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29 Cards in this Set

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What is an autotroph?
Any organism that manufactors its own organic molecules from inorganic materials
What is a chemotroph?
Simple autotrophic bacteria that use chemosynthesis to obtain energy for the manufacture of organic materials
How do photosynthetic bacteria work?
They lack chloroplasts but have membranes that function in a similar manner
Where does photosynthesis take place?
In chloroplasts that contain chlorophyll
Describe a chloroplast:
Chloroplasts are bounded by two membranes

Contains network of membranes called thylakoid membranes

Chlorophyll resides within the membrane

Thylakoid sacs are stacked into columns called grana

Fluid matrix of the chloroplast is called the stroma
What is chlorophyll?
Complex molecule containing over 100 atoms

Complexed with metal magnesium

When chlorophyll absorbs light, electrons in the ground state are boosted to an excited state and can be harnessed to drive the reactions of photosynthesis
Why is chlorophyll green?
Chlorophyll absorbs red and blue and reflects green wavelength
What are the two principle types of chlorophyll?
Chlorophyll a

Chlorophyll b

Both of which are part of two photosystems
What is chlorophyll a in photosystem I called?
P700 because it absorbs best at 700 nm
What is chlorophyll a in photosystem II called?
P680 because it absorbs best at 680 nm
What is the overview of photosynthesis?
Reduction of CO2 to carbohydrate accompanied by release of oxygen from water.

Net reaction is reverse of respiration - reduction occurs instead of oxidation

6CO2 + 12H2) + light -> C6H12O6 + 6O2 + 6H2O

Can be divided into two distinct reactions: light & dark
Overview of Light Reactions:
AKA Photolysis

Begin with absorption of a photon by a chlorophyll molecule

When light strikes the special chlorophyll a P700 molecule in photosystem I, it excites electrons to a higher energy level

These high energy electrons can flow along two pathways giving cyclic electron flow or noncyclic electron flow.
Describe Cyclic Electron Flow:
The excited electrons of P700 move along a chain of electron carriers

Series of redox reactions ultimatly returns the electrons to P700

Reactions harnessed to produce ATP from ADP and Pi in process called cyclic photophosphorylation

Coenzyme carrier ferrodoxin os one of the early electron carriers in this electron transport chain
Describe Noncyclic Electron Flow for P700:
Key pathway of the light reactions and involves reactions of both photosystems

Instead of running electron along chain, high-energy electrons are transferred to the electron acceptor NADP+

NADP+ accepts the high energy electrons and forms NADPH

P700 is left with electron "holes", therefore powerful oxidizing agent
Describe Noncyclic Electron Flow for P680:
Light strikes P680 in photosystem II, electrons excited

Travel same electron carrier chain used by cyclic electron fluw utnil they reach P700 and fill the electron "holes"

Produces ATP by noncyclic photophosphorylation

P680 now has "holes" and can oxidize water into 2 H ions and O atom, electrons reduce P680 and O2 is formed

Net result is production of NADPH and ATP and photolysis (breakdown) of water
Where does the oxygen produced by photosynthesis come from?
Photolysis of water, NOT CO2
What is the main purpose of the dark reaction?
AKA carbon-fixation or reduction synthesis reactions

Use ATP and NADPH to reduce CO2 to carbohydrates

These reactions don't directly require light, they will only occur during the day when the ATP and NADPH supply is replenished
Where does the oxygen produced by photosynthesis come from?
Photolysis of water, NOT CO2
What is the main purpose of the dark reaction?
AKA carbon-fixation or reduction synthesis reactions

Use ATP and NADPH to reduce CO2 to carbohydrates

These reactions don't directly require light, they will only occur during the day when the ATP and NADPH supply is replenished
What is the source of the carbon for carbohydrate production?
CO2
How many times must the dark reaction occur to produce a three carbon sugar from CO2?
Three Times
Where is the principle site for photosynthesis in leaves?
In the leaves
What are the several adaptations in leaves for photosynthesis?
Waxy Cuticle
Palisade layer
Spongy Layer
Guard Cells
What is the waxy cuticle?
Wax layer on top of leaves to prevent water loss
What is the palisade layer?
Elongated chloroplast-containing cells spread over a large surface area

Directly under upper epidermis and are well exposed to light
What is the spongy layer?
Stomatas open into air spaces which contact internal moist surface of loosely packed cells

Allows for diffusion as well as increased surface area for gas exchange
What are guard cells?
Surround each of the stomata on lower surface of leaf

Stomata open when there is increased turgor in them

Stomata close when there is descreased turgor in them
What is transpiration?
Water vapor loss from plants
How do the guard cells work?
During the day, guard cells contain chloroplasts and produce glucose

Presense of high glucose content in cells causes them to swell due to osmosis (turgor)

Inner wall of guard cell is thickened so an opening is created

At night, photosynthesis ceases, cell tugor decreases, and stomata close