AQA GCSE Biology 8461 Specification PDF

Get help and support GCSE...

Get help and support GCSE BIOLOGY Visit our website for information, guidance, support and resources at aqa.org.uk/subjects/8461 You can talk directly to the science subject team E: [email protected] (8461) T: 01483 477 756 Specification For teaching from September 2016 onwards For exams in 2018 onwards Version 1.0 21 April 2016 aqa.org.uk Copyright © 2016 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications, including the specifications. However, schools and colleges registered with AQA are permitted to copy material from this specification for their own internal use. G00568 AQA Education (AQA) is a registered charity (number 1073334) and a company limited by guarantee registered in England and Wales (company number 3644723). Our registered address is AQA, Devas Street, Manchester M15 6EX.  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 Contents 1 Introduction 5 1.1 Why choose AQA for GCSE Biology 5 1.2 Support and resources to help you teach 6 2 Specification at a glance 8 2.1 Subject content 8 2.2 Assessments 8 3 Working scientifically 9 4 Subject content 15 4.1 Cell biology 16 4.2 Organisation 24 4.3 Infection and response 31 4.4 Bioenergetics 37 4.5 Homeostasis and response 41 4.6 Inheritance, variation and evolution 51 4.7 Ecology 66 4.8 Key ideas 76 5 Scheme of assessment 77 5.1 Aims and learning outcomes 77 5.2 Assessment objectives 78 5.3 Assessment weightings 79 6 General administration 80 6.1 Entries and codes 80 6.2 Overlaps with other qualifications 80 6.3 Awarding grades and reporting results 80 6.4 Re-sits and shelf life 81 6.5 Previous learning and prerequisites 81 6.6 Access to assessment: diversity and inclusion 81 6.7 Working with AQA for the first time 81 6.8 Private candidates 82 7 Mathematical requirements 83 8 Practical assessment 85 8.1 Use of apparatus and techniques 85 8.2 Required practical activities 86 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 3 Are you using the latest version of this specification? You will always find the most up-to-date version of this specification on our website at aqa.org.uk/8461 We will write to you if there are significant changes to this specification. 4 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 1 Introduction 1.1 Why choose AQA for GCSE Biology Our philosophy: science for all We believe that science has something to offer every student. That’s why we have a suite of science qualifications for Key Stage 4 ‒ to suit students of all abilities and all aspirations. You’ll see that our GCSE Biology, along with Chemistry and Physics, is a clear straightforward specification, with clear straightforward exams, so all your students can realise their potential. Our specification has been developed with teachers We’ve involved over a thousand teachers in developing our specification, exams and resources. So you can be confident that our GCSE Biology is relevant and interesting to teach and to learn. We’ve ensured that: the subject content is presented clearly, in a logical teaching order. We’ve also given teaching guidance and signposted opportunities for skills development throughout the specification the subject content and required practicals in our GCSE Combined Science: Trilogy are also in our GCSE Biology, Chemistry and Physics. So you have the flexibility to co-teach or to move your students between courses all our science qualifications provide opportunities for progression. Our GCSE Biology includes progression in the subject content and consistency in the exam questions, so that your students have the best preparation for A-level. Our practicals have been trialled by teachers There’s no better way to learn about science than through purposeful practical activities as part of day to day teaching and learning. Our ten required practicals: are clearly laid out in the specification, so you know exactly what’s required are deliberately open, so you can teach in the way that suits you and your students have already been trialled in schools. You’ll find even more support and guidance in our practical handbook, which includes recommendations and advice from teachers in the trial. Straightforward exams, so students can give straightforward answers We’ve improved our question papers. You’ll find that our exams: use more straightforward language and fewer words so they’re easier to understand have fewer contexts so students don’t get confused have questions that increase in difficulty so students feel confident have been written with our GCSE Mathematics and A-level science teams, so students have consistency between content and questions. Over 3,000 students have sat our specimen question papers and they agree that they’re clearer and more straightforward than ever. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 5 We don’t profit from education – you do We are an educational charity focused on the needs of teachers and students. This means that we spend our income on improving the quality of our specifications, exams, resources and support. You can find out all about our Science qualifications at aqa.org.uk/science 1.2 Support and resources to help you teach We’ve worked with experienced teachers to provide you with a range of resources that will help you confidently plan, teach and prepare for exams. Teaching resources Visit aqa.org.uk/8461 to see all our teaching resources. They include: additional practice papers to help students prepare for exams schemes of work, written by experienced teachers, including a scheme of work specifically for Foundation tier students a practical handbook, including recommendations and advice from teachers who’ve trialled our practicals AQA approved textbooks reviewed by experienced senior examiners training courses to help you deliver AQA biology qualifications subject expertise courses for all teachers, from newly-qualified teachers who are just getting started to experienced teachers looking for fresh inspiration. Preparing for exams Visit aqa.org.uk/8461 for everything you need to prepare for our exams, including: past papers, mark schemes and examiners’ reports specimen papers and mark schemes for new courses Exampro: a searchable bank of past AQA exam questions exemplar student answers with examiner commentaries. Analyse your students’ results with Enhanced Results Analysis (ERA) Find out which questions were the most challenging, how the results compare to previous years and where your students need to improve. ERA, our free online results analysis tool, will help you see where to focus your teaching. Register at aqa.org.uk/era For information about results, including maintaining standards over time, grade boundaries and our post-results services, visit aqa.org.uk/results Keep your skills up-to-date with professional development Wherever you are in your career, there’s always something new to learn. As well as subject-specific training, we offer a range of courses to help boost your skills. Improve your teaching skills in areas including differentiation, teaching literacy and meeting Ofsted requirements. Prepare for a new role with our leadership and management courses. You can attend a course at venues around the country, in your school or online – whatever suits your needs and availability. Find out more at coursesandevents.aqa.org.uk 6 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 Help and support available Visit our website for information, guidance, support and resources at aqa.org.uk/8461 If you’d like us to share news and information about this qualification, sign up for emails and updates at aqa.org.uk/keepinformedscience Alternatively, you can call or email our subject team direct. E: [email protected] T: 01483 477 756 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 7 2 Specification at a glance This qualification is linear. Linear means that students will sit all their exams at the end of the course. 