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BIO203 > Photosynthesis I > Flashcards

Photosynthesis I Flashcards

1
Q

Why is understanding photosynthesis important?

A

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

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2
Q

What is photosynthesis?

A

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

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

Label the parts of the chloroplast.

A
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6
Q

What region of the chloroplast is chlorophyll associated with?

A

Inner membrane.

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7
Q

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

A

fluid, helps with movement of protons and pH changes

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8
Q

What are thylakoids and what do they do?

A

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

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9
Q

How are wavelength and light energy relateD?

A

Inversely proportional

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10
Q

What is the range of visible light?

A

400-700 nm

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11
Q

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

A

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

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12
Q

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

A

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)

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13
Q

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

A

Reflected

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14
Q

What colours does chlorophyll a mainly absorb? Chlorophyll b?

A

a: blue and red
b: blue

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15
Q

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

A

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

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16
Q

Explain the difference between excited states 1 and 2

A

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

17
Q

How do photosystems gather light energy?

A

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

18
Q

Differentiate between photosystems I and II.

A

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

19
Q

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

A
  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
20
Q

What is the charge problem in the z-scheme?

A

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

21
Q

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

A

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

22
Q

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

A
  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
23
Q

What is the point of photosynthesis II?

A

Carbon fixation

24
Q

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

A

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

25
Q

Where do the dark reactions of photosynthesis take place?

A

In the stroma

26
Q

What are the dark reactions?

A

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

27
Q

What is the first organic product of photosynthesis?

A

3-phosphoglycerate (3PGA)

28
Q

Describe the three stages of the Calvin cycle.

A

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

29
Q

What is the enzyme that produces 3PGA from RuBP?

A

Ribulose bisphosphate carboxylase (rubisco)

30
Q

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

A

6

31
Q

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

A

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

32
Q

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

A
  • Physiological & Biochemical
    responses
  • Organ movement
  • Organelle movement
  • Chloroplasts reposition
  • Grana rearrangements
33
Q

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

A

Carotenes, xanthophylls, chlorophylls

34
Q

What is the Rf value and how is it calculated?

A

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)

35
Q

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

A

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

BIO203 (12 decks)

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