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Define photosynthesis
a process whereby energy within light is captured and used to synthesize glucose and other organic molecules
T/F Nearly all organisms depend on photosynthesis either directly or indirectly
true
What are the two stages of photosynthesis?
light reactions and the calvin cycle
What happens in the first stage of photosynthesis?
light energy is absorbed by chlorophyll and converted to ATP and NADPH
What happens in the 2nd stage of photosynthesis?
ATP and NADPH are used to drive the synthesis of carbohydrates
Photosynthesis Equation?
CO2+H2O+light energy—> C6H12O6+O2+H2O
In the photosynthesis equation, what is reduced?
CO2
In the photosynthesis equation, what is oxidized?
H2O
Is photosynthesis a endergonic or exergonic rxn?
endergonic, requires an addition of free energy and does not proceed spontaneously
What type of energy drives an endergonic reaction with a free energy change of +685 kcal/mol?
energy from light
Which process is responsible for powering the biosphere?
photosynthesis
define biosphere
regions on the Earth and atmosphere where living organisms exist
What is the biosphere largely driven by?
The photosynthetic power of photosynthetic plants, algae, and cyanobacteria
What is the energy cycle?
a process whereby cells use organic molecules for energy and plants replenish those molecules using photosynthesis
What byproduct do plants produce during photosynthesis?
oxygen
How do heterotrophs sustain life?
must eat food(organic molecules from their environment) to sustain life
examples of heterotrophs
bacteria, protists, fungi, animals
How do autotrophs sustain life?
make organic molecules from inorganic sources
example of an autotroph
photoautotroph
How do photoautotrophs sustain life?
use light as an energy source to make organic molecules
examples of photoautotrophs
plants, algae, cyanobacteria
an important energy cycle between photosynthesis and cellular respiration
photosynthesis is a process in which light, CO2, and H2O are used to produce O2 and organic molecules
the organic molecules are broken down to CO2 and H2O via cellular respiration to supply energy in the form of ATP
for aerobic respiration, O2 is reduced to H2O
What is the chloroplast?
organelle in plants and algae that carries out photosynthesis
What is chlorophyll?
green pigment
Where does the majority of photosynthesis occur?
internally in leaves, in the mesophyll
What is the mesophyll?
the inner tissue of a leaf
What must mesophyll cells receive?
light, water, and carbon dioxide
How do carbon dioxide and oxygen move in and out of a leaf during photosynthesis?
carbon dioxide enters and oxygen exits leaves through pores called stomata
leaves are composed of layers of cells
the epidermal cells are on the outer surfaces w/ mesophyll cells in between
the mesophyll cells contain chloroplasts and are the primary sites of photosynthesis in most plants
What separates the outer and inner membrane of a chloroplast?
intermembrane space
What is the third membrane in a chloroplast called and what does it contain?
the thylakoid membrane, and it contains pigment molecules
What structures are formed by the thylakoid membrane?
thylakoids
What do thylakoids enclose?
the thylakoid lumen
What is a granum?
a stack of thylakoids
What are thylakoids?
flattened fluid-filled tubules
What is the stroma?
fluid-filled region between the thylakoid and inner membrane
CO2 enters the leaf via stomata
product of photosynthesis O2 exits via stomata
Where do light reactions take place?
thylakoid membranes
What do light rxns produce?
ATP, NADPH, O2
Is the calvin cycle a light dependent or independent rxn?
light independent
Where does the Calvin cycle take place?
the stroma
The calvin cycle uses ATP and NADPH to do what?
incorporate CO2 into carbohydrate
The calvin cycle in the stroma uses CO2, ATP, and NADPH to do what?
make carbohydrates
During photosynthesis, where is energy in the form of light transferred from?
the sun to a pigment molecule in a plant
Why is light essential?
to support life on Earth
What type of radiation is light?
electromagnetic radiation
How does light travel?
light travels as waves
What is the range of wavelengths in light?
short to long wavelengths
Define wavelengths
distance between the peaks in a wave pattern
What does the electromagnetic spectrum encompass?
all possible wavelengths of electromagnetic radiation
bottom portion of this figure emphasizes visible light
light in the visible portion of the electromagnetic spectrum drives photosynthesis
How does light behave besides traveling as waves?
as particles called photons
Define photons
massless particles traveling in a wavelength pattern and moving at the speed of light
What type of wavelength radiation carries more energy?
shorter wavelength radiation
How do molecules interact with the energy of visible light?
molecules can absorb the energy of visible light in a way that does not cause damage
What do pigments do with light energy?
pigments absorb some light energy and reflect others
Why are leaves green?
leaves are green because they absorb red and violet wavelengths and reflect green wavelengths
What happens to electrons during light absorption?
