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BL1101 > 13. Photosynthesis > Flashcards

13. Photosynthesis Flashcards

1
Q

Define photosynthesis

A

PHOTOSYNTHESIS: process by which cells synthesise organic compounds from inorganic molecules in the presence of sunlight and chlorophyll

Equation:

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2
Q

Photosynthesis - respiration relationship

A

Photosynthesis (anabolism) - respiration (catabolism) reverse reactions

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3
Q

Explain what is cholorphyll and why needed

A

Chlorophyll - green pigment responsible for light absorption - when absorbs releases e - used to synthesise ATP

Different chlorophylls but mostly absorb blue and red light, reflects green

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4
Q

Distinguish absorption spectrum and action spectrum

A

Absorption spectrum - which wavelengths chlorophyll absorbs

Action spectrum - which wavelengths needed for overall photosynthesis (all of pigments)

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5
Q

Main steps of photosynthesis

A
  1. Light dependent reactions: light absorbed by chlorophyll - ATP production - light absorbed by water -> photolysis of water -> O2 and H2 = in intermembrane space of thylakoids
  2. Light independent reactions: ATP and H2 (carrried by NADPH) transferred to light indep site - H2 combined with CO2 - organic compounds - ATP provides E for these anabolic reactions (fixing C molecules) = in stroma
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6
Q

What is chromatography used for?

A

Chromatography is used to separate componenst of a mixture

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7
Q

Procedure of pigment chromatography

A
  1. A mixture containing the pigment is dissolved - mobile phase
  2. Mobile phase is passed through a static material (stationary phase)
  3. Different pigments travel at different speed due to differences in mass - separated
  4. Retardation factor (Rf) calculated to compare components:

Rf = distance component travels/distance solvent travels

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8
Q

Conditions which influence photosynthesis

A
  1. Temperature
  2. Light intensity
  3. CO2 conc
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9
Q

Effect of temperature fluctuation on rate of photosynthesis

A
  1. As temp increased - rate increases (more Ek) to a certain point - enzymes denature - rate falls
  2. Photosynthesis controlled by temp sensitive enzymes
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10
Q

How does light intensity influence the arte of photosynthesis

A
  1. The higher light intensity - the higher rate (more photoactivated chlorophyll) to a certain point - raise light but no change - no more chlorophyll
  2. Different wavelengths of light - different rate
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11
Q

How does CO2 conc influence photosynthesis rate?

A
  1. The higher CO2 conc - the higher rate until certain point - plateau - enzymes for carbon fixation are saturated
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12
Q

What are the experiments to measure rate of photosynthesis in plants?

A
  1. CO2 uptake: changes water pH (alkaline)
  2. O2 release: attaching a sealed container to gas syringe
  3. Increase in biomass: weighted (dehydration must be done) / change in amount of starch - measured with calorimeter
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13
Q

Explain oxygenation of the Earth

A
  1. Earth was anoxic, non-aerobic organisms thrived, iron dominated rocks, oceans
  2. Rising O2 levels nurtured aerobic life instead of anaerobic - evolution of respiring organisms - rise in atmosphere oxygen to 20%
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14
Q

List light dependent reactions

A

In light dependent reactions pigments convert light E into chemical E

  1. Excitation of photosystems
  2. Production of ATP in ETC
  3. Reduction of NADP+ and phtolysis
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15
Q

Explain the first step of light dependent reactions

A

Excitation of photosystems

  1. Photosystems - groups of photosynthetic pigments embedded in thylakoid membrane
  2. Two types of photosystmes; PSI and PSII - according to max absorption wavelength
  3. When PS absrob light - delocalised e become excited
  4. Excited e are transferred to carrier molecules in thylakoid membrane
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16
Q

Explain the second step of light dependent reactions

A

Production of ATP via ETC

  1. Excited e from PSII transported to ETC in thylakoid membrane
  2. As e pass through ETC - lose E - used to translocate H+ into thylakoids - electrochemical gradinet - proton motive force
  3. H+ return to stroma due to gradinet through ATP synthase (chemiososmosis) - ATP produced - photophosphorylation
  4. De-energised e are taken up by PSI - re-energised by light
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17
Q

