cell biology

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what is cell Fractionation
cells are broke up and organelles are released
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what is homogenisation?
cell broken up by homogenisers (blenders) release organelles from the cell
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what is the name of the resultant fluid?
homogenate
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why is the homogenate filtered?
to remove any complete cells and large pieces of debri
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how can homogenising be done?
vibrating the cells/ grinding the cells in a blender
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why is the tissue placed in a cold solution?
prevent enzyme activity that might breakdown the organelle
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why is the tissue placed in a buffer solution?
to maintain a constant ph
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why is the tissue placed in an isotonic solution?
prevent bursting/ shrinking
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what does isotonic mean?
same water potential outside the organelle/ cell as there is inside it
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what is Ultracentrifugation?
a procedure to separate a particular organelle from the rest, the heaviest moves to the bottom at the slowestspead i.e. the nucleus
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describe ultracentrifugation:
homogenate is placed into a tube and put into an ultracentrifuge, separated aerial by spinning and is spun at low speed, the heaviest organelles- nuclei- flung to the bottom of the tub- form a thick sediment @ the bottom the rest stays suspended
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what is the thick sediment called?
pellet
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what is the suspension above the pellet called?
supernantant
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how long is the process repeated for? how are organelles separated?
until all the organelles have been separated out, by spinning at higher and higher speeds
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what is starch made up of?
two polysaccharides- amylose+amylopectin
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what do the polysaccharides compose of
long chains of alpha glucose linked together by GLYCOSIDIC BONDS
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how are the glycosidic bonds formed?
in a condensatin reaction
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what is starch broken down into and by what enzyme?
maltose, amylase
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where is the enzyme produced?
in the salivary glands and the pancreas
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what is maltose broken down into?
alpha glucose
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what is the test for starch?
add iodine dissolved in potassium iodide solution to the test sample- starch present= blue black colour
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what is the structure of the plasma membrane?
phospholipid bilayer (hydrophilic heads= outwards hydrophobic tails= inwards) compose of proteins and carbs
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why is it called the fluid mosaic layer?
fluid: phospholipids are constantly moving, mosaic= protein molecules are scattered through the layer like tiles in mosaics
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what are the roles of lipids?
an energy source, waterproofing, insulating, protection
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how are lipids an energy source?
when oxidised they can provide more than twice the energy in the same mass of carbohydrate
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how are lipids waterproofing? give an example
they are insoluble in water. boy plants and insects have waxy cuticles that conserve water while mammals produce an oily secretion from sebaceous glands in the skin
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how are lipids insulators?
fats are sow conductors of heat and shen stored beneath the body surface help retain body heat
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how are lipids good at protection?
fats often stored around delicate organs ei kidney.
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what is the main role of lipids in the plasma membrane?
contribute to flexibility of membranes and the transfer of lipid-soluble substances across them.
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what characteristics do the varied groups of lipids share?
contain carbon hydrogen and oxygen, the proportion of O2 + CO2 = smaller than in carbohydrates, insoluble in water, soluble in organc solvents eo a;cohols
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what are the main groups of lipids?
tryglycerides (fats and oils) phosolipids and waxes
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when are fats solid? how does this compare to oils
at room temperature 10-20 degrees, they are liquids
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why are tryglycerides called tryglycerides?
because they have three fatty acids combined with one glycerol
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how does each fatty acid for a bond with glycerol?
condensation reaction
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what bond is formed?
Ester bond
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what reaction breaks down a tryglyceride and what does this form?
Hydolisis, produces glycerol, and three fatty acids
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where does the different properties come from in different fats and oils?
variations in the fatty acids
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how many fatty acids are there? what do they all have?
