unit 1 revision cards


Enzyme Action

  • Enzymes control biochemical reactions in cells
  • they have a suffix -ase
  • they are catysts - that speed up a chemical reaction
  • they reduce the activation energy required to start a reaction between molecules
  • the substrates (reactants) are converted into products
  • reaction may not take place in absence of enzymes - each enzyme has a specific catalytic action
  • enzymes catalyse a reaction at max. rate at an optimum state
  • the substrate and the enzyme must collide with sufficient energy
  • once the substrate is inside the active site the enzyme changes shape slightly distorting the molecule in the active site and making it more likely to change into the product
  • enzymes can change the speed of a chemical reaction but cannot change the direction
  • when a substrate or molecule binds, the active site changes shape and fits itself around the molecule (induced fit mechanism)
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Factors affecting enzyme action

  • to measure the progress of an enzyme-catalysed reaction, its time course is measure.
  • the two events most frequentely measured are the colume of gas produced during a reaction and the disappearance of a substrate
  • enzymes have an optimum temperature at which they work fastest. For mammalian enzymes this is about 40*c but there are enzymes that work best at very different temperatures
  • the rate of reaction doubles, approx almost every 10 degrees
  • the rate of reaction will increase as temp increases. then once it reaches it optimum it will begin to decrease as the temp rises due to the active site being denatured
  • the thermal energy breaks the hydrogen bonds holding the secondary and tertiary structure of the enzyme together so the enzyme and the active site loses its shape to become a random coil
  • they have an optimum pH at which they work fastest.
  • For most enzymes this is about pH 7-8 but a few can work at a higher temp, such as protease enzymes in the human stomachs which have an optimum of pH 1
  • the pH affects the charge of the amino acids at the active site, so the properties of the active site change and the substrate can no longer bind.
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Enzyme Inhibitation

  • inhibitors inhibit the activity of enzymes, reducing the rate of their reactions. they are found naturally but are also used artificially as drugs, pesticides and research tools
    There are two kinds of inhibitors competitive inhibitors and non competitive inhibitors
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Competitive Inhibitor


  • a competitive inhibitor the molecule has a similar structure to the normal substrate molecule and it can fit into the active site of the enzyme
  • therefore competes with the substrate for the active site so the reaction is slower
  • it is the difference between the concentration of the inhibitor and the concentration of the substrate that determines the affect it has on the enzymes activity
  • the inhibitor is not permanently bonded to the active site so once it leaves a substrate molecule can take its place
  • eventually all the stubstrate molecules will be in the active sites, depending on the concentration of the inhibitor, the longer it will take
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Non-competitive Inhibitor


  • non-comp inhibs do not fit into the A Site they bind to another part of the enzyme molecule, changing the shape of the whole enzyme including the active site so that it can no longer bind substrate molecules
  • inhibitors that bind fairly weakly and can be washed out are sometimes called reversible inhibitors, while those that bind tightly and connot be washed out are called irreversible inhibitors.
  • poisons like cyanide, heavy metal ions and some insecticides are all non-competitive inhibitors
  • non competitive inhibitors therefore simply reduce the amount of active enzyme (just like decreasing the enzyme concentration)
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investigating the structure of cells


  • Lenses work more effectively if they are in a compound light microscope
  • light waves have a relatively long wavelength, therefore they can only distinguish between objects that are at least 0.2micro metres apart
  • beams of electrons have shorter wavelengths and are therefore able to distinguish between objects as close as 0.1 nm apart


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investigating the structure of cells


  • when viewed under a microscope, the material seen is called an image
  • maginificiation tells you how many times bigger the image is in relation to the actual size of the object it can be found using the following formula


  • the previous formula can also be rearranged to find the size of an object


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investigating the structure of cells


cell fractionation is the process where cells are broken up and the different organelles they contain are separated out.

Before franctionation begins, the cells are but in a solution that is

COLD - to reduction enzyme activity that might break down the organelles
ISOTONIC- to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water. an isotonic solution is one that has the same water potential as the orginal tissue
BUFFERED - to maintain a constant pH

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investigating the structure of cells


cells are broken up by a homogeniser that realease the organelles. the fluid is called a homogenatic. it is then filtered to remove complete cells and large pieces of debris.

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investigating the structure of cells


ultracentrifugation is the process by which the homogenate is separated in a machine called a centrifuge
this spns tubes of the homogenate, creating a centrifugal force that forces the mixture to separate

  • the tube of filtrate is placed in the ultracentrifuge and spun at a slow speed
  • the heaviest organells such as the nucleus are forced to the bottom where they form a thin sediment
  • the fluid at the top called the supernatant is removed leaving just the sediment of the nuclei at the bottom
  • the supernatant is then put in another tube where it is spun at an even higher speed than before
  • the next heaviest organelles (mitochondria) are forced to the bottom and the process continues until all the organelles are separated
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The electron microscope

  • As electrons are negatively charged the beam can be focused using an electromagnet
  • Because electrons are absorbed by molecules in the air, a near vacuum must be created within the chamber of an electron microscope




