Photosynthesis

Question 1

Process of light dependent reaction

Answer 1

-chlorophyll molecule absorbs light energy and a pair of e- is raised up energy level (excited) . e- leave chlorophyll - chlorophyll is ionised (photoionisation)
-excited e- passed from e- carrier to e- carrier in a series of redox reactions. series of e- carriers is located in the thylakoid membrane. each e- carrier is a lower energy level than previous one so e- loose energy
-the energy is used to pump H+ into the thylakoid space
-H+ move from high conc inside thylakoid to a lower conc in the stroma, through atp synthase.
Atp synthase comines ADP+Pi to form ATP
-H+ pass through ATP synthase and are taken up (along with e- bu NADP to form NADPH)
-Photolysis - splitting water with light provide e- to replace those lost from chlorophyll during photoionisation

Question 2

How ATP is made during LDR

Answer 2

-chlorophyll molecule absorbs light energy and a pair of e- is raised up energy levels so e- leave chlorophyll
-exited e- passed from e- carrier to e- carrier in a series of redox reactions
-series of e- carriers are located in thylakoid membrane
-each e- carrier is a lower energy level than previous one so e- lose energy
-energy is used to pump h+ into thylakoid space
-h+ move from high conc inside thylakoid to a lower conc in the stroma through ATP synthase
-ATP synthase combines ADP+pi to from ATP

Question 3

role of photolysis in LDR

Answer 3

-splitting water with light
-so provides e- to replace those lost from chlorophyll molecule during photoionisation
-h+ pass through atp synthase and are taken up (along with e-) by NADP to from NADPH

Question 4

How chloroplasts adapted to carry out LDR

Answer 4

-thylakoid membrane has large SA > chlorophyll, e- carriers and enzymes to attach
-proteins in grana > hold chlorophyll in precise place for max absorption of light
-ATP synthase in thylakoid membrane > atp production

Question 5

What does the LDR produce?

Answer 5

-reduced NADP (NADPH)
-ATP
-Oxygen (by-product)

Question 6

What are the products of the LDR needed for?

Answer 6

LIR

Question 7

What are the electrons produced in photolysis used for?

Answer 7

passed along chain of electron carrier proteins

Question 8

What are the H+ ions produced in photolysis used for?

Answer 8

-picked up by NADP to make NADPH

-pumped to create electrochemical gradient and diffuse through ATP synthase (allowing ATP to be formed)

Question 9

What causes chlorophyll to become ionised?

Answer 9

absorbs light energy, which raises energy level of electrons (excited state), causes them to leave chlorophyll

Question 10

What happens to the electrons after they leave chlorophyll?

Answer 10

they are passed along an electron carrier chain in thylakoid membrane

Question 11

What do the electrons passing through the chain do?

Answer 11

release/lose energy

Question 12

What is the energy released by electrons passing through the electron carrier chain used for?

Answer 12

to pump H+ ions into the lumen of the thylakoid

Question 13

What is created as H+ ions are pumped into the lumen of the thylakoid?

Answer 13

an electrochemical gradient

Question 14

What are the 3 main steps of the LDR?

Answer 14

photoionisation
chemiosmosis
photolysis

Question 15

How are electrons passed along the electron carrier proteins?

Answer 15

series of redox reactions

Question 16

What are the electrons used for after being passed along the electron transfer chain?

Answer 16

accepted alongside H+ to form NADPH

Question 17

What is the energy lost from the electrons used for?

Answer 17

pumping H+ ions against their electrochemical gradient

Question 18

What happens in photoionisation?

Answer 18

-light absorbed by chlorophyll
-raises electrons an energy level SO they are lost from the chlorophyl

Question 19

Why do plants benefit from having different coloured pigments?

Answer 19

absorb different/more wavelengths of light for the LDR

Question 20

Why might not all light be used in photosynthesis?

Answer 20

some could be reflected
some light is incorrect wavelength

Question 21

ATP produced by chemosmosis

Answer 21

-h+ pumped from stroma using hydrogen pump in the thylakoid membrane
-do this via the energy from e- released when water is split (photolysis) which also produces H+
-creates and maintains conc gradient of H+ across thylakoid membrane with high conc inside thylakoid space and low conc in stroma
-protons only cross thyalkoid membrane via ATP synthase
-as protons pass through ATP synthase they cause changes to structure of enzyme which then catalyses combination of ADP+Pi = ATP

Question 22

How co2 arrives in stroma of chloroplast

Answer 22

diffuse from atmosphere through stroma, spongy mesophyll and into palisade cell

Question 23

rubisco function

Answer 23

enzyme that catalyses reaction between RuBP and CO2

Question 24

Role of atp produced my LIR

Answer 24

convert GPP to TP to regenerate RuBP

Question 25

Fate of triose phosphate produced during calvin cycle

Answer 25

combined to form organic molecules including glucose. most is used to regenerate RuBP

Question 26

Explain how CO2 absorbed by plants is incorporated into organic molecule

Answer 26

-co2 enters stroma by diffusion and reacts with 5c ribulose biphosphate (RuBP) to form 2x molecules of 3C glycerate-3-phosphate (GP) -reaction catalysed by rubisco

Question 27

Roles of ATP and NADH in LIR

Answer 27

-atp =hydrolyse to convert glycerate-3-phosphate (GP) into triose phosphate (TP) and TP back into RuBP -NADH = convert GP into triose phosphate

Question 28

Describe events in calvin cycle

Answer 28

-CO2 and RuBP from 2x glycerate-3-phosphate in presence of rubisco -GP converted to triose phosphate with ATP and NADH -Some triose phosphate forms useful organic molecules eg glucose -majority of triose phosphate recycled to RuBP and ATP

Question 29

What is used in the Calvin cycle?

Answer 29

-NADPH -ATP -CO2

Question 30

What is required in order to form triose phosphate molecules?

Answer 30

ATP and a H from reduced NADP

Question 31

Give 2 examples of what the glucose can be used to make?

Answer 31

glycerol used to make lipids combine with nitrates to form amino acids stored as starch used in cell walls as cellulose

Question 32

How many times does the Calvin cycle need to happen before a hexose sugar (e.g glucose can be made)?

Answer 32

6

Question 33

Why is ATP needed for the second time in the Calvin cycle?

Answer 33

to regenerate the RuBP by joining a TP molecule to the molecule that donated it’s carbon atom for use in making organic molecules

Question 34

How many Carbon atoms leave the 2 x TP molecules to be used in organic molecules?

Answer 34

1

Question 35

What is GP reduced to form?

Answer 35

triose phosphate

Question 36

What is the role of the reduced NADP in the Calvin cycle?

Answer 36

donates H to reduce molecule GP

Question 37

Why won’t the LIR occur if the LDR doesn’t occur?

Answer 37

-no ATP -no NADPH -needed for LIR (converting GP to TP)

Question 38

Why will the rate of LIR decrease if rate of RuBisCo decreases?

Answer 38

-no CO2 reacts with RuBP -so no GP

Question 39

Where is RuBisCo found in a cell?

Answer 39

stroma of chloroplasts

Question 40

LIR

Answer 40

1) Co2 enters stroma via diffusion and reacts with RuBP (5C) - catalysed by rubisco 2) FoRMS 2x GP (3C) 3) NADPH from LDR used to reduce GPinto TP using energy from ATP $)NADP is reformed and goes back to LDR to be reduced again by accepting more H+ 5) some TP converted to useful organic substances eg glucose, strach, cellulose, nucleotides ect 6) most TP used to regenerate RuBP using ATP from LDR