Chapter 10: Photosynthesis

the process that converts solar energy into chemical energy
Photosynthesis is
photosynthesis nourishes almost the entire living world
Directly or indirectly
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without eating anything derived from other organisms
Autotrophs sustain themselves
Autotrophs are the producers of the ________producing organic molecules from CO2 and other inorganic molecules
photoautotrophs, using the energy of sunlight to make organic molecules
Almost all plants are
in plants, algae, certain other unicellular eukaryotes, and some prokaryotes
Photosynthesis occurs in
also most of the living world
These organisms feed not only themselves but
from other organisms
Heterotrophs obtain their organic material
of the biosphere
Heterotrophs are the consumers
photoautotrophs for food and O2
Almost all heterotrophs, including humans, depend on
the remains of organisms that died hundreds of millions of years ago
Earth’s supply of fossil fuels was formed from
solar energy from the distant past
In a sense, fossil fuels represent stores of
light energy to the chemical energy of food
Photosynthesis converts
and likely evolved from photosynthetic bacteria
Chloroplasts are structurally similar to
the chemical reactions of photosynthesis
The structural organization of these organelles allows for
are the major locations of photosynthesis
Leaves are
cells of the mesophyll
Chloroplasts are found mainly in
the interior tissue of the leaf
Cells of the mesophyll are
30-40 chloroplasts
Each mesophyll cell contains
CO2 enters and O2 exits the leaf through microscopic pores called
an envelope of two membranes surrounding a dense fluid
A chloroplast has
an envelope of two membranes surrounding a dense fluid
stroma is
connected sacs in the chloroplast which composes a third membrane system
Thylakoids are
Thylakoids may be ______ in columns.
stacks of of thylakoids in column
Grana are …
the pigment which gives leaves their green colour, resides in the thylakoid membrane
Chlorophyll is …which gives leaves their colour
a complex series of reactions
Photosynthesis is a
the reverse of the one that occurs during cellular respiration
The overall chemical change during photosynthesis is
split H2O into hydrogen and oxygen
incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product
In chloroplasts, the split of water and oxygen are
Photosynthesis reverses the direction of electron flow compared to
redox process in which H2O is oxidized and CO2 is reduced
Photosynthesis is a
endergonic process; the energy boost is provided by light
Photosynthesis is an
the light reactions (the photo part) and Calvin cycle (the synthesis part)
Photosynthesis consists of
Split H2O
Release O2
Reduce the electron acceptor NADP+ to NADPH
Generate ATP from ADP by photophosphorylation
The light reactions (in the thylakoids)
sugar from CO2, using ATP and NADPH
The Calvin cycle (in the stroma) forms
carbon fixation, incorporating CO2 into organic molecules
The Calvin cycle begins with
chemical factories
Chloroplasts are solar-powered
the chemical energy of ATP and NADH
Chloroplasts thylakoids transform light energy into
form of electromagnetic energy, from the light travels in the rythmic
Light is a
light travels in rhythmic waves
Like other electromagnetic energy,
a graph plotting a pigment’s light absorption versus wavelength
An absorption spectrum is
violet-blue and red light work best for photosynthesis
The absorption spectrum of chlorophyll a suggests that
profiles the relative effectiveness of different wavelengths of radiation in driving a process
An action spectrum
the main photosynthetic pigment
Chlorophyll a is
chlorophyll b
Accessory pigments, such as
broaden the spectrum used for photosynthesis
Chlorophyll b
to a slight structural difference between the pigment molecules
The difference in the absorption spectrum between chlorophyll a and b is due
Accessory pigments called _________ absorb excessive light that would damage chlorophyll
a ground state to an excited state, which is unstable
When a pigment absorbs light, it goes from
fall back to the ground state, photons are given off, an afterglow called fluorescence
When excited electrons
an isolated solution of chlorophyll will fluoresce, giving off light and heat
If illuminated
a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes
A photosystem consists of
pigment molecules bound to proteins
The light-harvesting complexes aka:
transfer the energy of photons to the reaction center
The light-harvesting complexes
excited electrons and is reduced as a result
A primary electron acceptor in the reaction center accepts
the first step of the light reactions
Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is
in the thylakoid membrane
There are two types of photosystems
functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm
Photosystem II (PS II)
The reaction-center chlorophyll a of PS II is called
is best at absorbing a wavelength of 700 nm
Photosystem I (PS I)
The reaction-center chlorophyll a of PS I is called
two possible routes for electron flow: cyclic and linear
During the light reactions, there are
the primary pathway, involves both photosystems and produces ATP and NADPH using light energy
Linear electron flow is
8 steps
There are _ _____ in linear electron flow
A photon hits a pigment and its energy is passed among pigment molecules until it excites P680
Step 1:
An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)
Step 2:
H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680
Step 3:
P680+ is the strongest known biological _________ agent
O2 is _______as a by-product of this reaction
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
__________ of H+ (protons) across the membrane drives ATP synthesis.
In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor
P700+ (P700 that is missing an electron) accepts an electron passed down from _____via the electron transport chain
Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)
The electrons are then transferred to NADP+ and reduce it to NADPH
the Calvin cycle
The electrons of NADPH are available for the reactions of ___ ______ _____.
