20409786
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Karteikarten von Czean Holgado, aktualisiert more than 1 year ago
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Erstellt von Czean Holgado
vor fast 5 Jahre
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| Frage | Antworten |
| Explain what a microscope is and describe its function. | A microscope is an instrument that enables us to magnify an object hundreds and thousands of times. Microscopes allow us to see many unicellular organisms that are not visible with the naked eye as well as allowing us to discover how details of their structures relate to their functions. |
| What does cell theory state? | -both plant and animal tissue is composed of cells -cells are the basic unit of all life -cells can only develop from existing cells |
| List three advantages of light microscopy. | -Easily available -Relatively cheap -Can be used to observe living as well as dead organisms/specimen |
| A compound light microscope has two lenses. What are they and how are they different from each other? | 1) Objective lens - placed near to the specimen 2) Eyepiece lens - lens through which the specimen is viewed |
| How does a light microscope work? | -The objective lens produces a magnified image, which is then magnified further by the eyepiece lens. Illumination is provided by a light underneath the sample which allows it to be visible. |
| Name the 4 different ways of preparing a sample and give examples of organisms/cells that can be viewed with each technique. | 1) Dry mount (muscle, plant tissue) 2) Wet mount (aquatic samples) 3) Squash slides (root tip cells) 4) Smear slides (blood cells) |
| Explain the benefit of having two lenses in a microscope. | -Having both the objective and eyepiece lens allows for much higher magnification and helps to reduce chromatic aberration. |
| Briefly describe the process of producing a dry mount sample. | 1) Solid specimens are viewed whole or they are cut into very thin slices - this is called 'sectioning'. 2) The specimen is placed onto the centre of a slide, and a coverslip is placed over the sample. Note - only hair, pollen, dust can be viewed whole - muscle tissue and plants have to be sectioned. |
| Briefly describe the process of producing a wet mount sample. | 1) Specimens are suspended in a liquid such as water or immersion oil. 2) A cover slip is placed on top of the specimen from an angle. |
| Briefly describe the process of producing a squash slide sample. | 1) A wet mount is prepared 2) Then a lens tissue is gently pressed onto a coverslip Damage to the coverslip can be avoided by squashing the sample between two slides. |
| Briefly describe the process of producing a smear slide. | 1) The edge of a slide is used to smear the sample, creating a thin, even coating on another slide. 2) A coverslip is placed over the sample. |
| Suggest a reason why a specimen must be thin, with reference to slide preparation. | 1) So light can shine through it 2) So details can be seen |
| Suggest a reason why the refractive index (ability to bend light) of the medium should be roughly the same as glass when pe preparing a wet mount. | 1) To reduce/prevent diffraction between the liquid and the glass 2) To prevent distortion of the image |
| Suggest a reason why a coverslip must be placed onto a wet mount at an angle. | 1) Helps to reduce/prevent air bubbles from being trapped as it pushes air to the sides. |
| Define the term 'resolution'. | How well you can distinguish two structures as being different from one another. |
| Define the term 'magnification' | How much bigger the image is compared to the object's original size. |
| Suggest two things that can limit resolution | 1) Wavelength of light 2) Diffraction of light as it passes through the sample |
| Define the term 'diffraction' | The tendency of light waves to spread as they pass close to physical structures. |
| Explain why staining is used in microscopy. | Staining provides contrast (1) as different cell components take up stains to different degrees. This allows components to become visible so they can be identified (2) |
| Name two examples of positively charged dyes that can be used in the staining of cell components. | 1) Crystal violet 2) Methylene blue |
| Explain how positively charged dyes work, in relation to staining. | They are attracted to negatively charged materials in the cytoplasm, leading to staining of cell components. |
| Name two examples of negatively cy charged dyes that can be used in the staining of cell components. | 1) Nigrosin 2) Congo red |
| Explain how negatively charged dyes work, in relation to staining, which is otherwise known as the negative stain technique. | Negatively charged dyes are repelled by cytosol, which is also negatively charged. These dyes stay outside of cells, leaving the cells unstained, which causes it to stand out against the stained background. |
| State two benefits of differential staining. | 1) Helps to distinguish between two types of organisms that would otherwise be hard to identify. 2) Helps to differentiate between different organelles found in a single organism's tissue sample. |
| Which type of cell is the gram stain technique used to separate? | It is used to separate bacteria into two groups, Gram-positive bacteria, and Gram-negative bacteria. |
