Capturing the Energy In Light Photosynthesis Capturing the Energy In Light

Photosynthesis The process by which autotrophs capture energy from sunlight and store it within organic compounds (carbohydrates such as glucose and starch). 6CO2 + 6H2O C6H12O6 + 6O2 sunlight Carbon Dioxide Water Glucose Oxygen

What is an autotroph? Eukaryotic organisms that can produce their own food using sunlight energy. Examples: plants, algae, euglena…

Heterotrophs Heterotrophs have to consume other organisms to meet their energy needs. What happens if a heterotroph attempts to absorb sunlight energy.

Investigating Photosynthesis Many Scientists Have Contributed To Understanding Photosynthesis Early Research Focused On The Overall Process Later Researchers Investigated The Detailed Chemical Pathways

Early Questions on Plants Several Centuries Ago, The Question Was: Does the increase in mass of a plant come from the air? The soil? The Water?

Van Helmont’s Experiment 1643 Planted a seed into A pre-measured amount of soil and watered for 5 years Weighed Plant & Soil. Plant Was 75 kg, Soil The Same. Concluded Mass Came From Water

Priestley’s Experiment 1771 Burned Candle In Bell Jar Until It Went Out. Placed Sprig Of Mint In Bell Jar For A Few Days. Candle Could Be Relit And Burn. Concluded Plants Released Substance (O2) Necessary For burning.

Ingenhousz’s Experiment 1779 Repeated Priestly experiment with & without sunlight

Results of Ingenhousz’s Experiment Showed That Priestley’s Results Only Occurred In The Presence Of Sunlight. Light Was Necessary For Plants To Produce The “Burning Gas” or oxygen

Julius Robert Mayer 1845 Proposed That Plants can Convert Light Energy Into Chemical Energy

Samuel Ruben & Martin Kamen 1941 Used Isotopes To Determine That The Oxygen Liberated In Photosynthesis Comes From Water RUBIN KAMEN

Melvin Calvin 1948 First to trace the path that carbon (CO2) takes in forming Glucose Does NOT require sunlight Called the Calvin Cycle or Light Independent Reaction Also known as the Dark Reaction

Energy for Life Processes Photosynthesis is a biochemical pathway Involves a complex series of chemical reactions in which the product of one reaction is consumed in the next reaction. Autotrophs use the biochemical pathways of photosynthesis to manufacture organic compounds from CO2 and water. In the process molecular oxygen O2 is released.

Energy for Life Processes Energy stored in organic compounds is released in a process called cellular respiration. Both autotrophs and heterotrophs perform cellular respiration. In cellular respiration organic compounds are combined with O2 to produce ATP. CO2 and water are the waste products of cellular respiration.

Photosynthetic Reactions

Light Reactions The initial reactions in photosynthesis are collectively known as the light dependent reactions. Begin with the absorption of light in chloroplasts. Chloroplasts are organelles present in plant cells and algae (some algae may have only one while a cell in a plant may have as many as 50).

Structure of the Chloroplast Double membrane organelle Outer membrane smooth Inside the inner membrane are another system of membranes arranged as flattened stacks of connected sacs called thylakoids Thylakoid stack is called the granun (grana-plural) Gel-like material around grana called stroma

Light and Pigments Energy From The Sun Enters Earth’s Biosphere As Photons Photon = Light Energy Unit Light Contains A Mixture Of Wavelengths Different Wavelengths Have Different Colors

Light and Pigments Light from the sun appears white When passed through a prism the white light’s component colors become visible, this is the visible spectrum Component colors may be transmitted, reflected or absorbed. Pigments are compounds that absorb light. Different colored pigments absorb different wavelengths of light.

Chloroplast Pigments A variety of pigments are located in the membrane of thylakoids. Chlorophyll The most important are chlorophylls Chlorophyll a and chlorophyll b are the most common. Neither abosorb much green light. Chlorophyll a is directly involved in the light reaction. Chlorophyll b assists in capturing light energy and is called an accessory pigment.

Carotenoids – Accessory pigments found in the thylakoid membranes yellow, brown, and orange in color Absorb colors that chlorophyll cannot absorb. Usually hidden by the overabundance of chlorophyll. Apparent in fruits and in fall leaves when plants lose chlorophyll.

Light Independent (dark) reactions. Use energy carrying compounds produced from the light dependent reactions and CO2 to make carbohydrates (including glucose).