OCR AS Biology : Unit 1 (F212) : Cells, exchange and ...



Cell structure - Textbook chapter 1Key objectives:What are cells?How do we measure cells?What is the difference between Magnification and Resolution?How do you calculating magnification?What are the different types of microscope?Background The history of microscopy dates back to Hooke (1665) and van Leeuwenhoek (1676) whose observations ultimately lead to development of the cell theory. The cell theory has four basic ideas:Cells are the smallest unit capable of independent life.Cells are the basic unit of all living organisms i.e. all living things are made of cells.Cells arise from other cells by a process of cell division.The cell contains information that acts as the instructions for growth. This information is passed on to new cells.There 3 types of microscope used to study cells: light microscope, transmission electron microscope (TEM) and Scanning electron microscope (SEM). Modern light microscopes can achieve an effective magnification of up to 1500x and have a maximum resolving power of 200nm. Electron microscopes can achieve magnifications of up to 500000x and resolutions of 1nm.The “power” of a microscope depends both on its magnification and resolution, the higher the resolution of a microscope the greater the detail you can see. The maximum resolution achievable with a microscope is equal to half the energy source used to create the image.Cell TheoryWhat is a cell? [2]Units of measurementComplete the diagram below to show: names of the units of measurement, unit symbols, mathematical operations for converting between units. Complete the table below to show the corresponding value nanometres, micrometres and millimetres for the measurements given in each row. The first row has been completed for you. Ensure that your answers use the correct unit symbols. NanometreMicrometreMillimetre50.0050.000005111370.5When studying cells structure using a microscope the smallest unit of measurement commonly used to describe findings is the nanometre. Explain why.Magnification and ResolutionDefine the following terms:Magnification:Resolution:Visible light has a wavelength of 400-700 nm. Calculate the best resolution achievable with a light microscope? Show your working out:If the electron gun produces an electron beam with 2 nm wavelength, what is the best resolution achievable?Calculating total Magnification of a compound light microscopeEyepiece MagnificationObjective MagnificationOverall MagnificationX10X4X10X10X10X40X10X100Calculating Cell Magnification from imagesThe diagram below shows the general structure of an animal cell as seen under an electron microscope. _________5mCalculate the magnification factor of the diagramCalculate the length of structure GCalculate the diameter of the nucleolus (structure B)Calculate the diameter of the nucleusCalculate the diameter of the cell at its widest pointThe diagram below shows the general structure of a plant cell when viewed under and electron microscope. ___________ 40mCalculate the magnification factor of the diagramCalculate the thickness of the cellulose cell wall. Calculate the length of the cell.Calculate the length of structure C.Calculate the length of the vacuole.Types of microscopeFeatureLight MicroscopeTransmission electron microscope (TEM)Scanning electron microscope (SEM)Source of imageHow is the beam focusedMaximum effectivemagnificationMaximum resolutionCan a live specimen be used?Section or external view of the specimen CostCan the image be viewed directly Is staining of the specimen required?Why is the maximum effective magnification of a light microscope said to be 1500x when it is possible to produce higher magnifications with improved lenses? Use a named example to explain the need for staining when using a light microscope.State a possible disadvantage of staining a specimen for observation when using a light microscope State 2 advantages of using electron microscopes to study cells over a light microscope.State 2 disadvantages of using electron microscopes to study cells. Describe with reference to the role of staining how the transmission electron microscope differs from a scanning electron microscope? Explain why a vacuum necessary in an electron microscope?Which microscope?State which type of microscope has been used to create the image below, give a reason for your answer.The two images below of human chromosomes were produced using a light microscope and SEM. State which is which; give a reason for your answer.The image below was produced by staining a section of gut epithelium. The image is not shown in false colour. Which type of microscope was used to produce