Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

Photosynthesis and Life During photosynthesis Organisms use the energy of light to build high-energy organic molecules. Plants, algae, and some bacteria can do this. Can make their own food using light Called photosynthetic autotrophs 99.9% of all life on earth relies on photosynthesis for their energy. Heterotrophs eat autotrophs. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

An Overview of Photosynthesis Photosynthesis occurs in Chloroplasts Contain the pigment that captures the energy in light Chlorophyll Found in membranous sacs called grana A stack of grana is called a thylakoid. Grana are suspended in a fluid-filled space called the stroma. During photosynthesis The energy in light is used to make ATP. The energy in ATP is used to make organic molecules such as glucose. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Photosynthesis, Chloroplasts, and the Structure of a Leaf Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

An Overview of Photosynthesis The chemical equation of photosynthesis: Light energy + carbon dioxide + water  glucose and oxygen The three events of photosynthesis Light-capturing events The pigment chlorophyll absorbs certain wavelengths of light and some of its electrons become excited. Light-dependent reactions These reactions use the energy in the excited electrons to make ATP and NADPH. Light-independent reactions ATP and NADPH from the light reactions is used to reduce carbon dioxide to make glucose. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

An Overview of Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light-Capturing Events: Fundamental Concepts Visible light Combinations of different wavelengths of light Can be seen as different colors Pigments are molecules that absorb light. Each pigment absorbs certain wavelengths of light. The wavelengths that they do not absorb, they reflect. This is the color we see. In photosynthesis, only the wavelengths that are absorbed can be used to do work. Chlorophyll: The main photosynthetic pigment Two forms: a and b Absorb light in the blue and red portions of the spectrum Reflect green wavelengths Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Electromagnetic Spectrum, Visible Light and Chlorophyll Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Other Types of Pigments Accessory pigments Include carotenoids Absorb blue and green wavelengths Reflect orange and yellow Found in leaves, masked by chlorophyll In the autumn, when chlorophyll disintegrates, accessory pigments show through (fall colors). Chlorophyll + accessory pigments Organized into photosystems that harvest the energy from many wavelengths of light Found in thylakoids of the chloroplasts When pigments absorb light Some of their electrons become “excited” Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light-Dependent Reactions: Fundamental Concepts The excited electrons from chlorophyll Are passed through an electron transport chain The energy released is used to pump protons up their concentration gradient. When protons diffuse through ATP synthase, ATP is made. Excited electrons passed to NADP+ to make NADPH Water is split Electrons are donated to chlorophyll to replace the donated electrons. Oxygen is produced. Occurs in the thylakoid membrane ATP and NADPH move to the stroma to be used in the dark reactions. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light-Independent Reactions: Fundamental Concepts The ATP and NADPH from the light-dependent reactions Provide the energy and electrons needed to build sugar from carbon dioxide CO2 is captured by an enzyme called RuBisCO Combines CO2 with ribulose to form a 6-carbon molecule This is immediately split into two 3-C molecules. NADPH is used to reduce these molecules. Glyceraldehyde-3-phosphate is formed. Can be used to make sugars, proteins, or fats Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Photosynthesis: Fundamental Description Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light-Capturing Events: The Details Packaged as photons Each photon has a distinct wavelength. The energy in a photon is related to its wavelength. When a photon hits a pigment molecule, electrons are excited. This means that the electrons jump up to a higher energy level. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light-Capturing Events: The Details Continued Photosystems Structures in which the light-capturing events take place Found in the thylakoid membranes Made up of antenna complexes and a reaction center Networks of chlorophyll and accessory pigments Capture the energy in many different wavelengths of light and pass it to the reaction center The reaction center is a special chlorophyll molecule that passes its excited electrons to an electron acceptor. There are two photosystems, I and II. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light Dependent Reactions: The Details Photosystem II (PSII) Occurs first Donates its excited electrons to the electron transport chain Splits water to replace the electrons it donated O2 is released. Photosystem I (PSI) Occurs second Donates its excited electrons to NADP+ to form NADPH NADPH released into the stroma Accepts electrons from the electron transport chain to replace the electrons it donated PS I and II are in the thlyakoid membrane. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Electron Transport Chain and ATP Synthesis Between PSII and PSI Electrons are passed through an electron transport chain (ETC). This releases energy. This energy is used to pump protons from the stroma into the thylakoid space. This creates a proton concentration gradient. Protons diffuse through ATP synthase. ATP synthase makes ATP that is released into the stroma. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

PS II and I: How They Interact Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light Independent Reactions: The Details Takes place in the stroma of the chloroplast Uses CO2 (from the atmosphere) ATP and NADPH (from the light-independent reactions) Ribulose (recycled) Also called the dark reactions Also called the Calvin cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Carbon Fixation and Sugar Formation Carbon dioxide gas is combined with a 5-carbon sugar called ribulose. Accomplished with an enzyme called ribulose bisphosphate carboxylase (RuBisCO) Forms a 6-carbon molecule Immediately broken down into two 3-carbon molecules These 3-carbon molecules are Energized by ATP Reduced by NADPH Glyceraldehyde-3-phosphate is formed. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Calvin Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glyceraldehyde-3-phosphate: The Product of Photosynthesis Glyceraldehyde-3-phosphate can be used for many things. Used to make glucose Used to recycle ribulose for the Calvin cycle Used to make the sugars needed to build ATP, DNA, and RNA Can be converted into lipids Can be converted into amino acids to make proteins Can be broken down in glycolysis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Other Aspects of Plant Metabolism Plant cells can use the organic molecules produced in photosynthesis to make Fats, proteins, and other carbohydrates Toxins for their protection Many of these are useful medicines. Some can be used as natural insecticides. Vitamins Molecules that we cannot make, but that we need Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Interrelationships Between Autotrophs and Heterotrophs Autotrophs use the energy in light to make food. Autotrophs use the food they make in cellular respiration. Plants use the sugar they make! Plants use the oxygen they make! Heterotrophs eat the autotrophs. Then use the food from the autotrophs to fuel cellular respiration They also use the excess oxygen given off by autotrophs. All organisms respire! The circle of life: Animals get sugar, oxygen, amino acids, fats, and vitamins from plants. Plants get carbon dioxide, water, and nitrogen from animals. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Relationship between Photosynthesis and Cellular Respiration Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.