16.1. Passage of information from parents to offspring
A subsection of Biology, 9700, through 16. Inheritance
Listing 10 of 75 questions
As part of the technique of In-vitro fertilisation (IVF), several oocytes are collected from a woman who is undergoing treatment. Each oocyte is checked under a microscope. Explain why oocytes that have a first polar body are used in the fertilisation process. It is possible to freeze embryos that are produced by IVF, using a solution containing sucrose and various salts. The embryos can later be thawed and implanted. A trial was carried out to compare the success rates of freezing oocytes in • solution A, the same solution as is used for freezing embryos • solution B, a different solution containing different concentrations of sucrose and salts. Oocytes were placed into either solution A or solution B. They were then frozen and stored at a temperature of −33 °C. Later, the oocytes were thawed and then fertilised, using intracytoplasmic sperm injection (ICS. When the oocytes were placed into solution A or solution B, they quickly reduced in size. Explain why this happened. Table 5.1 shows the results of the trial. Table 5.1 number of oocytes frozen number of oocytes thawed number of oocytes that survived after thawing number of oocytes that underwent ICSI number of oocytes that were successfully fertilised solution A solution B With reference to Table 5.1, explain which solution is the better solution to use. Suggest one advantage of being able to freeze and thaw oocytes as part of the IVF procedure.
9700_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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Spermatogenesis takes place in the seminiferous tubules, in the testis. is a diagram showing some of the cells in a small sector of a seminiferous tubule. spermatogonium primary spermatocyte secondary spermatocyte spermatid spermatozoan On , state whether each of the labelled cells is haploid or diploid. Write n if the cell is haploid and 2n if the cell is diploid. Spermatogenesis involves meiosis, mitosis, growth and maturation. State which of these processes is involved in each of the following steps in spermatogenesis. spermatogonium to primary spermatocyte spermatid to spermatozoan State one role of a Sertoli cell. In some men, spermatogenesis does not take place successfully and the sperm that are produced are unable to fertilise an egg. A form of IVF called intra-cytoplasmic sperm injection (ICSmay enable them to father a child with their partner. In ICSI, a sperm cell is inserted into a secondary oocyte using a very tiny needle. Outline the treatment required in order to obtain mature oocytes as part of an IVF procedure. One approach to helping an infertile man to father children is to extract immature spermatids from his testes and culture them in the laboratory, in conditions that may increase the number of them that develop into functioning sperm. These can then be used for IVF. An investigation was carried out to see if adding reproductive hormones to a culture of immature spermatids affects their development. Samples of spermatids were collected from men in whom the spermatids did not normally develop into functioning sperm. The spermatids were cultured in a suitable liquid medium, kept at 30 °C. The samples were divided into four groups. No hormones were added to one group. FSH, testosterone or both were added to the other groups. The percentage of spermatids that developed into elongated cells in each group after 24 hours and 48 hours was calculated. The results are shown in Table 4.1. Table 4.1 hormones added percentage of spermatids that developed into elongated cells after 24 hours after 48 hours none FSH testosterone FSH and testosterone With reference to Table 4.1, describe the effects of adding reproductive hormones on the development of the spermatids after 48 hours. Suggest a reason for the apparent reduction in the percentage of elongated cells between 24 hours and 48 hours in some of the samples. Suggest why the culture medium was maintained at a temperature of 30 °C, and not at core body temperature (37 °C).
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
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Spermatogenesis takes place in the seminiferous tubules, in the testis. is a diagram showing some of the cells in a small sector of a seminiferous tubule. spermatogonium primary spermatocyte secondary spermatocyte spermatid spermatozoan On , state whether each of the labelled cells is haploid or diploid. Write n if the cell is haploid and 2n if the cell is diploid. Spermatogenesis involves meiosis, mitosis, growth and maturation. State which of these processes is involved in each of the following steps in spermatogenesis. spermatogonium to primary spermatocyte spermatid to spermatozoan State one role of a Sertoli cell. In some men, spermatogenesis does not take place successfully and the sperm that are produced are unable to fertilise an egg. A form of IVF called intra-cytoplasmic sperm injection (ICSmay enable them to father a child with their partner. In ICSI, a sperm cell is inserted into a secondary oocyte using a very tiny needle. Outline the treatment required in order to obtain mature oocytes as part of an IVF procedure. One approach to helping an infertile man to father children is to extract immature spermatids from his testes and culture them in the laboratory, in conditions that may increase the number of them that develop into functioning sperm. These can then be used for IVF. An investigation was carried out to see if adding reproductive hormones to a culture of immature spermatids affects their development. Samples of spermatids were collected from men in whom the spermatids did not normally develop into functioning sperm. The spermatids were cultured in a suitable liquid medium, kept at 30 °C. The samples were divided into four groups. No hormones were added to one group. FSH, testosterone or both were added to the other groups. The percentage of spermatids that developed into elongated cells in each group after 24 hours and 48 hours was calculated. The results are shown in Table 4.1. Table 4.1 hormones added percentage of spermatids that developed into elongated cells after 24 hours after 48 hours none FSH testosterone FSH and testosterone With reference to Table 4.1, describe the effects of adding reproductive hormones on the development of the spermatids after 48 hours. Suggest a reason for the apparent reduction in the percentage of elongated cells between 24 hours and 48 hours in some of the samples. Suggest why the culture medium was maintained at a temperature of 30 °C, and not at core body temperature (37 °C).
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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Use shows a section through part of a human testis. A B Name structures A and B. A ……………………………………………………… B ……………………………………………………… Spermatogenesis, the production of sperm, begins in the testes of a boy around the age of 11 and can continue for the rest of his life. outlines the sequence of events that occur during spermatogenesis. germinal epithelium spermatogonium cell division 1 stage C cell division 2 cell division 3 maturation cell D cell E cell F spermatozoan Examiner’s Use With reference to , state which cell division is mitotic, state which cells are haploid, state what is happening to the cell during stage C. The middle piece of a spermatozoan contains many mitochondria. Suggest why a spermatozoan needs so many mitochondria. Some couples have difficulty in conceiving. This could be due to a problem with either the male or female reproductive systems. Suggest reasons why a man may be infertile. Examiner’s Use In vitro fertilisation (IVF) is a widely used treatment for infertility. Explain what is meant by the term in vitro fertilisation. At one IVF clinic, over 1000 treatment cycles were monitored. The number of live births was recorded as a percentage of the number of treatment cycles for each age group. The results are shown in Table 5.1. Table 5.1 age of women/years percentage of live births per treatment cycle under 34 27.6 34 to 36 22.3 37 to 39 18.3 40 to 42 10.0 above 42 less than 5.0 The data in Table 5.1 show that there is a decrease in the percentage of live births per treatment cycle with increasing age. Explain this trend.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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Questions Discovered
75