5A Photosynthesis

Question 1

Chloroplast structure

Answer 1

flattened organelles surrounded by a double membrane. Thylakoids are stacked up into grana which are linked by lamellae

Question 2

Where are photosynthetic pigments found

Answer 2

in chloroplasts, in the thylakoid membranes attached to protein

Question 3

What wavelength does photosystem 2 absorb light at

Answer 3

680nm

Question 4

Examples of photosynthetic pigments

Answer 4

chlorophyll a, chlorophyll b and carotene

Question 5

What is a photosystem

Answer 5

the protein and the pigment

Question 6

What wavelength does photosystem 1 absorb light at

Answer 6

700nm

Question 7

What is the stroma

Answer 7

a gel like substance containing enzymes, sugars and organic acids

Question 8

What are starch grains

Answer 8

carbohydrates produced by photosynthesis and not used straight away are stored as starch grains

Question 9

Describe light dependent reaction

Answer 9

Requires light energy
Takes place in thylakoid membranes
Light energy is absorbed by the chlorophyll
Light energy excites electrons in the chlorophyll
Chlorophyll has been photoionized
Some of the energy from the released electrons is used to add phosphate group to ADP to form ATP and some is used to form reduced NADP. ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction
During this process H2O is oxidised to O2

Question 10

Describe non cylic phosphorylation stage 1

Answer 10

Light energy is absorbed by PSII
Light energy excites electrons in chlorophyll
Electrons move to a higher energy level
High energy electrons are released from the chlorophyll and move down the electron transport chain to PSI

Question 11

Describe non cylic phosphorylation stage 2

Answer 11

As the excited electrons from chlorophyll leave PSII to move down the electron transport chain they need to be replaced
Light energy splits water into protons (H+ ions) electrons and oxygen - photolysis

Question 12

Describe non cylic phosphorylation stage 3

Answer 12

Excited electrons lose energy as the move down the electron transport chain
The energy is used to transport protons into the thylakoid membrane so that there is a higher concentration of in the thylakoid than the stroma this forms a proton gradient across the thylakoid membrane

Protons move down their concentration gradient into the stroma via the enzyme ATP synthase which is embedded in the thylakoid membrane this movements adds a phosphate to ADP to form ATP

Question 13

Describe non cylic phosphorylation stage 4

Answer 13

Light energy is absorbed by PSI which excites the electrons to an even higher energy level
Finally the electrons are transferred to NADP along with a proton from the stroma to form reduced NADP

Question 14

Cyclic phosphorylation only produces ATP because

Answer 14

the electrons from the molecule aren’t passed on to NADP they are passed back to PSI by electron carriers

Question 15

What is the light independent reaction called

Answer 15

the calvin cycle

Question 16

Where does the calvin cycle take place

Answer 16

in the stroma

Question 17

What are the products of the calvin cycle

Answer 17

triose phosphate and ribulose biphosphate

Question 18

Describe stage 1 of the calvin cycle

Answer 18

CO2 enters the leaf through stomata and diffuses into the stroma
CO2 is combined with ribulose biphosphate the reaction is catalysed by the enzyme rubisco
This gives an unstable 6 carbon compound which breaks down into glycerate 3-phosphate

Question 19

Describe stage 2 of the calvin cycle

Answer 19

the hydrolysis of ATP provides energy to turn the 3 carbon compound GP into a different a different 3 carbon compound triose phosphate
This reaction requires H+ ions which come from Reduced NADP which is recycled to NADP
some triose phosphate is then converted into useful organic compounds and some continues in the calvin cycle to regenerate RuBP

Question 20

Describe stage 3 of the calvin cycle

Answer 20

Five out of every six molecules of TP in the cycle are used to regenerate RuBP
This uses the rest of the ATP produced by the light dependent reaction

Question 21

How many turns of the calvin cycle produces six molecules of triose phosphate

Answer 21

six

Question 22

How many triose phosphate molecules to make one hexose sugar

Answer 22

2

Question 23

What does six turns of the cycle need

Answer 23

18 ATP and 12 reduced NADP from the light dependent reaction