PhotosynthesisChapter 8

Light & Color

Primary colors of light: red, green, blue White light = equal “amounts” of red, green, and

blue Pigments absorb certain colors of light and reflect

others Primary colors of pigment: yellow, cyan, magenta

Black = equal amounts of yellow, cyan, and magenta White = no pigment

Sun produces white light Objects appear the color of the wavelength of light

they reflect

Plant Pigments

Plants contain a number of pigments, yielding a variety of colors and shades Chlorophyll a is the primary pigment involved in

photosynthesis Blue-green in color

Accessory pigments = all other pigments

The Chloroplast

Chlorophyll and Photosystems

Chlorophyll is embedded in the thylakoid membrane

Photosystem = collectionof pigments inthylakoid membrane

Photosystems captureenergy from the sun tocarry out reactions ofphotosynthesis

Overview of Photosynthesis

Overall equation:

12 H2O + 6 CO2 6 H2O + 6 O2 + C6H12O6

Photosynthesis is a two-stage process: The Light Reactions

Hydrolyze water to obtain electrons and produce ATP and NADPH, oxygen is a waste product

The Calvin Cycle Products of the light reactions power this stage to

create sugar from carbon dioxide

lightenergy

The Light Reactions

1. Water is hydrolyzed by chlorophyll a when excited by light – Photosystem II

Electrons are liberated Two split waters = one oxygen molecule

2. Electrons pass through a series of proteins in the thylakoid membrane producing ATP

Electron Transport Chain

3. Electrons used to reduce NADP+ into NADPH – Photosystem I

NADPH is an electron carrier that delivers electrons to the Calvin Cycle

The Light Reactions

The Calvin Cycle

1. Carbon dioxide is fixed to RuBP (ribulose biphosphate), a 5-carbon molecule

Catalyzed by RuBisCO

2. Newly created 6-carbon molecule with two phosphates splits apart

3-carbon molecules created

3. ATP hydrolyzed to phosphorylate the 3-carbon molecule

4. NADPH is oxidized to NADP+ when it reduces the 3-carbon molecule

End product is a 3-carbon sugar = Glyceraldehyde 3-phosphate

(G3P)

The Calvin Cycle

Photosynthesis Animation

(view animation file on public server)

Arid Environments & Carbon Fixation

Plants close stomata on hot, dry days to avoid dehydration In leaf, CO2 level falls, O2 level rises Rubisco attaches oxygen to RuBP =

photorespiration C4 and CAM plants use alternative methods for

carbon fixation

C4 and CAM Plants