Edexcel GCSE Biology Combined Science Past Paper PDF

Head to www.savemyexams.com for more awesome resources Edexcel GCSE Biology: Your notes Combined Science 1.1 Cell Structure Contents 1.1.1 Eukaryotic Organisms 1.1.2 Eukaryotic Org...

Head to www.savemyexams.com for more awesome resources Edexcel GCSE Biology: Your notes Combined Science 1.1 Cell Structure Contents 1.1.1 Eukaryotic Organisms 1.1.2 Eukaryotic Organisms: Animals & Plants 1.1.3 Eukaryotic Organisms: Fungi & Protoctists 1.1.4 Prokaryotic Organisms 1.1.5 Specialised Cells 1.1.6 Microscopy 1.1.7 Practical: Microscopy 1.1.8 Using Units Page 1 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.1 Eukaryotic Organisms Your notes Common Features of Eukaryotic Organisms: Basics All living organisms can be grouped or 'classified' using a classification system that consists of five kingdoms. These five kingdoms are: Animals Plants Fungi Protoctists Prokaryotes The first four kingdoms in this list (the animals, plants, fungi and protoctists) can actually be grouped together, as they are all eukaryotic organisms (also known as eukaryotes) Animals, plants, fungi and protoctists are all eukaryotes Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane Page 2 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes An animal cell (left) and plant cell (right) as seen under a light microscope. They are both eukaryotic cells as they both have a distinct membrane-bound nucleus. Prokaryotic organisms (also known as prokaryotes) are in a separate kingdom and are different from eukaryotes as they are always single-celled and do not contain a nucleus (instead, the nuclear material of prokaryotic cells is found in the cytoplasm) Bacteria are prokaryotic organisms Prokaryotic cells are substantially smaller than eukaryotic cells Page 3 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.2 Eukaryotic Organisms: Animals & Plants Your notes 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 Cell Structures Found in Both Animal and Plant Cells Table Page 4 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 5 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Plants The main features of plants: Your notes 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 They store carbohydrates as starch or sucrose They do not have nervous coordination A typical plant cell Cell Structures Found Only in Plant Cells Table Page 6 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Exam Tip You need to be able to recognise, draw and interpret images of cells, so practice drawing and labelling animal and plant cells as part of your revision. Page 7 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.3 Eukaryotic Organisms: Fungi & Protoctists Your notes Fungi Main features of fungi: They are usually multicellular but some are single-celled (e.g. yeast) Multicellular fungi are mainly made up of thread-like structures known as hyphae that contain many nuclei and are organised into a network known as a mycelium Their cells contain a nucleus with a distinct membrane Their cells have cell walls made of chitin (chitinous cell walls) Their cells do not contain chloroplasts (so they cannot carry out photosynthesis) They feed by secreting extracellular digestive enzymes (outside the mycelium) onto the food (usually decaying organic matter) and then absorbing the digested molecules. This method of feeding is known as saprotrophic nutrition Some fungi are parasitic and feed on living material Some fungi store carbohydrates as glycogen They do not have nervous coordination Examples of fungi include: moulds, mushrooms, yeasts Page 8 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A typical fungal cell Page 9 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The typical structure of a multicellular fungus e.g. Mucor (bread mould) Page 10 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Protoctists Main features of protoctists: Your notes The protoctists are a very diverse kingdom of organisms that don't really belong in any of the other eukaryotic kingdoms (animals, plants and fungi) They are mainly microscopic and single-celled but some aggregate (group together) into larger forms, such as colonies or chains of cells that form filaments Their cells contain a nucleus with a distinct membrane Some have features making them more like animal cells e.g. Plasmodium (the protoctist that causes malaria) Some have features, such as cell walls and chloroplasts, making them more like plant cells e.g. green algae, such as Chlorella This means some protoctists photosynthesise and some feed on organic substances made by other living things They do not have nervous coordination Examples of protoctists include: amoeba, Paramecium, Plasmodium, Chlorella Two examples of protoctist cells Exam Tip You need to be able to recognise, draw and interpret images of cells. While you do not need to know the exact details of the structures of fungi and protoctists, you may be required to apply your knowledge of cells to these examples. Page 11 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.4 Prokaryotic Organisms Your notes Prokaryotes All living organisms can be grouped or ‘classified’ using a classification system that consists of five kingdoms. These five kingdoms are: Animals Plants Fungi Protoctists Prokaryotes The prokaryotes are different from the other four kingdoms (which are all eukaryotes) as prokaryotic organisms are always single-celled and do not contain a nucleus Instead, the nuclear material of prokaryotic cells is found in the cytoplasm Prokaryotic cells are also much smaller (about x1000 smaller) than eukaryotic cells They are too small to contain chloroplasts or mitochondria Bacteria are prokaryotic organisms Bacteria 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 present in prokaryotes - 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 eukaryotic 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) Page 12 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A typical bacterial cell Page 13 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.5 Specialised Cells Your notes Specialised Cells Specialised cells are those which have developed certain characteristics (known as adaptations) in order to perform particular functions 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 Examples of specialised cells in animals include: Sperm cells