storing of energy in organic compounds

what do photosynthetic pigments in the thylakoid do?

absorb light energy

what is done with the absorbed light energy from pigments?

passed onto other chemicals, resulting in the synthesis of glucose (high-energy)

what is the main photosynthetic (absorbs light) compound?

chlorophyll

why is chlorophyll green?

• reflects/transmits green light

• absorbs red & blue light

what do carotenoids (or accessory pigments) absorb & reflect?

• absorbs blue and green

• reflects yellow, orange, red

why are having a variety of pigments in plants helpful?

plants use more of the sun’s light since pigments absorb different wavelengths of light

chromatography

technique that separates molecules in a mixture (in this case, pigments from a plant sample)

how do you determine the solubility of a pigment?

travels further on paper from the dipping site

photosystems

bundle of pigments that absorb light energy

• starts the flow of electrons

where are photosystems located?

the thylakoid membrane

photosystem II (p700)

• discovered second, used 1st in photosynthesis

  • absorbs an average wavelength of 700 nanometers

photosystem I (p680)

• discovered first, used 2nd in photosynthesis

  • absorbs average wavelength of 680 nanometers

where does absorbed light energy go after being absorbed by pigment?

chlorophyll a (reaction center)

electron transport system (ETS)

chain of electron acceptors that get stronger

what does the ETS produce within cells?

ATP

what happens when an electron is transported down the ETS?

small # of energy releases which can be used to assemble certain compounds

explain the staircase model for the ETS.

1. chlorophyll electrons are energized by light energy

2. electrons move down as they are taken by stronger electron acceptors

3. released energy as electrons move down used to assemble ATP/NADPH

4. used in the light independent reaction which creates glucose

light dependent reaction

• solar energy used to make ATP and NADPH

• oxygen released

• does use sunlight

light independent reaction

energy in ATP & NADPH used to convert carbon dioxide to glucose

• does not use sunlight

where do the light dependent reactions of photosynthesis occur?

thylakoid membrane

what happens first in a light-dependent reaction?

• light energy energizes electron in photosystem II

• electron is transferred to an acceptor

• then, photolysis occurs.

photolysis

water is split with the use of solar energy

what atoms release from photolysis?

• hydrogen protons & electrons

• oxygen

what is the chemical formula for photolysis?

2H₂O_(l) + light → 4H⁺_(aq) + 4e^- + O_2(g)

• water + light → hydrogen protons + electrons + oxygen

where do the electrons that come from water (2H₂O_(l)) go after photolysis?

back to photosystem II so that it can continuously absorb light energy and continue the cycle

where does the oxygen that came from water (2H₂O_(l)) go after photolysis?

converted to molecular oxygen (O_2(g))

what happens second in a light-dependent reaction?

• electrons are transported down an ETS which release energy

• chemiosmosis uses this energy to create ATP

chemiosmosis

process that occurs when energy released from ETS forces hydrogen ions (from 2H₂O_(l)) across the thylakoid membrane

how do the ions move through a selectively permeable membrane during chemiosmisis?

1. hydrogen ions are initially present in the stroma before moving to the thylakoid

2. high concentration of hydrogen ions build up in thylakoid, creates a gradient

3. due to pressure hydrogen ions are forced through the membrane back into the stroma

how are hydrogen ions are forced through the membrane back into the stroma?

they move through an enzyme called the ATP synthase complex

ATP synthase complex

only path outside of the thylakoid back into the stroma

how is ATP produced in the stroma?

• hydrogen ions return to stroma like water turning a turbine

• ADP bonds to a phosphate molecule and creates ATP

draw a diagram of hydrogen ions moving from the stroma to the thylakoid and back to the stroma.

N/A

what happens third in a light-dependent reaction?

• light energy energizes an electron from photosystem I

  • this electron is replaced by the electron from photosystem II at the end of its electron transport system

what happens fourth in a light-dependent reaction?

electron acceptor sends electron through another electron transport system

what is created as the electron goes through the ETS?

• reduction reaction which makes NADP⁺ reduce into NADPH

  • this means that NADPH has more energy

draw a flowchart detailing a light-dependent reaction.

N/A

where do light-independent reactions occur?

stroma

what are ATP, NAPDH, and CO₂ used for in a light-independent reaction?

producing glucose

what happens first in a light-independent reaction?

• carbon dioxide enters the stroma via the stomata

what happens second in a light-independent reaction?

• combines with a RuBP molecule with 5 carbon (since CO₂ has one carbon) to create an unstable six-carbon compound

  • splits into two three carbon compounds called PGA

what happens third in a light-independent reaction?

• the 2 PGA are then reduced

  • activated by ATP, reduced by NADPH

  • gain 1 phosphate, and 1 hydrogen electron

• this creates 2 high energy molecules of PGAL which continue or leave

PGAL

high-energy sugar with 3 carbon molecules

how is the PGAL distributed at this point?

• some leave and produce other compounds the plant requires to live

• some continue to replace RuBP using ATP

what compounds do PGAL molecules that leave produce?

• glucose

• starch

• sucros

• glycerol

• celluose

• amino acids

• fatty acids

how many times does the cycle have to continue for to produce one molecule of glucose? (C₆H₁₂O₆)

6 times!

• create six molecules of carbon dioxide (CO₂)

• contains 6 carbon molecules, and glucose has 6 carbon molecules

what happens fourth in a light-independent reaction?

• the PGAL molecules create RuBP with ATP to replace the missing ATP

  • the remaining goes towards creating glucose

• plant cell makes all compounds from products of photosynthesis

why do we need six cycles to create one molecule of glucose?

• 12 PGAL molecules are made in total (two per cycle).

  • 10 PGAL are used for replacing RuBP, while the other two make glucose

what is the one common factor between all photosynthetic organisms?

chlorophyll, it makes photosynthesis possible

if NADPH is the reduced form of a chemical compound, then what is the oxidized form of it?

NADPH is reduced, more energy. NADP+ is oxidixed, less energy.

what is the flowchart one may use for representing the light dependent process?

Water --> Photosystem II --> Photosystem I --> NADPH

what is the flowchart one may use for representing the light independent process?

the more water generated from photolysis:

more light dependent reaction