70, a carboxyl group with a hydrogen chain attached
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what type of bond does a saturated fat have between the carbon atom and why?
a single bond. because all the carbon atoms are linked to the maximum possible number of hydrogen atoms
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what does an unsaturated fat have?
carbon carbon double bond
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how is the fat mono-unsaturated and polly unsaturated?
mono: if there is a single double bond, poly: more than one double bond present
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how are phospholipids different?
one of the fatty acids is replaced with a phosphate molecule
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what does polar mean?
molecules that have two ends but behave differently known
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what does the poler property cause phospholipids to do?
when they are placed in water they posision themselves so that the hydrophobic tails are as far away from the water as possible, and the heads are close to the water as possible
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what is the test for lipids?
the emulsion test
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how is the emulsion test carried out ?
take a completely dry and fat free test tube, 2 cm of the sample being collected add 5 cm3 of ethanol shake the tube, add water, then shake the tube
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what would you expect to see?
cloudy white colour- indicated the presence of a lipid
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what would be the control?
repeat the experiment using water
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why do you need to first shake the tube thoroughly?
to dissolve any lipid in the sample
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why is there a cloudy colour?
any lipid in the sample being dispersed in the water to form an emulsion
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why is lights passing through the emulsion retracted?
passes from oil droplets to water triplets therefore it appears cloudy
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what is the function of the mitochondria?
sites for the stages of respiration, responsible for the production of ATP from carbohydrates
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what is the structure of the mitochondrion
double membrane, cristae, matrix
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why does the mitochondria have a double membrane?
to surround the organelles, has an outer and inner membrane (folded to form extensions- cristae) controls the entry and exit of material
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why does the mitochondria have cristae?
provide a large surface area for the attachment of enzymes involved in respiration
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why does the mitochondria have a matrix and what does it make up? what does it contain?
the remainder of the mitochondrion it is semi rigid material which contains protein lipids and traces of DNA allows mitochondria to control the production of their own proteins. enzymes involved in respiration- found int he nucleus
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what is the endoplasmic reticulum (ER)?
elaborate three dimensional system of sheet like membranes spreading through the cytoplasm of cells. continuous with the outer nuclear membrane
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what does the ER enclose into?
flattered sacs= cristernae
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what are the two types of ER?
the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum(SER)
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describe the properties of the RER
has ribosomes present on the outer suffices of the membrane
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what is the RER's function?
provide a large surface area for the synthesis of proteins and glycoproteins, provide a pathway for the transport of materials especially proteins throughout the cell
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describe the properties of the SER?
lacks ribosomes on its surface, often tubular in appearance
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what are the functions of the SER
synthesis,store and transport lipids; synthesis store and transport Carbohydrate
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where does the golgi apparatus occur
in almost all eukaryotic cells
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what is the Golgis structure?
similar to the SER but more compact.
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what does the golgi consist of?
a stack of membranes that make up flattened sacs / cristernae, with small rounded hollow structures called vesicles.
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what happens to the potions and lipids produced by the ER?
[assed through the golgi apparatus in strict sequence, the golgi modifies proteins by adding non protein components i.e. carbs.
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what else does the ER do to proteins?
labels them allowing them to be accurately stored and sent to the correct destination
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what happens when the proteins and lipids are stored?
transported in a vesicle which are regularly pinched off the ends of the golgi cristernae, w
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what happens with the vesicles?
move to the cell surface were they fuse with the membrane and release their contents to the outside.
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what are the functions of the golgi?
add carbs to proteins = glycoproteins, add secretory enzyme ei those secreted by the pancreas, secrete carbohydrates ei those used in making cell walls in plants, transports modify and store lipids, form lysosomes.
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what are ribosomes?
small cytoplasmic granuos, bead like structure.
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where are ribosomes found?
endoplasmic reticulum and in the cytoplasm of all cells
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what is the difference between ribosomes found in eukaryotic cells and prokaryotic cells
E= 80s P= 70s
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what are their functions?
form proteins ( undergo protein synthesis)
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what are the functions of the nucleus ?
acts as a control centre of the cell through the production of MRNA= protein synthesis, retain the genetic material of the cell in form of DNA + Chromosomes, manufactures ribosomal RNA and Ribosomes
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what is the nucleus made up of?
nuclear envelop, nuclear pores, nucleoplasm, chromatin, nuclous
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what is the structure and function of the nuclear envelop?
double membrane that surrounds the nucleus outer membrane, allows substances in and out and contains the reactions taking place within it, continuous EPR + Ribosomes on surface
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what is the function of the nuclear pore?
passage of large molecules i.e. messenger RNA
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what is the function of nucleoplasm?
granular jelly like material, bulk of nucleus
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what is the function of chromatin?
