photosynthesis Flashcards by Eliza Mckeever

what is photosynthesis

synthesises large organic compounds from simple inorganic molecules using light energy

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what are adaptations of the palisade layer

large numbers of chloroplasts
-large vacuole so chloroplasts don’t shade each other
chloroplasts move depending on light intensity

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adaptations/features of of chloroplasts

-large surface area
-doubl;e membrane
contain thylakoid disks in granum stacks connected by lamellae.
-act as transducers- converts one form of energy to another.
-different pigments absorb different phtons of light thereofre having several differnet pigments increases range of wavel;enth absorbtion allowing ore phtosynthesis.

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name 3 different types of photosynthetic pigment

-chlorophyll A
-chlorophyll B
- carotenoids (e.g beta carotenoids or xanthophyll)

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what is the absorption spectrum

graph showing wavelengths of light at which different photosythetic pigments absorb photons.

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what is meant by an action spectrum

graph showing rate of photosynthesis at different wavelengths of light -is measured as the mass of carbohydrate produced.

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why do leaves turn yellow in autumn

chlorophyll breaks down allowing the visability of other pigments such as cartenoids

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why are algae different colours at different depths

different colours of light penetrate different depths e.g at deep depths algae can absorb blue/green light so have a pigment that mask chlorophyll

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where are photosystems found

in the thylakoid membrane

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what does each photosystem consist of

an antenna complex
-a reaction centre

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describe the process that occurs in the antenna complex

contain photosynthetic pigments chlorophyll and caretenoids embedded in the phospholipds biler of the thylakoid mebrane held together by protein.

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describe what occurs during the reaction centre

is found within antenna complex where the two primary pigments of chlorophyll a is found. As chlorophyll absorbs light it emits an electron. This electron passes to a higher energy state before being accepted by an electron acceptor

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why is chlrophyll a the most significant molecule in the recation centre?

it passes energy to the subsequent reactions of photosynthesis.

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which photosystem has the highest peak absorbance

ps1- 700nm compared to 680 of ps2

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what do both photosystems have in common

both ahs a reaction centre and antenna complex contain two chlorophyll a molecules.

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what are the two stages of photosynthesis

light dependant and ligh independant.

where do light dependant reactions occur

thylakoid membrane

where do light independant reactions occur

in stroma happens in light and dark

what is produced from the light dependant recations of photosynthesis

ATP providing chemical energy transduced from light.
-NADPH
- O2 form photolysis of water which diffuses out of chloroplasts

what are the two types of light dependant reaction

cyclic and non-cyclic

describe and explain the process of non-cyclic phosphorylation /the z scheme ( 9 marks )

pigments in antenna complex PS11 harvest light energy and pass to the reaction centre (1)
chlorophylls contain electrons raised to an excited state and passed to an electron acceptor (1)
-electron acceptor is reduced (1)
- chlorophyll oxidised (1)
-electrons pass through series of electron carriers (1)
-each electron is at a lower energy level than the previous (1)
- energy is released to pump protons (H+) from the stroma to thylakoid space/lumen (1)
-H+ flow down an electrochemical gradient ATP synthetase in a stalked particle in the thylakoid membrane. (1)
-ATP is formed in chemiosmosis (1)

what occurs at the same time as non-cyclic phosphorylatioin

PS1 is absrobing phtoons of light. Each chlorphyll has a n excited electron which pass to an electron acceptor . The elctrons combione with H+ and pass to NADP which form NADPH

what is the importance of NADPH

During photosynthesis, NADPH provides the electrons needed for ATP production

describe and explain cyclic phosphorylation- (4 marks )

-only involves ps1 (1)
-excited electrons emitted from PS1 pass back to Ps1 after moving through electron carriers (1)
-this provided energy for the proton pump and production of ATP (1)
-no NADPH is produced as the electrons are recyled so no photolysis required. (1)

describe the process of photolysis (4 marks)

electrons lost from ps 1 are replaced by tjhopse from ps11. Ps 11 now needsd its eletrons replaced by photolysis. Water split in thylakoid spaces by light H20-2H+ +2e- +1/2 02

describe what happens in light independent reactions-

ATP and NADPH from light dependant reactions are used to make glucose from c02. This occurs in the Calvin cycle

what is the name given to the cycle in the light independent reactions? (1 Mark)

Calvin cycle

describe and explain the Calvin cycle in the light independent reactions (6 marks )

- ATP used to make glucose from C02 using ATP and NADPH. -CO2 combined with 5c RuBP -reaction is catalysed by enzyme rubisco. this forms an unstable 6c molecule. -this 6c molecule breaks down into 2 molecules of 3c glycerate-3 phosphate (GP). -the glycerite is reduced using NADPH and energy from ATP. this forms a 3c triose phosphate. -5/6 of the triose phosphate formed are used to regenerate RuBP via ribulose phosphate -this requires ATP. 1/6 of the triose phosphate is used to form other organic substances such as glucose, lipids and amino acids.

what is involved in the hill reaction

isolated chloroplasts produce 02 from water in the presence of an oxidising agent. in the cell NADP is the oxidising agent that removes hydrogen from water. The blue dye DCPIP acts as a substitute for NADP and in the presence of light loses its colour when reduced. in chloroplasts when photosynthesis takes place they emit excited electrons this goes down the ETC but here som,e of the electrons will reduce DCPIP if photosynthesis is taking place.

Calvin experiment-lollipop

carbon-14 (14C) was introduced to the algae Chlorella in an apparatus called a lollipop Light was shone on the lollipop vessel containing the Chlorella to induce photosynthesis and carbon-14 was incorporated into the algae After varying time periods the algae was killed by heated alcohol which denatures proteins and enzymes within the cells and stops metabolic processes The pathway of the radioactive carbon was mapped and analysed throughout the algae using two-dimensional paper chromatography Chromatography separated out the different carbon compounds that had been made by the algae Any radioactive carbon-14 atoms (that had been incorporated into either intermediates or products of photosynthesis) were identified using autoradiography (x-ray) By comparing the different time periods in which the carbon compounds formed Calvin was able to map the order in which they were generated The results of the experiments showed that carbon was converted to carbohydrates during the light-independent reactions of photosynthesis

what is the colour of DCPIP when oxidesed

blue

what is the colour of DCPIP when reduced after photosynthesis

colourless

what does the law of limiting factors state

states that the rate of phycological process will be limited by the factor in shortest supply.

what is the light compensation point

is the light intensity at which co2 produced in respiration is sufficient to allow photosynthesis to occur. is the light intensity where photosynthesis= respiration.

how does the light compensation point differ from different types of plant.

shade plants has a compensation point at a lower light intensity.

why is light intensity a limiting factor

-a limited light intensity leads to less ATP and NADPH made in light dependant reactions. -less GP is reduced to TP. -less TP made into RuBP -so photosynthesis is reduced.

why is co2 a limiting factor

-if limited less GP is formed forming RuBP and less GP available to form TP and RuBP-so lack of Calvin cycle. so photosynthesis reduced.