Module 5.6

Question 1

Why is photosynthesis important ?

Answer 1

Photosynthesis is a physiological process used by plants , algae and some types of bacteria to convert light energy from sunlight into chemical energy .

Question 2

Why is photosynthesis important ? - what is meant by autotrophic nutrition

Answer 2

organisms , can use this chemical energy , to synthesise large organic molecules , which form the building blocks of living cells . From, simple inorganic molecules such as water and carbon dioxide- known as autotrophic nutrition .

Question 3

What are Photoautotrophs ?

Answer 3

organisms that photosynthesise , as they use light as the energy source for autotrophic nutrition .
-These organisms , are also described as producers , because they are at the beginning (first trophic level ) , o fa food chain and provide energy and organic molecules to other non-photosynthetic organisms .

Question 5

general equation for photosynthesis

Answer 5

…

Question 6

what is a photon

Answer 6

a photon is a particle of light each photon contain an amount (a quantum( of energy .

Question 7

what is the main product of photosynthesis

Answer 7

the main product of photosynthesis is monosaccharide sugar which can be converted into disaccharides for transport and then starch for storage .

Question 8

what is carbon fixation?
-Give an example

Answer 8

-Photosynthesis is an example of carbon fixation - the process by which, carbon dioxide is converted into sugars.
-The carbon for synthesising all types of organic molecules is provided by carbon fixation .

Question 9

What type of reaction is carbon fixation

Answer 9

endothermic, and so needs energy . Carbon fixation also needs electrons ;the addition of electrons is a reduction reaction .

Question 10

What is the purpose of carbon fixation

Answer 10

carbon fixation helps regulate , the concentration , of carbon dioxide , in the atmosphere , and oceans .
-Most forms of life on earth rely directly or indirectly on photosynthesis.

Question 11

respiration

Answer 11

plants, and other organisms , that photosynthesise also respire . During respiration , they oxidise , the organic molecules that they have previously synthesised by photosynthesis and stored, releasing chemical energy .

Question 12

-non-photosynthetic organisms

Answer 12

such as fungi , animals, many protoctists , and many types of bacteria are described as heterotrophs .They obtain , energy , by digesting , complex organic molecules of food to smaller molecules that they can use as respiratory substrates .They obtain energy from the products of digestion by respiration.

Question 13

what happens during respiration

Answer 13

glucose , and other organic compounds are oxidised to produce carbon dioxide and water . Respiration releases chemical energy 9IT IS EXOTHERMIC )
-THAT can drive the organismsmetabolism .

Question 14

how do photosynthesis and respiration interrelate ?

Answer 14

both photosynthesis and aerobic respiration are important in cycling the carbon dioxide and oxygen in the atmosphere. The products of one process are the raw materials for the other process . Aerobic respiration removes oxygen from the atmosphere and adds carbon dioxide while photosynthesis does the opposite .

Question 15

competition between plants
-fyi - plants respire all the time
-however , plants only photosynthesise during daylight.

Answer 15

-plants often compete with each other for light.
-the i intensity of light has to be sufficient , to allow photosynthesis at a rate that replenishes the carbohydrate stores used up by respiration .

Question 16

what happens at the compensation point?

Answer 16

when photosynthesis and respiration proceed at the same rate , so that there is no net gain or loss of carbohydrate , the plant is at its compensation point.

-The time a plant takes to reach its compensation point is called the compensation period.

Question 17

how compensation periods vary in different plants .

Answer 17

-the compensation period is different for different plant species . Shade plants can utilise light of lower intensity than sun plants can .
-When exposed to light after being in darkness , shaded plants reach their compensation point sooner (shorter compensation ) than sun plants , which requeue a higher light intensity to achieve their optimum rate of photosynthesis.

Question 18

what is granum (plural grana )

Answer 18

inner parts of chloroplast made of stcks of thylakoid memerbanes where the light dependant stage of photosyntheissi takes place .

Question 19

what is a photosynthetic pigment

Answer 19

pigment that absorbs specfici wavelengths of light and raps the energy associated with light , such pigments include chlorophlls a and b crotene and xanthophyll .

