CO2 + H2O --sun--> C6H12O6 + O PHOTOSYNTHESIS (rap) CO2 + H2O --sun--> C6H12O6 + O

Examples of Photoautotrophs Capture sunlight energy and use it to carry out photosynthesis Phytoplankton - the first step in ocean food chains Plants Some bacteria Many protistans

2 types of organisms: autotrophs Heterotrophs Carbon source is: Energy source is: Heterotrophs Carbon + Energy source are: carbon dioxide sunlight autotrophs! yum

Photosynthesis Cellular Respiration SUN energy SUGAR energy ATP energy

Photosynthesis Equation LIGHT ENERGY 12H2O + 6CO2 6O2 + C6H12O6 + 6H2O water carbon dioxide oxygen glucose water (note: copy on top of pp)

Let’s Balance This Equation ! 6 6 6 ___CO2 + ___H20  ___C6H12O6 + ___O2 The product of photosynthesis is GLUCOSE 1

inputs and outputs of the photosynthetic process.

Can affect rate of Photosynthesis Amount of Carbon Light Temperature

Leaves and Leaf Structure Plants are the only photosynthetic organisms to have _______ (and not all plants have leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells. leaves

Leaf Structure UPPER EPIDERMIS cuticle PALISADE MESOPHYLL xylem SPONGY phloem LOWER EPIDERMIS AIR SPACES CO2 one stoma O2

Tiny pores UNDER leaf  Stomata CO2 Allows ____________ in Allows ___________ out Allows___________ out K+ and H20 O2 H2O <<LINK>> K+ and H20

What Causes Stomata to Open? to close:

A. CHLOROPLAST STRUCTURE The number of chloroplasts in a cell varies from 20 – 100. THIS IS THE ORGANELLE THAT DOES PHOTOSYNTHESIS

Organelles of photosynthesis Chloroplasts Organelles of photosynthesis stroma Two membranes granum thylakoid

What is the structural unit of photosynthesis? WHERE LIGHT REACTION TAKES PLACE Thylakoids are stacked like pancakes in stacks known collectively as . The aeas between grana are referred to as? DARK REACTION TAKES PLACE HERE thylakoid grana stroma

STROMA THYLAKOID GRANA INTERMEMBRANE INNER OUTER

A. THE NATURE OF LIGHT What IS sunlight??? wavelengths Green plants use sunlight for photosynthesis Light energy is in form of . Light travels in “bundles” called What IS sunlight??? Sunlight = mixture of different wavelengths of light; many are visible to the eye (VISIBLE LIGHT SPECTRUM). wavelengths photons

Electromagnetic Spectrum Shortest Most Gamma rays wavelength energy X-rays UV radiation Visible light Infrared radiation Microwaves Longest Least Radio waves wavelength energy

Visible Light long waves short waves low energy high energy V I B G Y 10-5nm 10-3nm 1nm 103nm 106nm 109nm 1 m 103m V I B G Y O R

So, what IS a pigment?? Molecules that have evolved to absorb wavelengths in the visible region of the spectrum very well

Chlorophyll ________________, the green pigment common to all photosynthetic cells absorbs all wavelengths of visible light EXCEPT GREEN, which it REFLECTS to be detected by our eyes. Black pigments all of the wavelengths that strike them. White pigments/lighter colors all or almost all of the energy striking them. absorb reflect

CHLOROPHYLL - pigment found in green plant Chlorophyll a – (primary pigment); directly involved in the light dependent reactions Chlorophyll b - (accessory pigment); helps capture sunlight and transfer energy to chlorophyll a

a) Chlorophyll does not absorb most yellow and green light – these colors are reflected b) Chlorophyll b absorbs light with wavelengths of 480 nm (blue) and 650 nm (red) (more blue/less red) c) Chlorophyll a - absorbs light within wavelengths of 435 nm (blue) and 675 nm (red) (less blue/more red than Chl.b)

4. ACCESSORY Pigments - Pass their absorbed sunlight energy to chlorophyll, which passes the energy to the photosynthetic pathway. For this reason they are called “accessory” pigments Carotenoids – carotene & Xanthophylls Anthocyanins Phycobilins

Why do plants need accessory pigments? To utilize ALL wavelengths of light entering plant

a) Carotene – reflect yellow, red and a) Carotene – reflect yellow, red and orange; 450 nm and 500 nm; absorb blue and green. They are not water soluble. Found in carrots, oranges and autumn leaves

b) Xanthyphylls – reflect yellow and orange c)Anthocyanins - responsible for the red, purple, and blue colors of many fruits, vegetables, cereal grains, and flowers.

Overview of Photosynthesis equation: 6CO2 + 12H2O ----------> C6H12O6+ 6O2 + 6H2O Chlorophyll Light In two stages. . .

Stage 1 – Light Dependent Reactions Water is split into hydrogen ions (H+), electrons and oxygen (O2) The O2 diffuses out of the chloroplasts (by-product) The light energy is converted to chemical energy, which is temporarily stored in ATP and NADPH

Stage 2 – Calvin Cycle (light independent rxn) The chemical energy stored in ATP and NADPH powers the formation of organic compounds (sugars), using carbon dioxide (CO2)

(thylakoid membrane) stroma The Light Reactions occur in the the Dark Reactions occur in the stroma

A. Light Dependent Reaction 1. splits H2O into H+ (proton), electron(-) and O2 2. forms ATP 3. forms NADPH 4. releases O2

