• Created by: Rosa
  • Created on: 29-04-13 16:43

Investigating the structure of cells

Magnification :

  • material put under the microscope = OBJECT
  •  appearance of material under the microscope= IMAGE

Resolution : 

  • minimum distance apart two objects can be in order for them to appear seperate items under a microscope 
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Cell Fractionation

Cells are broken up and different organelles they contain are seperated out. At start tissue is placed in different solutions

  • cold- to reduce enzyme activity that might break down the organelles
  • isotonic - prevent organelles bursting/shrinking due to osmotic water loss/gain
  • buffered - to maintain a constant pH 

Cells are broken down by a HOMOGENISER (blender) .The resulting fluid HOMOGENATE is then filtered to remove debris 

Ultracentrifugationhomogenate materials are seperated in a machine called an ultracentrifuge - which spind the homgenate at high speed

  • homegenate in  ultracentrifuge and spun at low speeds
  • heaviest organelles NUCLEI are forced to bottom of tube & form thin sediment
  • fluid at top of tube SUPERNATANT removed leaving sediment of nuclei
  • supernatant transferred to another tube and spun at faster speed
  • next heaviest organelles , mitochondria forced to bottom of tube (lysomes,ribsomes)
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Electron Microscopes = electron beam & a very short wavelength - high resolution power. As electrons have a negative charge the beam can be focused using electromagnets.  (has to have a vacum)

Transmission electron microscope: 

  • gun that produces a beam of electrons at a specimen 
  • parts of specimen asbsorbs some electrons so  = darker/ pass through specimen=lighter
  • Limitations include - has to be in vacum therefore no living specimens
  • image only in black and white 
  • specimen must be very thin to allow electrons to penetrate- result 2D image
  • image may contain artefacts -  not part of natural specimen

Scanning electron microscope : same limitations as TEM .

  • BUT - specimens dont need to be extremely thin as electrons dont penetrate. 
  •  We can build a 3D image 
  • has a lower resolving power
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Structure Of Epithelial Cells

Epithelial Cells are eukaryotic cells , which have a  nucleus and have membrane-bounded organelles . The main function is to absorb and secrete

Nucleus - controls cells activities

  • Nuclear envelope= double membrane around the nucleus. It controls entrance and exit of materials in and out the nucleus and contains reactions taking place in it 
  • Nuclear pores= allow passage of large materials out of nucleus 
  • Nucleoplasm= granular , jelly like material which makes up bulk of nucleus
  • Chromatin= DNA found within nucleoplasm
  • Nucleolus= within the nucleoplasm it makes RNA and assembles Ribosomes

Main function of nucleus -

  • production of mRNA and hence protein synthesis 
  • holds genetic info of the cell in form of DNA or chromosomes
  • manufacture of RNA and ribosomes 
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Structure Of Epithelial Cells

Mitochondrion and made up of following structures: 

  • Double membrane = outer controls enrty and exit of material. Inner folded to form cristae
  • Cristae= whole width of mitochondrion- provide large SA for the attachement of enzymes involved in respiration 
  • Matrix=  contains proteins, lipids and traces of DNA therefore can control production of own proteins

Mitchondria= some stages of respiration- produces ATP.  

Rough endoplasmic reticulum (cytoplasm) - ribosomes on surface-  have a large SA for synthesis(makes proteins) of proteins- make a  pathway for the  proteins throughout the cell

Smooth endoplasmic reticulum (cytoplasm)- no ribosomes on surface- it synthesises(makes things) and transports lipids and carbohydrates 

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Structure Of Epithelial Cells

Golgi-  it consists of a stack of membranes that make up CISTERANE with small rounded hollow structures called veisicles. Proteins and lipids are passed through the golgi , it modifies them and adds things e.g. carbohydrate to them. It 'labels' them so they can be sent off to the right destinations. The modified proteins and lipids are transported in veisicles , veiscles then move to cell surface where they fuse with the membrane and release their contents to the outside.

Functions of golgi are to 

  • add carbohydrates which = glyco-proteins
  • produce secretory enzymes
  • secrete carbohydrates
  • transport modify and store lipids & form lysosomes

Lysosomes- formed when veiscles produced by Golgi contain enzymes such as protease and lipases.

