Photosynthesis Chapter 10

Photosynthesis Process that converts solar energy into chemical energy Directly or indirectly, photosynthesis food for almost the entire living world

Photosynthesis Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO H 2 O + Light energy  C 6 H 12 O O H 2 O

 Autotrophs= produce own food  Autotrophs are the producers of the biosphere, producing organic molecules from CO 2 and other inorganic molecules  Almost all plants are photoautotrophs  Uses the energy of sunlight to make organic molecules

Photosynthesis Initial Source of Energy for Most Systems Primary Producers= source of organic molecules for most other organisms – Terrestrial Systems= Plants – Aquatic Systems= Phytoplankton Consumers= heterotrophs= consume organic material from other organisms – Cellular Respiration Primary Producers Consumers Decomposers

Photosynthesis Plants use ~50% of sugars produced for cellular respiration to fuel own cellular processes Rest of sugar is used as building blocks for other organic molecules Ultimately, consumed by heterotrophs and used for cellular respiration

(a) Plants (b)Multicellular alga (c)Unicellular protists (d) Cyanobacteria (e)Purple sulfur bacteria 10  m 1  m 40  m Figure 10.2 Primary Producers: plants, algae, protists, and some prokaryotes These organisms feed not only themselves but also most of the living world.

 Heterotrophs are the consumers of the biosphere  Heterotrophs= obtain organic material from other organisms  Almost all heterotrophs, including humans, depend on photoautotrophs for food and O 2 Consumers

Humans rely on primary producers for other types of fuel The Earth’s supply of fossil fuels was formed from the remains of organisms that died hundreds of millions of years ago – In a sense, fossil fuels represent stores of solar energy from the distant past Biofuels

Chloroplasts Energy-producing organelle in plants Converts solar energy into chemical energy – Contains green pigment known as chlorophyll Light absorbing pigment Gives leaves the green color – All green parts of plant have chloroplasts Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf – Cells can have chloroplasts

Mesophyll Leaf cross section Chloroplasts Vein Stomata Chloroplast Mesophyll cell CO 2 O2O2 20  m Figure 10.4a

Outer membrane Intermembrane space Inner membrane 1  m Thylakoid space Thylakoid Granum Stroma Chloroplast Figure 10.4b

Photosynthesis Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO H 2 O + Light energy  C 6 H 12 O O H 2 O  Chloroplasts split H 2 O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product

Figure 10.5 Reactants: Products: 6 CO 2 6 H 2 O 6 O 2 12 H 2 O C 6 H 12 O 6 Photosynthesis

Endergonic reaction – Sunlight Energy stored in bonds of glucose Redox Reaction – Photosynthesis reverses the direction of electron flow compared to respiration – Oxidation= loss of electrons Water is oxidized – Reduction= gain of electrons Carbon dioxide is reduced

Figure 10.UN01 Energy  6 CO 2  6 H 2 O C 6 H 12 O 6  6 O 2 becomes reduced becomes oxidized Photosynthesis

Photosynthesis occurs in 2 stages Light Reactions (“photo) – Occurs in thylakoids – Split H 2 O – Release O 2 – Reduce NADP + to NADPH – Generate ATP from ADP by photophosphorylation

Light Light Reactions Chloroplast NADP  ADP + P i H2OH2O Figure

Light Light Reactions Chloroplast ATP NADPH NADP  ADP + P i H2OH2O O2O2 Figure

Photosynthesis occurs in 2 stages Dark Reactions: Calvin Cycle (“synthesis”) – Occurs in the stroma Uses ATP and NADPH from light reaction to reduce CO 2 and produce sugars Begins with carbon fixation, incorporating CO 2 into organic molecules

Light Light Reactions Calvin Cycle Chloroplast ATP NADPH NADP  ADP + P i H2OH2O CO 2 O2O2 Figure

Light Light Reactions Calvin Cycle Chloroplast [CH 2 O] (sugar) ATP NADPH NADP  ADP + P i H2OH2O CO 2 O2O2 Figure