PHOTOSYNTHESIS

6.1

The main form of energy from the sun is in the form of electromagnetic radiation

Visible radiation (white light) used for photosynthesis

Remember : ROY G. BIV?

The electromagnetic spectrum

A Red Object absorbs the blue and green wavelengths and reflects the red wavelengths

Why are plants green?

pigment a compound that absorbs light different pigments absorb different wavelengths of white

light.

chlorophyll is a pigment that absorbs red & blue light (photons) so green is reflected or transmitted.

Chlorophyll is located in the thylakoid membranes

So, Plants are green because the green wavelength is reflected, not absorbed.

2 types of chlorophyll Chlorophyll a – involved in light reactions

Chlorophyll b – assists in capturing light energy – accessory pigment

Carotenoids – accessory pigments – captures more light energy Red, orange & yellow

The electromagnetic wavelengths and the wavelengths that are absorbed by the chlorophyll

During the fall, what causes the leaves to change colors?

Fall Colors In addition to the chlorophyll

pigments, there are other pigments present

During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments

Carotenoids are pigments that are either red, orange, or yellow

Photosynthesis is -

conversion of light energy into chemical energy that is stored in organic compounds (carbohydrates > glucose)

Used by autotrophs such as: Plants Algae Some bacteria (prokaryotes)

glucose - energy-rich chemical produced through photosynthesis C6H12O6

Biochemical pathway – series of reactions where the product of one reaction is consumed in the next

E.g. photosynthesis product is glucose which is used in cellular respiration to make ATP

(carbohydrate)

Remember Redox Reaction

reduction/oxidation The transfer of one or more electrons from one reactant to another

Two types:1. Oxidation is the loss of e-

2. Reduction is the gain of e-

Oxidation Reaction

The loss of electrons from a substance or the gain of oxygen.

glucose

6CO2 + 6H2O C6H12O6 + 6O2

Oxidation

Carbon dioxide Water

Oxygen

Reduction Reaction

The gain of electrons to a substance or the loss of oxygen.

glucose

6CO2 + 6H2O C6H12O6 + 6O2

Reduction

Photosynthesis equation

Light energy

6CO2 + 6H2O C6H12O6 + 6O2

Chlorophyll

Reactants: Carbon dioxide and water

Products: glucose and oxygen which is a byproduct

Where does photosynthesis

take place?

Plants Mainly occurs in the leaves:

a. stoma - poresb. mesophyll cells

StomaMesophyllCell

Chloroplast

Mesophyll Cell of Leaf

Cell Wall

Nucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these cells!

Stomata (stoma)Pores in a plant’s cuticle through

which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere.

Guard CellGuard CellCarbon Dioxide (CO2)

Oxygen (O2)

Found on the underside of leaves

Stoma

Chloroplast

Organelle where photosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected together

Partschloroplasts – dbl membrane organelle that

absorbs light energyThylakoids – flattened sacs contain pigment -

chlorophyllGrana (pl: granum) – layered thylakoids (like

pancakes)Stroma – solution around thylakoidsStomata – pore on underside of leaf where O2 is

released and CO2 enters

Stroma : chloroplast :: cytosol : cytoplasm

Thylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Grana make up the inner membrane

What do cells use

for energy?

Energy for Life on Earth

Sunlight is the ULTIMATE energy for all life on Earth

Plants store energy in the chemical bonds of sugars

Chemical energy is released as ATP during cellular respiration

Structure of ATP ATP stands for adenosine

triphosphate It is composed of the nitrogen

base ADENINE, the pentose (5C) sugar RIBOSE, and three PHOSPHATE groups

The LAST phosphate group is bonded with a HIGH ENERGY chemical bond

This bond can be BROKEN to release ENERGY for CELLS to use

Removing a Phosphate from ATP

Breaking the LAST PHOSPHATE bond from ATP, will --- Release ENERGY for cells to use Form ADP (adenosine diphosphate) Produce a FREE PHOSPHATE

GROUP

High Energy Phosphate Bond

FREE PHOSPHATE can be re-attached to ADP reforming ATP

Process called Phosphorylation

Phosphorylation

Photosynthesis

1. Light Reaction -Produces energy from solar power (photons) in the form of ATP and NADPH.

2. Calvin Cycle Also called Carbon Fixation or

Carbon Cycle, Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

SUN

3 stages of photosynthesis-

Stages:

STAGE 1 - LIGHT REACTIONS - energy from sun is used to split water into H+ an O2

 STAGE 2 – energy is converted to chemical energy & stored in ATP & NADPH in stroma

STAGE 3 - CALVIN CYCLE where carbon is fixed into glucose

Light Reaction (Electron Flow)