Egg cells Ciliated epithelial cells Sperm cells Sperm cells are highly specialised for their role in reproduction i.e. to carry the DNA of the male to the egg cell (the ovum) of the female Sperm cell Sperm Cell Adaptations Table Page 14 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Egg cells Egg cells are also highly specialised for their role in reproduction i.e. to be fertilised by a single sperm and to develop into an embryo Egg cell Page 15 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Egg Cell Adaptations Table Your notes Ciliated epithelial cells Ciliated epithelial cells are highly specialised for their role in wafting bacteria and other particles (trapped by mucus) up to the throat (to be coughed out) or down to the stomach (to be digested) Page 16 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Ciliated epithelial cells Ciliated Epithelial Cell Adaptations Table Your notes Exam Tip Remember: Cilia and microvilli are not the same. Cilia are hair-like projections that can move ('waft') mucus along, whereas microvilli are multiple indentations of the small intestinal epithelial cell membrane, designed to increase the surface area for absorption. Microvilli cannot move by themselves as cilia can. Page 17 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.6 Microscopy Your notes A Brief History of the Microscope Microscopy techniques have developed over time, increasing our understanding of cell structures and organelles This has also increased our understanding of the role of subcellular structures The first light microscopes were developed in the 17th Century Scientists such as Anton van Leeuwenhoek and Robert Hooke are responsible for using microscopes to develop our first understanding of cells The first cells (of a cork) were observed by Robert Hooke in 1665 using a light microscope Light microscopes use light and lenses to form a magnified image of a specimen Over the centuries, the design of the light microscope has evolved, increasing magnification and resolution to enhance the detail of what can be visualised With a modern light microscope, it is possible to see images of cells and large subcellular structures (like nuclei and vacuoles), although stains are often required to highlight certain parts of cells The most powerful light microscopes today have a maximum magnification of approximately 1000 to 2000x The first electron microscopes were developed in the first half of the 20th Century (in the 1930s) Electron microscopes use beams of electrons, rather than light, to visualise specimens The wavelength of an electron beam is much smaller than that of visible light, which gives electron microscopes a much higher resolution and magnification Page 18 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Electron Microscopes An electron microscope has much higher magnification and resolving power than a light microscope Your notes They can therefore be used to study cells in much finer detail, enabling biologists to see and understand many more subcellular structures such as the mitochondria, chloroplasts and ribosomes They have also helped biologists develop a better understanding of the structure of the nucleus and cell membrane Electron microscopes have a maximum magnification of approximately 2,000,000x An example of an electron micrograph (of ciliated epithelium tissue) produced by an electron microscope. Notice the high level of detail included. The colour has been added by a computer programme. Page 19 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Magnification Calculations Magnification is calculated using the following equation: Your notes Magnification = Drawing size ÷ Actual size A better way to remember the equation is using an equation triangle: An equation triangle for calculating magnification 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 = actual size × magnification Remember magnification does not have any units and is just written as ‘X 10’ or ‘X 5000’ Page 20 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes 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: Worked example using the equation triangle for magnification You may also be asked to calculate the total magnification of a light microscope if given the magnification of the eyepiece lens and the magnification of the objective lens As these are two separate parts of a light microscope, each with its own magnifying power, you can simply multiply the two values to calculate the total magnification: Magnification of light microscope = Magnification of eyepiece lens × Magnification of objective lens Page 21 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Exam Tip Your notes It is easy to make silly mistakes with magnification calculations. To ensure you do not lose marks in the exam: 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! Learn the equation triangle for magnification and always write it down when you are doing a calculation – examiners like to see this! Page 22 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.7 Practical: Microscopy Your notes Practical: Microscopy Many biological structures are too small to be seen by the naked eye Optical microscopes are an invaluable tool for scientists as they allow for tissues, cells and organelles to be seen and studied Light is directed through a thin layer of biological material (containing the tissue(s), cell(s) or organelle(s) to be observed) that is supported on a glass slide This light is focused through several lenses so that an image is visible through the eyepiece Apparatus The key components of an optical microscope you will need to use are: The eyepiece lens The objective lenses The stage The light source The coarse and fine focus Other apparatus used: Forceps Scissors Scalpel Coverslip Slides Pipette Page 23 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The components of an optical microscope Method Specimens must be prepared on a microscope slide to be observed under a light microscope This must be done carefully to avoid damaging the biological specimen and the structures within it The most common specimens to observe under a light microscope are cheek cells (animal cells) and onion cells (plant cells) Preparing a slide using a liquid specimen: Add a few drops of the sample to the slide using a pipette Cover the liquid/smear with a coverslip and gently press down to remove air