5.1 Photosynthesis and respiration

Question 1

what is the equation for photosynthesis?

Answer 1

6CO₂ + 6H₂O = C₆H₁₂O₆ + 6O₂

Question 2

name the two stages of photosynthesis

Answer 2

1. light dependent reaction
2. light independent reaction

Question 3

where does the light dependent stage of photosynthesis take place?

Answer 3

the thylakoid membrane

Question 4

where does the light independent stage of photosynthesis take place?

Answer 4

the stroma

Question 5

what are the products of light dependent reactions?

Answer 5

ATP, NADPH (reduced NADP), O₂

Question 6

name the two uses of light energy in the light dependent stage of photosynthesis

Answer 6

1. photophosphorylation: adding an inorganic phosphate ion to ADP to make ATP
2. photolysis: splitting water into H+ ions and OH- ions

Question 7

define photophosphorylation

Answer 7

using light energy to add phosphate to a molecule

Question 8

define photolysis

Answer 8

using light energy to split a molecule

Question 9

define photoionisation

Answer 9

using light energy to to ionise an atom or molecule

Question 10

define electrochemical gradient

Answer 10

a concentration gradient of ions

Question 11

define oxidation

Answer 11

gain of oxygen, loss of electron or hydrogen

Question 12

define reduction

Answer 12

gain of electrons or hydrogen, loss of oxygen

Question 13

define chemiosmosis

Answer 13

the process of electrons flowing down the electron transport chain and creating an electrochemical gradient which drives ATP synthesis

Question 14

what products are released through non-cyclic photophosphorylation?

Answer 14

ATP, NADPH and oxygen

Question 15

what products are released through cyclic photophosphorylation?

Answer 15

ATP

Question 16

which photosystem is used first in non-cyclic photophosphorylation?

Answer 16

photosystem 2

Question 17

what wavelength of light does photosystem 2 absorb?

Answer 17

P680

Question 18

what wavelength of light does photosystem 1 absorb?

Answer 18

P700

Question 19

describe the process of cyclic photophosphorylation

Answer 19

excited electrons in photosystem 1 are released to electron carriers, which pass them straight back to photosystem 1, meaning the only product is ATP

Question 20

describe 4 differences between cyclic and non-cyclic photophosphorylation

Answer 20

1. photosystems 1 and 2 are used in non-cyclic, whilst only PS1 is used in cyclic
2. photolysis of water is only required in non-cyclic, not cyclic
3. NADPH is only synthesised in non-cyclic, not cyclic
4. non-cyclic produces ATP, NADPH and oxygen, whereas cyclic only produces ATP

Question 21

describe the process of light dependent reactions in photosynthesis [5]

Answer 21

1. light absorbed by chlorophyll excites electrons
2. electrons move out of chlorophyll molecule and along electron transfer chain, releasing energy
3. light energy is used for photophosphorylation to join ADP and Pi to form ATP
4. photolysis of water produces protons, electrons and oxygen
5. NADP is reduced when electrons and hydrogen join, becoming NADPH

Question 22

describe what happens during photoionisation in the light dependent reaction [2]

Answer 22

1. chlorophyll absorbs light and excites electrons
2. excited electrons are lost and chlorophyll become positively charged

Question 23

suggest and explain the advantage of having different coloured pigments in leaves [1]

Answer 23

absorbs different wavelengths of light for photosynthesis

Question 24

suggest two reasons why most of the light that falls on producers is not used in photosynthesis

Answer 24

1. light is reflected
2. light is wrong wavelength

Question 25

name the two products of the light-dependent reaction that are required for the light-independent reaction

Answer 25

1. ATP 2. reduced NADP (NADPH)

Question 26

explain how a reduced transfer of electrons down the chain reduces the rate of photosynthesis [4]

Answer 26

- reduced transfer of electrons leads to a reduced transfer of of protons across the thylakoid membrane - so less ATP is produced - and less NADPH is produced - so light-independent reaction slows

Question 27

what wavelength of light does photosystem II absorb?

Answer 27

680nm

Question 28

what wavelength of light does photosystem I absorb?

Answer 28

700nm

Question 29

name five differences between the processes of cyclic and non-cyclic photophosphorylation

Answer 29

1. in cyclic, only PSI is involved, whereas in non-cyclic, both PSI and PSII are involved 2. photolysis is only required in non-cyclic 3. oxygen is only produced in non-cyclic 4. NADPH is only synthesised in non-cyclic 5. ATP produced in cyclic is used by the cell, whereas ATP produced in non-cyclic is used for the light-independent reactions

Question 30

explain part 1 of the Calvin cycle

Answer 30

ribulose bisphosphate reacts with CO2 to produce two glycerate 3-phosphate molecules. the reaction is catalysed by rubisco enzymes

Question 31

what enzyme catalyses the reaction between ribulose bisphosphate and CO2?

Answer 31

rubisco

Question 32

what products are produced when ribulose bisphosphate and CO2 react?

Answer 32

two glycerate 3-phosphate molecules

Question 33

explain part 2 of the Calvin cycle

Answer 33

glycerate 3-phosphate molecules are reduced to triose phosphate. hydrolysis of ATP provides energy for reaction. reduced NADP provides H+ ions for the reaction.

Question 34

explain part 3 of the Calvin cycle

Answer 34

triose phosphate is used to regenerate ribulose bisphosphate or make hexose sugars. hydrolysis of ATP provides energy for this reaction

Question 35

how many turns of the Calvin cycle does it take to make one hexose sugar?

Answer 35

6

Question 36

how many carbon atoms are in a ribulose bisphosphate molecule?

Answer 36

5

Question 37

how many carbon atoms are in each glycerate 3-phosphate molecule?

Answer 37

3

Question 38

how many carbon atoms are in each triose phosphate molecule?

Answer 38

3

Question 39

how many ATP molecules are hydrolysed in one turn of the Calvin cycle?

Answer 39

3

Question 40

how many NADPH molecules are used in one turn of the Calvin cycle?

Answer 40

2