Photosynthesis Chapter 10
Photosynthesis • Converting solar energy (light) into chemical energy (organic compounds) • Performed by autotrophs -- the producers of the biosphere
Photoautotrophs • Plants are photoautotrophs : use energy of sunlight to make organic molecules from water and carbon dioxide Figure 10.1
Photosynthesis • Occurs in plants, algae, certain other protists, and some prokaryotes These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical globules) (c, d, e: LMs). (a) Plants (b) Multicellular algae (c) Unicellular protist 10 μ m 40 μ m (d) Cyanobacteria 1.5 μ m (e) Purple sulfur bacteria Figure 10.2
Heterotrophs • Heterotrophs obtain organic material from other organisms • Consumers (like us!)
The sites of photosynthesis Stomata, mesophyll, veins… Vein Leaf cross section Figure 10.3 Mesophyll CO 2 O 2 Stomata
Thylakoids, grana, stroma… Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm
The Overall Reaction 6 CO 2 + 12 H 2 O + Light energy → C 6 H 12 O 6 + 6 O 2 + 6 H 2 O
Where does everything come from??? 6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6 H 2 O 6 O 2 Figure 10.4
Photosynthesis is a Redox Reaction • Remember cellular respiration: • In photosynthesis: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes reduced becomes oxidized
Two Processes • The light reactions • Occur in the grana (thylakoids) • In: H 2 O, sunlight • Out: O 2 , ATP, NADPH • The dark reactions (Calvin Cycle) • Occur in the stroma • In: ATP, NADPH, CO 2 • Out: Sugar
An Overview H 2 O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP + ADP + P O 2 Figure 10.5 ATP
Purpose of the Light Reaction • To convert solar energy into chemical energy • In the form of high energy electrons stored as • ATP • NADPH
Light • Electromagnetic energy, in the form of waves • Wavelength : the distance between crests; the smaller the wavelength, the higher the energy • The spectrum Gamma rays X-rays UV Infrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m 380 450 500 550 600 650 700 750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy Figure 10.6
Visible Light • The color we can see • We see what is reflected • Photosynthesis is done with visible light waves
Pigments • Determine what light waves are absorbed • Spectrophotometer : sends light through pigments and measures the light that is transmitted • Gives you an absorption spectrum
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