4TH LE - BOT 14

Photosynthesis

An anabolic, endergonic, carbon dioxide (CO2 ) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose)

What is the chemical equation for photosynthesis?

Why is photosynthesis considered anabolic?

Why is photosynthesis considered endergonic?

Photosynthesis

It is a redox process where carbon dioxide is reduced and water is oxidized

Photosynthesis; photoautotrophs

_________________ - Enables plants, algae and other photosynthetic organisms to make their own food (organic molecules) using light energy (________________)

Photosynthesis

Ensures the availability of energy source for humans and other heterotrophs

• Provides oxygen, which is vital to respiration

Leaves

___________ are the major plant organ of photosynthesis

stomata

CO2 enters and O2 exits the through the __________

• xylem

• Sugars; phloem

• Water enters the leaf through veins (________)

• _________ (the products of photosynthesis) leave the leaf also through veins (________)

chlorophyll; chloroplasts

Green color is from __________, the green pigment within ___________

mesophyll

Chloroplasts are found mainly in cells of the ___________, the interior tissue of the leaf

CHLOROPLAST

It is a 3 membrane system, the organelle responsible for photosynthesis

thylakoids

Chlorophyll and other pigments are in the membranes of ___________ (connected sacs in the chloroplast);

grana

thylakoids may be stacked in columns called __________

stroma

Chloroplasts also contain __________, a dense interior fluid

1. sunlight

2. ATP; NADP+; NADPH

3. ATP; NADPH

Two stages of photosynthesis

Light reactions

1. capturing energy from ________;

2. using the energy to make ____ and to reduce the compound _________, an electron carrier, to ________
   

Calvin cycle

3. using the ____ and _______ to power the synthesis of organic molecules from CO2 in the air

electromagnetic spectrum

The _______________ is the entire range of electromagnetic energy (EME), or radiation hitting the Earth

• Wavelength

• Wavelength

• EME travels in rhythmic waves

• _____________ is the distance between crests of waves

• _____________ determines the type of EME

• photons

• 750-380

• EME consists of discrete particles, called _________; a photon has a fixed quantity of energy

• Visible light consists of wavelengths that produce colors we can see (ROYGBIV; ________ nm wavelength, respectively)

Pigments

• pigments

• reflected

__________ are substances that absorb visible light

• Different ______________ absorb different wavelengths

• Wavelengths that are not absorbed are _________ or transmitted

• Chlorophyll

• Leaves appear green because chlorophyll reflects and transmits green light

• ___________ is the main photosynthetic pigment

• Why are leaves green?

Chlorophyll a

• main photosynthetic pigment (specify)

• found in all photoautotroph

chlorophyll a

1. Chlorophyll b

2. Chlorophyll c

3. Chlorophyll d

Accessory chlorophyll pigments absorb different wavelengths of a light and pass the energy to ___________

1. Chlorophyll _

2. Chlorophyll _

3. Chlorophyll _

• porphyrin

• Mg

• hydrocarbon; thylakoid membranes

Structure of chlorophyll:

• _________ ring (absorbs light)

• central ___ atom

• __________ tail interacts with hydrophobic regions of proteins inside __________- of chloroplast

blue; red

• Carotenoids

• anthocyanins

• fucoxanthin

• xanthophylls

Chlorophyll a and b absorb mainly in the ______ (422-492 nm) and ______ (647-760 nm) regions

• Other pigments include:

  • __________ (yellow & orange);

  • __________ (red);

  • __________ (brown);

  • __________ (yellow)

F

Absorb excess light that CAN damage chlorophylls

T or F

Absorb excess light that cannot damage chlorophylls

• potential

• heat; fluorescence

What happens when light is absorbed by atoms or molecules?

• The photon boosts an electron to an orbital where it has more _________ energy

• If the illuminated molecule is isolated, its excited electron immediately returns to ground state, releasing _______ and ______________

pigment antenna complexes; reaction center

Photosystems I and II are light-harvesting units of the light-dependent reactions

A photosystem: _____________________ + _______________; found in thylakoid membrane

antenna complex/ light harvesting complex

consists of chlorophyll molecules and accessory pigment molecules, with pigment binding proteins

reaction center

specialized chlorophyll a molecules and proteins + a primary electron acceptor

• When a photon strikes a pigment molecule,

• the energy is transferred from one molecule to another until it is passed to the pair of chlorophyll a molecules in the reaction-center.

