IB Biology Paper 2 Section B Questions and Answers Already Passed

IB Biology Paper 2 Section B Questions and Answers Already Passed Draw a labelled diagram of the human adult male reproductive system. [5 marks] a. scrotum - shown around testes; b. testes/testis/testicles - shown inside scrotum; c. epididymis - shown adjacent to testis and connected to sperm duct; d. sperm duct/vas deferens - double line connecting testis/epididymis to urethra; e. seminal vesicle - sac shown branched off sperm duct (not off the urethra); f. prostate gland - shown positioned where sperm duct connects with urethra; g. urethra - shown as double line linking bladder to end of penis; h. penis - with urethra passing through it; Award [1] for each structure clearly drawn and labelled that conforms to the italicized guidelines given. Compare the processes of spermatogenesis and oogenesis. [8 marks] a. both produce haploid cells / both produce (mature/male/female) gametes b. both have mitosis at start/in epithelium / both involve mitosis and meiosis; c. both have cell growth before meiosis; d. both involve differentiation (to produce a specialised gamete); Oogenesis: a. eggs/ova produced in the ovaries b. process starts during development of embryo/fetus c. meiosis breaks occur in prophase I/ prophase II/ metaphase II d. cytoplasm split unequally / larger cell and smaller cells e. one cell/egg (per meiosis) / some become polar bodies f. one gamete (usually) at a time/per month/per menstrual cycle g. timing of release: on about Day 14/in middle of menstrual cycle/at ovulation h. stops at menopause Spermatogenesis: a. sperm (atozoa) produced in the testes b. process starts during puberty/adolescence c. no breaks in meiosis d. equal division of cytoplasm e. four sperm (per meiosis) / all cells become sperm f. many/far more/(hundreds of) millions daily/at a time gametes produced g. timing of release: continuously (from testis) / by ejaculation/intercourse h. goes on (throughout adult life/until death) Describe the consequences of the potential overproduction of offspring. [5 marks] a. more (offspring) than the environment can support / carrying capacity reached b. increased mortality/lower life expectancy/more deaths; c. competition (for resources) / struggle for survival; d. food/mates/nest sites/territory/other example of resource shortage / example of greater need; e. variation between members of population / example of variation; f. better adapted more likely to survive / converse; (reject Lamarckian statements such as those who adapt survive) g. better adapted reproduce / pass on (favourable) genes/traits / converse; h. natural selection / (survival of fittest) leads to evolution Outline the processes that occur during the first division of meiosis. [6 marks] a. (consists of) prophase, metaphase, anaphase and telophase; b. chromosome number halved/reduced/(diploid) to haploid; c. homologous chromosomes pair up/form a bivalent/synapsis in prophase; d. crossing over between non-sister chromatids/chromatids of different homologues; e. nuclear envelope breaks down (at end of prophase/start of metaphase); f. tetrads/bivalents/homologous pairs move to/align on equator/cell centre/on metaphase plate in metaphase; (accept homologous chromosomes without pairs if pairing has already been described) g. attachment of spindle fibres/microtubules to centromeres/kinetochores; h. (homologous) chromosomes separate/pulled to opposite poles in anaphase; i. nuclear envelopes reform/do not reform (because of meiosis II) in telophase; Accept the above points in a series of annotated diagrams. Reject answers with single chromatids forming pairs in metaphase or separating or moving to opposite poles in anaphase. Prior to cell division, chromosomes replicate. Explain the process of DNA replication in prokaryotes. [8 marks] a. DNA replication is semi-conservative; b. each (molecule formed) has one new strand and one from parent molecule; c. helicase uncoils DNA; d. helicase separates the two strands by breaking hydrogen bonds between bases; (reject unzips as an alternative to uncoils but accept as alternative to separates if breakage of hydrogen bonds is included) e. RNA primase adds primer / primase adds (short) length of RNA; f. DNA polymerase III binds to/starts at (RNA) primer; g. DNA polymerase (III) adds nucleotides/bases in a 5' → 3' direction; h. bases according to complementary base pairing / A-T and C-G; i. (leading strand) built up continuously (towards the replication fork); j. (lagging strand) built up in pieces/short lengths/Okazaki fragments; k. DNA polymerase I removes RNA/primers and replaces them with DNA; l. ligase seals gaps between nucleotides/fragments/makes sugar-phosphate bonds; m. nucleoside triphosphates provide the energy to add nucleotides; Accept the above points in annotated diagrams. Outline outcomes of the human genome project. [4 marks] a. complete human DNA/chromosomes sequenced; b. identification of all human genes / find position/map