IB Biology Course Preparation 2018 PDF

O X F O R D I B C O U R S E P R E P A R A T I O N BI O LO G Y F O R I B D I P L O M A C O U R S E P R E PA R AT I O N Marwa Bkerat  O X F O R D I B C O U R S E P R E P A R A T I O N BI O LO G Y...

O X F O R D I B C O U R S E P R E P A R A T I O N BI O LO G Y F O R I B D I P L O M A C O U R S E P R E PA R AT I O N Marwa Bkerat  O X F O R D I B C O U R S E P R E P A R A T I O N BI O LO G Y F O R I B D I P L O M A C O U R S E P R E PA R AT I O N Mar wa Bkerat 1  Acknowledgements 3 The authors and publisher are grateful to those who have given permission to reproduce the following extract and adaptation of Great Clarendon Street, Oxford, OX2 6DP, United Kingdom copyright material: Francis Crick: from What Mad Pursuit: A Personal View of Oxford University Press is a department of the University of Scientific Discovery, copyright © 1988. Reprinted by permission Oxford. It furthers the University’s objective of excellence in of Basic Books., an imprint of Perseus Books, LLC, a subsidiary of research, scholarship, and education by publishing worldwide. Hachette Book Group, Inc. 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Printed in India by Manipal Technologies Ltd Croydon CR0 4YY  Contents Introduction to the Diploma Programme iv 1 Cells 1.1 Cell structure and function 1 1.2 The cell membrane 10 1.3 Cell transpor t 12 1.4 Origin of cells 16 1.5 Cell division 18 2 Biological molecules 2.1 Essential elements for life 23 2.2 Water 25 2.3 Carbohydrates and lipids 27 2.4 Proteins and enzymes 34 2.5 Nucleic acids 39 3 The human body 3.1 The digestive system 47 3.2 Blood and circulation 53 3.3 Breathing and respiration 59 3.4 Body defence 64 3.5 The nervous system 69 3.6 The endocrine system, hormones and homeostasis 72 4 Plants 4.1 Photosynthesis 79 4.2 Plant transpor t 88 5 Genetics 5.1 The material of inheritance 93 5.2 Reproduction and meiosis 98 5.3 Inheritance 10 6 5.4 Biotechnology 120 6 Ecology, evolution and classication 6.1 Ecosystems 126 6.2 Energy and nutrient transfer: modes of nutrition 131 6.3 Energy transfer in ecosystems 134 6.4 Nutrient transfer in ecosystems 136 6.5 Climate change 139 6.6 Evolution 141 6.7 Classication 146 7 Tips and ad vice on successful learning 7.1 Approaches to your learning 154 7.2 Good study habits 154 7.3 Academic honesty 156 7.4 Preparation for examination 157 7.5 Tips when approaching examination papers 158 Appendix 160 Index 167 Answers to questions in this book can be found at www.oxfordsecondary.com/9780198423508 iii  Introduction to the Diploma Programme The Diploma Programme (DP) is a two-year Theory of knowledge (approximately 100 pre-university course for students in the 16–19 teaching hours) is focused on critical thinking age group. In addition to offering a broad-based and introduces you to the nature, structure and education and in-depth understanding of selected limitations of knowledge. An important goal of subjects, the course has a strong emphasis on theory of knowledge is to establish links between developing intercultural competence, open- different areas of shared and personal knowledge mindedness, communication skills and the ability and make you more aware of how your own to respect diverse points of view. perspective might differ from those of others. You may be reading this book during the rst few The extended essay is a structured and formally months of the Diploma Programme or working presented piece of writing of up to 4,000 words through the book as a preparation for the course. based on independent research in one of the You could be reading it to help you decide approved DP disciplines. It is also possible to whether the Biology course is for you. Whatever write an interdisciplinary extended essay that your reasons, the book acts as a bridge from your covers two DP subjects. The main purpose of earlier studies to DP Biology, to support your the extended essay activity is to develop the learning as you take on the challenge of the last high-level research and writing skills expected at stage of your school education. university. Chapters 1 through to 6 of this book explain Creativity, activity, service involves a broad the biology that you need to understand at the range of activities (typically 3–4 hours per week) beginning of a DP Biology course. You may that help you discover your own identity, adopt already have met some of this science, but the the ethical principles of the IB and become a book encourages you to begin to look at the responsible member of your community. These concepts that underpin biology as a whole. goals are achieved through participation in arts and creative thinking (creativity), physical Chapter 7 of this book has advice on effective exercises (activity) and voluntary work (service). study habits and preparing for tests and examinations. Early preparation is vital even though now they may seem a long way off. DP Biology syllabus The appendix lists information you will need Basics throughout the DP Biology course, such as maths The DP Biology course itself is divided into four and ICT skills. sections: Core syllabus, Additional Higher Level (AHL) material, and one of four possible Options DP course structure together with an internal assessment (IA). There The DP covers six academic areas, including is also a group4 project in which all science languages and literature, humanities and social students in a school participate. sciences, mathematics, natural sciences and The Biology course is designed so that a student creative arts. Within each area, you can choose can study the entire course at standard level with one or two disciplines that are of particular no prior knowledge of biology. At higher level, interest to you and that you intend to study however, some earlier study of the subject is further at the university level. Typically, three advisable. subjects are studied at higher level (HL, 240 Biology standard level: Core + one Option at teaching hours per subject) and the other three at SL + IA + group 4 standard level (SL, 150 hours). project In addition to the selected subjects, all DP Biology higher level: Core + AHL + one students must complete three core elements of Option at HL + IA the course: theory of knowledge, extended essay, + group 4 project and creativity, activity, service. iv  Introduction to the Diploma Programme Biology topics Internal assessment (IA) The Biology Guide is a document for teachers Biology is an experimental science. The ability that lists the areas that students are to be taught to plan and execute an experimental project is as a series of Topics. On page viii there is a table part of your assessment, which is where the showing the connections between this book and internal assessment (IA) comes in. The internal the distribution in the Guide of the various areas assessment may include theoretical investigations of biology between SL, HL and the Option topics. and laboratory work. About 10 hours will be devoted to the IA, probably towards the end Core topics of the course. Your teacher will support you in The six Core topics are taught and examined to carrying out the IA and you will be taught the the same standard at both levels. They are: required skills throughout the course. The IA Cell biology accounts for 20% of your overall examination marks. Molecular biology Genetics Group 4 project Ecology Most students who study a group 4 subject undertake a collaborative project within – or Evolution and biodiversity possibly beyond – their school. Group 4 students Human physiology work together on this project, for over about Many of these topics and sub-topics are covered 10hours. The project is not assessed formally. in this book. Itemphasizes the relationships between sciences AHL topics and how scientic knowledge affects other areas of knowledge. It can be experimental There are ve additional higher-level topics, or theoretical. Be imaginative in your project, which you will only study if you have chosen to and perhaps combine with a different IB World study biology at higher level: School on another continent to study a project of Nucleic acids (an extension of Molecular mutual interest. biology) Aims of group 4 Metabolism, cell respiration and photosynthesis (an extension of Cell biology) There are ten aims addressed by every group 4 subject. Each student should: Plant biology (an extension of Ecology) be challenged and stimulated to appreciate Genetics and evolution (an extension of science within a global context Evolution and biodiversity) develop scientic knowledge and a set of Animal physiology (an extension of Human scientic techniques physiology) apply and use the knowledge and techniques Options develop experimental and investigative There are four Options, from which you will study scientic skills one. Within each Option some topics correspond learn to create, analyse and evaluate scientic to Core areas and one or two additional areas are information studied only by HL students. The Options are: learn to communicate effectively using Neurobiology and behaviour modern communication skills Biotechnology and bioinformatics imaging realize the value of effective collaboration and Ecology and conservation communication in science Human physiology have an awareness of the ethical implications of science appreciate the possibilities and limitations of science understand the relationships between scientic disciplines and between science and other areas of knowledge. v  International mindedness is one of the social Key features of the DP Biology