the image? Explain your answer.The three images below are of human cheek cells. One image has been produced using a light microscope, one using a SEM and one using a TEM. For each image identify the microscope used and justify your choice. Cell structureKey objectives:What is the role of the cytoskeleton?Which organelles may be present in a cell and why?How can we recognise organelles in micrographs / diagrams?What are the differences between plant and animal cells?How do organelles in a cell work together?What are the differences between prokaryotic and eukaryotic cells?Background All living things are cells or are made of cells. From your GCSE course you should be familiar with the basic structure of plant and animal cells. Since the development of the electron microscope a large number of structures have been identified within cells; those structures with a specialised function are termed organelles. Organelles within a cell work together to enable the cell to carry out its function. The fact that each organelle performs a different function within the cell is referred to as division of labour. The type, number and position of organelles will vary between cells dependent upon the cells role, environment and “life stage”.CytoskeletonThere is a network of fine filaments or fibres that run through the cytoplasm of the cell. This is known as the cytoskeleton. There are three types of fibre:microfilamentsintermediate filamentsmicrotubulesComplete the table to compare the structure and functions of the components of the cytoskeleton:Cytoskeleton ComponentFunctionMicrotubuleSize:Composition:Describe two ways in which the cytoskeleton can aid the movement of an entire cell.Name a type of human cell (not a sperm cell) that is able to move and explain why this is important to the cells functionWhy might chloroplasts need to be moved around a plant cellMany of the cells that line the human respiratory system are ciliated. Explain whyWhich organelles may be present in a cell and what do they do?Organelle Diagram StructureFunctionAnimal cell?Plant cell? Visible under a light microscopeNucleus NucleolusThe nucleus is the largest organelle (10-20m diameter)Roughly spherical.Surrounded by a double membrane called the nuclear envelopeThe nuclear envelope contains openings called nuclear pores.Outer membrane joins up to the endoplasmic reticulum The nucleoplasm contains chromatin (DNA + histones) which can be seen as dark blobs or fibre.)Nucleolus is not surrounded by A membraneDense spherical structure inside the nucleusContains nearly all of a cells genetic material; instructions for making proteinsControls protein synthesis (makes mRNA)Nucleolus makes RNA and Ribsosmes. These pass into the cytoplasm through the nuclear poresYes Yes YesRibosomeRough endoplasmic reticulumSmooth endoplasmic reticulumGolgi apparatusMitochondrion(mitochondria) ChloroplastLysosomeCentriolesPlasma membrane Cellulose cell wall VacuoleVesicleDescribe three structures / organelles present in generalised plant cells but absent from animal cells. Name the structures in the diagram below Sperm cells contain large numbers of mitochondria. Explain why?4) What evidence can be seen in the diagram that suggests that the cell is:metabolically active and involved in secretion of enzymes [3]involved in production or modification of lipids? [1]95377015367020 μmACDBEFGH0020 μmACDBEFGHThe diagram is a line drawing of a cell as seen with an electron microscope. Complete the table by matching the label to the function and then naming the appropriate part. The first one has been completed for you.Function of StructureLabelName of Part of the CellControls the activity of the cell.ANucleusProtein/polypeptides are made here.Aerobic respiration takes place here.Produces secretary vesicles.Controls the entry of substances into the cell.Contains hydrolytic enzymes.Makes lipids, including steroids.By reference to the diagram: Is the cell that of an animal or a plant? Give a reason for your answer.Identifying organelles from micrographsName the large round organelle in the micrograph below Is it found in animal or plant cellsName the structures A,B and C Name the large organelle shown in the micrograph belowIs it found in animal or plant cells?Suggest what structure D could beName the organelle shown in the micrograph belowState the role of the organelleName the structures visible in the transmission electron micrographs belowName the structure shown in the micrographName the structure shown in the micrograph belowName the structure shown in the micrograph belowTest yourself on a full cell micrographIs this an animal or plant cell? Can you name the structure 