• This chlorophyll pair enables them to use the energy from light to boost their electrons to a higher energy level '

• and transfer it to the primary electron acceptor, a molecule capable of accepting electrons and becoming reduced.

• 680; P680

• 700; P700

• Photosystem II: absorption peak at ___ nm; also known as ____

• Photosystem I: absorption peak at ___ nm; also known as ____

NON CYCLIC/LINEAR ELECTRON FLOW

Continuous, one-way flow of e- from water (ultimate esource) to NADP+ (terminal eacceptor)

ATP synthesis

NON CYCLIC/LINEAR ELECTRON FLOW

E released is used to to drive _____________

NON CYCLIC/LINEAR ELECTRON FLOW

Overall pattern: Z-scheme or zigzag of E of the donated e-

1. Pigments; antenna complex

2. reaction center

3. 2; P680; e- acceptor

4. e- transport chain (ETC)

5. P700

NON CYCLIC ELECTRON FLOW

1. __________ in _____________ in PS II absorb a photon of light

2. Absorbed E transferred from one molecule to another until it reaches ______________

3. _ e- s in ________ are energized, ejected, and passed on to a primary ___________ in the reaction center,

4. then to an ___________

5. e-s are donated to ______ in PS 1

6. splitting water

7. .

8. e- acceptor; ETC; NADP+

9. NADP+; H+; NADPH

NON CYCLIC ELECTRON FLOW

6. PS II regains e- s by _________, leaving O2 gas as a by-product

7. PS I is activated when photon of light is absorbed (the same way as PS II)

8. Energized e-s flow from PS I to primary _________, to _____, finally to ________

9. ________ accepts 2 e-, unites with a ___ in the chloroplast to form ________

CYCLIC ELECTRON FLOW

Cyclic flow of electrons through PS I which produces ATP

CYCLIC ELECTRON FLOW

In the presence of light, energized e- from PS I do not go to NADP+, but pass through acceptor molecules and cycle back to PS I

CYCLIC ELECTRON FLOW

No H2O split, no O2 released

ferredoxin (Fd); cytochrome complex; plastocyanin (Pc)

• chemiosmosis; NADPH

CYCLIC ELECTRON FLOW

Photoexcited electrons from PS I are occasionally shunted back from _____________ to chlorophyll via the ____________ and _____________.

• This electron shunt supplements the supply of ATP (via ______________) but produces no _________

CYCLIC ELECTRON FLOW

Some organisms such as purple sulfur bacteria have PS I but not PS II

CYCLIC ELECTRON FLOW

It is thought to have evolved before linear e-flow

CYCLIC ELECTRON FLOW

It may protect cells from light-induced damage

uses membranes to couple redox reactions to ATP production

• H+ ions; stroma; thylakoid membrane; thylakoid lumen

• Thylakoid lumen; proton motive force

• H+ ions; ATP synthase

• ATP synthase; phosphorylation

• H+ ions; NADP+; NADPH

• ETC uses light energy to pump ________, from the _______ across the ____________, to the _____________
  

• _____________ becomes more acidic; a proton gradient is created (also called ______________); source of potential energy
  

• Accumulated ________ move back towards the membrane; pass through a channel in ____________
  

• ____________ uses the energy to produce ATP by ________________
  

• In the stroma, the _________ combine with ___________ to form ___________

nicotinamide adenine dinucleotide phosphate

NADP (___________________)

NADP

a co-enzyme that temporarily stores energized electrons (an electron carrier)

ATP

energy currency of the cells

hydrolysis

• phosphate

• endergonic

The bonds between the phosphate groups of ATP’s tail can be broken by __________

• Energy is released when the bonds between ____________ groups are broken

• Energy released used to drive an ___________ reaction in the cell

He discovered of the pathway by which plants convert CO₂ to sugars

the first product is a 3-C molecule (PGA)

Calvin Cycle also known as C3 pathway: because _____________________?

