Photosynthesis

2 Parts of Photosynthesis

Light Dependent Reaction

Calvin Cycle or Light Independent Rxn(aka Dark Reaction)

Structure of a Chloroplast

The light reactions take place in the thylakoid membrane

The dark reactions take place in the stroma

Light energy is packaged into photons.

Light is a form of Electromagnetic energy move in waves.

Each level of wavelength emits various amounts of energy.

Molecules of plants that absorb light are called Pigments.

Chlorophyll is the major absorbing pigment in green plants and photosynthesis.

Electromagnetic Spectrum

Why are plants green?

Absorption Spectrum of green plant.

Pigments

Pigments are light-absorbing compounds.

Pigments appear colored because they absorb light of certain wavelengths and reflect that of others.

Chlorophyll a is the primary pigment in green plants that absorbs red and blue/violet light and reflects green light.

Stomata

GAS EXCHANGE

Stomata Anatomy

1.Stomata are microscopic openings found on the bottom sides of the leaves.

2.The stomata is bounded by two half moon shaped guard cells.

3.Found on the bottom surface of the leaf because the guard cells are partially light activated, plants under direct light would constantly have their stomata open and would thus lose much water and the plant would die.

4.Guard cells

Each guard cell contains water and ions.

Stomata Physiology

1. LIGHT : Guard cells Swell; stomata open.

A. Carbon Dioxide diffuses into the cell to be used for photosynthesis.

B. Water and Oxygen diffuse out of the leaf.

2. DARK: Guard cells Shrink; stomata close

No photosynthesis takes place.

Light Reaction

Light Reaction

Also called Light Dependent ReactionPigments that are in the chloroplasts intercept light and begin the light reactions of photosynthesis.The light reactions occur in two photosystems (located in the thylakoid membrane):

Photosystem: a unit of several hundred chlorophyll a molecules and associated acceptor molecules

-photosystem I (PSI) -photosystem II (PSII)

Photosystems

Excited Electrons

NADPH

NADP+ is an electron acceptor

NADP+ + 2 e- + 2 H+ NADPH + H+

1. Light Energy is absorbed by the grana.

2. Water is split into H+ , and O2 The oxygen is then released.3. The Electrons from water are excited and passed down from PhotosystemII to PhotosystemI. The free Hydrogen ions are transported across the thylakoid membrane and are used to produce ATP and NADPH.

Steps of LIGHT Reaction

Photosystem II Photosystem II & Photosystem & Photosystem II

STEPS of LIGHT REACTION4. The electrons arrive at Photosystem I and are excited again by the sunlight .5. They are then passed to NADP and form NADPH.6. The build up of H+ inside the Thylakoid causes the H+ to move through ATP Synthetase.7. This energy forces a phosphate onto ADP to generate ATP. This movement is due to a difference in concentration.

ETC of Photosynthesis

to Calvin Cycle

AP Biology

From Light reactions to Calvin cycle Calvin cycle

chloroplast stroma

Need products of light reactions to drive synthesis reactions ATP NADPH

stroma

thylakoid

ATP

Dark Reaction

Dark ReactionThe dark reaction is also known as the Calvin Cycle, after an American scientist (Melvin Calvin) who figured out the pathway.The dark reaction is also known as the C3 Cycle because the first stable products of this pathway are molecules that contain three carbon atoms.The Calvin Cycle occurs in the stroma.

12 NADPH + H+

~

e12 ADP + P

12 ATP

12 NADP+

e-

10 PGAL

~

e6 ADP + P

6 ATP

6 CO2C

6 RuBPC C C C C

12 PGAC C C

12 PGALC C C

2 PGALC C C

GlucoseC C C C C C

C C C C C C

unstablecompound

Calvin Cycle1. Takes place in the stroma

2. Carbon dioxide is fixed to RuBP by the enzyme Rubisco.3. One - 3 Carbon molecule known as G3P is formed for each Carbon dioxide(3) that gets fixed. It takes two turns of the cycle to produce ONE 6 carbon molecule of sugar.4. ATP and NADPH are necessary to run this reaction and generate ADP, and NADP+ for the light reactions.

Adenosine triphosphate

ATP Synthesis in the Cell

ENERGY from food

1.Compounds that store energy are ATP, NADPH, FADH, & NADH2. The most important energy storing compound is ATP (Adenosine triphosphate.)3. ATP releases energy when a bond holding a phosphate group is broken. This creates a new molecule called ADP (adenosine di-phosphate)4. What is the difference between ATP and ADP? # of Phosphates5. Cells generate 10 million new ATP molecules per second.

ATP – P = ADP

ADP + P = ATP

Adenosine Monophosphate

Adenosine Diphosphate

7.3 kcal/mole energy released

Adenosine Triphosphate

T/F Questions

ATP has more energy than ADP.

T/F

There are three phosphate atoms in ATP?

T/F

You are storing energy right now in your body in the phosphate bonds of ATP.

T/F

ATP is made of a sugar, the base adenine and a phosphate.