Biology for CAPE Unit 1 Chapter 11 Answers

    Biology for CAPE Original material © Cambridge University Press 2011 1   11 Answers to end-of-chapter questions 1 C [1] 2 B [1]  3 B [1]  4 C [1]  5 C [1]  6   B  [1] 7   C  [1] 8   D [1] 9 C [1] 10 C [1] Structured questions 11 a  I – fibrous layer II – vascular bundle III – tapetum IV – filament V – inner layer of fibrous layer 2 labels [1]   VI – pollen mother cells / developing pollen grains [max 3] b  Length of scale bar = 6 mm Therefore 6 mm = 200 μ m Length from A to B = 104 mm Complete calculation [1] Actual length = 104/6 ×  200 = 3467 μ m Partial [1] c •   Pollen mother cells undergo meiosis •   Each produces a tetrad of 4 haploid cells •   Cells absorb nutrients from tapetum •   Cells increase size •   Secretion of exine / outer walls •   Pollen grains separate •    Nucleus of each pollen grain divides by mitosis •   Produces generative and pollen tube nuclei Every 2 points [1] •   Exine complete their development [max 4] d Meiosis occurs •   Produces gametes which contain haploid number of chromosomes   •   This is important because in sexual reproduction fertilisation of gametes occurs   •   This allows for restoring of chromosome number / maintenance of a constant chromosome number / meiosis allows the chromosome number to remain constant in each generation 3–4 points [2] •   Crossing over leads to genetic variation 1–2 points [1] e    Biology for CAPE Original material © Cambridge University Press 2011 2   Well drawn [2] Labels [2] 12 a I – pollen tube   II – locule III – nucellus IV – antipodal cells V – primary endosperm nucleus VI – egg cell 8–9 points [4] VII – synergids 6–7 points [3] VIII – funicle 4–5 points [2] IX – placenta 2–3 points [1] b Each point [1] c •   Both serve as attachment points •   VIII attaches ovule to ovary wall  / IX attaches ovary to rest of plant Any point [1] d •   Haploid nucleus of pollen grain divides by mitosis •   Produces 2 nuclei – generative and pollen tube (B) •   The generative nucleus then divides by mitosis to give 2 male 4 points [3] gametes (A) 3 points [2] •   Both A and B are haploid 2 points [1] e Micropyle allows pollen tube to enter the ovule so fertilisation can take place [1] f •   C / ovary becomes the fruit [1] •   D / integuments become the testa [1] g  See diagram above / should be through the locule, close to ovary wall Each point [1] ovule embryo sac    Biology for CAPE Original material © Cambridge University Press 2011 3   13 a i Meiosis [1] ii • Three of the four cells / megaspores nearest the micropyle degenerate [1]   •   Leaving one megaspore to develop [1] iii Haploid ( n ) / one set of chromosomes [1] iv Mitosis occurs three times [1] v 3 antipodal 2 polar 4 points [3] 2 synergids 3 points [2] 1 egg nucleus 2 points [1] vi Generative [1] vii 2 male nuclei [1] 1 pollen tube nucleus [1] b   • Separation of male and female plants / dioecious •   Eg marijuana, pawpaw, chenet •   Monoecious / separation of male and female flowers but on same plant •   Eg castor oil, corn, pumpkin •   Protandry / anthers mature before stigma •   Eg rose-bay willow herb, fireweed •   Protogyny / stigmas mature before anthers •   Eg avocado, soursop •   Self-incompatibility / if pollen grain with same allele as stigma, does not germinate •   Eg tobacco, cabbage Any mechanism [1] •   Heterostyly: specialised pollination structures, pin and thrum example [1] •   Eg red cordial, primrose [max 4] Essay questions 14 a Self-pollination Asexual •   meiosis occurs •   mitosis occurs •   some genetic variation in offspring / crossing over •   genetically identical offspring / clones •    produces gametes •   no gametes produced •   fertilisation •   no fertilisation •    produces seeds •   no seeds produced •   uses gametes / reproductive •   uses vegetative structures to multiply Each comparison [1] [max 3]  b i • Self-fertilisation   •   Since plants are widely scattered, would not be close to other  plants to pollinate / pollinating agents scarce •    No wastage of gametes •   Plants would be well adapted to the environment •   Can also be asexual