2: Photosynthesis I: The Light Reaction

Question 1

Photosynthesis

Answer 1

Life on Earth depends on energy derived from sun

CO2 + water –> glucose and Oxygen

photosynthetic organisms use solar energy to make complex compounds like glucose.

Energy stored used later to power cellular processes and can serve as energy source for all forms of life

Question 2

Light as a wave

Answer 2

Characterized by wave length (Lambda)

frequency is number of wave crests that pass an observer in a given time

light wave is a transverse electromagnetic wave

Question 3

Light as Particle

Answer 3

Light is a photon

photon contains quantum (energy)

photon depends on frequency of light according to Planck’s Law

Question 4

Properties of Light

Answer 4

sunlight is like rain of photons of different frequencies

humans only sensitive to visible-light region of electromagnetic radiation spectrum

Question 5

Light is absorbed by pigment molecules

Answer 5

molecules that absorb light are called pigments

When atoms absorb light, they change electronic state

wrong wavelength of light will not be absorbed, when it is correct, it will be absorbed

Question 6

Chlorophyll Energy disposal

Answer 6

Fluorescence - return to its ground state; release of photon

Relaxation - return to its ground state but no release of photon

Energy transfer - transfer energy to another molecule

Photochemistry - energy of the excited state causes chemical reactions

Question 7

Chlorophyll

Answer 7

contained by photoautotrophic organisms

all pigments are found in chloroplast

Question 8

Chlorophyll structure

Answer 8

Contain porphyrin ring

Magnesium as center ring

long hydrophobic tail; phytol tail

Question 9

Chlorophyll absoroption

Answer 9

Chlorophyll a absorbes violet and orange light

chlorophyll b absorbs blue and yellow light

Question 10

Cartenoids

Answer 10

Responsible for orange-yellow colors observed in leaves of plants

minor role in accessory light-harvesting pigments

structural role in assembly of light-harvesting complexes

protect photosynthetic apparatus from photo oxidative damage

Question 11

Chlorplast structure

Answer 11

site of biophysical and biochemical reaction of photosynthesis

includes :
- double membrane system, - internal membrane system ~thylakoid (grana; and stromal thylakoids)
- stroma - fluid medium
- lumen - internal space

Question 12

Organization of Photosynthetic apparatus

Answer 12

Pigments

Electron transfer carriers

ATP Synthase

Question 13

Photosystems

Answer 13

Pigment + protein complexes

Components:
- Antenna complex - absorb light energy and transfer to reaction center
- reaction center - electron transfer

chlorophyll excited in two ways:
- direct absorption of photon
- upon receipt of excitation energy from antenna ~ resonance

Question 14

Light harvesting complex proteins

Answer 14

associated with antenna pigments

PS II associated proteins -
LHC II
PS I associated proteins - LHC I

Question 15

PS II/P680

Answer 15

Synthesize ATP

Absorb longer wavelengths

ight driven water-plastoquinone oxidoreductase

Question 16

PS I/P700

Answer 16

Synthesize ATP and NADPH

Absorb shorter wavelengths

light driven plastocyanin-ferrodoxin oxidoreductase

Question 17

Major protein complexes in thylakoid

Answer 17

Cytochrome - electron transport chain; connect PS 1 and 2

Plastocyanin - Mediates electron transfer

ATP Synthase - catalyzes formation of ATP using ADP and inorganic Phosphate (Pi)

Question 18

Chemiosmosis

Answer 18

the process of making ATP.

flow of electrons down electron transport chain