course aspects of science reected in the IB mission The following components are incorporated into statement, which emphasizes the importance the DP Biology course: of intercultural understanding and respect for The nature of science ( ) is the overarching creating a better and more peaceful world. theme in all IB science subjects, including International mindedness is actively promoted biology. Throughout the course you will through all DP subjects by encouraging you to encounter many examples, activities and embrace diversity and adopt a global outlook. questions that go beyond the studied subject Biology is an experimental science that provides and demonstrate key principles of the scientic you with numerous opportunities to develop a approach to exploring the natural world. For broad range of practical and theoretical skills. example, the development of cell theory was Practical skills ( ) are required for setting based on experimental evidence that had been up experiments and collecting data. Typical accumulated by many generations of scientists laboratory works are described throughout this and shared within the scientic community book and include measuring enzyme activity through collaboration and communication, (2.4 Proteins and enzymes), quadrate sampling bolstered by innovations in microscope (6.1 Ecosystems), paper chromatography technology (1.1 Cell structure and function). (4.1 Photosynthesis) and use of potometers to Nature of science studies are not limited to the measure the rate of transpiration by plants scientic method but cover many other aspects (4.2 Plant transport). of science, from the uncertainty and limitations Maths skills ( ) are needed for processing of scientic knowledge to the ethical and social experimental data and solving problems. In implications of scientic research. Raising these addition to elementary mathematics, the IB issues will help you understand how science and Biology syllabus requires the use of statistics, scientists work in the 21st century. such as the calculation of standard deviation Theory of knowledge ( ) is another common and error, and the use of charts and graphs. feature of the DP Biology syllabus. In addition These maths skills are outlined in the appendix to the stand-alone theory of knowledge course on page 160 of this book. taken by all DP students, much of the material Approaches to learning ( ) are a variety of in Biology topics can prompt wider discussions skills, strategies and attitudes that you will be about the different ways of knowing used by encouraged to develop throughout the course. The scientists for interpreting experimental results. Diploma Programme recognizes ve categories Although theory of knowledge is not formally of such skills: communication, social, self- assessed in the DP Biology course, it facilitates management, research and thinking. These skills the study of science, just as the study of science are discussed in more detail in 7 Tips and advice supports you in their theory of knowledge course. on successful learning on page 154 of this book. vi  Introduction to the Diploma Programme Assessment over view In addition to the internal assessment discussed earlier, the external assessment is carried out at the end of the DP Biology course. Both HL and SL students are expected to take three papers as part of their external assessment. You will usually take papers 1 and 2 at one sitting with paper 3 a day or two later. The question papers are as follows:* Paper SL SL duration and marks HL HL duration and marks 1 30 multiple-choice 45 minutes; 40 multiple-choice questions 60 minutes; questions on Core material 30 marks; on Core and AHL material 40 marks; 20% of marks 20% of marks 2 Shor t and ex tended 75 minutes; Shor t written answer and 135 minutes; written answer questions 50 marks; ex tended written answer 72 marks; on Core material; 40% of marks questions on Core and AHL 36% of marks data-based question material; data-based question 3 Section A: 60 minutes; Section A: 75 minutes; Data-based questions 35 marks; Data-based questions 45 marks; and questions based on 20% of marks and questions based on 24% of marks experimental work experimental work Section B: Questions on Section B: Questions on your your chosen Option chosen Option The internal and external assessment marks are combined to give your overall DP Biology grade, from 1 (lowest) to 7 (highest). The nal score is calculated by combining grades for each of your six subjects. Theory of knowledge and extended essay components can collectively contribute up to three extra points to the overall Diploma score. Creativity, activity, service activities do not bring any points but must be authenticated for the award of the IB Diploma. Using this book eectively Throughout