biology EXAM #3 pt.4 Flashcards
Photosynthesis is the process that
Photosynthesis converts
It happens in the
Plants and other
Plants use the energy of …….. = _________
converts solar energy into chemical energy
light energy to the chemical energy of food
chloroplast
autotrophs are the producers of the biosphere
sunlight to make organic molecules from water and carbon dioxide= PHOTOAUTOTROPHS
Photosynthesis occurs in
plants, algae, certain other protists, and some prokaryotes
Chemosynthesis
Organisms (bacteria) in hydrothermal vents use
Produce energy (food) mediated by
Bacteria use
chemicals coming from these places
chemical reactions, use chemicals as source of energy
water, dissolved carbon dioxide, and hydrogen sulfide to create sugar and sulfur compounds1
Heterotrophs:
-Obtain their organic material from :
-Are the…
-Some _____________________; others, called ______________, __________________
-Almost all heterotrophs, including humans, depend on:
other organisms
consumers of the biosphere
Some eat other living organisms; others, called decomposers, consume dead organic material or feces
photoautotrophs for food and O2
Earth’s supply of fossil fuels was formed from
Fossil fuels are
Researchers are exploring methods of
the remains of organisms that died hundreds of millions of years ago
being consumed faster than they are being replenished
using the photosynthetic process to produce alternative fuels
Leaves are the major
Chloroplasts are found mainly in
Each mesophyll cell contains ____ chloroplasts
CO2 enters and O2 exits the leaf through microscopic pores called _______
locations of photosynthesis in plants
cells of the mesophyll, the interior tissue of the leaf
30–40
stomata
A chloroplast has an envelope of
__________ are connected sacs in the chloroplast that compose a third membrane system
These may be stacked in columns called ____
Chlorophyll, the pigment that gives leaves their green color, resides in the ______________
two membranes surrounding a dense fluid called the stroma in mitochondria = matrix
Thylakoids
grana
thylakoid membranes
Photosynthesis is summarized as
(formula)
Chloroplasts split water into _____________, incorporating the :
6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2 O
hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules
Photosynthesis is a redox process where water is ________, carbon dioxide is _______
Photosynthesis is an ________ process; the energy boost is provided by:
Photosynthesis consists of two processes:
water is oxidized, carbon dioxide is reduced
endergonic; light
The light reactions
The Calvin cycle or C3
The light reactions occur :
Splits:
The Calvin cycle
Occurs in the:
Forms :
in the grana (granum), in thylakoids
H2O, release O2, produce ATP, and form NADPH
stroma
sugar from carbon dioxide, using ATP for energy and NADPH for reducing power
The light reactions convert
Light - Is a form of ______________, also called:
Electromagnetic energy travels
Wavelength is
solar energy to the chemical energy of ATP and NADPH
electromagnetic energy, also called electromagnetic radiation
in rhythmic waves
the distance between the crests of waves and determines the type of electromagnetic energy
The visible light spectrum includes
Includes the wavelengths (380nm to 750 nm) that
The other wavelenghts are
Light also behaves as thought it consists of
The electromagnetic is the
the colors of light we can see
produce the colors that we see and that drive photosynthesis
screened out by the atmosphere
discrete particles, or PHOTONS
entire range of electromagnetic energy, or radiation
Pigments are
Different pigments absorb
Wavelengths that are not absorbed are
Leaves appear green because
substances that absorb visible light
different wavelengths
reflected or transmitted
chlorophyll reflects and transmits green light
The spectrophotometer is a
An absorption spectrum is a
machine that sends light through pigments and measures the fraction of light transmitted at each wavelength
graph plotting a pigment’s light absorption versus wavelength
The absorption spectrum of chlorophyll a suggests that
An action spectrum profiles the
violet-blue and red light work best for photosynthesis
relative effectiveness of different wavelengths of radiation in driving a process
The action spectrum for photosynthesis is
Accessory pigments, such as chlorophyll b, broaden the
The difference in the absorption spectrum between chlorophyll a and b is due to a
broader than the absorption spectrum of chlorophyll
spectrum used for photosynthesis
slight structural difference between the pigment molecules
Chlorophyll a is the
Chlorophyll b is an
Other accessory pigments absorb
Other pigment is
main photosynthetic pigment
accessory pigment
different wavelengths of light and pass the energy to chlorophyll a
carrotenoid
In the last decade, two other forms of chlorophyll were discovered—______________________—that absorb:
The cyanobacterium, Chroococcidiopsis thermalis, uses
chlorophyll d and chlorophyll f; higher wavelengths of light
chlorophyll f in place of chlorophyll a in shaded conditions
When a pigment absorbs light, it goes from a
When excited electrons fall back to the
In isolation, some pigments also
ground state to an excited state, which is unstable
ground state, excess energy is released as heat
emit light, an afterglow called fluorescence
A photosystem is composed of a
The reaction-center complex is an
reaction center surrounded by a number of light-harvesting complexes
association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor
The light-harvesting complexes consist of
Funnel the energy of
These chlorophyll a molecules can
pigment molecules bound to particular proteins
photons of light to chlorophyll a molecules in the reaction center complex
transfer exited electrons to a different molecule
A primary electron acceptor in the reaction center accepts
what is the first step of the light reactions?
