Higher Human Biology Past Paper (2022-2023) - SQA

Higher Human Biology Course code: C840 76 Course assessment code: X840 76 SCQF: level 6 (24 SCQF credit points) Valid from: session 2022–23 This document provides detailed information about the course and cour...

Higher Human Biology Course code: C840 76 Course assessment code: X840 76 SCQF: level 6 (24 SCQF credit points) Valid from: session 2022–23 This document provides detailed information about the course and course assessment to ensure consistent and transparent assessment year on year. It describes the structure of the course and the course assessment in terms of the skills, knowledge and understanding that are assessed. This document is for teachers and lecturers and contains all the mandatory information you need to deliver the course. The information in this publication may be reproduced in support of SQA qualifications only on a non-commercial basis. If it is reproduced, SQA must be clearly acknowledged as the source. If it is to be reproduced for any other purpose, written permission must be obtained from [email protected]. This edition: August 2022 (version 4.1) © Scottish Qualifications Authority 2013, 2018, 2019, 2020, 2022 Contents Course overview 1 Course rationale 2 Purpose and aims 2 Who is this course for? 3 Course content 4 Skills, knowledge and understanding 5 Skills for learning, skills for life and skills for work 23 Course assessment 24 Course assessment structure: question papers 24 Course assessment structure: assignment 26 Grading 31 Equality and inclusion 32 Further information 33 Appendix 1: course support notes 34 Introduction 34 Developing skills, knowledge and understanding 34 Approaches to learning and teaching 34 Preparing for course assessment 89 Developing skills for learning, skills for life and skills for work 89 Appendix 2: question paper brief 92 Course overview The course consists of 24 SCQF credit points which includes time for preparation for course assessment. The notional length of time for candidates to complete the course is 160 hours. The course assessment has three components. Component Marks Scaled mark Duration Question paper 1: 25 not applicable 40 minutes multiple choice Question paper 2 95 not applicable 2 hours and 20 minutes Assignment 20 30 8 hours of which a maximum of 2 hours is allowed for the report stage Recommended entry Progression Entry to this course is at the discretion of  Advanced Higher Biology the centre.  other qualifications in biology or related areas Candidates should have achieved the  further study, employment and/or National 5 Biology course or equivalent training qualifications and/or experience prior to starting this course. Conditions of award The grade awarded is based on the total marks achieved across all course assessment components. Version 4.1 1 Course rationale National Courses reflect Curriculum for Excellence values, purposes and principles. They offer flexibility, provide time for learning, focus on skills and applying learning, and provide scope for personalisation and choice. Every course provides opportunities for candidates to develop breadth, challenge and application. The focus and balance of assessment is tailored to each subject area. Biology, the study of living organisms, plays a crucial role in our everyday life, and is an increasingly important subject in the modern world. Biology affects everyone, and biologists work to find solutions to many of the world’s problems. Advances in technology have made human biology more exciting and relevant than ever. The Higher Human Biology course gives candidates the opportunity to understand and investigate the living world in an engaging and enjoyable way. It develops candidates’ abilities to think analytically, creatively and independently, and to make reasoned evaluations. The course provides opportunities for candidates to acquire and apply knowledge to evaluate biological issues, assess risk, make informed decisions and develop an ethical view of complex issues. Candidates are able to develop their communication, collaborative working and leadership skills, and are able to apply critical thinking in new and unfamiliar contexts to solve problems. The course uses an experimental and investigative approach to develop knowledge and understanding of concepts in biology. Due to the interdisciplinary nature of the sciences, candidates may benefit from studying human biology along with other science subjects and mathematics, as this may enhance their skills, knowledge and understanding. Purpose and aims The course develops candidates’ interest and enthusiasm for human biology in a range of stimulating, relevant and enjoyable contexts. It also allows flexibility and personalisation by offering a choice of contexts to study. The skills of scientific inquiry and investigation are developed throughout the course. This will enable candidates to become scientifically-literate citizens. The course provides a broad-based, integrated study of a range of biological topics which develop the concepts of human biology. The content is set in contexts that are of particular significance and relevance to the human species. The course allows candidates to acquire a deeper understanding of cellular processes, physiological mechanisms and their impact on health, aspects of the nervous system, and defence mechanisms as they apply to the human species. The development of skills enables candidates to adapt their learning to new situations, solve problems, make decisions based on evidence, and evaluate the impact of scientific developments on their health and wellbeing, society and the environment. By setting the Version 4.1 2 acquisition of knowledge and skills in the context of Higher Human Biology, a stimulating, relevant and enjoyable curriculum prepares candidates for further education, training or employment, in areas associated with life sciences. The course aims to:  develop and apply knowledge and understanding of human biology  develop an understanding of human biology’s role in scientific issues and relevant applications of human biology, including the impact these could make in society  develop scientific inquiry and investigative skills  develop scientific analytical thinking skills, including scientific evaluation, in a human biology context  develop the skills to use technology, equipment and materials safely in practical scientific activities  develop planning skills  develop problem-solving skills in a human biology context  use and understand scientific literacy to communicate ideas and issues and to make scientifically informed choices  develop the knowledge and skills for more advanced learning in human biology  develop skills of independent working Who is this course for? The course is suitable for candidates who are secure in their attainment of National 5 Biology or an equivalent qualification. It may also be suitable for those wishing to study biology for the first time. The course emphasises practical and experiential learning opportunities, with a strong skills- based approach to learning. It takes account of the needs of all candidates, and provides sufficient flexibility to enable candidates to achieve in different ways. Version 4.1 3 Course content The course content includes the following areas of human biology: Human cells The key areas covered are:  division and differentiation in human cells  structure and replication of DNA  gene expression  mutations  human genomics  metabolic pathways  cellular respiration  energy systems in muscle cells Physiology and health The key areas covered are:  gamete production and fertilisation  hormonal control of reproduction  the biology of controlling fertility  antenatal and postnatal screening  the structure and function of arteries, capillaries and veins  the structure and function of the heart  pathology of cardiovascular disease (CVD)  blood glucose levels and obesity Neurobiology and immunology The key areas covered are:  divisions of the nervous system and neural pathways  the cerebral cortex  memory  the cells of the nervous system and neurotransmitters at synapses  non-specific body defences  specific cellular defences against pathogens  immunisation  clinical trials of vaccines and drugs Version 4.1 4 Skills, knowledge and understanding Skills, knowledge and understanding for the course The following provides a broad overview of the subject skills, knowledge and understanding developed in the course:  demonstrating knowledge and understanding of human biology by making accurate statements, describing information, providing explanations and integrating knowledge  applying human biology knowledge to new situations, analysing information and solving problems  planning and designing experiments/practical investigations to test given hypotheses or to illustrate particular effects  carrying out experiments/practical investigations safely, recording detailed observations and collecting data  selecting information from a variety of sources  presenting information appropriately in a variety of forms  processing information (using calculations and units, where appropriate)  making predictions and generalisations from evidence/information  drawing valid conclusions and giving explanations supported by evidence/justification  evaluating experiments/practical investigations and suggesting improvements  communicating findings/information effectively Version 4.1 5 Skills, knowledge and understanding for the course assessment The following table provides details of skills, knowledge and understanding sampled in the course assessment. The course support notes