Chapter 10 - Photosynthesis

Question 1

who is performing photosynthesis?

Answer 1

Plants, algae (protists), some prokaryotes - all photoautotrophic organisms perform photosynthesis

Question 2

what is the largest biosynthetic activity on the planet?

Answer 2

photosynthesis - it creates 160 billion tons of carbohydrate per year - lots of biomass being produced

Question 3

what produces almost all of the organic material required by consumers?

Answer 3

photosynthesis

Question 4

where does photosynthesis occur (in land plants)?

Answer 4

in the chloroplasts of green plant tissues

Question 5

how many membranes does a chloroplast have?

Answer 5

2

Question 6

how many chloroplasts (on average) are in a green plant cell?

Answer 6

usually 30-40

Question 7

what are the important parts of chloroplasts?

Answer 7

inner and outer membranes, intermembrane space, thylakoid, thylakoid space, granum

Question 8

what are chloroplasts similar too?

Answer 8

mitochondria

Question 9

what is photosynthesis biochemically?

Answer 9

water + carbon dioxide + light -> sugar + oxygen

Question 10

the correct formula for photosynthesis

Answer 10

6 H20 + 6 CO2 + light energy -> C6H12O6 + 6 O2

Question 11

the three steps of photosynthesis

Answer 11

1. photochemistry (light reaction) 2. electron transfer and production of NADPH and ATP (light reaction) 3. incorporation of CO2 into carbohydrate and production of O2 (dark reaction/Calvin cycle)

Question 12

what is light?

Answer 12

electromagnetic radiation, characterized by its energy (wavelength is lambda)

Question 13

relationship between wavelength and energy

Answer 13

High wavelength = low energy, low energy = high wavelength

Question 14

what happens when light meets matter (3 options)

Answer 14

reflected, transmitted (goes through the matter and nothing happens), or absorbed

Question 15

the three classes of light-absorbing compounds (pigments) found in plants

Answer 15

chlorophylls (chl a and chl b), carotenoids, phycobilins (only found in red algae and cyanobacteria)

Question 16

what do pigments do?

Answer 16

absorb certain wavelengths of the visible light (and reflect or transmit the rest) - each pigment has its own absorption spectrum

Question 17

why is the world green?

Answer 17

chlorophylls absorb about 70% of red and blue wavelength, while the green light is reflected or transmitted and bounces back to the eye - so everything appears green (note that chloroplasts do NOT absorb green light)

Question 18

difference between chl a and chl b

Answer 18

CH3 in chl a and CHO (aldehyde group) in chl b

Question 19

how is chlorophyll capturing the light?

Answer 19

there are a whole bunch of double bonds that are organized in an alternating pattern with single bonds, which make the uptake of photons really easy, because the energy is dissipated along the whole plane of molecules

if a photon of the right energy level (colour) hits the chlorophyl, an electron gets excited and moves orbitals (doesn’t leave the molecule, just gets excited and moves to a new orbital) then releases that extra energy (as heat or a photon) it gained very quickly, and falls back down into its normal energy state

the emitted photon is of a different colour (because some of the energy was also released as heat) so the new light is a different energy, and thus different wavelength (colour)

Question 20

how is excitation energy exploited in the chloroplasts?

Answer 20

the pigments are linked together in ‘light harvesting complexes’ (chl a, chl b, and carotenoids transfer energy (not electrons)) which are connected to ‘reaction centres’ - the transfer of electrons to primary electron acceptor

Question 21

describe photosystem II and the steps

Answer 21

1. light excited pigment in PSII -> as excited electron falls to ground state, another electron is excited, which continues until P680 is excited
2. transfer of electron from chloropyll a pair (P680) to primary electron acceptor
3. electron hole in P680+ must be filled -> pulls it from water

Question 22

describe electron transport chain and photosystem II and the steps

Answer 22

in the thylakoid membrane, two photosystems (PS I with P700 and PS II with P680)

1. PS I gets excited by light
2. P700 looses an electron
3. electron “hole” is filled with an electron coming from PS II

Question 23

what is the solution to the fact that dark reactions require more ATP than NADPH, but in photosystem I and II ATP and NADH have been produced in a 1:1 ratio?

Answer 23

electron recycling: cyclic electron flow within PS I

Question 24

what gradient is used to produce ATP?

Answer 24

conversion of light energy to H+ gradient -> H+ (pH) gradient used for ATP synthesis

Question 25

what happens in plants when the lights go out?

Answer 25

all light reactions stop (photochemistry, electron transport, splitting of water/O2 production, H+ gradient generation)

however, CO2 absorption and sugar production continues (as long as substrates are available)

Question 26

what are the dark reactions?

Answer 26

the Calvin cycle (incorporation of CO2 into carbohydrates) (because it can occur in the dark) -> involves proteins that transfer chemical energy

Question 27

three steps of the Calvin cycle (occur in the stroma and do not require light)

Answer 27

1. carbon fixation
2. reduction
3. regeneration

Question 28

how many turns of the Calvin cycle are needed to produce one molecule of glucose?

Answer 28

6