PHOTOSYNTHESIS

“LIFE from LIGHT and AIR”PRODUCERS/AUTOTROPHS – CONVERT LIGHT ENERGY TO CHEMICAL ENERGY; SYNTHESIZE ORGANIC MOLECULES

CONSUMERS/HETEROTROPHS – CONSUME OTHERS FOR ORGANIC MOLECULES AND ENERGY

glucose + oxygen carbon dioxide + water + energy

carbon dioxide + water + energy glucose + oxygen

What’s the connection?

PHOTOSYNTHEIS:REDUCTION = ENDERGONIC

CELLULAR RESPIRATION:OXIDATION = EXERGONIC

OVERVIEW

6 CO2 + 6 H20 C6H1206 + 6O2

carbon dioxide water glucose oxygen

6 CO2 + 12 H20 C6H1206 + 6O2 + 6H20

HOW DO PLANTS ACQUIRE ENERGY AND RAW MATERIALS?

H2O enters roots

Leaves are “solar collectors”Organ of photosynthesis

CO2 enters through stomates

Roots take up needed nutrients: N, P, K, S, Fe, Mg………………….

HOW IS A LEAF ORGANIZED TO BE A “SOLAR COLLECTOR”?

stomate – opening for gas exchange

air space – gas exchange

vascular bundle – transport tissues of plant/ xylem & phloem; visible as leaf “vein”

mesophyll –photosynthesis

MESOPHYLL CELLS

CHLOROPLASTLIGHT REACTIONS?

CALVIN CYCLE?

Chlorophyll and other pigments?

LIGHTLIGHT a form of energy called electromagnetic a form of energy called electromagnetic

radiationradiation Kinetic energyKinetic energy It has a dual nature: behaves like a wave It has a dual nature: behaves like a wave

and behaves like a discrete particleand behaves like a discrete particle

Light - wavesLight - waves

Light causes disturbance in electric and Light causes disturbance in electric and magnetic fields – like a pebble thrown magnetic fields – like a pebble thrown into waterinto water

Each form of electromagnetic radiation Each form of electromagnetic radiation has a specific wavelength and frequencyhas a specific wavelength and frequency

Light - particlesLight - particles

Photon – particles of lightPhoton – particles of light NOT A TANGIBLE PARTICLE RATHER NOT A TANGIBLE PARTICLE RATHER

A DISCRETE BUNDLE OF ENERGY A DISCRETE BUNDLE OF ENERGY THAT BEHAVES LIKE A PARTICLETHAT BEHAVES LIKE A PARTICLE

Amount of energy is INVERSELY related Amount of energy is INVERSELY related to wavelength – the shorter the to wavelength – the shorter the wavelength the greater the energy of the wavelength the greater the energy of the photonphoton

VISIBLE SPECTRUM – 380 - 750 nm – MOST IMPORTANT IN BIOLOGY

WHEN LIGHT MEETS WHEN LIGHT MEETS MATTER . . . MATTER . . . Light is reflected – We see the wavelengths of Light is reflected – We see the wavelengths of

light that are reflectedlight that are reflected Light is transmitted – Passes through the objectLight is transmitted – Passes through the object Light is absorbed – WORK MAY BE DONELight is absorbed – WORK MAY BE DONE PIGMENT – substance that absorbs lightPIGMENT – substance that absorbs light

Chlorophyll is green because it reflects green Chlorophyll is green because it reflects green wavelengths and absorbs or transmits other wavelengths and absorbs or transmits other wavelengthswavelengths

THINK ABOUT ITTHINK ABOUT IT

Why do some objects appear white?Why do some objects appear white? Why do some objects appear black?Why do some objects appear black?

Which car remains cooler in summer – Which car remains cooler in summer – one with white paint or one with black one with white paint or one with black paint?paint?

SPECTROPHOTOMETERSSPECTROPHOTOMETERS Device for measuring amount of light absorbed or Device for measuring amount of light absorbed or

transmitted by a pigmenttransmitted by a pigment

ABSORPTION SPECTRUMABSORPTION SPECTRUM

Chlorophyll a absorbs red and blue light Chlorophyll a absorbs red and blue light best; very little green light is absorbedbest; very little green light is absorbed

Other plant pigments have different Other plant pigments have different molecular structures – absorb different molecular structures – absorb different wavelengthswavelengths

BUT HOW DO WE KNOW WHICH BUT HOW DO WE KNOW WHICH WAVELENGTHS ARE IMPORTANT WAVELENGTHS ARE IMPORTANT IN PHOTOSYNTHESIS?IN PHOTOSYNTHESIS?

Grow plants under different colors of light Grow plants under different colors of light and see which ones stimulate greatest and see which ones stimulate greatest amount of oxygen – ACTION amount of oxygen – ACTION SPECTRUMSPECTRUM

How could you measure rate of How could you measure rate of photosynthesis?photosynthesis?

Measure disappearance of reactants - Measure disappearance of reactants - carbon dioxide or watercarbon dioxide or water

Measure appearance of products – oxygen Measure appearance of products – oxygen or glucoseor glucose

Measure change in energy of the systemMeasure change in energy of the system

Oxygen is easiest to measure – use a Oxygen is easiest to measure – use a water plant and count the bubbles that rise water plant and count the bubbles that rise to the surfaceto the surface

ENGLEMANN - 1883ENGLEMANN - 1883

Grew filamentous algae under light that Grew filamentous algae under light that had been passed through a prismhad been passed through a prism

Aerobic bacteria grew in greatest Aerobic bacteria grew in greatest numbers on part of filament exposed to numbers on part of filament exposed to red light and blue light – very little on part red light and blue light – very little on part exposed to green lightexposed to green light

ENGLEMANN - 1883ENGLEMANN - 1883

ConclusionConclusion

Chlorophyll’s action spectrum overlaps its Chlorophyll’s action spectrum overlaps its absorption spectrumabsorption spectrum

These are the wavelengths of light that These are the wavelengths of light that power photosynthesispower photosynthesis

CHLOROPHYLL CHLOROPHYLL aa

Only chlorophyll Only chlorophyll aa can participate directly can participate directly in the light reactions – no chlorophyll a in the light reactions – no chlorophyll a means no photosynthesismeans no photosynthesis

Color – blue-greenColor – blue-green

Chlorophyll Chlorophyll bb

An ACCESSORY PIGMENTAn ACCESSORY PIGMENT Its absorption spectrum is not identical to Its absorption spectrum is not identical to

chlorophyll a; increases the amount of chlorophyll a; increases the amount of visible light that can be used for visible light that can be used for photosynthesisphotosynthesis

Transfers the energy it absorbs to Transfers the energy it absorbs to chlorophyll achlorophyll a

Color – yellow-green Color – yellow-green

CarotenoidsCarotenoids An ACCESSORY PIGMENTAn ACCESSORY PIGMENT Its absorption spectrum is not identical to Its absorption spectrum is not identical to

chlorophyll a or b; increases the amount of chlorophyll a or b; increases the amount of visible light that can be used for visible light that can be used for photosynthesisphotosynthesis

Transfers the energy it absorbs to chlorophyll Transfers the energy it absorbs to chlorophyll aa

Color – yellow to orangeColor – yellow to orange Also “sun screen” to protect plant DNA from Also “sun screen” to protect plant DNA from

UV radiationUV radiation