1-414439901108710001409065223583500160909019024600030683202125345003068320180149500309689514109700020504151508760001755140594360003068320100139500306832048704500Use the word bank at the bottom of the page to label this plant cell25107902425700003081020369633500305562040074850016567154098925001751965363537500218059032893000030683203181985002015490295910000306832028517850030683202331085003111512382500-35115579375Nuclear envelope, Nucleolus, Chloroplast, Mitochondria, cytoplasmEndoplasmic reticulum, starch grain, Cell wall, plasma membrane, vacuole00Nuclear envelope, Nucleolus, Chloroplast, Mitochondria, cytoplasmEndoplasmic reticulum, starch grain, Cell wall, plasma membrane, vacuoleParts of the cell working togetherComplete the paragraph below to describe how organelles in a cell work together to produce and secrete proteins such as hormonesThe nucleus carries all the necessary instructions for the cell to function. The code for protein synthesis is carried in the ____________ which are made of ____________ or histones. The instructions are ____________ or copied into mRNA (messenger ribonucleic acid). The mRNA then leaves the nucleus via the _________________ and travels to the ______________ where the message is read and translated into protein. The newly manufactured proteins are transported to forming face of Golgi body/apparatus in transport __________. Within the Golgi apparatus the proteins are processed. Vesicles are budded off from the maturing face of Golgi and are transferred to the ___________________ for secretion. Glandular cells (e.g. pancreas) contain large amounts of __________________ (this is encrusted with ribosomes and is where protein synthesis takes place) and Golgi body. These cells also contain many mitochondria since protein synthesis requires a lot of __________.(ii) State the function of structures B. [1](iii) Describe the role of structure C in secretion. [3]Prokaryotes and EukaryotesThe diagram below shows Staphylococcus, which is a prokaryotic cell. Label parts A to DThe following table compares some features of a prokaryotic and eukaryotic animal cell. Complete the table by using ‘present’, ‘absent’ or a short descriptive phrase. The first has been completed for you. Cellular FeatureProkaryotic CellEukaryotic Animal CellCell wallPresentAbsentCell surface membraneNucleusMembrane bound organellesDNAPlasmids in the cytoplasmRead p14-15 OCR Biology text bookFill in the gapsIt was once common practice to classify all living organisms as either animals or plants. With improved knowledge of living things it has become apparent that there are ______ fundamentally different types of cell. The most obvious difference between the two types is that one possesses a nucleus and the other does not.The cells of animals, ___________ and fungi contain many organelles some of which are bound by a membrane. These are referred to as ______________ cells. The cells of bacteria are very different, they lack membrane bound organelles such as a _____________. This type of cell is referred to as a _______________ cell (meaning before nucleus). Prokaryotic cells are about 1000 to 10000 times smaller than eukaryotic cells and are much simpler in structure. Biologists believe eukaryotes evolved from ________________.Eukaryotic cells contain membrane bound organelles, give 5 examples:Prokaryotic cells have one membrane, where is it? Use table 1 to compare plant (eukaryote), animal (eukaryote) and prokaryotic cells. For each cell type indicate whether the feature is present or absent using a tick or cross.FeaturePlant cellsAnimal cellsProkaryote cellsChloroplastsLarge permanent vacuoleCellulose cell wallPeptidoglycan (murein) cell wallLinear chromosomeCircular chromosome PlasmidsEndoplastic ReticulumGolgi bodyDNA free in the cytoplasmATP is produced in the mitochondriaATP is produced at infolded regions of the cell membrane called mesosomesUndulipodia contain 9 + 2 circular arrangement of microtubulesFlagella made form spiral protein called FlagellinRibosomesCell membraneGive 2 ways in which prokaryotes are useful to humansMitochondria and chloroplasts contain small loops of DNA similar to the plasmids found in prokaryotic cells. These organelles also contain ribosomes that are the same size as prokaryotic ribosomes. Can you suggest an explanation for these features? Give one way in which a eukaryotic plant cell is similar to a prokaryote.Give two ways in which a eukaryotic plant cell is different from a prokaryote.539115381000Label the highlighted features on the diagram of the bacterium E.coli shown in the diagram below. ................
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