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transmission electron microscope

Transmission electron miscoscope

  • the TEM has a gun that fires electrons which are focused onto the specimen by a condenser electromagnet
  • some of the electrons are absorbed by the specimen and appear dark on the image
  • other parts allow the electrons to get through and so appear light = an image of the specimen (image is called a photomicrograph) 
  • process takes place in a vacuum, so living specimens cant be observes
  • a complex staining process is required 
  • the image is in black and white
  • specimen must be extremely thin
  • artefacts may appear on the image, these appear as a results of thew ay the specimen is prepared
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Scanning electron microscope

All the limitation of the TEM apply to the SEM

  • BUT the specimen doesnt have to be extremely thin as the electron from the scanning microscope do not penetrate
  • The beam of electrons is directed over the surface of the specimen in a regular pattern
  • the electrons bounce on the contours of the specimen and are scattered
  • the scattering of the electrons can be analysed and from this an image can be produced using a computer
  • the SEM has a lower resolving power than the TEM (20nm) but is still ten times better than a light microscope
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Structure of epithelial cells - nucleus

  • Epithelial cells are eukaryotic cells.
  • the nucleus controls the cells activities and contains hereditory material
  • a double membrane that surrounds the nucleus. its outer membrane is continuous with the endoplasmic reticulum
  • often has ribisomes on its suface
    it controls the substance entering and leaving the nucleus
  • allow the passage of large materials into and out of the nucleus
    a granular jelly like material that makes up the bulk of the nucleus
    is the DNA found within the nucleoplasm, this is the DNA found within the nucleoplasm the diffuse form chromosomes take up when not dividing
  •  makes ribosomal RNA and assembles ribosomes 
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Structure of epithelial cells - mitochondria

The mitochondria has

  • a double membrane surrounding the organelle
  • the outer one controls the entry and exit of the material
  • the inner one is folded to form extrensions known as CRISTAE
  • are shelf like extension of the inner membrane
  • they provide large surface area for the attachment of enzymes during respiration
  • makes up the remainder of the mitochondria.
  • it is semi rigid material that contains proteins, lipids, and traces of DNA
  • these allow the mitochondria to control the production of its own proteins 

note: the mitochondria are responsible for the production of the energy-carrier molecule ATP 

because of this, high numbers of mitochondria are found in cells where there is a high lievel of metabolic activity

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Structure of epithelial cells - ER

Endoplasmic Reticulum (2 types) 

Rough Endoplasmic Reticulum -

  • has ribosomes present on the outer surface of the membranes. 
    its functions are: 
  • provide a large surface area for the making of proteins and glycoproteins
  • provide a pathway for the transport of material, especially proteins throughout the cell

Smooth Endoplasmic reticulum-

  • lacks ribosomes on its surface and its often more tubular in appearance
    its functions are:
  • synthesise, store and transport lipids
  • synthesise store, and transport carbohydrates 
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Structure of epithelial cells - Golgi Apparatus

The golgi apparatus is similar to the SER in structure but is more compact

  • consists of a stack of membranes, that form flattened sacks, or cisternae with small rounded hollow structures called vesicles
  • the proteins and lipids produced in the endoplasmic reticulum are passed through the golgi in a strict sequence
  • the golgi modifies these proteins often by adding non-protein structures to them such as carbs. 
  • it also labels them so they can be sorted and sent to their correct destination.
  • once sorted and modified, proteins are transported in vesicles which are regulary removed from the edge of the golgi cisternae
  • the vesicles move to the cell membrane where they fuse and release their contents to the outside
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Structure of epithelial cells - lysosomes

lysosomes are formed when a vesicle contains enzymes

lysosomes isolate potentially dangerous enzymes from the rest of the cell before releasing them outside of the cell or into phagocytic vesicles within the cell

lysosomes digest worn out organells so that the useful chemicals they are made of can be reused

they can completely break down cells after they have died 

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Structure of epithelial cells - ribosomes

Ribosomes occur in either the cytoplasm or the Rough endoplasmic reticulum

there are two types depending on which cell they are found in

  • 80s type- found in eukaryotic cells around 25nm in diameter
  • 70s type- found in prokaryotic cells, slightly smaller
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Structure of epithelial cells - microvilli

microvilli are finger like projections of the epithelial cells. there function is to increase the surface area for diffusion

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  • contain carbon, hydrogen and oxygen
  • the proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
  • they are insoluble in water
  • they are soluble in organic solvents such as alcohol and acetone
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Role of lipids

Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them

lipids can be used as

  • an energy source - lipids can provide more than twice the energy of carbs
  • waterproofing - lipds are insoluble in water so suitable for waterproofing
  • insulation - fats are slow conductors of heat, kept under skin to retain heat in the body
  • protection- often stored around the delicate organs

triglycerides are so called because they have

  • 3 fatty acids
  • combined with glycerol (glyceride) 

note: each fatty acid combines with glycerol in a condensation reaction

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Phospholipids are similar to lipids except that one of the fatty acid is replaced with a phosphate molecule

fatty acid molecules repel water whereas phosphate molecules are attracted to water