Occurs in the Thylakoid membranes

2 possible routes for electron flow:Use Photosystem I and Electron Transport Chain (ETC) and generate ATP only

OR use Photosystem II and Photosystem I with ETC and generate O2, ATP and NADPH

Photosynthesis animation

http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm

ELECTRON TRANSPORT - LIGHT REACTIONS in 5 steps

Photosystem I and II Step 1 – light excites e- in photosystem II Step 2 – e- move to primary e- acceptor

Step 3 – e- move along electron transport chain (etc)

Step 4 – light excites e- in photosystem I Step 5 – e- move along 2nd (etc) End – NADP+ combine H+ to make NADPH

Light reaction animation

http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html

Electron transport chain song

Play the "Come On Down (The Electron Transport Chain)" song performed by Sam Reid. 

Photolysis –photo-chemical splitting of water (restoring photosystem II)

Chemiosmosis – synthesis of ATP

Powers ATP synthesis Takes place across the

thylakoid membrane Uses ETC and ATP synthase H+ move down their

concentration gradient forming ATP from ADP

Concentration of protons is greater in thylakoid than stroma

ChemiosmosisH+ H+

ATP Synthase

H+ H+ H+ H+

H+ H+high H+

concentration

H+ADP + P ATP

PS II PS IE

TC

low H+

concentration

H+ThylakoidSpace

Thylakoid

SUN (Proton Pumping)

The Calvin Cycle

6.2

Calvin Cycle - Biochemical pathway in photosynthesis that

produces organic compounds using ATP & NADPH

Carbon fixation – carbon atoms from CO2 are bonded or ‘fixed’ into carbohydrates

occurs in stroma

Calvin Cycle Carbon Fixation C3 plants (80% of plants on

earth) Occurs in the stroma Uses ATP and NADPH from light

reaction as energy Uses CO2

To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

Chloroplast

GranumThylakoid

STROMA– where Calvin Cycle occursOuter Membrane

Inner Membrane

Calvin Cycle (C3 fixation)

6CO2

6C-C-C-C-C-C

6C-C-C 6C-C-C

6C-C-C-C-C

12PGA

RuBP

12G3P

(unstable)

6NADPH 6NADPH

6ATP 6ATP

6ATP

C-C-C-C-C-CGlucose

(6C)(36C)

(36C)

(36C)

(30C)

(30C)

(6C)

6C-C-C 6C-C-C

C3

glucose

Calvin Cycle

Remember: C3 = Calvin Cycle

C3

Glucose

Step 1 -

CO2 diffuses fr cytosol & combines with RuBP which splits into pair of PGA

Step 2 -

PGA gets phosphate gr fr ATP gets proton fr NADPH to become PGAL

Reaction produces: ADP, NADP+ & phosphate to be used again

Step 3 -

PGAL converts back to RuBP

Allows Calvin cycle to continue

Alternates:

C3 plants – use Calvin cycle exclusively Form 3-carbon compounds

C4 pathway – evolved in hot, dry climate Form 4-carbon compounds Partially close stomata E.g. Corn, sugar cane, crabgrass

CAM – open stomata at night, close in day Grow slow, lose less water E.g. cactus, pineapple

C4 Plants Hot, moist

environments 15% of plants

(grasses, corn, sugarcane)

Photosynthesis occurs in 2 places: Light reaction -

mesophyll cells Calvin cycle -

bundle sheath cells

C4 Plants

Mesophyll Cell

CO2

C-C-C

PEP

C-C-C-CMalate-4C sugar

ATP

Bundle Sheath Cell

C-C-C

Pyruvic Acid

C-C-C-C

CO2

C3

Malate

Transported

glucoseVascular Tissue

CAM Plants Hot, dry environments 5% of plants (cactus and ice

plants) Stomates closed during day Stomates open during the

night Light reaction - occurs

during the day Calvin Cycle - occurs when

CO2 is present

CAM PlantsNight (Stomates Open) Day (Stomates Closed)

Vacuole

C-C-C-CMalate

C-C-C-CMalate Malate

C-C-C-CCO2

CO2

C3

C-C-CPyruvic acid

ATPC-C-CPEP glucose

Rate of photosynthesis is effected by - light intensity, CO2 or temperature

High intensity or high CO2 = high rate Growth graph levels off (plateau)

High temp = initial high rate but peaks Rate drops when stomata closes

Recap Photosynthesis converts light energy into chemical

energy thru series of biochemical pathways Electrons excite in photosystem II – move along

ETC to photosystem I electrons are replaced when water is split oxygen is byproduct ATP synthesized across thylakoid Calvin cycle – carbon is fixed & sugar produced 3 turns produce PGAL (PGAL keeps cycle going Other pathways – C3, C4, CAM

References

www.biologyjunction.com