HBIO: PHOTOSYNTHESIS

Leaf Anatomy Cuticle – waxy coating to

prevent desiccation Epidermis – outer layer of

protective cells Vascular Bundle - vein

Xylem – delivers water from roots

Phloem – delivers sugars from leaves

Mesophyll Palisade – tightly packed

photosynthetic cells Spongy – loose arrangement of

photosynthetic0 cells w/air spaces

Stoma – openings allow for gas exchange

Guard Cells – regulate stoma

Homework:

Draw or describe the carbon cycle

Explain how it relates to photosynthesis

Do Now:

Homework on Desk Grab your clickers!

Which leaf structure is responsible for gas exchange?

1 2 3 4 5 6

0% 0% 0%

7%

50%

43%

1. Epidermis2. Cuticle3. Mesophyll4. Guard cells5. Xylem 6. Phloem

Which leaf structure is responsible for transport of water?

1 2 3 4 5 6

0% 0%7%

93%

0%0%

1. Epidermis2. Cuticle3. Mesophyll4. Guard cells5. Xylem 6. Phloem

Which leaf structure is responsible for synthesis of sugars?

1 2 3 4 5 6

0% 0%

40%

0%

7%

53%

1. Epidermis2. Cuticle3. Mesophyll4. Guard cells5. Xylem 6. Phloem

Which process increases C in the atmosphere?

1 2 3

7%

93%

0%

1. Reforestation2. Coal formation3. Burning fossil

fuels

Chloroplasts

Chloroplasts found in cells of mesophyll (interior tissue of leaf)

CO2 enters and O2 exits through stomata (pores)

Chlorophyll - green pigment absorbs light energy found in thylakoid membranes

Thylakoids stacked in grana

Stroma – fluid in chloroplast

Electromagnetic Spectrum

Spectrophotometer Measures the ability for a

pigment to absorb various wavelengths of light

Directs a beam of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelength

Absorption spectrum plots a pigment’s light absorption vs. wavelength

ALL wavelengths are equally effective for photosynthesis

1 2 3

33%

7%

60%1. True2. False3. Cannot be

determined

The colors of light most useful in photosynthesis are

1 2 3 4

47%

0%

7%

47%1. green, yellow,

and orange2. red, violet, and

blue3. infrared, red,

and yellow4. red, white, and

blue

Big Picture: Energy Cycles All energy ultimately

comes from sun Light reactions of

photosynthesis Take place in thylakoid

Carbon fixation -all C in living things ultimately from CO2 Dark reactions of

photosynthesis Take place in stroma

Photosynthesis and cellular respiration are reverse reactions

Redox

Redox Rxns w/ transfer of e Oxidation – loss of e Reduction – gain of e Both photosynthesis and cellular respiration

use redox rxns in a series of steps Electron transport chain (ETC) breaks the

fall of electrons into several Energy releasing steps using proteins in the cell membrane

Photosystem

Photosystem – reaction center surrounded by light harvesting complexes called pigments (chlorophyll a, chlorophyll b, xanthrophyll, carotenoids, etc) Pigment – absorbs photon E transferred from

pigment to chlorophyll a rxn center Rxn Center – protein complex w/ primary e

acceptor 2 photosystems used in light reactions

Photosystem II – p680 chlorophyll a rxn center Photossystem I – p700 chlorophyll a rxn center

Light Reactions: Non-Cyclic e flow

Photons absorbed by pigments and funneled to p680 in PSII excites e to higher energy state

E is captured by primary e acceptor

Enzyme splits H2O 2e + 2 H+ + O (will form O2)

Excited e passes thru etc to rxn center in PSI

Exergonic rxns in etc provide E for synthesis of ATP

Photons excite e in p700 in PSI excites e to higher energy state

E is captured by primary e acceptor and passed down 2nd etc

NADP+ transfers 2e from etc to form NADPH

OR Light Reactions: Cyclic e flow

Uses PSI only! (not PSII) Excited e from primary e

acceptor to 1st etc produces ATP and e falls back to replace lost e from p700 No water splitting No production of NADPH Increases production of

ATP for Calvin Cycle (req. more ATP then NADPH)

Chemiosmosis

etc passes e thru carrier proteins in thylakoid membrane creating a H+ gradient (pumps H+ from stroma (pH8) into thylakoid space pH5)

Chloroplasts – photophosphorylation

ATP synthase embedded in same membrane (as H+ diffuse down gradient ADP is phosphorylated into ATP on stroma side of thylakoid)

NADPH also made on stroma side of membrane

Classwork:

Draw a flowchart (or diagram) of the light dependent reactions

Do Now

Good Morning! Grab your Clicker Take out your photosyntehsis pogil Have out your homework ws (light

reactions)

The light dependent reactions take place in the

1 2 3 4

0% 0%7%

93%1. Cloroplast

membrane2. Thylakoid3. Stroma4. Cytoplasm

NADP+ NADPH is an example of

1 2 3 4 5

40%

0%

13%13%

33%

1. Reduction2. Oxidation3. Chemiosmosis4. Photophosphorylat

ion5. None of the above

During what stage of photosynthesis is O2 produced?

1 2 3 4 5

20%

80%

0%0%0%

1. Photosystem I2. Photosystem II3. ETC4. Photophosphoryla

tion5. O2 is not

produced

The photophosphorylation of ATP is due to

1 2 3 4 5

13%

47%

0%

27%

13%

1. Chemiosmosis of H+

2. ATP synthase3. Electron

Transport Chain4. All of the above5. None of the

above

Dark Rxns: Calvin Cycle Anabolic rxns – consuming E to build

sugar C enters Calvin cycle as CO2 C exits Calvin cycle as 3C sugar called

G3P Uses ATP as E source (ATP) from light

rxns Uses NADPH as reducing agent to add

high E e (NADPH from light rxns) Phase I: Carbon Fixation

CO2 + RuBP (5C sugar) 2 3-phosphoglycerate

Phase II: Making Sugar Each 3-phosphoglycerate + P (from

ATP) 1,3-biphosphoglycerate + 2e (from NADPH) G3P

Phase III: Regenerating RuBP (5) G3P + 3ATP 3 RuBP (ready for C

fixation phase I) 3 molecules CO2 1 molecule G3P 6 molecules CO2 2 G3P (Glucose) Must go thru Calvin Cycle 6x to

make 1 molecule of glucose!

Alternate Methods of C Fixation Hot/Dry day – stomata close to prevent

water loss Stomata close – limits CO2 from entering

leaves, O2 builds up from light rxns

Photorespiration occurs on hot/dry days No ATP produced nor sugar Due to excess O2 instead of CO2 a 2C compound

is produced and rearranged and released as CO2 No advantage

Alternate Methods: C4 Plants

Minimizes Photorespiration Forms a 4C compound as 1st product

(instead of 3) Ex. Sugar cane, corn, grass Photosynthesis occurs between 2

separate cells Mesophyll cells

CO2 reacts with Phophonolpyruvate (PEP) Oxaloacetate (4C cmpd)

Bundle Sheath Cells 4C cpmd CO2 Calvin Cycle

Alternate Methods: CAM Plants

Succulent plants ex. Cacti and pinapple

Photosynthesis occurs in same cell, but at different times

Stomata open at night and close during day

Crassulacean Acid Metabolism (CAM) Calvin cycle produces organic

acids at night and mesophyll cell store in vacuoles until morning

During day light rxns supply ATP and NADPH for Calvin cycle, then CO2 is released from organic acids stored in vacuoles