provide further detail on the depth of knowledge required for each key area of the course. The key areas of the course, the apparatus and techniques noted below, and the depth of knowledge required for each key area noted in the course support notes can be assessed in the question paper. Human cells 1 Division and differentiation in human cells (a) Division of somatic and germline cells. Somatic stem cells divide by mitosis to form more somatic cells. Germline stem cells divide by mitosis and by meiosis. Division by mitosis produces more germline stem cells. Division by meiosis produces haploid gametes. (b) Cellular differentiation Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell. This allows a cell to carry out specialised functions. Embryonic and tissue stem cells. Cells in the very early embryo can differentiate into all the cell types that make up the individual and so are pluripotent. Tissue stem cells are involved in the growth, repair and renewal of the cells found in that tissue. They are multipotent. (c) Therapeutic and research uses of stem cells. Therapeutic uses involve the repair of damaged or diseased organs or tissues. Research uses involve stem cells being used as model cells to study how diseases develop or being used for drug testing. The ethical issues of using embryonic stem cells. (d) Cancer cells divide excessively because they do not respond to regulatory signals. This results in a mass of abnormal cells called a tumour. Cells within the tumour may fail to attach to each other, spreading through the body where they may form secondary tumours. Version 4.1 6  Human cells 2 Structure and replication of DNA (a) Structure of DNA — nucleotides (deoxyribose sugar, phosphate and base), sugar–phosphate backbone, base pairing (adenine–thymine and guanine–cytosine) by hydrogen bonds and double stranded antiparallel structure, with deoxyribose and phosphate at 3’ and 5’ ends of each strand respectively, forming a double helix. (b) Replication of DNA by DNA polymerase and primers. DNA polymerase adds DNA nucleotides, using complementary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming. Fragments of DNA are joined together by ligase. (c) Polymerase chain reaction (PCR) amplifies DNA using complementary primers for specific target sequences. Repeated cycles of heating and cooling amplify the target region of DNA. Practical applications of PCR. 3 Gene expression (a) Gene expression involves the transcription and translation of DNA sequences. Transcription and translation involves three types of RNA (mRNA, tRNA and rRNA). Messenger RNA (mRNA) carries a copy of the DNA code from the nucleus to the ribosome. Transfer RNA (tRNA) folds due to complementary base pairing. Each tRNA molecule carries its specific amino acid to the ribosome. Ribosomal RNA (rRNA) and proteins form the ribosome. (b) The role of RNA polymerase in transcription of DNA into primary mRNA transcripts. RNA splicing forms a mature mRNA transcript. The introns of the primary transcript are non-coding regions and are removed. The exons are coding regions and are joined together to form the mature transcript. (c) tRNA is involved in the translation of mRNA into a polypeptide at a ribosome. Translation begins at a start codon and ends at a stop codon. Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids. Peptide bonds join the amino acids together. Each tRNA then leaves the ribosome as the polypeptide is formed. Version 4.1 7  Human cells 3 Gene expression (d) Different proteins can be expressed from one gene, as a result of alternative RNA splicing. Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained. (e) Amino acids are linked by peptide bonds to form polypeptides. Polypeptide chains fold to form the three-dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids. Proteins have a large variety of shapes which determines their functions. Phenotype is determined by proteins produced as the result of gene expression. 4 Mutations (a) Mutations are changes in the DNA that can result in no protein or an altered protein being synthesised. (b) Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides. Nucleotide substitutions — missense, nonsense and splice-site mutations. Nucleotide insertions or deletions result in frame-shift mutations. (c) Chromosome structure mutations — duplication, deletion, inversion and translocation. The substantial changes in chromosome mutations often make them lethal. 5 Human genomics (a) The genome of an organism is its entire hereditary information encoded in DNA. A genome is made up of genes and other DNA sequences that do not code for proteins. In genomic sequencing the sequence of nucleotide bases can be determined for individual genes and entire genomes. (b) An individual’s genome can be analysed to predict the likelihood of developing certain diseases. Pharmacogenetics and personalised medicine. Version 4.1 8  Human cells 6 Metabolic pathways (a) Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell. Metabolic pathways can have reversible steps, irreversible steps and alternative routes. Reactions within metabolic pathways can be anabolic or catabolic. Anabolic reactions build up large molecules from small molecules and require energy. Catabolic reactions break down large molecules into smaller molecules and release energy. (b) Metabolic pathways are controlled by the presence or absence of particular enzymes and the regulation of the rate of reaction of key enzymes. Induced fit and the role of the active site of an enzyme in affecting activation energy and the affinity of the substrate and products for the active site. The effects of substrate and product concentration on the direction and rate of enzyme reactions. Control of metabolic pathways through competitive, non-competitive and feedback inhibition of enzymes. 7 Cellular respiration (a) Metabolic pathways of cellular respiration. Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm. ATP is required for the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis. This leads to the generation of more ATP during the energy pay-off stage and results in a net gain of ATP. In aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A. In the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate. During a series of enzyme-controlled steps, citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide. The citric acid cycle occurs in the matrix of the mitochondria. Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH. This occurs in both glycolysis and the citric acid cycle. The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane. Version 4.1 9  Human cells 7 Cellular respiration (b) ATP synthesis — electrons are passed along the electron transport chain releasing energy. This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane. The flow of these ions back through the membrane protein ATP synthase results in the production of ATP. Finally, hydrogen ions and electrons combine with oxygen to form water. (c) The role of ATP in the transfer of energy. 8 Energy systems in muscle cells (a) Lactate metabolism During vigorous exercise, the muscle cells do not get sufficient oxygen to support the electron transport chain. Under these conditions, pyruvate is converted to lactate. This conversion involves the transfer of hydrogen ions from the NADH produced during glycolysis to pyruvate in order to produce lactate. This regenerates the NAD needed to maintain ATP production through glycolysis. Lactate accumulates and muscle fatigue occurs. The oxygen debt is repaid when exercise is complete. This allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver. (b) Types of skeletal muscle fibres Slow-twitch muscle fibres contract relatively slowly, but can sustain contractions for longer. They are useful for endurance activities such as long-distance running, cycling or cross- country skiing. Fast-twitch muscle fibres contract relatively quickly, over short periods. They are useful for activities such as sprinting or weightlifting. Most human muscle tissue contains a mixture of both slow- and fast-twitch muscle fibres. Athletes show distinct patterns of muscle fibres that reflect their sporting activities. Version 4.1 10  Physiology and health 1 Gamete production and fertilisation (a) Gamete production in the testes Testes produce sperm in the seminiferous tubules and testosterone in the interstitial cells. The prostate gland and seminal vesicles secrete fluids that maintain the mobility and viability of the sperm. (b) Gamete production in the ovaries The ovaries contain immature ova in various stages of development. Each ovum is surrounded by a follicle that protects the developing ovum and secretes hormones. (c) Fertilisation Mature ova are released into the oviduct where they may be fertilised by sperm to form a zygote. 