CCHY 2020 Bio Yearly TYS ANS

6093 Biology Yearly TYS 2020 No Paper 1 Marks Remarks 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 10 1 11 1 12 1 13 1 14 1 15 1 16 1 17 1 18 1 19 1 20 1 21 1 22 1 23 1 24 1 25 1 26 1 27 1 28 1 29 1 30 1 31 1 32 1 33 1 34 1 35 1 36 1 37 1 38 1 39 1 40 1 Total 40

Paper 2 Section A 1a A: ovary B: oviduct/ fallopian tube C: cervix 1 1 1 1b X on one of the oviduct nearer to an ovary 1 1c Fertilised egg becomes a zygote + cilia sweep the zygote along oviduct + peristaltic movements help to move zygote along the oviduct to the uterus; Zygote divides by mitosis to form embryo + embryo embeds/implants itself in the uterine lining seven d ays after fertilisation; Amniotic sac begins to develop + encloses the embryo in the amniotic cavity containing amniotic fluid/ villi containing blood capillaries of embryo grow from embryo into the uterine wall making up a placenta + umbilical cord attaches embryo to placenta; 1 1 1 formation of amniotic sac/fluid or placenta 1di sweep the zygote along oviduct 1 1dii respiratory system 1 Total 9

2a D: interphase + each chromatin thread undergoing DNA replication, resulting in a pair of sister chromatids, causing the mass of DNA to double from 8 a.u. to 16 a.u.; E: cytokinesis + division of cell to produce two identical daughter cells each containing the same number of chromatin threads causing mass of DNA to decrease to 8 a.u.; 1 1 2bi anaphase 1 2bii before: metaphase after: telophase 1 1 2biii haploid number: 3 explanation: gametes are haploid means they contain half the number of chromosomes as normal plant cells produced when cells in the ovary or pollen grain/gonads undergo meiosis; 6 chromosomes will result in 3 homologous chromosomes + after meiosis, each daughter cell will contain 3 daughter chromosomes; 1 1 1 2c Homologous chromosomes may cross over in prophase I of meiosis + exchange of genes between the paternal and maternal chromosome producing new combinations of genes along the chromosomes which leads to genetic variation; Random arrangement of chromosomes in metaphase I in meiosis + chromosome randomly line up + random separation of homologous ch romosomes at anaphase I + independent assortment of chromosome + producing different combinations of genetic material in gametes + increasing genetic variation; Random fertlisation + nuclues of any sperm fuses with nucleus of any egg + producing offspring of different combination of genotypes + can lead to genetic variation; 1 1 1 Total 11

3a 1 1 1 3b codominance results when the two alleles controlling a trait both express themselves in the organism; multiple alleles is a term used for a gene that exists in more than two alleles for a given trait; human blood group, A, B, AB and O are determined by three alleles, IA, IB and IO + a person can have any two of the alleles but not all three + IA and I B exhibit co -dominance and a re dominant over I O + individuals with alleles IA and IB will have AB blood group; 1 1 1 3c discontinuous variation is difference in traits between individuals of the same species + which is controlled by one or a few genes / that show clear-cut phenotypes with no intermediate forms/ which is easily distinguishable and are not affected by environmental conditions 1 3d a gene is a unit of inheritance , born on a p articular locus of a chromosome + small segment of DNA in a chromosome that controls a particular characteristic or protein in an organism; Alleles are different forms of the same gene that occupy the same relative positions (locus) on a pair of homologous chromosomes; 1 1 Total 9 IAIO IOIO father mother Genotype of parents Gametes Genotype of offspring IA IO IO IO IAIO IOIO IAIO IOIO

4a The younger the age men starts to smoke regularly, the higher the chances of dying when they reach ages between 40 to 60 years old; men who started regular smoking at age 10 to 14 years old has a higher death rate of 2 a.u. compared to men who started regular smoking at 25 to 29 years old whose death rate is at 1.25 a.u.; when men start to smoke regularly at a young age, th e effect of tobacco smoke can occur earlier in their life + frequent exposure to tobacco smoke may increase the risk of lung diseases such as chronic bronchitis, emphysema an d lung cancer + eventually increase risk of death at ages 40 to 60; 1 1 1 4b occlusion (blockage) of coronary arteries greatly reduce the blood supply to the heart muscles + eventually blood flow is blocked + causing heart attack; causing red uce/no supply of oxygen and nutrients such as glucose to heart muscles/ heart muscles do not receive enough oxygen and nutrients; heart muscles die + extensive heart muscle damage is fatal as the heart is no longer able to pump blood to the various part o f the body; 1 1 1 4c mothers who smoke may develop occlusion in their blood vessels + reducing blood supply to the placenta; causing reduced supply of oxygen and nutrients to the placenta + fetus does not receive enough nutrients; lacking of proteins and fats for the building of protoplasm and new cells + leading to low body mass of babies; 1 1 1 Total 9

5a 40.00 ÷ 0.04 = 1000 1 5b chemicals in insecticides are cannot be broken down by microorganisms/ bacteria + when consumed, cannot be excreted but stored in fatty tissues of organisms who consume food that contains the chemicals; bioaccumulation + chemicals accumulate in the bodies of primary consumer (small fishes) transferred to secondary consumer (large fishes) and eventually t ertiary consumers (fish -eating birds) through feeding; bioamplification + increase in the concentration of chemicals as you move up the food chain + higher proportion of fish-eating birds (top of food chain) died compared to other consumers in the food chain; 1 1 1 5c number of large fishes increases rapidly due to the absence of a predator (fish-eating birds); number of small fishes decreases as the increased number of l arge fish es results in increase feeding/ consumption of small fishes; 1 1 1 Total 7

6ai thick elastic layer of arteries is needed to withstand the high blood pressure in the artery; elasticity enables the artery wall to stretch and recoil/ spring back, pushing the blood in spurts, preventing damage/ bursting of blood vessel; 1 1 6aii contraction and relaxation of muscle fibres in the arterial wall bring about constriction and dilation of the artery; when artery constricts, lumen becomes narrower and less blood flows through per unit time/ when artery dilates, lumen becomes wider and more blood flows through it per unit time; 1 1 6b valves/ internal valves/ semi-lunar valves 1 Total 5

Section B 7ai Axes labelled + all ticks labelled at equal intervals; Best fit line + no shading + smooth curve; All points plotted accurately; Maximise the size of grid provided; 4 7aii number of people worldw ide who has HIV increases every year from 2010 to 2014; increase by 0.5 millions from 2010 to 2011 + consistent yearly increase by 0.6 millions from 2011 to 2016; number of people who had HIV is accumulative over the years; 1 1 1 7b keep to one sex partner; males to wear a condom if they are not sure whether their partners or themselves are infected with AIDS; do not abuse drugs or share instruments that could break the skin; use sterilised or disposable instruments for acupuncture, ear - piercing or tattooi