[BOTAONE-LE2] photosynthesis

PHOTOSYNTHESIS

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

• How water, sunlight, and carbon dioxide are used to form oxygen and glucose.

• Is a redox process → Water is oxidized, carbon dioxide is reduced

6CO2 + 12H2O + light energy > C6H12O6 + 6O2

Complete equation for photosynthesis

In all photoautotrophic organisms.

Where does photosynthesis take place?

Heterotrophic

• Humans, animals, fungi, most protozoa

• Ingests food for energy
  Requires complex organic compounds of nitrogen and carbon (such as that obtained from plant or animal matter) for metabolic synthesis

Autotrophic

• Plants, lichens, and algae

• Produces its own food
  A living thing that can make its own food from simple chemical substances such as carbon dioxide

Anabolic

• build

• Small molecules are assembled into large ones and energy is needed. Build complex molecules from simple ones.
  Example: amino acid to proteins and Photosynthesis (builds sugar from smaller molecules)

Catabolic

• break

• Large molecules into simpler molecules, release energy.
  Example; Breaking down of glucose molecules and Cellular respiration (breaking down of glucose)

Endergonic Reaction (ENDO - "In")

• Absorbs energy

• Non-spontaneous reaction

• Absorbs energy, meaning it requires energy

• Examples: Photosynthesis and when energy is absorbed in the ATP-ADP cycle

Exergonic Reaction (EXO - "Out")

• Releases energy

• Spontaneous reaction

• Can happen even with little or no energy

Example: Cellular respiration and when energy is released in the ATP-ADP cycle

the leaves, specifically in mesophyll (chloroplasts)

Where are the major site of photosynthesis in true leaves

Light dependent reactions

Light independent/ calvin cycle/ dark reactions

The two processes of photosynthesis

The light dependent reactions

• Conversion of light (solar) energy to chemical energy (ATP and NADPH)

• photochemical procesS

• Need sunlight

• Inside the thylakoids.

• Oxidizes water into oxygen.

• Some energy is used to make ATP.

  • Reactants:
    Water
    Light

    NADP+

    ADP+P

  • Products:
    ATP

    NADPH

LIGHT

• Consists of certain particles called photons;
  each photon has a fixed quantity of energy.
  Is a form of electromagnetic energy, which travels in waves

Wavelength

What is the distance between crest waves that determines the electromagnetic energy

Electromagnetic spectrum

entire range of electromagnetic energy or radiation

Visible light spectrum

Includes the colors of light we can see (reflected radiation)
Includes the wavelengths that drive photosynthesis.
Photosynthetic pigments absorb the visible spectrum.

Chlorophyll a

• (blue-green-color pigment) absorbs red-orange and blue-violet regions

• main light capturing or photosynthetic pigment

• Found in all autotrophic organisms.

Chlorophyll B

• accessory pigment that broadens the spectrum used for photosynthesis.

• (yellow-green-colored pigment) absorbs light from the red-blue region

• In all true plants

a slight structural difference between the pigment molecules.

What is The difference in the absorption spectrum between chlorophyll a and b

Carotenoids

• accessory pigments that absorb excessive light that would damage chlorophyll.

• (orange-colored pigment) absorbs blue-green and violet region

THE ACTION SPECTRUM FOR PHOTOSYNTHESIS

Description: A graph plotting a pigment's light absorption versus wavelength

Profiles the relative effectiveness of different wavelengths of radiation in driving a process.

• Absorption spectrum of Chlorophyll A - suggests that violet-blue and red light work best for photosynthesis.

Thylakoids

• in cell membrane in cyanobacteria

• In chloroplasts in algae

WHERE ARE THE PHOTOSYNTHETIC PIGMENTS FOUND? (1. Generally, 2. In Cyanobacteria, and 3.Algae)

Photosystems

Thylakoids have organized complexes Called..

PS1, PS2, ATP synthase

What is a photosystem composed of

Photosystem I (PS I) : P700

Photosystem II (PS II): 680

The thylakoid membrane is populated by two types of photosystems which are

1. Their large nitrogen requirement for Rubisco and other photosynthetic enzymes (need rubisco)

   • Rubisco accounts for about 25% of the nitrogen in photosynthetic cells

2. Their dependence on products of the light-harvesting reactions (ATP and NADPH), which in turn depend on irradance, i.e. the light received by the photosynthetic cell (no light no reaction)

3. majority of g3p will regenrate RuBP to turn half a glucose thats why its so inefficient

What are the 3 most notable features of carbon-fixation reactions

Calvin Cycle or C₃ pathway

is the main biosynthetic pathway of carbon fixation.