the book you will encounter separate text boxes to alert you to ideas and concepts. Here is an overview of these features and their icons: Icon Feature Description of feature WE Worked example A step-by-step explanation of how to approach and solve a biology problem. A biology problem to solve independently. Answers to these questions can be found Q Question at www.oxfordsecondary.com/9780198423508 Denes an impor tant scientic concept used in biology. It is impor tant to be familiar Key term with these terms to prepare you for the DP Biology course. DP ready – Nature Relates a topic in biology to the overarching principles of the scientic approach to of science exploring the natural world and the way discoveries are made. DP ready – Approaches to Highlights the skills of an eective learner necessary for the DP. learning DP ready – Theory Features ideas or concepts in biology that prompt wider discussions about the of knowledge dierent ways of knowing. Provides a reference to somewhere within this book with more information on a topic discussed in the tex t, given by the section number and the topic name. For example, Internal link 6.2 Energy and nutrient transfer: modes of nutrition refers to the second section in Chapter 6 of this book and covers the ways organisms transfer energy and nutrients. Provides a reference to a section of the DP Biology syllabus for fur ther reading on a DP link cer tain topic. Maths skills Explains an impor tant mathematical skill required for the DP Biology course. Relates the scientic theory to the practical aspects of biology you will encounter on Practical skills the DP Biology course. *Correct at the time of printing vii  Linking this book to the DP Biology syllabus This textbook can be read linearly, but you might nd it most useful to dip into specic sections to support different areas of your learning. For example, if you are at the start of your course, you might spend some time reading 7 Tips and advice on successful learning to develop your study skills. Alternatively, if you are learning about Darwin’s theory of evolution in class, read through the parts of 6 Ecology, evolution and classication that explain the conceptual basis of evolution. The following grid gives a comparison between the chapters of this book and all of the IB Diploma Programme Biology course topics. DP Topic Title Sub-topics Chapter in this book 1 Cell biology 1.1 Introduction to cells 1.2 Ultrastructure of cells 1.3 Membrane structure 1 1.4 Membrane transpor t 1.5 The origin of cells 1.6 Cell division 2 Molecular biology 2.1 Molecules to metabolism 2.2 Water 2.3 Carbohydrates and lipids 2.4 Proteins 2.5 Enzymes 2, 3, 4 2.6 Structure of DNA and RNA 2.7 DNA replication, transcription and translation 2.8 Cell respiration 2.9 Photosynthesis 3 Genetics 3.1 Genes 3.2 Chromosomes 3.3 Meiosis 5 3.4 Inheritance 3.5 Genetic modication and biotechnology 4 Ecology 4.1 Species, communities and ecosystems 4.2 Energy ow 6 4.3 Carbon cycling 4.4 Climate change 5 Evolution and biodiversity 5.1 Evidence for evolution 5.2 Natural selection 6 5.3 Classication of biodiversity 5.4 Cladistics 6 Human physiology 6.1 Digestion and absorption 6.2 The blood system 6.3 Defence against infectious disease 3 6.4 Gas exchange 6.5 Neurons and synapses 6.6 Hormones, homeostasis and reproduction 7 Nucleic acids (AHL) 7.1 DNA structure and replication 7.2 Transcription and gene expression 5 (very briey) 7.3 Translation 8 Metabolism, cell 8.1 Metabolism respiration and 8.2 Cell respiration 3,4 (very briey) photosynthesis (AHL) 8.3 Photosynthesis 9 Plant biology (AHL) 9.1 Transpor t in the xylem of plants 9.2 Transpor t in the phloem of plants 4 (briey) 9.3 Growth in plants 9.4 Reproduction in plants 10 Genetics and evolution 10.1 Meiosis (AHL) 10.2 Inheritance 5, 6 (very briey) 10.3 Gene pools and speciation 11 Animal physiology (AHL) 11.1 Antibody production and vaccination 11.2 Movement 3 11.3 The kidney and osmoregulation 11.4 Sexual reproduction viii  1 Cells A cell has a history; its structure is inherited, it grows, divides, and, as in the embryo of higher animals, the products of division dierentiate on complex lines. “ Living cells, moreover, transmit all that is involved in their complex heredity. ” Sir Frederick Gowland Hopkins, ‘Some Aspects of Biochemistry’, The Irish Journal of Medical Science (1932), 79, 346 Chapter contex t Key terms introduced All living organisms are made of cells. Since the 17th century, ➔ Cells tissues from dierent living organisms have been examined ➔ Dierentiation under microscopes and have shown that cells are the smallest ➔ Organelles unit of life. Some organisms are made of one cell, while others ➔ Prokaryotic cells and prokaryotes are made of many. Evolution has resulted in a great diversity ➔ Eukaryotic cells and eukaryotes between cells from the very simple prokaryotic cells to the most ➔ Magnication and resolution complex eukaryotic cells. Regardless of the dierences between ➔ Stem cells cells, there are many common features among them. All cells ➔ Hyd roph i l ic ( pola r ) a nd hyd rophobic contain genetic material, cytoplasm and a plasma membrane ( non- pola r ) substa n ces that controls the composition of the cell. New cells come from ➔ Integral and peripheral proteins pre-existing cells by cell di vision. ➔ A queous, con centrated a nd d i l u te sol u tions Learning objectives ➔ Hy poton ic, hy per ton ic a nd i soton ic In this chapter you will learn about: sol u tions ➔ E ndosy m biotic theor y ➔ the cell theory ➔ I nterphase a nd DN A r epl ication ➔ the basic structure of cells ➔ Mitos i s ➔ transpor t in cells ➔ Cy tok i nes i s ➔ cell division in prokaryotes and eukaryotes. ➔ Mu tations a nd me tastas i s 1.1 Cell structure and function Since the 17th century, microscopes have been used to examine tissues DP link from different living organisms. This resulted in the development of The structure and function of the cell theory, which states that: cells will be explained fur ther 1. All living organisms are composed of cells in 1.1 Introduction to cells 2. Cells are the smallest unit of life. in the IB Biology Diploma Programme. 3. Cells come from pre-existing cells and cannot be created from non- living material. Division of cells results in the formation of new cells. Regardless of the differences between cells, all cells share some common features. All cells are surrounded by a plasma membrane, which separates the contents of the cell from its surroundings. All cells contain genetic material, which holds the information needed for the cell to carry out its activities. All cells contain cytoplasm where chemical reactions take place. 1  DP ready Nature of science Key term Trends and discrepancies Cells are the building Most organisms conform to cell theory, some do not. The cell theory blocks of life. was based on the work of several scientists over many years where various trends among the cells of living organisms were discovered. Some discrepancies have been discovered but they were not enough to discard the cell theory. Many organisms consist of cells that are considered atypical. Examples of atypical cells include the striated muscle bres which are larger than most animal cells and have many nuclei. Another example is giant algae (such as acetabularia) which are single-celled organisms with a much larger size than a normal cell. Unicellular versus multicellular Unicellular organisms, which are also known as single-celled organisms, are made up of a single cell. Examples of unicellular organisms include bacteria, amoeba, chlorella, paramecium and euglena. In unicellular organisms, the single cell is responsible for carrying out all the functions of life that are necessary for its survival. Table 1 indicates the seven functions of life that are necessary for the survival of any organism. Table 1. The seven functions of life necessary for the survival of any organism Function of life Description Metabolism The chemical reactions that take place inside the cell Response The ability to react towards a stimulus Homeostasis Keeping the internal environment of the cell within limits Growth The increase in size Key term Reproduction The production of ospring (sexual or asexual) The plasma membrane Excretion The removal of waste products from the cell (cell membrane) surrounds Nutrition Getting the material needed for growing and producing the cell and separates the energy contents of the cell from its surroundings. Multicellular organisms, which are also known as multi-celled organisms, are made up of more than a single cell. Examples of multicellular Cytoplasm is found within organisms include plants and animals. The cells of multicellular all cells, it is where the organisms differentiate to make different tissues that perform specialized cellular chemical reactions functions. For example, red blood cells are specialized to carry oxygen, take place. whereas nerve cells are specialized to pass a nerve impulse. Differentiation is the process by which a cell becomes more specialized. During the process of differentiation, some genes in the cell are “switched on”. This means the gene starts to be used in the function of the cell, and we refer to the gene as being expressed. Other genes are switched off (or unexpressed). This results in cells that are more specialized and perform different functions. Differentiated cells form tissues, tissues form organs, organs form organ systems and organ systems form the multicellular organism. Prokaryotes versus eukaryotes Living organisms can be divided