IGCSE Biology CIE Past Paper Notes - Cell Structure PDF

Head to savemyexams.co.uk for more awesome resources YOUR NOTES IGCSE Biology CIE  2. Organisation...

Head to savemyexams.co.uk for more awesome resources YOUR NOTES IGCSE Biology CIE  2. Organisation of the Organism CONTENTS 2.1 Cell Structure & Size of Specimens 2.1.1 Cell Structure 2.1.2 Organisation of Cells 2.1.3 Magnification Formula 2.1.4 Converting Between Units: Extended Page 1 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 2.1 Cell Structure & Size of Specimens YOUR NOTES  2.1.1 Cell Structure Animal & Plant Cells Animals The main features of animals: They are multicellular Their cells contain a nucleus with a distinct membrane Their cells do not have cellulose cell walls Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis) They feed on organic substances made by other living things They often store carbohydrates as glycogen They usually have nervous coordination They are able to move from place to place A typical animal cell Plants The main features of plants: They are multicellular Their cells contain a nucleus with a distinct membrane Their cells have cell walls made out of cellulose Their cells contain chloroplasts (so they can carry out photosynthesis) They feed by photosynthesis Page 2 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources They store carbohydrates as starch or sucrose YOUR NOTES They do not have nervous coordination  A typical plant cell Page 3 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Cell Structures Found in Both Animal and Plant Cells Table YOUR NOTES  An animal and plant cell as seen under a light microscope Page 4 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Cell Structures Found Only in Plant Cells Table YOUR NOTES  Page 5 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Bacteria Cells YOUR NOTES Bacteria, which have a wide variety of shapes and sizes, all share the following  biological characteristics: They are microscopic single-celled organisms Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move Examples of bacteria include: Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk) Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia) A typical bacterial cell Page 6 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Identifying Cell Structures & Function YOUR NOTES Within the cytoplasm, the following organelles are visible in almost all cells except  prokaryotes when looking at higher magnification (ie using an electron microscope): Mitochondria (singular: mitochondrion) are organelles found throughout the cytoplasm Ribosomes are tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of Rough Endoplasmic Reticulum (often shortened to R.E.R.) Vesicles can also be seen using a higher magnification - these are small circular structures found moving throughout the cytoplasm Structures in an animal cell visible under a light microscope and an electron microscope Page 7 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Structures in a plant cell visible under a light microscope and an electron microscope Page 8 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 2.1.2 Organisation of Cells YOUR NOTES  Producing New Cells The cells in your body need to be able to divide to help your body grow and repair itself Cells grow and divide over and over again New cells are produced by the division of existing cells Page 9 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Specialised Cells YOUR NOTES Specialised cells in animals  Specialised cells are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus Cells specialise by undergoing differentiation: this is a process by which cells develop the structure and characteristics needed to be able to carry out their functions Specialised Cells in Animals Table Page 10 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Diagrams of specialised cells in animals: Page 11 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Ciliated cell Nerve cell Page 12 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Red blood cells Sperm cell Page 13 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Egg cell Examples of specialised cells in plants: Page 14 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Diagrams of specialised cells in plants: Page 15 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Root hair cell Page 16 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Xylem structure Page 17 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Palisade mesophyll cell Page 18 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Levels of Organisation in an Organism YOUR NOTES  Levels of organisation Page 19 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Page 20 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Your syllabus states that you should be able to identify the different levels of YOUR NOTES organisation in drawings, diagrams and images of familiar material  An example of this is shown in the exam question below: Typical levels of organisation question  Exam Tip Most incorrect answers here come from not being able to identify a tissue, so it’s worth making sure you understand and remember that tissues are always made up of only one type of cell. Page 21 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 2.1.3 Magnification Formula YOUR NOTES  Magnification Formula Calculating magnification and specimen size using millimetres as units Magnification is calculated using the following equation: Magnification = Image size ÷ Actual size A better way to remember the equation is using an equation triangle: Magnification equation Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle - whatever you are trying to find, place your finger over it and whatever is left is what you do, so: Magnification = image size / actual size Actual size = image size / magnification Image size = magnification x actual size Remember magnification does not have any units and is just written as ‘x 10’ or ‘x 5000’  Worked Example An image of an animal cell is 30 mm in size and it has been magnified by a factor of x 3000. What is the actual size of the cell? To find the actual size of the cell: Page 22 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Worked example using the magnification equation  Exam Tip This skill most frequently comes up in paper 5 and 6 (although it also comes up in the multiple choice and occasionally the theory paper) and you will definitely have to calculate either magnification, drawing size or actual size in a least one paper.To ensure you do not lose marks: 1. Always look at the units that have been given in the question - if you are asked to measure something, most often you will be expected to measure it in millimetres NOT in centimetres - double check the question to see! 2. Learn the equation triangle for magnification and write it on the page straight away 3. Don’t forget that magnification has NO UNITS - students often lose a mark because they put one in Page 23 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources 2.1.4 Converting Between Units: Extended YOUR NOTES  Converting Between Units: Extended Using millimetres and micrometres as units The table below shows how millimetres are related to two other measures of length What this basically means is that 1mm = 1000µm and 1cm = 10,000µm This usually comes up in questions where you have two different units and you need to ensure that you convert them both into the same unit before proceeding with the calculation For example: Page 24 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources YOUR NOTES  Example extended magnification question Page 25 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to savemyexams.co.uk for more awesome resources Remember 1mm = 1000µm YOUR NOTES 2000 / 1000 = 2 so the actual thickness of the leaf is 2mm and the drawing  thickness is 50mm Magnification = image size / actual size = 50 / 2 = 25 So the magnification is x 25 (NO UNITS)  Exam Tip If you are given a question with two different units in it, make sure you convert them to the same unit before doing your calculation.If you don’t, there is a good chance that your answer will be the same as one of the incorrect options in a multiple choice question so you may think you got it right when, in fact, you haven’t!The following diagram may help with unit conversion between mm and µm: Page 26 of 26 © 2015-2021 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers