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Photosynthesis Flashcards

1
Q

what is photosynthesis?

A

a process that synthesises large organic molecules from simple inorganic molecules using the energy from sunlight

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2
Q

give the photosynthesis equation

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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3
Q

where are photosynthates produced?

A

at the source (the leaves)

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4
Q

what is the main photosynthetic tissue in a leaf?

A

palisade mesophyll

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5
Q

label the structure of a leaf

A

refer to page 2 of the photosynthesis booklet

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6
Q

what are stomata essential for?

A

for gas exchange in a leaf, without which photosynthesis would not occur

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7
Q

what method can we use to study the density of stomata?

A

1- apply clear nail polish to the lower epidermis of a leaf between the veins and allow it to dry

2- using forceps, peel the nail polish from the leaf to produce a replica of the lower epidermis

3- place the replica on a microscopic slide and count the number of stomata using the microscope

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8
Q

other than the presence of stomata, give three adaptations of the leaf for photosynthesis

A

large SA

thin so light penetrates photosynthetic tissues

densely packed palisade layer, palisade cells contain chloroplasts, air spaces to allow carbon dioxide to diffuse to photosynthesising cells

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9
Q

label the structure of a chloroplast

A

refer to page 3 in photosynthesis booklet

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10
Q

what do biochemical reactions in cells involve and where?

A

often involve cyclic metabolic pathways which occur in compartments (e.g. chloroplasts) inside cells

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11
Q

why is it important that biochemical reactions involve cyclic metabolic pathways in compartments in cells?

A

reactions can occur in small volume/isolation of enzymes/reactants

membranes isolate reactions within organelles, keeping products separate from the cytoplasm

mitochondria can be positioned close to areas needing ATP, and organelles can move within the cytoplasm

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12
Q

give the two different stages of photosynthesis

A

light dependent stage

light independent stage

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13
Q

what is the location and function of the light dependent stage?

A

location: thylakoid membrane and thylakoid space of chloroplast

function: involves the conversion of light energy into chemical energy (ATP and NADPH)

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14
Q

what is the location and function of the light independent stage?

A

location: stroma of chloroplast

function: uses the products of the light dependent reaction (ATP and NADPH) to produce organic molecules such as glucose

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15
Q

describe photosynthetic pigments, where they are located and their role

A

they are located within the thylakoid membranes of chloroplasts

during photosynthesis, different wavelengths of light strike the leaf and are absorbed by various pigments

their role is to capture light energy from the sun and convert it into chemical energy

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16
Q

what are the two main types of photosynthetic pigments in flowering plants?

A

primary pigment

accessory pigments

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17
Q

describe primary pigments

A

chlorophyll a absorbs blue and red wavelengths of light

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18
Q

describe accessory pigments

A

chlorophyll b absorbs blue and red wavelengths of light

carotenoids (xanthophyll & carotene) absorb violet/blue light

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19
Q

why are accessory pigments important?

A

as they absorb wavelengths of light not absorbed by the primary pigments

this ensures a wider range of wavelengths of light are absorbed, increasing the efficiency of photosynthesis

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20
Q

what macronutrient is needed to produce chlorophyll a?

A

magnesium

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21
Q

what can chromatography be used for?

A

to separate photosynthetic pigments

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22
Q

how does chromatography work? (there are 6 steps)

A

1- tear up leaves and grind with acetone to form a dark green pigment solution

2- use a capillary tube to spot the pigment on to chromatography paper

3- place the chromatography paper into a solvent (e.g. acetone/petroleum)

4- remove the chromatography paper once the solvent has travelled to the top of the strip
observe the different distances the pigments have travelled

5- calculate the Rf value for each pigment (distance travelled by the pigment divided by the distance travelled by the solvent)

6- identify each pigment by comparing the Rf values to known values

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23
Q

chromatography: why do we add acetone? (it is an organic solvent)

A

dissolve the phospholipid membrane to extract pigments

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24
Q

chromatography: why do we need a solvent to put the chromatography paper in?