into two main groups based on the presence or absence of a nucleus and membrane-bound organelles: prokaryotes and eukaryotes 2  1 Cells Prokaryotic cells have a simple structure as they lack a nucleus and Key term membrane-bound organelles. The genetic material (DNA) is not Dierentiation is the process enclosed inside a nucleus but rather found in a region called the by which a cell becomes nucleoid. Prokaryotes include bacteria and archaea (ancient bacteria). more specialized. When a Escherichia coli (E. coli) is an example of a bacterium. The structures gene is switched on during found in most prokaryotic cells are described in gure 1 and table 2. this process, we say the gene is being expressed. When pili a gene is switched o, it is cell wall unexpressed. plasma membrane DP link nucleoid containing naked DNA The prokaryotic and eukaryotic cells will be explained further cytoplasm in 1.2 Ultrastructure of cells 70S ribosomes in the IB Biology Diploma plasmid Programme. flagella Key term Organelles are structures found inside cells that perform a specic function. Figure 1. Prokaryotic cell structure (E. coli) Key term Table 2. The function of the main structures of prokaryotic cells Prokaryotic cells are simple Structure Description Function cells that lack a cell nucleus and membrane-bound Cell wall Made of Maintains the shape of the cell and peptidoglycan prevents the cell from bursting organelles. (a polysaccharide) Prokaryotes, such as Plasma A selectively Controls the substances moving into bacteria and archea, are membrane permeable and out of the cell single-celled organisms that membrane do not contain a nucleus or Cytoplasm A gel-like substance Contains enzymes to catalyse any membrane-bound cell enclosed within the chemical reactions taking place inside organelles. cell the cell Pili Hair-like structures Help bacteria to adhere to each other Internal link found on the for the transfer of DNA from one surface cell to another by a process called DNA will be explained in more conjugation detail in section 2.5 Nucleic Flagella A whip-like Helps bacteria move around acids of this book. (singular structure agellum) Key term Ribosomes 70S type Protein synthesis Eukaryotic cells are complex Nucleoid A region containing Contains the DNA which holds the the naked DNA genetic information that controls the cell cells that contain a cell nucleus and membrane- Plasmid A small ring of DNA Helps bacteria adapt to unusual bound organelles. situations such as antibiotic resistance Eukaryotes are single-celled or multicellular organisms Eukaryotic cells are more complex than prokaryotic cells as they whose cells contain a cell contain a nucleus and membrane-bound organelles. The genetic nucleus and membrane- material (DNA) is enclosed in a nucleus. Eukaryotes include plants, bound cell organelles. animals, fungi and protists. 3  Eukaryotes may be unicellular or multicellular. An amoeba is an Key term example of a unicellular eukaryote. Animals and plants are examples When discussing ribosomes, of multicellular eukaryotes. the S in 70S or 80S stands The structures found in most eukaryotic cells in animals and plants are for the Svedberg unit, which described in gure 2 and table 3, and gure 3 and table 4, respectively. is named after the Swedish chemist Theodor Svedberg. plasma membrane The value of S refers to golgi apparatus how fast the molecule will mitochondrion sediment if centrifuged. smooth endoplasmic reticulum The speed of the molecule to sediment is related to its nucleolus density, mass and shape. 80S ribosomes The higher the value of S, the rough endoplasmic reticulum more dense and massive nuclear membrane (nucleus) it is and the faster it will Figure 2. Eukaryotic cell structure (animal cell) sediment when centrifuged. Table 3. The function of the main structures of eukaryotic cells (animal cells) Structure Description Function Ribosomes Found either as 70S or 80S. Protein synthesis Could be found free in the cytoplasm or attached to the rough endoplasmic reticulum Smooth No ribosomes on the surface Lipid synthesis and endoplasmic transpor t reticulum Rough A network of tubules that Protein synthesis and Key term endoplasmic ex tend from the nucleus to the transpor t reticulum rest of the cell ATP (adenosine Lysosome Contains many enzymes Digests waste structures triphosphate) is a high- within the cell such as energy molecule that is dead organelles and composed of adenosine and foreign par ticles three phosphate groups. Its Golgi Consists of many attened Processing of proteins main function is to supply apparatus sacs stacked on top of each received from the rough energy for the chemical other. Has two sides, the cis endoplasmic reticulum. This reactions that take place in side, which receives products