Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
6 Sexual reproduction in mammals and plants Answers to Exam practice questions 1 A and B [1] 2 D [1] 3 C [1] 4 a) Structure A B Name Tail/flagellum Middle piece/collar C Head Function Enables sperm to swim Carries mitochondria/produces ATP/provides energy (for swimming) Carries chromosomes/carries DNA/has hydrolytic enzymes For B, do not allow ‘produces energy’ [6] b) Width of head measured as 10 mm = 10 000 μm; Correct calculation using: magnification = size of image size of object = 10000 3 = × 3333.3 ; [2] 5 a) (Petal of flower) = 44; (Zygote) = 44; (Endosperm) = 66; [3] b) Nucleus formed by fusion/fertilisation of one male gamete and two polar nuclei; All three nuclei are haploid/contain 22 chromosomes; [2] 6 a) Capacitation of sperm must occur before sperm are able to fertilise secondary oocyte; Capacitation) occurs in uterus/in oviduct; (Without capacitation) glycoproteins remain on head of sperm; (Without capacitation) no acrosome reaction occurs/no hydrolysis of zona pellucid; [4] b) Any four of the following points: • The cortical reaction; • Meiosis II is completed; • Cleavage divisions produce more cells/blastomeres; • Solid ball of blastomeres; • Blastocyst is formed as a hollow ball of cells; • (Blastocyst contains) inner cell mass and outer trophoblasts; Credit appropriate descriptions of cortical reaction and meiosis II [4] © Hodder & Stoughton Limited 2015 6 Sexual reproduction in mammals and plants Answers to Exam practice questions 7 a) Embryos and endosperm contain variable amount of water; (Without water) can make valid comparisons of mass; [2] b) Heat to a temperature that evaporates water but does not burn the embryos or endosperm; Until mass is constant; Credit heat to any temperature between 80 °C and 100 °C [2] c) Subtract mass of embryo at day 0 from mass of embryo at day 4 and divide by 4; -1 (Give value as) g per day/g day ; st Credit (6.9 – 5.1) ÷ 4 as equivalent to 1 marking point [2] d) Growth of embryo uses amino acids to produce new protein/β-glucose to produce new cellulose; Growth of embryo uses ATP/energy from respiration; Endosperm depleted as sources of amino acids/β-glucose/respiratory substrates used up; [3] 8 a) Pin-eyed have longer style/higher stigma than thrum-eyed; Position of anthers in pin-eyed is halfway down the flower, in thrum-eyed anthers are near the top of the flower; b) i) [2] Cross pollination occurs when pollen from one plant lands on stigma of another plant; Pollen from thrum-eyed flower sticks to top of bee’s mouthparts; This pollen is not at the same level as this flower’s stigma; If bee visits a pin-eyed plant, the pollen is at the same level as this flower’s stigma; Allow converse descriptions of pollen sticking to mouthparts of a bee that visits a pineyed flower ii) [4] Reduces likelihood of mutant alleles/alleles that are detrimental becoming homozygous; Since half of plant’s gametes likely to contain a copy of the detrimental allele; Maintains genetic diversity in population; [3] Stretch and challenge questions 8 9 a) 3.4 × 10 . 340 million is not acceptable, since an answer in standard form was required. b) Chance of any sperm reaching the secondary oocyte is small; because uterus/oviduct is –3 hostile to sperm. With only 20 000 sperm mm , it is unlikely that any of this man’s sperm will reach the secondary oocyte stage. c) He is possibly fertile; since his fertility index is 10. © Hodder & Stoughton Limited 2015 6 Sexual reproduction in mammals and plants Answers to Exam practice questions 9 a) Use an eye-piece graticule; calibrated using a stage micrometer. b) The length of the pollen tubes increases in (direct) proportion to time; the range of lengths/variation in length increases as the tubes get longer. c) Pollen tube growth involves production of new proteins; the difference between the normal growth medium and the medium with actinomycin D is likely to be due to chance/not (statistically) significant; because the standard deviations overlap; with actinomycin D, the pollen tube is using mRNA (for protein production) already present in the pollen grain/is not producing new mRNA; with cytochalasin, the existing mRNA cannot be translated/cannot be used by ribosomes to produce new protein (for growth). © Hodder & Stoughton Limited 2015