2 Hormonal control of reproduction (a) Hormonal influence on puberty. (b) Hormonal control of sperm production. (c) Hormonal control of the menstrual cycle The menstrual cycle takes approximately 28 days with the first day of menstruation regarded as day one of the cycle. FSH stimulates the development of a follicle and the production of oestrogen by the follicle in the follicular phase. Oestrogen stimulates proliferation of the endometrium preparing it for implantation, and affects the consistency of cervical mucus making it more easily penetrated by sperm. Peak levels of oestrogen stimulate a surge in the secretion of LH. This surge in LH triggers ovulation. In the luteal phase the follicle develops into a corpus luteum which secretes progesterone. Progesterone promotes further development and vascularisation of the endometrium preparing it for implantation if fertilisation occurs. The negative feedback effect of the ovarian hormones on the pituitary gland and the secretion of FSH and LH prevent further follicles from developing. The lack of LH leads to degeneration of the corpus luteum with a subsequent drop in progesterone levels leading to menstruation. Version 4.1 11  Physiology and health 3 The biology of controlling fertility Infertility treatments and contraception are based on the biology of fertility. (a) Women show cyclical fertility leading to a fertile period. Men show continuous fertility. Identification of the fertile period. (b) Treatments for infertility Stimulating ovulation Ovulation is stimulated by drugs that prevent the negative feedback effect of oestrogen on FSH secretion. Other ovulatory drugs mimic the action of FSH and LH. These drugs can cause super ovulation that can result in multiple births or be used to collect ova for in vitro fertilisation (IVF) programmes. Artificial insemination Several samples of semen are collected over a period of time. Artificial insemination is particularly useful where the male has a low sperm count. If a partner is sterile a donor may be used to provide semen. Intra-cytoplasmic sperm injection (ICSI) If mature sperm are defective or very low in number, ICSI can be used. The head of the sperm is drawn into a needle and injected directly into the egg to achieve fertilisation. In vitro fertilisation (IVF) Surgical removal of eggs from ovaries after hormone stimulation. Incubation of zygotes and uterine implantation. The use of IVF in conjunction with pre-implantation genetic diagnosis (PGD) to identify single gene disorders and chromosomal abnormalities. (c) Physical and chemical methods of contraception. Biological basis of physical methods used to prevent pregnancy. The oral contraceptive pill is a chemical method of contraception. It contains a combination of synthetic oestrogen and progesterone that mimics negative feedback preventing the release of FSH and LH from the pituitary gland. The progesterone-only (mini) pill causes thickening of the cervical mucus. Emergency hormonal contraceptive pills prevent or delay ovulation. Version 4.1 12  Physiology and health 4 Antenatal and postnatal screening A variety of techniques can be used to monitor the health of the mother, developing fetus and baby. (a) Antenatal screening Antenatal screening identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered. Ultrasound imaging Pregnant women are given two ultrasound scans. Dating scans which determine pregnancy stage and due date are used with tests for marker chemicals which vary normally during pregnancy. Anomaly scans may detect serious physical abnormalities in the fetus. Blood and urine tests Routine blood and urine tests are carried out throughout pregnancy to monitor the concentrations of marker chemicals. Diagnostic testing Amniocentesis and chorionic villus sampling (CVS) and the advantages and disadvantages of their use. Cells from samples can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions. (b) Analysis of patterns of inheritance in genetic screening and counselling. Patterns of inheritance in autosomal recessive, autosomal dominant, incomplete dominance and sex-linked recessive single gene disorders. (c) Postnatal screening. Diagnostic testing for phenylketonuria (PKU). In PKU a substitution mutation means that the enzyme which converts phenylalanine to tyrosine is non-functional. Version 4.1 13  Physiology and health 5 The structure and function of arteries, capillaries and veins (a) Blood circulates from the heart through the arteries to the capillaries then to the veins and back to the heart. There is a decrease in blood pressure as blood moves away from the heart. (b) The structure and function of arteries, capillaries and veins: endothelium, central lumen, connective tissue, elastic fibres, smooth muscle and valves. The role of vasoconstriction and vasodilation in controlling blood flow. (c) The exchange of materials between tissue fluid and cells through pressure filtration and the role of lymphatic vessels. Tissue fluid and blood plasma are similar in composition with the exception of plasma proteins, which are too large to be filtered through the capillary walls. 6 The structure and function of the heart Blood flow through the heart and its associated blood vessels. (a) Cardiac output and its calculation. (b) The cardiac cycle. Functions of diastole, atrial systole and ventricular systole. Effect of pressure changes on atrio-ventricular (AV) and semi lunar (SL) valves. (c) The structure and function of the cardiac conducting system. Control of contraction and timing by cells of the sino-atrial node (SAN) and transmission to the atrio-ventricular node (AVN). Impulses in the heart generate currents that can be detected by an electrocardiogram (ECG). The medulla regulates the rate of the sino-atrial node through the antagonistic action of the autonomic nervous system (ANS). A sympathetic nerve releases noradrenaline which increases the heart rate, whereas a parasympathetic nerve releases acetylcholine which decreases the heart rate. (d) Blood pressure changes in the aorta during the cardiac cycle. Measurement of blood pressure using a sphygmomanometer. Hypertension (high blood pressure) is a major risk factor for many diseases including coronary heart disease. Version 4.1 14  Physiology and health 7 Pathology of cardiovascular disease (CVD) (a) Process of atherosclerosis, its effect on arteries and blood pressure. Atherosclerosis is the root cause of various cardiovascular diseases (CVD) — angina, heart attack, stroke and peripheral vascular disease. (b) Thrombosis — endothelium damage, clotting factors and the role of prothrombin, thrombin, fibrinogen and fibrin. Thrombus formation and the formation and effects of an embolus. A thrombosis in a coronary artery may lead to a myocardial infarction (MI), commonly known as a heart attack. A thrombosis in an artery in the brain may lead to a stroke. Cells are deprived of oxygen leading to death of the tissues. (c) Causes and effects of peripheral vascular disorders. Peripheral vascular disease is narrowing of the arteries due to atherosclerosis of arteries other than those of the heart or brain. The arteries to the legs are most commonly affected. Pain is experienced in the leg muscles due to a limited supply of oxygen. A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, most commonly in the leg. This can break off and result in a pulmonary embolism in the lungs. (d) Control of cholesterol levels in the body. Cholesterol is a type of lipid found in the cell membrane. It is also used to make the sex hormones — testosterone, oestrogen and progesterone. Cholesterol is synthesised by all cells, although 25% of total production takes place in the liver. A diet high in saturated fats or cholesterol causes an increase in cholesterol levels in the blood. Roles of high density lipoproteins (HDL) and low density lipoproteins (LDL). LDL receptors, negative feedback control and atheroma formation. Ratios of HDL to LDL in maintaining health. The benefits of physical activity and a low fat diet. Reducing blood cholesterol through prescribed medications. Version 4.1 15  Physiology and health 8 Blood glucose levels and obesity (a) Chronic elevated blood glucose levels lead to atherosclerosis and blood vessel damage. (b) Pancreatic receptors and the role of hormones in negative feedback control of blood glucose through insulin, glucagon and adrenaline. (c) Type 1 and type 2 diabetes Type 1 diabetes usually occurs in childhood. A person with type 1 diabetes is unable to produce insulin and can be treated with regular doses of insulin. Type 2 diabetes typically develops later in life. The likelihood of developing type 2 diabetes is increased by being overweight. In type 2 diabetes, individuals produce insulin but their cells are less sensitive to it. This insulin resistance is linked to a decrease in the number of insulin receptors in the liver, leading to a failure to convert glucose to glycogen. In both types of diabetes, individual blood glucose concentrations will rise rapidly after a meal. The kidneys will remove some of this glucose resulting in glucose appearing in urine. The glucose tolerance test is used to diagnose diabetes. (d) Obesity Obesity is a major risk factor for cardiovascular disease and type 2 diabetes. Obesity is characterised by excess body fat in relation to lean body tissue such as muscle. Obesity may impair health. Body mass index (BMI) is commonly used to measure obesity but can wrongly classify muscular individuals as obese. Role of diet and exercise in reducing obesity and cardiovascular disease (CVD). Version 4.1 16  Neurobiology and immunology 1 Divisions of the nervous system and neural pathways (a) Structure of the central nervous system (CNS) and the peripheral nervous system (PNS). The somatic nervous system contains sensory and motor neurons. The autonomic nervous system (ANS) consists of the sympathetic and parasympathetic systems. The antagonistic actions of the sympathetic and parasympathetic systems on heart rate, breathing rate, peristalsis and intestinal secretions. (b) Structure and function of converging, diverging and reverberating neural pathways. 2 The cerebral cortex (a) The cerebral cortex is the centre of conscious thought. It also recalls memories and alters behaviour in the light of experience. There is localisation of brain functions in the cerebral cortex. It contains sensory areas, motor areas and association areas. There are association areas involved in language processing, personality, imagination and intelligence. (b) Information from one side of the body is processed in the opposite side of the cerebrum. Transfer of information between the cerebral hemispheres occurs through the corpus callosum. 