Functions of Lysosomes: 

  • isolate potentially harmful enzymes from the rest of the cell 
  • breaks down material ingested by phagocytic cells - e.g. white blood cells
  • release enzymes to outside of the cell in order to destroy material around the cell
  • digest worn out cells so that useful chemicals can be re-used
  • completley break down the cells after they have dies
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Structure Of Epithelial Cells

Ribosomes- small cytoplasmic grannuels found in all cells. Found in cystoplasm or in RER.  2 types 

  • 80S type - found in Eukaryotic cells 
  • 70S type - found in prokaryotic cells - smaller

They occur in vast numbers and are important in protein synthesis 

Microvilli - are finger-like projections of the epithelial cell that increase SA to allow more efficient absorption 

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  • Contain Carbon , Hydrogen and Oxygen 
  • Insoluble in Water - but soluble in organic solvents such as alchohols 

Roles of Lipids 

  • plasma membrane phospholipids contribute to flexibility of membranes 
  • transfer lipid-soluble susbstances accross membrane
  • energy source 
  • waterproofing- lipids insoluble in water 
  • insulation - fats are slow conductors of heat - help reatain body heat
  • protection - stored around delicate organs such as the kidneys 

Triglcerides -

  • have 3 fatty acids combined with glycerol (glyceride) - 
  • each fatty acid forms a bond with glycerol in a condensation reaction 
  • If the chain has no carbon-carbon double bonds the fatty acid is described as saturated because all the carbon atoms are linked to the max no. of hydrogen atoms. If there is a single double bond it is mono-unsaturated ; if there is more than one double-bond present it is poly-unsaturated 
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They are similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule. 

Fatty acids molecules repel water (hydrophobic) , phosphate molecules attract water (hydrophillic)- phospholipid made of twp parts: 

  • HYDROPHILIC head ; which interacts with water
  • HYDROPHOBIC tail ; orients itself away from water but mixes readily with fat


  • cloudy-white colour means presence of a lipid 
  • as a control repeat procedures using water instead of the sample 
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Cell-Surface Membrane

Cell-surface membrane is the plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the environment - controls movement of susbstances in and out of cell 


  • They form a bi-layer sheet - one layer of phospholipids has its heads pointing inwards (interacting with water) , the other layer of phospholipids has its hydropholic heads pointing outwards (interacting with water which surrounds cells) . Hydrophobic tails of both phospholipids layer point into centre of the membrane- protected from water on both sides 
  • allow lipid-soluble substances to exit and enter cell  - make the membrane flexible

Proteins - they are arranged more randomly than the regualr phospho-lipids and are embedded in the phospholipid  bilayer in 2 ways : 

  • extrinsic proteins - on surface of bilayer  - they give mechanical support to the membrane-  cell receptors for molecules such as hormones
  • Intrinsic - span the whole of bilayer from 1 side to the other- some act as carriers to transport water-soluble molecules across the membrane while others act as enzymes 
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Function of proteins in the membrane : 

  • provide structual support
  • transports water-soluble substances across the membrane
  • allow active transport across the membrane by forming ion channels 
  • act as receptors 

Fluid-mosaic model of the cell-surface membrane - known as this because: 

  • fluid - membrane has a flexible structure that is constantly changing shape
  • mosaic - proteins that are embedded in the phospholipid bilayer vary in shape , size and pattern in the same ways as tiles in mosaics
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'The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower.'

  • greater the difference in the concentration of molecules either side of an exchange surface , the faster the rate of diffusion 
  • larger the area over which diffusion takes place  =the fater the rate of diffusion 
  •  the thinner an exchange surface =  the faster the rate of diffusion 

Diffusion is proportional to - SA X difference in concentrarion / length of diffusion path 

Diffusion however is also affected by the nature of the plasma membrane (composition and no. of pores) , and the size and nature of the diffusing molecule e.g. small molecules diffuse faster - fat soluble molecule faster

Facilitated Diffusion -occurs down a conc gradient - a passive proccess therefore relies on kinetic energy-no external ene.

  •  specific points on plasma membrane are special protein molecules. 
  • These proteins form protein channels across the membrane , which allow water-soluble ions and molecules e.g. glucose to pass through
  • the channels only open to presence of specific molecule -some control over entrance and exit of substances
  • Alternative form of faciliated diffusion involves carrier proteins that span accross plasma membrane - when specific molecule is present it binds with the protein , this causes it to change shape so that the molecule is released to the inside of the membrane  
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'the passage of water from a region where it has a high water potential to a region where it has a lower water potential thrrough a partially permeable membrane'

A solute is any subastance that is dissolved in a solvent e.g. water. Solvent and solute together form a solution ( water potential measured in kPa): 

  • addition of water to solute will lower its water potential 
  • water potential of a solution (water + solute) must be less then zero - so negative
  • more solute that is added (more concentrated solution) the lower , more negative its water potential 
  • water moves from an area of higher water potential (less negative) to one of a lower water potential (more negative) 

Molecules move randomly due to kinetic energy,partyailly permeable only water molecules pass through.  When water molecule on either side of the plasma membrane are equal a dynamic equilibrium is established -no net movement of water. 