Question 20

what is a photosytem

Answer 20

system of phtoosytnhetic pigments found in thylakoids and chloroplasts , each photoytem contains aout moelcules of chlorphyll tht traps photons and pass thheir eergy to a primary pigment reaction cener ,a moleucle of chlorphyll , a during the light dependet stage of photosynthesis .

Question 21

what is stroma

Answer 21

fluid filled matrix of chloroplasts , where the light independent stage of photosyntehsis akes place .

Question 22

what is a thylakoid

Answer 22

flattneed emmbrane bound sac found isnide chloroplasts contians phtoosyntehtic pigments / photosytems and is the site of the light dependent stage of photosyntehsis ..

Question 23

structure of chloroplasts

Answer 23

–chlroroplasts are the organelles within plant cells where photosynthesis takes place .
-algae have chloroplasts but photosynthetic bacteira do not .

-+Most plant chloroplasts are disc shaped and around - 2-10 micrometers long . Each is surrounded by a double membrane , the envelope with an INTERMEMEBRAE SPACE of width 10-20 nanometeres . ebtween the inner and outer memebrane .

OUTER MEMBRAN EIS HIGHY PERMEAE .

Question 24

there are two distinct region visible on an electron micrograph

Answer 24

the fluid filled matrix called the stroma and the grana that consists of stacks of thylakoid membranes .
-check page 116

Question 25

grana (1) check page 117

Answer 25

-first stage of photosyntheiss is the light - dependent stage , this takes place in the grana ,

Question 26

how many membranes do chloroplasts have explain them

Answer 26

chloroplasts have three distinct membranes - outer , inner and thylakoid , giving these separate internal compartmenet s- the intermemebranse space , the stroma , nd the thylakoid space . --The thylakoids within a granum may be connected to thylakoids within nother granum by intergranal lamellae (also knwon as intergranal thylakoids )

Question 27

what is the thylakoid membrane of each chloroplast

Answer 27

-the thylakoid membrane of each chloroplasts is less permemable and is foled into flattened dis like sacs called thylKOIDS THAT FORM STACKS . -eACH STACK , OF THYLAKOIDS , IS called a granum , . One granum may contain 100 thylakoids

Question 28

with many grana in every chloroplast and with many chloroplasts in each photosynthetic cells , there is a huge surface are for what

Answer 28

-The distribution of the photosytems that contain the photosynthetic pigments that trap sunlgiht energy . -the electrons carries and ATP synthase enzymened need to conver that lgiht energy into ATP .

Question 29

why are proteins embedded in the thyLAKOID MEMBRANE >

Answer 29

To hold the photosytems in palce . -The gana are surroudned by the stroma , so the products of the light dependent stage can easily pass to the stroma to be used in the light independent stage .

Question 30

what is in the stroma

Answer 30

the strom is the fluid filled matrix , it contins the enzmes needed to catalyse the reactions of light independent stage of photosynhtesis as well as strach grians oil droples , small ribsosomes ismilr to those found in porkaryote cells . -the loop of dna contains genes that code for some of the porteins needed for photosyntheiss . These proteins are assmled at the chloroplass ribosomes .

Question 31

where are photosyntheitc pigments and what is their purpose

Answer 31

within the thylakoid membranes of each chloroplasts are funnel shaped strucutures called photsytems . These photosytems contain photosynthetic pigemnts . -Each pIgement absorbs light o a particular wavelength and reflects other wavelength s of light . -Each pigment appears to our eyes and brain , the clolour o fthe wavelngth of ligh t it is reflecting .

Question 32

what happens to the energy associated witht he wavelengths

Answer 32

it is funneled down to the primary pigement reaction cenre cosniting of a type of chlorphyll at the base of the photosytem . check page 117 figure 3

Question 33

wgat are chlorophylls

Answer 33

chlorophylls arre a mixture of pigments all hae a similar molecular strucuure consiting of a porphyrin group in which is a magnesiuma tom and a long hdyrocarbon chain .

Question 34

what is chlorphyll a

Answer 34

there are two forms of chorms of chlorophyll a - both of which appear blue - green . Both are situaated at the center of photosytems , both absorb red ligh t buthey have different absoprtion .

