Photosynthesis

Question 1

Photosynthesis

Answer 1

process plants, algae and some bateria use to conver light energy to chemical energy
supports all life (except in hydrothermal vents)
produces O2 gas and sugar
algae responsible for 50-60% and plants do most of the rest
CO2 + H2O + light -> C6H12O6 + O2 + H2O
source of O2 is H2O

Question 2

Requirements for photosynthesis

Answer 2

light, pigment to absorb light energy, access to CO2 to be incorporated into sugars
requirements usually found in leaves

Question 3

Chloroplasts

Answer 3

located in mesophyll cells
contains thylakoid and stroma
pigments absorb red and blue light
absorbs photons (wavelenghts not absorbed but reflected to give pigment its color)
uses different electron carriers and different reducing agents than mitochondria
for electron transport

Question 4

Thylakoid

Answer 4

in chloroplasts
site of light reactions in membrane
site of light capture and pigment regeneration

Question 5

stroma

Answer 5

in chloroplasts

site of dark reactions

Question 6

Light reactions

Answer 6

produce ATP and NADPH to provide energy and reducing power for building sugars
uses potential energy from H+ gradient produced by cature of light energy

Question 7

Light

Answer 7

form of electromagnetic energy
units: photons
energy content is inversely proportional to wavelength (small wavelength = high energy)
high energy = ionizing radiation
visible light (380-750nm) can raise electrons to higher energy levels

Question 8

Absorption spectra

Answer 8

show which wavelengths are absorbed by a given molecule

when matching with action spectra = relevent pigment

Question 9

Action spectra

Answer 9

shows which wavelengths are effective for specific processes

when matching with absorption spectra = relevent pigment

Question 10

Carotenoids

Answer 10

accessory pigments

Question 11

Chlorophyl

Answer 11

major photosynthetic pigment
alternating single and double bonds (delocalized electrons)
light absorbed by porphyrin ring
hydrocarbon tail helps anchor the molecule in the thylakoid membrane where it is bound to apoprotein

Question 12

Antenna system

Answer 12

contains ~200 chlorophyll a & b, ~50 carotenoids

Question 13

Chlorophyll a

Answer 13

reaction center of antenna system

adjacent to the primary electron acceptor of the electron transport system (ETS)

Question 14

Chemiosmotic ATP synthesis

Answer 14

conversion of light energy to metabolic energy

1) light capture increases potential energy of electron
2) energy released during electron transfer drives movement of H+ into the thylakoid and creates a pH gradient
3) potential energy of pH gradient drives ATP synthesis

Question 15

Photosystem (PS) I

Answer 15

has P700 at reaction center: requires wavelength of 700 to raise electron to higher energy level
most primitive form

Question 16

Cyclic electron transfer

Answer 16

when PSII is absent
produces 1 ATP per 2 electrons, no O2 of NADPH produced
reduces NADPH production until balanced with needs

Question 17

Non-cyclic photophosphorylation

Answer 17

requires PSI and PSII
PSII splits water, electron used to regenerate PSI, electron used to make NADPH
produces ATP and NADPH
uses 4 photons (split water, make NADPH, make ATP)
takes place in thylakoid membrane (inside 1000 times higher H+ concentration than in stroma - movement down gradient drives ATP synthesis)
advantages:
-water splitting amplifies pH gradient which drives more ATP synthesis
-produces NADPH which has reducing power required for dark reactions

Question 18

Photosystem (PS) II

Answer 18

strong oxidant

splits water

Question 19

Dark reactions

Answer 19

take place in the stroma
use more ATP than NADPH (from light reactions)
light independent (but always occur in light)
In corporate CO2 into sugars
2 pathways: C3 and C4

Question 20

C3

Answer 20

Calvin-Benson cycle
occurs in all plants
3 main parts:
-carboxylation
-reduction and sugar production
-regenerate RuBP (sugar shuffle)
consumers 3 ATP, 2 NADPH per CO2 fixed
one C fixed per turn (need 6 turns for entire sugar)

Question 21

3PG

Answer 21

3 carbon compound including a carboxyl group
must be reduced to form carbohydrate
accumulates in dark reactions (reduction requires light)

Question 22

Photorespiration

Answer 22

occurs at high temperatures and in light
water splitting in light reactions produces O2 and at high temperatures the stomata starts to close (to prevent water loss) which causes decreased CO2 gas exchange. this causesincreased dissolved O2/CO2 ratio. O2 competes with CO2 to bing to Rubisco
consumes O2 and releases CO2

Question 23

C4

Answer 23

uses different initial incorporation step than C3 (usesPEP rather than rubisco)
C4 compound is made in the mesophyll and transported to an adjacent bundle sheath cell where it is released and refixed via the calvin cycle

Question 24

C4 plants

Answer 24

have a Kranz anatomy where bundle sheath cells are ringed by mesophyll
the calvin cycle occurs in cells with high CO2/O2 ratio
bundle sheath plastids have more starch grains than mesophyl (stored sugar)
C4 plants have separate pathways spacially of initial CO2 fixation and calvin cycle

Question 25

Crassulacean acid metabolism (CAM)

Answer 25

plants adapted to arid environments
water loss is minimized by reversing normal stomatal cycle (stomata open during night and closed during day to limit water loss in hot areas)
uses the C4 pathway
have temporal separation of C3 and C4 pathways