Photosynthesis Ms. Napolitano & Mrs. Haas CP Biology

Recall:  Autotrophs – organisms that are able to make their own food (through sun or chemical energy)  Heterotrophs – obtain energy from the foods they consume  ATP – stores and releases energy  Bonds broken = energy released (ATP  ADP)  Bonds formed = energy stored (ADP  ATP)

Photosynthesis  Photosynthesis – plants use energy from the sun to convert water & CO 2 into carbs  Divided into the Light Dependent Reactions & the Light Independent Reactions  Photosynthesis Equation: Sunlight + 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2

Photosynthesis:

Anatomy of a Leaf  Stoma (pl. stomata) – allows for CO 2 & O 2 exchange  Mesophyll – layer of leaf where photosynthesis occurs  Vein – supplies H 2 O from roots (xylem) & delivers glucose to rest of plant (phloem)

Anatomy of a Chloroplast  Thylakoids – photosynthetic discs  Site of light reactions  Photosystems made of pigments  Pigments absorb light  Chlorophyll – main pigment of plants  Grana – stacks of thylakoids  Stroma – space outside thylakoids  Site of dark reactions

Electron (e - ) Carriers  High-energy e - need special carriers  Electron transport – a carrier accepts a pair of e - and transfers them (with most of their energy) to another molecule  NADP + accepts and holds e - with H +, eventually making NADPH  Transfers e - to other parts of the cell

Light Dependent Reactions (LDR)  AKA “Light Reactions”  Occurs in the thylakoid membrane  Chemical Equation: Water + Light  O 2 + ATP + NADPH  Divided into 2 parts – Photosystem II and Photosystem I

LDR: Photosystem II  Discovered after photosystem I  Steps:  Chlorophyll & other pigments absorb light  e - become excited (energy level increases) & go to the electron transport chain  2H 2 O  4H + + O 2 + 4e -  4e - replace excited e - from sunlight  O 2 gets released into air as byproduct

LDR: Electron Transport Chain  Between photosystems II & I  Excited e - jump through electron transport chain and power proton pumps  Transfer H + into thylakoid spaces

LDR: Photosystem I  Pigments in photosystem I reenergize e -  e - continue through electron transport chain  NADP + picks up 2 high-energy e - and H +  Becomes NADPH

LDR: After Photosystem I  H + are still being pumped into thylakoid spaces  Space = + charge, membrane = - charge  Difference in charges provides energy for ATP  ATP synthase (protein) allows for diffusion of H + through the membrane  Rotates like a turbine & binds ADP + phosphate to make ATP

Light Dependent Reactions

WHEW!! One part left (& it’s much easier!)

Light Independent Reactions (LIR)  AKA “Dark Reactions” or “The Calvin Cycle”  Light is NOT required  Occurs in stroma of chloroplasts  RECALL: ATP and NADPH were made from the LDR  High-energy sugars made (such as glucose)  Chemical equation: ATP + NADPH + CO 2  Glucose

The Calvin Cycle  Steps :  6CO 2 enters the cycle from the atmosphere  Energy is received from ATP and NADPH, making ADP & NADP +  C from CO 2 rearranged into glucose  Other C and more ATP is needed for next cycle

The Calvin Cycle

Let’s Sum It Up... Light Dependent ReactionsLight Independent Reactions

Let’s Sum It Up... Light Dependent ReactionsLight Independent Reactions Requires: Light & H 2 O Products: O 2 (released into atmosphere), ATP, NADPH Occurs in thylakoid Divided into photosystem II & I Electron Transport Chain between II & I and after I ATP Synthase makes ATP at the end Requires: CO 2 (as well as ATP & NADPH from LDR) Products: sugar (glucose) Occurs in stroma ATP becomes ADP and NADPH becomes NADP +

Factors Affecting Photosynthesis  Water availability  Temperature  Denatures necessary enzymes  Evaporation  Light intensity  Increases rate of photosynthesis (to a point)...so take care of your plants!