| Briefly describe the stages in the gram stain technique. | 1) Crystal violet applied to specimen 2) Iodine then added (fixes dye) 3) The slide is washed with alcohol - gram-positive bacteria retain the crystal violet stain and appear blue/purple 4) Gram-negative bacteria have thinner cell walls and therefore lose the stain. 5) These are stained with safranin dye (counterstain), which make it appear red. |
| Suggest why Gram-negative infections are more difficult to treat than Gram-positive infections. | Gram-negative bacteria have much thinner cell walls that are not susceptible to the antibiotic penicillin, which inhibits cell wall formation. |
| The acid-fast technique is another method of differential staining. Which type of cell is it used to differentiate? | It is used to differentiate species of mycobacterium from other bacteria. |
| Briefly describe the stages involved in the acid-fast technique. | 1) A lipid solvent is used to carry carbolfuchsin dye into the cells 2) Cells are washed with a dilute acid-alcohol solution - mycobacterium are not affected by the acid-alcohol and retains the carbolfuchsin stain, which makes it appear red. 3) Other cells lose the stain and are exposed to methylene blue, making the other cells appear blue. |
| Name and explain the 4 stages involved in the production of sample slides. | 1) Fixing - chemicals like formaldehyde used to preserve specimens 2) Sectioning - specimens dehydrated with alcohols and placed in a mould, then cut into thin slices 3) Staining - specimens treated with different stains 4) Mounting - specimens secured onto a microscope slide |
| Many of the stains used in the preparation of slides are toxic or irritants. State two precautions you should take when handling these chemicals. | 1) Avoid skin or eye contact 2) Wear gloves 3) Wear goggles |
| Name some of the rules used in the production of good scientific drawings. | 1) Include a title 2) State magnification 3) Use a sharp pencil for drawings and labels 4) Use white, unlined paper 5) Draw smooth, and continuous lines 6) Do not shade 7) Draw clearly defined structures 8) Label lines with a ruler 9) Ensure proportions are correct. |
| State the equation used to calculate magnification. | Magnification = size of image / actual size of object |
| How many nanometres (nm) is 1 micrometre? | 1 micrometre (um) = 1000 nanometres (nm) |
| How many micrometres (um) is 1 millimetre? (mm) | 1 millimetre (mm) = 1000 micrometres (um) |
| How many millimetres (mm) is 1 metre (m) | 1 metre (m) = 1000 millimetres (mm) |
| Describe what an eyepiece graticule is, and explain its function. | It is a glass disc marked with a fine scale of 1 to 100 and it is used to measure the size of a sample under a microscope. |
| Describe what a stage micrometer is and state the actual size of each division. | It is a microscope slide with a very accurate scale in micrometres (um) engraved on it. 100 divisions = 1mm so 1 division is 10um. |
| State the formula used to find 1 graticule division. | 1 graticule division = number of eyepiece divisions/ number of micrometres. |
| Define the term 'contrast'. | This is the difference in colour/shade between two objects. |
| Describe what electron microscopy is and explain its uses. | A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen. Electron microscopy produces images with magnifications of up to 500,000 that still have a clear resolution that allows us to see the ultrastructure of cells. |
| State three disadvantages of using electron microscopes. | 1) very expensive 2) can only be used inside a carefully controlled environment 3) specimens can be damaged by the electron beams. |
| Name the two types of electron microscope. | 1) Transmission electron microscope (TEM) 2) Scanning electron microscope (SEM) |
| Explain how a transmission electron microscope works. | A beam of electrons is transmitted through a specimen and focused to produce an image. This produces the best resolution with a resolving power of 0.5nm and produces 2D images of structures. |
| Explain how a scanning electron microscope works (SEM). | A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected. This type of electron microscopy produces a 3D image of a surface but has a lower resolution of 3-10nm. |
| Explain the importance of the production of a three-dimensional image from a scanning electron microscope. | Gives us valuable information about the appearance of different cells and organisms. |
| Suggest a reason for fixation, in relation to the preparation of samples in electron microscopy. | 1) Stabilises the sample and prevents decomposition |
| Suggest a reason for dehydration, in relation to the preparation of samples in electron microscopy. | 1) Prevents the vaporisation of water in the vacuum, which would otherwise damage the sample. |
| Suggest a reason for the embedding of the sample in resin, in relation to the preparation of samples in electron microscopy. | 1) Allows thin slices to be obtained (sectioning) |
| Suggest a reason for staining with heavy metals, in relation to the preparation of samples in electron microscopy. | 1) Staining with heavy metals helps to create contrast when using electron beams. |
| State 5 differences between light and electron microscopy. | LIGHT 1)Cheap and easy to operate 2) Small and portable 3) Up to x2000 magnification 4) Resolving power of 200nm 5) Specimens can be living or dead ELECTRON 1) Expensive and more difficult to operate 2) Large and needs to be installed 3) Over x500,000 magnification 4) Resolving power of 0.5nm (TEM) and 3-10nm (SEM) 5) Specimens are dead |
