photosynthesis and respiration


ATP the energy currency

  • ATP is the shortened version of the word adenosine triphosphate
  • it is described as a phosphorylated nucleotide  
  • the general structure is an adenine group attached to a ribose sugar and attached to the ribose are three phosphate groups. 
  • this ability to store and release energy makes it the universal energy currency in organic beings
  • ATP can detach one of the phosphate groups via hydrolysis to releases energy that can be used by cells

once a phosphate is lost ATP becomes ADP this can be turned back into ATP using an protein complex ATP synthase that combines ATP and an inorganic phosphate group

uses of ATP 

  • muscle contraction 
  • active transport 
  • macromolecule synthesis 
  • stimulates the breakdown of substrates 
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photosytesis and why it is important

photosynthesis is the process of transforming light energy into chemical energy 

the  genral equation for photosystesis =6H2O + 6CO2==LIGHT===>C6H12O6 +  6O2

this is a very important reaction as it produces oxygen that all animals need to live 

these are always at the beginning of a food chain as they transform light into chemical energy that is then available to primary consumers and decomposers

all organisms that use light in this way are called photoautotrophs this means that they synthesise complex organic molecules from simple organic molecules using sunlight 

photosynthesis takes place in organelles called plastids the particular plastids for photosynthesis is chloroplasts

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structure of a chloroplast


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functions of the chloroplast

the thylakoids are phospholipid bilayers they are located throughout the chloroplast these are surrounded by an oily liquid that contains starch granules and other enzymes used for photosynthesis 

this oily liquid is called the stroma 

along these thylakoid membranes theirs are several key substances needed for photosynthesis 

photosystems one and two containing chlorophyll molecules 

accessory pigments need for photosynthesis 

electron carrier molecules 

through the chloroplast the thylakoid membranes stack atop of each other creating grana these grana are linked by integral lamella (thylakoids)

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Theirs are two main photosystem in the chloroplast photosystem one and photosystems two they are made up of a series of light absorbing pigments called chlorophyll A 

however chlorophyll a can only absorb light wavelengths of 6800nm-700nm this is only a very limited amount of light wavelengths

to absorb more light, there are accessory pigments that absorb other wavelengths of lights these include carotenoids and colorfully B

in this way the maximum amount of light can be absorbed and used to power photosynthesis 

green light is the only wavelenght that is reflected this is what makes leaves green 

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the light dependent reactions of photosynthesis

this is the first part of photosynthesis 

two molecules of water are split into oxygen gas 4H^+ ions and 4e^- 

this splitting by sunlight is called photolysis 

the oxygen is released as a waste product 

the electrons are taken in by photosystem two and then passed onto an electron carrier they then reach photosystem one where they are energised and then passed on through more electron carries till the electrons are picked up by NADP^+ along with two hydrogens 

this from NADPH2^+ or reduced NADP that is used in the light independent stage of photosynthesis or the DARK REACTIONS

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noncyclic photophosphorylation

cyclic photophosphorylation is the normal pathway for the light-dependent reactions 

H2O is split the electrons pass into PSI(photosystem one) then to an electron acceptor that then passes it to 

 PSII(photosystem two) producing one ATP this is 

where they are energised then they are passed onto another electron receptors 

this passes the electrons to NADP^+ 

meanwhile, the hydrogens are all stuck in the thylakoid space want to escape. this is only possible through protein channels connected to the protein ATP synthase the movement of H^+ ions powers this protein combining ADP and a inorganic phosphate. 

the process of making a hydrogen potential in the thylakoid space is called chemosis 

the two hydrogen is then picked up by NADP^+ along with four electrons 

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cyclic photophosphorylation and diagram

this happens at only at phtosystem one an electron is passed onto an electron carrier and then back to photosystem one 

this cretes atp that can be used 

( cyclic photophosphorylationcyclic

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light independent stage of photosynthesis

this is konow as the dark reactions or the calvin cycel 

this uses the two products of the light dependt stage ATP and reduced NADP

the start of this cycel a five carbon molocule called RuBP is commbined with Carbon dioxide 

this is done by a enzyme called rubisco this makes an unstabel six carbon intermidate that splits into 2 three carbon molocules called(GP) this process happens three times to make six GPs 

these six GPs are then changed into TP(trisose phosphate) they are then reduced by 3 reduced NADP's and are phosporrlated by three ATP's

five of these are turned back into three RuBP's and one TP is reased to be used 

the conversion of five of the TP's back into RuBP's makes three ATP's 

this cycle has to go round six times produceing Two TP's used to poduce hexose sugars that can be used to make starch and cellulose the rest are converted back into RuBP

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limiting factors of photosynthesis


carbon dioxide is a key element in photosynthesis if there is not enough carbon dioxide then the rate of photosynthesis will be severely limited as such it is a limiting factor 

another major limiting factor is the light intensity the higher the light intensity the higher the light intensity the faster respiration can happen if light intensity is too low the plant will stop photosynthesizing  

finally the enzymes in a plant will work best at their optimum temperature if it falls below the optimum the rate of photosynthesis  will slow dramatically above the optimum the enzymes would begin to denature and photosynthesis would cease to happen when all of the enzymes have denatured 

