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Chapter 8 Photosynthesis 8-1 Energy and Life 8-2 Photosynthesis: An Overview 8-3 The Reactions of Photosynthesis 8-1 Energy and Life Key Concepts: – Where do plants get the energy they need to produce food? – What is the role of ATP in cellular activities? Vocabulary: – Autotroph – Heterotroph – Adenosine triphosphate (ATP) Autotrophs: (auto = “self”) – Organisms that make their own food (energy). (plants and some bacteria) Heterotrophs: (hetero = other) – Obtain energy from food they consume. Chemical Energy and ATP – Energy can be stored in many forms: Light Heat Electricity Chemical Compounds (BONDS!) ATP – Adenosine TriPhosphate Adenine (N) 5-Carbon Sugar (Ribose) 3-phosphate groups ADP – Adenosine DiPhosphate Adenine (N) 5-Carbon Sugar (Ribose) 2-phosphate groups ATP and Energy ATP- stores energy in living things – JUST ENOUGH energy……. The characteristics of ATP make it an exceptionally useful molecule that is used by all types of cells as their BASIC energy source. Energy is released when ATP is converted to ADP Energy is stored when a phosphate group is added to ADP •Please draw the molecular structure of ATP in your notes Ready to power the cell Energy is stored when a Energy is released when phosphate group is added ATP is converted to ADP to ADP •Is this ATP or ADP? •Is it ready to release or store energy? Use of ATP Ways cells use ATP: Active transport (Sodium/Potassium Pump) Movement in the cell – Organelles moving along the cytoskeleton use energy in the form of ATP ATP: – Efficient in transferring energy – Not very good for storing large amounts of energy long term. Useful for a few seconds – A single molecule of sugar (glucose) stores more than 90 times the chemical energy of a molecule of ATP Cells regenerate ATP by using the energy in carbs like glucose……so more efficient for the cell to keep a small supply of ATP on hand. Review…with the person sitting next to you… What is the difference between ADP and ATP? What happens when a phosphate group is removed from ATP? Is ATP for short term or long term storage of energy (why?) How do the cells regenerate ATP? 8-2 Photosynthesis Key Concepts: – What did the experiments of van Helmont, Priestley, and Ingenhousz reveal about how plants grow? – What is the overall reaction for photosynthesis? – What is the role of light and chlorophyll in photosynthesis? Vocabulary: – Photosynthesis – Pigment – chlorophyll 8-2 Photosynthesis: An Overview Photosynthesis: – Plants use the energy of sunlight to convert water and carbon dioxide into oxygen and high energy carbohydrates (sugars and starches). H2O + CO2 + Sunlight O2 + Carbohydrates (glucose) SCIENCE HISTORY… 3 different scientists helped identify the components of the photosynthesis equation – Van Helmont – Priestley – Ingenhousz Jan Baptiste Van Helmont The Von Helmont Problem QUESTION: Do plants grow by taking material out of the soil? • He put a 2.3 kg. (5 lb.) willow tree in 90.8 kg (200 lbs). of soil. • The tree received only rainwater for five years. • After 5 years, Von Helmont found that the soil only weighed 57 g less than when the experiment began. • The willow tree now weighed 76.8 kg (169 lbs. 3 oz.). What did Helmont conclude was responsible for most of the tree weight gain? -WATER! Is this the only thing responsible? -NO Joseph Priestley In 1772 another Englishman, Joseph Priestly (1733-1804), reported the results of an important experiment. He found that a sprig of mint would not die when placed in air that had been “spent” (used) by burning a candle in it. To the contrary, in such air the plant would grow and the air would then, to his astonishment, again support a candle flame. Priestly inferred that the mint produced a substance that was required for burning. What is that substance? J. Ingenhousz The Dutch physician, Jan Ingenhousz, published Experiments on Vegetables, which supplied experimental evidence stating that the effect observed by Priestly occurred only in