Phospholipids have a hydrophillic head which means they are attracted to water, which is the phosphate molecule

whereas the fatty acids are hydrophobic so are the tails that repel water

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Test for lipids

1. Take a dry, grease free test tube

2. take 2cm^3 of the sample being tested and add 5cm^3 of ethanol

3. shake the test tube and dissolve the lipds

4. add 5cm^3 of water and shake gently

5. a cloudy white colour indicates the presence of lipids

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The cell surface membrane - phospholipids

phospholipids are important in cell surface membrane because

  • one layer of the phospholipids has its hydrophilic head pointing inwards towards the water in the cytoplasm. 
  • the other has its head pointing outwards, interacting with the water surrounding the cell
  • the hydrophobic tail point inwards - they dont like water

the function of a phospholipid in the cell membrane are to: 

  • allow lipid-soluble substances to enter and leave the cell
  • prevent water soluble substances entering and leaving the cell 
  • make the membrane more flexible
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The cell surface membrane - proteins

the proteins in the phospholipds bilayer are arranged randomnly in two main ways

Extrinsic Proteins

  • appear on the surface or partially imbedded
  • they provide mechanical support of when in conjuction with glycolipids act as cell receptors for molecules such as hormones

Intrinsic Proteins

  • span the phospholipids bilayer. some transport water soluble molecules across the membrane, others are enzymes

protein molecules in the membrane allow active transport by forming ion channels so sodium, potassium etc.

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Fluid mosaic model of the cell surface membrane

Fluid - because the phospholipids molecules can move relative to each other, giving it a flexible structure

Mosaic - because the proteins are imbedded in the structure in a similar way that stones are imbedded in a mosaic

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  • diffusion is defined as the net movement of molecules or ions from a region where they are more highly concentrated to an area where their concentration is lower
  • all particles are constantly in motion due to the kinetic energy that they possess
  • the motion is random and there is no set pattern to the way they move 


  • the greater the difference in concentration, the greater the rate of diffusion
  • the larger the area of an exchange surface, the greater the rate of diffusion
  • the thinner the exchange surface, the faster the rate of diffusion
  • the nature of the plasma membrane, its composition and the number of the pores
  • the size and nature of the diffusing molecule for e.g smaller molecules diffuse faster than larger ones 

Diffusion equation:


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Facilitated diffusion

  • Facilitated is a passive process as it only relies on the kinetic motion of the particles
  • facilitated diffusion can only occur at specific points along the plasma membrane where there are special protein molecules
  • the proteins for special are for water filled channels
  • the channels only open for specific molecules
  • this allows water soluble ions and molecules to
  •  pass through. such molecules such as glucose and amino acids would take much longer to diffuse through the phospholipids bilayer
  • when a molecule that is specific to the carrier protein is present, the carrier protein changes shape, causing it to release the molecule on the other side of the plasma membrane
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Osmosis is 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

water protential is measured in PASCALS

  • under standard conditions of temperature (25*c) pure water has a water potentional of 0 
  • water molecules move from one side where the water potential is higher (less negative) across a partially permeable membrane to another side where the water potential is lower (more negative) 
  • the water moves along a water potential gradient
  • at the point where the water potentials on either side of a partially permeable membrane are EQUAL a dynamic equilibrium is established and there is NO NET MOVEMENT of water
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Osmosis in animal cells

If a red blood cell is placed in pure water it will absorb water by osmosis because it has a lower water potential

the cell surface membrane will eventually burst if too much water enters the cells

to prevent cells bursting due to too much water entering the cells, cells are often bathed in solutions where the water potential outside the cell is the same as the water potential inside the cell. This is called isotonic solution

A hyPOtonic solution is one where the concentration outside is greater than the concentration inside

A hyPERtonic solution is one where the water potential outside the cell is lower than the water potential inside the cell 

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Active transport

  • active transport allows cells to exchange molecules against a concentraion gradient
  • metabolic energy is required for this process
  • active transport s the movement of molecules or ions into or out of a cell from region of low concentration to a region of higher concentration using energy and carrier molecules
  • metabolic energy is needed in the form of ATP
  • active transport used ATP in two mains ways 
  • by using ATP to directly move molecules
  • by using concentration gradient that has already been set up by direct active transport. this is known as co-transport
  • the carrier molecules accept molecules or ions to be transport on one side of it
  • the molecules of the ions bind to the receptors of the channels of the carrier protein

occasionally the molecule or ion is moved into the cell at the same time as a different one is being removed from it. e.g sodium potassium pump

sodium ions are actively taken in by the cell whilst potassium ones are actively removed from the cell

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Absorption in the small intestine

Villi and Microvilli

  • villi have walls lined with epithelial cells
  • villi are situated at the interface between the lumen of the intestines, the blood and the other tissues inside the body

Their properties increase the efficiency of absorption because:

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

the epithelial cells possess microvilli which further increase the surface for diffusion (situation in the cell surface membrane)
villi contain muscles which move the food ensuring the glucose is absorbed from the food adjacent to the villi, new glucose rich food replaces it, so maintains a concentration gradient for diffusion 