Question 35

p680

Answer 35

is found in photosytems ii and its peak of absoprtion is lioght of wavelength 680nm .

Question 36

p700

Answer 36

is found in photosytem I , and its peak of absoption is light of wavelength 700 nm . -chlrophyll a also aborbs some blue light , of wavelength around 440 nm .

Question 37

what does chlorphyll b absorb

Answer 37

chlorophyll b absorbs light of wavelengths 400-500nm and 640 nm it appears yellow green .

Question 38

what are accessory pigments

Answer 38

cartenoids absorb blue light of wavelengths 400-500 nm . They reflexct yellow nd orsange light . -XAnthophylls absorb blue and green light sof wavelgnths 375-550 nm they reflect yellow light .

Question 39

how to separate photosynthetic pigments

Answer 39

using thin layer chromaatorpahy , mashing green leaf to separate pigmens in chlorpjull ,t hen spot oto tlc materia , olven separates the pigments as they hae differeet rf vlaues . -useing high flammable solvent ehtnol make sure no anked flames .

Question 40

where does the light dependent stage of photosyntheissi occur and what does it invovle

Answer 40

where does the light dependent stage of photosyntheiss occurs in the grana (thylakoids) of chloroplasts and invovles photosytems - it invovled the direct use of ligh energy .

Question 41

what des the light dependent stage conist of

Answer 41

1. light harvesting at the photosyems . 2.photolysis of water . 3.photophosphortlatui 0 tge production of ATP in he prescence of light , 4.atHE FORMATION OF REDUCED NADP . -Oxygen the by product of photosynheiss is also produced in the light dependant stage .

Question 42

what are the two different types of photosytems

Answer 42

there are two different types of photosytems -In photosytems I (PSI) , the pigment , at the primary reaction centre is a type of chlorophyll a , which was a peak absoprtion of red light of wavelength 700 nm (P700) .

Question 43

what is the second photosytem II (PSII)

Answer 43

In photosytems II (PSII) , the pigment at the primary reaction centre is also a type of chlorophyll a , but this has a peak absoprtion of red light of wavelegnth 680nm 9P600) .

Question 44

Tthe role of water in the light depednet stage light ,

Answer 44

In PSII , there is an eznyme that in the presence of light , splits water molecules into protons (hdyrogen ions ) , electrons and oxygen . The splitting of water in this way is called photolysis . 2H20--H+ +4e-+O2 -Some of the oxygen produced during phtolysis is used by plant cells for aerobic respiration , but during periods of high light intenitsty , the rate of photosynthesis is greater than the rate of respiration in the plant , so much of the oxygen by product will diffuse out of the leves through stomta intot he surroudning atmOSPHERES

Question 45

WHAT IS the function of water in a plant

Answer 45

-is the source of protons (hdyrogen ions ) , that will be used in photophosphorylation . -donates electrons to chlorophyll to replace those lost when light strikes chlorophyll . -is the source of the by product , oxygen . -keeps plabt cells turgid , enabling them to function .

Question 46

what is photophosphorylation

Answer 46

the generationo f ATP , from ADP , and inoranic phosphate in the presence of light .

Question 47

there are two types of phosphorylation ...

Answer 47

noncylcic nd cyclic

Question 48

what is non cyclic photophospphorylation

Answer 48

it invovles PSI and PSII , it porduced ATP , oxygen nd reduced NADP .

Question 49

what is cyclic photophosrylation

Answer 49

It invovles only PSI , it produced ATP , but in smaller qunatities than are made by non-cyclic photophosrylatuib , BUT BOTH PROCESSES invovle iron containng proteins embdeed in the thylakoid meembranes that accpet and donate electrons and form electron transport systems .

Question 50

stage one of non-cyclic photophosphorylation

Answer 50

-When a photon of light strikes PSII (P680) , is energy is channelled to the primary pigment reaction centre .

Question 51

stge two of non-cyclic photophosphorylation

Answer 51

the light energy excites a pair of eelctrons inside the chlorophyl moelcule .

Question 52

stge three of non cyclic photophosphorylation

Answer 52

the energised electrons escape fromt he chlorophyll moelcule and are captured by an electron carrier which is a portein wih iron at its center embedded in the thylakoid membrane .