A

dissolve spot and carry pigment up chromatography paper

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25
chromatography: why do the pigments travel different distances?
more soluble substances move further
26
what is the absorption spectrum?
it is a graph that shows the amount of light absorbed by chlorophyll a and the accessory pigments at each wavelength of light
27
why is so little light absorbed between 530nm and 640nm?
green light is reflected
28
what is the action spectrum?
a graph that shows the rate of photosynthesis at different wavelengths of light
29
suggest an experiment that you could conduct to measure the rate of photosynthesis
count no. of bubbles produced by pond weed over a set period of time
30
describe the relationship between absorption spectrum a and action spectrum b
there is a close correlation between the two spectra this suggests that the light absorbed by the pigments is used in photosynthesis
31
fully explain the results of Engelmann's experiment (page 8 in booklet)
photosynthesis produces oxygen as a by-product. aerobic bacteria are attracted to the oxygen most bacteria are in the blue and red regions/few bacteria in green region most photosynthesis in this region
32
where are photosystems located?
on the thylakoid membranes of chloroplasts
33
what is the role of photosystems?
absorb photons of light energy act as transducers, transferring this light energy to high-energy electrons this energy is then used to fuel proton pumps and synthesise ATP
34
describe the structure of photosystems and how light energy is passed through it (there are 4 things) (good images on page 9 in booklet)
accessory pigments are grouped into clusters with associated proteins, forming an antenna complex these pigments absorb photons of light energy and funnel this energy down the antenna complex to the reaction centre chlorophyll a molecules are found in the reaction centre, below the antenna complex when photons of light energy reach chlorophyll a, electrons are excited to become high-energy electrons
35
what are two photosystems involved in the light dependent reaction?
photosystem I (PSI) /P700 photosystem II (PSII) /P680
36
what is the difference between photosystem I and photosystem II
PSI best absorbs light at 700nm wavelength PSII best absorbs light at 680nm wavelength
37
describe the simple process of the light dependent reaction
requires light energy takes place in the thylakoid membrane and thylakoid space (cavity) involves the synthesis of ATP from ADP and Pi (via photophosphorylation) involves the splitting of water using light (photolysis) involves the reduction of NADP to form NADPH/H+ (reduced NADP) releases oxygen gas as a by-product
38
what are the two light dependent reactions and in what plants do they both occur in?
in higher plants non-cyclic photophosphorylation cyclic photophosphorylation
39
explain what happens at photosystem II during non-cyclic photophosphorylation (diagram to help on page 11 in booklet) (there are 5 things)
photons of light are absorbed by PSII and passed to chlorophyll a in the reaction centre this excites two electrons in chlorophyll a to a higher energy level, causing them to be emitted, passed to electron acceptors and then transferred along a chain of carriers (which includes a proton pump) to photosystem I as the electrons move along the chain, they release energy, which is used to pump hydrogen ions (protons) from the stroma across the thylakoid membrane into the thylakoid space this creates an electrochemical gradient due to the high H+ concentration in the thylakoid space and low H+ concentration in the stroma H+ flow down this proton gradient through a proton channel connected to ATP synthase (in a stalked particle) providing energy for the formation of ATP from ADP and Pi
40
explain what happens at photosystem I during non-cyclic photophosphorylation and why its called non-cyclic photophosphorylation (there are 4 things)
photons of light are absorbed by PSI, causing two electrons in chlorophyll a to be raised to a higher energy level, emitted, and passed to another electron acceptor the electron acceptor transfers the electrons to protons outside the thylakoid membrane into the stroma, which then reduce NADP to NADPH the use of H+ to reduce NADP lowers their concentration in the stroma, helping to maintain the electrochemical gradient between the thylakoid space and the stroma the emitted electrons do not return to their original source, so this process is known as non-cyclic photophosphorylation
41
suggest the effect of the high concentration of H+ ions in the thylakoid space
more acidic
42
describe photolysis (which occurs during non-cyclic photophosphorylation)
it is the splitting of water using light occurs in the thylakoid space water splits into oxygen, protons and electrons the electrons replace those lost by photosystem II, making the chlorophyll molecule stable the protons help to maintain the electrochemical gradient between the thylakoid space the stroma
43
where does cyclic photophosphorylation take place and why do they also take place in higher plants?
occurs in bacteria and primitive plants higher plants also use this pathway to provide extra ATP, especially when CO2 is in short supply, or if levels of reduced NADP are very high
44
what photosystem is involved in cyclic photophosphorylation?
photosystem I only light energy is absorbed at PSI and channelled to chlorophyll a
45
explain what happens during cyclic photophosphorylation (helpful diagram on page 13 in booklet) (there are 5 things)
light energy is absorbed at PSI and channelled to chlorophyll a electrons in the chlorophyll a become excited, energised and released they are accepted by an electron acceptor and eventually passed along the same transfer chain as that used by the electrons from PSII protons are pumped into the thylakoid space and ATP is produced from ADP + Pi the same chemiosmotic theory as that used to describe the Z scheme is believed to be involved in the production of ATP the electrons excited and released from PSI return to PSI
46
in non-cyclic photophosphorylation, what happens to oxygen produced from photolysis?
oxygen is released as a waste gas or used during respiration
