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Biology 1.1.1
AS OCR biology - cell structure
| Question | Answer |
|---|---|
| What were the first components of the cell theory? | All organisms are composed of 1 or more cells (Schleiden + Schwann, 1838-9), cell is basic unit of life in all living things (S+S, 1838-9), all cells are produced from division of pre-existing cells (Virchow- 1858). |
| What are some more recent parts of the cell theory? | The cell is the smallest unit of life capable of surviving independently, cells contain genetic material passed from parent to daughter cells, metabolic processes take place in cells. |
| What is magnification and how is it calculated? | The number of times larger an image is compared with the real size of the object- magnification = image size/ actual size. |
| What is resolution? | The degree to which it is possible to distinguish between two separate points that are close together. Shorter wavelength means higher resolution, which means more detailed image |
| How do you convert between a) micrometers and metres b) milimetres and nanometres? | a) divide by 1,000,000. b) mutliply by 1,000,000 |
| What objects are measured in micrometers, nanometres and picometres? | Micrometres - cells. Nanometres - organelles and viruses. Picometres - atoms |
| How do light microscopes work? | Light from a bulb is focussed onto the specimen by a condenser lens. Objective lens focuses rays of light to form an image which is further magnified by the eyepiece lens (x10) |
| What is the maximum resolution of a light microscope and why? | 200nm- wavelength of light varies between 400&750 nm. When light goes through the edge of an object, it difracts and refracts slightly. This effect is most notable when the size of the object is equal to the wavelength of light, so the edges are fuzzy. |
| What is the max magnification and what is this equal to? | x1500. Equal to magnification of eypiece x magnification of objective lens. To change magnification, there are different objective lenses that can be rotated into position: x4, x10, x40, x100 (oil immersion) |
| What is a graticule? | A lens with a small ruler etched on it to measure the specimen - it has arbitrary units as it represents different lengths at different magnifications. |
| How do you calibrate the graticule? | A stage micrometer is placed on the stage (1micrometer long, divisions are 10mm). Work out how many graticule units are represented by 10/100mm. Calculate the length of 1 arbitary graticule unit in microms. Times by length of specimen in graticule units |
| How do you prepare a specimen for a light microscope? | Fix the specimen in glutaraldehyde to imobolise enzymes and keep tissue firm and in place. If the sample is dead, dehydrate by placing ethanol around tissue to encourage osmosis out of cells, lowering water potential (if alive, skip). Embed in wax so |
| Continued | it can be cut without distorting structure. Cut into sections 5-10 micrometers thick with microtome /diamond knife. Stain with coloured chemicals/ fluoroscent dyes which bind to chemicals in cells to see sample clearly and reveal features. Mount on slide |
| Give two examples of colour dyes for preparing a specimen for a light microcope | Gentian violet stains bacterial cell walls. Acetic orcein stains DNA dark red. |
| What are the advantages and disadvantages of using a light microscope? | Adv: cheap, easy to use, maintains natural sample colour, small and portable, living tissue can be viewed e.g. Euglena. Disadv: max magnification is only x1500, max resolution is only 200nm so structures closer than 200nm appear as one image - less detail |
| How do electron microscopes work? | An electron gun generates a beam of electrons which are focussed by magnets onto the specimen and form a greyscale image called an electron micrograph. |
| What is the maximum resolution? | 0.2 nm because the wavelength of a beam of electrons is 0.04 nm |
| Why is there a vacuum? | If air particles were present, electrons would collide with particles and would scatter, making it impossible to achieve a clear image. |
| What is a TEM? | Transmission electron microscope- electrons penetrate through very thin sample, and pass through denser parts less easily providing contrast. Max magnification is x500,000. Final image is 2D, shown on fluorescent screen, shows sample's internal structure |
| What is an SEM? | Scanning electron microscope- electrons are reflected off the sample, max magnification is x100,000, final image is 3D, shown on monitor, gives information about the detail of contours. |
| What steps are there in preparing specimens for an electron microscope? | Fix in glutaraldehyde to immbolise enzymes +keep tissue firm and in place. Dehydrate it by surrounding with ethanol to cause osmosis out of sample, lowering water potential - this means living tissue can't be viewed. embed in solid resin to allow sample |
| Continued | to be cut without distorting it. Cut with microtome or diamond knife into sections (50-100nm). Stain with heavy metal salts (lead, uranium) to reflect and scatter electrons differently, producing contrast and revealing certain features. Mount on slide |