Question 53

stage four of non cylic photophosphorylation

Answer 53

rhwse electrons are replced b electrons derived from photolysis .

Question 54

stage five of non cyclic photophosrylation

Answer 54

when this iron combine with an electron it becomes reduced FE2+ . It can be then donate the electron becoming rexidised (FE3+) too the next electroncarrier in the chain .

Question 55

stage six of nonn cyclic photphosrylation

Answer 55

at electrons are passed along a chain of electron carrier embedded in the thylakoid membrane t each step some energy associated with the electrons is released .

Question 56

stage seven of non cyclic photphosrylation

Answer 56

this energy is used to pump protions across the thylakoid membrane in the thylakoid space .

Question 57

stage eight of non cyclic photophosrylation

Answer 57

eventually the electrons are captured by anothe rmoleucle of chlorphyll a in PSI . These electrons replce those lost from PSI due to excitation by light energy .

Question 58

stage nine of non cyclic photophosrylation

Answer 58

a protein iorn sulfur compex called ferredoxin accpets the electrons from PSI and passes them to NADPp in the stroma

Question 59

Stage ten of non cyclic photophosrylation

Answer 59

as protons accumualte in the thylakoid spce a proton gradient forms across the membrane .

Question 60

stage 11 of non cyclic photophsorylation

Answer 60

protons diffuse down their cocentration gradient htrough special channels in the memrbarane associated with ATP synthase enzymes ,a nd , as they do so , the flow of protons caused ADP and inorgnic phophate to join forming ATP .

Question 61

stage 12 of non cyclic photophosrylation

Answer 61

as the protons pass thorugh the channel , they are accepted along withe elctrons by NADP , which become reduced ,t he reduction of NADP is catalysed by the enzyme NADP reductase .

Question 62

conclusion of non cyclic photophosphorlation

Answer 62

the light enrgy has been converted into chemical neegy int he form of ATP by photoposphorylation . Atp nd reduced Nadp are mow in the stroma ready for the light independent stage of phottosytnehsis .

Question 63

what is the meaning of electron carriers

Answer 63

moelcules that can accept one or more electrons and then donte those electrons to another carrier . -Proteins embdedded in thylakoid membranes are electron carriers , and form an electron transport chain or system , Ferredoxin , NAD and NADP , are also electron crriers .

Question 64

what is NADP

Answer 64

nicotineamide adenine dinucleotide phosphate a coenzyme and electron and hydrogn carrier .

Question 65

wht does cyclic photosphosphorylation (1)

Answer 65

this uses only PSI (P700) , as light strikes PSI , a apir of electrons in the chlorophyll molecule at the reaction center gain energy and become excited . THey escape , from the chlorophyll and pass to an electron carrier system and then pass back to the PSI .

Question 66

cylic photopshophorylation (2)

Answer 66

during the passage of electrons along the electron carriers a small amount of ATP is generated . However , no phtolysis of wateer occurs , so no protons or oxygen are produced . No reduced NADP is generated .

Question 66

cyclic photophosrylation (3)

Answer 66

chloroplasts , in guard cells contin only PSI . The produce only ATP , which actively brings potassium ions into the cells lowerring the water potenitl so that water follows by osmosis . This causes the guard cells to swell nd open the stoma . F-2 , summarisws thw main events cyclic noncylic photophosrylation in a digaram known as the Z scheme .

Question 67

whatis the calvin cycle

Answer 67

metaboilc pathway of the light - independNant stage of photosynthesis ocurring (in eukaryotic cells 0 , in the stroma o chloroplasts where carbon dioxide is fixed with the products of the light , -dependent stage to make organic compounds . The calvin cycle also occurs in many photoautotrophic bacteria .

Question 68

glycerate - 3 - phosphate (GP0

Answer 68

an intermediate compound in the calvin cycle .

Question 69

ribulose biphosphate (RuBP)

Answer 69

a five carbon compound present in chloroplast , a carbondioxoide acceptor

Question 70

triose phosphte (TP)

Answer 70

a three carbon compound ,a nd the porduct of the calvin cycle , canbe used to mke other larger organic molecules .