3 Memory (a) Memory involves encoding storage and retrieval of information. All information entering the brain passes through sensory memory and enters short-term memory (STM). Information is then either transferred to long-term memory (LTM) or is discarded. (b) Sensory memory retains all the visual and auditory input received for a few seconds. (c) Short-term memory (STM) STM has a limited capacity and holds information for a short time. The capacity of STM can be improved by ‘chunking’. STM can also process data, to a limited extent, as well as store it. This ‘working memory model’ explains why the STM can perform simple cognitive tasks. (d) Long-term memory (LTM) LTM has an unlimited capacity and holds information for a long time. The transfer of information from STM to LTM by rehearsal, organisation and elaboration. Retrieval is aided by the use of contextual cues. Version 4.1 17  Neurobiology and immunology 4 The cells of the nervous system and neurotransmitters at synapses (a) Structure and function of neurons — dendrites, cell body and axons. Structure and function of myelin sheath. Myelination continues from birth to adolescence. Certain diseases destroy the myelin sheath causing a loss of co-ordination. Glial cells produce the myelin sheath and support neurons. (b) Neurotransmitters at synapses. Chemical transmission at the synapse by neurotransmitters — vesicles, synaptic cleft and receptors. The need for removal of neurotransmitters by enzymes or reuptake to prevent continuous stimulation of postsynaptic neurons. Receptors determine whether the signal is excitatory or inhibitory. Synapses can filter out weak stimuli arising from insufficient secretion of neurotransmitters. Summation of a series of weak stimuli can release enough neurotransmitter to trigger an impulse. (c) Neurotransmitter effects on mood and behaviour. The functions of endorphins. Endorphin production increases in response to severe injury, prolonged and continuous exercise, stress and certain foods. The function of dopamine. (d) Neurotransmitter-related disorders and their treatment. Many drugs used to treat neurotransmitter-related disorders are agonists or antagonists. Other drugs act by inhibiting the enzymes that degrade neurotransmitters or by inhibiting reuptake of the neurotransmitter at the synapse causing an enhanced effect. Version 4.1 18  Neurobiology and immunology 4 The cells of the nervous system and neurotransmitters at synapses (e) Mode of action of recreational drugs. Recreational drugs can also act as agonists or antagonists. Recreational drugs affect neurotransmission at synapses in the brain altering an individual’s mood, cognition, perception and behaviour. Many recreational drugs affect neurotransmission in the reward pathway of the brain. Drug addiction is caused by repeated use of drugs that act as antagonists. Drug tolerance is caused by repeated use of drugs that act as agonists. 5 Non-specific body defences (a) Physical and chemical defences. Epithelial cells form a physical barrier. Chemical secretions are produced against invading pathogens. (b) The inflammatory response. (c) Phagocytes Phagocytes recognise pathogens and destroy them by phagocytosis. Phagocytes release cytokines which attract more phagocytes to the site of infection. Version 4.1 19  Neurobiology and immunology 6 Specific cellular defences against pathogens (a) Lymphocytes Lymphocytes are the white blood cells involved in the specific immune response. Lymphocytes respond to specific antigens on invading pathogens. Antigens are molecules, often proteins located on the surface of cells that trigger a specific immune response. There are two types of lymphocytes — B lymphocytes and T lymphocytes. B lymphocytes produce antibodies against antigens and this leads to the destruction of the pathogen. B lymphocytes can respond to antigens on substances that are harmless to the body, eg pollen. This hypersensitive response is called an allergic reaction. T lymphocytes destroy infected body cells by recognising antigens of the pathogen on the cell membrane and inducing apoptosis. Apoptosis is programmed cell death. T lymphocytes can normally distinguish between self-antigens on the body’s own cells and non-self-antigens on infected cells. Failure of the regulation of the immune system leads to T lymphocytes responding to self-antigens. This causes autoimmune diseases. (b) Some of the cloned B and T lymphocytes survive long-term as memory cells. When a secondary exposure to the same antigen occurs, these memory cells rapidly give rise to a new clone of specific lymphocytes. These destroy the invading pathogens before the individual shows symptoms. The human immunodeficiency virus (HIV) attacks and destroys T lymphocytes. HIV causes depletion of T lymphocytes which leads to the development of AIDS (acquired immune deficiency syndrome). Version 4.1 20  Neurobiology and immunology 7 Immunisation (a) Vaccination Immunity can be developed by vaccination using antigens from infectious pathogens, so creating memory cells. Antigens are usually mixed with an adjuvant when producing the vaccine. (b) Herd immunity Herd immunity occurs when a large percentage of a population is immunised. Establishing herd immunity is important in reducing the spread of diseases. Non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals. The herd immunity threshold depends on the type of disease, the effectiveness of the vaccine and the density of the population. Mass vaccination programmes are designed to establish herd immunity to a disease. Difficulties can arise when widespread vaccination is not possible due to poverty in the developing world, or when vaccines are rejected by a percentage of the population in the developed world. (c) Antigenic variation Some pathogens can change their antigens. This means that memory cells are not effective against them. Role and impact of antigenic variation in influenza. 8 Clinical trials of vaccines and drugs Vaccines and drugs are subjected to clinical trials to establish their safety and effectiveness before being licensed for use. The design of clinical trials to test vaccines and drugs involves randomised, double-blind and placebo-controlled protocols. The importance of group size in reducing experimental error and establishing statistical significance. Version 4.1 21 Apparatus and techniques In addition to the key areas, candidates must have knowledge of the following pieces of apparatus and have opportunities to become familiar with the following techniques. Apparatus  beaker  balance  measuring cylinder  dropper/pipette  test tube/boiling tube  thermometer  funnel  syringe  timer/stopwatch  Petri dish  water bath  colorimeter  pulsometer  sphygmomanometer Techniques  using gel electrophoresis to separate macromolecule, for example DNA fragments  using substrate concentration or inhibitor concentration to alter reaction rates  measuring metabolic rate using oxygen, carbon dioxide and temperature probes  using a respirometer  measuring pulse rate and blood pressure  measuring body mass index The course support notes provide a list of suggested learning activities. Choosing from the activities suggested in the course support notes, or carrying out any other appropriate activities, allows candidates to become familiar with the apparatus and techniques listed above. Where it is not possible to carry out a particular technique other resources could be utilised. Skills, knowledge and understanding included in the course are appropriate to the SCQF level of the course. The SCQF level descriptors give further information on characteristics and expected performance at each SCQF level, and can be found on the SCQF website. Version 4.1 22 Skills for learning, skills for life and skills for work This course helps candidates to develop broad, generic skills. These skills are based on SQA’s Skills Framework: Skills for Learning, Skills for Life and Skills for Work and draw from the following main skills areas: 1 Literacy 1.2 Writing 2 Numeracy 2.1 Number processes 2.2 Money, time and measurement 2.3 Information handling 5 Thinking skills 5.3 Applying 5.4 Analysing and evaluating 5.5 Creating Teachers and/or lecturers must build these skills into the course at an appropriate level, where there are suitable opportunities. Version 4.1 23 Course assessment Course assessment is based on the information provided in this document. The course assessment meets the key purposes and aims of the course by addressing:  breadth — drawing on knowledge and skills from across the course  challenge — requiring greater depth or extension of knowledge and/or skills  application — requiring application of knowledge and/or skills in practical or theoretical contexts as appropriate This enables candidates to apply:  breadth and depth of skills, knowledge and understanding from across the course to answer questions in human biology  skills of scientific inquiry, using related knowledge, to carry out a meaningful and appropriately challenging task in human biology and communicate findings The course assessment has three components: two question papers and an assignment. The relationship between these three components is complementary, to ensure full coverage of the knowledge and skills of the course. Course assessment structure: question papers Question paper 1: multiple