Presentation on theme: "Photosynthesis. Overview All energy on earth comes from the sun. We depend on: –Plants –Algae (underwater plants) –Cyanobacteria (photosynthetic bacteria)"— Presentation transcript:
Leaves and Leaf Structure The Raw Materials of Photosynthesis Enter the Cells of the Leaf –Water and Carbon Dioxide The Products of Photosynthesis Leave the Leaf –Sugar and Oxygen
Overview Carbon dioxide and water are taken in by plants Plants absorb light energy and convert it to a usable form. –ATP Energy is used to “fix” the carbon in carbon dioxide into sugar molecules –Chemical energy Sugar is converted to starch and stored for use by the plant, and by animals when they eat plants.
Photosynthetic Reactions The Overall Equation for Photosynthesis Is Deceptively Simple In Fact, a Complex Set of Physical and Chemical Reactions must Occur in a Coordinated Manner for the Synthesis of Carbohydrates To Produce a Sugar Molecule such as Sucrose, Plants Require nearly 30 Distinct Proteins that Work within a Complicated Membrane Structure
Organelles in a Plant Cell Location of Photosynthesis? Chloroplasts
Have TWO membranes –A “bi-bilayer!” The inner membrane is called the thylakoid. The thylakoid is folded and looks like stacks of coins called granum (grana singular). The stroma is the space surrounding the granum
The Process of Photosynthesis does NOT Happen all at Once; rather it occurs in TWO STAGES:
STAGE 1 - CALLED THE LIGHT REACTIONS OR LIGHT DEPENDENT REACTIONS. Energy is Captured from Sunlight. Water is Split into Hydrogen Ions, Electrons, and Oxygen (O 2 ). The O 2 Diffuses out of the Chloroplasts (Byproduct). The Light Energy is Converted to Chemical Energy, which is Temporarily Stored in ATP and NADPH.
STAGE 2 - CALLED THE CALVIN CYCLE. The Chemical Energy Stored in ATP and NADPH powers the formation of Organic Compounds (Sugars), Using Carbon Dioxide, CO 2.
How plants harness energy from sunlight… Photosynthetic pigments Chlorophyll a – the “main” photosynthetic pigment Chlorophyll b Accessory pigments.. Carotenoids
Chloroplasts Chlorophyll molecules are embedded in the thylakoid membrane Act like a light “antenna” These molecules can absorb sunlight energy.
Photosynthetic pigments are arranged as “photosystems”
2 Photosystems Light reactions elevate electrons in 2 steps (PS II & PS I) Photosystem II generates energy as ATP Photosystem I generates reducing power as NADPH
Electron Transfer The energy changes of electrons as they flow through the light reactions are analogous to the cartoon. As complicated as the scheme is, don’t lose track of its functions: The light reactions use solar power to generate ATP and NADPH which provide chemical energy and reducing power to the sugar making reactions.
Light (dependent) Reactions Happen ONLY in sunlight –Hence they depend on light! 1.Light is absorbed by chlorophyll molecules 2.The energy generates molecules of ATP
Light Independent Reactions (formerly the “dark reactions”) Happen in sunlight, and in the dark. –Hence “independent of light” 1.ATP generated by sunlight drives the Calvin Cycle. 2.Monosaccarides (eg. glucose) are manufactured in the cycle. 3.Monosaccarides are used to “build” polysaccharides (eg. Starch).
Light Independent Reactions ‘Calvin Cycle’ ‘Carbon Reactions Pathway’ Do not Require Light Energy to Occur –Do Require Energy Captured by Light Reactions