2.1 Subject content 1. Cell biology (Page 16) 2. Organisation (Page 24) 3. Infection and response (Page 31) 4. Bioenergetics (Page 37) 5. Homeostasis and response (Page 41) 6. Inheritance, variation and evolution (Page 51) 7. Ecology (Page 66) 8. Key ideas (Page 76) 2.2 Assessments Paper 1 + Paper 2 What’s assessed What’s assessed Topics 1 – 4: Cell biology; Organisation; Topics 5 – 7: Homeostasis and response; Infection and response; and Bioenergetics. Inheritance, variation and evolution; and Ecology. How it’s assessed How it’s assessed Written exam: 1 hour 45 minutes Written exam: 1 hour 45 minutes Foundation and Higher Tier Foundation and Higher Tier 100 marks 100 marks 50 % of GCSE 50 % of GCSE Questions Questions Multiple choice, structured, closed short Multiple choice, structured, closed short answer and open response. answer and open response. 8 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 3 Working scientifically Science is a set of ideas about the material world. We have included all the parts of what good science is at GCSE level: whether it be investigating, observing, experimenting or testing out ideas and thinking about them. The way scientific ideas flow through the specification will support you in building a deep understanding of science with your students. We know this will involve talking about, reading and writing about science plus the actual doing, as well as representing science in its many forms both mathematically and visually through models. This specification encourages the development of knowledge and understanding in science through opportunities for working scientifically. Working scientifically is the sum of all the activities that scientists do. We feel it is so important that we have woven it throughout our specification and written papers. Our schemes of work will take this further for you and signpost a range of ways to navigate through this qualification so your students are engaged and enthused. These free resources support the use of mathematics as a tool for thinking through the use of mathematical language in explanations, applications and evaluations. The tables below show examples of the ways working scientifically could be assessed. 1 Development of scientific thinking Students should be able to: Examples of what students could be asked to do in an exam WS 1.1 Give examples to show how scientific methods Understand how scientific methods and theories and theories have changed over time. develop over time. Explain, with an example, why new data from experiments or observations led to changes in models or theories. Decide whether or not given data supports a particular theory. WS 1.2 Recognise/draw/interpret diagrams. Use a variety of models such as representational, Translate from data to a representation with a spatial, descriptive, computational and model. mathematical to solve problems, make predictions and to develop scientific explanations Use models in explanations, or match features and understanding of familiar and unfamiliar of a model to the data from experiments or facts. observations that the model describes or explains. Make predictions or calculate quantities based on the model or show its limitations. Give examples of ways in which a model can be tested by observation or experiment. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 9  Students should be able to: Examples of what students could be asked to do in an exam WS 1.3 Explain why data is needed to answer scientific Appreciate the power and limitations of science questions, and why it may be uncertain, and consider any ethical issues which may arise. incomplete or not available. Outline a simple ethical argument about the rights and wrongs of a new technology. WS 1.4 Describe and explain specified examples of the Explain everyday and technological applications technological applications of science. of science; evaluate associated personal, social, Describe and evaluate, with the help of data, economic and environmental implications; and methods that can be used to tackle problems make decisions based on the evaluation of caused by human impacts on the environment. evidence and arguments. WS 1.5 Give examples to show that there are hazards Evaluate risks both in practical science and the associated with science-based technologies wider societal context, including perception of which have to be considered alongside the risk in relation to data and consequences. benefits. Suggest reasons why the perception of risk is often very different from the measured risk (eg voluntary vs imposed risks, familiar vs unfamiliar risks, visible vs invisible hazards). WS 1.6 Explain that the process of peer review helps to Recognise the importance of peer review of detect false claims and to establish a consensus results and of communicating results to a range about which claims should be regarded as valid. of audiences. Explain that reports of scientific developments in the popular media are not subject to peer review and may be oversimplified, inaccurate or biased. 