When a reaction-center chlorophyll molecule absorbs energy, …..
excited electrons and is reduced as a result
Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor
one of its electrons gets bumped up to a primary electron acceptor
The thylakoid membrane is populated by
Photosystem II (PS II) functions _____
The reaction-center chlorophyll a of PS II is called P680 because it is best at absorbing a wavelength of 680 nm
Photosystem I (PS I) is best at absorbing a wavelength of 700 nm
The reaction-center chlorophyll a of PS I is called P700
two types of photosystems, I and II
first
Noncyclic electron flow is the
primary pathway of energy transformation in the light reactions
During the light reactions, there are two possible routes for electron flow:
cyclic and linear
Linear electron flow, the _______ pathway, involves :
Produces :
primary pathway, both photosystems
NADPH, ATP, and oxygen
eight steps in linear electron flow:
1) A photon hits a pigment in a light-harvesting complex of PS II, and its energy is passed among pigment molecules until it excites P680
2) An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)
3) H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680
P680+ is the strongest known biological oxidizing agent
The H+ are released into the thylakoid space
O2 is released as a by-product of this reaction
4) Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I.
Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane.
5) Potential energy stored in the proton gradient drives production of ATP by chemiosmosis
6) In PS I (like PS II), transferred light energy excites P700, which loses an electron to the primary electron acceptor
P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain.
7) Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)
8) NADP+ reductase catalyzes the transfer of electrons to NADP+, reducing it to NADPH
The electrons of NADPH are available for the reactions of the Calvin cycle
This process also removes an H+ from the stroma
The energy changes of electrons during linear flow through the light reactions can be shown in a
mechanical analogy
Under certain conditions, photoexcited electrons take
In cyclic electron flow, only
electrons cycle back from
Cyclic electron flow uses only
an alternative path
photosystem I is used
Fd (protein ferredoxin) to the PS I reaction center via a plastocyanin molecule (Pc)
photosystem I and produces only ATP, but not NADPH. No O2 is released
Several groups of photosynthetic bacteria have
For these organisms, cyclic electron flow is the only means of
Photosynthesis may have first evolved in
Cyclic electron flow may protect cells from
only a single photosystem related to either PS II or PS I
generating ATP during photosynthesis
the ancestors of these bacteria in a form similar to cyclic electron flow
light-induced damage
Cyclic electron flow is probably, in part an
Cyclic electron flow may have some _____________ _______; plants that do not have it:
“evolutionary leftover” in organisms with both photosystems
photoprotective capability; grow well in low light, but cannot grow well in intense light
Chloroplasts and mitochondria generate ATP by
Mitochondria transfer ……….; chloroplasts transform………
Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities
chemiosmosis, but use different sources of energy
chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP
Although the spatial organization of chemiosmosis differs slightly, there are similarities
In mitochondria, protons are :
In chloroplasts, protons are :
In both organelles redox reactions of electron transport chains generate :
ATP synthase uses:
pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
pumped into the thylakoid space and drive ATP synthesis on the stroma side of the membrane as they diffuse back into the stroma
generate a H+ gradient across a membrane
this proton-motive force to make ATP
The light reactions and chemiosmosis:
______________ are produced on the side facing the _______, where the ________ ________ takes place
In summary, light reactions generate ____ and increase: by …..
