Photosynthesis process by which plants algae and some

Photosynthesis process by which plants, algae and some bacteria use light energy to convert inorganic compounds into organic compounds

Overall Reaction light 6 CO 2 + 6 H 2 O → → → C 6 H 12 O 6 + 6 O 2 Reverse of cellular respiration

Plants use glucose to: n n generate ATP molecules during cellular respiration build more complex organic molecules → fats (oils, waxes) → starch → proteins → nucleic acids (DNA and RNA)

Importance of Photosynthesis n n food source for other organisms provides oxygen gas in atmosphere

Site of Photosynthesis: Chloroplast

n n n Grana: stacks of thylakoids that contain chlorophyll and photosynthetic enzymes Stroma: thick fluid that suspends the grana Chloroplasts, like mitochondria, have a double membrane

Electromagnetic Spectrum

Light is composed of photons of energy that travels in waves The wavelength of light determines its color.

Plants absorb most wavelengths of light except green n. Green light waves are reflected – which is why plants look green n

Chlorophyll is the most abundant photosynthetic pigment n chlorophyll a & b absorb red and blue light, reflect green light

Carotenoids n absorb blue-green light n reflect yellow, orange, red wavelengths n pass energy to chlorophyll a or absorb and dissipate excessive light energy that would damage chlorophyll

n n having several types of pigments in a leaf allows the plant to absorb more of the light In this way more energy is available for photosynthesis

Photosynthesis n Occurs in two stages: n n Light reactions: occur in the grana Dark reactions (Calvin cycle): occur in the stroma

Stage I: Light (Photochemical) reactions

Photosystems n n each is a cluster of several hundred pigment molecules found in the thylakoid membranes when a photon strikes a pigment molecule, the energy jumps from pigment to pigment until it reaches the reaction center

Two Types of Photosystems n n In photosystem II, water molecules are split using light energy This is called photolysis → releases O 2 in the atmosphere

n Photosystem I produces NADPH by transferring light-excited electrons from chlorophyll to NADP+

n An electron transport chain pumps hydrogen ions generated by the photosystems across the membrane and ATP synthases use the energy to make ATP

H 2 O CO 2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O 2 [CH 2 O] (sugar) Primary acceptor Elec Pq 2 H+ + O 2 Light e H 2 O tron trans port Fd chai e n Cytochrome complex e– NADP+ reductase PC e– Light ATP Photosystem II (PS II) Photosystem-I (PS I) NADP+ + 2 H+ NADPH + H+ P 700 e– P 680 Figure 10. 13 El Tra ectro ns n ch port ain

n n http: //www. stolaf. edu/people/giannini/flashanimat/metabolism/photosynthe sis. swf http: //www. fw. vt. edu/dendro/forestbiology/photosynthesis. swf http: //www. science. smith. edu/departments/Biology/Bio 231/ltrxn. html http: //highered. mcgrawhill. com/sites/0072437316/student_view 0/chapter 10/animations. html#

Stage II: Dark reactions (Calvin Cycle)

n n Using carbon from CO 2, ATP and high-energy electrons from NADPH, the Calvin cycle synthesizes an energy-rich sugar molecule (glyceraldehyde 3 -phosphate or G 3 P) G 3 P is a raw material used to make glucose and other organic molecules

Calvin Cycle

n For every 3 CO 2 used, 1 G 3 P is formed