10 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 2 Experimental skills and strategies Students should be able to: Examples of what students could be asked to do in an exam WS 2.1 Suggest a hypothesis to explain given Use scientific theories and explanations to observations or data. develop hypotheses. WS 2.2 Describe a practical procedure for a specified Plan experiments or devise procedures to purpose. make observations, produce or characterise Explain why a given practical procedure is well a substance, test hypotheses, check data or designed for its specified purpose. explore phenomena. Explain the need to manipulate and control variables. Identify in a given context: the independent variable as the one that is changed or selected by the investigator the dependent variable that is measured for each change in the independent variable control variables and be able to explain why they are kept the same. Apply understanding of apparatus and techniques to suggest a procedure for a specified purpose. WS 2.3 Describe/suggest/select the technique, Apply a knowledge of a range of techniques, instrument, apparatus or material that should be instruments, apparatus, and materials to select used for a particular purpose, and explain why. those appropriate to the experiment. WS 2.4 Identify the main hazards in specified practical Carry out experiments appropriately having due contexts. regard for the correct manipulation of apparatus, Suggest methods of reducing the risk of harm in the accuracy of measurements and health and practical contexts. safety considerations. WS 2.5 Suggest and describe an appropriate sampling Recognise when to apply a knowledge of technique in a given context. sampling techniques to ensure any samples collected are representative. WS 2.6 Read measurements off a scale in a practical Make and record observations and context and record appropriately. measurements using a range of apparatus and methods. WS 2.7 Assess whether sufficient, precise measurements Evaluate methods and suggest possible have been taken in an experiment. improvements and further investigations. Evaluate methods with a view to determining whether or not they are valid. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 11 3 Analysis and evaluation Apply the cycle of collecting, presenting and analysing data, including: Students should be able to: Examples of what students could be asked to do in an exam WS 3.1 Construct and interpret frequency tables and Presenting observations and other data using diagrams, bar charts and histograms. appropriate methods. Plot two variables from experimental or other data. WS 3.2 Translate data between graphical and numeric Translating data from one form to another. form. WS 3.3 For example: Carrying out and represent mathematical and use an appropriate number of significant statistical analysis. figures find the arithmetic mean and range of a set of data construct and interpret frequency tables and diagrams, bar charts and histograms make order of magnitude calculations change the subject of an equation substitute numerical values into algebraic equations using appropriate units for physical quantities determine the slope and intercept of a linear graph draw and use the slope of a tangent to a curve as a measure of rate of change understand the physical significance of area between a curve and the x-axis and measure it by counting squares as appropriate. WS 3.4 Apply the idea that whenever a measurement is Representing distributions of results and make made, there is always some uncertainty about estimations of uncertainty. the result obtained. Use the range of a set of measurements about the mean as a measure of uncertainty. WS 3.5 Use data to make predictions. Interpreting observations and other data Recognise or describe patterns and trends in (presented in verbal, diagrammatic, graphical, data presented in a variety of tabular, graphical symbolic or numerical form), including identifying and other forms. patterns and trends, making inferences and drawing conclusions. Draw conclusions from given observations. 12 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 Students should be able to: Examples of what students could be asked to do in an exam WS 3.6 Comment on the extent to which data is Presenting reasoned explanations including consistent with a given hypothesis. relating data to hypotheses. Identify which of two or more hypotheses provides a better explanation of data in a given context. WS 3.7 Apply the following ideas to evaluate data to Being objective, evaluating data in terms suggest improvements to procedures and of accuracy, precision, repeatability and techniques. reproducibility and identifying potential sources An accurate measurement is one that is close of random and systematic error. to the true value. Measurements are precise if they cluster closely. Measurements are repeatable when repetition, under the same conditions by the same investigator, gives similar results. Measurements are reproducible if similar results are obtained by different investigators with different equipment. Measurements are affected by random error due to results varying in unpredictable ways; these errors can be reduced by making more measurements and reporting a mean value. Systematic error is due to measurement results differing from the true value by a consistent amount each time. Any anomalous values should be examined to try to identify the cause and, if a product of a poor measurement, ignored. WS 3.8 Present coherent and logically structured Communicating the scientific rationale for responses, using the ideas in 2 Experimental investigations, methods used, findings and skills and strategies and 3 Analysis and reasoned conclusions through paper-based and evaluation, applied to the required practicals, and electronic reports and presentations using verbal, other practical investigations given appropriate diagrammatic, graphical, numerical and symbolic information. forms. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 13 4 Scientific vocabulary, quantities, units, symbols and nomenclature Students should be able to: Examples of what students could be asked to do in an exam WS 4.1 The knowledge and skills in this section apply Use scientific vocabulary, terminology and across the specification, including the required definitions. practicals. WS 4.2 Recognise the importance of scientific quantities and understand how they are determined. WS 4.3 Use SI units (eg kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate. WS 4.4 Use prefixes and powers of ten for orders of magnitude (eg tera, giga, mega, kilo, centi, milli, micro and nano). WS 4.5 Interconvert units. WS 4.6 Use an appropriate number of significant figures in calculation. 14 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4 Subject content This specification is presented in a two column format. The left hand column contains the specification content that all students must cover, and that can be assessed in the written papers. The right hand column exemplifies some key opportunities for the following skills to be developed: WS refers to Working scientifically, MS refers to Mathematical requirements and AT refers to Use of apparatus and techniques. These are not the only opportunities. Teachers are encouraged to introduce all of these skills where appropriate throughout the course. Each topic begins with an overview. The overview puts the topic into a broader context and is intended to encourage an overarching approach to both the teaching and learning of each of the topic areas. It is not directly assessed. Any assessable content in this overview is replicated in the left hand column. Most of the content is common with and co-teachable with GCSE Combined Science: Trilogy. Content that is only applicable to biology is indicated by (biology only) either next to the topic heading where it applies to the whole topic or immediately preceding each paragraph or bullet point as applicable. Content that is only applicable to Higher Tier is indicated by (HT