includes packaging and cells. from endoplasmic reticulum. modifying proteins to be The trans side, which is the side used either inside the cell or through which vesicles are excreted outside the cell released Mitochondrion Contains its own ribosomes Production of ATP in and DNA. It is made of aerobic respiration Internal link two membranes: an outer Aerobic respiration membrane and an inner and using glucose membrane that is folded to make ATP will inward to increase surface area be discussed in Nucleus It is surrounded by a porous Contains the genetic 3.3 Breathing and double membrane material (DNA) which hold respiration the genetic information that controls the cell Nucleolus Found inside the nucleus Ribosomes synthesis 4  1 Cells cell wall plasma membrane cytoplasm vacuole chloroplast 80S ribosome nucleus Figure 3. Eukaryotic cell structure (plant cell) Table 4. Structures that are only found in plant cells Structure Description Function Cell wall Made of cellulose Strengthens and suppor ts the (a polysaccharide) cell, maintains the shape of the cell and prevents the cell from bursting Chloroplasts Surrounded by two Photosynthesis membranes. It contains its own ribosomes and DNA Vacuoles Storage organelles that Store water and food (cell come from the Golgi sap) apparatus DP ready Nature of science Key term Improved tools allow for new scientic discoveries Magnication is the size of The electron microscope has a much greater magnication and image enlarged. higher resolution than the light microscope. It enables scientists to see the details of the organelles inside the cell. Resolution is the clarity of the view or image. Table 5. Dierences between prokaryotic cells and eukaryotic cells Feature Prokaryotic cells Eukaryotic cells Nucleus No nucleus Have nucleus DNA Found in the cytoplasm in a DNA found in the nucleus region named the nucleoid. enclosed in a nuclear envelope. Circular DNA Linear DNA Single strand Double helix Mitochondria No mitochondria Have mitochondria Ribosomes 70S (smaller) 80S (larger) Membrane- No membrane-bound Membrane-bound bound organelles organelles such as organelles Golgi apparatus and the endoplasmic reticulum Plasmid May have plasmid No plasmid Size Small < 10 µm Large > 10 µm Complexity Simple Complex 5  Table 6. Dierences between animal cells and plant cells Key term Feature Animal cell Plant cell Compare and contrast Cell wall No cell wall Have a cell wall (made of means to state the cellulose) similarities and dierences. Chloroplasts No chloroplasts Have chloroplasts Compare means to state the Vacuoles Do not usually contain Have a large central vacuole similarities. any vacuoles and if present they are small or Distinguish means to state temporary the dierences. Shape Rounded Angular Command terms and their meanings are available in the appendix. Q Question 1 Distinguish between the genetic material present in prokaryotes and eukaryotes. 2 Compare and contrast the structure of animal cells with plant cells. Maths skills: Standard form You can use “standard form” to write very big or very small numbers in a more condensed form. When writing in “standard form” we use exponents of base 10. Here are two examples: 6 1. The number 2 500 000 can be written as 2.5 × 10 –5 2. The number 0.0000543 can be written as 5.43 × 10 Follow these steps to express a number in standard form: Write down the rst few signicant gures (numbers including and following the rst digit that is not zero) that appear in the number as a number between 1 and 10 (the rst example above would give 2.5, and the second example 5.43). Write × 10 after this number. Count the number of places the decimal point would have to move from its original position to be between the rst two signicant gures of the number. This number becomes the exponent that you apply to 10. If the decimal point is moved to the left, then the exponent is positive. If the decimal point is moved to the right, then the exponent is negative. So, for the examples above: 1. 2 500 000: In this case, the decimal point is at the end of the number (2 500 000.0). The decimal point would have to move six places to the left to be between digits 2 and 5, so it is 6 therefore written as 2.5 × 10 2. 0.0000543: The decimal point moves ve places to the right, so it –5 is therefore written as 5.43 × 10 6  1 Cells Maths skills: Signicant gures The signicant g ures of a numbe r are the dig its of a numb er starting from the rs t no n-ze ro dig i t. S ig ni c ant  g ures are a good indication of the a cc ura cy of a m easurem e nt. For exam pl e, if the number is 3.0 it i ndic ates that the measureme nt was m ad e accurate to the tenth ( 0.1) and if the num ber is 3.00 it ind i cates that the measurem e nt was m ade ac c ura te to the hund red th (0.01). Therefore,