Converts water and carbon dioxide from the environment into organic food

molecules and oxygen gas

PHOTOSYNTHESIS

Uses energy from sunlight

Photosynthetic organisms – many kinds, terrestrial and aquatic

Grasslands

Oceans

Freshwaters

Two Sets of Reactions

- thylakoid membranes

- chlorophyll absorbs sunlight

- makes energy molecules ATP

- Makes O2 gas

- reduces electron carrier NADP+

1. Light-dependent (“light”) Reactions

2. Light-independent reactionsCalvin cycle (“dark” reactions)• Uses energy molecules from

light reactions• “Fixes” carbon dioxide

– Changes inorganic CO2 into a compound plants can use

• Oxidizes NADPH• Makes glucose

6 CO2 + 6 H2O C6H12O6 + O2

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Sunlight is white light, containing all colors

Visible light drives the light reactions

Colors of light

Depends on wavelength ()

-Shorter wavelength

- blue-violet end of spectrum

higher energy

-Longer wavelength

-red-orange end of spectrum

lower energy

Visible light: small part of Electromagnetic spectrum

travels as a wave ---- behaves as a particle (photon)

Shorter wavelength

Higher energy

Shorter wavelength

Higher energy

Plants absorb blue and red light best

Absorption of Light Energy

Photosynthetic pigments

•Plants have multiple pigments to absorb as much sun energy as possible

•Chlorophyll a is the primary pigment – starts the chain of reactions

•Chlorophyll b, carotenes, xanthophylls and others are accessory pigments.

•They absorb wavelengths that chlorophyll a cannot absorb use more of sunlight

ChromatographySeparates a liquid mixture

by solubility

Chlorophyll absorbs mostly from the red and blue ends of the spectrum - reflects green.

Colors of light absorbed by a chloroplast

Colors NOT absorbed are reflected or transmitted

-- the colors we SEE

Absorbed light energy is transferred to

electrons in pigment

-- energized electrons

Parts of a chloroplast

Granum – stack of thylakoid sacs

Stroma – fluid surrounding thylakoids

- site for 2nd set of reactions

Thylakoid membranes

- have chlorophyll

- absorb sunlight

- site for 1st set of reactions

Parts of a Leaf

What is a Photosystem?

• Capture light energy

• Energized electrons begin reaction chains that make ATP and NADPH

A cluster of pigments and other molecules in thylakoid membranes

What are electron carriers?

Electron carriers are compounds that accept high-energy electrons from one molecule in a chain of reactions and transfer them to another molecule in a later reaction.

a. Also usually accept hydrogen ions (H+)

b. Transferring electrons and H+ transfers energy

c.In photosynthesis, NADP accepts electrons and H+, becoming NADPH

d.Helps change sunlight to chemical energy

Light reactions are a series of oxidation and reduction reactions

• Oxidation – losing energy– Lose an electron (alone or on atoms)– Lose a hydrogen atom (H+ + e-)

– Lose a phosphate group (PO4)

– Be broken apart (decomposed, hydrolyzed)

• Reduction – gain energy– Gain electrons (alone or on atoms)

What is NADP?• NADP accepts electrons and H+ ions

NADP + H NADPH

• H comes from water in “light” reactions

• Gives H to CO2 in “dark” reactions

• Electron energy helps power reactions

Coenzyme – helps in a reaction but is not the catalyst

The Light Reactions 1. Photosystems absorb sunlight

a. excited electrons from chlorophyll transfer to Electron Transport Chains

b. Make ATP and NADPH

2. Light splits a water molecule

H2O 2 H+ + 2 e- + O

b. H+ reduce NADP + Oxygen O2

c.Electrons -- replace electrons lost from chlorophyll

Light reactions

Electron Transport Chain

Electrons pass from one acceptor molecule to the next in a series (chain) of oxidation-reduction reactions

Energy from electrons pumps H+ across membrane

proton gradient in thylakoid space

Chemiosmosis and ATP Synthase

• ATP Synthase – an enzyme in thylakoid membrane• Electron transport chain generates H+ gradient• H+ ions diffuse through ATP synthase• activate synthase enzyme• Phosphorylates ADP

(ADP + P)• Makes ATP

ADP + P ATP

Chemiosmosis

Summary of Light reactions

1. Capture light energy, make ATP

2. Split water (H2O) into 2 H+ + O + 2e-

1) Electrons replace those lost from chlorophyll

2) O makes oxygen gas

3. Add H+ and e- to NADP NADPH1) Later they become part of glucose molecule

Light Reactions

Calvin Cycle “Dark” reactions, or Light-Independent Reactions

In stroma of chloroplast

• Uses ATP made in light reactions

• Fixes CO2 from air

• Adds H+ ions from water

• Adds electrons from ETC

Makes GLUCOSE

How is sugar made?CO2 + H PGAL

(3 carbon sugar)

2 PGAL 1 glucose

Carbon fixing – CO2 gas made into an organic compound

Energy needed to make glucose comes from ATP made in the light reactions

2 PGA (3-C)

Citric Acid (6-C)

Carbon is “fixed”