47
when might plants shift from non-cyclic to cyclic photophosphorylation?
the conc. of reduced NADP in the chloroplast may help regulate which pathway electrons take through the light reactions when chloroplast runs low on ATP for the Calvin cycle, NADPH will accumulate and the plant may shift from noncyclic to cyclic electron flow
48
what is the light independent stage also known as?
Calvin cycle
49
does the light independent stage require light?
no
50
describe briefly the light independent stage
it uses ATP and reduced NADP from the light-dependent stage to fix carbon dioxide into organic molecules e.g. glucose
51
where does the light independent stage take place? (diagram on page 15 in booklet)
occurs in the stroma of the chloroplast (discovered by Melvin Calvin)
52
what happens during the light independent stage? (helpful diagram on page 16 in booklet) (there are 7 steps) (application of Calvin cycle on page 17 in booklet)
CO2 from the atmosphere is fixed with RuBP(5C) the enzyme RuBisCo catalyses this reaction this results in the formation of an unstable 6C compound which splits into two molecules of Glycerate-3-phosphate (3C) Glycerate-3-phosphate is then reduced using reduced NADP produced during the light dependent stage ATP from the light dependent stage is also required ATP is hydrolysed and the phosphate is transferred to Glycerate-3-phosphate, resulting in the formation of two molecules of triose phosphate (3C) one carbon atom of the 6 available is removed from the Calvin cycle and can be used to produce organic molecules such as glucose five carbon atoms remain in the Calvin cycle and are used to regenerate RuBP so the cycle can begin again
53
describe what happens to the one carbon that leaves the Calvin cycle to form organic molecules
they are not 'recycled' they leave the Calvin cycle and form hexose phosphates, which ultimately yield sucrose, starch and cellulose the sugars produced during carbon metabolism can also act as carbon skeletons and can be used for other metabolic reactions like the production of amino acids and lipids
54
give three inorganic nutrients that have a role in plant metabolism
nitrates magnesium phosphates
55
how are nitrates taken up by plants?
taken up by roots transported as nitrates in xylem and amino acids in the phloem
56
how is magnesium taken up by plants?
absorbed as Mg2+ and transported in the xylem
57
how are phosphates taken up by plants?
absorbed as PO4- by the roots and transported in the xylem
58
what is the function of nitrates in plants?
synthesis of proteins synthesis of nucleic acids
59
what is the function of magnesium in plants?
synthesis of chlorophyll ATPase activation
60
what is the function of phosphates in plants?
form phospholipids form nucleotides along with nitrogen (ATP/DNA/RNA)
61
what is the symptoms of deficiency of nitrates in plants?
reduced growth of organs chlorosis- yellowing leaves due to inadequate chlorophyll production so plant no longer able to absorb light energy
62
what is the symptom of deficiency of magnesium in plants?
pronounced chlorosis between veins of older leaves as existing Mg2+ is moved and transported to new leaves
63
what is the symptom of deficiency of phosphates in plants?
stunting of plant growth
64
why does photosynthesis have a lot of limiting factors?
since it involves hundreds of chemical reactions, where the products of one reaction serve as reagents for the next any step in this process can limit the overall rate of photosynthesis
65
what are some limiting factors of photosynthesis?
temperature carbon dioxide conc. light intensity
66
how does temperature affect light intensity?
temperature influences enzyme activity provided temperatures do not cause enzyme denaturation, an increase in temperature generally enhances enzyme activity, thereby increasing the rate of photosynthesis
67
describe the effect of enzyme denaturation on the rate of photosynthesis
tertiary structure changes, active site changes shape, substrate no longer complementary, no enzyme substrate complexes form, rate slows
68
suggest why an increase in temperature speeds up the rate of the light independent stage more than it speeds up the rate of the light dependent reaction and explain the implication on the overall rate of photosynthesis?
photophosphorylation is less dependent on enzyme activity than Calvin cycle increased temp. increases Calvin cycle more than photophosphorylation products of photophosphorylation (ATP, reduced NADP) not enough for Calvin cycle and rate of photosynthesis is limited by supply of reduced NADP and ATP
69
how might carbon dioxide affect the rate of photosynthesis? (application of this on page 20 in booklet)
during photosynthesis carbon dioxide is fixed to form carbohydrates carbon dioxide makes up only 0.035% of atmospheric air and therefore the concentration often limits the rate of photosynthesis (optimum CO2 levels for photosynthesis: 0.4%)
70
describe a physical change that could occur in the leaf that might result in the rate of photosynthesis decreasing at very high carbon dioxide concentrations
stomata close to prevent CO2 diffusing in and dissolving in cytoplasm, forming carbonic acid (catalysed by carbonic anhydrase) this would dissociate into HCO3- ions and H+ ions which lowers pH of mesophyll cells, denaturing enzymes
71
how does light intensity affect the rate of photosynthesis and explain the effect this will have on the yield of photosynthates?
light is essential for the excitation of electrons and for photolysis in the light dependent reaction as light intensity increases so too does the rate of cyclic and non-cyclic photophosphorylation as photophosphorylation speeds up, ATP and reduced NADP are produced at a faster rate therefore organic molecules are produced in the Calvin cycle at a faster rate
72
describe a physical change that could occur in the leaf that might result in the plateau at high light intensity and explain the advantage of this to the plant (more questions on page 21 in booklet)
at high light intensities, temperatures are also high so stomata close to reduce transpiration

biolala (31 decks)

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