1. one; phosphate; 5-C sugar phosphate

2. • CO₂; Ribulose Bisphosphate (RuBP)

   • 3-Phosphoglycerate (PGA)

3. • PGA

   • BPG

4. • NADPH; BPG

   • BPG; G3P

Calvin Cycle

1. ___ ATP is used to power the addition of a __________ to a _____________

2. Carbon Fixation:

   • ____ (1C) + _______________ (5C)
     →

   • 2 Molecules of ________________ (3C)

3. Reduction Phase:

   • 2 ATP’s add phosphates to the

   • 2 molecules of ____ resulting to

   • 2 molecules of (____)

4. Reduction Phase:

   • 2 ______ add electrons to ____;

   • each ____ is reduced to ____

5. For every 1 CO2 (1C)fixed → 2 G3P (3C) formed

6. Regeneration of the CO2 acceptor

RuBisCO (Ribulose Bisphosphate Carboxylase/Oxygenase)

Carbon Fixation in the Calvin cycle is catalyzed by the enzyme _____ (__________________________________)

RuBisCO (Ribulose Bisphosphate Carboxylase/Oxygenase)

Known as the most abundant protein on earth

Carbon is converted from an inorganic form into an organic form and thereby “FIXED”.

Why is it called carbon fixation?

G3P (3C)

It is used to build sugars; also used to regenerate Ru5P (5C) in the first reaction of the cycle

three; 3

• 3; 6
  

1; 6; 5; 3

For net synthesis of 1 G3P, the cycle must take place ______ times, fixing _ molecules of CO2

• For every _ CO2 → _ G3P is produced in total
  

But only _ G3P out the _ G3P can be counted as a gain and can exit the cycle to be used for the synthesis of sugars as the _ G3P are rearranged into _ Ru5P

PHOTORESPIRATION

Observed in C3 plants when stomata are closed during hot, dry days

PHOTORESPIRATION

Thought to be an evolutionary relic (Rubisco’s affinity for O2 remains)

PHOTORESPIRATION

CO₂ levels ↓ & O₂ levels ↑

• rubisco binds with O₂ instead of CO₂

PHOTORESPIRATION

Drains the Calvin cycle (↓ photosynthetic output)

PHOTORESPIRATION

• No G3P produced

• Considered to be wasteful and no benefit known

photorespiration; CO₂

Rubisco and O₂ under conditions of CO₂ limitations initiates ____________ which breaks down sugars into ____

PHOTORESPIRATION

It occurs in the light (photo); consumes O2 while producing CO2 (respiration); and uses up ATP but produces no sugar molecules.

PHOTORESPIRATION; 50%

______________ reduces photosynthetic efficiency of the Calvin cycle by as much as ___

four-carbon; mesophyll

Some plants minimize photorespiration – by incorporating CO₂ into ___________ compounds in _________ cells

Alternative pathways to minimize photorespiration

1. Hatch-Slack pathway or C4 pathway

2. Crassulacean Acid Metabolism or CAM

Alternative pathways to minimize photorespiration

1. _________________________________

2. _________________________________

• rice

• wheat

• potatoes

• barley

• rye

• coconut

• soybean

• peanut

• sunflower

What are plants can conduct the C3 pathway?

1. Mesophyll

2. PEP carboxylase

3. PEP (phosphoenolpyruvate); Oxaloacetate

4. Malate; bundle sheath; plasmodesmata

5. bundle sheath cells

6. mesophyll; stomata

C4 PATHWAY

1. ___________ cells carry out C4 pathway

2. _____________ binds CO₂ even at low CO₂ concentrations inside leaf

3. CO₂ and ____________ combine to produce a 4-C compound called _____________

4. _________ (4C) is delivered to __________ cell through _____________

5. Calvin cycle (C3) pathway is confined to ______________

6. CO₂ is continually fed into the Calvin cycle from the _________ cells even when the _________ are closed.

7. A high CO₂ concentration is maintained for the Calvin cycle, which minimizes photorespiration.

Which alternative pathway?

Hot, dry environments (tropical grasslands)

Which alternative pathway?

Evolved 30 – 35 million years ago

Which alternative pathway?

3% of all land plants

Which alternative pathway?

79% of the ___ plants species are grasses and sedges

Which alternative pathway?

Examples: corn, sugarcane, sorghum, millet, carabao grass, Bermuda grass, cogon, tumbleweed

Which alternative pathway?

spatial separation of C4 and C3 pathways

Which alternative pathway?

Adapted in arid environments (high light intensity, little precipitation)

Which alternative pathway?

7% of land plants

Which alternative pathway?

Close their stomata during the day and open them only at night. (reverse of typical plants)

Which alternative pathway?

Organic compounds made are “stored” at night in their vacuoles when the stomata are open then used later during the day.

Which alternative pathway?

Common in succulent plants such as: pineapple and cacti and stonecrops

Which alternative pathway?

temporal separation of C4 and C3 pathways