DNA found within the nucleoplams (made proteins and DNA) diffuse and form chromosomes
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what is the function of the nucleolus?
makes ribosomes and manufactures ribosomal RNA spherical beady in nucleoplasm
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how are lysosomes formed?
when the vesicles produced by the golgi contain enzyme such as proteases and lipase.
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how many enzymes can be contained in a lysosome?
50
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what is the diameter of the lysosome?
up to 1.0 microm
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what do lysosomes do with these enzymes?
isolate them from the rest of the cell before releasing them to the outside/in to a phagocytic vesicle within the cell.
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what is the function of lysosomes?
break down material ingested by phagocytic cells, release enzymes to the outside of the cell (exocytosis.- to destroy material around the cell, digest worn out organelles- useful chemicals, completely break down cells after they have died.
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what is the microvilli and what is their function?
are finger-like projections of the epithelial cell that increase its surface area- allow more efficient absorption.
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why are phospholips important components of the cell surface membrane?
one laye of the phospholipid= hydrophilic heads pointing inwards (interacting with H2O in the cell cytoplasm), another layer has the hydrophilic heads pointing outwards( interacting with water- surrounds cell), hydrophobic tails point inwards .
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what are the functions of phospholipids in the membrane?
allow lipid soluble substances to enter and leave the cell, prevent water soluble substances entering and leaving the cell, make the membrane flexible
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what is an intrinsic protein?
proteins which completely span the phospholipid bilayer from one side to the other.
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what is the role of an intrinsic protein?
act as carriers to transport water soluble material across the membrane, enzyme
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what is an extrinsic protein?
occur on the suface of the bilayer/ only partly embedded in it
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what is the role of an extrinsic protein?
give mechanical support to the membrane/ in conjunction with glycolipids as scull receptors for molecules such as hormones.
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what are the functions of proteins in the membrane?
provide structural support, act as carriers transporting water-soluble substances across the membrane, allow active transport across the membrane, form ion channels, form recognition sites-identifying cells, help cells adhere together, act receptors
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how to particles move?
contatly, due to cthe kinetic energy they posses, the motion is random, no set pattern, particle constantly bounce off one another.
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what factors effect the rate of diffusion?
concentration gradient, surface area, thickness of exchange surface
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what is the equation for diffusion
diffusion is propersional to= surface area*difference in concentration/ length of the diffusion pathway
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what else is diffusion effected by?
the nature of the llama membrane- composition and number of pores, the size and nature of the diffusing molecule i.e. small molecules diffuse faster
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what is facilitated diffusion?
a passive process which relies only on kinetic energy of diffusing molecules, no external input of energy, it occurs down a concentration grandiant.
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where does facilitated diffusion differ?
occurs at specific points on the plasma membrane where there are special protein molecules
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what do the protein channels form?
water filled channels across the membrane
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what do the water channels allow?
water soluble ions and molecules i.e. glucose and amino acids to pass through
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why are only specific molecules past through?
because the channels are selective and ech opening only opens in the presence of a specific molecule
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what does another form a facilitated diffusion involve?
a carrier protein that span the plasma membrane
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how do carrier proteins function?
when a particular molecule that is specific to the protein is present it binds with the protein, causing the protein to change shape in such a way that the molecule is released into the inside of the membrane
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is external needed for this process?
no, molecules move down a concentration gradient by kinetic energy.
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define osmosis
the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a partially permeable membrane
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what size molecules to partially permeable molecules not let through?
large molecules
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how is water measured?
kilopascals (kPa)
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what is water potential?
the pressure created by water molecules
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what water potential does distilled water have?
