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 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.

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

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 Photosynthesis, chloroplasts, and the structure of a leaf

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 An overview of photosynthesis

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 The electromagnetic spectrum, visible light and chlorophyll

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”

Carotenoids in Tomato

Figure 7.5 Photosynthesis and Structure of a Plant leaf

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 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 Photosynthesis: Fundamental description

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)

Figure 7.10 Foxglove

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 The relationship between photosynthesis and cellular respiration