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the compensation point of photosynthesis

when there is too little light for photosynthesis to occur the plants will respire, however, there is a point where there is enough light for photosynthesis to occur and respiration is still happening 

at this point all the oxygen produced by respiration is used up by photosynthesis and the oxygen produced b photosynthesis is used in respiration


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respiration is used to make ATP that powers the metabolic reactions in animals 

respiration happens in four steps 

1)glycolysis this is the step where glucose is broken down into pyruvate for the start of respiration 

2)the lynx reaction this is where pyruvate is turned into a 2 carbon compound acetyl and is then        taken to stage three by acetyl coenzyme A 

3)this is where most of the reduced NAD is produced as well as some ATP 

4)reduced NAD is used to power the production of ATP in the electron transport chain 

step one occurs in the cytoplasum of the cell 

steps 2-4 happen in different areas of the mitochondria 

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the structure of the mitochondria

( second and third stages of respiration occur in the matrix of the mitochondria

the electron transport chain happens in the cristae of the mitochondria 

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step one glycolysis

the steps of glycolysis

  • this occurs in the cytoplasm 
  • glucose is phosphorylated by one ATP
  • it is now glucose six phosphate
  • glucose six phosphate is now changed to fructose six phosphate
  • fructose six phosphate is phosphorylated again by another ATP
  • this makes the molecule hexose 1,6 bisphosphates
  • this is then split into two triose phosphates
  • the two triose phosphates are then oxidised by the dehydrogenase enzyme and the hydrogens are taken by 2 NAD^+'s makeing two reduced NADS 
  • while this happens two ATPs are also produced from this reaction this
  • this makes and intermediate compound that is then changed into pyruvate
  • this change produces two more ATP's so theirs is a net gain of two ATP's 
  • the final product of this is pyruvate 
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steps 2&3 the links reaction and the krebs cycle

the link reaction is where a molecule of pyruvate is reduced and a carbon is lost making it into a two carbon chains

  • pyruvate dehydrogenase removes hydrogen from the pyruvate these are picked up by an NAD^+ makeing red NAD 
  • pyruvate carboxylase removes a carboxyl group in the form of carbon dioxide 
  • this is now acetate the coenzyme A picks this up becoming Acetyl coenzyme A and takes the acetate to the Krebs cycle 
  • the Krebs cycle this happens twice for every molocule of glucose 
  • the acetate is taken off  of the acetyl coenzyme A and is combined with a four-carbon compound oxaloacetate
  • this makes citric acid 
  • this is then decarboxylated and dehydronated making reduced NAD and carbon dioxide 
  • the now five-carbon compound is again decarboxylated and dehydrogenated and becomes a four carbon compound producing another red NAD
  • the four carbon is then reconfigured into a different four carbon compound this process also produces one ATP this is then dehydrogenated again giving two hydrogens to FAD^+ making reduced FAD 
  • finally, the compound is dehydrogenate one more time producing one more red NAD 
  • were are now back at the starting point oxaloacetate 
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step 4 electron transport chain oxidative phosphor

this occurs at the cristae of the mitochondria 

this is where most of the ATP is produced using the protein ATP synthases 

the feed source for this process is reduced NAD and reduced FAD 

reduced NAD is split into NAD^+ and 2H^+ and 2e^- the electrons are picked up by cytochrome complex one and passed onto electron crisis this provides enough energy fro the two H^+ to be pumped into the intermembrane space this creates a proton gradient 

FAD also releases two electrons which are used to actively pump hydrogen and its two hydrogens are released and picked up by oxygen

the protons can not escape except through a special protein channel linked to ATP synthase the movement of hydrogen through these channels powers ATP synthase combining ADP and inorganic phosphate 

these hydrogens are then picked up along with the four electron from NAD & FAD and FADS to hydrogens by oxygen to make two molecules of water 

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how much ATP is produced by respiration

what is produced in stages 1-3 

ATPS = 4

reduced NAD = 10

reduced FAD= 2

electron transport chain 

every NAD produces 2.6 ATPS 

every FAD produces 2 ATPS 

so ATP' produced at the end of the electron transport chain = 30


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anaerobic respiration animals and yeast

Lactate fermentation occurs when mammals when they do rigours activity’s the demand for ATP by the body is high and there is a deficits of oxygen 

The reduced NAD becomes reoxised by pyruvate

Pyruvate becomes lactate which can be used to produce some ATP 

this cycle can continue providing cautious energy by making reduced NAD and reoxidising it using pyruvate into lactic acid

When there is more oxygen lactic acid can be broken down and glycolysis can continue normally 

Anaerobic respiration of yeast 

Yeast can anaerobically respire breaking down pyruvate using pyruvate decarboxylase into ethanal this can then be used to deoxidise NAD the product of the reoxidisation of NAD is ethanol

The NAD can now be reused 

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