1. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany CONCEPTS IN BIOLOGY TWELFTH EDITION Enger Ross Bailey CHAPTER 7

2. 2 7.1 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. Figure 7.1 Photosynthetic Autotrophs (a) Algae (b) Plants

4. 4 7.2 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. 5 Photosynthesis, chloroplasts, and the structure of a leaf

6. 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. 7 An overview of photosynthesis

8. 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 (p. 132) – Two forms; a and b – Absorb light in the blue and red portions of the spectrum – Reflect green wavelengths

9. 9 The electromagnetic spectrum, visible light and chlorophyll

10. 10 Other types of pigments Accessory pigments (p. 132) – 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 (p. 133r) – Some of their electrons become “excited”

11. Carotenoids in Tomato

12. Figure 7.5 Photosynthesis and Structure of a Plant leaf

13. 13 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.

14. 14 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 (p. 134) – Combines C0 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

15. 15 Photosynthesis: Fundamental description

16. 16 7.4 Other aspects of plant metabolism Plant cells are able to manufacture organic molecules from inorganic molecules – Fats, proteins and other carbohydrates – Toxins for their protection (p. 139) Many of these are useful medicines. (p. 139) Some can be used as natural insecticides. – Vitamins Molecules that we cannot make, but that we need (p. 139)

17. Figure 7.10 Foxglove

18. 18 7.5 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.

19. 19 The relationship between photosynthesis and cellular respiration