Biochemistry of photosynthesis 1

Question 1

2 stages of photosynthesis

Answer 1

light dependent and light independent

Question 2

what stage occurs first

Answer 2

light dependent reactions occur first and light independent reactions occur after

Question 3

function of light dependent reactions

Answer 3

produce materials that are used in light independent reactions

Question 4

when does whole process take place

Answer 4

during the hours of daylight but the light independent reactions can also continue when dark

Question 5

where does the light dependent stage take place

Answer 5

on the thylakoid membranes of the chloroplast

Question 6

2 main functions of light dependent stage

Answer 6

-split water molecules in photochemical reaction
-produce ATP which is needed to supply energy to produce carbs

Question 7

function of photochemical reaction

Answer 7

-splitting of water molecules
-provides hydrogen ions to reduce carbon dioxide and produce carbs in the light independent stage

Question 8

structure of light

Answer 8

form of electromagnetic radiation and smallest unit of light is a photon

Question 9

what happens when a photon of light hits a chlorophyll molecule

Answer 9

the energy is transferred to the electrons of that molecule

Question 10

what happens to electrons when they gain energy

Answer 10

they are excited and raised to higher energy levels
-if electron raised high enough they will leave chlorophyll molecule completely

Question 11

what happens to excited electron leaving chlorophyll molecule

Answer 11

can be picked up by electron acceptor and result in synthesis of ATP

Question 12

2 ways electron can be picked up by electron acceptor and synthesise ATP

Answer 12

cyclic and non cyclic photophosphorylation

Question 13

similarities of cyclic and non cyclic photophosphorylation

Answer 13

-both take place at same time and in both cases ATP is formed as excited electron is passed along electron transport chain

Question 14

whats different about non cyclic photophosphorylation

Answer 14

reduced NADP is also produced

Question 15

evidence for photosynthesis being a 2 stage process 1

Answer 15

-photochemical reactions get energy from light so temp should not affect rate of photosynthesis but when investigated shows temp had clear effect
-light dependent reactions limiting overall rate of reaction so temp has no effect
-however once light available process limited by different temp sensitive reactions
-suggests 2 phases one light dependent and other controlled by temp sensitive enzymes

Question 16

evidence for photosynthesis being 2 stage process 2

Answer 16

plant given different amounts of light produced more carbs than plant in one light
-explanation is light dependent and independent reaction
-in continuous light product builds up as light independent stage cant keep up
-as conc rises inhibits enzymes controlling light independent reactions from making carbs
-period of darkness ensures all of light stage products converted without conc getting to high

Question 17

what does cyclic photophosrylation involve

Answer 17

involves only photosystem 1 and drives the production of ATP

Question 18

what happens when a photon hits a chlorophyll molecule in PS1

Answer 18

-a light excited electron leaves the molecule
-its take up by electron acceptor and passed directly along electron transport chain to produce ATP

Question 19

electron that returns to chlorophyll in PS1

Answer 19

it can be excited in same way

Question 20

what happens during non cyclic photophosphorylation

Answer 20

water molecules are split providing hydrogen to reduce to NADP
-ATP is also produced
-involves PS1 AND PS2

Question 21

photon activity under light conditions in non cyclic

Answer 21

constantly hit chlorophyll molecules in PS1 AND PS2 exciting electrons to high enough level for them to be lost and picked up by electron acceptor

Question 22

another electron acceptor in PS2
non cyclic

Answer 22

-another excited electron from PS2 picked up by another electron acceptor and passes along electron transport chain to PS1
-produced one molecule of ATP

Question 23

what does PS1 receive after letting second electron go to acceptor

Answer 23

gets an electron to replace one that was lost to light dependent reactions

Question 24

state of chlorophyll molecule in PS2 after losing electron

Answer 24

short of electron and unstable
-original electron cannot be returned to chlorophyll because it has continued on to PS1
-electron comes from splitting of water to restore chlorophyll to original state

Question 25

photolysis

Answer 25

splitting of water that produces electron
-light dependent

Question 26

how does photolysis provide another electron for chlorophyll in PS2

Answer 26

-water randomly dissociates into hydrogen and hydroxide ions resulting in plenty of ions being present in cell including chloroplasts and replacing lost electrons

Question 27

what happens once PS2 has its electrons restored

Answer 27

-it is restored to its original state ready to be excited again when hit by another photon of light

Question 28

function of electrons in PS1

Answer 28

also excited by light and lost an electron acceptor
-electrons are carried down an electron transport chain and taken up by an electron acceptor NADP

Question 29

role of NADP non cyclic photophosphorylation

Answer 29

-NADP takes up hydrogen ion from dissociated water at same time to form reduced NADP

Question 30

function of NADP and ATP during non cyclic photophosphorylation

Answer 30

go on to be used as source of reducing power and energy in light dependent reactions of photosynthesis to make glucose

Question 31

equation for 4 chlorophylls regaining electrons in production of 1 molecule of oxygen

Answer 31

4OH- + 4e-(lost to chlorophyll) = O2 + 2H2O

Question 32

explanation for 1 oxygen molecule and 2 water molecules being produced at end of light dependent stage

Answer 32

-lots of photosynthesis occurs in millions of chloroplasts
-many hydrogen ions removed by NADP and many hydroxide ions left behind
-hydroxide ions react to form water and oxygen
-as a result electrons freed and taken up by chlorophyll
-4 chlorophyll molecules regain electrons in production of 1 molecule of oxygen

Question 33

what happens at light independent stage of photosynthesis

Answer 33

uses the reducing power NADP and ATP produced by light stage to build carbs

Question 34

calvin cycle

Answer 34

series of reactions that take place as result of the light independent stages

Question 35

where does the light independent stage take place

Answer 35

in the stroma of the chloroplast

Question 36

result of the calvin cycle

Answer 36

-results in the reduction of carbon dioxide from the air to bring about the synthesis of carbs
-each stage controlled by enzymes