Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without no

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

2. 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.

3. 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.

4. Photosynthesis, Chloroplasts, and the Structure of a Leaf

5. 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.

6. An Overview of Photosynthesis

7. 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

8. The Electromagnetic Spectrum, Visible Light and Chlorophyll

9. 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”

10. 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.

11. 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

12. Photosynthesis: Fundamental Description

13. 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.

14. 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.

15. 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.

16. 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.

17. PS II and I: How They Interact

18. 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

19. 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.

20. The Calvin Cycle

21. 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

22. 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

23. 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.

24. The Relationship between Photosynthesis and Cellular Respiration