Photosynthesis C1.3

Question 1

What are phototrophs?

Answer 1

organisms that use sunlight to make carbon compounds from water and O2.

Question 2

What are heterotrophes?

Answer 2

organisms that obtain food from other organisms.

Question 3

What light does photosynthesis use?

Answer 3

visible range of the electromagnetic spectrum

Question 4

What is the wavelength of visible light?

Answer 4

400-700mm

Question 5

What is dispersion?

Answer 5

the separation of visible light into different colors” red, orange, yellow, green, blue, violet

Question 6

What affects the bend of the light wave?

Answer 6

frequency and wavelength upon passage through a prism.

Question 7

What is pigment?

Answer 7

chemical molecules that absorb visible light and reflect light which includes the colors that we see.

Question 8

Which colors are absorbed and which are reflected?

Answer 8

red/blue absorbed
green reflected

Question 9

What are photosynthetic pigments responsible for?

Answer 9

the absorption of light in plant leaves

Question 10

Where are photosynthetic pigments?

Answer 10

embedded in the thylakoid

Question 11

What is the porphyrin ring?

Answer 11

light absorbing head with magnesium center of a chlorophyll

Question 12

What is the hydrocarbon tail of

Answer 12

tail of the chlorophyll that interact with hydrophobic regions of proteins inside the thykaloid membranes

Question 13

What is the photosynthesis equation?

Answer 13

6CO2 + 6H2O –> C6H12O6 + 6O2

Question 14

What are three limiting factors of photosynthesis?

Answer 14

temperature, CO2, light

Question 15

How does temperature limit photosynthesis?

Answer 15

as temperature rises, the rate of collision also increases. an optimum is reached and begins decreasing when the temperature starts to denature enzymes

Question 16

How does CO2 limit photosynthesis?

Answer 16

When CO2 is low, there isn’t enough CO2 for plants to use for photosynthesis, but when there is too much CO2, the plants can not use all of it, so they reach a plateau/another factor has become limiting.

Question 17

How does light limit photosynthesis?

Answer 17

When light is low, there isn’t enough light (energy) for plants to use for photosynthesis, but when there is too much light, the plants can not use all of it, so they reach a plateau/another factor has become limiting.

Question 18

Why are factors affecting rate of photosynthesis considered limiting factors?

Answer 18

each factor can limit the rate if they are below the optimal level. HOWEVER, in combination, only one factor will limit the rate. the factor furthest from its optimum.

Question 19

Absorbtion spectrum

Answer 19

a graph showing the relative amount of light absorbed at each wavelength by each pigment of a plant

Question 20

Action spectrum

Answer 20

a graph showing relative effectiveness of photosynthesis at different wavelengths.

Question 21

What is the photosystem?

Answer 21

a protein complex found in the thylakoid membrane inside chloroplasts. they harvest light by passing on energy from photons until it reaches the reaction center chlorophyll.

Question 22

What is the photosystem composed of?

Answer 22

reaction center which are two special chlorophyll a molecules and light harvesting antenna pigments which are pigments bound to proteins.

Question 23

What happens when electrons drop down to ground state?

Answer 23

heat and energy is released.

Question 24

Explain the process of light hitting photosystem II?

Answer 24

• accessory pigments in photosystem II absorb light causing the electrons to get excited.
• this energy is absorbed by adjacent pigment molecules to become excited too
• this process of excitation energy transfer is repeated across the antenna pigments
• the energy is transferred until the reaction center chlorophyll is reached.
• at the reaction center chlorophyll, the electrons are transferred to an electron acceptor

Question 25

What are the advantages of the structured array of different types of pigment molecules in a photosystem?

Answer 25

- different pigment molecules can absorb light in different ranges of wavelengths thus maximizing ability to use light - antenna pigment molecules are in close and precise orientation which is crucial for efficient energy transfer - more pigments to intercept randomly scattered photons which means a higher chance of absorption - pigment molecules in the photosystem are interdependent which means they cannot perform photosynthesis individually

Question 26

What is the light dependent reaction?

Answer 26

conversion of light energy into chemical energy in the form of ATP and NADPH and waste product of O2. carried out in the thylakoid membrane

Question 27

What are outcomes of light dependent reaction in photosystem II?

Answer 27

- generation of oxygen - production of ATP - reduction of NADP

Question 28

What are the steps of oxygen generation by photosystem II?

Answer 28

1. photolysis 2. photo-activation 3. redox reaction

Question 29

1. Explain the 3 steps of oxygen generation in PSII

Answer 29

1. H2O is split by the energy of light and enzymes to produce electrons, protons, and oxygen. - the electrons replenish the chlorophyll a pigment to return it to its ground state by filling the "holes" 2. a photon of light is absorbed by a pigment in PSII and transferred to other pigments until it reaches chlorophyll a at the reaction center. - the energy excited an electron to a higher energy 3. chlorophyll a is oxidized when the electron leaves to the acceptor and the primary electron acceptor is reduced when the electron attached.

Question 30

2. Explain the steps of ATP production by chemiosmosis

Answer 30

4. the excited electron pass from the primary electron acceptor down to an electron transport chain. - energy is lost at each transfer 5. with energy from the electron transport chain, H+ ions from the stoma are pumped into the thylakoid space. - generating a concentration gradient of H+ 6. chemiosmosis - accumulating H+ causes the pH to drop and the establishment of a proton gradient. - the flow of protons through ATP synthase allows phosphorylation of ADP +Pi --> ATP 7. electrons keep moving down to the next electron carrier

Question 31

3. Explain the steps of reduction of NADP by photosystem I

Answer 31

8. at the same time, a photon of light is absorbed by a pigment in photosystem I, resulting in displacement of a electron from P700 and transfer of an electron with a higher energy state to lower. - the denergized electron from PSII fills the vacancy 9. electron with higher energy is passed down an electron transport chain to carrier ferrodoxin 10. enzyme NADP reductase catalyzes transfer if electrons from ferrodoxin to carrier NADP+. - two electrons required to fully reduce NADP+ --> NADPH REPEAT 2X

Question 32

What is the cyclic photosynthesis?

Answer 32

instead of excited electrons going to ferrodoxin then NADP+ reductase, it goes back to the cytochrome complex to become cyclic. - electrons move down remaining ETC from the cytochrome complex to allow ATP production via chemiosmosis

Question 33

What is special about cyclic photosynthesis?

Answer 33

- only occurs in bacteria - ATP generated more rapidly

Question 34

What is the great oxidation event?

Answer 34

a period in earth's history, roughly 2.4 billion years ago, when the atmosphere experienced a significant rise in oxygen levels

Question 35

What are some outcomes of the great oxidation event?

Answer 35

- first glaciation event due to a reduction in green house effect - a drop in temperature as a result of decrease in CO2 and methane - oxidation of dissolved iron in water, resulting in precipitation of it, resulting in formation of bonded iron structures seen in many iron ores today

Question 36

Light independent reaction

Answer 36

aka the calvin cycle, is when CO2 is foxed by combining it with a molecule called ribulose bisphosphate to produce an intermiediate product. it follows the light dependent reaction and require ATP and NADPH to produce sugars like glucose.

Question 37

What are the stages of the calvin cycle?

Answer 37

1. carbon fixation 2. triosephosphate synthesis 3. rubisco regeneration

Question 38

What happens during carbon fixation of the calvin cycle?

Answer 38

3 CO2 molecules combine with 3 RuBP (that has 5 carbons) to form 3 short lived unstable 6 carbon compound... which immediately splits into 6 separate 3 carbon molecule (PGA)

Question 39

What is rubisco?

Answer 39

an enzyme which catalyzes the binding of CO2 to RuBP. it is the most abundant enzyme. a high concentration of it is needed in the stoma because it works relatively slowly and are not effective in low concentrations when doing carbon fixation

Question 40

What happens during synthesis of triosephosphate of the calvin cycle?

Answer 40

6 PGA molecules are reduced by 6 NADPH, donating its electrons. those 6 PGA also become phosphorylated by 6 ATP into 6 ADP. then, 6 triosephosphates are created, 1/6 going to make carbohydrates, amino acids, carbon compounds

Question 41

What happens during the rubisco regeneration of the calvin cycle?

Answer 41

5/6 of the triosephosphate used for regeneration ribulose bisphosphate, 3 ATP phosphorylates into 3 ADP

Question 42

Synthesis of starch using products of calvin cycle and where they are stored?

Answer 42

many glucose monomers joined together through condensation reactions. temporarily stored in chloroplasts, they look like white blobs.

Question 43

What is the connection between LDR and LIR?

Answer 43

- lack of light stops LIR because it needs the ATP and electron carriers produced by LDR, which requires light - lack of CO2 prevents PSII from functioning because CO2 is an electron acceptor in PSII, no CO2 means the electrons have no where to go in the ETC to create energy.