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role of AT in absorption

the way in which most glucose is absorbed from small intestine is an example of co-transport

1. sodium ions are actively transported out of the epithelial cells by the sodium potassium pump

2. there is now a much higher concentraion of sodium ions in the lumen than in the cells

3. the sodium ions diffuse into the cells down a concentration gradient. as they flood back into the cells they are coupled with glucose molecules which are drawn in with them

4. the glucose diffuses into the blood through the carrier protein

it is the sodium ion concentraion rather than the ATP directly, that powers the movement of glucose into the cell

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Structure of a bacteria cell

Structure of a bacteria cell

  • all bacteria possess a cell wall that is made up of a mixture of polysacharides and peptides
  • many bacteria also protect themselves by producing a capsule of mucliaginous slime around the wall
  • flagells occur at certain types of bacteria
  • insides the cell surface membrane is the cytoplasm that contains ribosomes that are small than the ones found in eukaryotic cells
  • bacteria store food as glycogen granules and oil droplets
  • the genetic material is found in the form of a circular strand of DNA
  • separate from this are smaller circular pieces of DNA called plasmids 
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How the cholera bacterium causes disease

  • Almost all cholera bacteria ingested by humans are killed by the low pH in the stomach but many can still survive especially if the pH is above 4.5
  • when the bacteria enter the lumen of the small intestine they use their flagella to propel themselves through the mucus lining of the intestinal wall
  • they then start to produce a toxic protein which has two parts- 
  • one part binds to the carb receptors or the intestinal epithelial cells
  • the other part enters the epithelial cells
  • this causes the the ion channels of the cell membrane to open, anbd the chloride ions that are normally contained within the epithelial cells flood into the lumen of the intestine

the loss of chloride ions from the cells increases the water potential in the cell but lowers the water potential outside the cells 
this causes water to move into the small intestine

the loss of ions from the cells establishes a concentration gradient. ions move by diffusion into the epithelial cells. creating a water potential gradient that causes water to move by osmosis from the blood and other tissues into the small intestine  

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Oral rehydration therapy

what causes diarrhoea?
damage to the epithelial cells in the lining of the small intestine - loss of microvilli due to toxins 
and excessive secretion of water due to toxins

  • what is oral rehydration therapy?
  • drinking water to treat diarrheoa is ineffective because:
  • water is not being absorbed by the intestine, in the case of cholera water is being lost from the cells
  • the drinking water does not replace electrolytes that are being lost from cells of the intestine
  • as sodium ions are being absorbed the water potential falls and water enters the cells by osmosis
    a rehydration solution should contain
  • water- to rehydrate the tissues
  • sodium- to replace the ions lost from the epithelial of the small intestine and to make optimum use of the soidum-glucose proteins
  • glucose- to stimulate the uptake of sodium ions from the intestine and to provide energy
  • potassium- to replace lost potassium ions and to stimulate appetite
  • other electrolytes- such as chloride and citrate ions, to prevent electrolyte imbalance
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Structure of the human gas exchange system

all aerobic organisms require a constant suppy of exygen to release energy in the form of ATP during respiration

  • lungs are kept inside the body the body because air is not dense enough to support and protect the delicate structure
  • they are a pair of lobed structures made up of a series of bronchioles when end in tiny air sacs called alveoli
  • the trachea brances into smaller airways, the left and right bronchi which lead to the 2 lungs
  • the left long is longer and narrower  and has a smaller volumes because it shares space on the left side with the heart
  • right lung is divided into 3 lobes and each love is supplied by 1 of the secondary bronchi. it has an indentation called the cardiac notc for the apex of the heart
  • the bronchi divide times before branching into smaller airways called bronchioles
  • the airways are held open by flexible, fibrous, connective tissue called cartilage. circular airway muscles can dilate or constricts the airways
  • at the end of each bronchiole are thousands of small air sacs called alveoli. 
  • together the millions of alveoli form a huge surface area
  • the aleveolar walls have a dense network called capillaries
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Breathing mechanism

the process of breathing is called ventilation

inspiration: air pressure in the atmosphere is grather than the air pressure in the lungs, air is drawn in
expiration: when air pressure in the lungs is greater than the air pressure of the outside atmosphere air is forced out 

during inspiration the external muscles contract. during expiration the external muscles relax and internal muscles contract

Inspiration (requires energy)

in order to respire the internal muscles relax while the external muscles contract

as a result the ribs move upwards and outwards increasing the volume of lungs and the diaphram mucles contract and flatten. further increasing the volume

due to the increase in volume the air pressure drops and is then lower than the pressure outisde of the lungs. so air is drawn in

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Pulmonary ventilation


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exchange of gas in the lungs

gas exchange is the process by which oxygen moves and enters the blood and carbon dioxide is moved out

