Chapter 7 - How Cells Capture Light Energy via Photosynthesis

Process of photosynthesis capture ? energy and uses this energy to synthesize ?

CO2 is ?

H2O is ?

Capture light energy, synthesize carbohydrates

CO2 is reduced

H20 is oxidized

General equation for photosynthesis is:

6CO₂  +  6H₂O  +  Light energy  →  C₆H₁₂O₆  +  6O₂ 

            ΔG = +686 kcal/mol

Energy from light drives this ? reaction

endergonic

Biosphere refers to ? on the surface of the earth and ? where living organisms exist.

Regions, atmosphere

Autotrophs

make organic molecules from inorganic sources; plants

Photoautotrophs are most and use ? as a source of energy

Light as source of energy

Heterotrophs must?

consume food; acquire organic molecules from their envrionment

Life is primarily driven by the ? activity of ?, ? and ?

Driven by photosynthetic activity, of Plants, Algae, and Cyanobacteria

Which organelle carry out photosynthesis; containing the pigment chlorophyll.

Chloroplasts

In most plants, photosynthesis occurs in the leaves, specifically within the ? cells

Mesophyll cells

Opening int he leaf surface, called?

allow the passage of ? and ?

Stomata

CO2 and O2

Chloroplast structures include:

the outer membrane, intermembrane space, inner membrane, stroma, thylakoid membranes (stacked to form grana), and the thylakoid lumen

The light reactions involve a series of ? conversions, starting with ? energy and ending with ? energy stored in ? and ?

Energy conversions, starting with light energy, ending with chemical energy stored in NADPH and ATP

ATP and NADPH provide the ? and ? needed to make ? during the ? cycle.

Energy and electrons needed to make Carbs during the Calvin cycle

Light is a type of ? radiation; it consists of?

Electromagnetic radiation, consists of energy in the form of electric and magnetic fields.

Light travels as ?

waves

Light also behaves as particles called ?

Photons

When light encounters a molecule:

1. It may pass through the molecule

2. It may bounce off the molecule, changing its path toward a different direction

3. It may be absorbed by the molecule, pigments are molecules that can absorb light

Pigments absorb some ?

Light energy and reflect other; the wavelegnth of light that pigment absorbs depends on amount of energy needed to boost an electron to a higher orbital.

After an electron absorbs energy,

It is an excited state and usually unstable

The electron may release energy in different ways:

1. As heat

2. As light (fluorescence)

3. Excited electrons in pigments can be transferred to another molecule or “captured”

Two types of chlorophyll pigments:

Chlorophyll a and chlorophyll b

Chlorophyll a and chlorophyll b are found in

Green plants and green algae.

Chlorophyll a and chlorophyll b:

Contain porphyrin ring with a delocalized electron; delocalized electron can absorb light energy

Hydrocarbon tail anchors the pigment to proteins withn the thylakoid membrane

Carotenoids are another type of ?

Pigment

Having different pigments allows plants to

Absorb light at many diff wavelengths

An absorption spectrum is a graph that depicts the

Wavelengths that are absorbed by diff pigments

An action spectrum depicts the

Rate of photosynthesis by a whole plant at specific wavelengths

The thylakoid membranes contain 2 distinct complexes of proteins and pigment molecules called?

Photosystem I and Photosystem II

Light excited pigment molecules in both:

PS II and PS I

The combined action of PS II and PS I is termed ?

Linear electron flow; this process produces O2, ATP and NADPH.

Role of photosystem II in linear electron flow:

The initial step in photosynthesis

Excited electrons travel from PS II to PS I

Oxidized water, generating O2 and H+

Releases energized electrons to electron transport chain (some energy used to make H+ electrochemical gradient.

Role of photosystem I in linear electron flow:

Primary role to make NADPH

Addition of H+ to NADPH+ contributes to H+ gradient that fuels ATO synthase activity

The process of ATP production in the chloroplast is called

Photophosphorylation

Linear electron flow produces ATP and NADPH is roughly

Equal amounts, however the Calvin cycle uses more ATP than NADPH

Another path of electron flow called?

