Topic 5 - Energy transfers

Question 1

state the two stages of photosynthesis

Answer 1

LDR (light dependent reaction)

LIDR (light independent reaction) - also known as the dark reaction

Question 2

where does LDR occur

Answer 2

thylakoid membrane of chloroplast

Question 3

where does LIDR occur

Answer 3

stroma of chloroplast

Question 4

describe the structure of chloroplasts

Answer 4

did you mention:
double membrane (envelope), stoma containing thylakoid membrane, 70s ribosomes, circular DNA, starch granules, lamella, grana

Question 5

describe photoionisation in the LDR

Answer 5

• chlorophyll absorbs light energy which exites its electrons (higher energy levels)
• so electrons are released from chlorophyll (chlorophyll becomes positively charged)

Question 6

describes what happens after photoionisation in the LDR

Answer 6

some energy from electrons released in photoionisation is conserved in the production of ATP./reduced NADP:

• electrons move along electron transfer chain (electron carriers), releasing energy
• energy is used to actively pump pprotons from stroma into thylakoid
• protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase
• energy used to join ADP and Pi to form ATP (photophosphorylation
• NADP accepts a proton and an electron to become reduced NADP

Question 7

state 3 products of LDR

Answer 7

ATP, reduced NADP, half an O2 molecule

Question 8

describe photolysis of water in the LDR

Answer 8

water splits to produce protons, electrons and oxygen (H2O –. 0.5 O2 + 2e- + 2H+)

electrons replace those lost from chlorophyll

Question 9

what is the light independent reaction known as (2 names)

Answer 9

the dark reaction or the calvin cycle

Question 10

where does the LIDR occur

Answer 10

stroma of the chloroplast

Question 11

what 2 products of the LDR is used in the LIDR

Answer 11

reduced NADP and ATP

Question 12

why are reduced NADP and ATP used in the LIDR

Answer 12

to reduce CO2

Question 13

describe the LIDR

Answer 13

• CO2 reacts with ribulose bisphosphate (RuBP) and is catalysed by the enzyme rubisco
• this forms 2 glycerate 3-phosphate (GP) molecules [3C]
• GP is then reduced to triose phosphate (TP) [3C]. this uses reduced NADP oxidised into NADP and ATP reduced into ADP + Pi
• some TP is converted into useful organic substances e.g. glucose (6C)
• some TP is used to regenerate RuBP (5C) in the calvin cycle using energy from ATP (ATP is reduced into ADP + Pi)

Question 14

does LIDR require light?

Answer 14

not directly

Question 15

describe how temperature affects rate of photosynthesis

Answer 15

temperature increases = rate increases
above optimun temperature, rate decreases

Question 16

explain how temperature affects rate of photosynthesis

Answer 16

temp increases because enzymes like rubisco gain kinetic energy

enzymes will denature above optimun temperature. H bonds in tertiary structure break = fewer ES complexes form

Question 17

describe how light intensity affects rate of photosynthesis

Answer 17

light intensity increases as rate increases but above a certain light intensity, rate stops increasing

Question 18

explain how light intensity affects rate of photosynthesis

Answer 18

light increases as rate increases
LDR increases so more ATP and reduced NADP produced so LIDR increases as more GP reduced to TP and more TP regenerates RuBP

above certain light intensity, rate stops increasing
another factor is limiting when light intensity rate stops increasing e.g. tmeperature or Co2 concentration

Question 19

describe how CO2 conc affects rate of photosynthesis

Answer 19

as CO2 conc increases, rate increases

above certain CO2 conc, rate stops increasing

Question 20

explain why CO2 conc affects rate of photosynthesis

Answer 20

rate increases as CO2 increases
LIDR increases as more CO2 combines w RuBP to form GP so more GP reduced to TP so more TP converted to organic substances and more RuBP regenerated

rate stopping after certain CO2 conc
another factor is limiting e.g. temp or light intensity