  • celluar respiration creates a constant demand for oxygen
  • the movement of o2 is independant of the movement of c02
  • diffusionn occurs when there is a difference in concentration
  • particles move down a concentration gradient
  • CO2 will not diffuse out if the concentration is higher outside the lungs
  • gas exchange surface - where gas enters and leaves the lungs
  • single cell organisms can use there cell membrane as a surface for gas exchange
  • many organism have developed specialised gas exchange structures called lungs
  • mammals exchange respiratory gases mainly thorugh the alveoli
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Ficks Law




 having a vast number of capillaries is important 

walls of the alveoli are very thin and close together. these allows efficient gas exchange

cells in the alveoli wall are flattened with only a thin layer of cytoplasm between the cell membranes. this reduces the distance for diffusion

the lumen of the capillary is so narrow that the red blood cells slow down as they pass through it

they are flattened against the alveoli.

this bring haemoglobin very close to the alveoli air

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epithelium and endothelium

Epithelial cells - cells from epithelium tissue that lines the internal and external cavity

Endothelium - is a specialised type of epithelium that lines the inner surface of blood vessels

Alveoli Structure

  • The wall of the alveoli is made of epithelial cells
  • the inner surface of the aleveoli wall is covered in water,this is because the plasma membrane of its cells are permeable in water
  • the film of water slows down the rate of diffusion because it has increase the distance the gases need to travel
  • for a membrane to be permeable to oxygen it must also be permeable in water
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TB is an infectious disease caused by an airborne rod-shaped pathagen called myocobacterium tuberculosis

  • most commonly affects the lungs- almost any part of body can be infected by the pathogen
  • tb is the leading cause of death from bacterial infection -the disease affects almost 1.7 billion 
  • it has an extremely slow growth rate - divides once every 16-20 hours
  • very resistant and can survive weak disinfectants and several weeks in dry state
    Contracting Tb
  • most people with tb can only exhale a few bacteria in each breath, can only contract the disease after prolongued exposure
    people who are at risk are:
  • people who have HIV
  • people taking immune suppressant drugs
  • those undergoing cancer treatment
  • the very young/old
  • those who live in LDC's
  • those who inject drugs, or drink too much alcohol 
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  • it is a bacterium that can be treated with antibiotics 
  • most tb is curable using a combination of 4 different types of antibiotics
  • the antiobiotics are affective against most strains of the bacteria - taken for 6-9 month


  • persisten cough
  • chest pain
  • coughing up blood
  • chill + fever
  • night sweat
  • loss of appetite
  • unexplained weight loss
  • fatigue

Death occurs when the sufferer has lost too much weight

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Tuberculosis - disease progression

  • your immune system kills the bacteria and no furter symptoms are experienced
  • immune system responds, bacteria are then engulfed by a type of white blood cell called macrophages which do not actually destroy bacteria
  • tb bacteria have a cell wall made of a complex, waxy material that protects it from the macrophages
  • the infection can lead to inflammation and enlargement of the lymph nodes responsible for that area of the lung
  • after 3-6 weeks another white blood cell called T - lymphocytes arrive at the site and activate the macrophages so they can destroy the bacteria
  • lysosomes in the macrophagues contain enzymes that break down the waste materials
  • in a healthy person they are few, if any symptoms and the infection is controlled within weeks
    Active Tb
  • the bacteria can multiply within the macrophages and eventually cause the cell to burst releasing the bacteria
  • these bacteria are then engulfed by more macrophages and the cycle continues 
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  • occurs when scars form on the epithelium causing them to be irreversibly thickened
  • patients suffering from the disease cannot diffuse oxygen into their blood as efficiently
  • its diagnosed by a lung biopsy
  • the fibrous tissue also reduces the elasticity of the lungs, this makes it harder to ventilate the lungs


  • shortness of breath - occurs due to the lack of oxygen diffusing into the blood as a results of the lengthened pathway and shallower concentration gradient
  • chronic dry cough - bodies reflex to try and remove the fibrous tissue. however the tissie is irremovable
  • pain and discomfort in the chest - caused by the pressure and damage caused by the tissue
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allergens cause a chemical called histamine to be produced, which cause the airways to be thickened

  • the linging of these airways becomes inflamed 
  • goblet cells secrete more mucus
  • fluid leaves capillaries and enters the lungs
  • the mucles surrounding the bronchi and bronchioles contract


Difficulty breathing - due to constriction of airways

A wheezing sound when breathing - caused by air passing through the restricted airways

A tight feeling in chest - consequence of not being able to ventilate the lungs properly

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In emphysematous tissue the elastin has become permanently stretched and the lungs are no longer able to force all the air out of the alveoli


Shortness of breath - air cannot be ventilated as effectively. this causes the concentration gradient to become shallower. as a result, the rate of diffusion is reduced and less gas exchange will take place

chronic cough - bodies reflex to try and remove damaged tissue

bluish skin colourisation - due to the lower leevls of oxygen within the blood as a result of poor gas exchange

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The heart and disease

  • blood moves down concentration gradients, from hight to low pressures
  • the heart produces the main pressure gradient, although contractions of skeletal muscles also push blood along muscles

The circulatory system

  • mammals have a double circulatory system as blood passes through twice on one complete circulation of the body
  • the pulmonary circulation pumps blood to be oxygenated 
  • the systemic circulation pumps oxygenated blood to every other part of the body that uses oxygen

The human heart

  • consists mainly cardiac muscle
  • its pumping action ensures that fresh supplies of oxygen and nutrients are constantly being supplied to all living cells of the body
  • it is divided into a left and right side by a septum
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  • the heart is covered by a double layer of tough, inelastic membranes which form the pericardium
  • pericardium fluid is secreted by the membranes and reduces friction, allowing them to move freely over eachother 
  • this sac protects the heart, anchors its surrounding structures and prevents overfilling of the heart with blood.