Question 71

The light independant stage of photosynthesis tkes place in the stroma of chloroplasts

Answer 71

Although , it does not directly use light , energy it is uses the products of the light - dependant stage . If the palnt is not illuminated , the light-independant stage soon ceases because ATP , and hydrogen are not available to reduce the carbon dioxide and synnthesise alrge complex organic moleucles .

Question 72

As the role of carbon dioxide (1)

Answer 72

carbon dioxide is the source of carbon for the production of all organic moelucles found in all the carbon - based life forms on Earth . These organic moleucles may be used as structures ( cell membranes , antigens ,e nzymes , muscle proteins , celluose cell walls ) , or act as energy stores (starch and glycogen )

Question 73

role of carbon dioxide (2)

Answer 73

carbon dioxide ina ir enters the leaf through the stomata and diffuses thorugh the spongy mesophyll layer to the palisade layer into the palisade cells . thorugh their thin cellulsoe cell walls and hen through the chlrooplast envelope into the stroma n. The fixation of carbon dioxide in the stroma maintaisna concentration gradient that aids this diffucion . Carbondioxide that is a by - product of respriation in plant cells may also be used for this stage of photosytnehsis .

Question 74

what is the calvin cycle simple odefiniton

Answer 74

thee series of reactions whebr carbon dioxide is converted to organic moleucles is called the calvin cycle .

Question 75

stage one of the calvin cycle

Answer 75

carbon dioxide combines with a carbondioxide acceptor , a five carbon compound called ribulose biphosphae (RuBP) , This reaction is catalksed b the enzyme RuBisCo

Question 76

Stage four of the calvin cycle

Answer 76

Gp is then reduced , using hdyrogens fromt he reduce Nadp ,MADE during the light dependent stage , to triose phophate . -Eneergy from ATP ,a lso made during the light dependent stage is used at this stage at the rate of two meolecules of ATP , for every moelcule of carbon diocide fixed during stage 3

Question 76

stage two of the calvin cyle

Answer 76

RuBP , by accepting the carboxyl (COO-) , group becomes carboxylated , forming an unstable intermediate six-carbon compound that immediately breaks down .

Question 76

stage three of the calvin cycle

Answer 76

the product , of this reaction is tw omoelucles of a three carbon compound GP , THe carbon dioxide has now been fixed .

Question 77

stage five of the calvinc ycle

Answer 77

in 10 of ever 12 Tp molecules , the atoms are rearranged to regenerate six moelcules of RuBpP , . This process reqruies phospahte groups . Chloroplasts contain onl low levels of RubBP as it is continully being converted to GP , but is also continuall being regenrated . The remainig two of th 12 moelcules of TP are the product .

Question 77

WHy does the calvin cycle only run during the daylight part oen

Answer 77

as already mentioned , the products of the light-dependant stage , maley ATP , and reduced NADP are continously neneded for the calvin cyle to run .

Question 78

why does calvin cycle onl run during the daylight part two

Answer 78

-During the light-dependent stage , hdyrogen ions are pumped from the stroma into the thylakoid spaces so the cocenration of free protons in the stroma falls rising the Ph to around 8 which is optimum for enxyme RuBisCO which is also activaed by the prescence of EXTRA ATP INT HE STROMA .

Question 79

why does calvin cycle only during the daylight part three

Answer 79

in daylight the cocnetration , o magensium ion sincereases int he stroma . These ions atatch to the active site of RrubisCo , acting as cofactros , to activate it . The ferredoxin that is reduced b electrons from PSI , activates enzymes involved in the reactions of the calvin cycle .

Question 80

The use of triose ohisohate (TP) (1)

Answer 80

Some TP molecule , are used to synthesise organic compounds for example ; -some glucose is converted to sucrose some to stratch and some to cellulose .

Question 81

The use of triose phosphate (2)

Answer 81

-Some TP , is used to synthesisie amino acids , fatty acids , gllycerol , the rest of the TP is recycled to regenrate the supply of RuBP , . -Five moeleucles , of the three carbon compound TP , intereact to form three moelcules of the five carbon compound RuBP .

Question 82

what is light intentisty

Answer 82

levels of lihg

Question 83

what is water stress

Answer 83

the condiiton of a plant will expeirence whn water supply becomes limiting .

