Chapter 17 Photosynthesis

Question 1

What is the process of chemiosmosis within photosynthesis?

Answer 1

Excited electrons pass through the electron transport chain, between carrier molecules
As the electron moves down the chain, energy is transferred to the surroundings
At the cytochrome complex, this energy is used to pump hydrogen ions into the thylakoid membrane from the stroma
Due of the natural concentration gradient, H + diffuse through the enzyme ATP synthase into the stroma, with the enzyme harnessing the proton motive force to produce ATP from ADP and P

Question 2

What is the process of Non-Cyclic phosphorylation?

Answer 2

Light is absorbed by electrons in PSII causing electrons to excite
The electrons are passed to electron acceptor molecules, passing through the electron transport chain, eventually leading to PSI
Energy is transferred from the high energy electrons to pump protons from the stroma into the thylakoid lumen. Protons diffuse back into the thylakoid via ATP synthase, which harnesses the energy from the proton motor force to phosphorylate ADP into ATP. THIS IS CHEMIOSMOSIS
Photolysis of water, with the electrons replacing that lost at P680, catalysed
At the same time, electrons are excited from P700 passing to another electron transport chain, generating more ATP via chemiosmosis
The final electron acceptor is NADP, which is reduced with electrons and protons to NADPH

Question 3

What is the process of cyclic phosphorylation?

Answer 3

Electrons excited at PSI
Passed to electron carrier molecules, which return the electron to PSI
Enables chemiosmosis to occur due to energy pumping hydrogen ions, so produces ATP
But as electrons not being replaced, cannot produce NAPDH

Question 4

When does cyclic photophosphorylation occur?

Answer 4

When there is little NADP available
When there are particularly high ATP demands

Question 5

What is photolysis?

Answer 5

The breakdown of water using light, into oxygen, hydrogen ions, and electrons, catalysed by enzymes

Question 6

What are the stages of the light dependent stage of photosynthesis? Titles only

Answer 6

Excitation of electrons at PSII
Electron transport chain to PSI
Chemiosmosis to produce ATP
Photolysis of water to replace electrons lost
Excitation of electrons at PSI
NADP reductase to form NAPDH
Cyclic Photophosphorylation

Question 7

What happens during the light independent stage of photosynthesis?

Answer 7

Ribulose Biphosphate (5C) combines with Carbon Dioxide in the stroma, catalysed by RuBisCO
Unstable intermediate breaks down into 2 glycerate-3-phosphate GP molecules
Using energy from ATP and Hydrogens from NADPH, GP is turned into 2 Triose Phosphate molecules
Most of the TP is used to regenerate RuBP, a small amount the starting point for other complex molecules e.g carbohydrates

Question 8

What are the names of the 3 main stages of the Calvin Cycle?

Answer 8

Fixation- of CO2 into GP
Reduction- of GP into TP
Regeneration- of RuBP

Question 9

How many turns of the Calvin cycle are needed to produce a glucose molecule?

Answer 9

6
So 6 CO2 is needed
10 TP used to regenerate RuBP, 2 TP used to form glucose

Question 10

What is the compensation point and compensation period?

Answer 10

The rate at which photosynthesis is equal to respiration- amount of CO2 uptake cancels production
Period- amount of time needed to reach the compensation point

Question 11

What are the components of chloroplasts?

Answer 11

Starch granules
Ribosomes
DNA
Intergranal Lamellae
Thylakoids and Granum
Stroma

Question 12

What parts of the chloroplast are adapted for photosynthesis and how?

Answer 12

Thylakoid Membranes- contain photosynthetic pigments
Stroma- contains enzymes for light independent reaction

Question 13

What is an antennae complex?

Answer 13

The arrangement of the photosynthetic pigments into a cone shape

Question 14

What is a photosystem?

Answer 14

The collection of light harvesting pigments (antennae complex) and reaction centre (Chlorophyll)

Question 15

What happens when light hits a photosystem?

Answer 15

May hit the reaction centre directly
Or excitation of electrons within other photosynthetic pigments leads to energy transferred eventually to the reaction centre

Question 16

What are the different types of chlorophyll and what do they absorb?

Answer 16

Chlorophyll A P680- absorbs wavelengths of light up to 680 nm
Chlorophyll A P700- absorbs wavelengths of light up to 700nm
Chlorophyll B- absorbs wavelengths of light up to 450nm

Question 17

What are accessory pigments and examples?

Answer 17

Pigments which absorb wavelengths of light that chlorophyll doesn’t, passing energy to the reaction centre
e.g Cartenoids, Xanthophylls

Question 18

What is the composition of PSI and PSII?

Answer 18

PSI- antennae complex and chlorophyll p700 at the centre
PSII- antennae complex and chlorophyll P680 at the centre

Question 19

Why is photosynthesis endothermic in terms of bonds?

