Unit 5-Photosynthesis

Question 1

Equation for photosynthesis?

Answer 1

Carbon dioxide + water —> glucose + oxygen

Question 2

What happens in the light dependent reaction?

Answer 2

Light energy is used to split water

Making ATP, oxygen and energetic hydrogen atoms

Question 3

Where does the light dependent stage happen?

Answer 3

Thylakoid membrane

Question 4

What happens in the light independent stage?

Answer 4

The hydrogen atoms from LDR are fixed with Carbon dioxide using ATP to make glucose

Question 5

Why can the light independent reaction not happen without the light?

Answer 5

Needs products from LDR (hydrogen atoms)

Question 6

Where does the light independent reaction occur?

Answer 6

Stroma

Question 7

Structure of chloroplasts:

Answer 7

Double membrane (envelope)
Disc shaped vesicles called thylakoid
Stacks of thylakoid called grana
Bridges between granum containing ATP synthase called lamellae
DNA,tRNA and ribosomes packed in a large vesicles called the starch grain

Question 8

What are the 2 main types of photosynthetic pigments?

Answer 8

Chlorophyll (green)

Carotenoids (red/orange)

Question 9

What does the absorption spectra show?

Answer 9

The specific wavelengths that are absorbed by these different pigments

Question 10

What is the action spectrum?

Answer 10

A measure of The rate of photosynthesis against different wavelengths

Question 11

What are photosystems?

Answer 11

A complex structure of many chlorophyll and other pigments held together by proteins and lipids on the thylakoid membrane

Question 12

Why are photosystems found on the thylakoid membrane?

Answer 12

This is the best location to maximise absorption of photons

Question 13

What happens in photosystem ii?

Answer 13

Chlorophyll in the huge complex on the thylakoid membrane absorb photons
This excited electrons causing a build up of charge (charge separation)
The charge difference drives the photolysis (splitting) of water into oxygen, protons and electrons

Question 14

What happens to the oxygen produced in the photolysis of water? And where does this occur?

Answer 14

Occurs in photosystem 2

Oxygen diffuses out of chloroplast into the air

Question 15

What happens after photosystem 2 up to photosystem 1?

Answer 15

Electrons pass along the chain of proteins in the thylakoid membrane pumping H+ ions into the thylakoid vesicle (lumen)

Question 16

What happens at photosystem 1?

Answer 16

More photons are absorbed, and the energy excites electrons pumping more H+ ions into the thylakoid lumen from the stroma creating a proton gradient

Question 17

What terminates the electron chain in photosynthesis?

Answer 17

A final protein complex in the thylakoid membrane combines the electron with a H+ to form hydrogen which then reduces coenzyme NADP into NADPH

Question 18

How is ATP generated from photosynthesis?

Answer 18

The proton gradient across the thylakoid membrane is used, as H+ ions diffuse through ATP synthase back into the stroma generating an ATP

Question 19

What is the production of ATP in the light dependent reaction called?

Answer 19

Photophosphorylation (using light energy to phosphorylate ADP)

Question 20

What part of photosynthesis is the Calvin cycle found?

Answer 20

Light independent

Question 21

What is the problem with rubisco enzyme?

Answer 21

It is super slow and inefficient, so large amounts of it are needed

Question 22

Summary of the Calvin cycle

Answer 22

CO2 binds with RuBP —> 2GP (3C), which are reduced by NADPH and activated by ATP (products of LDR) —> GALP, this either binds with another GALP to form glucose (opposite to respiration) or regenerates RuBP

Question 23

What 2 products of LDR are needed for LIR? And why?

Answer 23

ATP, to activate GP

NADPH, to reduce GP

Question 24

Where does the Calvin cycle branch off or repeat?

Answer 24

Once GALP is formed, either 2 GALP combine to make glucose or are regenerated into RuBP

Question 25

What is rubisco?

Answer 25

The enzyme that binds CO2 with RuBP to form 2 molecules of GP

Question 26

How does temperature effect the rate of photosynthesis?

Answer 26

Temp effects the rate of enzyme reactions, eg rubisco

Question 27

What factors affect the rate of photosynthesis?

Answer 27

Temp
CO2 concentration
Light intensity

Question 28

How does CO2 conc effect rate of photosynthesis?

Answer 28

CO2 is needed for Calvin cycle, so the higher the conc the faster the rate of the Calvin cycle

Question 29

When does cyclic photophosphorylation occur?

Answer 29

When there is no available NADP to get reduced from excited electrons

Question 30

What occurs in cyclic photophosphorylation?

Answer 30

Photons in photosystem 1 excite an electron, which passes to the next electron carrier
The energy from the excited electron pumps protons into the thylakoid lumen
The electron returns to PS1
The proton gradient is used to make ATP via ATP synthase

Question 31

What is the purpose of cyclic photophosphorylation?

Answer 31

Non cyclic makes equal quantities of NADP and ATP
Plants need more ATP than NADP
Cyclic only makes ATP

Question 32

Summary of photophosphorylation?

Answer 32

1) light is absorbed by chlorophyll in PS11 to photolysis water
2) high energy electrons are passed along chain of proteins in thylakoid membrane, the energy pumps H+ across membrane
3) electron is finally taken up by NADP to make NADPH
4) H+ gradient is used to make ATP in the ATP synthase enzyme

Question 33

What factors may affect/limit rate of photosynthesis?

Answer 33

CO2 levels
Light intensity
Temperature

Question 34

In tropical climates the rate of O2 production is very high, how may this cause problems?

Answer 34

Oxygen is an inhibitor of carbon fixation as it competes for the active site on rubisco

Question 35

In a hypothetical experiment how could we tell that temperature was not the limiting factor, looking at just yield

Answer 35

And increase in temperature would have no effect on yield as it is not the limiting factor