Heart Chambers

  • the two upper chambers are called the atria and the two lower chambers are called the ventricles
  • the atria recieve blood from veins, the ventricles pump blood into arteries
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  • the heart is covered by a double layer of tough, inelastic membranes which form the pericardium
  • pericardium fluid is secreted by the membranes and reduces friction, allowing them to move freely over eachother 
  • this sac protects the heart, anchors its surrounding structures and prevents overfilling of the heart with blood.

Heart Chambers

  • the two upper chambers are called the atria and the two lower chambers are called the ventricles
  • the atria recieve blood from veins, the ventricles pump blood into arteries
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the right and left side of the heart


  • the right atrium recieves deoxygenated blood from the systemic circulation through the vena cava
  • each atrium is elastic so it can stretch as it fills up with blood
  • atria have only a thin musclular wall as they only need to pump blood a short distance to the ventricle
  • the right ventricle pumps deoxygenated blood through the pulmonary artery, to the pulmonary circulation
  • the pulmonary artery is the only artery to carry deoxygenated


  • the left atrium recieves oxygenated blood from the pulmonary vein
  • the pulmonary vein is the only vein to carry oxygenated blood
  • the left ventricle pumps oxygenated blood through the aorta into the systemic circulation
  • ventricle walls are thicker than that of the atria as they have to pump blood over a greater distance
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  • the right ventricle pumps blood to the lungs 
  • where the left ventricle has to pump blood to the whole body
  • although the volume of the blood they hold is the same
  • left ventricle has a thicker muscular wall
  • a thicker muscular wall will allow a stronger contraction to push blood further
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  • there are 4 valves in the mammalian heart
  • one between each atrium and ventricle
  • and one at the base of each artery leading from the ventricles
  • the tricuspid valve between the right atrium and the right ventricle has three flaps
  • the bucuspid valve between the left atrium and the left ventricle has two flaps 
  • the pulmonary semi - lunar valve is between the right ventricle and the pulmonary artery
  • the aortic semi lunar valve is between the left ventricle and aorta

How valves work

  • they prevent the back flow of blood
  • valves in the heart are designed to open where there is high pressure forcing the blood on the correct direction
  • if high pressure forces the blood in the wrong direction, the valves shut
  • thin tendons join to the edges of the valve flaps to the wall of each ventricle
  • these tendons do not stretch, they stop the valves turning inside out 
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Coronary arteries

  • some of the blood leaving the left ventricle goes to the coronary arteries
  • theres arteries branch out to supply the thick heart muscle with oxygen and nutrients
  • the coronary arteries are much narrower than many other arteries so can become blocked more easily 
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The cardiac cycle

  • the 4 chambers in the heart are constantly contracting and relaxing in a definite sequence
  • the cardiac cycle is the sequence of stages that take place in one heart beat
  • when a chamber is contracting it is in systole
  • when its relaxing it is in diastole

The stages of the cardiac cycle

  • there are 3 stages of the cardiac cycle
    atrial systole
    ventricular systole
  • Atrial systole refers to the contracting of the atrial myocardium (heart muscle) 
  • Ventricle systole refers to the contracting of the ventricular myocardium 
  • between heart beats the myocardium of both atria and ventricles are relaxed - this is known Diastole
  • both sides of the heart contract together, this mean that the atria will contract and relax at the same time and so will the two ventricles 
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  • ventricular and atrial myocardium relaxes at the same time, blood returning to the heart fills the atria
  • the higher pressure in teh atria than the ventricles, forces the atrioventricular valves to open
  • even though the atria arent contracting, blood flows from the atria to the ventricles
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Atrial Systole

  • the myocardium of both atria contract
  • this raises the pressure in the atria, pushing more blood into the ventricles
  • the atrioventricular valves open
  • more blood passes through these valves into the ventricles
  • both semi-lunar valves are closed
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Ventricular systole

  • the myocardium of both ventricles contract
  • the atria are relaxed
  • the ventricles continue to fill with blood
  • this quickly raises the pressure of the ventricles higher than that of the atria
  • both atrioventricular valves are forced closed
  • when the pressure of the ventricles exeedsthat of the arteries, the pulmonary and aortic valves are forced open
  • blood is pushed out of the heart into the pulmonary artery and aorta
  • the semi - lunar valves close, stopping blood moving back into the heart
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Pressure changes