Answer 19

Lots of energy is needed to break the strong bonds in inorganic molecules
The bonds formed between organic molecules are weaker as non polar, so give out less energy, so exothermic

Question 20

Why is respiration exothermic in terms of bonds?

Answer 20

Little energy is needed to break the weak non polar bonds between organic molecules
The inorganic molecules formed contain much stronger bonds, releasing more energy when formed than taken in so exothermic

Question 21

What is the fate of triose phosphate?

Answer 21

5/6 used to regenerate RuBP which requires ATP
Converted into starch, sucrose and glucose
Converted into glycerol
Converted into amino acids
Converted into nucleic acids

Question 22

How do plants make fats?

Answer 22

TP converted into glycerol
GP converted into fatty acids
Condensation between them to form fats

Question 23

What is a limiting factor? What are the limiting factors of photosynthesis?

Answer 23

Something that limits the rate (of photosynthesis) as it is in short supply, or currently provides sub-optimum conditions

Light intensity, temperature, and carbon dioxide concentration

Question 24

How does a low light intensity affect the rate of photosynthesis? What happens to each of the products and why?

Answer 24

Decreases the rate
Fewer electrons excited from photo systems, resulting in less chemiosmosis and less ATP and reduced NADP forming
In the light independent stage, RUBP can still be converted to GP, but GP cannot be converted to TP. And so less TP can be regenerated into RUBP
So the concentration of RUBP and TP decreases, whilst GP increases

Question 25

How does carbon dioxide concentration affect the rate of photosynthesis?

Answer 25

Needed in the Calvin cycle, a substrate in an enzyme controlled reaction
Decrease concentration means a reduction in the collision frequency, and so reduced production of GP, so less TP
RuBP thus builds up

Question 26

How does temperature affect the rate of photosynthesis?

Answer 26

Enzyme controlled reactions, increased kinetic energy, increased collision frequency, but too high and it denatures, too low and the frequency is too low of collisions

If too low, the rate of photolysis is too low, less NADPH and ATP for photolysis
Lower rates of diffusion of H+

In the light independent stage, decrease in concentration of everything as all enzyme controlled, need to look at specific enzymes and what is being recorded in the experiment

Question 27

What are primary pigments?

Answer 27

Found at reaction centres, chlorophyll A

Question 28

Why do plants in the ocean have different accessory pigments?

Answer 28

Shorter wavelengths can reach the ocean so these can be absorbed
Other wavelengths cannot reach the bottom of the ocean

Question 29

What is the process of extracting photosynthetic pigments?

Answer 29

Grind leaves into a fine powder
Mix with propanone
Stir and move green layer with a pipette

Work quick to reduce damage to pigments

Question 30

How do you use DCPIP to test the rate of photosynthesis?

Answer 30

Cut leaves, grind in sucrose solution to homogenise
Filter, centrifuge
The superlatant is the liquid, the residue is the pellets containing chlorophyll
Resuspend pellet into buffer solution (no sucrose)
Add DCPIP and test in different conditions

DCPIP is an electron acceptor, replaces NADPH and becomes colourless when reduced, when photosynthesis has taken place
Can measure time to become colourless

Question 31

What do you need to talk about when talking about what can be concluded from an experiment? Photosynthesis

Answer 31

Not just photosynthesis did or did not happen
Specifically explain why this happens and thus what it shows

e.g superlatant did not change colour, means chloroplasts in residue not superlatant
e.g did not change colour when test-tube boiled, photosynthesis needs intact membranes/proteins

Question 32

What does sucrose do in homogenising experiments? What else can be done?

Answer 32

Helps prevent damaged to organelles and keeps them intact
Ice-cold solutions reduces damage to components

Question 33

What do plants respire more during the day?

Answer 33

Generally higher temperatures during the day
Increase kinetic energy of enzymes, increases rate of enzyme-substrate collisions, increases rate of respiration

Question 34

How can prevention of the light-independent stage affect the light-dependent reaction?

Answer 34

If NADPH is not oxidised when GP is converted to TP, no final electron carriers for PS1
Non-cyclic photophosphorylation cannot take place

Question 35

What variables should you control in a photosynthesis experiment and how?

How can you measure oxygen concentration?

Answer 35

CO2 conc- supply with excess with NaHCO3
Temperature- water bath
Light sources- intensity and type, use a lamp above, measure lux
pH with buffers
Size of plant, including the size of its leaves
Let plant acclimatise

Could count bubbles
But more accurate with an oxygen sensor, establish baseline first

Question 36

How can you tell the type of habitat a plant is from, from a rate of photosynthesis light intensity graph?

Answer 36

If the optimum rate of photosynthesis occurs at lower light intensities, it suggests the plant is from a low light intensity habitat