| Why is the sample dehydrated? | Because water boils at room temperature in a vacuum and there is a vacuum in the microscope. |
| Why can't living tissue be viewed in an electron microscope? | Specimen must be dehydrated and tissue can't live when all water has been removed |
| What are false-colour electron micrographs? | Electron micrographs that have had artificial colours added afterwards with computer software |
| What are the advantages and disadvantages of using an electron microscope? | Adv: high mag, high resolution (200x light microscope), SEM produces 3D. Disadv: expensive, large, black and white, vacuum, live tissue can't be viewed, preparation of samples requires skill and is a lengthy process. |
| What are the two categories of cells? | Prokaryotic - no nucleus (e.g. bacteria). Eukaryotic - cells contain a nucleus in a nuclear envelope, as well as other membrane-bound organelles. |
| What are some differences between eukaryotic and prokaryotic cells? | p- nucleoid instead of nucleus, e- nucleus in nuclear envelope. p- circular DNA, e-chromosomes. p- no chloroplasts, some have photosynthetic lamellae, e- chloroplasts in plant and algae cells. p- only memrbane is cell surface membrane, p- cell surface |
| Continued | membrane + membrane-bound organelles (ER, golgi). p- peptidoglycan cell wall, e- cellulose or chitin cell wall where present. p- 70s ribosome, e- 80s. p- flagella lack 9+2, e-flagella have 9+2. p- ATP production in mesosomes, e- in ribosomes, size |
| What are the sizes of prokaryotic and eukaryotic cells? | Prokaryotic: 1-5 mcirometers. Eukaryotic: 10-100 micrometers. |
| What are the features of prokaryotic cells (list)? | Nuceloid, chromosomal DNA, plasmids, cell wall made of peptidoglycan, capsule, cell surface membrane, mesosome, flagellum, pili, ribosomes, glycogen granules, lipid droplets, photosynthetic lamellae. |
| What is the nucleoid and the types of DNA in prokaryotic cells? | Nucleoid is a region containing genetic material without a membrane around it. Chromosomal DNA possesses genetic material for replication. Plasmids possess genetic material for adverse situations. |
| What are the properties/ functions of the cell wall and capsule of prokaryotic cells? | Cell wall - peptidoglycan, polysaccharide cross-linked by peptide molecules, physical barrier to protect against damage. Capsule protects bacterium from other cells + helps bacteria stick together for protection. |
| What are the properties/ functions of the cell membrane, pili and mesosomes? | Cell membrane controls movement of substances in and out of cell. Pili help cells stick together or to other surfaces. Mesosomes- specialised infolded regions of cell surface that provide a large SA for respiratory enzymes to attach |
| What are the properties/ functions of the flagellum, ribosomes, glycogen granules, lipid droplets, and photosynthetic lamellae? | Flagellum helps cells spin through fluids (lack 9+2 structure). Ribosomes- 70s type, site of protein synthesis. Glycogen granules- store of carbohydrate for respiration. Lipid droplets- energy store. PL contain enzymes and chlorophyll for photosynthesis |
| What are some uses of prokaryotic cells to humans? | In food industry eg. production of yoghurt + cheese, bacteria help with vitamin K production + digestion in intestines, cover skin to prevent entry of pathogens, sewage treatment and natural recycling rely on bacteria digesting waste material |
| What components of plant cells aren't present in animal cells? | Cell wall, plastids (e.g. chloroplasts), starch grains for glucose storage, large central vacuole, tonoplast |
| What components of animal cells aren't present in plant cells? | Centrioles, cilia, flagella, glycogen granules for glucose storage |
| Can all animal and plant cells divide? | All animal cells can undergo cell division but not all plant cells can |
| What is a cell's ultrastructure? | The detailed structure of its components seen under an electron microscope |
| What is division of labour? | Any system in which different parts perform specialised functions that contribute towards the functioning of the whole e.g. organelles in a cell |
| What is the cytoskeleton of a cell? | Network of protein fibres in cell. Structure and mechanical strength. Actin filaments (fibres) move against each other so move organelles. Microtubules (fibres) cylinders 25nm diameter made of tubulin. Microtubule motor proteins use ATP to move organelles |
| Give 2 examples of when microtubule motors move organelles in a cell | Chromosomes are moved during cell division, vesicles are moved from RER to Golgi apparatus in the secretion of proteins. |
| What are vesicles? | Membrane-bound sacs used to carry substances around cells e.g. proteins |
| What is cell fractionation? | Separates major organelles of cells so they can be studied individually - tissues are chopped and homogenated to break down cell membranes, and are spun in a process called centrifugation. |
| What is the structure and function of the nucleus? | Structure: contains chromatin (DNA + proteins). Surrounded by nuclear envelop - 2 porous, phospholipid bilayers with fluid filled intermembrane space in between, 20-40nm thick. Nuclear pores are gaps in nuclear envelope allowing RNA to pass in/out. |
