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microscopy ASlevel
| Question | Answer |
|---|---|
| Scanning Electron Microscope (SEM) | passes a focused beam of electrons across the surface of a specimen to produce detailed, three-dimensional images of its exterior, does not need thin specimen, expensive, can’t see internal structures. |
| Transmission Electron Microscope (TEM) | Uses electromagnets to focus a beam of electrons that passes through a very thin specimen to produce a high-resolution, two-dimensional grayscale image of internal cell structures. Dead specimen only, expensive |
| What is a stain used for | to increase contrast so that transparent or colourless cellular structures become visible, differential staining allows for different structures or organisms to be distinguished clearly within a single preparation |
| Acetic Orcein | Binds to DNA and stains chromosomes red. |
| Eosin | Stains cytoplasm pink or red |
| Iodine | Stains cellulose in plant cell walls yellow and starch granules blue-black. |
| Methylene blue | Stains DNA in animal cells blue. |
| Sudan Red | Stains lipids |
| Name the two ways to set up a stage | Dry mount - make it thin so light passes through , place coverslip, place on stage. Wet Mount - pipettes to add water, no air, coverslip, add stain |
| What is the formula for each division on an eyepiece lens | Length of stage Micrometer/ number of eyepiece divisions. |
| What is the difference between a eukaryotic and prokaryotic cell | Eukaryotic contains membrane bound organelles I.e DNA, prokaryotic tends not to. |
| Structure of nucleus | Nucleus - large, spherical organelle that houses linear, membrane bound DNA (chromosomes), has nucleoplasm which is a jelly like layer that has dissolved ions, enzymes and nucleotides required for protein synthesis |
| Structure and function of nuclear envelope | A double membrane structure that surrounds the nucleus, consisting of two phospholipid bilayers. The outer membrane is often continuous with RER. It separates the contents of the nucleus from the cytoplasm, has nuclear pores which allow mRNA and ribosomes |
| Structure of chromatin and nucleolus | The general bulk of tangled threads. It is made of linear DNA molecules tightly coiled and wound around histone proteins, until mitosis where it becomes chromosome. primary role is to synthesise rRNA and assemble the subunits of ribosomes |
| Rough endoplasmic reticulum | Membrane with filled cavities (cisternae) coated with ribosomes. Forms channels to transport form one area to another, large SA for ribosomes to synthesise, proteins then pass through in vesicles to Golgi apparatus. |
| Smooth endoplasmic reticulum | Have enzymes to catalyse lipid metabolic processes ie, synthesis of cholesterol, lipids or phospholipids depending on the cells needs, and of steroid hormones. Involved absorption of lipids, has cisternae. |
| Golgi apparatus | Stack of flattened membrane sacs secretory vesicles bring proteins which need to be modified by adding sugars(glycoproteins) or lipids(lipoproteins) and are folded into 3d shapes, proteins packaged, vesicles pinched, stored in cell and moved to membrane. |
| Lysosomes | Made from Golgi apparatus, store hydrolytic enzymes such as neutrophils and macrophages that engulf pathogens, digests dead organelles and foreign matter and return the digested matter to cell for reuse |
| Cilia, Undulipodia and flagella | Protrusions from cell surrounded by cell membrane, contain micro tubules and are formed from centrioles, on epithelial cells has receptors that detect signals and allow movement |
| Ribosomes | Small spherical organelles made of ribosomal RNA. Ribosomes bound to RER are mainly synthesising of proteins for outside cell. Ribosomes free in cytoplasm are the site of assembly of proteins for inside cell. |
| Centrioles | 2 bundles of micro tubules at right angles to each other form a cylinder, before mitosis the spindle made of Tubulin forms centrioles chromosomes attach to the middle part of spindle and motorproteins walk along tubulin threads pull apart. |
| Cytoskeleton | Microfilaments, Intermediate Filaments and Microtubules. Provides structure and shape to cell, moves organelles in cell, anchors organelles in place allows for movement of mRNA and exocytosis |
| Microfilaments | Made of actin protein Partner with the motor protein myosin to slide past each other, causing muscle fibres to move and help support cell and movement |
| Intermediate filaments | provide mechanical strength and structural stability to animal cells and tissues And anchor down organelles, made of many different protein I.e keratin |
| Micro tubules | Help move substances and organelles move through cytoplasm and form spindle before cell divides which enables chromosomes to move within cell making up cilia and centrioles. |
| Cellulose cell wall | Made up of cellulose fibres, prevents cell from osmotically bursting when turgid, partially permeable and allows substances ie dissolved mineral ions to pass through. Fungi cell walls made of chitin. Bacterial cell walls made of peptidoglycan. |
| Vacuoles | Membrane(Tonoplast)selectively permeable. It controls the exchange of chemicals and small molecules between the vacuole and the cytoplasm (Cell Sap): an aqueous solution.Maintaining Turgor Pressure. This creates an outward hydrostatic pressure . plus more |
| Choloroplasts | Chloroplasts are double-membrane organelles where thylakoids/grana run light-dependent stages and the stroma runs the Calvin cycle. They contain 70S ribosomes, circular DNA, and rubisco. |
Created by:
sonia.