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a-level biology > 5.2.1 Photosynthesis > Flashcards

5.2.1 Photosynthesis Flashcards

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1
Q

thylakoid disc

A

site of light-dependent reaction
contains photosynthetic pigments embedded in the thylakoid membrane

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2
Q

purpose of photosynthesis

A

conversion of light energy to chemical energy in organic molecules

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3
Q

granum

A

stack of thylakoid discs

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4
Q

stroma

A

fluid-filled space of chloroplasts surrounding the thylakoids
light-independent stage of photosynthesis takes place
contains enzymes involved in the light-independent reaction (Calvin cycle)

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5
Q

intergranal lamellae

A

connects grana
allows the sharing of resources

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6
Q

primary pigments

A

chlorophyll a
absorb protons and excite electrons

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7
Q

structure of chloroplast

A

outer membrane
inner membrane
stroma
thylakoid discs - stack to form a grana
intergranal lamellae
70s ribosome
starch grains
circular DNA

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8
Q

accessory pigments

A

chlorophyll b,c,d
channel light energy towards the primary pigment
increase the range of wavelengths of light that can be absorbed

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9
Q

use of the products of photolysis

A

H+ forms proton gradient
e- replace lost electrons in photosystem 2
oxygen - respired aerobically or diffuses out of stomata

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10
Q

cyclic phosphorylation

A

electrons excited from photosystem 1 are unable to be accepted by NADP

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11
Q

outline the importance of photosynthetic pigments in photosynthesis

A

pigments absorb light/photons

electrons excited to a higher energy level

accessory pigments pass energy to reaction centres, channel light towards primary pigment, increase the wavelengths of light that can be absorbed

primary pigments absorb light and excite electrons which pass electrons to ETC for light-dependent reaction

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12
Q

the precise location of photosynthetic pigments in a chloroplast

A

photosystems in thylakoid membranes

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13
Q

explain why temperature has a greater effect on the rate of the light-independent stage

A

the light-independent stage is controlled by enzymes
a higher temperature will increase the kinetic energy of enzymes
more successful collisions /ESCs formed
enzymes may be denatured at high temperatures

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14
Q

absorption spectra

A

show the range of wavelengths of light that can be absorbed by certain pigments

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15
Q

action spectra

A

show the rate of photosynthesis at each wavelength of light

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16
Q

photosystem

A

system of photosynthetic pigments found in thylakoids of chloroplasts; each photosystem contains numerous accessory pigments that trap photons and pass their energy to a molecule of chlorophyll a during the light-independent stage of photosynthesis

17
Q

light-dependent reaction

A

photons channeled through PS 2, towards reaction centre and hit chlorophyll a
water is split in photolysis by water-splitting enzyme
chlorophyll a excites e- which is accepted by e- acceptor protein
e- lose energy as they move through chain of e- carrier proteins
energy is transferred to H+ where H+ is pumped from stroma into thylakoid lumen, across thylakoid memb.
H+ flow through ATP synthase channels down E.C gradient - allows ADP + Pi = ATP
e- accepted by PS 1 and re-excited by photon
e- pass through chain of e- carrier proteins and lose energy - transferred to H+ pump
e- recombine with H+ = H
H + NADP = NADPH (NADP reductase req.)

18
Q

photolysis

A

enzyme-catalysed splitting of water into H+, electrons and oxygen in the presence of light

19
Q

ATP synthase

A

transmembrane protein
H+ flow through ATP synthase by chemiosmosis and proton motive force
energy is converted from kinetic to chemical

20
Q

cyclic phosphorylation

A

e- excited by PS1 but unable to be accepted by NADP
e- return to PS1 via chain of e- carrier proteins
ATP still made as steep H+ gradient is maintained

21
Q

light-independent reaction
Calvin cycle

A

does not require photons to occur
occurs in stroma
requires products of light-dependent
NADPH - provides reducing power
ATP - releases energy when hydrolysed to ADP + Pi

22
Q

first reaction of Calvin cycle

A

CO2 from atmosphere diffuses into plant via stomata
CO2 combines with RuBP (5C) catalysed by the enzyme RuBisCo
an unstable 6C intermediate is formed

23
Q

second reaction of Calvin cycle

A

the unstable 6C intermediate compound splits into 2 molecules of glycerate-3-phosphate (3C)

24
Q

third reaction of Calvin cycle

A

GP is reduced to form triose phosphate (3C)
reduced using H atoms from NADPH -> NADP
ATP hydrolysed to ADP + Pi (x2)

25
Q

TP leaving Calvin cycle

A

1/6 of TP leaves cycle
can be converted into glucose, cellulose, starch, amino acids, glycerol- depends on metabolic requirements of the plant

26
Q

regeneration of RuBP

A

5/6 of TP used to regenerate RuBP
ATP hydrolysed: ATP -> ADP +Pi

27
Q

describe the fate of triose phosphate

A

5/6 regenerated to form RuBP
1/6 exits cycle + converted to glucose, cellulose, starch

28
Q

explain the role of ATP in the light independent stage

A

ATP releases energy when its hydrolysed to ADP +Pi
for GP -> TP, TP -> RuBP

29
Q

RuBisCo

A

enzyme that catalyses the fixation of carbon dioxide

30
Q

explain why the conc. of GP in chloroplasts increases as light intensity decreases (sunset)

A

fewer photons to excite electrons
less ATP made, less NADPH made
CO2 is still available so RuBP -> 2x GP
GP cannot be converted to TP
increased conc. of GP

31
Q

state and explain the effect of a decrease in CO2 conc. on conc. of RuBP, GP & TP in chloroplasts

A

less CO2 means less RuBP fixed to GP so less GP
if GP conc. decreases, TP conc. decreases
RuBP accumulates, conc. increases

32
Q

factors affecting photosynthesis

A

light intensity
CO2 concentration
temperature

33
Q

light intensity affecting photosynthesis

A
  1. as light intensity increases, more photons = more e- excited
    more ATP is formed = more NADPH formed = increases rate of photosynthesis
  2. other factors start to become limiting
  3. light intensity is no longer limiting, CO2 conc. and temp is limiting
34
Q

CO2 conc. affecting photosynthesis

A
  1. increasing CO2 conc. = greater rate of carbon fixation by RuBisCo ( RuBP -> GP)
  2. other factors become limiting e.g. temp/light intensity
35
Q

temperature affecting photosynthesis

A

low temp: enzymes & substrates have low KE so are unlikely to form ESCs
as temp increases: enzymes & substrates gain KE = frequency of successful collisions increases
higher temp: active site starts to change shape - tertiary structure changes = denaturation

36
Q

water stress

A

stomatal closure
not enough water in soil
occurs when there’s insufficient water in soil
Abscisic acid (ABA) synthesised in roots & transported up xylem in transpiration stream

37
Q

ABA

A

abscisic acid
acts on receptors on guard cell, plasma membranes
ions are pumped (AT) put of guard cells
water follows ions by osmosis = decrease water potential
guard cells become flaccid!

38
Q

compensation points

A

differ for every plant species
based on temp & light intensity
rate of PS = rate of respiration at CP
net CO2 uptake = net CO2 production
net sugar production = net sugar use

a-level biology (26 decks)

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