Action of Photosystem I And II

The high energy electrons leave the chlorophyll and travel to a: Light energy strikes the: Electrons of specialized chlorophyll molecules in Photosystem (Ps II) absorb the energy and become “ ” (raised to a higher energy level. The high energy electrons leave the chlorophyll and travel to a: primary electron acceptor. chlorophyll excited

electron transport chain The primary acceptor donates the electrons to a series of molecules (electron acceptors) in an . As they do, the energy level of the electrons is reduced. The energy released is used to move into the thylakoids. 4. At the same time, Photosystem I (Ps I) absorbs light energy, raising the energy level of the electrons in chlorophyll again. These electrons are replaced by the electrons from Photosystem II (Ps II). electron transport chain H+

5. These “excited” electrons are passed to a different primary electron acceptor and then through another ETC. These electrons are moved to the stroma side of the membrane. 6. The energy and electrons are then combined with a H+ proton and NADP+ forming NADPH

Pigments in a Photosystem reaction center (a specialized chlorophyll a molecule)

released into atmosphere The electrons from Photosystem I & II must be replaced. The source of electrons is the splitting of (HYDROLYSIS): 2 H2O 4 H+ + 4 e- + O2 What happens to the oxygen?? water released into atmosphere

NADPH NADP+ + H+ H+ H+ H+

PRODUCTION OF ATP = A process called chemiosmosis 8. Chemiosmosis relies on a concentration gradient of protons (H+) across the thylakoid membrane. 9. Where do we get these H+ protons?? produced from: other protons are pumped into the thylakoid the breakdown of water molecules

10. Both these mechanisms act to build up a concentration gradient of protons (H+). The concentration of protons (H+) is higher in the ____________________ than in the stroma. 11. The protons (H+) can only pass through special protein channels of ATP synthase, thus converting ADP + P to __________ thylakoid ATP

It’s a CYCLE ! autotrophs heterotrophs Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy- pathway oxygen carbon dioxide releasing Requires Releases

Lecture 6.2 – Light Independent Reaction aka – Dark Reaction = Carbon Fixing Cycle = Calvin-Benson Cycle = C3 Pathway

The reactions in this process were worked out by Melvin Calvin, 1961.

Light-Independent Reactions (DARK) Synthesis part of photosynthesis Makes: From: Can proceed in the OR LIGHT Take place in the CO2 GLUCOSE dark stroma

ribulose biphosphate (RuBP). The Calvin Cycle occurs in the stroma of chloroplasts where would it occur in a prokaryote? Carbon dioxide is captured by the chemical – -C carb compound. How many molecules of CO2 will enter cycle to yield one molecule of glucose?? cytoplasm ribulose biphosphate (RuBP). 5 6 C6H12O6

A. Summary ATP light reaction CO2 H carbohydrates stroma Energy from _______ from ____________ is used to combine ________ from air with ___ from NADPH from light reaction to make ________________ . 12 NADPH + 18 ATP + 6CO2 C6H12O6 (glucose) + 12 NADP+18P + 6 H2O The “Dark” phase takes place in the light reaction CO2 H carbohydrates stroma

B. PROCESS: CALVIN CYCLE (Carbon Fixation) CO2 diffused into the chloroplasts and combines with a 5-C sugar (RuBP ribulose biphosphate) to form an unstable 6-C sugar. The enzyme required for this reaction 2. 6-C sugar immediately splits into 2 3-C compounds ( ) 3. PGA combines with H from NADPH to form a 3-C sugar ( ) ribulase PGA – phosphoglycerate PGAL phosphoglyceraldehyde

Some G3P (PGAL) is converted to ; most is used toward building more ; 1 turn  ______ ATP _______ NADPH ________ CO2 How many turns to make a GLUCOSE? 5. Energy for reactions comes from _________ 6. ____________ is produced as a by-product glucose RuBP 3 2 1 6 ATP Water

NOTE: Glucose is not a direct product of photosynthesis. The 3-C compound PGAL produced are combined to form starch may later be converted to sucrose The sucrose and starch are converted to glucose for cellular respiration

Calvin-Benson Cycle Overall products Overall reactants Carbon dioxide ATP NADPH Overall products Glucose ADP NADP+ Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

A CYCLE SAVES: E N E R G Y

sucrose starch The most easily transported plant carbohydrate Phosphorylated glucose is the building block for: sucrose The most easily transported plant carbohydrate starch The most common storage form <<LINK>> what happens to glucose?

CO2 RuBP PGA ATP ATP NADPH PGAL sugar

diffusion through stomata BACKGROUND: How does CO2 enter autotrophic cells? Land plants must guard against drying out (desiccation) and so have evolved specialized structures known as: to allow gas to enter and leave the leaf. diffusion through stomata stomata

The C3 Pathway the C3 pathway a three-carbon PGA What is the first stable molecule made? Because the first intermediate has three carbons, the pathway is called the C3 pathway a three-carbon PGA

C3 Plants in HOT WEATHER On hot, dry days stomata close Inside leaf Oxygen levels ? Carbon dioxide levels ? RuBP attaches to _______ instead of carbon dioxide Only one PGAL forms instead of two oxygen

C4 and CAM pathways are “PRE-CYCLES” They get molecules PREPARED to enter the normal dark cycle if conditions are unfavorable

C4 Plants CO2 C4 CO2 C3

CAM Plants CO2 CAM CO2 C3

C3 C4 CAM Ex.-Pineapple, cactus… Stores 4C molecule until daytime CO2 + PEP (3-C) = 4-C molecule Ex.-Corn, sugarcane… Stores 4C molecule in separate cells from cycle CO2 + PEP (3-C) = 4-C molec CO2 + RuBP (5-C) = two 3-C molecules Ex.-Pineapple, cactus… Stores 4C molecule until daytime