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Photosynthesis

Photosynthesis. Modes of Obtaining Food. Autotrophs organisms that produce their own food utilizing energy from the environment Heterotrophs Organisms that must consume food for energy. METABOLISM. ANABOLIC REACTIONS Reactions where simple substances join to form complex ones.

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Photosynthesis

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  1. Photosynthesis

  2. Modes of Obtaining Food • Autotrophs • organisms that produce their own food utilizing energy from the environment • Heterotrophs • Organisms that must consume food for energy

  3. METABOLISM • ANABOLIC REACTIONS • Reactions where simple substances join to form complex ones. examples: protein synthesis, photosynthesis

  4. METABOLISM (CONTINUED) • CATABOLIC REACTIONS • Reactions where complex substances are broken down into simpler substances. • Examples – digestion, cellular respiration

  5. METABOLISM (CONTINUED) • Metabolism is the sum total of all anabolic and catabolic activities.

  6. ENERGY REACTIONS • ENDERGONIC REACTIONS – means energy inward – is a reaction that absorbs free energy from its surroundings. Photosynthesis is an example. • EXERGONIC REACTIONS – means energy outward – is a reaction that allows for a net release of energy. Cellular respiration is an example.

  7. Glucose is the main source of energy for living organisms. • Energy is released when glucose is broken down. • The energy is stored in a compound called ATP – adenosine triphosphate.

  8. ATP • ATP consists of an adenine group, ribose and three phosphate groups attached – hence the name – adenosine triphosphate.

  9. Adenine Ribose 3 Phosphate groups Chemical Energy • ATP – adenosine triphosphate • Primary compound used by all organisms as energy currency

  10. Chemical Energy • Energy is stored by adding a phosphate to ADP, making ATP • Energy can be released from ATP by removing a phosphate • This makes ADP (adenosine diphosphate)

  11. ADP↔ATP

  12. Famous Experiments • Jean van Helmont – 1600s • Discovered that the mass of a plant increases without a decrease in the mass of the soil • This means that the plant is getting the materials for growth from elsewhere • CO2 in air, H2O in soil

  13. Famous Experiments • Joseph Priestley – 1700s • Found that a plant produces a gas (oxygen) that allows a candle to be relit in a sealed container

  14. Jan Ingenhousz (1779) • Discovered that aquatic plants produce oxygen bubbles in the light but not in the dark. • Concluded that plants need sunlight to produce oxygen.

  15. Light and Pigments • Pigments (chlorophyll a and b) absorb light energy • Accessory pigments absorb different colors of light

  16. Absorbs: Blue Violet Red Reflects: Green Yellow Chlorophyll Absorption Spectrum

  17. Photosynthesis - DRAW

  18. Photosynthesis Equation • Light energy from sun is used to turn carbon dioxide and water into sugar and oxygen • Produces ALL food and oxygen on Earth!

  19. The “Real” Photosynthesis Sun Light Carbon Dioxide Water Oxygen Glucose Chloroplast

  20. Chloroplasts • Photosynthesis takes place inside chloroplasts (organelle) • Thylakoids • Stacks of membrane sacs – when stacked together referred to as the grana • Light-dependent reaction here • Photosystems are embedded in the thylakoid membranes • Photosystems are made up of clusters of chlorophyll molecules • The two photosystems are: Photosytem I Photosystem II • Stroma • Space between thylakoids and inner membrane • Light-independent (Calvin Cycle) reaction here

  21. Chloroplasts

  22. Light Dependent Reactions • Light Energy is converted to chemical Energy • Light energy is absorbed by chlorophyll (and other pigment molecules) in the grana of the chloroplast (remember – grana is just “stacks” of thylakoid membranes) • This increases the energy level (or excites) certain electrons in the pigments. These electrons are at a higher energy level. • Does chlorophyll ever run out of electrons? NO! Electrons are returned to chlorophyll from the break down of water. • As the electrons of the pigments return to their “unexcited” state, or to a lower energy level, energy is given off.

  23. LIGHT DEPENDENT REACTION (CONTINUED) • Electrons return to a lower energy level by being passed down an electron transport chain. Energy is released from the electron during this time and ATP is formed. The ATP produced in the light reaction will be used in the dark reaction. • Light splits water – (photolysis) - The oxygen is given off – ex – bubbles on a leaf of a water plant. • Hydrogen bonds with NADP+ (Nicotinamid Adenine Dinucleotide Phosphate) • to form NADPH which is used later in the light independent or dark reaction.

  24. NADPH • Electron carrier • Transports high energy electrons around during photosynthesis • Like a school bus – picks up at point A, drops off at point B

  25. LIGHT INDEPENDENT REACTION – DARK REACTION – CALVIN CYCLE • The reaction can occur in light but light is NOT needed for the reaction to occur. ***The reaction was named after Melvin Calvin and each step is controlled by enzymes. ***The light dependent reaction MUST occur before the light independent reaction. ***Occurs in the stroma of the chloroplast (the area between the thylakoids.)

  26. LIGHT INDEPENDENT REACTION OR CALVIN CYCLE (CONTINUED) • Carbon dioxide combines with RuBP (ribulose biphosphate – 5 carbon sugar) • This produces an unstable six carbon sugar • This six carbon sugar splits into two molecules of a 3 carbon sugar called PGA (or phosphoglyceric acid.)

  27. LIGHT INDEPENDENT REACTION (CONTINUED) • PGA combines with the hydrogen from NADPH (From the light dependent reaction when water broke apart) and forms PGAL. • PGAL formation requires a large amount of energy which is supplied by ATP (formed during the light dependent reaction.)

  28. LIGHT INDEPENDENT REACTION (CONTINUED) USES FOR PGAL: • Some PGAL can be used directly as an energy source for cell activity. • Most of the PGAL molecules are used to form more RuBP to start the Calvin Cycle all over again. • Some PGAL molecules are used to form glucose. (Combine 2 PGAL molecules, remove the phosphate and replace it with a hydrogen atom for each PGAL molecule and you will have glucose.)

  29. INFLUENCES ON THE RATES OF PHOTOSYNTHESIS • Amount of light – the rate of photosynthesis will increase as the light intensity increases up to a point (9,000 lumens of light intensity.) • Temperature – the rate of photosynthesis will increase until about 90 degrees F. Then the rate will dramatically decrease due to heat denaturing the enzymes. • The amount of available water. A shortage of water can even stop photosynthesis.

  30. Light Dependent Rxn

  31. Light Dependent Rxn • e- passes down an electron transport chain • Energy is released to help pump H+ into inner thylakoid space • Creates a H+ gradient to be used later • e- • More light = more energy to e- • e- jumps off PS I into NADP+ with H+ from water

  32. Light Dependent Rxn • H+ inside thylakoid space exits through a protein called ATP synthase • Energy stored in H+ gradient makes ATP • NADPH and ATP go to Calvin cycle

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