  • the events of the cardiac cycle create pressure changes
  • pressure changes are responsible for moving blood through the heart and into the systemic and pulmonary circulations
  • valves open or close when the balance or pressure on opposite sides of the valves changes
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controlling the cardiac cycle

  • myogenic contractions are contractions originating from within the muscle, rather than by the nervous system
  • myogenic contractions of the mycocardium are largely responsible for the cardiac cycle
  • the cardiac cycle starts at the sinoatrial node (SA node)
  • the SA node is a group of cells found out the top of the right atrium which acts as a natural pacemaker and initiates the heart beat
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Cardiac cycle

Starting the cardiac cycle

  • the SA node produces waves of electrical impulses called cardiac impulses
  • this tissue conducts the impulses throughout the atria, stimulating the myocardium of the atria to contract
  • the contraction spreads outwards and downwards, from the top of the atria, squeezing blood toward the ventricles

Continuing the cardiac cycle

  • the electrical activity connot pass from the wall of the atria to wall of the ventricles, cos it is stopped by a wall of fibrous tissue called the atrioventricular system
  • this stops the waves of the atrial muscle contraction continuing through the ventricle muscles as the blood would be forced to the bottom of the heart
  • there is only one location where the impulse can travel from atrium to ventricle - though the atrioventricular node (AV node) 
  • the vells in the AVN can conduct electriciy but only shortly after a slight delay
  • the delay allows time for the atria to complete their cycle
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Contraction of the ventricles

  • from the AVN two specialised bundles of purkinje tissue run down the atrioventricular septum and up the ventricular wall
  • bundles of His conduct electrical impulses rapidly down the atrioventricular septum to the bottom of the heart
  • these fibres stimulate the muscles of the ventricles to contract rapidly, from the base of the heart upwards

Cardiac output

  • the volume of blood from ventricles in one minute
  • measured in DM ^3min^-1
  • the volume pumped by both ventricles pumped is the same
  • the cardiac output depends on two features
    how quickly the heart is beating
    and the stroke volume (amount of blood in one beat)

CARDIAC OUTPUT= heart rate (min^-1) x stroke volume (dm^3)  

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Heart disease - atheroma


  • begins as fatty streaks which are deposits of white blood cells that have taken up low density lipoproteins
  • these streaks enlarge to form an irregular patch, or atheromous plaque
  • athermanous plaques are made up of cholestrol, fibres and dead muscle cells


  • if an atheroma breaks through the endothelium of the blood vessel, it forms a rough surface that interupts smooth blood flow
  • this may cause a thrombus (blood clot) that will stop the flow of blood
  • the region of tissue deprived of blood due to the thrombus will not be able to respire as a result of no oxygen, glucose and other nutrients being transported to the tissue


atheromas that form thrombosis can weaken artery wall, causing them to swell to form a balloon like blood filled structure

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heart disease - continued

Myocardial infarction

occurs when the heart stops beating otherwise known as a heart attack


  • carbon monoxide combines easily, but irreversibly with haemoglobin, thus reducing the o2 carry capability of the blood
  • in order to supply tissue with the same amount of oxyen the heart must work harder, thereby increasing blood pressure
  • nicotine stimulates the production of adrenalin which will increase heart rate and blood pressure

blood pressure

if the blood pressure in the arteries is high, the heart must work harder to pump blood into them

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heart disease

Blood Cholestrol

  • high density lipoproteins - remove cholestrol from the tissue and transport it to the liver for excretion. they help protect arteries against heart disease
  • low density lipoproteins - which transport cholestrol from the liver to the tissue, including the artery walls which they infiliterate leading to the development of atheroma and hence a heart attack


  • high levels of salt raise blood pressure
  • high levels of saturated fat increase the low density lipoprotein levels and hence blood cholestrol concentration
  • foods that act as antioxidants e.g vitamin c, reduce the risk of heart disease, and so does non-starch polysacharides
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Defence mechanisms

Non specific - mechananism that do not distinguish between one type of pathogen and another, but respond to all them in the same way.
these mechanism act immediately and take two forms
a) barrier of entry
b) phagocytosis

Specific - mechanisms that do distinguish between different pathogens. the response is less rapid but provides long lasting immunity.

the response involves a type of white blood cell called a lymphocyte and can take two forms
a) cell mediated response (T - lymphocytes)
b) humoral responses (B-Lymphocytes)

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there are two different types of white blood cells phagocytes and lymphocytes

