5.1 Photosynthesis

Question 1

Which reactants/products of photosynthesis are used up/produced in the LDR?

Answer 1

Water (& light)
Oxygen

Question 2

Which reactants/products of photosynthesis are used up/produced in the Calvin cycle?

Answer 2

CO2
Glucose

Question 3

Where does each step of photosynthesis take place?

Answer 3

LDR: chloroplast (thylakoid membrane)

Calvin: stroma of chloroplast

Question 4

What is a lamella and what is it made of?

Answer 4

Connects the grana together
Made of thylakoid membrane!

Question 5

Do chloroplasts have ribosomes

Answer 5

YES (think enzymes embedded in the membrane - ATP synthase etc!)

Question 6

Chloroplasts structure to function (x3)

Answer 6

1. thylakoid membranes/grana: large SA for light absorption & reactions; membrane-bound enzymes & photosystems; high density of chlorophyll for light absorption
2. low-volume thylakoid spaces: rapid generation of H+ gradient for chemiosmosis
3. enzyme-rich stroma for CC: contains rubisco for carboxylation of RuBP; fluid for easy diffusion

Question 7

Why are there different types of chlorophyll?

Answer 7

Not all wavelengths of light are equally absorbed, and different chlorophylls absorb more strongly in different parts of the visible spectrum

Question 8

Typical chlorophyll light absorption (describe the graph)

Answer 8

x-axis: wavelength (red-blue)
y-axis: absorption

cosine wave (lowest at green, highest at red & blue)

Question 9

Is reduced NADP an oxidising or reducing agent?

Answer 9

REDUCING!!
which means it itself is oxidised :)

Question 10

What is a photosystem and how do they work?

Answer 10

Funnel-shaped structures that sit on the thylakoid membranes.

Accessory pigments absorb light of different wavelengths & pass energy down the photosystem. Eventually the energy reaches the primary pigment which absorbs a specific wavelength that acts as a reaction centre.

Question 11

PSI vs PSII

Answer 11

PSI: absorption peak at 700nm (chlorophyll a)

PSII: absorption peak at 680nm (chlorophyll b)

Question 12

LDR Stage 1

Answer 12

1. photoionisation of chlorophyll: chlorophyll molecules in PSII absorb photons of light, exciting 2 chlorophyll electrons to a higher energy level
2. this causes the electrons to move to an electron acceptor protein molecule/e- carrier
3. this causes the photolysis of water (to replace the lost electrons)

Question 13

Photolysis of water in more detail

Answer 13

2H2O = O2 + 4H+ + 4e-

Question 14

What happens to each product of photolysis of water?

Answer 14

Oxygen produced diffuses out of chloroplast & into the air
Protons are released into thylakoid lumen
Electrons replace excited electrons that have been ejected from chlorophyll in PSII

Question 15

Where is the endpoint of the electron transport chain in the LDR?

Answer 15

Reduced NADP/NADP reductase

Question 16

LDR Stage 2

Answer 16

1. The excited electrons pass along a chain of electron transport proteins in the thylakoid membrane
2. The energy in the electrons is used to pump protons from stroma to thylakoid lumen, creating a proton gradient across the thylakoid membrane
3. In PSI, more photons of light are absorbed and passed to the electrons, causing further excitation

Question 17

LDR Stage 3

Answer 17

1. The electrons are eventually recombined with some of the protons to form H atoms
2. These are taken up by molecules of NADP so reducing it to reduced NADP: NADP + H+ + e- = reduced NADP
3. The reduced NADP moves to the stroma for the Calvin cycle

Question 18

LDR Stage 4

Answer 18

1. The remaining protons diffuse down their gradient from the thylakoid lumen to the stroma through ATP synthase (chemiosmosis)
2. This spins the enzyme, opening up its active sites and allowing the production of ATP (ADP + Pi = ATP)

Question 19

What is the general name for ATP synthesis?

Answer 19

photophosphorylation!

because it uses light energy to phosphorylate ADP :)

Question 20

What abiotic factor is the CC most prominently affected by and why?

Answer 20

Temperature - enzymes are involved!

Question 21

What products of the LDR are used in the CC?

Answer 21

ATP and reduced NADP

Question 22

Three steps of the CC in a nutshell

Answer 22

1. Carbon fixation
2. Reduction
3. Regeneration of RuBP

Question 23

How many times is ATP used in the CC, and when?

Answer 23

2 times

1. GP converted to triose phosphate
2. Triose phosphate converted to RuBP

Question 24

What is another name for carbon fixation?

Answer 24

Carboxylation by rubisco

Question 25

What happens during carbon fixation?

Answer 25

One molecule of CO2 binds to the 5-carbon sugar ribulose bisphosphate (RuBP) to form two molecules of the 3-carbon compound glycerate 3-phosphate (GP).

This reaction is catalysed the enzyme ribulose bisphosphate carboxylase (rubisco).

Question 26

What happens during reduction?

Answer 26

GP is reduced/converted and activated to form triose phosphate (TP) using two ATP and two reduced NADP.

This produces 2 ADP and 2 NADP+ which go back to the thylakoid membrane to take part in the LDR.

Question 27

What happens after triose phosphate is produced?

Answer 27

One carbon from the two triose phosphate molecules is used to make glucose, so one molecule of glucose is produced every 6 turns of the cycle.

Most of the triose phosphate is used to regenerate RuBP using ATP.

Question 28

Limiting factors graphs: what are the x and y axes?

Answer 28

x axis: limiting factor
y axis: rate of photosynthesis

Question 29

What are the four limiting factors of photosynthesis?

Answer 29

1. Light intensity
2. CO2 concentration
3. Temperature
4. Available chlorophyll

Question 30

Why does rate of photosynthesis increase as light intensity increases?

Answer 30

More energy is supplied to the plant, and therefore the LDR can occur faster.

This produces more ATP and reduced NADP for the CC, which can also occur at a faster rate

Question 31

Why does rate of photosynthesis increase as CO2 concentration increases?

Answer 31

CO2 is one of the raw materials required for photosynthesis.

It is required for the CC - CO2 combines with RuBP during carbon fixation.

This means the more CO2 is present, the faster this step of the CC can occur and the faster the overall rate of photosynthesis.

Question 32

Why does rate of photosynthesis increase as temperature increases?

Answer 32

The CC is affected by temperature (LDR not so much - driven by light energy), as the CC consists of enzyme-controlled reactions (e.g. rubisco)

Question 33

What are the benefits of using hydroponics?

Answer 33

1. Doesn’t require as much land
2. Conditions can be controlled

Question 34

RP7 (chromatography): what are the four pigments from most to least soluble?

Answer 34

Carotene
Xanthophyll
Chlorophyll a
Chlorophyll b