Question

Answer

Photosynthesis Combines:

CO2 + H2O + light to make carbohydrates

Oxygenic Photosynthesis (using O2) is carried out by:

cyanobacteria, 7 groups of algae, and all land  plants (in chloroplast)

Photosynthesis has two stages:

light-dependent reactions and carbon fixation reactions

Where does light-dependent reaction occur?

Thylakoid membrane of chloroplast

Grana

are stacks of flattened sacs of thylakoid membrane

What are thylakoid membranes surrounded by?

semiliquid called stroma

Where does the carbon fixation reaction (Calvin Cycle) take place?

In the stroma

Pigment absorb photons...

which are inversely proportional to wavelength

The visible spectrum colors:

400nm (blue, high energy)
740nm (red, low energy)

What does absorption of the spectrum do?

gives range and efficiency of molecules to absorb photons

What are two general pigments present in green plants?

chlorophyll (a and b) and carotenoids

What happens only to the chlorophyll-a in the reaction center?

it absorbs red and blue light and converts it to chemical energy

Where are pigments present?

in the antenna complex surrounding chlorophyll-a reaction center

What are the differences between the chlorophylls (a and b)?

a: has CH3 group
b: aldehyde CHO

What do accessory pigments do?

absorbs light in different regions

Porphyrin Ring

Mg in the center of an unsaturated ring structure in chlorophylls

What happens in the porphyrin rings?

photons excite the electrons and the electrons are shuttled away from the ring

What do carotenoids have?

have chains of alternating double bonds and also serve as antioxidants

Light that is captured by 2 photosystems (PSI, PSII) is composed of:

antenna complex + reaction center

Pigments in antenna

gather photons and feed the reaction center, the process is complementary

2P680 chlorophyll-a in PSII

absorb 2 photons and excite 2 electrons that move to the plastoquinone (PQ)

What happens to the lost electrons in PSII?

They are replaced by electrons from oxidation H2O to O2

What do electrons in the PQ go through?

the b6f that then pumps protons into the thylakoid space

What is the proton gradient used for?

The Proton gradient created is used to make ATP by chemiosmosis in ATP synthase

Break

Where does the electron b6f move to?

plastocyanin (PC) and to the PSI whose chlorophyll-a takes 2 electrons

Photons that excite 2 electrons that move...

via ferredoxin to NADP reductase, to make NADPH

Photosystem II has...

10 proteins + 4Mn + electron transfer components + 2P680 chlorophyll-a units

What is b6f complex?

a proton pump embedded in the thylakoid membrane that passes electrons to PC

Photosystem I has..

12-14 proteins + 2P700 chlorophyll-a, accepts PC electrons to make NADPH

Sulfur bacteria have...

One cyclic photosystem. The purple non-sulfur bacteria reaction center is P870.

How is additional ATP in plants produced?

by skipping PSI, making it cyclic photophosphorylation

How do cells use ATP?

from cyclic and noncyclic photophosphorylation, and NADPH from PSI to make sugars

Calvin cycle 3 steps

1.) Add CO2 to RuBP to form PGA
2.)PGA is reduced to G3P, which ic used to
3.) regenerate RuBP

What can the Calvin cycle also be called?

C3 photosynthesis because the first intermediate has 3 carbons (G3P)

What is the enzyme used in Calvin cycle?

RUBISCO

What does RUBISCO do?

carboxylation in normal conditions and oxygenation of RuBP in hot conditions

Three turns of Calvin's cycle...

produce a new G3P/2G3P and are used to make 1 glucose outside the cyle

Glucose + Fructose make...

Sucrose as a vehicle to transport glucose for starch and cellulose syntheses

What does photosynthesis use as a starting substrate?

the product of respiration (namely CO2)

What does respiration use as a starting substrate?

the product of photosynthesis (namely glucose)

What happens to the stroma, in the heat?

Stroma in leaves close (to save water), O2 accumulates and CO2 can't enter

What do CO2 and O2 compete for?

active site of RuBP which explains the name of the enzyme

What are plants in the Calvin cycle called?

C3 plants. There are also C4 plants and CAM plants

Corn and many grasses (C4 plants)

add CO2 to pyruvate to make oxaloacetate (C4) in mesophyll

What is Oxaloacetate converted to?

malate which releases CO2 for the Calvin cycle in bundle-sheath

What does the C4 pathway require?

12 more ATPs compared to the Calvin cycle but is advantageous in hot dry climate

What happens to the CAM plants at night?

CAM plants (succulents:cati, pineapples) open stomata at night, take CO2, and make malate from PEP

What happens to CAM plants during the day?

Stomata close and remove CO2 from the malate to use it in the Calvin cycle

What do C4 and CAM use?

C3 and C4 pathways but in C4 plants both pathways occur in different cells

How does photosynthesis occur in C3 and CAM plants?

in bundle-sheath cells

How does photosynthesis occur in the C4 plants?

in mesophyll cells and then in bundle sheath cells