Cyclic electron flow, produces additional ATP

Cyclic electron flow produces

Only ATP

Cyclic flow is favored when the level of ? is low and ? is high; it is also favored when ? levels are low.

When the level of NADP+ is low and NADPH is high; it is also favored when ATP levels are low.

PS I and PS II have 2 main components:

Light harvesting complex, and a Reaction Center

Light-Harvesting (aka ?) is composed of dozens of

AKA antenna complex

Composed of dozens of pigment molecules anchored to transmembrane proteins.

Directly absorbs photons of light and transfers energy between pigments by a process of resonance energy transfer.

Light-Harvesting Complex directly absorbs..

Photons of light and transfers energy between pigments by a process of resonance energy transfer

Reaction Center is the site where

The redox reaction takes place; it contains P680, a special pigment molecule.

P680 is a:

It releases?…

Special pigment molecule

Releases its high energy electron and is oxidized

P680* → P690+ + e-

Water is ? to replace the electrons on P680+

Oxidized

PS II is the only known protein complex that can ?

Oxidize water, resulting in the release of O2

The Z scheme is a model developed in ? that proposed….

1960, Proposed that photosynthesis involved 2 events of light absorption.

Z scheme is consistent with linear flow:

PS II to PS I to NADPH

The ATP and NADPH generated during the light reactions are used during the

Calvin Cycle, to make Carbs

The reactions of the Calvin cycle require a ?

Massive input of energy

For every 6 CO2 incorporated, how many ATP and NADPH must be used?

18 ATP and 12 NADPH

The product of the Calvin cycle is ?

Glyceraldehyde-3-phosphate (G3P), a carb with 3 carbon atoms that can be used in the synthesis of glucose and other organic molecules.

The Calvin Cycle is divided into 3 phases:

Carbon Fixation

Reduction and Carbohydrate Production

Regeneration of RuBP

Carbon Fixation

CO2 is incorporated into RuBP, a 5-carbon sugar; the enzyme rubisco catalyzes this reaction and the 6-carbon intermediate splits into two 3-carbon molecules

Reduction and Carbohydrate Production

ATP is used as a source of energy and NADPH is used as a source of high-energy electrons; G3P is produced

Regeneration of RuBP

Most of the G3P is used to regenerate RuBP, allowing the cycle to continue

What conditions can alter the operation of the Calvin Cycle?

Environmental Conditions:

Temp, Water availability, and Light intensity

Most plants (~?%) are called ? plants because the…

~90%, C3 plants because the first molecule that CO2 is incorporated into (3PG) is a 3-carbon molecule

Photorespiration occurs when ?

Rubisco adds O2; as intermediates are processed, a molecule of CO2 is released.

Considered wasteful since loss of carbon can limit plant growth

If C3 plants are subjected to hot and dry environments, as much as ?-?% of their photosynthetic work is ? by photorespiration.

25-50%, Reversed by Photorespiration

What plants make oxaloacetate (4 carbon molecule) in the first step of carbon fixation?

C4 Plants

Leaves have two-cell layer organization:

Mesophyll cells

Bundle-sheath Cells

Mesophyll cells capture

CO2 into oxaloacetate (using enzyme that only binds CO2) that transport the captured carbon to the bundle-sheath cells.

Bundle-sheath cells

where the calvin cycle occurs

CAM plants open their?

What is captured and stored?

Stomata at night

CO2 captured and stored

Stomata close during the day to conserve?

During the day, stored ? is released and enters the Calvin cycle.

Water; CO2

You can tell whether the C3 or C4 plant is better because

Of the environment

In cooler climates, C3 used ? energy to fix CO2

Less energy

C4 and CAM plant adaptations evolved to help plants living in hot and dry environments to?

Conserve water and minimize photorespiration