| Define the term 'artefact', giving one example. | An artefact is a visible structural detail/ distorted cell structure present in an electron micrograph caused by the processing of the specimen. This means that it is not actually a feature of the specimen. An example of this would be the bubbles trapped by the coverslip as it is placed on top of the sample. |
| State an example of a structure in a cell that is now known to scientists as an 'artefact'. | 'Mesosomes' - inward foldings found in bacterial cell membranes after they were chemically fixed. These were thought to be normal structures found within prokaryotes but it is now known that these were actually caused through chemical fixation. |
| Define the term 'fluorescence'. | This is the emission of light that has been absorbed. |
| Explain how a laser scanning confocal microscope works. | 1) A single spot of focused light (laser) moves across a specimen, causing fluorescence from cell components that have been labelled with a 'dye'. 2) The emitted light from the specimen is filtered through a pinhole aperture where an image can be seen. |
| State why lasers are used to provide illumination in laser confocal microscopy. | Lasers have higher intensities than light, which improves illumination and increases resolution. |
| Explain why you would see more detail wit an electron microscope than with a light microscope. | Electron microscopes use electrons instead of light. Electrons have a shorter wavelength than light, which produces images with a higher resolution. |
| Explain the purpose of pinhole aperture in confocal microscopy. | Only light radiated from very close to the focal plane is detected. Any other light outside of it would cause blurring, so it is eliminated which helps to increase resolution. |
| List 5 advantages of laser scanning confocal microscopy. | 1) Very high resolution images obtained (due to pinhole aperture) 2) 2D and 3D images can be produced (use different focal planes) 3) Non-invasive technique - used in the diagnosis of diseases in the eye 4) Currently being developed for use in endoscopic procedures 5) Can be used to see the distribution of molecules within cells - used to develop new drugs |
| Name an example of a fluorescent tag. | Green fluorescent protein (GFP) |
| Explain how GFP can be used to study the production and distribution of proteins in cells and organisms. | 1) GFP molecules have been engineered to fluoresce different colours - allowing us to study different components of a specimen at the same time 2) The gene for GFP can be isolated and attached to genes that code for proteins 3) This can be used to see where the protein goes within the cell |
| Name the two types of cells, and give examples of organisms in each type. | 1) Eukaryotic (plants, animals, fungi) 2) Prokaryotic (bacteria) |
| Describe what a prokaryote is. | Prokaryotes are single-celled organisms with a simple structure of a single, undivided internal area called the cytoplasm (composed of cytosol) |
| Describe what a eukaryote is. | Eukaryotes are multicellular organisms that have a much more complicated internal structure, containing a membrane-bound nucleus and a cytoplasm containing many other membrane-bound organelles. |
| Define the term 'metabolism' | This is a process that involves both the synthesis and breaking down of molecules. |
| What are organelles? | They are membrane-bound compartments that provide distinct environments for different cellular reactions. |
| State two functions of membranes. | 1) Selectively permeable - control movement of substances into and out of the cell and organelles 2) Physical barriers - control which substances enter and exit cells. |
| Draw a typical animal cell | |
| Describe what a 'nucleus' is and its function. | This is a single rounded organelle that contains genetic material in the form of DNA. DNA directs the synthesis of all proteins required by the cell and controls the metabolic activities that occur within the cell. |
| Describe what a 'nuclear envelope' is and its function. | This is a double membrane that helps to protect the genetic material from damage in the cytoplasm. It contains nuclear pores that allow molecules to move into and out of the nucleus. |
| Explain why DNA cannot leave the nucleus and explain how it can be transported out. | DNA itself is too large to leave the nucleus, so instead, it is transcribed into smaller RNA molecules that are exported via the nuclear pores to the site of protein synthesis (ribosomes). |
| Explain how chromosomes are formed. | 1) DNA associates with proteins called histones to form a complex called chromatin. 2) Chromatin coils and condenses to form structures known as chromosomes. |
| What is the nucleolus? | This is an area within the nucleus which is composed of proteins and RNA, which is responsible for the production of ribosomes. |
| State two functions of RNA. | 1) Used to transport DNA to the site of protein synthesis. 2) Used to produce ribosomal RNA (rRNA) which is then combined with proteins to form ribosomes. |
| Describe what 'mitochondria' are and explain its function. | These are oval-shaped organelles that are the site for the final stages of cellular respiration where energy in the form of ATP is produced for cell activity. |
