7.1-7.5 Chloroplasts

All life on earth depends on solar energy

Photosynthetic organisms (algae, plant and cyanobacteria) transform solar energy into the chemical energy of carbohydrates.

• called autotroph because they produce their own food

Photosynthesis

A process that captures solar energy. Transforms solar energy into chemical energy. Energy ends up stored in a carbohydrate.

(Photo-synthesizers produce food energy) feed themselves as well as heterotrophs (like humans)

Heterotrophs

Are known as consumers. Both autotrophs and heterotrophs use organic molecules produced by photosynthesis as a source of chemical energy for cellular work.

Photosynthesis in flowering plants

Photosynthesis takes place in the green portions of plants.

• the leaf of the ___ contains mesophyll tissue

• Cells containing chloroplasts are specialized to carry out photosynthesis

The raw materials for photosynthesis are carbon dioxide and water

• Roots absorb water that move up the vascular tissue.

• Carbon dioxide enters a leaf through small openings called stomata and diffuses into chloroplast in mesophyll cells

• The Thylakoid membranes of chloroplasts in mesophyll cells and other pigments that can absorb the solar energy that drives photosynthesis

• Electrons are energized in the process then, carbon dioxide is reduced to form a carbohydrate.

• In the stroma , CO2 combines either H2O to form C6H12O6 sugar

Light reactions

Take place only in the presence of light. They are energy-capturing reactions. Chlorophyll absorbs solar energy(This energizes electrons) Electrons more down an electron transport chain

• The electron transport chain pump is H+ into thylakoids.

• The electron transport chain is used to make ATP out of ADP, and NADPH out of NADP+

Calvin cycle reactions

Take place in the stroma

• CO2 is reduced to a carbohydrate

• Reactions use ATP and NADPH to produce carbohydrate

• Reactions were named after Melvin Calvin, who used carbon isotope to trace carbon in photosynthesis

Photosynthesis involves?

• Oxidation - is the loss of, and reduction is the gain of electrons

• In ____ , carbon dioxide is reduced and water is oxidized

Pigments and Photosynthesis

• Chemicals that absorb certain wavelengths of light are ___

• Wavelengths that are not absorbed by ___ are reflected or transmitted

Absorption Spectrum

Pigments found in chlorophyll absorb various portion of the various colors of the rainbow. Chlorophyll is green because it absorbs much of the reds and blues of white and reflects green light

Carotenoids

Are necessary pigments which absorb light in the violet-blue-green range and reflect yellow and orange light

Fall example 🍂

The lack of chlorophyll reveals yellow and orange pigments that were already in the leaves. Darker red leaves 🍁 are the result of a chemical change:

Sugars that can get trapped in the leaves produce new pigments (called anthocyanin) that weren’t part of the leaf in growing season

Electron flow in the light reactions

Consist of : Noncyclic pathways

____ capture light energy with photosynthesis ( there are two, PS1 & PS2)

• a photosystem is a pigment complex that helps collect solar energy, like an antenna

• Photosystems are located in the thylakoid membranes. Both cyclic and noncyclic pathways produce ATP. The non-cylic pathway also produces NADPH

PS2 function

Captures light energy. Noncyclic pathways begins with photosystem 2. It causes an electron to be ejected from the reaction center (chlorophyll a)

• Electrons travel down a transport chain (ETC) to PS1

• Replaced with an electron from water, which is split to form O2 and H+

• This causes H+ to accumulate in the thylakoid chambers (inside)

• The H+ gradient is used to produce ATP

PS1 function

Captures light energy and ejects an electron.

• The electron is transferred permanently to a molecule of NADP+

• Causes NADPH production

PS2 consists?

• Pigment complex and electron acceptors

• Receives electrons from splitting of water

• Oxygen is released as gas

PS1 consists?

• Pigment complex and electron acceptors

• Adjacent to the enzyme that reduces NADP+ to NADPH

Electron transport chain

Consists of cytochrome complexes and plastoquinone

• Carries electron between PS2 and PS1

• Also pumps H+ from the stroma into the thylakoid space

ATP Production

The thylakoid space acts as a reservoir for hydrogen ions (H+). Each time water is oxidized, two H+ remain in the thylakoid space. Transfer of electrons in the electron transport chain yields energy.

• This energy is used to pump H+ across the thylakoid membranes.

• Protons move from the stroma into the thylakoid space.

The flow of H+ back across the thylakoid membrane?

Energizes ATP synthase.

ATP synthase enzymatically produces ATP from ADP+ phosphate.

