Photosynthesis Chapter 6

Obtaining Energy  Almost all of the energy in living systems comes from the sun.

Obtaining Energy Gets energy directly Gets energy indirectly AUTOTROPHS HETEROTROPHS

PHOTOSYNTHESIS Converting light energy into chemical energy

Visible Spectrum Light can be reflected, transmitted or absorbed by the object Pigments: compounds that absorb light. This subtracts them from the visible spectrum

Visible Spectrum  Chlorophyll is a pigment  Reflects green  Absorbs blue and red  Carotenoids are accessory pigments  Absorb green  Enable plants to capture more energy

PHOTOSYNTHESIS 6CO 2 + 6H 2 O C 6 H O 2 light energy Reactants for photosynthesis Products of photosynthesis Products of cellular respiration Reactants for cellular respiration

PHOTOSYNTHESIS Light Reactions: Stage 1 o Light energy (absorbed from the sun) is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH.

PHOTOSYNTHESIS  Calvin Cycle: Stage 2  Organic compounds are formed using CO 2 and the chemical energy stored in ATP and NADPH.

How it all works Light Reactions followed by Dark Reactions

Light Reactions  In the chloroplasts, thylakoids are arranged as flattened sacs called grana. Surrounding the grana is a solution called stroma.

Light Reactions  Need sunlight  Occur in the membrane of the thylakoid  Light reactions begin by pigments absorbing light (starts the electron transport chain)

Light Reactions  Water is split by an enzyme to keep the reaction going  Hydrogen ions (H+) from water are used to make ATP in a process called chemiosmosis  Oxygen from water is released

Calvin Cycle: Dark Reactions No sunlight is needed Series of enzyme-assisted chemical reaction that produces a three-carbon sugar

Calvin Cycle: Dark Reactions  Carbon atoms from carbon dioxide (CO 2 ) in the atmosphere are bonded or “fixed” into organic compounds  Occurs in the stroma of the chloroplast

Summary of Photosynthesis

Alternative Pathways  CAM and C4 pathways  Hot, dry environment

Factors that Affect Photosynthesis With your table partner, interpret the graph provided to you and determine how either: Light intensity Carbon dioxide levels Temperature affects photosynthesis. Be prepared to share.