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botany > Photosynthesis 2 > Flashcards

Photosynthesis 2 Flashcards

1
Q

Light Independent Reactions names

A
  • Calvin cycle
  • Calvin Benson cycle
  • Carbon fixing reactions
  • Carbon reducing reactions
  • Dark reactions
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2
Q

Dark reactions

A

a misnomer as the reactions
do not occur in the dark. They are sometimes
called this as the reactions do not TRAP light
but they occur in the light.

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3
Q

B) Light Independent Reactions what happens

A

-Carbon fixation:
B) Occurs in light (not in dark)
C) The energy that was trapped as ATP and NADPH in light reactions
powers the Calvin cycle and ends up in carbohydrates
D) Regeneration of substrate =
RuBP

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4
Q

Carbon fixation:

A

Carbon dioxide that enters through stomates is trapped.
Carbon from CO2 is fixed into chemical bonds of carbohydrates e.g. glucose

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5
Q

Regeneration of substrate in the light-independent reactions =

A

RuBP (Ribulose bisphosphate)

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6
Q

rubisco

A

*Rubisco is the most abundant enzyme in the world!!
*Rubisco is partially coded for by chloroplast DNA and nuclear DNA.
*Rubisco is light activated (why the reactions do not occur in dark)
*All photosynthesizing plants use Rubisco in the Calvin Cycle to make carbohydrates
( but not all plants use Rubisco to fix atmospheric CO2!)

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7
Q

do all plants use rubisco the fox atmospheric co2

A

no

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8
Q

Calvin Cycle step 1

A

Six molecules of CO2 combine with six
molecules of RuBP (ribulose 1,5-bisphosphate)
in the carbon fixing step.

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9
Q

calvin cycle step 2

A

For every 6 CO2’s fixed, one molecule of glucose
(which contains 6 carbons) is produced

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10
Q

calvin cycle step 3

A

NADPH and ATP from the light dependent
reactions supply energy and electrons that
result in the production of glucose

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11
Q

calvin cycle step 3

A

The cycle regenerates the substrate RuBP.

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12
Q

Photorespiration

A

A special type of respiration that occurs in plants
in the light (in addition to aerobic cellular
respiration)

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13
Q

RuBP carboxylase/oxygenase
has 3 possible substrates

A
  1. RuBP (always one of the substrates)
  2. CO2
  3. O2
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14
Q

co2 in

A

Calvin cycle (Rubisco acting as carboxylase)

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15
Q

o2 in

A

Photorespiration (Rubisco acting as oxygenase)

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16
Q

what 2 chemicals Compete for the Active Site

A

co2 and o2

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17
Q

Photorespiration versus Aerobic Cellular Respiration

photoresperation

A

Photorespiration is a seemingly
wasteful process
1. No ATP is produced
2. Release of CO2 (loss of CO2 is of
significance to plants)
3. No net carbon fixation.
4. When rubisco is active in
photorespiration, it is not
available for the Calvin cycle.
5. However allows plants that have
it (C3 plants) to survive under
hot dry conditions and helps
prevent photooxidative damage

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18
Q

Photorespiration versus Aerobic Cellular Respiration

Aerobic cellular respiration

A
  1. ATP produced
  2. Release of CO2
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19
Q

Does Rubisco tend to act more as a
carboxylase or as an oxygenase?

calvin cycle

A

carboxylase

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20
Q

Does Rubisco tend to act more as a
carboxylase or as an oxygenase?

photoresperation

A

oxygenase

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21
Q

Atmospheric concentrations

of o2

A

20-21 percent o2

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22
Q

Atmospheric concentrations

of co2

A

0.04 percent and raising

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23
Q

Does Rubisco tend to act more as a
carboxylase or as an oxygenase?

A

The high O2 concentration in the atmosphere means
that Rubisco often acts as an oxygenase Photorespiration is promoted by the relative O2 /CO2
concentrations in atmosphere

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24
Q

Different Photosynthetic Strategies

A

A. C3
B. C4
C. CAM

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25
Q

C4 and CAM plants have

A

evolved strategies
to deal with photorespiration

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26
Q

C3 Plants

A

-Produce 3-carbon compounds during first step of
atmospheric carbon fixation (3PGA)
-Use Calvin cycle to fix atmospheric CO2
* C3 plants can have much photorespiration
* If one pumps CO2 into a greenhouse or a growth
chamber with C3 plants, that will cut down on
photorespiration.

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27
Q

C3 Plants
examples

A
  • Spinach
  • Soybeans
  • Oats
  • Wheat
  • Rye
  • Many grasses (not all)
  • Oaks
  • Maples
28
Q

Some plants don’t use Rubisco to

A

fix
atmospheric CO2 .