ATP and NADPH are oxidized

2 PGAL (G3P) 1 glucose

Remaining PGAL RuBP

RuBP (5-C)ribulose bisphosphate

Calvin Cyclein stroma

LE 7-5

Light

ChloroplastH2O

LIGHTREACTIONS

(in thylakoids)

ATP

NADPH

Electrons

O2

CO2

Sugar

PADP

NADP

CALVINCYCLE

(in stroma)

Absorbs light energy

Makes energy molecules ATP, NADPH

Uses energy molecules made in light

Makes sugar

Photosynthesis uses light energy to make food molecules

Light splits water -makes O2

“Fixes” carbon (CO2 becomes part of organic

molecule)

Starch

Lipids

proteinscellulose

Factors Affecting Photosynthesis1. Light – bright sun, more energy

a. Long days (summer), more light absorbedb. Wavelength – cannot absorb green light

2. Temperature – warm, but not too hota. Hot days – stomata close to save water

3. Water – soil must be moista. Water comes up through xylem in veinsb. Exits through open stomatac. Water low? – stomata close

C 3 plants in hot weather?C-3 – carbon fixed into 3-carbon compound

In hot, dry weather, C-3 plants:

• leaf openings close to save water

• No more CO2 comes in

• Photorespiration – Intermediate products used for energy by plant– No glucose made

Guard cells open/close stomata

Close when CO2 or water is low in plant

- saves energy

C-4 Plants

Corn Sugar Cane crabgrass

C-4 plants fix and store CO2 in a 4-carbon compound while stomates are open

- use stored carbon when stomates close

- in hot weather, can still make sugar

C-4 Pathway

Stores carbon as a 4-carbon compound in special cells around veins called bundle sheath cells

When stomates close, stored carbon is

changed back to CO2 for Calvin cycle

CAM Plants

Fix CO2 during the night, when it is cool enough for open stomates

- Do photosynthesis during the day, using the stored carbon

Succulents cacti pineapples

Parasitic plants Supplement nutrition by taking from other organisms

Dodder Plant Pure parasite – cannot photosynthesize

- Special roots tap into veins of host plant

Mistletoe – supplements photosynthesistaps into host cell veins – drains sap

Carnivorous Plants Eat insects to get nitrogen

Live where decomposition is slow

Pitcher plant

Pitcher plantSweet nectar at bottom of tube

- Insects stuck in nectar, digested

Sundew – eats insectsSugary “dew” attracts insects

Insects get stuck

-Leaves enclose and digest

-Absorb nutrients from insect

Venus Fly TrapHinged leaves with “trigger” hairs

Insect walking on leaves touches hairs

- Leaves close, insect digested

Indian Pipe

Cannot photosynthesize

Where can we see carotenes, xanthophylls, and other pigments besides in autumn leaves?

Carotenes in nature

Photosynthesis reduces atmospheric CO2

• Excess greenhouse gases:

• - from human activity

• -burning fossil fuels

• - deforestation

• - increases global warming

• - photosynthesis removes CO2 and helps moderate warming

Greenhouse - Traps heat indoors

TALKING ABOUT SCIENCE

• Nobel Prize winner Mario Molina has studied how pollutants are affecting Earth's ozone layer

• Solar radiation converts O2 high in the atmosphere to ozone (O3)

• The ozone layer shields organisms on Earth's surface from damaging UV radiation

• CFCs have caused dangerous thinning of the ozone layer

• International restrictions on CFC use are allowing a slow recovery

7.14 Mario Molina talks about earth’s protective ozone layer

LE 7-14b

Southern tip ofSouth America

Antarctica

The ozone layer

Pond Mud and its Bacteria (Winogradsky Column)

Anaerobic Phototrophs - purple bacteria - green sulfur bacteria

TRANSPORT IN A LEAF

Water enters a leaf through the veins; xylem carries water up from the soil. Water then diffuses from the veins into the mesophyll cells.

-Carbon dioxide diffuses into the leaf through small openings on the surface called stomates

-Phloem carries the newly synthesized glucose to other parts of the plant where it can be used for energy or stored.

The Light Reactions of Photosynthesis – one (of two) electron transport chains

Chlorophyll absorbs sunlight

-Energized electrons in chlorophyll go to E.T.C

-ETC makes ATP (ADP + P)

- Water is split; electrons from water replace the electrons lost from chlorophyll

-Another chlorophyll also absorbs sunlight

-This pathway makes NADPH (NADP + H)

Photosystem – cluster of chlorophyll, other pigments, proteins and other molecules that all work together to harvest light energy and package it in ATP and NADPH

ATP synthesis

As in cell respiration, electron transport chain powers production of ATP by chemiosmosis through enzyme ATP synthase

The Dark (Light-Independent) Reactions of Photosynthesis

Calvin Cycle

-Uses energy molecules made in light reactions

-ATP, NADPH

-a 5-carbon compound in the stroma is used in the reactions and then recycled

-CO2 combines with hydrogen (from NADPH) to make 3-carbon PGAL

-2 PGAL combine to make one glucose

Overview of Photosynthesis