This method of producing ATP is called chemiomosis because ATP production is tied to the establishment of an H+ gradient.

A cylical series of reactions.

Utilizes atmosphere carbon dioxide to produce carbohydrates. Known as C3 photosynthesis.

Involved three stages

• Carbon dioxide fixation

• Carbon dioxide reduction

• RuBP regeneration

Step 1: Fixation of Carbon Dioxide)

CO2 is attached to a 5-Carbon RuBP by the enzyme RuBP carboxylase.

• Results in a 6-Carbon molecule

• This splits into two 3-Carbon molecules (3PG)

• Reaction is accelerated by RuBP carboxylase (Rubisco) CO2 is now “fixed” because it is part of a carbohydrate.

Step 2: Reduction of Carbon dioxide

3PG is reduced to BPG

BPG is then reduced to G3P

Electrons and energy are required for this stage. This stage utilizes NADPH and some ATP produced in the light reactions

• G3P id reduced and chemically able to store more energy and form larger organic molecules such as glucose.

Reduction of carbon dioxide

As 3PG becomes G3P, ATP becomes ADP+ phosphate and NADPH becomes NADP+

The importance of the Calvin cycle

G3P (glyceraldchyde-3-phosphate) can be converted to many other molecules. The hydrocarbon skeleton of G3P forms:

• Fatty Acids and glycerol to make plant oils

• Glucose phosphate (simple sugars)

• Fructose (which with glucose = sucrose)

• Starch and cellulose

• Amino acids

The majority of plants carry out?

C3 photosynthesis

• These use RuBP carboxylase to fit CO2 to the RuBP in the mesophyll cells.

In hot dry climates:

• Stomata must close to avoid wilting

• CO2 decreases and O2 increases

• O2 starts combining with RuBP, leading to the production of CO2.

• This is called photorespiration

C4 plants

Solve the problem of photorespiration. Fix CO2 to PEP (a C3 molecule) The result is oxaloscetate, a C4 molecule

In hot and dry climates:

• C4 plants avoid photorespiration

• Net productivity is about 2 to 3 times greater than C3 plants

C3 plants

In cool and moist enviroments, C4 plants cant compete with C3 plants

CAM Photosynthesis

Crassulaccan-acid metabolism.

__ Plants portion carbon fixation by time

During the night

• __ plants fix CO2

Form C4 molecules, which are stored in large vacuoles

During daylight

• NADPH and ATP are available

• Stomata are closed for water convervation

• C4 molecules release CO2 to calvin cycle

Photosynthesis and Adaption to the environment

The differences between methods in photosynthesis have their advantages and disadvantages.

• depends on the climate

C4 plants most adapted to:

• High light intensity

• High temperature

• Limited rainfall

C3 plants most adapted to:

• Cold (below 25C)

• High moisture

CAM plants are better adopted to?

Extreme acidity

• CAM occurs in 23 families of flowering plants

• They are also found among non flowering plants

Thylakoid

Small disk like structure

Stroma

Fluid filled space that surrounds the thylakoid

Light dependent reactions occur in the?

Thylakoid

Calvin cycle occurs in the?

Stroma

Photons

Smallest unit of light. Isolate along a path and are measured as wavelengths

Electromagnetic spectrum

Light emitted from the sun contains photons in a wide spectrum of wavelengths

Photolysis

Splitting molecules of water releasing electrons ( the electrons being generated during ___ replenish the electrons being lost in PS2) also creating gas

ATP and NADPH

Are used in the calvin cycle reaction and are recycled back into light reactions as ADP and NADP+

Calvin cycle begins with

3 molecules of carbon dioxide (3 CO2)

3 CO2 is combined with 3 RuBP

(Process is called CO2 fixation)

Which then splits and creates 6 3PG C3

The second part of the Calvin cycle (reduction)

Uses energy products made during light reactions to reduce 3PG

(requires an input of energy which is supplied by 6 ATP)

Which turns into 6 ADP + 6 phosphate

Reduction involves a addition of electrons

In the calvin cycle it is supplied by 6 NADPH which turns into 6 NADP+

The reduction of electrons reduces 3PG into G3P

And 6 NADP+ and 6 ADP + phosphate return to light reactions.

Third cycle of Calvin cycle ( regeneration of RuBP

The last step is a recycling stage ♻

5 G3P is modified using ATP ( which originated in the light reactions )

Creating 3 ADP + 3 phosphate

RuBP produced by this stage may be used to fix more CO2 restarting the cycle