photosynthesis

Question 1

what is photosynthesis

Answer 1

the process by which light energy from the sun is converted into chemical energy and used to synthesis large organic molecules from inorganic substances

Question 2

compare autotrophs and heterotrophs

Answer 2

difference
only autotrophs can synthesise complex organic molecules from simple inorganic ones. only autotrophs use light energy

similarities
both can respite and can both hydrolyse complex organic molecules

Question 3

what is a photosynthetic pigment

Answer 3

a substance that absorbs some wavelengths of light but not others
they are present in the thylakoid membrane and arranged in photosystems
they are also use in light dependent stage

Question 4

describe chlorophyll a

Answer 4

primary pigment in the reaction centre

comes in two forms
P680 in photosystem 2
P700 in photosystem 1

it appears yellow green and absorbs red and blue light

contains an Mg atom which excites electrons

Question 5

name and describe the accessory pigments

Answer 5

chlorophyll b absorbs light between 500-640nm and appears blue green

carotenoids absorbs blue light
reflects yellow and orange light

Question 6

what part of the chloroplast can be considered the light harvesting part

Answer 6

photosystem s

Question 7

where does light independent stage of photosynthesis take place

Answer 7

stroma

Question 8

where does light dependent stage of photosynthesis take place

Answer 8

thylakoids membrane

Question 9

run down of light dependent reaction

Answer 9

takes place in the thylakoid membrane

light energy is absorbed by photosynthetic pigments in the photosystems and converted into chemical energy

light energy is used to add a phosphate group to ADP to for ATP and to reduce NADP to form reduced NADP
ATP transfers energy and reduced NADP transfers hydrogen to LIR

during the process H2O is oxidised toO2

Question 10

run down of light independent reaction

Answer 10

calvin cycle

takes place in stroma

ATP and reduced NADP from LDR supply energy and hydrogen to make glucose from carbon dioxide

Question 11

4 stages of non- cyclic photophosphorylations

Answer 11

1. light energy excites electrons in chlorophyll
2. photolysis of water produced protons and electrons and oxygen
3. energy from excites electrons make ATP
4. and generated reduced NaDP

Question 12

stage 1 of non cyclic photophosphoylation

Answer 12

light energy is absorbed by PSII
the light energy excites electrons in chlorophyll
the electrons move to a higher energy level

these higher energy electron move along the electro transport chain to PSI

Question 13

stage 2 of non cyclic photophosphorylation

Answer 13

as excites electrons leave PSII to live along the electron transport chain they must be replaced

light energy splits water into protons electrons and oxygen

Question 14

stage 3 of non cyclic photophosphorylation

Answer 14

the excited electrons lose energy as they move along the electron transport chain

this energy is used to transport printing into the thylakoid via the proton pump. the thylakoid has a higher concentration of protons then the stroma. this forms a proton gradient across the membrane

protons move down their conc graduation into the stroma via ATP synthase. the energy from this movement combines ADP and inorganic phosphate to form ATP

Question 15

stage 4 of non cyclic photophosphorylation

Answer 15

light energy is absorbed by PSI which excites the electron again to an even higher energy level

finally the electrons are transferred to NADP along with a proton from the stroma to form reduced NADP

Question 16

cyclic photophosphorylation

Answer 16

only uses PSI

electrons from the chlorophyll molecule aren’t passed onto NADP but passed back into PSI via electron carriers.

This means the electrons are recycled and can repeatedly flow through PSI.

This process doesn’t produce and reduced NADP of oxygen

it only process small amounts of ATP

Question 17

3 stages of calvin cycle

Answer 17

1. carbon dioxide is combined with ribulose bisphosphate to form 2 molecules of glycerate-3-phosphate
2. ATP and reduced NaDP are required for the reduction of GP to triode phosphate
3. Ribulose bisphosphate is regenerated

Question 18

stage 1 of calvin cycle

Answer 18

carbon dioxide enters the lead through the stomata and diffuse into the stroma of the chloroplast

it combines with RuBP - 5 carbon compound- to form an unstable 6 carbon compound which quickly breaks down into two molecules of GP which is 3 carbon compound

RuBisCO catalyses the reaction

Question 19

stage 2 of calvin cycle

Answer 19

ATP from the light dependent reaction provides energy to turn the GP into TP

this reaction also requires H+ which comes from reduced NADP which turns into NaDP which goes back into LdR

TP is then converted into may useful organic compounds

Question 20

stage 3 of calvin cycle

Answer 20

5 out of every 6 molecules of TP are used to regenerate RuBP
this used the rest of the ATP produced by light dependent reaction

Question 21

how many turns if the calvin cycle produces glucose

Answer 21

6

Question 22

what can TP be converted into

Answer 22

carbohydrate
lipids
amino acids

Question 23

how many AtP and reduced NaDP is used for each turn in the calvin cycle

Answer 23

3 ATP
2 reduced NADP

Question 24

the effect of changing the light intensity for calvin cycle

Answer 24

GP cannot be reduced to TP

TP levels fall and GP build up

if TP levels fall then RuBP cannot be regenerated

Question 25

the effect of changing the carbon conc

Answer 25

i RuBP cannot accept it
GP cannot be made
TP cannot be made

Question 26

how can water stress affect photosynthesis

Answer 26

if plants don’t have enough water they will close the stomata to preserve the water leading to less carbon dioxide entering the leaf for the calvin cycle

Question 27

how does temp affect calvin cycle

Answer 27

at low temps the reaction are slower as enzyme work slowly

levels of RuBP and GP and TP will fall

very high temp denatures enzymes

Question 28

thin layer chromatography for photosynthetic pigments

Answer 28

1. grind up several leaves with some anhydrous sodium sulphate and propanone
2. transfer the liquid to test tube, add some petroleum ether and gently shake test tube
   two layers form top being the pigments
3. transfer some of the liquid from top layer into a second tes tube with anhydrous sodium sulphate
4. draw a horizontal line with pencil and the bottom of the chromatography plate. add some spot of the solution on the line ensuring it’s dry
5. put the plate into a glass beaker with some prepared solvent so that the point of origin is a little bit above the solvent. put a lid on the beaker and leave the plate
6. when the solvent has nearly reached the top take the plate out and mark the solvent front with a pencil and leave the plate to dry
7. calculate the Rf value and use database to indenting the pigment