PhotosynthesisMs. Napolitano & Mrs. HaasCP 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)

PhotosynthesisPhotosynthesis – plants use energy from

the sun to convert water & CO2 into carbs

Divided into the Light Dependent Reactions & the Light Independent Reactions

Photosynthesis Equation: Sunlight + 6CO2 + 6H2O C6H12O6 + 6O2

Photosynthesis:

Anatomy of a Leaf Stoma (pl. stomata) – allows for CO2 & O2 exchange

Mesophyll – layer of leaf where photosynthesis occurs

Vein – supplies H2O from roots (xylem) & delivers glucose to rest of plant (phloem)

Anatomy of a Chloroplast Thylakoids –

photosynthetic discs Site of light reactions Photosystems made of

pigmentsPigments absorb lightChlorophyll – 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 O2 + ATP + NADPH

Divided into 2 parts – Photosystem II and Photosystem I

LDR: Photosystem IIDiscovered after photosystem ISteps:

Chlorophyll & other pigments absorb light

e- become excited (energy level increases) & go to the electron transport chain

2H2O 4H+ + O2 + 4e-

4e- replace excited e- from sunlightO2 gets released into air as byproduct

LDR: Electron Transport ChainBetween photosystems II & IExcited e- jump through electron

transport chain and power proton pumpsTransfer H+ into thylakoid spaces

LDR: Photosystem IPigments 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 IH+ are still being pumped into thylakoid

spaces Space = + charge, membrane = - charge Difference in charges provides energy for

ATPATP 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 + CO2 Glucose

The Calvin CycleSteps:

6CO2 enters the cycle from the atmosphere

Energy is received from ATP and NADPH, making ADP & NADP+

C from CO2 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 & H2O

• Products: O2 (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: CO2 (as well as ATP & NADPH from LDR)

• Products: sugar (glucose)

• Occurs in stroma

• ATP becomes ADP and NADPH becomes NADP+

Factors Affecting PhotosynthesisWater availabilityTemperature

Denatures necessary enzymesEvaporation

Light intensityIncreases rate of photosynthesis (to a

point)

...so take care of your plants!