sunlight. He showed that only the green parts of plants, especially the leaves, have this capacity. Review…with the person sitting next to you… What were the contributions of… – Van Helmont? – Priestly? – Ingenhousz? (Before the REAL fun begins!) Photosynthesis light 6H2O + 6CO2 ----------> C6H12O6+ 6O2 chlorophyll •Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into oxygen and high energy sugars •C6H12O6 = sugar •Plants use the sugars to produce complex carbohydrates such as starches. Light & Pigment In addition to water and carbon dioxide, plants need light and chlorophyll The sun’s energy travels to earth as light – Colors we see= visible spectrum – Different wavelengths= different colors Chlorophyll=pigment (molecule) in plants Light & Pigment White light is actually a mixture of different wavelengths of light. Plants gather the sun’s energy with light absorbing molecules called PIGMENTS. The plant’s principle pigment is chlorophyll and there are 2 main types: “a” and “b.” – Plants also contain red and orange pigments such as carotene which absorbs light in other areas of the spectrum. Energy absorbed by chlorophyll is transferred directly to electrons in the chlorophyll molecule. These high energy electrons make photosynthesis work. So why are leaves green? •Look at the wavelengths of light that chlorophyll absorbs & uses in photosynthesis •The colors that are left are reflected back and that is what you see. Chlorophyll absorbs mostly red and blue wavelengths of light Since light= energy – Chlorophyll absorbs energy, which is transferred to electrons that can do work Review…with the person sitting next to you… What is the photosynthesis equation? What is the function of chlorophyll? Would a plant grow well in green light? Explain! 8-3 The Reactions of Photosynthesis Key Concepts – What happens in the light-dependent reactions? LIGHT REACTIONS – What happens in the light-independent reactions? DARK REACTIONS Vocabulary – NADP+ / NADPH – ADP / ATP – Chlorophyll – Chloroplast – Glucose – Light Reactions – Dark Reactions In the last section, we learned – Pigments, such as chlorophyll absorb sunlight – Pigments are found in leaf cells – Plant leaves have openings (called stomata) where Carbon Dioxide enters – Water is brought into a plant by the roots light 6H2O + 6CO2 ----------> C6H12O6+ 6O2 chlorophyll CHLOROPLAST CROSS-SECTION This is where photosynthesis occurs… Thylakoid= cluster of proteins and pigments tha capture the sun’s energy – In stacks called grana Stroma= space on the interior of a chloroplast Before we get to the hard stuff… When the sun excites electrons, they increase in energy They are so “hot” that they need an electron carrier – Ex: Hot coals An electron carrier moves high energy electrons from chlorophyll to other molecules (without using much energy itslef) – In photosynthesis, this electron carrier is NADPH – Empty dump truck (NAD+) vs. full dump truck (NADPH) To simplify the very complex process of photosynthesis, we are going to set up the 2 reactions (Light and Dark) as a chart in our notes. NADP-H H20 CO2 ATP Light “Dark” Glucose Reactions Reactions C6H12O6 Thylakoids Stroma NADP+ O2 H20 ADP (waste) (waste) Equation for Photosynthesis sunlight 6H2O + 6CO2 ----------> C6H12O6+ 6O2 chlorophyll The Light Reactions: USE PRODUCE Water Oxygen (O2) ADP ATP NADP+ NADPH Light Energy Write this info in your notes! The Dark Reactions: USE PRODUCE Carbon Dioxide (CO2) Glucose ATP ADP NADPH NADP+ Factors Affecting Photosynthesis Water supply Temperature – Some of the enzymes function best between 0-35 degrees Celsius. Intensity of light – As light intensity increases, so does the rate of photosynthesis (to a point) Review Which reaction is “light independent”? What is the name of the electron carrier in photosynthesis? What are the 3 things needed for the Dark Reaction to occur? What is the main product of photosynthesis? What 2 things are “recycled” back to the light reaction?
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