only) either next to the topic heading where it applies to the whole topic or immediately preceding each paragraph or bullet point as applicable. It is good practice to teach and develop all of the mathematical skills throughout the course. Some mathematical skills will only be assessed in certain subject areas. These are detailed in Mathematical requirements. Science is a practical subject. Details of the assessment of required practicals can be found in Practical assessment. Working scientifically and Use of apparatus and techniques skills will be assessed across all papers. Fundamental biological concepts and principles Students should have a basic understanding of the following biological principles and be able to apply them in either paper: The structure and functioning of cells and how they divide by mitosis and meiosis from sections Cell biology and Meiosis. That variation occurs when gametes fuse at fertilisation from section Sexual and asexual reproduction. The two essential reactions for life on Earth: photosynthesis and respiration from sections Photosynthetic reaction and Aerobic and anaerobic respiration. Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are made or broken down from section Metabolism. All molecules are recycled between the living world and the environment to sustain life from section How materials are cycled. Students should be able to recall and use this knowledge in questions that link different areas of the specification to develop coherent arguments and explanations. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 15 4.1 Cell biology Cells are the basic unit of all forms of life. In this section we explore how structural differences between types of cells enables them to perform specific functions within the organism. These differences in cells are controlled by genes in the nucleus. For an organism to grow, cells must divide by mitosis producing two new identical cells. If cells are isolated at an early stage of growth before they have become too specialised, they can retain their ability to grow into a range of different types of cells. This phenomenon has led to the development of stem cell technology. This is a new branch of medicine that allows doctors to repair damaged organs by growing new tissue from stem cells. 4.1.1 Cell structure 4.1.1.1 Eukaryotes and prokaryotes Content Key opportunities for skills development Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus. Bacterial cells (prokaryotic cells) are much smaller in comparison. They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids. Students should be able to demonstrate an understanding of the scale MS 1b, 2a, 2h and size of cells and be able to make order of magnitude calculations, WS 4.4 including the use of standard form. Use prefixes centi, milli, micro and nano. 4.1.1.2 Animal and plant cells Content Key opportunities for skills development Students should be able to explain how the main sub-cellular structures, WS 1.2 including the nucleus, cell membranes, mitochondria, chloroplasts in Recognise, draw and plant cells and plasmids in bacterial cells are related to their functions. interpret images of cells. Most animal cells have the following parts: a nucleus cytoplasm a cell membrane mitochondria ribosomes. In addition to the parts found in animal cells, plant cells often have: chloroplasts a permanent vacuole filled with cell sap. Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell. 16 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 Content Key opportunities for skills development Students should be able to use estimations and explain when they MS 1d, 3a should be used to judge the relative size or area of sub-cellular AT 7 structures. Images of cells in videos, bioviewers, photographs and micrographs can be used as comparison for students own drawings. Required practical activity 1: use a light microscope to observe, draw and label a selection of plant and animal cells. A magnification scale must be included. AT skills covered by this practical activity: AT 1 and 7. This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development. 4.1.1.3 Cell specialisation Content Key opportunities for skills development Students should be able to, when provided with appropriate information, explain how the structure of different types of cell relate to their function in a tissue, an organ or organ system, or the whole organism. Cells may be specialised to carry out a particular function: sperm cells, nerve cells and muscle cells in animals root hair cells, xylem and phloem cells in plants. 4.1.1.4 Cell differentiation Content Key opportunities for skills development Students should be able to explain the importance of cell differentiation. As an organism develops, cells differentiate to form different types of cells. Most types of animal cell differentiate at an early stage. Many types of plant cells retain the ability to differentiate throughout life. In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 17 4.1.1.5 Microscopy Content Key opportunities for skills development Students should be able to: WS 1.1 understand how microscopy techniques have developed over time explain how electron microscopy has increased understanding of sub-cellular structures. Limited to the differences in magnification and resolution. An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures. Students should be able to carry out calculations involving MS 1a, 1b, 2h, 3b magnification, real size and image size using the formula: WS 4.4 size of image magnification = size of real object Use prefixes centi, milli, micro and nano. Students should be able to express answers in standard form if appropriate. 18 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.1.1.6 Culturing microorganisms (biology only) Content Key opportunities for skills development Bacteria multiply by simple cell division (binary fission) as often as MS 1a, 1b, 1d, 2a, 2h once every 20 minutes if they have enough nutrients and a suitable Calculate the number of temperature. bacteria in a population after a certain time if given Bacteria can be grown in a nutrient broth solution or as colonies on an the mean division time. agar gel plate. MS 5c Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics. Calculate cross-sectional areas of colonies or clear areas around colonies using πr². Students should be able to describe how to prepare an uncontaminated WS 2.2, 2.4 culture using aseptic technique. They should be able to explain why: Petri dishes and culture media must be sterilised before use inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame the lid of the Petri dish should be secured with adhesive tape and stored upside down in school laboratories, cultures should generally be incubated at 25°C. Students should be able to calculate cross-sectional areas of colonies or MS 5c clear areas around colonies using πr². Students should be able to calculate the number of bacteria in a MS 1a, 2a, 2h population after a certain time if given the mean division time. (HT only) Students should be able to express the answer in standard MS 1b form. Required practical activity 2: investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition. AT skills covered by this practical activity: AT 1, 3, 4 and 8. This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development. There are links with this practical to Antibiotics and painkillers. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 19 4.1.2 Cell division 4.1.2.1 Chromosomes Content Key opportunities for skills development The nucleus of a cell contains chromosomes made of DNA molecules. WS 1.2 Each chromosome carries a large number of genes. Use models and analogies to develop explanations of In body cells the chromosomes are normally found in pairs. how cells divide. 4.1.2.2 Mitosis and the cell cycle Content Key opportunities for skills development Cells divide in a series of stages called the cell cycle. Students should be able to describe the stages of the cell cycle, including mitosis. During the cell cycle the genetic material is doubled and then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide to form two identical cells. Students need to understand the three overall stages of the cell cycle but do not need to know the different phases of the mitosis stage. Cell division by mitosis is important in the growth and development of multicellular organisms. Students should be able to recognise and describe situations in given contexts where mitosis is occurring. 20 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.1.2.3 Stem cells Content Key opportunities for skills development A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation. Students should be able to describe the function of stem cells in embryos, in adult animals and in the meristems in plants. Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant. Knowledge and understanding of stem cell techniques are not required. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning an embryo is produced with the same genes as WS 1.3 the patient. Stem cells from the embryo are not rejected by the patient’s Evaluate the practical body so they may be used for medical treatment. risks and benefits, as well as social and ethical The use of stem cells has potential risks such as transfer of viral issues, of the use of stem infection, and some people have ethical or religious objections. cells in medical research Stem cells from meristems in plants can be used to produce clones of and treatments. plants quickly and economically. Rare species can be cloned to protect from extinction. Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 21 4.1.3 Transport in cells 4.1.3.1 Diffusion Content Key opportunities for skills development Substances may move into and out of cells across the cell membranes WS 1.2 via diffusion. Recognise, draw and interpret diagrams that Diffusion is the spreading out of the particles of any substance in model diffusion. solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. WS 1.5 Some of the substances transported in and out of cells by diffusion are Use of isotonic drinks oxygen and carbon dioxide in gas exchange, and of the waste product and high energy drinks in urea from cells into the blood plasma for excretion in the kidney. sport. Students should be able to explain how different factors affect the rate of diffusion. Factors which affect the rate of diffusion are: the difference in concentrations (concentration gradient) the temperature the surface area of the membrane. A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism. Students should be able to calculate and compare surface area to MS 1c, 5c volume ratios. Students should be able to explain the need for exchange surfaces and a transport system in multicellular organisms in terms of surface area to volume ratio. Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials. In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism’s needs. The effectiveness of an exchange surface is increased by: having a large surface area a membrane that is thin, to provide a short diffusion path (in animals) having an efficient blood supply (in animals, for gaseous exchange) being ventilated. 22 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.1.3.2 Osmosis Content Key opportunities for skills development Water may move across cell membranes via osmosis. Osmosis is the WS 1.2 diffusion of water from a dilute solution to a concentrated solution Recognise, draw and through a partially permeable membrane. interpret diagrams that model osmosis. Students should be able to: MS 1a, 1c use simple compound measures of rate of water uptake use percentages calculate percentage gain and loss of mass of plant tissue. Students should be able to plot, draw and interpret appropriate graphs. MS 4a, 4b, 4c, 4d Required practical activity 3: investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue. AT skills covered by this practical activity: AT 1, 3 and 5. This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development. 4.1.3.3 Active transport Content Key opportunities for skills development Active transport moves substances from a more dilute solution to a more There are links concentrated solution (against a concentration gradient). This requires with this content to energy from respiration. Cell specialisation. Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration. Students should be able to: describe how substances are transported into and out of cells by diffusion, osmosis and active transport explain the differences between the three processes. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 23 4.2 Organisation In this section we will learn about the human digestive system which provides the body with nutrients and the respiratory system that provides it with oxygen and removes carbon dioxide. In each case they provide dissolved materials that need to be moved quickly around the body in the blood by the circulatory system. Damage to any of these systems can be debilitating if not fatal. Although there has been huge progress in surgical techniques, especially with regard to coronary heart disease, many interventions would not be necessary if individuals reduced their risks through improved diet and lifestyle. We will also learn how the plant’s transport system is dependent on environmental conditions to ensure that leaf cells are provided with the water and carbon dioxide that they need for photosynthesis. 4.2.1 Principles of organisation Content Key opportunities for skills development Cells are the basic building blocks of all living organisms. MS 1c Students should be A tissue is a group of cells with a similar structure and function. able to develop an Organs are aggregations of tissues performing specific functions. understanding of size and scale in relation to Organs are organised into organ systems, which work together to form cells, tissues, organs and organisms. systems. 