The highest water potential = water = 0 , all other values are negative . Animal cells are normally bathed in a liquid which has the same water potential(e.g. blood plasma and red blood cells)  as our cells to prevent swelling and shrinking- if water potenial is higher (less negative ) outside the cell it will swell and burst as if the water potenital is lower (more negative) the cell will shrink

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Osmosis in Plants

  • Central Vacuole - contains a solution of salts , sugars and organic acids in water
  • Protoplast- consiting of the outer cell-surface membrane , nucleus , cytoplasm and the inner vacuole membrane
  • Cellulose cell wall - a tough , inelastic covering that is permeable to even large materials 

Plant cells are unable to control the composition of the fluid around their cell - normally water 

  • If water potential is higher and less negative around cell solution then water enters the cell ans the protoplast swells and becomes turgid as , protoplast is pushed against cell wall 
  • If the water potential around cell soloution is lower and more negative then water leaves cell and causes the cell to shrink , and the condition if the cell is plasmolysed , the protoplast is completley pulled away from cell wall 
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Active Transport

'the movement of molecules or ions in or out of a cell from a region of lower concentration to a region of higher concentration using energy and carrier proteins'

It differs from passive energy as :

  • Metabolic energy in the form of ATP is needed
  • Materials moved AGAINST a conc gradient - from low to high
  • carrier proteins acting as pumps are involved
  • proccess is selected with only specific substances being transported

Active transport is used in 2 ways 

  • using ATP directly to move molecules
  • using a conc gradient that has already been set up by direct active transport - CO-TRANSPORT
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Active Transport

Direct Active Transport ; 

  • Carrier proteins span the cell-surface membrane and accept and transport molecules or ions to be transported on one side of it 
  • molecules or ions bind to receptors on channels of carrier proteins 
  • One side ATP , bind to the protein causing it to split into ADP and a phosphate molecule. As a result , the protein molecule changes shape and opens to the opposite side of membrane
  • molecules or ions then released to other side of membrane 
  • phosphate molecule is released from protein and recombines with ADP to form ATP
  • Causes protein to revert to its original shape , ready for process to be repeated


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Absorption in the small intestine

Villi & Microvilli- villi have thin walls lined with epithelial cells , on the other is a rich network of blood capillaries - villi increase surface area of small intestine and therefore accelerate the rate of absorption- they are situated between lumen of the intestines and the blood and tissue inside the body. They are part of a specialised exchange surface adapted for absorption of the products of digestion , such as glucose

  • They increase SA for diffusion 
  • they are very thin walled , reducing the distance over which diffusion takes place
  • they are able to move and so help to maintain a diffusion gradient 
  • they are well supplied with blood vessels so that blood can carry away absorbed molecules and hence maintain a diffusion gradient. 

The epithelial cell lining that villi possess microvilli - finger like projections of the cell membrane (look like bristles on a brush). 

Role of diffusion in absorption - carbohydrates are constantly being digested , there is normally a greater conc. of glucose within the small intestine than in the blood. Therefore there is a conc. gradient down which glucose diffuses from inside the small intestine in to the blood - blood is constntly being pumped by heart , glucose into the blood is continously being removed by the cellsas they use it up during respiration- helps to maintain conc.gradient between small intestine and blood . Villi contains muscles which regulary contract and relax , mixing contents of the small intestine which ensures that as glucose is absorbed from the food, new glucose rich food replaces , maintaining a conc. gradient and allows diffusion to continue  

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Role of Active Transport in absorption

The reason why some glucose does not pass out the body is because glucose is already being absorbed by active transport , this means that all the glucose should be absorbed into the blood

  • sodium cells are activley transported out of the epithelial cells , by the sodium-potassium pump into the blood - this takes in one type of protein-carrier molecule found in the cell-surface membrane of epithlial cells 
  • Now a much higher conc. of sodium ions in the lumen of the intestine than inside the epithlial cells 
  • Sodium ions diffuse into epithelial cells down this concentration gradient through a different type of a carrier protein (co-transport protein) in the cell-surface membrane. As sodium ions flood back in through this second carrier protein , they couple with glucose molecule which are then carried into the cell with them 
  • glucose passes into blood plasma by facilitated diffusion using another type of carrier protein 

Sodium ions move DOWN conc gradient , Glucose molecules UP their conc.gradient - sodium ion conc that powers the movement of glucose into the cells - indirect active transport

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Structure of Bacterial Cell- they all have a cell wall which is made up of a peptidoglycan (polysaccahrides and peptides), many bacteria protect themselves further by having a capsule of slime around this wall. Flagella occurs in some bacteria which is a rigid corckscrew shape rotating base which enables bacteria to spin through fluids. Inside cell wall they have a cell-surface membrane within which is ribosomes (70s type- smaller than 80s in eukaryotic cells but stilll synthesise cells) and cytoplasm. Bacteria store food reserves as glycogen granules. Genetic material of bacteria in the form of a circular strand of DNA. Seperate from these are smaller circular pieces of DNA called plasmids. these can re-produce themselves and give resistance to harmful chemicals such as antibitoics

