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A-level Aqa Biology > (11) photosynthesis > Flashcards

(11) photosynthesis Flashcards

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1
Q

what is the equation for photosynthesis?

A

6CO2 + 6H2O ——light——–> C6H12O6 + 6O2
carbon dioxide + water -> glucose and oxygen

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2
Q

why do plants photosynthesise?

A
  1. complex organic molecules needed for growth (glucose, amino acids, nucleic acids)
  2. energy for processes
  3. oxygen (respiration)
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3
Q

what are the 3 stages of photosynthesis?

A
  1. capturing of light energy
  2. light dependent reaction
  3. light independent reaction
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4
Q

what are some adaptations for leaves for photosynthesis?

A

broad leaf - large SA to absorb maximum amount of sunlight possible

transparent cuticle and epidermis to let light through to mesophyll cells underneath

mesophyll cells packed with chloroplasts to collect sunlight

numerous stomata for gaseous exchange (mesophyll cells are short diffusion pathway from one)

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5
Q

what are the adaptations of chloroplasts for photosynthesis?

A

grana - stacks of thylakoids with pigment chlorophyll
stroma - fluid matrix where light independent stage of photosynthesis takes place

grana membrane has large SA for photosynthetic pigments, electron carriers and enzymes (LDR)

short pathway for substances to travel

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6
Q

what is the definition of a photosynthetic pigment?

A

a coloured biological compound that is present in chloroplasts and photosynthetic bacteria, which captures light energy for photosynthesis

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7
Q

what are the photosynthetic pigments?

A

carotene
phaeophytin
xanthopyll
chlorophyll A
chlorophyll B

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8
Q

what colour light does chlorophyll reflect?

A

green light

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9
Q

what colour light does carotenoids reflect?

A

red, orange, yellow light

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10
Q

what does NADP stand for?

A

Nicotinomide Adenine Dinucleotide Phosphate

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11
Q

what are the features and function of NADP?

A

adenine base, nicotinomide base, phosphate backbone, ribose sugars

functions:
coenzyme used in photosynthesis
accepts electrons (and H+ ions) by becoming reduced NADP
can be oxidised back into NADP

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12
Q

where does the light dependent reaction take place?

A

in the thylakoid membrane of the chloroplasts

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13
Q

where are photosystems 1 and 2 located?

A

PS1 intergranal membrane
PS2 on grana

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14
Q

what is the energy from the light-dependent reaction used for?

A
  1. to add an inorganic phosphate to ADP to make ATP
  2. to split water into H+ ions and OH- ions (photolysis)
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15
Q

what is oxidation?

A

when a substance is oxidised,
it loses electrons or
loses hydrogen or
gains oxygen

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16
Q

what is reduction?

A

when a substance is reduced?
it gains electrons or
gains hydrogen
or loses oxygen

17
Q

what is photoionisation?

A

when a chlorophyll molecules absorbs light energy, raising its pair of electrons to a higher energy level (excited state) and they leave the chorophyll molecule

18
Q

what happens during photolysis?

A

(in the thylakoid lumen) water molecules are split by light energy to form hydrogen ions, electrons and oxygen gas
H+ ions are used to reduce NADP, electrons are passed to PS2
O2 is released as a waste product

19
Q

what is the equation for photolysis?

A

H2O —–> 2H+ + 1/2 O2 + 2e-

20
Q

what happens during cyclic photophosphorylation?

A

(within thylakoid)
1. when light hits PS1, it excites 2 electrons which leave the PS and are picked up by electron acceptors
2. electrons are passed along the electron transport chain, providing energy to make ATP from ADP + Pi
3. electrons pass back to PS1 -> no electrons are lost

21
Q

what happens during noncylic photophosphorylation?

A
  1. when light hits PS2 , it excites 2 electrons which leave the PS and are picked up by electron acceptors
  2. electrons are passed along the electron transport chain, providing energy to make ATP from ADP + Pi
  3. electrons arrive at PS1, PS2 now lacks 2 electrons
  4. light hits PS1, exciting a new pair of electrons to the electron acceptor
  5. ETC uses energy and electrons to reduce NADP -> NADPH
22
Q

what is chemiosmosis?

A

the movement of hydrogen ions across a biological membrane generates ATP

23
Q

explain the mechanism by which ATP is produced through the chemiosmotic theory.

A
  1. energy for this process comes from photolysis when the electrons are released from the splitting of water by light
  2. excited electrons gradually release their energy, which is used to actively transport H+ ions across the thylakoid membrane from the stroma to the thylakoid lumen by a proton pump
  3. this creates a proton gradient w a high conc of protons in the thylakoid lumen and low conc in the stroma
  4. protons return to stroma (moving down the concentration gradient) by facilitated diffusion through the transmembrane ATP synthase (chemiosmosis)
  5. process provides energy to synthesis ATP by ADP +Pi
24
Q

how is the chloroplast adapted to carry out the light dependent reaction?

A

thylakoid membrane = large SA for attachment of chlorophyll, electron carriers and enzymes

granal membranes have ATP synthase channels within them (catalyse the production of ATP
-> membrane = selectively permeable which allows establishment of a proton gradient

chloroplasts contain DNA and ribosomes so they can quickly manufacture proteins involved in LDR

25
Q

where does the light dependent reaction take place?

A

in the stroma of the chloroplast

26
Q

what is the process of the calvin cycle?

A
  1. CO2 diffuses into leaf through stomata and dissolves in water of mesophyll cells, then diffuses through membranes into the stroma of the chloroplast
  2. the enzyme rubisco catalyses the carboxylation (combining w CO2) of ribulose biphosphate (RUBP - 5C) , producing an unstable 6C compound that breaks down into 2 molecules of Glycerate-3-phosphate (GP - 3C )
  3. GP is reduced by the energy from ATP and the H+ and e- from NADPH
    -> forms 2 molecules of triose phosphate (TP)
    (used to build carbs e.g glucose and other complex molecules e.g amino acids)
  4. most TP is recycled to make more RUBP (requires phosphate ion from ATP to complete

for every 1 glucose made, 5 RUBPs are made

27
Q

what is the input of the calvin cycle?

A

RUBP + CO2 + ATP + NADPH

28
Q

what are the useful products in the calcin cycle?

A

complex molecules

29
Q

what is recycled in the calvin cycle?

A

ADP + Pi
NADP

30
Q

how is the chloroplast adapted to carrying out the light-independent reaction?

A

fluid of the stroma contains all enzymes needed to carry out LIR

stroma fluid surrounds the grana so products of LDR can diffuse into the stroma

contains DNA and ribosomes to quickly manufacture any proteins involved in the LIR

31
Q

what factors affect the rate of photosynthesis?

A

light intensity
co2 concentration
temperature

32
Q

how does light intensity affect the Rate of photosynthesis?

A

light + essential for photolysis and photophosphorylation

more light the more reduced NADP and ATP is made (necessary for calcin cycle)

33
Q

how does CO2 conc affect the R of photosynthesis?

A

f CO2 levels are low, rubisco cannot convert RuBP to GP in step one of the Calvin Cycle. This leads to accumulation of RuBP and an overall slowing of the Calvin Cycle, which results in a fall in the production of TP

34
Q

how does temperature affect the rate of photosynthesis?

A

photosynthesis = enzyme-catalysed reaction
increase in temp, increase in kinetic energy, increase in collisions more ESC’s

optimum temp = reaches, denaturation

A-level Aqa Biology (9 decks)

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