Third step of light dependent reactions

A

Reduction of NADP+ and photolysis

  1. Excited e from PSI might be trasnferred to NADP+ to reduce it into NADPH - needed for light indep reactions
  2. Lost e from PSII are replaced by e from photolysis - water split by light E into H+, e and O2
18
Q

Overview of light dependent reactions

A
19
Q

Steps of light independent reactions

A

Light independent reactions use chemical E from light dependent to synthesise organic molecules

  1. Carbon fixation
  2. Reducation of glycerate-3-phosphate
  3. Regeneration of RuBP
20
Q

First step of light independent reactions (Calvin cycle)

A

Carbon fixation

  1. Calcin cycle begins with 5C (rubisco biphosphate - RuBP) - RuBP carboxylase (Rubisco) catalyses CO2 attachment to RuBP - 6C
  2. 6C unstable - breaks down into two 3C (glycerate-3-phospahte - GP)
  3. One Calvin cycle involves 3 RuBP combining with 3 CO2 => 6 GP
21
Q

Second step of light independent reactions (Calvin cycle)

A

Reduction of glycerate-3-phosphate (GP)

  1. GP converted into triose phosphate (TP) using oxidation of NADPH and ATP - binds H and ATP supplies E for that
22
Q

Third step of light dependent reactions (Calvin cycle)

A

Regeneration of RuBP

  1. In one cycle 6 TP produced - one may be used for half sugar molecule - two cycles for single glucose
  2. Other 5TP - combined to regenerate stocks of RuBP (5 x 3C into 3 x 5C) - uses ATP
23
Q

Lollipop experiment

A

Determines order of compounds (RuBP, GP, TP) in Calvin cycle - how C fixed in sugars

  1. Radioactive C-14 injected into lollipop container containing green algae (Chlorella)
  2. Light shone to induce phtotsynthesis - C-14 taken from solution
  3. Some algae taken - killed by hot alcohol
  4. Samples analysed in 2D chromatography - separates compounds - any radioactive compounds identified with x-ray film
  5. Comapring samples from different periods of light exposure - order of compounds identified by mass difference => Calvin cycle determined by this experiment
24
Q

Calvin cycle (light independent reactions) compounds

A
25
Q

Chloroplast anatomy

A
26
Q

Evidence that chloroplasts were independent organisms once

A
  1. Double membrane
  2. Own DNA
  3. Certain metabolic processes susceptible to antibiotics that plants are not
27
Q

Adaptation of chloroplast structure for function

A
  • thylakoids: flattened - small volume - conc builds up more quickly
  • grana - thylakoids arranged into sacs to increase SA:V ratio of thylakoid membrane
  • photosystems: proteins arranged into PS to maximise light absorption
  • stroma: cavity with suitable enzymes and pH for Calvin cycle
  • lamella: connects and separates grana to amximise photosynthetic efficiency
28
Q

Chloroplasts in micrographs

A
29
Q

ETC in respiration vs photosynthesis

A
30
Q

Carbon fixation differences in C3, C4 and CAM plants

A
31
Q

GAP project

A

Global Artificial Photosynthesis Project - produce clean E + fix CO2 + generate O2

32
Q

What are the unique features of plant cells?

A
33
Q

What are the specific features of plant cell walls?

A
34
Q

What composes the plant vacuoles?

A
35
Q

What are the function of plant vacuoles?

A

Large vacuoles - large cells - higher surface area - more surface for Sun light absorption (maximised light capture)

36
Q

What are the plant plastids and what are their functions?

A

Proplastids - the start of chloroplasts, chromoplasts and amyloplasts (very small)

  • Chloroplasts (site of photosynthesis)
  • Chromoplasts (store pigments)
  • Amyloplasts (store sugars - starch)

Plastids - unusual organelles - can interconvert between each other (depending on environment)

37
Q

Explain chromoplasts

A
  • dark spots - pigments
    *
38
Q

Explain amyloplasts

A

unusual strcuture - large globules - starch

39
Q

What was the method which allowed to determined the structure / model of photosystem proteins?

A
40
Q

Photosynthesis review picture

A

BL1101 (32 decks)

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