How to cholera bacterium cause disease - main symptoms of cholera are diarrohea and then dehydration - VIBIRO CHOLREAE is transmitted by ingestion of water that has been contamintated with faecal material containing the pathogen

  • Almost all VIBRIO CHOLERAE bacteria ingested by humans are killed by the acidic conditions in the stomach- however some may survive especially if pH is above 4.5
  • when bacteria reach the small intestine they use their flagella to propel themselves through mucus lining in intestial wall
  • They then start to produce a toxic protein which has 2 parts. 1 part binds to specific carbohydrate receptors on the cell-surface membrane - only epithelial cells of the small intestine have these specific receptors - why cholera only affects this region in the body. The other tocix part eneters the epithelial cells which causes ion channels of the cell-surface membrane to open , so that the chloride ions that are normally contained within epithelial cells flood into lumen of the small intestine 
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Cholera continued

  • loss of chloride ions from epithelial cells raises the water potential , while the increase of chloride ions in the lumen of the intestine lowers its water potential - water therefore flows from the cells in to the lumen 
  • loss of ions from epithelial cells establishes a conc gradient- ions therefore move by diffusion into the epithelial cells from the surrounding tissues , including the blood. This establishes a water potential gradient that causes water to move by osmosis from the blod and other tissues into the intestine 
  • the loss of water from blood and other tissue into the intestine causes the symptons of cholera , namley severe diorhea and dehudration 
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Oral re-hydration therapy

What causes dioarrhoea ? - diarrohea is an intestinal disorder in which water faeces are produced frequently  , the causes: 

  • damage to epithelial cells lining of the intestine 
  • loss of microvilli due to toxins 
  • excessive secretion of water due to toxins 

Diarrhoea causes excessive fluid loss from the body and insufficent fluid uptake to make up for the loss 

What is oral rehydration therapy? - Just drinking water isnt effective as 

  • water is not being absorbed by the intestine (for cholera water is being lost from the cells)
  • drinking of water does not replace ions that are being lost from the epithelial cells

What is required is a suitable mixture of substances that taken safley be taken by mouth (drip needs training staff)and which are absorbed by small intestine , as there is more than one type of carrier protein in the cell-surfac membrane of the epithelial cells that absorb sodium ions , therefore to develop a rehydration soloution that uses these alternative pathways. So rehydration solution needs to conatin: 

  • water to rehydrate the tissue & sodium to replace the sodium ions lost from the epithelium cells of the intestine
  • glucose to stimulate the uptake of sodium ions from the intestine and to provide energy 
  • potassium- to replace loss potassium ions and stimulate appetite (all packaged into a powder-no training-big lots)
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Lungs and Lung Disease

  • Lungs= efficent gas exchange between air & blood = absorb O2 and remove CO2 
  • Lungs in body because air cannot support & protect them & dry out. 
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The Mechanism of Breathing

  • Diaphragm= muscle that seperates the thorax from the abdomen 
  • intercostal muscles contract/relax allowing ribs to move up & down. 

Inhalation = external intercostal muscles contract , internal interostal muscles relax - ribs move up & out & diaphragm muscles contract = flat = reduction of pressure in lungs =  pressure in alveoli decreases - increase in vol. of thorax - air will always move from higher to lower pressure

Exhalation REVERSE. 

Pulmonary Venetalation = Volume air moved into the lungs per minute = tidal volume (volume of air taken in at each breath) X ventelation (no.of breaths in per min) 

Exchange of gases in the lungs -

  • constant supply of O2 ( via diffusion or AT) = diffusion gradient must be maintained
  • Exchange surfaces have - large SA:VOL ratio (speed up rate of exchange) , very thin (diffusion pathway short) , partially permeable(diffuse easily) , movement of air and blood. 
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Role of Alveoli

Around each alveolus are lots of very narrow pulmonary capillaries (single layer of walls- rapid diffusion), flattening & squeezing red blood cells through.

Rapid diffusion of gases between alveoli (across capillaries) & blood because:  

  • red blood cells slowed  - more time for diffusion 
  • flattened red blood cells = short distance between alveolar air and red blood cells 
  • walls of alveoli + capillaries v.thin
  • alveoli + pulmonary capillaires = v.large total SA 
  • breathing = constant ventilation of lungs 
  • heart = constant circulation of blood around the alveoli 
  • Together these = steep conc. gradient of gas exchange - ALWAYS MOVING 
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