| Describe the structure of mitochondria. | 1) Have a double membrane 2) Inner membrane is highly folded to form cristae (containing enzymes used for aerobic respiration) 3) Fluid interior is called the matrix |
| Describe what a 'vesicle' is, and its function. | They are membranous sacs that consist of a single membrane with fluid inside. They are used to transport materials inside the cell. |
| Describe what a lysosome is. | -These are specialised vesicles that contain hydrolytic enzymes. |
| State three functions of lysosomes. | 1) Break down waste material in cells (such as old organelles) 2) Break down pathogens ingested by phagocytic cells 3) Play an important role in apoptosis (programmed cell death) |
| What is the cytoskeleton? | It is a network of fibres that is present throughout the cytoplasm of all eukaryotic cells. |
| State three functions of the cytoskeleton. | 1) Provides shape and stability for a cell 2) Holds organelles in place 3) Controls cell movement and movement of organelles within cells. |
| Name the three components that make up the cytoskeleton. | 1) Microfilaments 2) Microtubules 3) Intermediate fibres |
| Describe the structure of microfilaments, and explain its function. | These are contractile fibres (made from actin) which are responsible for cell movement and cell contraction during cytokinesis (cytoplasm divides to form two daughter cells). |
| escribe the structure of microtubules and explain its function. | These are globular tubulin proteins that polymerise to form tubes to form a scaffold-like structure that determines the shape of a cell. They act as tracks for the movement of organelles, such as vesicles, around the cell. |
| Microtubules also make up a structure that has a role in the physical segregation of chromosomes in cell division. Name this structure | Spindle fibres. |
| Explain the function of intermediate fibres. | -These give mechanical strength to cells and help to maintain their integrity. |
| Explain why the membrane that surrounds the lysosome is so important. | -the membrane helps to compartmentalise the hydrolytic enzymes away from cell structures that could be damaged by the activity of the enzyme. |
| Define the term 'compartmentalisation;. | -cell compartmentalisation refers to the way eukaryotic cells live, and how they have seperate areas within the cell that are responsible for carrying out different functions and chemical reactions. |
| Explain why cells need to be compartmentalized and describe three examples of compartmentalization within an animal cell. | -Different chemical reactions may require different conditions that are only provided using different cell compartments, e.g in the mitochondria, lysosome, chloroplast. |
| What are centrioles, and what are their function? | -These are a component present in the cytoskeleton of most eukaryotic cells, except in flowering plants and most fungi. These are composed of microtubules and are involved in the assembly and organisation of the spindle fibres during cell division. |
| Describe what flagella are, and explain their function. | These are whip-like extensions that protrude from some cell types. These are used primarily to enable a cell's mobility. |
| Describe what cilia are, and explain its function. | These are hair-like extensions that protrude from some cell types. These can be mobile or stationary and have important functions in movement of materials. |
| Name the two types of cilia, where they can be found and their functions. | 1) Mobile - present in the trachea - beat in a rhythmic manner to create a current that causes fluids or objects adjacent to the cell to move - helps to move mucus away from the lungs and keep air passages clean - also present in fallopian tubes to move egg cells from the ovary to the uterus 2) Stationary cilia - present on the surface of many cells - have an important function in sensory organs such as the nose. |
| Name the three primary organelles responsible for protein synthesis | 1) Ribosomes 2) Endoplasmic reticulum 3) Golgi apparatus |
| Describe what the endoplasmic reticulum is, and name the two types and their functions. | It is a network of membranes enclosing flattened sacs called cisternae. The two types are: 1) Smooth endoplasmic reticulum - responsible for lipid and carbohydrate synthesis and storage 2) Rough endoplasmic reticulum - has ribosomes bound to its surface, and is responsible for the synthesis and transport of proteins. |
| Describe what ribosomes are and explain their function. | These are organelles constructed of RNA and can be found free-floating in the cytoplasm or attached to RER. They are not surrounded by a membrane and are the sites for protein synthesis. |
| Describe the structure of the golgi apparatus, and explain its function | -compact structure formed of cisternae -does not contain ribosomes -used to modify proteins and 'package' them into vesicles. |
| What is the difference between the proteins that are packaged into secretory vesicles and lysosomes? | -Secretory vesicles transport proteins 'out' of the cell, and lysosomes contain proteins that stay within the cell. |
