Chapter 4

•Photosynthesis

– Photosynthesis is the process by which certain organisms use light energy• To make sugar and oxygen gas from carbon dioxide and water

• What does it need? (Input)• What does it make? (Output)

Lightenergy

PHOTOSYNTHESIS

6 CO2 6+ H2O

Carbon dioxide Water

C6H12O6 6+ O2

Glucose Oxygen gas

Trophic Roles• Autotrophs

Producers of the biosphere:– produce organic

molecules from CO2 & inorganic raw materials

• Heterotrophs consumers

Learning Target

1. Describe Oxidation & Reduction reactions

REDOX Reactions

LEO th

e Lio

n Say

s GER

REDOX Reactions

• Oxidation– When a compound loses electrons

• Reduction– When a compound gains electrons

• CO2 + H2O + energy → C6H12O6 + O2

– CO2 is reduced to form glucose

– Water is oxidized to form O2

•Photosynthesis is a redox process, as is cellular respiration– In photosynthesis

• H2O is oxidized and CO2 is reduced

Figure 7.4A, B Reduction

Oxidation

6 O2 6 H2O

Reduction

Oxidation

6 O26 CO2 6 H2O C6H12O6

C6H12O6 6 CO2

Learning Check

• If H2O is losing electrons than it is being reduced/oxidized

• Co2 is being reduced/oxidized, which means it is gaining/losing electrons.

Photosynthesis Overview

• Light reactions– Depend on light– Occur in Thylakoid

Membrane

• Light Independent (“Dark”) reactions– Does NOT need light– Occurs in the Stroma

Learning Target

12.Compare & contrast the structure & function of mitochondria & chloroplast

15. Determine what factors affect the process of photosynthesis & cellular respiration

Location, location, location

Where does the Light Dependent Reaction occur?The Light Independent reaction?

Chloroplast Structure

• Found in mesophyll – 1 mesophyll

cell may have 30 chloroplasts

• Stomata regulate passage of CO2, O2 and H2O

Learning Check

Where does the Light Dependent Reaction occur?

The Light Independent reaction?

• What factors could affect the process of photosynthesis?

Learning Targets

11. Describe the purpose of Chlorophyll & Accessory pigments.

Pigments• Pigments

– Absorb light energy– Boost e- become unstable!

• Chlorophyll– Chlorophyll a main pigment

blue-green– Chlorophyll b accessory

pigment yellow-green• Other accessory pigments

absorb different wavelengths of light– Carotenoids yellow-orange– Xanthophyll yellow– Rhodophyll red– Fucoxanthin brown

Why are plants

green?

Why are plants changing color?

Photosystems• Pass energy

reaction center (chlorophyll a molecule) transfers energy to primary electron acceptor

• antenna pigments are primarily chlorophyll b, carotenoids & xanthophyll

Learning Check

• What is the purpose/function of pigments?

Photosynthesis Overview• Light reactions

– light energy chemical energy (ATP and NADPH) and produce O2

• Light Independent (“Dark”) reactions– Using ATP and NADPH

from the light reactions form sugar from CO2

Learning Target

7. Contrast Chemiosmosis in Cellular Respiration and Photosynthesis

6. Explain how electron transport chains (ETC) establish an electrochemical gradient across membranes.

ETC, Chemiosmosis & ATP Synthase

• Powers ATP synthesis in light reactions• electrons (e-) are passed along a chain of proteins (called the ETC) in

the membrane H+ pumped into Thylakoid space (chemiosmosis)

• H+ diffuse back across the membrane through ATP synthase powers the phosphorylation of ADP to produce ATP (photophosphorylation)

Photophosphorylation http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

Learning Check!

• ETC uses the energy of e- being passed along to pump _______ from the ________ into the thylakoid _______

• Chemiosmosis is the movement of ______ to create a ________concentration.

Learning Target

3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle.

4. Explain the role of NADH, FADH2, and NADPH.

14. Summarize how energy is transferred during photosynthesis and cellular respiration.

Electron Carriers• NAD+

– Reacts with C-H bonds to become NADH

• NADP+– Reacts with free e- and H+ ions

• ADP ATP– diffusion of H+ through ATP Synthase

LDR

• Inputs?• Outputs?

• Two types:– Noncyclic

Photophosphorylation – Cyclic

Photophosphorylation

Non-cyclic photophosphorylation

Learning Target

12. Describe the connection between PS2 & PS1

LIGHTREACTOR

NADP+

ADP

ATP

NADPH

CALVINCYCLE

[CH2O] (sugar)STROMA(Low H+ concentration)

Photosystem II

LIGHT

H2O CO2

Cytochromecomplex

O2

H2OO2

1

1⁄2

2

Photosystem I

Light

THYLAKOID SPACE(High H+ concentration)

STROMA(Low H+ concentration)

Thylakoidmembrane

ATPsynthase

PqPc

Fd

NADP+

reductase

NADPH + H+

NADP+ + 2H+

ToCalvincycle

ADP

P

ATP

3

H+

2 H++2 H+

2 H+

Light Dependent RXN animation

• http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html

• http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie-flash.htm

Cyclic Photophosphorylation

• Primitive used by bacteria

• Electron boosted out of P1 ETC returned to P1

• Electron drives proton pumps chemiosmosis ATP

Learning Targets

3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle.

4. Explain the role of NADH, FADH2, and NADPH.

15. Summarize how energy is transferred during photosynthesis and cellular respiration.

Calvin Cycle/Light Independent Reactions

• Occur in the dark or the light• Light independent reactions• 3 steps

– Carbon fixation– Reduction– Regeneration of RuBP

Step 1:Carbon Fixation

• RuBP (ribulose bisphosphate)– 5 C sugar– Catalyzed by Rubisco

(RuBP carboxylase)

– Adds CO2

• Creates an unstable 6 C molecule that splits

• Creates PGA (3 C moleucle

Step 2:Reduction

• PGA gets phosphorylated by ATP (gets it’s energy)

• Reduced by NADPH (gets it’s e-)

• Produces G3P (PGAL)

– some G3P glucose

– most G3P regenerate RuBP

Step 3:Regeneration of RuBP

• 1 G3P moves out to eventually become glucose

• G3P rearranged into RuBP

• Requires input of 3 ATP• Takes 6 turns of cycle

1 glucose

http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

Alternative mechanisms:Photorespiration

• C3 plants rice, wheat, soybeans

• Uses Co2 directly to make PGA

• On hot, dry days they close their stomata– no CO2 taken in and O2 builds up

– rubisco substitutes O2 for CO2

– Creates a 2 C compound

• 2 C compound gets broken down releases CO2 & water

• Called photorespiration– Uses light, releases CO2 and water

– Doesn’t make glucose

Alternative mechanisms:C4 Plants

• Sunny ecosystems • C is fixed into 4 C molecule• Carbon fixed outside cells (in

bundle sheath cells very efficient requires extra ATP

• Only fixes C, not oxygen• Donates the carbon to Calvin

Cycle• Balances out photorespiration &

saves water

• Corn and sugarcane are a C4 plants

Alternative mechanisms:CAM Plants

• Crassulacean acid metabolism Hot/dry climates

• Orchids, cacti, pineapple etc.

• Stomates open at night to reduce water loss evaporation

• CO2 is fixed into a 4 C compound, used later