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 CO H 2 0 C 6 H O 2 carbon dioxide water glucose oxygen 6 CO H 2 0 C 6 H O 2 + 6H 2 0

HOW DO PLANTS ACQUIRE ENERGY AND RAW MATERIALS? H 2 O enters roots Leaves are “solar collectors” Organ of photosynthesis CO 2 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

CHLOROPLAST LIGHT REACTIONS? CALVIN CYCLE? Chlorophyll and other pigments?

LIGHT  a form of energy called electromagnetic radiation  Kinetic energy  It has a dual nature: behaves like a wave and behaves like a discrete particle

Light - waves  Light causes disturbance in electric and magnetic fields – like a pebble thrown into water  Each form of electromagnetic radiation has a specific wavelength and frequency

Light - particles  Photon – particles of light  NOT A TANGIBLE PARTICLE RATHER A DISCRETE BUNDLE OF ENERGY THAT BEHAVES LIKE A PARTICLE  Amount of energy is INVERSELY related to wavelength – the shorter the wavelength the greater the energy of the photon

VISIBLE SPECTRUM – nm – MOST IMPORTANT IN BIOLOGY

WHEN LIGHT MEETS MATTER...  Light is reflected – We see the wavelengths of light that are reflected  Light is transmitted – Passes through the object  Light is absorbed – WORK MAY BE DONE  PIGMENT – substance that absorbs light  Chlorophyll is green because it reflects green wavelengths and absorbs or transmits other wavelengths

THINK ABOUT IT  Why do some objects appear white?  Why do some objects appear black?  Which car remains cooler in summer – one with white paint or one with black paint?

SPECTROPHOTOMETERS  Device for measuring amount of light absorbed or transmitted by a pigment

ABSORPTION SPECTRUM  Chlorophyll a absorbs red and blue light best; very little green light is absorbed  Other plant pigments have different molecular structures – absorb different wavelengths

BUT HOW DO WE KNOW WHICH WAVELENGTHS ARE IMPORTANT IN PHOTOSYNTHESIS?  Grow plants under different colors of light and see which ones stimulate greatest amount of oxygen – ACTION SPECTRUM  How could you measure rate of photosynthesis?

 Measure disappearance of reactants - carbon dioxide or water  Measure appearance of products – oxygen or glucose  Measure change in energy of the system  Oxygen is easiest to measure – use a water plant and count the bubbles that rise to the surface

ENGLEMANN  Grew filamentous algae under light that had been passed through a prism  Aerobic bacteria grew in greatest numbers on part of filament exposed to red light and blue light – very little on part exposed to green light

ENGLEMANN

Conclusion  Chlorophyll’s action spectrum overlaps its absorption spectrum  These are the wavelengths of light that power photosynthesis

CHLOROPHYLL a  Only chlorophyll a can participate directly in the light reactions – no chlorophyll a means no photosynthesis  Color – blue-green

Chlorophyll b  An ACCESSORY PIGMENT  Its absorption spectrum is not identical to chlorophyll a; increases the amount of visible light that can be used for photosynthesis  Transfers the energy it absorbs to chlorophyll a  Color – yellow-green

Carotenoids  An ACCESSORY PIGMENT  Its absorption spectrum is not identical to chlorophyll a or b; increases the amount of visible light that can be used for photosynthesis  Transfers the energy it absorbs to chlorophyll a  Color – yellow to orange  Also “sun screen” to protect plant DNA from UV radiation