| Describe the stages involved in protein synthesis. | 1) proteins synthesised on ribosomes found on RER 2) proteins pass into cisternae and packaged into transport vesicles 3) vesicles move towards golgi apparatus via the cytoskeleton 4) vesicles fuse with cis face of golgi and proteins enter 5) proteins are structurally modified and leave golgi via the trans face 6) secretory vesicles carry proteins to be released from the cell - move towards cell surface membrane and fuses - contents are released by exocytosis. 7) some vesicles form lysosomes - contain enzymes for use within cell. |
| Define the term 'exocytosis'. | -This is the process in which cell contents are secreted out of the cell through fusion of the cell surface membrane and a secretory vesicle. |
| Describe the structure and function of cell walls found in plants. | -made of cellulose, a complex carbohydrate -freely permeable so substances can pass into and out of the cell -cell walls help to give the plant shape and provides support -contents of the cell wall allows plant cells to rigid -cell wall acts as a defense mechanism, protecting it from pathogen invasion |
| Draw a typical plant cell. | |
| Describe the structure and function of a vacuole. | -membrane lined sacs found in the cytoplasm containing cell sap -generally quite large -helps in the maintenance of turgor, keeping the cell rigid -has a membrane called the tonoplast - selectively permeable -only appears in animal cells as small and transient (not permanent) vacuoles. |
| Describe the structure of a chloroplast | -found in green parts of the plant such as leaves (not roots) -have a double membrane structure (like mitochondria) -fluid interior is called the stroma -internal network of membranes forming flattened sacs called thylakoids -several thylakoids stacked together called a granum (plural grana) -grana are joined by membranes called lamellae -starch produced by photosynthesis is present as starch grains. |
| Explain the importance of the internal membranes, in relation to photosynthesis. | -they help to provide the large surface area needed for enzymes, proteins, and pigment molecules necessary for photosynthesis. |
| Explain what is meant by the term 'extremophile', and name some examples of some that still exist today. | -Extremophiles are cells that are adapted to living in extremes of salinity, pH, and temperature. -They can be found in hydrothermal vents and salt lakes, and more recently in more hospitable environments such as the soil and the human digestive system. |
| To which domain do extremophiles belon to? | -Archaea |
| Define the term 'cell ultrastructure' | -This is the fine structure within a cell that is only visible with high magnifications obtained by electron microscopes. |
| Describe the characteristics making up prokaryotic cells. | -unicellular, simple structure -nucleus not present -DNA is circular -have organelles but are not membrane-bound -generally only have one molecule of DNA, found in a supercoiled chromosome -smaller 70s ribosomes -cell wall made from peptidoglycan/murein -flagella much thinner than in eukaryotes -cell surface membrane present -reproduces through binary fission -cytoskeleton is present -extra chromosomal DNA is found as circular DNA called plasmids |
| Describe the characteristics making up eukaryotic cells. | -Multicellular -DNA is linear -DNA associated with histones -membrane-bound organelles present -cell walls made from chitin (fungi), cellulose (plants), not present in animals -larger 80s ribosomes -cytoskeleton present -reproduces asexually or sexually -cell surface membrane present -extra chromosomal DNA only present in organelles such as chloroplasts and mitochondria |
| Suggest why the lack of membrane-bound organelles does not stop prokaryotic cells from making proteins. | -Prokaryotic cells still have ribosomes that are needed for protein synthesis. Ribosomes are not membrane-bound. |
| Human genomes contain many more genes than bacterial genomes, and they are much longer. Discuss the way in which this affects the packing of DNA in eukaryotes and prokaryotes. | -Eukaryotic cells have to be more efficient in packing DNA, as the genomes are longer. They are packed into multiple chromosomes that are supercoiled, wrapping around a number of proteins called histones. This complex is called chromatin and condenses and coils to form chromosomes. Prokaryotic cells only have one molecule of DNA, but they do not have histones, so instead, proteins are folded and condensed and supercoiled into a singular chromosome. |
| What is the endosymbiotic theory? | -States that mitochondria and chloroplasts (and other possibly eukaryotic organelles) were formerly free-living bacteria (prokaryotes) and were taken inside another cell as an endosymbiont - an organism that lives within the body or cells of another organism which eventually led to the evolution of eukaryotic cells. |
| State any evidence that supports the endosymbiotic theory. | 1) Mitochondria/chloroplasts the same size as bacteria 2) Both mitochondria/chloroplasts have a double membrane 3) Both contain their own DNA necessary for protein synthesis and replication |
| Give three functions of plant cell walls. | 1) prevent cells bursting 2) allows turgidity 3) helps to keep plants upright (rigid structure) |
| State similarities and differences between a human cell and a plant root cell. | 1) Both have mitochondria, endoplasmic reticulum, and ribosomes 2) Only plants have large central vacuoles and chloroplasts and cell walls 3) Centrioles and lysosomes only present in animal cells |
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