4.2.2 Animal tissues, organs and organ systems 4.2.2.1 The human digestive system Content Key opportunities for skills development This section assumes knowledge of the digestive system studied in Key Stage 3 science. The digestive system is an example of an organ system in which several organs work together to digest and absorb food. Students should be able to relate knowledge of enzymes to Metabolism. Students should be able to describe the nature of enzyme molecules and relate their activity to temperature and pH changes. Students should be able to carry out rate calculations for chemical MS 1a, 1c reactions. Enzymes catalyse specific reactions in living organisms due to the shape of their active site. 24 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 Content Key opportunities for skills development Students should be able to use the ‘lock and key theory’ as a simplified WS 1.2 model to explain enzyme action. Students should be able to use other models to Students should be able to recall the sites of production and the action explain enzyme action. of amylase, proteases and lipases. Students should be able to understand simple word equations but no chemical symbol equations are required. Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream. Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch. Proteases break down proteins to amino acids. Lipases break down lipids (fats) to glycerol and fatty acids. The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration. Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of fat breakdown by lipase. Required practical activity 4: use qualitative reagents to test for a range of carbohydrates, lipids and proteins. To include: Benedict’s test for sugars; iodine test for starch; and Biuret reagent for protein. AT skills covered by this practical activity: AT 2 and 8. This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development. Required practical activity 5: investigate the effect of pH on the rate of reaction of amylase enzyme. Students should use a continuous sampling technique to determine the time taken to completely digest a starch solution at a range of pH values. Iodine reagent is to be used to test for starch every 30 seconds. Temperature must be controlled by use of a water bath or electric heater. AT skills covered by this practical activity: AT 1, 2, 5 and 8. This practical activity also provides opportunities to develop WS and MS. Details of all skills are given in Key opportunities for skills development. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 25 4.2.2.2 The heart and blood vessels Content Key opportunities for skills development Students should know the structure and functioning of the human heart and lungs, including how lungs are adapted for gaseous exchange. The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body. Knowledge of the blood vessels associated with the heart is limited to the aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries. Knowledge of the names of the heart valves is not required. Knowledge of the lungs is restricted to the trachea, bronchi, alveoli and the capillary network surrounding the alveoli. The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate. The body contains three different types of blood vessel: arteries veins capillaries. Students should be able to explain how the structure of these vessels relates to their functions. Students should be able to use simple compound measures such as MS 1a, 1c rate and carry out rate calculations for blood flow. 4.2.2.3 Blood Content Key opportunities for skills development Blood is a tissue consisting of plasma, in which the red blood cells, AT 7 white blood cells and platelets are suspended. Observing and drawing blood cells seen under a Students should know the functions of each of these blood components. microscope. WS 1.5 Evaluate risks related to use of blood products. Students should be able to recognise different types of blood cells in WS 3.5 a photograph or diagram, and explain how they are adapted to their functions. 26 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.2.2.4 Coronary heart disease: a non-communicable disease Content Key opportunities for skills development Students should be able to evaluate the advantages and disadvantages WS 1.4 of treating cardiovascular diseases by drugs, mechanical devices or WS 1.3 transplant. Evaluate methods of In coronary heart disease layers of fatty material build up inside the treatment bearing in coronary arteries, narrowing them. This reduces the flow of blood mind the benefits and through the coronary arteries, resulting in a lack of oxygen for the heart risks associated with the muscle. Stents are used to keep the coronary arteries open. Statins are treatment. widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit. In some people heart valves may become faulty, preventing the valve from opening fully, or the heart valve might develop a leak. Students should understand the consequences of faulty valves. Faulty heart valves can be replaced using biological or mechanical valves. In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery. 4.2.2.5 Health issues Content Key opportunities for skills development Students should be able to describe the relationship between health and disease and the interactions between different types of disease. Health is the state of physical and mental well-being. Diseases, both communicable and non-communicable, are major causes of ill health. Other factors including diet, stress and life situations may have a profound effect on both physical and mental health. Different types of disease may interact. Defects in the immune system mean that an individual is more likely to suffer from infectious diseases. Viruses living in cells can be the trigger for cancers. Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma. Severe physical ill health can lead to depression and other mental illness. Students should be able to translate disease incidence information MS 2c, 2g, 4a between graphical and numerical forms, construct and interpret frequency tables and diagrams, bar charts and histograms, and use a scatter diagram to identify a correlation between two variables. Students should understand the principles of sampling as applied to MS 2d scientific data, including epidemiological data. