in each stage of the cell cycle. The total length of time taken for meristematic cells of A. cepa to complete one cell cycle at 25 °C is 12 hours. Using sections similar to the one in , the length of time spent in each stage of the cell cycle can be estimated. To obtain the estimate, the percentage of cells in that stage is calculated. Using the data in Table 2.1, calculate: • the percentage of cells in anaphase • the mean length of time in minutes for anaphase. Show your working. percentage of cells in anaphase = % mean length of time in anaphase = min State one event that occurs during cytokinesis in the cell cycle of plant cells, such as those shown in .
9700_w19_qp_23
THEORY
2019
Paper 2, Variant 3
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In the immune system, a plasma cell develops from an activated B-lymphocyte. Mature plasma cells synthesise and secrete antibody molecules. is a diagram of a transmission electron micrograph of a plasma cell. The plasma cell can be seen in greater detail using an electron microscope compared with using a light microscope. Describe the extra detail of the nucleus that can be seen using an electron microscope. Explain why cell structures, such as ribosomes and the rough and smooth endoplasmic reticulum, cannot be seen using a light microscope. The transition from the activated B-lymphocyte to the fully mature plasma cell requires a number of mitotic cell cycles to occur. This process, which is known as clonal expansion, results in a large number of genetically identical plasma cells. describes events, A to F, that occur during the mitotic cell cycle of the B-lymphocyte. A centrioles replicate B DNA polymerase catalyses the formation of phosphodiester bonds C condensation of chromosomes D nuclear envelope reassembles around each set of daughter chromosomes E centromeres move towards poles F chromosomes line up at spindle equator Table 4.1 lists the stages occurring during one cell cycle of the B-lymphocyte. These stages are not in the correct order. Table 4.1 stage of cell cycle correct letter from G2 phase metaphase F cytokinesis prophase S phase anaphase G1 phase telophase Complete Table 4.1 by writing the letter of the event described in that correctly matches the stage of the cell cycle listed. Leave a blank space if there is no matching description for the stage in the list. Use each letter once only. One of the letters in Table 4.1 has already been added for you. Clonal expansion also results in the production of memory B-lymphocytes. Explain the importance of clonal expansion and the production of memory B-lymphocytes in providing protection for a person against an infectious disease. Myasthenia gravis is an example of a disease where the immune system fails to distinguish between self and non-self. Explain what is meant by this statement.
9700_w20_qp_22
THEORY
2020
Paper 2, Variant 2
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Questions Discovered
324