0
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what is the water potential of a solution?
a negative value
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how can you find the water potential of cells or tissues?
place them in a series of solutions of different water potentials , where there is no net gain/loss the water potential inside= same as external potential
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what will happen is a red blood cell is placed in water?
will absorb water by osmosis = a lower water potential, cell surface membrane will break, bursting the cell and reeasing its contents.
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why will a red blood cell burst?
surface membrane = thin (7nm) cannot stretch.
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how is red blood cells prevented from bursting inside animal cells?
bathed in a liquid = same water potential as the cells
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define active transport:
the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier molecules.
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how does active transport differ from passive forms of transport?
metabolic neergy in the form of AT, materials are moved against a concentration gradient, carrier protein molecules act as 'pumps'= involved, process is selective
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how does active transport use ATP?
directly to move molecules, using concentration gradient that has already been set up = direct active transport,= co transport
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how does active transport of a single molecule occur?
carrier protein accepts the molecule, which binds to the receptors in the channels of them, inside the cell STP binds to the protein causing it to spit- ADP and a phosphate molecule causing the protein molecule to change shape, molecules = released,
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what happens when the molecule is released?
phosphate molecule is released from the protein and recombines with the ADP to form ATP, protein reverts into its original shape.
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where are the villi situated?
at the surface between the lumen of the intestines and the blood and other tissues inside the body
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what are the villi part of?
a soecialised exchange surface adapted for the absorption of the products of digestion i.e. glucose.
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how do the villas properties increase the efficiency of absorption?
increase the surface area for diffusion, they are thin walls - reduce the diffusion pathway, they are able to move- maintain a diffusion gradient, well supplied with blood vessels- blood can carry away absorbed molecules= maintain-diffusion gradient
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how doe you calculate magnification?
size of the image/size of the object
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how do you calculate the size of the object?
size of image/magnification
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how many nanometers is in a millimetre?
1000
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what are the characteristics of a light microscope?
long wave length, poor resolution, can only distinguish between two objects if they are 0.2 micrometers/ further apart
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what are the advantages of an electron microscope?
electron beam has a very short wavelength and the microscope can therefore resolve objects well - high resolving power, electrons=negatively charged, beam can be focused using electromagnets
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what are the two types of election microscope?
transmission election microscope (TEM), scanning election microscope (SEM)
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what does the TEM consist of?
electron gun that produces a beam of electrons focused onto the specimen by condenser electromagnets.
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how does the TEM work?
beam passes through thin sectarian of specimen, parts of the specimen allow the electrons to pass through so appear bright, an image is produced on a screen= photographed-give a photomicrograph
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what is the resolving power of the TEM ?
0.1m,
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why can't the resolving power always be achieved?
problems with the specimen preparation
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what are the limitations of the TEM?
whole system must be in a vacuum (living organism can't be observed, a complex staining process = required and even then the image= black and white, specimen must be extremely thin, image may contain artefacts
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what are artefact?
things that result from the way the specimen is prepared , not part of the natural specimen - not always easy to be sure what you see on a photomicrograph- really exists
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what kind of image is produced in the TEM?
2D image.
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what is an SEM?
beam of electron scans move over the specimen and knocks electrons loose from the specimens surface, the electrons are captures and a computer processes the info assembling a detailed 3D image
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what is the advantages of the SEM?
the depth and the field of view = much greater than the TEM , can process a 3D image, specimen doesn't have to be thing and can be seen in colour.
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what are the disadvantages of the SEM?
maximum magnification is less than the TEM, lower resolving power around 20nm,
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define resolution:
the minimum distance spar that the two objects can be in order for them to appear as separate items
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define magnification:
how many times bigger the image is when compared to the object.
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what is the wavelength in a light microscope?
0.2 micro meters, only two objects which are 0.2 microm apart / more apart will be seen separately, any objects closer will appear as a single item.
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will increasing the magnification increase the resolution? why?
no because every microscope has a limited resolution.
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