2 Photosynthesis occurs in chloroplasts inplant cells• Chloroplasts consist of an envelope of twomembranes, which encloses an inner compartmentfilled with a thick fluid called stroma that containsa system of interconnected membranous sacscalled thylakoids.© 2015 Pearson Education, Inc.7.2 Photosynthesis occurs in chloroplasts inplant cells• Thylakoids• are often concentrated in stacks called grana and• have an internal compartment called the thylakoidspace, which has functions analogous to theintermembrane space of a mitochondrion in thegeneration of ATP.© 2015 Pearson Education, Inc.7.2 Photosynthesis occurs in chloroplasts inplant cells• Thylakoid membranes also house much of themachinery that converts light energy to chemicalenergy.• Chlorophyll molecules• are built into the thylakoid membrane and• capture light energy.© 2015 Pearson Education, Inc.2019/11/198© 2015 Pearson Education, Inc.Figure 7.2-2Mesophyll CellChloroplastGranumInner and outermembranesThylakoidThylakoid spaceStroma© 2015 Pearson Education, Inc.Figure 7.2-3Mesophyll CellChloroplast© 2015 Pearson Education, Inc.Figure 7.2-4ChloroplastGranumStroma2019/11/1997.3 Scientists traced the process ofphotosynthesis using isotopes• Scientists have known since the 1800s that plantsproduce O2. But does this oxygen come fromcarbon dioxide or water?• For many years, it was assumed that oxygen wasextracted from CO2taken into the plant.• However, later research using a heavy isotope ofoxygen, 18O, confirmed that oxygen produced byphotosynthesis comes from H2O.© 2015 Pearson Education, Inc.© 2015 Pearson Education, Inc.Figure 7.37.3 Scientists traced the process ofphotosynthesis using isotopes• Experiment 1: 6 CO2 12 H2O → C6H12O6 6 H2O 6 O2• Experiment 2: 6 CO2 12 H2O → C6H12O6 6 H2O 6 O2© 2015 Pearson Education, Inc.2019/11/19107.4 Photosynthesis is a redox process, as iscellular respiration• Photosynthesis, like respiration, is a redox(oxidation-reduction) process.• CO2 becomes reduced to sugar as electrons, alongwith hydrogen ions (H+) from water, are added to it.• Water molecules are oxidized when they loseelectrons along with hydrogen ions.