| Continuation | Nucleoplasm is gelatinous liquid around nucleolus, water with nuecloetides and enzymes in. Nucleolus - dense structure in centre that makes RNA and ribosomes. Functions: regulates cell activity and contains genetic material |
| What is the structure of mitochondria? | Structure: 0.5-1µm long, 2 phospholipid bilayers with fluid filled intermembrane space. Cristae are invagination of inner membrane increasing SA to speed up rate of ATP prodcution. Matrix is viscous, gel-like medium continaing enzymes + DNA. |
| What is the function of mitochondria? | The sites of respiration where ATP is produced - the energy released from breaking down ATP is used to drive metabolic processes. |
| What is the structure and function of ribosomes? | Structure: 20nm long, 2 subunits, small subunit (40s) and large subunit (60s), composed of rRNA and protein. Function: where translation occurs in protein synthesis, so mRNA from nucleus is used to assemble proteins from amino acids |
| What is the structure and function of rough endoplasmic reticulum? | Structure: 100nm deep, series of flattened membrane-bound sacs called cisternae, continuous with nuclear envelope, minimises distance travelled by mRNA, studded with ribosomes. Function: involved in synthesis of proteins, transportation to golgi. |
| What is the structure and function of the smooth endoplasmic reticulum? | Structure: 100nm deep, series of flattened, membrane-bound sacs called cisternae, continuous with nuclear envelope. functions: works in cell metabolism, synthesises steroids and lipids and stores them, releases glucose in liver cells. |
| What is the structure and function of the Golgi apparatus? | Structure: 2500nm across, series of flattened, membrane-bound sacs called cisternae. Function: receives proteins from RER, modifes them (e.g. adding carbohydrate molecules) and packages them into vesicles. Produce lysosomes. |
| What is the structure and function of lysosomes? | Structure: 0.1-0.2µm long, spherical sacs with a single membrane, contain digestive enzymes, acidic environment as optimum pH for enzymes is low. Function: enzymes break down macromolecules e.g. food, cells |
| What is the structure and function of centrioles? | Structure: 300-700nm long, 9 triplets of microtubules (small tubulin cylinders) in a ring, 9+3 structure, found in pairs at 90o. Function: in cell division, they move to poles of nucleus and form fibres called spindle, moves chromosomes. Animal cells |
| What is the structure and function of chloroplasts? | 4-10nm long, 2 phospholipid bilayer membranes separated by fluid-filled intermembrane space. A thylakoid is a flattened membrane sac continuous with inner membrane, stack is granum. Chlorophyll molecules present on thylakoids and integranal membranes. |
| Continuation | Stroma is the space inside the cholorplast. Stroma lamellae are tunnels connecting granum. Starch grains are found within stroma. Function: trap light energy which is used to drive enzyme-catalysed reactions of photosynthesis, carbohydrates are made |
| What is the structure and function of the central vacuole? | Plant. Structure: organelle containing water, eznymes waste, nutrients, pigments. Tonoplast is phospholipid bilayer membrnae. Function: maintains cell structure by pushing cell membrane against cell wall, turgid. Stores water, waste, cellular materials. |
| What is the structure and function of undulipodia? | Animal cells. Structure: membrane bounding 9 pairs of microtubules in a ring (9+2 structure), occur in ones or twos on a cell. Function: microtubules use energy from ATP to allow them to move e.g. the tail of a sperm cell. |
| What is the structure and function of cilia? | Animal cells. Structure: <10µm long, membrane bounding 9 pairs of microtubules in a ring (9+2 structure), occur in large numbers on a cell. Function: microtubules use energy from ATP to move e.g. cilia on ciliated epithelial cells waft mucus / egg cells |
| What is difference between cytoplasm and cytosol? | Cytoplasm is a jelly-like material with organelles in. Cytosol is the soluble part of the cytoplasm exlcuding the organelles - water with dissolved substances in. |
| What is the structure and function of the cell membrane? | Structure: phosholipid bilayer, heads stick out into water, tails face inwards, specialised components e.g. proteins, carbohydrates, water permeable, 7-10nm thick. Function: cell recognition + signalling, controls movement of substances in/out, separation |
| What is the structure and function of the cell wall? | Structure: cellulose (structural carbohydrate, beta gluocse subunits, high tensile and mechanical strength), plasmodesmata are gaps allowing communication and transport. Function: cell shape and structure, support plant, prevent overexpansion, tall plants |
| What are the processes involved in the production and secretion of proteins? | Transcription of DNA. mRNA leaves nucleus through nuclear pores, attaches to a ribosome on RER. Ribosome assembles protein. Vesicles buds off containing protein, transported to golgi. Golgi apparatus modifies +packages protein, transported to cell surface |
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