bubbles Wear gloves to ensure there is no cross-contamination of foreign cells Preparing a slide using a solid specimen: Use scissors to cut a small sample of the tissue Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide (using a scalpel or forceps) Some tissue samples need to be treated with chemicals to kill/make the tissue rigid Gently place a coverslip on top and press down to remove any air bubbles Page 24 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources A stain may be required to make the structures visible depending on the type of tissue being examined. Commonly used stains include methylene blue to stain cheek cells and iodine to stain onion cells Your notes Take care when using sharp objects and wear gloves to prevent the stain from dying your skin When using an optical microscope always start with the low power objective lens: It is easier to find what you are looking for in the field of view This helps to prevent damage to the lens or coverslip in case the stage has been raised too high Preventing the dehydration of tissue: The thin layers of material placed on slides can dry up rapidly Adding a drop of water to the specimen (beneath the coverslip) can prevent the cells from being damaged by dehydration Unclear or blurry images: Switch to the lower power objective lens and try using the coarse focus to get a clearer image Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly There could be cross-contamination with foreign cells or bodies Page 25 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Care must be taken to avoid smudging the glass slide or trapping air bubbles under the coverslip Page 26 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Results: using a graticule to measure cells, cell structures and organelles In order to take measurements of cells, you need to use a calibrated graticule Your notes An eyepiece graticule and stage micrometer are used to measure the size of the object when viewed under a microscope The three lines of a stage micrometer and the 100 division-markings of the eyepiece graticule, as seen if looking down the lens of a light microscope Results - producing labelled scientific drawings from observations Producing biological drawings of what you see under the microscope is a key skill The key is not to try to be too artistic with your drawings – they are supposed to be scientific so make sure you follow the rules Page 27 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Biological drawings should be as large as possible – aim to take up at least half of the space available on the page with your drawings Limitations The size of cells or structures of tissues may appear inconsistent in different specimen slides Cell structures are 3D and the different tissue samples will have been cut at different planes resulting in inconsistencies when viewed on a 2D slide Page 28 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that cannot be seen The treatment of specimens when preparing slides could alter the structure of cells Your notes Page 29 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1.1.8 Using Units Your notes Converting Units You may be given a question in your Biology exam where the measurements for a magnification calculation have different units You need to ensure that you convert them both into the same unit before proceeding with the calculation (usually to calculate the magnification) Remember the following to help you convert between mm (millimetres), µm (micrometres) and nm (nanometres): Converting between mm (millimetres), µm (micrometres) and nm (nanometres) If you are given a question with two different units in it, make sure you make a conversion so that both measurements have the same unit before doing your calculation For example: Page 30 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Worked example Your notes Page 31 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Step One: Remember that 1 mm = 1000 µm Your notes So to get from µm to mm you need to divide by 1000 Step Two: Calculate the thickness of the leaf in mm 2000 ÷ 1000 = 2, so the actual thickness of the leaf is 2 mm and the drawing thickness is 50 mm Step Three: Put these values into the equation for calculating magnification Magnification = image size ÷ actual size = 50 ÷ 2 = 25 So the magnification is x 25 Standard form When doing calculations and unit conversions, it is common to come across very big or very small numbers Standard form can be useful when working with these numbers Standard form is a way of writing very big and very small numbers using powers of 10 How to use standard form Using standard form, numbers are always written as follows: a × 10n The rules: 1 ≤ a < 10 (the number 'a' must always be between 1 and 10) n > 0 for LARGE numbers ('n' = how many times 'a' is multiplied by 10) n < 0 for SMALL numbers ('n' = how many times 'a' is divided by 10) Using standard form to convert between units For example, you can write 1 metre in millimetres using standard form: 1 m = 1000 mm So, 1 m = 1 mm × 1000 So, 1 m = 1 mm × 10 × 10 × 10 So, as we had to multiply 1 mm by 10 three times to get 1 m, we write this as: 1 m = 1 × 103 mm Writing 1 millimetre in metres using standard form is also possible and is just the opposite: 1 mm = 0.001 m So, 1 mm = 1 m ÷ 1000 So, 1 mm = 1 m ÷ 10 ÷ 10 ÷ 10 So, as we had to divide 1 m by 10 three times to get 1 mm, we write this as: Page 32 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1 mm = 1 × 10-3 m Exactly the same process can be used if you needed to convert micrometres into millimetres. For example: Your notes 1 µm = 0.001 mm So, 1 µm = 1 mm ÷ 1000 So, 1 µm = 1 mm ÷ 10 ÷ 10 ÷ 10 So, as we had to divide 1 mm by 10 three times to get 1 µm, we write this as: 1 µm = 1 × 10-3 mm Examples of using standard form in conversion calculations You could be asked to state 45 centimetres in millimetres using standard form: 1 cm = 10 mm So, 45 cm = 450 mm So, 45 cm = 4.5 mm × 10 × 10 So, as we had to multiply 4.5 mm by 10 two times to get 45 cm, we write this as: 45 cm = 4.5 × 102 mm You could also be asked to state 250 micrometres in millimetres using standard form: 1 µm = 0.001 mm So, 250 µm = 0.25 mm So, 25 µm = 2.5 mm ÷ 10 So, as we had to divide 4.5 mm by 10 just once to get 250 µm, we write this as: 250 µm = 2.5 × 10-1 mm Page 33 of 33 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers