Lecture 2 - Beth Dyson

Question 1

What is photosynthesis? [1]

Answer 1

Photosynthesis is how plants make ‘food’ from light.

Question 2

What % of life on Earth does photosynthesis provide energy for? [2]

Answer 2

99% of life acquires its energy from photosynthesis.

Question 3

How many Gt of carbon dioxide is taken up by plants per year?

Answer 3

120Gt of CO2 is taken up by plants each year.

Question 4

How much CO2 is released as part of anthropogenic emissions?

Answer 4

9Gt of CO2 is released as part of anthropogenic emissions.

Question 5

How old is photosynthesis in deep time?

Answer 5

3800Ma

Question 6

What other compounds can be used for photosynthesis? [2]

Answer 6

Sulphur compounds and hydrogen can be used in some forms of photosynthesis.

Question 7

What type of photosynthesis led to mass divergence and when? [2]

Answer 7

Oxygenic photosynthesis in cyanobacteria back 2400Ma.

Question 8

Give two similarities of photosynthesis and respiration. [2]

Answer 8

They both involve production of ATP via phosphorylation and an electron transport chain.

Question 9

Give two differences between photosynthesis and respiration. [2]

Answer 9

Photosynthesis is anabolic while respiration is catabolic.

Photosynthesis uses light to split water and build sugars, while respiration breaks down sugars and produces water as a waste product.

Question 10

Name five features of the chloroplast. [5]

Answer 10

Double membraned.
Stroma
Thylakoids
Granum
Lamella

Question 11

What is the stroma and what does it contain? [3]

Answer 11

The stroma is a colourless fluid within chloroplast.

It also has a suitable pH for Calvin Cycle and contains lots of enzymes

Question 12

What are granum? [1]

Answer 12

Granum are flat membrane stacks.

This is good for an increased surface area:volume ratio.

Question 13

What are lamella? [1]

Answer 13

Lamella connect and separate thylakoid stacks.

Question 14

What are thylakoids? [1]

Answer 14

Thylakoids are the location for light-dependant reactions.

Where light absorption occurs.

Question 15

Where does the Calvin Cycle happen? [1]

Answer 15

In the stroma.

Question 16

What do light dependant reactions produce? [2]

Answer 16

NADPH and ATP

Question 17

What do light independent reactions produce? [1]

Answer 17

Sugars.

Question 18

What’s the ‘basic’ idea of the ETC? [1]

Answer 18

The basic idea of the ETC is that some energy is lost in each step.

This energy can be used by the plant.

Question 19

Name in order the six parts of the Electron Transport Chain. [6]

Answer 19

PSII
Pheophytin
Plastoquinone
Cytochrome b6f
Plastocyanin
PS1

Question 20

Where is Photosystem II located? [1]

Answer 20

PSII is located in grana within the thylakoid membrane.

Question 21

What is the composition of Photosystem II in terms of subunits and cofactors? [2]

Answer 21

PSII is a protein complex, with 20 subunits and 99 + co-factors (35 chlorophylls, 12 β-carotenes).

Question 22

What two complexes exist within Photosystem II? [2]

Answer 22

PSII contains:
Light harvesting complexes.

A P680-containing reaction centre complex.

Question 23

What happens when light hits PSII? [3]

Answer 23

Light initially hits at the chlorophyll-filled LHC.

This energy is funnelled along many LHC until it reaches the P680 dimer in the RCC.

P680 then passes It to pheophytin.

Question 24

How does PSII regain the electron lost to pheophytin? [1]

Answer 24

It splits water via photolysis.

Two photons are needed to split H2O, while a full O2 molecule requires four photons to be created.

Question 25

What does pheophytin do? [1]

Answer 25

Pheophytin passes an electron to plastoquinone.

Question 26

Where is plastoquinone located?

Answer 26

Plastoquinone is in the chloroplast membrane.

Question 27

What does plastoquinone do? [2]

Answer 27

Plastoquinone passes an electron to cytochrome b6f.

Excess energy moves a H+ ion to the lumen.

Question 28

What does cytochrome b6f do? [2]

Answer 28

Cytochrome b6f passes an electron to plastocyanin.

Excess energy moves a H+ ion to the lumen.

Question 29

What does plastocyanin do?

Answer 29

Plastocyanin passes an electron to Photosystem I.

Question 30

How does Photosystem I differ from Photosystem II? [3]

Answer 30

PSI is a far larger complex with PSII.

PSI’s LHC contains P700, rather than P680.
pigments.

PSI takes its electron from plastocyanin not water.

Question 31

What does Photosystem I do?

Answer 31

It takes light in from plastocyanin and through P700 passes it to ferredoxin.

Question 32

What does Ferredoxin do? [1]

Answer 32

Ferredoxin provides energy, allowing FNR to make NADPH (reducing NADP+ with the extra electron).

Question 33

What is the Z scheme? [1]

Answer 33

The ETC pathway of energy transfer.

It has two ‘peaks’ when P680 and P700 gain an electron, but between them energy is reduced at each step.

Question 34

Where is ATP synthase located? [1]

Answer 34

ATP synthase is located in the thylakoid membrane.

Question 35

What ‘drives’ ATP synthase? [1]

Answer 35

H+ ions released in the lumen, from Plastoquinone and Cytochrome b6f.

Question 36

What does ATP synthase do? [2]

Answer 36

ATP synthase acts as a ‘motor’.

Protons pass through the enzyme and they’re used to form ATP (from ADP) and NADPH (form NADP+)

Question 37

What is cyclic electron transport? [2]

Answer 37

In CET, ferredoxin passes its electron back to Cytochrome b6f, which pumps more H+ ions through the membrane.

The extra H+ is good for producing ATP.