OCR A biology 2020 depth (as level) paper & 2020 paper 2 november mark scheme., Exams of Biology

Download OCR A biology 2020 depth (as level) paper & 2020 paper 2 november mark scheme. and more Exams Biology in PDF only on Docsity! N20/4/BIOLO/HP2/ENG/TZO/XX/M 13 pages Markscheme November 2020 Biology Higher level Paper 2 a PC Macey icy Programme du dipl6éme eerste Rs 0) ley -2- N20/4/BIOLO/HP 2/ENG/TZO/XX/M No part of this product may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems, without written permission from the IB. Additionally, the license tied with this product prohibits commercial use of any selected files or extracts from this product. Use by third parties, including but not limited to publishers, private teachers, tutoring or study services, preparatory schools, vendors operating curriculum mapping services or teacher resource digital platforms and app developers, is not permitted and is subject to the IB’s prior written consent via a license. 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(Question 1 continued) N20/4/BIOLO/HP 2/ENG/TZO/XX/M d i Montreal because it has the lowest number of days below 0°C without snow cover; Do not award the mark 1 for Montreal if the reason is not given d ii | a cities with more days without snow cover have positive correlation between distance 2 max from city center and HCN / vice versa for Montreal; b fewer plants with HCN within cities that have more days without snow cover/have more exposure to freezing temperatures / converse for Montreal which has fewer days without snow cover; c HCN is 0.2 (or less) HCN in cities that have more days without snow cover proportion whereas city with fewer days/Montreal it is 0.5/more than 0.4; d_ in Toronto cyanogenic and non-cyanogenic plants show little difference in herbivory; e support for hypothesis/exposure to freezing temperatures as reason; Do not accept ‘Yes’ unqualified as an answer, but accept it if supported by reasoning e i hours of daylight/light intensity/soil pH/soil nutrients/mineral nutrients/watering Mark the first answer 1 regime/humidity/ /population plants came from/location plants were adapted to/duration of | given only. Reject cold period/ nutrition and sunlight /size of plant pot/size of plant/wind speed/carbon dioxide concentration; unqualified. Reject number of plants. e ii | Lowest: non-cyanogenic and_produces A; Do not accept 2 Highest: non-cyanogenic and produces neither (chemical); genotypes (continued...) (Question 1 continued) N20/4/BIOLO/HP 2/ENG/TZO/XX/M e iii Comparing the first and second bar with the third and fourth: a_ higher survival with aa than Aa / allele/gene A lowers survival; b higher survival if substrate/chemical A not produced / substrate/chemical A lowers survival; Comparing the first bar with the second: c no significant difference between A_L_ and A_Il /if Ais present LA doesn't affect survival; d conversion of substrate/chemical A to cyanide does not affect survival; Comparing the fourth bar with the third: e higher survival with aall than aaL_/if Ais not present L reduces survival; f lowers survival if chemical L/enzyme produced even if substrate/chemical A not produced; Comparing the fourth bar with the other three: g_ highest survival with aall/homozygous recessive h_ chemicals A and L/substrate and enzyme both lower survival; Do not accept L decreases survival unqualified as it does not for plants with allele A. Do not accept lower survival in A_II than A_LI as the difference is unlikely to be significant. Do not accept ranking the four genotypes in order of survival probability without more analysis. Accept any of these points if given as the converse, for example for mph ‘highest survival without either chemical. Accept ‘withstand freezing’ in place of ‘survival’ in any mark point. 3 max N20/4/BIOLO/HP 2/ENG/TZO/XX/M i a_ part hydrophobic/not attracted to water/non-polar AND part hydrophilic/attracted to Do not allow water 2 max water/polar; lovingMating in mpa or b bilayer formed (formed naturally by phospholipids in water); mpc c hydrophilic heads/parts face outwards and hydrophobic tails/parts face inwards; ii | a controls/regulates/reduces fluidity of membrane / prevents crystallization of Do not accept ‘stabilizes | 1 max phospholipids; membrane’ b reduces permeability to some substances; a nuclear membrane breaks down/disappears (in prophase/at start of mitosis); 2 max b nuclear membrane reforms around two new nuclei (in telophase/at end of mitosis); c plasma membrane pulled inwards at equator / cleavage furrow formed; d membrane pinches apart to form two cells / cytoplasm divided / cytokinesis; i synapse/synaptic Allow any answer 1 max including either of these terms unless out of context ii | a depolarization of pre-synaptic membrane / action potential/nerve impulse arrives; 3 max b uptake of calcium / calcium ions diffuse in / calcium channels open; c_ structures containing neurotransmitter/vesicles move to/fuse with membrane; d neurotransmitter/acetylcholine released by exocytosis into cleft/binds to postsynaptic membrane/receptors; Must see exocytosis -10- N20/4/BIOLO/HP 2/ENG/TZO/XX/M Section B Clarity of communication: [1] The candidate’s answers are clear enough to be understood without re-reading. The candidate has answered the question succinctly with little or no repetition or irrelevant material. Question Answers Notes Total a a two amino acids correctly drawn; nH BR Uo HB Uo 3 b — removal/production of H2O molecule shown; ee ey c_ peptide bond labelled between C of C=O and N of N-H; H + 4 oH Hm RR WE 0 DN-C4G=NE-C—Cy H20 H I 1 OH H | H Peptide Bond Accept specific examples of amino acids correctly drawn for example glycine with H instead of R mpc can be awarded if the peptide bond is shown as in the dipeptide diagram but there are errors elsewhere b a digested by peptidases/proteases; Peptidase can be accepted instead of endopeptidase in | 4 max b pepsin/pepsinogen/endopeptidase secreted by mpc, but not in mpb or mpd stomach (lining)/digests proteins in stomach; Cc pancreas secretes/pancreatic juice contains endopeptidase/trypsin/peptidase; d endopeptidase digest proteins/polypeptides to shorter chains of amino acids/shorter peptides; e amino acids absorbed by active uptake/transport; f — in small intestinefleum; g__ villi increase the surface area for absorption; h_ absorbed into bloodstream/into capillaries; (continued...) -11- N20/4/BIOLO/HP 2/ENG/TZO/XX/M (Question 6 continued) 6 c a mRNA is translated; Marks can be awarded in an annotated diagram 8 max b mRNA binds with ribosome/with small subunit of ribosome; Accept UAA, UAG or UGA instead of stop codon in c tRNA-activating enzymes/aminoacyl tRNA synthetases | mpm or mpn but do not accept terminator sequence. attach specific amino acid to tRNA; Do not award mpk for the ribosome moving to the start d anticodon of 3 bases/nucleotides on tRNA; codon in a 5’ to 3’ direction. e — start codon/AUG on mRNA; f tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds); g _ anticodon (on tRNA) binds to codon (on mRNA); h complementary base pairing (between codon and anticodon): i tRNA for next codon binds to A site/amino acyl site; J peptide bond forms between amino acids (on tRNAs) at P and A sites; k ribosome moves along MRNA to next codon/by three bases/in 5’ to 3'direction; | tRNA released from E/exit site; m_process/cycle repeats to elongate the polypeptide/until stop codon is reached; n_ release of polypeptide and mRNA/disassembly of ribosome complex at stop codon; -12- N20/4/BIOLO/HP 2/ENG/TZO/XX/M a water (molecules) are polar/dipolar/have partially positive and negative poles/have 5+ and _ | Marks can be 3 max 5-; awarded in an b attraction/bonding between positive and negative (poles); annotated diagram c hydrogen bond formed between hydrogen and oxygen; Reject if H and O in same molecule | Reject answers d__ bond/attraction between different water molecules/intermolecular; Stating or implying that there are whole positive or negative charges for mpa a water moved/transported in xylem vessels; Do not award 4 max b transported under tension/suction/pulled up (in xylem vessels); marks for c_ transpiration/loss of water (vapour) generates pulling forces/ow pressure/tension; absorption of water d__tension/pull generated when water evaporates from cell walls (in mesophyll); by roots e transpiration is loss of water vapour from leaf (surface)/stomata; f — cohesivity/cohesion in water due to hydrogen bonding/attractions between water molecules; g cohesionWTTE so chain/column of water (molecules) doesn't break/remains continuous; h transpiration stream is a column of/flow of water in xylem from roots to leaves; a osmoregulation is regulation of water and solute/salt balance/solute concentrations; Reject ‘water 8 max b nephron (is the functional unit of the kidney/osmoregulates); balance’ and ‘water c ultrafiltration in glomerulus / glomerular filtrate collected by Bowman's capsule; concentration’ for d__ loop of Henle establishes/maintains hypertonic conditions in medulla; mpa e osmosis/reabsorption of water (from filtrate) in the collecting duct; f — brain/hypothalamus monitors blood solute concentration / pituitary secretes ADH; g ADH secreted when solute concentration of blood is too high/hypertonicAvhen dehydrated; h_ ADHincreases permeability of collecting duct to water; i ADH causes more aquaporins (in membranes of collecting duct wall cells); j more water reabsorbed resulting in more concentrated/hypertonic urine/less volume of urine; k_ less/no ADH secreted when solute concentration (of blood) is too low/hypotonic; I less water reabsorbed resulting in dilute/hypotonic urineAarge volume of urine;