choice 25 marks Question paper 2 95 marks The question papers have a total mark allocation of 120 marks. This is 80% of the overall marks for the course assessment. Marks are distributed proportionally across the course content. The majority of marks are awarded for demonstrating and applying knowledge and understanding. The other marks are awarded for applying scientific inquiry, scientific analytical thinking, problem-solving skills and the impact of applications of human biology on society. The question papers assess breadth, challenge and application of skills, knowledge and understanding from across the course. They assess the application or extension of knowledge and/or skills in unfamiliar situations, practical and theoretical contexts. They also assess scientific inquiry skills, analytical thinking skills and problem-solving skills. Version 4.1 24 The question papers give candidates an opportunity to demonstrate the following skills, knowledge and understanding:  demonstrating knowledge and understanding of human biology by making accurate statements, describing information, providing explanations and integrating knowledge  applying human biology knowledge to new situations, analysing information and solving problems  planning or designing experiments/practical investigations to test given hypotheses or to illustrate particular effects  selecting information from a variety of sources  presenting information appropriately in a variety of forms  processing information (using calculations and units, where appropriate)  making predictions and generalisations based on evidence/information  drawing valid conclusions and giving explanations supported by evidence/justification  evaluating experiments/practical investigations and suggesting improvements Question paper 1: multiple choice Question paper 1 contains multiple-choice questions. Question paper 2 Question paper 2 contains restricted-response and extended-response questions. Setting, conducting and marking the question papers The question papers are set and marked by SQA, and conducted in centres under conditions specified for external examinations by SQA. Candidates have 40 minutes to complete question paper 1. Candidates have 2 hours and 20 minutes to complete question paper 2. Specimen question papers for Higher courses are published on SQA’s website. These illustrate the standard, structure and requirements of the question papers candidates sit. The specimen papers also include marking instructions. Version 4.1 25 Course assessment structure: assignment Assignment 20 marks The assignment has a total mark allocation of 20 marks. This is scaled to 30 marks by SQA to represent 20% of the overall marks for the course assessment. The assignment assesses the application of skills of scientific inquiry and related human biology knowledge and understanding. It allows assessment of skills that cannot be assessed by a question paper; for example, handling and processing data gathered through experimental work and research skills. Assignment overview The assignment gives candidates an opportunity to demonstrate the following skills, knowledge and understanding:  applying knowledge of human biology to new situations, interpreting information and solving problems  planning, designing and safely carrying out experiments/practical investigations to test given hypotheses or to illustrate particular effects  selecting information from a variety of sources  presenting information appropriately in a variety of forms  processing information (using calculations and units, where appropriate)  making predictions and generalisations based on evidence/information  drawing valid conclusions and giving explanations supported by evidence/justification  evaluating experiments/practical investigations and suggesting improvements  communicating findings/information effectively The assignment offers challenge by requiring candidates to apply skills, knowledge and understanding in a context that is one or more of the following:  unfamiliar  familiar but investigated in greater depth  integrating a number of familiar contexts Candidates research and report on a topic that allows them to apply skills and knowledge in human biology at a level appropriate to Higher. The topic must be chosen with guidance from teachers and/or lecturers and must involve experimental work. The assignment has two stages:  research  report Version 4.1 26 The research stage must involve experimental work which allows measurements to be made. Candidates must also gather data/information from the internet, books or journals. Candidates must produce a report of their research. Setting, conducting and marking the assignment Setting The assignment is:  set by centres within SQA guidelines  set at a time appropriate to the candidate’s needs  set within teaching and learning and includes experimental work at a level appropriate to Higher Conducting The assignment is:  an individually produced piece of work from each candidate  started at an appropriate point in the course  conducted under controlled conditions Version 4.1 27 Marking The assignment has a total of 20 marks. The table gives details of the mark allocation for each section of the report. Section Expected response Marks Aim An aim that describes clearly the purpose of 1 the investigation. Underlying biology An account of human biology relevant to the 4 aim of the investigation. Data collection and handling A brief summary of the approach used to 1 collect experimental data. Sufficient raw data from the candidate’s 1 experiment. Data, including mean values, presented in a 1 correctly produced table. Data/information relevant to the experiment 1 obtained from an internet/literature source. A citation and reference for a source of 1 internet/literature data or information. Graphical presentation An appropriate format from the options of line 1 graph or bar graph. The axes of the graph have suitable scales. 1 The axes of the graph have suitable labels 1 and units. Data points are plotted accurately with a line 1 or clear bar tops (as appropriate). Analysis A correct comparison of the experimental data with data/information from the internet/literature source or a correctly 1 completed calculation(s) based on the experimental data, linked to the aim. Conclusion A valid conclusion that relates to the aim and 1 is supported by all the data in the report. Evaluation Evaluation of the investigation. 3 Structure A clear and concise report with an 1 informative title. TOTAL 20 The report is submitted to SQA for external marking. All marking is quality assured by SQA. Version 4.1 28 Assessment conditions Controlled assessment is designed to:  ensure that all candidates spend approximately the same amount of time on their assignments  prevent third parties from providing inappropriate levels of guidance and input  mitigate concerns about plagiarism and improve the reliability and validity of SQA awards  allow centres a reasonable degree of freedom and control  allow candidates to produce an original piece of work Detailed conditions for assessment are given in the assignment assessment task. Time It is recommended that no more than 8 hours is spent on the whole assignment. A maximum of 2 hours is allowed for the report stage. Supervision, control and authentication There are two levels of control. Under a high degree of supervision and Under some supervision and control control  the use of resources is tightly prescribed  candidates do not need to be directly  all candidates are within direct sight of the supervised at all times supervisor throughout the session(s)  the use of resources, including the  display materials which might provide internet, is not tightly prescribed assistance are removed or covered  the work an individual candidate submits  there is no access to e-mail, the internet for assessment is their own or mobile phones  teachers and/or lecturers can provide  candidates complete their work reasonable assistance independently  interaction with other candidates does not occur  no assistance of any description is provided The assignment has two stages. Stage Level of control  research conducted under some supervision and control  report conducted under a high degree of supervision and control Version 4.1 29 Resources Please refer to the instructions for teachers and lecturers within the assignment assessment task. It is not permitted at any stage to provide candidates with a template or model answers. In the research stage:  teachers and/or lecturers must ensure that a range of topics is available for candidates to choose from  teachers and/or lecturers must minimise the number of candidates investigating the same topic within a class  teachers and/or lecturers must agree the choice of topic with the candidate  teachers and/or lecturers must provide advice on the suitability of the candidate’s aim  teachers and/or lecturers can supply a basic list of instructions for the experimental procedure  candidates must undertake research using websites, journals and/or books Teachers and/or lecturers must not:  provide an aim  provide candidates with experimental data  provide candidates with a blank or pre-populated table for experimental results  provide candidates with feedback on their research The only materials that can be used in the report stage are:  the instructions for candidates, which must not have been altered  the candidate’s raw experimental data, which may be tabulated, however must not have additional blank or pre-populated columns for mean and derived values  data/information taken from the internet or literature  a