Ch. 10 Photosynthesis

dialed.

Photosynthesis

conversion of light energy to chemical energy

performed by photoautotrophs (use light)

Autotroph

Organism that produces their own food (organic molecules)

Use simple substances in their surroundings

Producers

Heterotrophs

Organisms unable to make their own food

Live off of other organisms
Consumers

Photosynthesis first evolved in ___ organisms

prokaryotic

Cyanobacteria

early prokaryote capable of photosynthesis

oxygenated atmosphere of early earth

Evolution of Photosynthesis

Photosynthesis first evolved in prokaryotic organisms

Cyanobacteria

Prokaryotic photosynthesis pathways were the foundation if Eukaryotic photosynthesis

Location of Photosyntehsis

Leaves are primary area of photosynthesis in most plants

Contain chloroplast

Chloroplast

Organelle for the location of photosynthesis

Found in mesophyll (tissue cells of leaf)

stomata

Mesophyll

plant tissue cells

Stomata

pores in leaves

allows CO₂ in and O₂ out

Structure of Chloroplast

Chloroplasts surrounded by double membrane

Stroma

Thylakoids

Chlorophyll

Stroma

Aqueous fluid

Inside Inner Membrane

Thylakoids

Form stacks

aka grana

segregates stroma from thylakoid space

Chlorophyll

green pigment

In thylakoid membrane of chloroplast

Photosynthesis Formula

6 CO₂ + 6 H₂O + light energy →

C₆H₁₂O₆ + 6O₂

Photosynthesis splits H₂O into ___ and ___

Into H and O

Redox reaction

Reaction involving complete/partial transfer of 1 or more electrons

1 Reactant → To another reactant

Where are the electrons transferred in photosynthesis

Electrons are transferred with H⁺ (from split H₂O) to CO₂

Reduces it to sugar

Key role in both photosynthesis and cellular respiration

OIL RIG

Oxidation is Losing electrons

Reduction is Gaining electrons

What are the 2 stages of photosynthesis

The light reaction and Calvin cycle (aka light independent/dark)

Location of light reaction

thylakoid membrane in the photosystems

Location of Calvin Cycle

stroma

Light

electromagnetic energy

made of energy particles (photons)

travel in waves

Wavelength

The distance between crests (top of wave) in waves

Electromagnetic spectrum

Range of wavelengths

380 nm → 750 nm is visible light

Why are leaves green?

Because chlorophyll absorbs violet-blue & red

Reflects green

How does wavelength correlate to energy?

Shorter wavelengths = higher energy

Longer wavelengths= lower energy

3 ways light interacts with matter

Reflection

Transmitted

Absorbed

Pigments are able to ___ visible light

Pigments able to absorb visible light

The color we see is the ___ wavelengths

Reflected

3 different photosynthetic pigments

Chlorophyll a, b and Carotenoids

Chlorophyll a

primary pigments

involved in light reactions

blue/green pigments

Chlorophyll b

Accessory pigment

yellow/green pigments

Carotenoids

Accessory pigment

Broaden spectrum of colors

Yellow/orange pigment

think carrot

Photoprotecion

carotenoids absorb and dissipate excessive light energy that could damage chlorophyll or interact with oxygen

Which color would have more energy yellow (590 nm) or purple (410 nm)

purple because wavelength is shorter = higher energy

Light reaction converts solar energy to?

chemical energy

2 forms of Chemical energy

NADPH and ATP

The cell accomplishes this conversion by using ___ energy (photons) to excite electrons

light

Chlorophyll absorbs a ___ of light

photon

What happens when Chlorophyll absorbs photons

electrons boost from ground → excited state

electron is unstable, causes it to fall back to a ground state

Releases energy as heat

Emits photons as fluorescence

Photosystems

Reaction centers surrounded by light capturing complexes

PSII surrounded by P680

Reaction center

a complex of proteins

associated with chlorophyll A and an electron acceptor

Light capturing complexes

pigments associated with proteins

(antenna for reaction centers)

PS II

reaction center P680

absorbs light at 680 nm

occurs first

discovered 2nd

PS I

reaction center P700

absorbs light at 700 nm

discovered 1st

Explain 5 steps/roles of PSII in the light reaction

1st step Photo-Excitation- light energy strikes a chlorophyll pigment in PSII; excites the electron

2nd Step ETC- electron in PSII becomes energized and can no longer stay in PSII; gets passed down ETC (membrane protons)

Releases energy (thylakoid region) as electron passes through ETC; helps pump Hydrogen ions into thylakoid space

Reaches PSI

3rd step Photolysis- H2O splits into Hydrogen and Oxygen and Electrons

Oxygen released into air

Electron from replaces electron that left PSII

Hydrogen Ions build up in thylakoid. (Creates a hydrogen ion gradient)

4th step Chemiosmosis- energy from ETC will push Hydrogen ions down concentration gradient through ATP synthase

5th step Reduction- hydrogen ions through redox reaction helps converts ADP to ATP

Explain 2 steps/roles of PSI in the light reaction

1st step Photo-excitation - Light energy excites electron in PSI; electron jumps down ETC

2nd step Reduction - Electron reaches stroma, NADP + reduced to NADPH

Does the Generation of ATP require energy?

No

How is ATP generated from the light reaction?

• The “fall” of electrons from PSII to PSI provides energy to form ATP

• The Hydrogen (H+) gradient is a form of potential energy

• ATP synthase couples the diffusion of H+ to the formation of ATP

Inputs of Light reactions

• ADP

• H2O

• NADP+

• LIGHT

Outputs of Light reactions

• ATP

• O2

• NADPH

The Light Reaction converts ___ energy to ___ energy

Solar → chemical

The Calvin cycle is ___ electron flow

Cyclic

What are the reactants/products of the Calvin Cycle

Uses ATP and NADPH

To reduce CO2 to sugar (G3P)

How many times must the Calvin Cycle take place for 1 net synthesis of 1 G3P molecule?

3

3 phrases & order of the Calvin Cycle

1. Carbon fixation

2. Reduction

3. Regeneration of RuBP

Carbon Fixation

1st step of Calvin Cycle

CO2 enters Calvin cycle one at a time

Each CO2 attaches to a molecule of RuBP by rubisco enzyme (catalyzes)

Forms 3-phosphoglycerate (PGA)

Reduction

2nd step of Calvin Cycle

Each 3-phosphoglycerate molecule is phosphorylated by ATP ( uses 6 total) → forms 1 3-bisphosphoglycerate

6 NADPH molecules donate electrons to the 3-bisphosphoglycerate molecule → Reduces to G3P (glyceraldehyde 3-phosphate)

6 Molecules of G3P form; 5 used to regenerate RuBP

What is the net gain of G3P in the reduction phase of the Calvin Cycle

1

Because other 5 use to regenerate RuBP

Regeneration of RuBP

3rd step of Calvin Cycle

5 G3P molecules use to regenerate 3 RuBP molecules

Requires energy ( 3 ATP)

After step is complete; cycle now ready to take in CO2 again

Is the regeneration of RuBP endergonic or exergonic?

endergonic

Is Calvin cycle Exergonic or Endergonic?

Endergonic

Inputs of Calvin Cycle ( 1 G3P Molecule)

3 CO2

9 ATP

6 NADPH

Outputs of Calvin Cycle ( 1 G3P Molecule)

1 G3P

9 ADP

6 NADP+