Barriers of entry

  • a protective covering - the skin covers the bodys surface creating a barrier that is hard for pathogens to penetrate
  • epithelia covered in the mucus - many epithelia produce mucus. in the lungs pathogens are often caught in the mucus and moved by the cilia
  • Hydrochloric acid in the stomach - provides a low pH that denatures the pathogens enzymes
  • pathogens are engulfed by phagocytes, in the form of vesicles which are formed on the cell surface membrane
  • chemical products of the pathogen act as attractants which draw the phagocyte towards it
  • phagocytes attach themselves to the surface of the pathogen
  • they engulf the pathofen to form a vesicle known as a phagosome
  • enzymes within the lysosomes join with the phagosome and release their contents. the enzymes within the lysosomes digest the pathogen
  • the soluble products of the pathogen are absorbed into the cytoplasm of the phagocyte
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  • Antigens: is any part of an organism or subatance that is recognised as foreign and stimulates a response from the immune system
  • antigens are normally proteins that are part of the organisms cell surface membrane
  • Lymphocytes
  • B-Lympho - are assosciated with humoral immunity i.e immunity involving antibodies that are present in the body fluids
  • T-Lympho - are associated with cell mediated immunity i.e immunity involving body cells
  • both types of lymphocytes are formed from stem cells in the bone marrow.
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cell mediated immunity

  • t-lymphocytes can distinguish foreign material from the bodies own tissue because:
  • phagocytes have engulfed and broken down a pathogen and have presented some of its antigens on its own cell surface membrane
  • body cells that have been invaded by a virus also mange to present some of the virus' antigens on its surface as a sign of disress
  • cancer cells also present antigens on its cell surface membrane

T-Lymphocytes only respond to antigens that are attached to a body cell. this type of response is called cell-mediated immunity
A) pathogens invade body cells or are taken in by phagocytes
B) the phagocyte places the antigen on its own cell surface membrane
C) receptors on certain T helper cells fit exactly onto these antigens
D) this stimulates other T cells to divide rapidly by osmosis to form a clone
the cones T cells:
a) develop memory cells that proved rapid responses in the future
b) stimulate phagocytes to engulf the bacteria by phagocytosis
c)stimulate B cells to dive  
d) kill infected cells 

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B cells and humoral immunity

Humoral immunity is so called because it involves antibodies which are soluble in the blood and tissue fluiid
each B vell develops into two different types of cell
PLASMA CELLS - secrete antibodies directly. they only live for a few days but produce more than 2000 antibodies every second
MEMORY CELLS - live for decades in some cases. when they encounter the same antigen they divide rapidly into plasma cells and more memory cells. the memory cells provide long term immunity. this is known as the secondary immune response
1. the surface antigens of the invading pathogen are taken up by the B cells
2. the B cells process the antigens and present them on their surface
3. T helper cells attach to the processed antigens and B cells thereby activating them
4. the B cells are now activated to divide by mitosis to give a clone of the plasma cells
5. the cloned plasma cells produce antibodies that exactly fit the antigens on the pathogens surface
6. the antibodies attach to antigens on the pathogens and destroy them. this is the primary immune response 7.B cells develop into memory cells. these can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies. (this is the secondary immune response

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antibodies are proteins synthesised by B cells, antibodies react with antigens by binding together
antibodies ae made up of 4 different polypeptide chains

  • the chains of 1 pair are long and called heavy chains while the other pair have shorter chains and are called light chains
  • antibodies have a binding site that is very specific to the antigen once together they form and an antigen-antibody complex
  • the binding site is different for all antibodies and is known as the variable region
  • the rest of the antibody is the same and is called the constant region 
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enzyme and digestion

Glands produce enzymes that are used to break down large molecules into smaller ones that are ready for absorption
major parts of the digestive system
oesophagus - made up of thick muscular wall. adapted so that food can pass down it easily from the mouth to the stomach. used for transport as appose to digestion
stomach - muscular sac with an inner layer that produces enzymes. its roles are to store and digest food (especially proteins) there are glands within it that produce enzymes to digest protein. mucus is also produced in the stomach by glands. the mucus prevents the stomach being digested by its own enzymes

small intestine - a long muscular tube. food further digested here. enzymes enter the small intestine through its walls and gland. inner walls are folded into villi, which gives large surface area. villi is further increased by having million of tinier projections called microvilli. microvilli are found on the epithelial cells of each villus. this adapts the small intestince so that it can absorb substances in to the blood stream

large intestine - absorbs water. water is reabsorbed by the secretion of digestive glands. because there is little water within the large intestine the food becomes drier, forming poo.

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  • the rectum - is where poo is stored before it is removed through the anus in a process called egestion
  • salivary glands are positioned near the mouth. they pass there secretion via a duct into the mouth. this secretion will contain the enzyme amylase
  • the pancreas is a large gland situated near the stomach. it secretes pancreatic juice. this contains protease, lipase and amylase

2 stages of digestion - physical breakdown and chemical digestion

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  • large peices of food are broken down into small peices by processes such as chewing and the churning of food in the stomach. this makes it possible to not only absorb food but to increase its surface area, making it easier for chemical absorption. 


  • process of breaking down large molecules into smaller ones so they can be absorbed
  • carried out by enzymes that are functioned by hydrolysis which is the process of splitting up molecules by adding water to the bonds that hold them together
  • the enzymes are called hyrolases - because they are specific more than one is needed to break down a large molecule usually an enzyme will break down a molecule into smaller sections
    carbohydrases - break starch molecules down until they become monosacharides
    lipase - break down lips into glycerol and fatty acids
    protease - break down protein into amino acids
    once broken down they are absorbed into the body and built back up to form large molecules 
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