Photosynthesis I

Question 1

Why is understanding photosynthesis important?

Answer 1

Almost every living thing
on the planet is
dependent upon this
process.
Every C molecule in organisms was once CO2 that was then fixed in a chloroplast
Oxygen is a by-product of carbon fixation

Question 2

What is photosynthesis?

Answer 2

Conversion of C from CO2 to organic C
(CH2O) using light as the source of
energy

Question 3

What is the pigment involved in photosynthesis called? Where is it located?

Answer 3

The pigment which absorbs light for
photosynthesis is chlorophyll,
contained within chloroplasts.

Question 4

Explain the structure of the pyrrole tail of chlorophyll and how it is important.

Answer 4

Long, lipid-soluble hydrocarbon. This means it can anchor itself into the lipid bilayer of the chloroplast membrane.

Question 5

Label the parts of the chloroplast.

Answer 5

Question 6

What region of the chloroplast is chlorophyll associated with?

Answer 6

Inner membrane.

Question 7

What is the lumen of the chloroplast? What does it do?

Answer 7

fluid, helps with movement of protons and pH changes

Question 8

What are thylakoids and what do they do?

Answer 8

Membrane structures
that absorb light and
use the energy from
light to do work

Question 9

How are wavelength and light energy relateD?

Answer 9

Inversely proportional

Question 10

What is the range of visible light?

Answer 10

400-700 nm

Question 11

Why is are visible light wavelengths the most likely to be used by biological systems?

Answer 11

below these goes into energies that cause damage; above does not provide sufficient energy for biochemical work

Question 12

What is a photon? How are photons related to wavelength and energy?

Answer 12

Photons are packets of light energy. Each photon has a specific amount of energy (quantum)
that is related to the wavelength of light (shorter
wavelengths have more energy)

Question 13

Is light that we see absorbed or reflected by the pigment?

Answer 13

Reflected

Question 14

What colours does chlorophyll a mainly absorb? Chlorophyll b?

Answer 14

a: blue and red
b: blue

Question 15

ow do we know chlorophyll is the most
important pigment for photosynthesis?

Answer 15

red and blue have the best rates of photosynthesis with red and blue wavelengths, chlorophylls in particular absorb these well.

Question 16

Explain the difference between excited states 1 and 2

Answer 16

High energy blue light drives electrons into an outer orbit: Excited state 2
Lower energy red light drives electrons into an inner orbit: Excited state 1

Question 17

How do photosystems gather light energy?

Answer 17

Pigment molecules arranged in antenna complex, gather light and funnel energy towards reaction center.

Question 18

Differentiate between photosystems I and II.

Answer 18

PSI is richer in chl a and
absorbs most at ~700nm
(P700)
PSII is richer in chl b and
absorbs more below 680nm
(P680)

Question 19

Use this image as a guide to explain What happens when light is absorbed by the
photosystems. (5 steps). What is this known as?

Answer 19

1. Light is absorbed by photosystem II, releasing 2 electrons
2. Electrons are held by an electron receptor temporarily
3. The electrons pass
   through an electron
   transport chain in
   the thylakoid membrane
   and are passed to PSI
4. Light absorbed by PSI boosts the electrons to a
   higher state
5. Electrons in
   this high
   energy state
   are used
   to make
   energy-rich
   compounds.
   This is known as the
   Z-scheme, or non-cyclic
   photophosphorylation

Question 20

What is the charge problem in the z-scheme?

Answer 20

The 2 electrons which leave the PS II must be replaced in the
chlorophyll otherwise it would assume a +ve charge & be unstable

Question 21

How is the charge problem in the z-scheme resolved?

Answer 21

In the PSII complex, water is ‘split’ to give H+ and ½ O in the light reaction….
photolysis of water

Question 22

How is light energy converted to
chemical energy? Use this image as a guide.

Answer 22

1. H+ produced by PSII and during the movement of the e- from PSII to
   PSI are released into the lumen of the thylakoids
2. H+ causes an ionic imbalance between the inside & outside of the thylakoid
3. The ions are released to the outside through special channels (down a concentration
   gradient).
4. As this occurs, an enzyme associated with them utilizes the energy to produce ATP from
   ADP + Pi

Question 23

What is the point of photosynthesis II?

Answer 23

Carbon fixation

Question 24

List the products of the light reactions in photosynthesis and their fates afterwards.

Answer 24

Oxygen from the photolysis of water. Released by the plant
NADPH: powerful reducing agent that takes part in biochemical reactions
ATP, a source of energy for biochemical reactions

Question 25

Where do the dark reactions of photosynthesis take place?

Answer 25

In the stroma

Question 26

What are the dark reactions?

Answer 26

The dark reactions are those in which the CO2 is converted to sugars

Question 27

What is the first organic product of photosynthesis?

Answer 27

3-phosphoglycerate (3PGA)

Question 28

Describe the three stages of the Calvin cycle.

Answer 28

Calvin cycle has three stages: 1. Carbon fixation - ribulose 1,5 bisphosphate, acquires carbon from CO2 and generates 2 3PGA 2. Reduction phase - requires NADPH 3. Regeneration of Ribulose

Question 29

What is the enzyme that produces 3PGA from RuBP?

Answer 29

Ribulose bisphosphate carboxylase (rubisco)

Question 30

How many turns of the Calvin cyle are required to produce one molecule of glucose?

Answer 30

6

Question 31

Why is sucrose the most prevalent final product of photosynthesis as opposed to glucose?

Answer 31

twice as much carbon in sucrose can be transported than in glucose.

Question 32

how can plants respond to protect themselves from too much light?

Answer 32

- Physiological & Biochemical responses * Organ movement * Organelle movement * Chloroplasts reposition * Grana rearrangements

Question 33

List the photosynthetic pigments tested in the lab in order from MOST hydrophobic to LEAST hydrophobic.

Answer 33

Carotenes, xanthophylls, chlorophylls

Question 34

What is the Rf value and how is it calculated?

Answer 34

The relative solubilities of pigments can be compared by calculating the Rf (Relative to the front) value. The Rf value is calculated as the distance from the origin (o) to the sample (s) divided by the distance from the origin (o) to the solvent front (f). Rf = (s – o) / (f – o)

Question 35

Define the following terms (as relevant to this lab): a. Absorption spectrum b. Action spectrum

Answer 35

a) Spectrum of light each pigment absorbs b) Rate of photosynthesis at each wavelength of light.