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 27 4.2.2.6 The effect of lifestyle on some non-communicable diseases Content Key opportunities for skills development Students should be able to: WS 1.4 discuss the human and financial cost of these non-communicable diseases to an individual, a local community, a nation or globally explain the effect of lifestyle factors including diet, alcohol and smoking on the incidence of non-communicable diseases at local, national and global levels. Risk factors are linked to an increased rate of a disease. WS 1.5 Interpret data about risk They can be: factors for specified aspects of a person’s lifestyle diseases. substances in the person’s body or environment. A causal mechanism has been proven for some risk factors, but not in others. The effects of diet, smoking and exercise on cardiovascular disease. Obesity as a risk factor for Type 2 diabetes. The effect of alcohol on the liver and brain function. The effect of smoking on lung disease and lung cancer. The effects of smoking and alcohol on unborn babies. Carcinogens, including ionising radiation, as risk factors in cancer. Many diseases are caused by the interaction of a number of factors. Students should be able to understand the principles of sampling as MS 2d applied to scientific data in terms of risk factors. Students should be able to translate information between graphical MS 2c, 4a and numerical forms; and extract and interpret information from charts, graphs and tables in terms of risk factors. Students should be able to use a scatter diagram to identify a correlation MS 2g between two variables in terms of risk factors. 28 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.2.2.7 Cancer Content Key opportunities for skills development Students should be able to describe cancer as the result of changes in cells that lead to uncontrolled growth and division. Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body. Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours. Scientists have identified lifestyle risk factors for various types of cancer. There are also genetic risk factors for some cancers. 4.2.3 Plant tissues, organs and systems 4.2.3.1 Plant tissues Content Key opportunities for skills development Students should be able to explain how the structures of plant tissues AT 7 are related to their functions. Observation and drawing of a transverse section of Plant tissues include: leaf. epidermal tissues palisade mesophyll spongy mesophyll xylem and phloem meristem tissue found at the growing tips of shoots and roots. The leaf is a plant organ. Knowledge limited to epidermis, palisade and spongy mesophyll, xylem and phloem, and guard cells surrounding stomata. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 29 4.2.3.2 Plant organ system Content Key opportunities for skills development Students should be able to explain how the structure of AT 3, 4, 5 root hair cells, xylem and phloem are adapted to their Measure the rate of transpiration by the functions. uptake of water. Students should be able to explain the effect of AT 6, 7 changing temperature, humidity, air movement and Investigate the distribution of stomata and light intensity on the rate of transpiration. guard cells. MS 2a, 2d, 5c Process data from investigations involving stomata and transpiration rates to find arithmetic means, understand the principles of sampling and calculate surface areas and volumes. Students should be able to understand and use simple MS 1a, 1c compound measures such as the rate of transpiration. Students should be able to: MS 2c, 4a, 4c translate information between graphical and numerical form plot and draw appropriate graphs, selecting appropriate scales for axes extract and interpret information from graphs, charts and tables. The roots, stem and leaves form a plant organ system for transport of substances around the plant. Students should be able to describe the process of transpiration and translocation, including the structure and function of the stomata. Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport. Xylem tissue transports water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream. The role of stomata and guard cells are to control gas exchange and water loss. Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation. Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls. Detailed structure of phloem tissue or the mechanism of transport is not required. 30 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.3 Infection and response Pathogens are microorganisms such as viruses and bacteria that cause infectious diseases in animals and plants. They depend on their host to provide the conditions and nutrients that they need to grow and reproduce. They frequently produce toxins that damage tissues and make us feel ill. This section will explore how we can avoid diseases by reducing contact with them, as well as how the body uses barriers against pathogens. Once inside the body our immune system is triggered which is usually strong enough to destroy the pathogen and prevent disease. When at risk from unusual or dangerous diseases our body’s natural system can be enhanced by the use of vaccination. Since the 1940s a range of antibiotics have been developed which have proved successful against a number of lethal diseases caused by bacteria. Unfortunately many groups of bacteria have now become resistant to these antibiotics. The race is now on to develop a new set of antibiotics. 4.3.1 Communicable diseases 4.3.1.1 Communicable (infectious) diseases Content Key opportunities for skills development Students should be able to explain how diseases caused by viruses, WS 1.4 bacteria, protists and fungi are spread in animals and plants. Students should be able to explain how the spread of diseases can be reduced or prevented. Pathogens are microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and can be spread by direct contact, by water or by air. Bacteria and viruses may reproduce rapidly inside the body. Bacteria may produce poisons (toxins) that damage tissues and make us feel ill. Viruses live and reproduce inside cells, causing cell damage. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 31 4.3.1.2 Viral diseases Content Key opportunities for skills development Measles is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is spread by inhalation of droplets from sneezes and coughs. HIV initially causes a flu-like illness. Unless successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells. Late stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles. Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis. 4.3.1.3 Bacterial diseases Content Key opportunities for skills development Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions. In the UK, poultry are vaccinated against Salmonella to control the spread. Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete. Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom. 4.3.1.4 Fungal diseases Content Key opportunities for skills development Rose black spot is a fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced. It is spread in the environment by water or wind. Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves. 32 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.3.1.5 Protist diseases Content Key opportunities for skills development The pathogens that cause malaria are protists. The malarial protist has a life cycle that includes the mosquito. Malaria causes recurrent episodes of fever and can be fatal. The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten. 4.3.1.6 Human defence systems Content Key opportunities for skills development Students should be able to describe the non-specific defence systems of the human body against pathogens, including the: skin nose trachea and bronchi stomach. Students should be able to explain the role of the immune system in the defence against disease. If a pathogen enters the body the immune system tries to destroy the pathogen. White blood cells help to defend against pathogens by: phagocytosis antibody production antitoxin production. 