photosynthesis

Question 1

name 6 components of a chlorplast?

Answer 1

outermembrane

lamellae

grana

thylakoid

stroma

DNA- circular

Question 2

where does the light dependent stage of photosynthesis take place?

Answer 2

thylakoids

Question 3

where does the light independent stage of photosynthesis take place?

Answer 3

stroma

Question 4

what is the light harvesting system?

Answer 4

accessory pigments held by proteins and arranged into a funnel shape

it absorbs light energy and passes the energy to the action centre/ primary pigment

gives energy for electron excitement

Question 5

what do the light harvesting system and primary pigment together form?

Answer 5

photosystem

Question 6

what are the 2 main photosystems and what is their maximum absorption?

Answer 6

photosystem I absorbs to 700nm

photosystem II sbosrbs to 680nm

Question 7

describe the non cyclic photophosphorylation in the light dependent stage of photosynthesis

Answer 7

electrons are excited from PSII, they move down the electron transport chain, forming ATP by chemiosmosis

the electrons lost from PSII are replaced by electrons from photolysis

electrons are excited from PSI and move down electron transport chain producing ATP. electrons lost from PSI are replaced by electrons excited in PSII

electrons excited from PSI with H+ from photolysis reduce NADP

Question 8

describe the cyclic photophosphorylation in the light dependent stage of photosynthesis

Answer 8

when electrons excited from PSI return to PSI instead of being replaced by electrons from PSII. no reduced NADP is formed

Question 9

equation for photolysis?

Answer 9

H2O ——–> 2H+ + 2e- + 1/2 O2

Question 10

what is RuBisCO and what does it do?

Answer 10

Ribulose bisphosphate carboxylase

enzyme that catalyses fixation of carbon dioxide

Question 11

what is RuBP?

Answer 11

5 carbon compound called Ribulose Bisphosphate

Question 12

describe the calvin cycle

Answer 12

carbon dioxide fixation
carbon dioxide combines with RuBP, catalysed by RuBisCO

forms a very unstable 6 carbon compound which breaks down immediately into 2 glycerate 3-phosphate molecules

each GP molecule is converted into Triose phosphate by reduction using reduced NADP and energy from ATP, both produced in the light dependent stage

triose phosphate mostly regenerates into RuBP but some used to start the synthesis of complex biological molecules

Question 13

what are 3 factors limiting the rate of photosynthesis?

Answer 13

light intensity

CO2 concentration

temperature

Question 14

how does light intensity affect photosynthesis?

Answer 14

it is the energy source of the reaction so increasing light intensity increases ATP and reduced NADP produced in light dependent

Question 15

how does light intensity affect the levels of GP, TP and RuBP?

Answer 15

low light intensity = less ATP and reduced NADP produced so:

increases GP

decreases TP

decreases RuBP

Question 16

how does carbon dioxide concentration affect photosynthesis?

Answer 16

its needed as a source of carbon, increase CO2 concentration increases carbon fixation in the calvin cycle

Question 17

how does carbon dioxide concentration affect the levels of GP, TP and RuBP?

Answer 17

low CO2 concentration:

decreases GP

decreases TP

increases RuBP

Question 18

how does temperature affect photosynthesis?

Answer 18

it increases the rate of enzyme activity as it increases the frequency of sucessful collisions

RuBisCO which catalyses calvin cycle increases in activity when temperature increases until its too hot and dentures

Question 19

how does temperature affect the levels of GP, TP and RuBP?

Answer 19

low temperature:

decrease GP

decrease TP

decrease RuBP

Question 20

What happens during water stress?

Answer 20

stomatal closure

prevents CO2 diffusion into leaf so reduces rate of photosynthesis

Question 21

why is water not seen as a limiting factor of photosynthesis?

Answer 21

by the time water potential is low enough to be a limiting factor, the stomata have already closed to prevent water loss and photosynthesis has stopped due to low CO2 concentration.

Question 22

what inhibits RuBisCO?

Answer 22

oxygen, competitive inhibition

Question 23

what is accesory pigment?

Answer 23

(accessory) other part of photosystem/antenna unit/surround reaction centre;
(accessory) absorb different wavelengths of light (not absorbed by primary);
(accessory pigments) transfer energy to primary pigments;

Question 24

what is primary pigment?

Answer 24

(primary) act as reaction centres/where electrons are excited;

Question 25

describe calvin cycle

Answer 25

1 occurs in stroma ;
2 a series of enzyme-controlled reactions ;
3 carbon dioxide fixed by RuBP ;
4 carboxylation ;
5 enzyme is Rubisco ;
6 (unstable) 6C intermediate ;
7 forms (2 molecules) of GP ;
8 forms TP ;
9 using ATP (linked to point 8) ;
10 reduction step ;
11 using reduced NADP ;
12 ref to either ATP or NADP red coming from light dependent reaction ;
13 (most of) TP regenerates RuBP ;
14 rearrangement of carbons to form pentose sugars ;
15 ATP required, for phosphorylation / ribulose phosphate to ribulose
bisphosphate ;
16 AVP ; e.g. TP can be used to form, lipids / amino acids / hexose sugars
/ suitable named example

Question 26

Outline the ways in which heterotrophic organisms are dependent on plants.

Answer 26

1 animals / heterotrophs (need to) ,
eat / obtain organic material from / AW ,
plants / autotrophs ;
2 (plants / autotrophs) produce
 (named) organic molecules during ,
photosynthesis / Calvin cycle /
light independent stage ;
3 (plants / autotrophs) produce oxygen during ,
photosynthesis / photolysis /
light dependent stage;
4 glucose / carbohydrate / oxygen ,
(produced in photosynthesis)
are used in respiration by ,
animals / heterotrophs ;

Question 27

what is an autotroph

Answer 27

can make organic molecules from inorganic molecules

Question 28

what is a heterotroph

Answer 28

needs to use organic molecules made by other organisms

Question 29

what are compensation points?

Answer 29

when carbohydrate produced by photosynthesis equals the carbohydrate used in respiration