Bell work Do you think photosynthesis could be considered the primary source of energy for life? Explain your answer.

7.1 Sunlight powers life Life on earth is solar-powered. Biologists classify organisms according to how they obtain food. Autotrophs “self-feeder”, also name producers They convert inorganic compounds to organic compounds. Plants use the sun’s energy to convert water and carbon dioxide into sugars. Heterotrophs Organisms that cannot make their own food Also known as consumers Depend on producers

7.2 Food stores chemical energy Energy is the ability to perform work. There are different forms of energy: Kinetic energy Potential energy Thermal energy Chemical energy – depends on the structure of molecules; energy stored in bonds

Energy Endergonic or endothermic reactions Photosynthesis: CO2 + H2O glucose Absorbs energy Feels cold to the touch Exergonic or exothermic reactions Cellular respiration: glucose CO2 + H2O Release energy Feels warm to the touch

Calories The amount of energy required to raise the temperature of 1 gram (g) of water by 1 degree Celsius (°C). 1 kilocalorie = 1000 calories = 1 Calorie food calorie Energy required to raise the temperature to 26 °C 25 °C 1 gram

Photosynthesis

Figure 8-2 Photosynthesis takes place in cellular organelles called chloroplasts. In this sunflower, the greatest numbers of chloroplasts are located in the leaves. Chlorophylls give the chloroplasts—and in turn the leaves—their green color.

Chloroplast Disc-shaped structures are called grana, which are surrounded by the stroma. Each disc-shaped structure is called a thylakoid. In the thylakoid is the chlorophyll and other pigments needed for photosynthesis

Chlorophyll Pigment Photoreceptor Absorbs the energy from the sun

Electromagnetic Spectrum Figure 8-5 Different forms of electromagnetic energy have different wavelengths. Shorter wavelengths have more energy than longer wavelengths.

Types of Chlorophyll These two kinds of chlorophyll complement each other in absorbing sunlight. Plants can obtain all their energy requirements from the blue and red parts of the spectrum, however, there is still a large spectral region, between 500-600nm, where very little light is absorbed. This light is in the green region of the spectrum, and since it is reflected, this is the reason plants appear green.

Figure 8-7 The laboratory technique of paper chromatography can be used to analyze the pigments in a leaf.

Figure 8-4 This "road map" shows the two main stages of photosynthesis: the light reactions, which occur in the thylakoids, and the Calvin cycle, which occurs in the stroma. Double membrane Stroma Grana Thylakoid

Light-dependent Reactions: Photosystems I and II Figure 8-8 When light strikes the chloroplast, pigment molecules absorb the energy. This energy jumps from molecule to molecule until it arrives at the reaction center.

Excited electrons http://earthguide.ucsd.edu/earthguide/diagrams/absorption/absorption.html

Light-dependent reactions Hydrolysis = Break water Steps of e-: Water Photosystem I Electron Transport Chain Photosystem II NADPH Movement of e- powers ATP formation

Figure 8-11 In this "construction analogy" for the light reactions, the input of light energy is represented by the large yellow mallets. The light energy boosts the electrons up to their excited states atop the platform in each photosystem. The energy released as the electrons move down the electron transport chain between the photosystems is used to pump hydrogen ions across a membrane and produce ATP.

Light-dependent Reactions Overview What do I need? water, sunlight What do I get? ATP, NADPH (energy molecules) oxygen

Light-independent reaction: Calvin Cycle 3PGA = 3-phosphoglyceric acid G3P = glyceraldehyde phosphate

Calvin Cycle NADPH and ATP give the energy to be stored in glucose. What do I need? ATP, NADPH and 6 carbon dioxide molecules What do I get? Glucose (1 glucose for every 6 CO2)

Photosynthesis Overview C6H12O6 Figure 8-14 The light reactions and the Calvin cycle together convert light energy to the stored chemical energy of sugar. The plant can use the sugar to build other organic molecules.

Photosynthesis Chemical Reaction Overall formula: 6CO2 + 6H2O + sunlight  C6H12O6 + 6O2