4.3.1.7 Vaccination Content Key opportunities for skills development Students should be able to explain how vaccination will prevent illness WS 1.4 in an individual, and how the spread of pathogens can be reduced by Evaluate the global use immunising a large proportion of the population. of vaccination in the prevention of disease. Vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection. Students do not need to know details of vaccination schedules and side effects associated with specific vaccines. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 33 4.3.1.8 Antibiotics and painkillers Content Key opportunities for skills development Students should be able to explain the use of antibiotics WS 1.4 and other medicines in treating disease. Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from There are links with this content to infectious bacterial diseases. However, the emergence of Culturing microorganisms (biology only). strains resistant to antibiotics is of great concern. There are links with this content to Resistant bacteria. Antibiotics cannot kill viral pathogens. Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens. It is difficult to develop drugs that kill viruses without also damaging the body’s tissues. 4.3.1.9 Discovery and development of drugs Content Key opportunities for skills development Students should be able to describe the process of discovery and development of potential new medicines, including preclinical and clinical testing. Traditionally drugs were extracted from plants and microorganisms. The heart drug digitalis originates from foxgloves. The painkiller aspirin originates from willow. Penicillin was discovered by Alexander Fleming from the Penicillium mould. Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant. New medical drugs have to be tested and trialled before being used to WS 1.6 check that they are safe and effective. Understand that the results of testing and trials New drugs are extensively tested for toxicity, efficacy and dose. are published only after Preclinical testing is done in a laboratory using cells, tissues and live scrutiny by peer review. animals. Clinical trials use healthy volunteers and patients. Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. In double blind trials, some patients are given a placebo. 34 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.3.2 Monoclonal antibodies (biology only) (HT only) 4.3.2.1 Producing monoclonal antibodies Content Key opportunities for skills development Students should be able to describe how monoclonal antibodies are produced. Monoclonal antibodies are produced from a single clone of cells. The antibodies are specific to one binding site on one protein antigen and so are able to target a specific chemical or specific cells in the body. They are produced by stimulating mouse lymphocytes to make a particular antibody. The lymphocytes are combined with a particular kind of tumour cell to make a cell called a hybridoma cell. The hybridoma cell can both divide and make the antibody. Single hybridoma cells are cloned to produce many identical cells that all produce the same antibody. A large amount of the antibody can be collected and purified. 4.3.2.2 Uses of monoclonal antibodies Content Key opportunities for skills development Students should be able to describe some of the ways in which WS 1.3 monoclonal antibodies can be used. Appreciate the power of monoclonal antibodies Some examples include: and consider any ethical for diagnosis such as in pregnancy tests issues. in laboratories to measure the levels of hormones and other chemicals in blood, or to detect pathogens in research to locate or identify specific molecules in a cell or tissue by binding to them with a fluorescent dye to treat some diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other cells in the body. Students are not expected to recall any specific tests or treatments but given appropriate information they should be able to explain how they work. Monoclonal antibodies create more side effects than expected. They WS 1.5 are not yet as widely used as everyone hoped when they were first Evaluate the advantages developed. and disadvantages of monoclonal antibodies. Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration 35 4.3.3 Plant disease (biology only) 4.3.3.1 Detection and identification of plant diseases Content Key opportunities for skills development (HT only) Plant diseases can be detected by: WS 1.4 stunted growth The everyday application spots on leaves of scientific knowledge to detect and identify plant areas of decay (rot) disease. growths malformed stems or leaves discolouration the presence of pests. (HT only) Identification can be made by: reference to a gardening manual or website taking infected plants to a laboratory to identify the pathogen using testing kits that contain monoclonal antibodies. Plants can be infected by a range of viral, bacterial and fungal WS 1.4 pathogens as well as by insects. The understanding of ion deficiencies allows Knowledge of plant diseases is restricted to tobacco mosaic virus as a horticulturists to provide viral disease, black spot as a fungal disease and aphids as insects. optimum conditions for Plants can be damaged by a range of ion deficiency conditions: plants. stunted growth caused by nitrate deficiency chlorosis caused by magnesium deficiency. Knowledge of ions is limited to nitrate ions needed for protein synthesis and therefore growth, and magnesium ions needed to make chlorophyll. 36 Visit aqa.org.uk/8461 for the most up-to-date specification, resources, support and administration  GCSE Biology (8461). For exams 2018 onwards. Version 1.0 4.3.3.2 Plant defence responses Content Key opportunities for skills development Students should be able to describe physical and chemical plant There are links with this defence responses. content to Adaptations. Physical defence responses to resist invasion of microorganisms. Cellulose cell walls. Tough waxy cuticle on leaves. Layers of dead cells around stems (bark on trees) which fall off. Chemical plant defence responses. Antibacterial chemicals. Poisons to deter herbivores. Mechanical adaptations. Thorns and hairs deter animals. Leaves which droop or curl when touched. Mimicry to trick animals. 4.4 Bioenergetics In this section we will explore how plants harness the Sun’s energy in photosynthesis in order to make food. This process liberates oxygen which has built up over millions of years in the Earth’s atmosphere. Both animals and plants use this oxygen to oxidise food in a process called aerobic respiration which transfers the energy that the organism needs to perform its fu