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7-1 Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

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Presentation on theme: "7-1 Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes."— Presentation transcript:

1 7-1 Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

2 Photosynthesis animation mwx88 mwx88 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-2

3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-3 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.

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-4 An Overview of Photosynthesis Photosynthesis occurs in – Chloroplasts Contain the pigment that captures the energy in light – Chlorophyll – Found in membranous sacs called thylakoids – A stack of thylakoid is called a granum (pl. grana). – 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.

5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-5 Photosynthesis, Chloroplasts, and the Structure of a Leaf

6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-6 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.

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-7 An Overview of Photosynthesis

8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-8 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

9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7-9 The Electromagnetic Spectrum, Visible Light and Chlorophyll

10 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”

11 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.

12 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 CO 2 is captured by an enzyme called RuBisCO – Combines CO 2 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

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

14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Light-capturing Events: The Details Light – 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.

15 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.

16 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 O 2 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.

17 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.

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

19 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 – CO 2 (from the atmosphere) – ATP and NADPH (from the light-independent reactions) – Ribulose (recycled) Also called the dark reactions Also called the Calvin cycle

20 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 bisphospate 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.

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

22 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

23 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

24 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. – Autuotrophs 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.

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


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