Absorption boosts electrons to higher energy levels.
What determines the wavelength of light that a pigment absorbs?
the amount of energy needed to boost an electron to a higher orbital
How do different pigments benefit plants?
allows plants to absorb light at many different wavelengths
What happens to an electron after it absorbs energy?
it is in an excited state and usually unstable
How does an electron release energy?
as heat or light
What can happen to excited electrons in pigments?
can be transferred to another molecule or "captured"
What do different pigment molecules in plants absorb?
the light energy used in photosynthesis
What do chlorophylls a and b contain?
a porphyrin ring
What is bound to the porphyrin ring in chlorophyll?
a magnesium ion
What are carotenoids and where are they commonly found?
another pigment in chloroplasts and are often the major pigments in flowers and fruit
What does an absorption spectrum plot?
a pigment’s light absorption as a function of the light's wavelength
In which parts of the spectrum do chlorophylls absorb light strongly and what do they reflect?
chlorophylls absorb light strongly in the red and violet parts of the spectrum and reflect green
Which wavelengths of light do carotenoids absorb and reflect?
carotenoids absorb blue and blue-green visible light and reflect yellow and red
What does an action spectrum plot?
the rate of photosynthesis as a function of the wavelength of light
How do different pigments benefit plants in terms of light absorption?
different pigments allow plants to absorb light at many different wavelength
With which wavelengths do the highest rates of photosynthesis in green plants correlate?
the wavelengths that are strongly absorbed by chlorophylls and carotenoids
these absorption spectra show the absorption of light by chlorophyll a, b, and b-carotene
shows the action spectrum of photosynthesis depicting the relative rate of photosynthesis in green plants at different wavelengths of light
What can captured light energy be transferred to, and what does it produce
other molecules to produce energy-intermediate molecules for cellular work
What do the thylakoid membranes of chloroplasts contain?
two distinct complexes of molecules, Photosystem I (PSI) and Photosystem II (PSII)
Which photosystem was discovered first?
Photosystem I (PSI) was discovered first
Which photosystem is involved in the first step of photosynthesis?
Photosystem II (PSII)
What happens when light excites pigment molecules?
t happens in both PSII and PSI
What is the initial step in photosynthesis?
light exciting electrons in pigment molecules within the light-harvesting complex of photosystem 2
Where is energy transferred in Photosystem II?
the P680 pigment molecule
What does Photosystem II do to water molecules?
oxidizes water, generating O₂ and H⁺
Where do electrons go after exiting PSII?
electrons exit PSII and enter an electron transport chain
What is the energy from the electrons used for in the electron transport chain?
used to make an H⁺ electrochemical gradient
Primary role of photosystem 1?
to make NADPH
What happens when light hits the light-harvesting complex of PSI(photosystem 1)?
a high-energy electron is removed from the P700 pigment molecule and transferred to a primary electron acceptor
What role does ferredoxin play in Photosystem I?
accepts two high-energy electrons and transfers electrons to NADP⁺ reductase
How is NADPH produced in Photosystem I?
electrons are transferred to NADP⁺, which also accepts an H⁺ to produce NADPH
What is linear electron flow in Photosystem I?
the movement of electrons linearly from PSII to PSI to reduce NADP⁺ to NADPH
the movement of electrons from photosystem 2 to photosystem 1 to NADPH is called linear flow
How is ATP synthesis in chloroplasts achieved?
by a chemiosmotic mechanism called photophosphorylation
What drives the synthesis of ATP in chloroplasts?
the flow of H⁺ from the thylakoid lumen into the stroma via ATP synthase
How is the H⁺ gradient generated in chloroplasts?
Increase of H⁺ in the thylakoid lumen by the splitting of water
Increase of H⁺ by the electron transport chain (ETC) pumping H⁺ into the lumen
Increase of H⁺ in the stroma from the formation of NADPH
How is oxygen (O₂) produced in the thylakoid lumen?
by the oxidation of H₂O by PSII
What happens to the electrons from the oxidation of H₂O?
they are transferred to P680⁺ molecules
How is NADPH produced in the stroma?
high-energy electrons that start in PSII and are boosted in PSI
What is the chemical reaction for the production of NADPH?
NADP⁺ + 2 electrons + H⁺ → NADPH
How is ATP produced in the stroma?
by ATP synthase using the H⁺ electrochemical gradient
In noncyclic electron flow, where do electrons begin and where do they eventually transfer to?
electrons begin at PSII and eventually transfer to NADPH, following a linear process
What does noncyclic electron flow produce?
both ATP and NADPH in equal amounts
Note 
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