29
Q

All photosynthesizing plants use Rubisco in

A

the Calvin cycle to make carbohydrates

30
Q

C4 Plants

A

C4 plants have way to deal with photorespiration
* They have additional pathway

31
Q

additional pathways c4 plants

A

Have C3 pathway (Calvin cycle just like all
photosynthesizing plants) and C4 pathway

32
Q

When c4 plants fix atmospheric co2 they produce

A

they produce a 4 carbon compound

33
Q

C4 Plants
number of species and famalies

how many monocots
dicots

A

> 1000 species in 18 different plant families
– 3 monocot families, 15 dicot families
– All of these 18 plant families have C3 and C4 members
– Suggests C4 syndrome has arisen a number of times

33
Q

The 4-Carbon Pathway (C4 pathway)

A

Produces 4-carbon compound OAA
instead of 3-carbon PGA during fixation of atmospheric CO2

33
Q

c4 plants ex

A

C4 Plants:
– Corn
– Sugar cane
– Cat tails
– Crab grass (weedy), more of a problem in heat of summer
– Pigweed (weedy)
– Many tropical grasses and arid-region plants

34
Q

Kranz anatomy

A

C4 plants have Kranz anatomy (Kranz = German for wreath).
– Enlarged bundle sheath cells with large chloroplasts and
numerous starch grains
* © Kingsley Stern

35
Q

what is combine, with aid of the
enzyme PEP carboxylase in mesophyll cells

A

PEP (phosphoenolpyruvate) and CO2

36
Q

PEP carboxylase acts as a

A

carboxylase only, not an oxygenase

37
Q

step 1 of c4 pathway

A

Oxaloacetic acid (4C) is produced as first stable product of
atmospheric CO2 fixation instead of PGA (3C)

38
Q

step 2 of c4 pathway

A

CO2 is transported as malic acid to bundle sheath cells

39
Q

step 3 of c4 pathway

A

CO2 is released and is re-fixed in Calvin cycle.

40
Q

step 4 of c4 pathway

A

CO2 is concentrated in bundle sheath cells around Rubisco, so
Rubisco acts like a carboxylase and photorespiration is
minimized.

41
Q

C4 plants have spatial separation between:

A

Calvin cycle in Bundle Sheath cells & C4 pathway in
Mesophyll cells

42
Q

c4 or c3 plants which is better

A

c4 plants perform better in hotter weathere

43
Q

At low temperatures, C3
plants are more

A

efficient, and
they outcompete C4 plants because Costs extra ATPs for C4
photosynthesis

44
Q

C4 plants do best when it is

A

hot and dry. They can have
stomates partially open to
conserve water but they do
well since they are so
efficient at trapping CO2
* E.g. Crab grass does better in
heat of summer

45
Q

At lower temperatures,

A

C3 plants outcompete C4 plants

46
Q

At higher temperatures,

A

C4 plants outcompete C3 plants

47
Q

Research to try to Convert C3 Plants to C4
Plants

A
  • Need to change anatomy of leaf to Kranz
    anatomy
  • Need to introduce more PEP carboxylase as
    well as the C4 pathway into mesophyll cells
  • Need to take Rubisco out of the mesophyll
    cells and put in bundle sheath cells
48
Q

CAM Plants

A

Tend to grow in dry environments
* In about 30 plant families

49
Q

CAM Plants plant famalies

A

Crassulaceae
Orchidaceae
Cactaceae
Bromeliaceae

50
Q

Crassulaceae

A
  • Jade plants
  • Mother of thousands
51
Q

Orchidaceae

A

orchids

52
Q

Cactaceae

A

cacti

53
Q

Bromeliaceae

A
  • Bromeliads
  • A lot of air plants = epiphytes; e.g. Spanish moss
54
Q

step 1 CAM Photosynthesis stomates

A

are opened at night

55
Q

step 2 CAM photosynthesis Atmospheric CO2 is fixed at

A

night by PEP
carboxylase into malic acid (4C

56
Q

step 3 cam photosynthesis Malic acid is stored in the

A

vacoule

57
Q

step 4 Stomates are closed during day to (CAM photosynthesis)

A

conserve water

58
Q

step 5 (CAM Photosynthesis ) CO2 is released from malic acid during the

A

day

59
Q

step 6 of cam photosynthesis
Now there is a high concentration of CO2
inside the plant, and

A

Rubisco will act like a
carboxylase and re-fix the CO2 into
carbohydrates Organic acids accumulate at night (stomata
open).

60
Q

CAM plants have time-based separation between activity
of:

A

PEP carboxylase fixes CO2 at night and Rubisco fixes CO2 during day

61
Q

CAM photosynthesis allows plants to function well under

A

limited water supply, as well as high light intensity.

62
Q

However CAM plants have low

A

productivity

63
Q

CAM plants Grow slowly

A

under natural conditions (in hot, dry
environments)

64
Q

Obligate CAM =

A

always show CAM photosynthesis

65
Q

Facultative CAM plants exhibit

A

CAM photosynthesis under
certain conditions (e.g. hot, dry) and the rest of the time
they act like C3 plants
– E.g. Mother of thousands

botany (25 decks)

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