3.2 photosynthesis Flashcards by Ellie Thomas

what is photosynthesis?

the process by which carbohydrates are synthesised from carbon dioxide and water using light energy

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why does photosynthesis take place?

to make glucose as plants are producers and need to make their own food

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what part of the lead has the most chloroplasts?

palisade/mesophyll cells

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in what ways is a lead adapted for photosynthesis? (3)

spongy mesophyll for gas exchange
waxy cuticle - waterproof and transparent
thin - short diffusion pathway

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in what ways are chloroplasts adapted for photosynthesis? (3)

thylakoids - large SA
lots of them - abundant
can move around to trap maximum light energy

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define energy transducer

converts light energy into chemical energy

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why do plant looks green?

they reflect green light and absorb all other colours

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what are the 2 types of graphs called?

absorption sprectrum
action spectrum

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what does an absorption spectrum show?

the absorbance of different wavelengths of light by a pigment

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what does an action spectrum show?

the rate of photosynthesis at different wavelengths of light

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what is a photosynthetic pigment?

a chemical substance that is present in chloroplasts to absorb the light energy necessary for photosynthesis

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what are the 2 photosynthetic pigments that green plants have?

chlorophyll
carotenoids

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what are the different forms of chlorophyll?

chlorophyll a and chlorophyll b

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what is the most common form of carotenoid?
what colour is it?
what is the name of the yellow form?

carotene
orange
xanthophyll

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which is the primary pigment and where is it found in the photosystem?

chlorophyll a found in the reaction centre

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why is chlorophyll a called the primary pigment?

it passes the energy from light
to the subsequent reactions of photosynthesis

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where are the accessory pigments found in the photosystem and what are they?

chlorophyll b, xanthophyll and carotene
found in the antennas

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where are photosystems found?

embedded in the thylakoid membranes

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what does the antenna complex contain?

many different light absorbing pigments

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what are the 2 types of photosystems and at what wavelength can chlorophyll a absorb light in each?

photosystem 1 - absorb at 700nm
photosystem 2 - absorb at 680nm

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what are the light dependent stages of photosynthesis?
where in the chloroplasts do these occur?

cyclic and non cyclic photophosphorylation
occur in the thylakoid membranes

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what is the point of the light dependent stages?

make ATP
make reduced NADP

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explain what happens in cyclic photophosphorylation

2 electrons are excited from PS1 due to light energy
these electrons get picked up by an electron acceptor
then pass down the electron transport chain via electron carriers where ADP is phosphorylated into ATP
they then return to the PS1 by chemiosmosis when more ADP is phosphorylated

what the of reaction occur along the electron transport chain?

redox reactions

what happens during chemiosmosis?

electrons want to get out and can only be done by spinning ATP synthetase which makes ATP and the H+ flows back into the stroma

explain what happens in non cyclic photophosphorylation (Z scheme)

- 2 electrons are excited from PS2 and are picked up by an electron acceptor - these travel down the electron transport chain and ADP is phosphorylated into ATP - the electrons enter PS1 to replace the one that are taken by NADP and then are excited and picked up by another electron acceptor - however they are then picked up by NADP and lost

how does PS2 get more electrons? define it

due to photolysis (H20 -> 2e- + 2H+ + 02) splitting water using light

where does the hydrogen in photolysis go?

combined with NADP and the 2 electrons to make reduced NADP (NADPH2)

where does reduced NADP go and what happens?

into the Calvin cycle, gives it 2 H+ to glycerine 3 phosphate to become deoxidised then comes back into non cyclic photophosphorylation

where do protons (H+) go to and from?

to thylakoid lumen from stroma

what happens if the plant doesn't get any light?

can't make ATP and reduced NADP for light independent stage and so the plant will eventually stop producing glucose and die

what is the light independent stage called?

Calvin cycle

what is the point in the Calvin cycle?

fixes CO2 into carbohydrates (sugar)

where does the Calvin cycle happen?

in the stroma

how does the CO2 in the Calvin cycle get in?

diffuses in through the stomata

what is the basic version of the Calvin cycle?

- CO2 joins with ribulose bisphosphate to make unstable 6C - dissociates into 2x glycerate 3 phosphate - reduced to become 2x triose phosphate - a carbon is removed to become ribulose phosphate - ATP is added to become ribulose bisphosphate

what are the 3 stages called? | calvin cycle

1. fixation 2. reduction 3. regeneration of RuBP

what enzyme catalyses RuBP and CO2?

rubisco

how is GP reduced? using what?

ATP

what type of reaction occurs when GP becomes TP? expand

redox reaction GP is reduced and NADP is reoxidised

what does NADP do when it becomes reoxidised?/how is GP reduced?

gives 2 H+ to GP to become reduced

where does the ATP that is used at stage 2 come from?

the Z scheme

what happens to the 1 carbon released from TP to make it RuP?

used to produce glucose every 6 rotations, 1 glucose is made

what can happen to the glucose produced during the Calvin cycle?

can be converted into any other carbohydrate that the plant requires e.g. fructose

how can plants use the GP? what does this require?

to synthesise (make) amino acids - requires nitrate ions, absorbed from the soil

what are these amino acids converted into? | plants using GP to synthesis amino acids

protein

what are nitrates needed for in plants? what is nucleic acid production needed for?

amino acid and protein production to make DNA for new cells

what does a nitrogen deficiency in plants cause?

stunted growth

what is magnesium essential for in plants and where?

chlorophyll production at the centre of the head of the chlorophyll molecule

what is a magnesium disease known as and what is the visual symptom?

chlorosis - yellowing of the leaves

what does chlorosis affect about the plant and what will this cause?

affect it's photosynthetic abilities which may cause it to die unless it's magnesium insufficiency is treated

what are the 3 main factors that the rate of photosynthesis depends on?

light intensity CO2 concentration temperature

what happens if one of the 3 main factors is in short supply?

it will limit the rate of photosynthesis

what does the law of limiting factors state?

the rate of a process will be limited by the factor which is in shortest supply

what does the plateau of a graph mean in terms of listing factors and the rate of photosynthesis?

that another factor (besides the one in the graph) has become limiting