2020 GCE O Level Bio Suggested Answer (FPE Edited)

2020 GCE O Level Biology Suggested Answer Paper 1 1 2 3 4 5 6 7 8 9 10 D B B D C A C A B D 11 12 13 14 15 16 17 18 19 20 C B A C A A D B D D 21 22 23 24 25 26 27 28 29 30 C D B A D B B A C D 31 32 33 34 35 36 37 38 39 40 D D A C B C B D A D Paper 2 (Section A) 1 (a) State A: ovary [1] B: oviduct [1] C: cervix [1] (b) Place an X on Fig. Mark ‘X’ on oviduct [1] (c) Describe Peristaltic movement in the wall of the oviduct and the cilia lining the wall of the oviduct sweep the zygote/embryo to the uterus. [1] The zygote divides by mitosis to form the embryo. [1] The embryo implants in the uterus lining about 7 days after fertilisation.[1] (d) (i) Suggest The cilia help to sweep the embryo along the oviduct towards the uterus where implantation can occur [1]. (ii) State Respiratory system [1] Questions to note: 2, 12, 21, 25 Question to note: 9E(b)

2 (a) Suggest D: DNA replication is taking place during interphase as the mass of DNA in the cell doubles from 8 arbitrary units to 16 arbitrary units [1]. E: Cytokinesis is taking place as t he mass of DNA in the cell is halved from 16 arbitrary units to 8 arbitrary units .[1]. (b) (i) State Anaphase [1] (ii) State Before: Metaphase [1] After: Telophase [1] (iii) Determine and explain Haploid number = 3 [1] Explanation: The cell in the diagram shows 6 sister chromatids which have been pulled apart to opposite poles of the cell forming 6 daughter chromosomes on each end of the pole of the cell[1]. Hence, diploid number of the plant species is 6 and the haploid number is 3, which is half of the diploid number [1]. (c) Describe • Crossing over during prophase I and exchanging of homologous segments of DNA between homologous chromosomes results in DNA recombination which leads to variation. • Independent assortment of chromosomes when pairs of homologous chromosomes line up at random along the equator during metaphase I of meiosis results in variation. • Random fusion of sperm and egg cell to form a zygote during fertilisation results in variation.

3 (a) (b) Explain Codominance occurs when two alleles controlling a trait both express themselves in an organism. In human blood group, IA allele and IB allele are codominant. A person with IAIB genotype have both alleles expressed, giving rise to blood group AB [1]. Multiple alleles refers to a gene that consists of more than 2 different type of alleles that controls a specific trait/ phenotype [1]. In human blood group system, there are three alleles, IA, IB and IO which give rise to 4 different blood groups A, B, AB and O. [1]. (c) Explain Discontinuous variation refers to a trait that has clear cut phenotypes with no intermediate forms. They are usually controlled by one or a few genes [1]. (d) Distinguish A gene is a small segment of DNA that controls a specific trait or the production of a particul