Three Stages of Photosynthesis

Question 1

what are the three stages of photosynthesis?

Answer 1

1. capturing light energy on the surface of thylakoids
2. use the light energy to make ATP and reduced NADP+
3. use the free energy of ATP and the reducing power of NADH to synthesize organic compounds of glucose from carbon dioxide (Calvin cycle)

Question 2

what is a photon?

Answer 2

a packet of electromagnetic radiation

Question 3

what are photosystems?

Answer 3

clusters of photosynthetic pigment

Question 4

where of photosystems located?

Answer 4

embedded in the thylakoid membrane

Question 5

what do photosystems do?

Answer 5

absorb photons of particular wavelengths and through the light reactions transfer their energy to ADP and Pi and NADP+ to form ATP and NADPH

Question 6

what is an electromagnetic spectrum?

Answer 6

light from the sun is a mixture of photons of different energies. when passed through a spectroscope photons separate based on their energy

Question 7

why is chlorophyll a important?

Answer 7

its the only pigment that can transfer the energy of light to the carbon fixation reactions of photosynthesis

Question 8

what do other chlorophylls do?

Answer 8

they act merely as accessories to absorb photons that chlorophyll absorbs poorly or not at all

the accessories can absorb light energy but must pass it on to chlorophyll a in order for the reactions of photosynthesis to commence

Question 9

what is photoexcitation?

Answer 9

the absorption of a photon by an electron of chlorophyll (marks the beginning of the light reactions in photosynthesis)

Question 10

what are the steps of photoexcitation?

Answer 10

Step 1: Accessory Pigments of the Antenna Complex
light photons are absorbed by pigment molecules
light is not absorbed by individual pigment molecules but rather clusters of pigment molecules photosystems

Step 2: Energy Transfer to the Reaction Center
the absorbed energy is transferred from pigment to pigment until it reaches chlorophyll a in the reaction center

Step 3: Chlorophyll a and Excitation
energy from light interacts with the electron from chlorophyll increasing its energy level i.e excitation

Step 4: Redox Reaction
the excited electron is transferred to the primary electron acceptor pheophytin. chlorophyll a is oxidized it losses and electron and pheophytin is reduced it gains an electron

Question 11

where are photosystems located?

Answer 11

chlorophyll a and accessory pigments are associated in clusters on the surface of the thylakoid membrane

Question 12

what is the peak absorption of photosystem 1?

Answer 12

the chlorophyll a at the reaction center has a peak absorption of 700nm

Question 13

what is the peak absorption of photosystem 2?

Answer 13

a peak absorption of 680 nanometers