Rubisco

both a carboxylase and an oxygenase.
As a carboxylase, it initiates carbon fixation reactions.
As oxygenase, it catalyzes a reaction between Rubisco and oxygen under conditions of CO2

photorespiration

• Initiates breakdown of sugars to CO2

• It occurs in the light (photo);consumes 02 while producing CO2 (respiration); and uses up ATP but produces no sugar molecules.

• Photorespiration reduces photosynthetic efficiency of the Calvin cycle by as much as 50%.

Carbon fixation

occurs in the dark reaction or light-independent reaction of the photosynthesis process.

The Calvin Cycle or dark reactions

takes place in the stroma of the chloroplast. Unlike in the Krebs cycle wherein the products are used for ATP synthesis, the product of the this cycle is used for the production of glucose.

carbon fixation, carbon activation & reduction, and RuBP regeneration

The 3 parts of calvin cycle

C4 plants

• Live in hot, moist environments

• 15% of plants

• Grasses, corn, sugarcane

• Divides photosynthetic spatially

• Light rn - mesophyll cells

• Calvin cycle - bundle sheath cells

CAM plants

cactus

• 5% of plants

• Live in hot, dry environments

• Cactus, ice plants

• Stomates closed during the day and open during the night.

• Light rxn- occurs during the day.

• Calvin cycle - occurs when CO2 is present.

Hatch and Slack Pathway

To fix carbon dioxide, this pathway is the alternate to the C3 cycle.

C3 plants

C3 vs C4

Uses calvin cycle for the dark reaction of photosynthesis

C3 Plants

C3 vs C4

These plants are cool-season plants commonly found in cool and wet areas

C3 plants

• 80% of total green plants are..

• Its product is also a 3 carbon compound (phosphoglyceric acid)

C3

C3 vs C4

these plants are abundant in temperate conditions

C4

C3 vs C4

• These plants use hatch-slack pathway for the dark reaction in photosynthesis

• warm-season plants, commonly found in dry areas

C4

C3 vs C4

• the product is a 4 carbon compound (oxaloacetic acid)

• About 15% of plants are…

C4

C3 vs C4

These plants are abundant in tropical conditions

C3 plants

C3 vs C4

• In this, the bundle sheath cells do not contain chloroplasts.

• ___plants possess only one CO2 acceptor. __ plants do not consist of secondary CO2 acceptor.

• It performs photosynthesis only when stomata are open.

C4 plants

• In this, the bundle sheath cells contain chloroplasts.

• __ plants possess two CO2 acceptors. ___ plants consist of secondary CO2 acceptor.

• It performs photosynthesis even when stomata are close.

Calvin cycle > glucose

Glycolysis > atp,nad, pyruvate

Acetyl Coa> fadh, acetyl coa

Citric acid cycle > nadh, fadh, atp

Electron transport chain or Oxidative phosphorylation > conversion of nadh and fadh to ATP

Overall process of atp production

C3 plants

• The optimum temperature for photosynthesis is very low.

• less efficient in photosynthesis.

• The photorespiration rate is very high.

• CO2 fixation is slow

• In this, the dark reaction takes place only in the mesophyll cells.

C4 plants

• The optimum temperature for photosynthesis is high.

• C4 plants are more efficient in photosynthesis.

• Photorespiration is absent.

• CO2 fixation It is comparatively faster .

• In this, mesophyll cells will only perform the initial steps of the cycle. main steps are carried out in bundle sheath cells.

Rice, Wheat, Soybean, Oats

Example of C3 plants

Corn, Sugarcane, Sorghum

Examples of c4 plants

Light reactions (summary)

• Are carried out by molecules in the thylakoid membranes

• Convert light energy to the chemical energy of ATP and NADPH

• Split H20 and release O, to the atmosphere

Calvin cycle reactions (summary)

• Take place in the stroma

• Use ATP and NADPH to convert
  CO, to the sugar G3P

• Return ADP, inorganic phosphate, and NADP+ to the light reactions

“photo”

Light reaction (thylakoid)

“synthesis”

Calvin cycle (stroma)

Light dependent reaction process summary

Photo-excitation (PS2)

Pushes to ETC (PS2)

Photolysis (split of H2O) (in thylakoids)

Chemiosmosis (H+ goes down ATP synthase)

ADP > ATP reduction

NADP+ > NADPH reduction