Photosynthesis Last Topic How do we burn glucose

Photosynthesis

• Last Topic= How do we burn glucose to make energy • This Topic=How do organisms make glucose

Photosynthesis = Capture Sunlight energy and convert it into the chemical energy stored in glucose 12 + 6 H 2 O

What do we mean by “sunlight energy? ”

Sunlight • Light=radiation • Radiation travels in waves Frequency=number of waves in a defined time

Wavelengths Visible Light Spectrum

Photons Although a wave, light travels in energy bundles called PHOTONS

What part of a plant absorbs these photons?

Photosynthetic Pigments • Chlorophyll a – Absorbs red and blue, Reflects green • Chlorophyll b – Absorbs red and blue, Reflects green • Carotenes – Reflects Orange • Xanthophylls – Reflects Yellow

Chlorophyll Structure More Similar or Different?

Purpose of Accessory Pigments • Ex. Carotenes and Xanthophylls • Capture additional wavelengths of light and pass energy onto the chlorophylls

Who has which pigments? • Plants, green algae, euglenoids: – Chlorophyll a and b and carotenoids • Brown algae, diatoms, dinoflagellates: – Chlorophyll a and carotenoids • Red Algae: – Chlorophyll a, carotenoids and phycobilins

Brown Algae Red Algae Tide Green Algae

Absorption Spectrum

In the absence of sunlight which color of light bulb is best to grow plants?

• Best: Red and Blue (Absorbed) • Worst: Green (Reflected)

Chloroplast Anatomy Grana= Stacks of sacs filled with Chlorophyll = Each sac is called a thylakoid = Reactions occur along the membranes of the thylakoids Stroma=Gel-like material around grana

Reactions of Photosynthesis • Light-Dependent Reactions – Held in Grana – Need Sunlight or Red or Blue light • Light-independent reactions (a. k. a. Carbon Fixation Reactions or Calvin Cycle) – Held in Stroma – Can occur day or night

Light-Dependent Reactions

Light-Dependent Reactions

Light-Depdendent Reactions 1. Photosystem II molecules of chlorophyll absorb light and get excited. 2. H 2 O is split (Photolysis) • • • Electrons passed to thylakoid cytochromes in membrane for electron transport/chemiosmosis Free H+s created O 2 waste created

Light Reactions 3. ATP created along ETC chain 4. Electrons from Photosystem II passed to Photosystem I chlorophyll 5. Photosystem I gets excited with absorption of light and electrons passed to 2 nd ETC 6. Last receiver of electrons is NADP+ (with Hs of photolysis you get NADPH)

Light Reactions

Light-Independent Reactions (In Stroma) 3 Cycles goes 6 times around to make 1 glucose

Overall Photosynthesis

Factors affecting photosynthesis • • Light intensity Temp Water minerals

C 4 and CAM Plants • C 4 – Corn, Sugarcane, Tropical Grasses – On hot days they close their stomata to conserve water – Altered photosynthesis procedure • CAM – Cacti – Close stomata during day – Altered photosynthesis procedure