record of the source(s) of internet or literature data/information  the experimental method, if appropriate  extract(s) from internet/literature sources to support the underlying biology, which must not include sample calculations Candidates must not have access to a previously prepared draft of a report or any part of a report. In addition, candidates must not have access to the assignment marking instructions during the report stage. Candidates must not have access to the internet during the report stage. Teachers and/or lecturers must not provide any form of feedback to a candidate on their report. Version 4.1 30 Following completion of the report stage, candidates must not be given an opportunity to redraft their report. Teachers and/or lecturers must not read the reports before they are submitted to SQA. Reasonable assistance The term ‘reasonable assistance’ is used to describe the balance between supporting candidates and giving them too much assistance. Candidates must undertake the assessment independently. However, reasonable assistance may be provided before the formal assessment process (research stage and report stage) takes place. If candidates have been entered for the correct level of qualification, they will not require more than a reasonable level of assistance to carry out the assignment. Evidence to be gathered The following candidate evidence is required for this assessment:  a report The report is submitted to SQA, within a given timeframe, for marking. The same report cannot be submitted for more than one subject. Volume There is no word count. Grading Candidates’ overall grades are determined by their performance across the course assessment. The course assessment is graded A–D on the basis of the total mark for all course assessment components. Grade description for C For the award of grade C, candidates will typically have demonstrated successful performance in relation to the skills, knowledge and understanding for the course. Grade description for A For the award of grade A, candidates will typically have demonstrated a consistently high level of performance in relation to the skills, knowledge and understanding for the course. Version 4.1 31 Equality and inclusion This course is designed to be as fair and as accessible as possible with no unnecessary barriers to learning or assessment. For guidance on assessment arrangements for disabled candidates and/or those with additional support needs, please follow the link to the assessment arrangements web page: www.sqa.org.uk/assessmentarrangements. Version 4.1 32 Further information The following reference documents provide useful information and background.  Higher Human Biology subject page  Assessment arrangements web page  Building the Curriculum 3–5  Guide to Assessment  Guidance on conditions of assessment for coursework  SQA Skills Framework: Skills for Learning, Skills for Life and Skills for Work  Coursework Authenticity: A Guide for Teachers and Lecturers  Educational Research Reports  SQA Guidelines on e-assessment for Schools  SQA e-assessment web page The SCQF framework, level descriptors and handbook are available on the SCQF website. Version 4.1 33 Appendix 1: course support notes Introduction These support notes are not mandatory. They provide advice and guidance to teachers and/or lecturers on approaches to delivering the course. You should read these in conjunction with this course specification and the specimen question paper and coursework. Note: the depth of knowledge required for each key area of the course can be assessed in the question papers. Developing skills, knowledge and understanding This section provides further advice and guidance about skills, knowledge and understanding that teachers and/or lecturers could include in the course. Teachers and/or lecturers have considerable flexibility to select contexts that will stimulate and challenge candidates, offering both breadth and depth. The ‘Approaches to learning and teaching’ section provides suggested activities that teachers and/or lecturers can build into their delivery to develop these skills, knowledge and understanding. Approaches to learning and teaching Learning and teaching approaches should develop candidates’ knowledge and understanding, and skills for learning, life and work. Teachers and/or lecturers can base a related sequence of activities on a context appropriate to Higher Human Biology. Learning could be led by candidates. It should be experiential, active, challenging and enjoyable, and include appropriate practical activities. Teachers and/or lecturers can use a variety of active learning approaches, including peer teaching and assessment, individual and group presentations, role-playing and game-based learning, with candidate-generated questions. Teachers and/or lecturers should allow opportunities for candidates to take responsibility for their learning. Learning and teaching should build on candidates’ prior knowledge, skills and experiences and allow candidates of different abilities to demonstrate achievement. Candidates can actively develop their skills, knowledge and understanding by investigating a range of applications and issues relevant to human biology. Teachers and/or lecturers can adopt a holistic approach to encourage candidates to simultaneously develop their conceptual understanding and skills. Investigations and experiments are part of the scientific method of working and, where appropriate in Human Biology, candidates should have the opportunity to select activities and/or carry out extended study. All learning and teaching should offer opportunities for candidates to work collaboratively. Practical activities and investigative work can offer opportunities for group work. Group work Version 4.1 34 approaches can be helpful to simulate real-life situations, share tasks, and promote team- working skills. Practical activities must include the use of the apparatus listed and, where possible, the use of technology and equipment that reflects current scientific use in human biology. Practical activities must also allow candidates to become familiar with the techniques listed. Appropriate risk assessment must be undertaken. Effective partnership working can enhance the learning experience. Where possible, teachers and/or lecturers should arrange visits and invite guest speakers from, for example, industry, and further and higher education to bring the world of human biology into the classroom. Learning about Scotland and Scottish culture enriches the learning experience and helps candidates to develop the skills for learning, life and work they need to prepare them for taking their place in a diverse, inclusive and participative Scotland and beyond. Where there are opportunities to contextualise approaches to learning and teaching to Scottish contexts, teachers and lecturers should consider this. Information and Communications Technology (ICT) can make a significant contribution to practical work in Higher Human Biology. Computer-interfacing equipment can detect and record small changes in variables allowing experimental results to be recorded over long or short periods of time. Results can also be displayed in real time, helping to improve understanding. Data-logging equipment and video cameras can be set up to record data and make observations over periods of time (longer than a class lesson) that can then be downloaded and viewed for analysis. Assessment is integral to learning and teaching. It should provide candidates with supportive feedback and help them to prepare for the course assessment. Teachers and/or lecturers should use self- and peer-assessment techniques wherever appropriate and use assessment information to set learning targets and next steps. As part of learning, teaching and preparation for course assessment, candidates should carry out several investigations that meet the requirements of the assignment. This should help candidates develop the necessary skills and prepare them for the report stage of the assignment. The following table provides an outline of the depth of knowledge candidates require for each key area, along with suggested learning activities. The key areas are from the ‘Course content’ section of this course specification. The depth of knowledge required provides further detail of the key areas and an outline of the level of demand. The key areas and the depth of knowledge required can be assessed in the question papers. The suggested learning activities are not compulsory. The contexts for each key area are open to personalisation and choice, so teachers and/or lecturers may also devise learning activities. However, teachers and/or lecturers must give candidates the opportunity to experience the use of the apparatus and the techniques listed below as these can be assessed in the question papers. Version 4.1 35 Note: the key areas and the depth of knowledge required can be assessed in the question papers. Human cells Key areas Depth of knowledge required Suggested learning activities 1 Division and differentiation in human cells (a) Division of somatic and germline cells. A somatic cell is any cell in the body other than cells involved in reproduction. Germline cells are gametes (sperm and ova) and the stem cells that divide to form gametes. Somatic stem cells divide by mitosis to form more somatic cells. Germline stem cells divide by mitosis and by meiosis. Division by mitosis produces more germline The nucleus of a germline stem cell can stem cells. divide by mitosis to maintain the diploid chromosome number. Diploid cells have 23 pairs of homologous chromosomes. Division by meiosis produces haploid The nucleus of a germline stem cell can gametes. divide by meiosis. It undergoes two divisions, firstly separating homologous chromosomes and secondly separating chromatids. Haploid gametes contain 23 single chromosomes. Further detail of the process of meiosis is not required. Version 4.1 36  Human cells Key areas Depth of knowledge required Suggested learning activities (b) Cellular differentiation. Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell. This allows a cell to carry out specialised functions. Embryonic and tissue stem cells. Cells in the very early embryo can All the genes in embryonic stem cells can be differentiate into all the cell types that make switched on so these cells can differentiate up the individual and so are pluripotent. into any type of cell. Tissue stem cells are involved in the growth, Tissue stem cells are multipotent as they can repair and renewal of the cells found in that differentiate into all of the types of cell found tissue. They are multipotent. in a particular tissue type. For example, View digital resources on the origin of blood blood stem cells located in bone marrow can cells and their functions. give rise to red blood cells, platelets, phagocytes and lymphocytes. Version 4.1 37  Human cells Key areas Depth of knowledge required Suggested learning activities (c) Therapeutic and research uses of stem cells. Therapeutic uses involve the repair of The therapeutic uses of stem cells should be Study potential therapeutic uses of stem damaged or diseased organs or tissues. exemplified by how they are used in corneal cells. repair and the regeneration of damaged skin. Research uses involve stem cells being used Stem cells from the embryo can self-renew, as model cells to study how diseases under the right conditions, in the lab. develop or being used for drug testing. Stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work. The ethical issues of using embryonic stem Use of embryonic stem cells can offer Debate the ethics surrounding stem cell cells. effective treatments for disease and injury; research and the sources of stem cells. however, it involves destruction of embryos. (d) Cancer cells divide excessively because they do not respond to regulatory signals. This results in a mass of abnormal cells called a tumour. Cells within the tumour may fail to attach to each other, spreading through the body where they may form secondary tumours. Version 4.1 38  Human cells Key areas Depth of knowledge required Suggested learning activities 2 Structure and replication of DNA (a) Structure of DNA — nucleotides The base sequence of DNA forms the Examine research that led to an (deoxyribose sugar, phosphate and base), genetic code. understanding of the structure of DNA. sugar–phosphate backbone, base pairing Studies could include Chargaff’s base ratios, (adenine–thymine and guanine–cytosine), by X-ray crystallography of Wilkins and Franklin, hydrogen bonds and double stranded and Watson and Crick’s development of the antiparallel structure, with deoxyribose and double helix model. phosphate at 3’ and 5’ ends of each strand respectively, forming a double helix. (b) Replication of DNA by DNA polymerase Prior to cell division, DNA is replicated by a Carry out digital or physical modelling of DNA and primers. DNA polymerase. DNA polymerase needs replication. primers to start replication. A primer is a short strand of nucleotides which binds to the Examine Meselson and Stahl’s experiments 3’ end of the template DNA strand allowing on DNA replication. polymerase to add DNA nucleotides. DNA polymerase adds DNA nucleotides, DNA is unwound and hydrogen bonds using complementary base pairing, to the between bases are broken to form two deoxyribose (3’) end of the new DNA strand template strands. DNA polymerase can only which is forming. add DNA nucleotides in one direction resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments. Fragments of DNA are joined together by ligase. Version 4.1 39  Human cells Key areas Depth of knowledge required Suggested learning activities (c) Polymerase chain reaction (PCR) In PCR, primers are short strands of Carry out PCR using a thermal cycler or amplifies DNA using complementary primers nucleotides which are complementary to water baths. for specific target sequences. specific target sequences at the two ends of the region of DNA to be amplified. Repeated cycles of heating and cooling DNA is heated to between 92 and 98°C to amplify the target region of DNA. separate the strands. It is then cooled to between 50 and 65°C to allow primers to bind to target sequences. It is then heated to between 70 and 80°C for heat-tolerant DNA polymerase to replicate the region of DNA. Practical applications of PCR. PCR can amplify DNA to help solve crimes, Use gel electrophoresis to analyse DNA settle paternity suits and diagnose genetic samples (from kits) to determine criminality disorders. or paternity. Version 4.1 40  Human cells Key areas Depth of knowledge required Suggested learning activities 3 Gene expression (a) Gene expression involves the Only a fraction of the genes in a cell are transcription and translation of DNA expressed. sequences. Transcription and translation involves three RNA is single stranded and is composed of Carry out digital or physical modelling of types of RNA (mRNA, tRNA and rRNA). nucleotides containing ribose sugar, transcription and translation. phosphate and one of four bases: cytosine, guanine, adenine and uracil. Messenger RNA (mRNA) carries a copy of mRNA is transcribed from DNA in the the DNA code from the nucleus to the nucleus and translated into proteins by ribosome. ribosomes in the cytoplasm. Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid. Transfer RNA (tRNA) folds due to A tRNA molecule has an anticodon (an complementary base pairing. Each tRNA exposed triplet of bases) at one end and an molecule carries its specific amino acid to the attachment site for a specific amino acid at ribosome. the other end. Ribosomal RNA (rRNA) and proteins form the ribosome. Version 4.1 41  Human cells Key areas Depth of knowledge required Suggested learning activities (b) The role of RNA polymerase in RNA polymerase moves along DNA transcription of DNA into primary mRNA unwinding the double helix and breaking the transcripts. hydrogen bonds between the bases. RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing. RNA splicing forms a mature mRNA Uracil in RNA is complementary to adenine. transcript. The introns of the primary transcript are non- coding regions and are removed. The exons are coding regions and are joined The order of the exons is unchanged during together to form the mature transcript. splicing. (c) tRNA is involved in the translation of mRNA into a polypeptide at a ribosome. Translation begins at a start codon and ends at a stop codon. Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids. Peptide bonds join the amino acids together. Each tRNA then leaves the ribosome as the polypeptide is formed. Version 4.1 42  Human cells Key areas Depth of knowledge required Suggested learning activities (d) Different proteins can be expressed from one gene, as a result of alternative RNA splicing. Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained. (e) Amino acids are linked by peptide bonds Details of other interactions and levels of Use digital resources to examine the shape to form polypeptides. Polypeptide chains fold protein structure are not required. and structure of proteins. to form the three-dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids. Proteins have a large variety of shapes which determines their functions. Phenotype is determined by proteins Environmental factors also influence produced as the result of gene expression. phenotype. Version 4.1 43  Human cells Key areas Depth of knowledge Suggested learning activities 4 Mutations (a) Mutations are changes in the DNA that Carry out experiments to investigate the can result in no protein or an altered protein effects of UV radiation on UV-sensitive yeast. being synthesised. (b) Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of the substitution, insertion or deletion of nucleotides. Nucleotide substitutions — missense, Missense mutations result in one amino acid Study human conditions caused by single nonsense and splice-site mutations. being changed for another. This may result in gene mutations. Examples could include a non-functional protein or have little effect sickle-cell disease (missense), on the protein. phenylketonuria (PKU) (missense), Duchenne muscular dystrophy (nonsense) Nonsense mutations result in a premature and beta thalassemia (splice-site mutation). stop codon being produced which results in a shorter protein. Splice-site mutations result in some introns being retained and/or some exons not being included in the mature transcript. Nucleotide insertions or deletions result in Frame-shift mutations cause all of the Study human conditions caused by frame- frame-shift mutations. codons and all of the amino acids after the shift mutations. Examples could include Tay- mutation to be changed. This has a major Sachs disease (frame-shift insertion) and effect on the structure of the protein cystic fibrosis (frame-shift deletion). produced. Version 4.1 44  Human cells Key areas Depth of knowledge Suggested learning activities (c) Chromosome structure mutations — Duplication is where a section of a Study human conditions caused by duplication, deletion, inversion and chromosome is added from its homologous chromosome structure mutations, for translocation. partner. example: Deletion is where a section of a chromosome  Cri-du-chat syndrome — caused by is removed. deletion of part of the short arm of chromosome 5. Inversion is where a section of chromosome  Haemophilia A — one cause is an is reversed. inversion within the gene that produces a clotting factor (factor VIII). Translocation is where a section of a  Chronic myeloid leukaemia — caused by chromosome is added to a chromosome, not a reciprocal translocation of sections of its homologous partner. chromosome 22 and chromosome 9. The substantial changes in chromosome mutations often make them lethal. Version 4.1 45  Human cells Key areas Depth of knowledge Suggested learning activities 5 Human genomics (a) The genome of an organism is its entire Study the procedures used to determine the hereditary information encoded in DNA. human genome. A genome is made up of genes and other DNA sequences that do not code for proteins. In genomic sequencing the sequence of Computer programs can be used to identify nucleotide bases can be determined for base sequences by looking for sequences individual genes and entire genomes. similar to known genes. To compare sequence data, computer and Study potential uses of bioinformatics. statistical analyses (bioinformatics) are required. (b) An individual’s genome can be analysed to predict the likelihood of developing certain diseases. Pharmacogenetics and personalised Pharmacogenetics is the use of genome medicine. information in the choice of drugs. An individual’s personal genome sequence can be used to select the most effective drugs and dosage to treat their disease (personalised medicine). Version 4.1 46  Human cells Key areas Depth of knowledge Suggested learning activities 6 Metabolic pathways (a) Metabolic pathways are integrated and Use simple respirometers to measure controlled pathways of enzyme-catalysed metabolic rate. reactions within a cell. Carry out experiments to measure metabolic rate using oxygen, carbon dioxide and temperature probes. Metabolic pathways can have reversible steps, irreversible steps and alternative routes. Reactions within metabolic pathways can be anabolic or catabolic. Anabolic reactions build up large molecules from small molecules and require energy. Catabolic reactions break down large molecules into smaller molecules and release energy. (b) Metabolic pathways are controlled by the Carry out enzyme induction experiments presence or absence of particular enzymes such as the breakdown of ONPG by beta and the regulation of the rate of reaction of galactosidase in E. coli, with lactose acting key enzymes. as an inducer. Induced fit and the role of the active site of Induced fit occurs when the active site Carry out activation energy experiments, an enzyme in affecting activation energy and changes shape to better fit the substrate after comparing heat, manganese dioxide and the affinity of the substrate and products for the substrate binds. catalase action on hydrogen peroxide. the active site. The substrate molecule(s) have a high affinity for the active site and the subsequent Version 4.1 47  Human cells Key areas Depth of knowledge Suggested learning activities products have a low affinity allowing them to leave the active site. The effects of substrate and product Some metabolic reactions are reversible and Carry out experiments on the effect of concentration on the direction and rate of the presence of a substrate or the removal of increasing substrate concentration on enzyme reactions. a product will drive a sequence of reactions reactions. Examples could include using in a particular direction. hydrogen peroxide and adding filter paper discs soaked in catalase. Control of metabolic pathways through Competitive inhibitors bind at the active site Carry out experiments on the effect of competitive, non-competitive and feedback preventing the substrate from binding. inhibitors on reactions. Examples could inhibition of enzymes. Competitive inhibition can be reversed by include the inhibition of beta galactosidase by increasing substrate concentration. galactose and its reversal by increasing ONPG concentration. Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding. Non-competitive inhibition cannot be reversed by increasing substrate concentration. Feedback inhibition occurs when the end- Carry out experiments on end-product product in the metabolic pathway reaches a inhibition using phosphatase and critical concentration. The end-product then phenolphthalein phosphate. inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product. Version 4.1 48  Human cells Key areas Depth of knowledge required Suggested learning activities 7 Cellular respiration (a) Metabolic pathways of cellular respiration. Carry out experiments using different sugars as respiratory substrates for yeast. Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm. ATP is required for the phosphorylation of Carry out experiments using glucose-1- glucose and intermediates during the energy phosphate (a phosphorylated form of investment phase of glycolysis. This leads to glucose). the generation of more ATP during the energy pay-off stage and results in a net gain of ATP. In aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A. In the citric acid cycle the acetyl group from Carry out experiments on the inhibition of the acetyl coenzyme A combines with citric acid cycle by malonic acid using DCPIP oxaloacetate to form citrate. During a series as an indicator of dehydrogenase activity. of enzyme-controlled steps, citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide. The citric acid cycle occurs in the matrix of the mitochondria. Version 4.1 49  Human cells Key areas Depth of knowledge required Suggested learning activities Dehydrogenase enzymes remove hydrogen Carry out experiments with yeast ions and electrons and pass them to the dehydrogenase using resazurin dye as an coenzyme NAD, forming NADH. This occurs indicator. in both glycolysis and the citric acid cycle. The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane. (b) ATP synthesis — electrons are passed The electron transport chain is a series of along the electron transport chain releasing carrier proteins attached to the inner energy. mitochondrial membrane. This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane. The flow of these ions back through the membrane protein ATP synthase results in the production of ATP. Finally, hydrogen ions and electrons combine with oxygen to form water. (c) The role of ATP in the transfer of energy. ATP is used to transfer energy to cellular Carry out experiments on ATP-dependent processes which require energy. reactions such as luminescent reactions using luciferase. Version 4.1 50  Human cells Key areas Depth of knowledge required Suggested learning activities 8 Energy systems in muscle cells (a) Lactate metabolism. During vigorous exercise, the muscle cells do not get sufficient oxygen to support the electron transport chain. Under these conditions, pyruvate is converted to lactate. This conversion involves the transfer of hydrogen ions from the NADH produced during glycolysis to pyruvate in order to produce lactate. This regenerates the NAD needed to maintain ATP production through glycolysis. Lactate accumulates and muscle fatigue occurs. The oxygen debt is repaid when exercise is complete. This allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver. (b) Types of skeletal muscle fibres. Slow-twitch muscle fibres contract relatively Slow-twitch muscle fibres rely on aerobic slowly, but can sustain contractions for respiration to generate ATP and have many longer. They are useful for endurance mitochondria, a large blood supply and a activities such as long-distance running, high concentration of the oxygen-storing cycling or cross-country skiing. protein myoglobin. The major storage fuel of slow-twitch muscle fibres is fats. Version 4.1 51  Human cells Key areas Depth of knowledge required Suggested learning activities Fast-twitch muscle fibres contract relatively quickly, over short periods. They are useful Fast-twitch muscle fibres can generate ATP for activities such as sprinting or weightlifting. through glycolysis only and have fewer mitochondria and a lower blood supply compared to slow-twitch muscle fibres. The major storage fuel of fast-twitch muscle fibres is glycogen. Most human muscle tissue contains a mixture of both slow- and fast-twitch muscle Compare the ratios of slow-twitch muscle fibres. Athletes show distinct patterns of fibres to fast-twitch muscle fibres between muscle fibres that reflect their sporting elite athletes in different sports. activities. Version 4.1 52  Physiology and health Key areas Depth of knowledge required Suggested learning activities 1 Gamete production and fertilisation (a) Gamete production in the testes. Testes produce sperm in the seminiferous tubules and testosterone in the interstitial cells. The prostate gland and seminal vesicles secrete fluids that maintain the mobility and viability of the sperm. (b) Gamete production in the ovaries. The ovaries contain immature ova in various stages of development. Each ovum is surrounded by a follicle that protects the developing ovum and secretes hormones. (c) Fertilisation. Mature ova are released into the oviduct where they may be fertilised by sperm to form a zygote. Version 4.1 53  Physiology and health Key areas Depth of knowledge required Suggested learning activities 2 Hormonal control of reproduction (a) Hormonal influence on puberty. The pituitary gland is stimulated to release follicle stimulating hormone (FSH), luteinising hormone (LH) or in