the organization of the thylakoid membrane
ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place
ATP; the potential energy of electrons by : moving them from H2O to NADPH
The Calvin cycle, like the citric acid cycle regenerates
The Calvin cycle is _________; it builds
It occurs in the ____
its starting material after molecules enter and leave the cycle
anabolic; sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH
stroma
Carbon enters the cycle as _____ and leaves as a ______ named _____
For net synthesis of one G3P, the cycle must take place
The Calvin cycle has three phases:
CO2; leaves as a sugar named G3P
three times, fixing three molecules of CO2
Carbon fixation
Reduction
Regeneration of the CO2 acceptor
Phase 1: Carbon fixation
The binding of CO2 to a ………. is catalyzed by ………
The six-carbon intermediate molecule is immediately split into :
five-carbon sugar named (RuBP) is catalyzed by RuBP, or rubisco
two molecules of 3-phosphoglycerate
Phase 2: Reduction
Each molecule of 3-phosphoglycerate is altered through
For every three CO2 molecules that enter the cycle,
Only one of these can be counted as a
phosphorylation by six ATP and reduction by six NADPH to ultimately produce a G3P sugar
six molecules of G3P are formed
net gain of carbohydrate
Phase 3: Regeneration of the CO2 acceptor (RuBP)
The remaining five molecules of G3P are
Three additional molecules of ATP are
rearranged in a complex series of reactions yielding three molecules of RuBP
used to facilitate the regeneration of RuBP
Dehydration is a problem for plants, sometimes requiring
On hot, dry days, plants :
Conserving water but …
The closing of stomata reduces
These conditions favor an apparently
trade-offs with other metabolic processes, especially photosynthesis
close their stomata
limiting access to CO2 and photosynthesis
access to CO2 and causes O2 to build up
wasteful process called photorespiration
In most plants (_____ plants), (3-phosphoglycerate)
In photorespiration, rubisco adds
Photorespiration consumes
C3 plants; initial fixation of CO2, via rubisco, forms a three-carbon compound
O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound
O2 and organic fuel and releases CO2 without producing ATP or sugar
Photorespiration may be an evolutionary relic because
Photorespiration limits
In many plants, photorespiration is a problem because on a hot, dry day it can
In some plant species, alternate modes of carbon fixation have evolved to
rubisco first evolved at a time when the atmosphere had far less O2 and more CO2
damaging products of light reactions that build up in the absence of the Calvin cycle
drain as much as 50% of the carbon fixed by the Calvin cycle
minimize photorespiration and optimize the Calvin cycle
___ plants minimize the :
by incorporating …..
There are two distinct types of cells in the leaves of C4 plants:
C4 plants minimize the cost of photorespiration
by incorporating CO2 into four carbon compounds in mesophyll cells or oxaloacetate.
Bundle-sheath cells
Mesophyll cells
Bundle-sheath cells are
Mesophyll cells are
In hot, dry weather, C4 plants partially close their _______, conserving ……
C4 has evolved :
Important agricultural examples include:
arranged in tightly packed sheaths around the veins of the leaf. They release CO2 used in the Calvin cycle
loosely packed between the bundle sheath and the leaf surface
stomata, conserving water but reducing CO2
several times and is used by several thousand species in at least 19 different families
sugarcane and corn
Sugar production in C4 plants occurs in a three-step process:
1) The production of the four-carbon precursors is catalyzed by the enzyme PEP carboxylase in the mesophyll cells.
2) These four-carbon compounds are exported to bundle-sheath cells
3) Within the bundle-sheath cells, they release CO2 that is then used in the Calvin cycle
Since the Industrial Revolution in the 1800s, CO2 levels have risen greatly
Increasing levels of CO2 may affect C3 and C4 plants differently, perhaps changing the…
The effects of such changes are unpredictable and a cause for concern
relative abundance of these species
Suitable agricultural land is ______ due to the effects of climate change, while the world demand for food continues to increase
__ photosynthesis uses less water and resources than ___ photosynthesis
Scientists have genetically modified rice, a C3 plant, to carry out C4 photosynthesis
They estimate 30–50% increase in yield compared to C3 rice
decreasing; because of climate change but demand for food is rising
C4 less water than C3
Some plants, including succulents, use
CAM plants :
During the day, the stomata
crassulacean acid metabolism (CAM) to fix carbon
open their stomata at night, incorporating CO2 into organic acids
close and the CO2 is released from the organic acids for use in the Calvin cycle
The CAM pathway is similar to the C4 pathway in that they both incorporate
The C4 pathway structurally separates the
In the CAM pathway, these steps occur in
CO2 into organic intermediates before it enters the Calvin cycle
initial steps of carbon fixation from the Calvin cycle
the same cell, but are separated in time
The energy entering chloroplasts as sunlight gets stored as
Sugar made in the chloroplasts supplies
Plants store excess sugar as
chemical energy in organic compounds
chemical energy and carbon skeletons to synthesize the organic molecules of cells
starch in chloroplasts and other structures such as roots, tubers, seeds, and fruits
review photosynthesis
Light reactions:
* Are carried out by
* Convert light energy to
* Split
Calvin cycle reactions:
* Take place in the stroma
* Use _________ to convert __________
* Return
molecules in the thylakoid membranes
the chemical energy of ATP and NADPH
H2O and release O2 to the atmosphere
the stroma
ATP and NADPH to convert CO2 to the sugar G3P
ADP, inorganic phosphate, and NADP+ to the light reactions