Question 84

what are limiting factors , give an overveiw

Answer 84

-the factirs tgat afect the rate of the complex process of photosynthesisie operate simultaneously . These faactors incldue the raw materials - carbondioxide and water as well as the eergy source - light intenist , plus availabiltiy of chlorphll , elecctron carriers and relevant enzymes . Other factors , nclduing temperature and turgidity of cells are also important . -At any given momen ,, the rate of a ametanlolic process that depends on a nuber of factors is limited y the factor that is preent at it slest favourable (lowest level )

Question 85

limiting factor (1) light intensity

Answer 85

light provides he enrgy to power the first stage of photosynheis and porduce ATP and reduced NADP needed for the next stage . -Light also causes tomata to open so that gaseous exchange . When stomta are open transpiration also cocurs and this lead to uptake of etaer and its delviery to leaves

Question 86

limiting factor (2) light intenisty

Answer 86

at a constant favourable emperature and constant suitable carbon dioxid concentration light intensity is the limiting factor . When light ntnsit is low , the rate of photosythesisi is low . As light increases , the rate of photosyntheis sincreases . -At a cerain point , even when light intenisty increases , the rate of photosynthesis DOES NOT INCREASES , now another fctor other than light intenisty is a limtiign t=fctor .

Question 87

carbon dioxide concentration as a limiting facotr

Answer 87

the levels of carbon dioide in the atmosphere and in aquatic habitats are high rnough tht carbon dioicdie is not usually a limtiing factor .

Question 87

the effect of changing the carbon dioxide concenration on the calvin cycle

Answer 87

if the cocnentration of carbon dioixide falls below a.a1% 1.RuBP cannot accep tit and accumulates . 2.GP cannot be made . 3.Therefore TP cannot be mde ..

Question 87

what does the effect of changing the light intenisty do to the calvin cycle -F3 - SHOWS what happens when there is little or no light

Answer 87

1.GP canno be reduced to TP 2.TP levels fall and accumulates 3.If TP levels fall RuBP cannot be regenerated (check the graph )

Question 88

temperaure as a limiting factor part one - intro and -hten low temps 25-30

Answer 88

the calvin cycle invovles many enzyme - catalyed reactions and therefore is sensitive to temperature . -Tthe effects oc changing temperture on the calvin cycle . -FROMW low tempratures to temperatures of 25-30 degrees if plant have enough water and carbon dioxide and a suficent light inenisty the rate of phottosyntheiss icnreases as temperature increases .

Question 89

temperature above 30 degrees 0 temperature as a limiting factor a

Answer 89

at temperatures above 30 degrees for most plantns , gorwth rtes mayr educe due to photorespiration , oxygen competes with carbondioxide for the enzyme RuBisCo's active site . -This reduces the munt of carbon dioxide being ccpeed by RuBP and subsequetnl reduces the quantiti of GP and thereofre of TP being prpoduced , whilst itiallky causing an accumulation of RuBP . However , due to lack of TP RuBP cannot be regenrated ..

Question 90

temperatrues bove 45 degrees - temperature as a limiing factor

Answer 90

at tempertures , above 45 enzymes involved in photosynthesis may e denaturued . This would reduce the cocnenration of GP and Tp and eventuall RuBP as it could not be regeneraed due to lack f TP .

Question 91

Explain water sress

Answer 91

if a plant has cess to sufficent water in the soil then the transpiration stream has a cooling effect ont he water passing up the xylem to the leaeaves also keep plant cells turgid , so they can function , Turgid guard cells eeo yp , stomata open for gaesoueexchange .

Question 92

water stress (2)

Answer 92

-Plants roots produce abscisic aci when translocated to leaves , causes stomata to close reducing gaseous exchange . -Tissues become flaccid and leaves wilt . -The rate of photosyntheisis , gretl reduces . TUP - CELL BECOEMS PLASMOLSYED btu the tissues become flaccid .

Question 92

What will happen if there is not enough water in the plant (water stress) part one

Answer 92

-If the roots are unable tot ake up enough water to replace that lost via transpiration . --cells lost water and become plasmolysed .