The process of transferring an electron to NADP+ also removes an ___ from the stroma
electrons cycle back from Fd to the PS I reaction center.
In cyclic electron flow
photosystem I and produces ATP, but not NADPH
Cyclic electron flow uses only
In cyclic electron flow no _______ is released.
PS I but not PS II
Some organisms such as purple sulfur bacteria have
linear electron flow.
Cyclic electron flow is thought to have evolved before
light-induced damage
Cyclic electron flow may protect cells from
cyclic and linear
During the light reactions, there are two possible routes for electron flow:
primary pathway, involves both photosystems and produces ATP and NADPH using light energy
Linear electron flow is the
cycle back from Fd to the PS I reaction center
In cyclic electron flow the electrons
Cyclic electron flow uses only photosystem I and produces ___, but not _____.
In the cyclic electron flow process no __ is released.
chemiosmosis, but use different sources of energy
Chloroplasts and mitochondria generate ATP by
food to ATP
Mitochondria transfer chemical energy from
the chemical energy of ATP
chloroplasts transform light energy into
Spatial organization of chemiosmosis differs between _________ and __________ but also shows ______.
pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
In mitochondria, protons are
pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma
In chloroplasts, protons are
Calvin cycle
ATP and NADPH are produced on the side facing the stroma, where the ______ ______ takes place
moving them from H2O to NADPH
In summary, light reactions generate ATP and increase the potential energy of electrons by
molecules enter and leave the cycle
The Calvin cycle, like the citric acid cycle, regenerates its starting material after
using ATP and the reducing power of electrons carried by NADPH
The cycle builds sugar from smaller molecules by
a sugar named glyceraldehyde 3-phospate (G3P)
Carbon enters the cycle as CO2 and leaves as
For net synthesis of 1 G3P, the cycle must take place______ times.
After the cycle takes place three times it fixes _ molecules of ___
1) Carbon fixation (catalyzed by rubisco)
2) Reduction
3) Regeneration of the CO2 acceptor (RuBP)
The Calvin cycle has three phases:
Carbon fixation is catalyzed by…
(Ribulose Bisphosphate carboxylase-oxygenase
RuBP is also known as
Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially _______________.
On hot, dry days, plants close ________.
conserves H2O but also limits photosynthesis
By closing the stomata in a plant the plant …
CO2 and causes O2 to build up
The closing of stomata reduces access to
favors conditions in hot arid climates that is considered wasteful
three-carbon compound (3-phosphoglycerate)
In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a
O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound
In photorespiration, rubisco adds
organic fuel
Photorespiration consumes __ and ______ ____ and releases ___ without producing ___ or _______.
rubisco first evolved at a time when the atmosphere had far less O2 and more CO2
Photorespiration may be an evolutionary relic because
light reactions that build up in the absence of the Calvin cycle
Photorespiration limits damaging products of
50% of the carbon fixed by the Calvin cycle
In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as
chemical energy in organic compounds
The energy entering chloroplasts as sunlight gets stored as
carbon skeletons to synthesize the organic molecules of cells
Sugar made in the chloroplasts supplies chemical energy and
starch in structures such as roots, tubers, seeds, and fruits
Plants store excess sugar as
the O2 in our atmosphere
In addition to food production, photosynthesis produces
-Are carried out by molecules in the thylakoid membranes
-Convert light energy to the chemical energy of ATP and NADPH
-Split H2O and release O2 to the atmosphere
Light Reactions
-Take place in the stroma
-Use ATP and NADPH to convert CO2 to the sugar G3P
-Return ADP, inorganic phosphate, and NADP+ to the light reactions
Calvin Cycle Reactions
Autotrrophes, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.
Which of the following statements is a correct distinction between autotrophs and heterotrophs?
Chlorophyll absorbs all of the visible spectrum of light except green, which it reflects.
What property of the pigment chlorophyll makes it appear green?
Through the stomata
How does carbon dioxide enter the leaf?
The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.
During the Calvin cycle, what happens during the carbon fixation phase?
They are the ultimate sources of organic compounds for all nonautotrophic organisms.
Why are most autotrophs referred to as the producers of the biosphere?
NADPH; ATP; oxygen
The light reactions of photosynthesis generate high-energy electrons, which end up in __________. The light reactions also produce __________ and __________.
Thylakoid membrane
The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives this chemiosmosis is formed across which structure(s)?
While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.
You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?
ATP and NADPH produce in the light reactions provide the energy for the production of sugars in the Calvin cycle
The Calvin cycle could not occur without the light reactions. Which of the following statements describes why this is the case?
CO2 is reduced.
Of the following, which occurs during the Calvin cycle?
The light reactions of photosynthesis supply the Calvin cycle with __________.
The light reactions by linear electron flow
During which process is molecular oxygen produced in photosynthesis?
Oxidative phosphorylation in cellular respiration
In the light reactions of photosynthesis, ATP is produced by photophosphorylation. Which of the listed processes is most similar to photophosphorylation?
movement of H+ through a membrane
The energy used to produce ATP in the light reactions of photosynthesis comes from __________.
Thylakoid membranes
Chlorophyll molecules are in which part of the chloroplast?
The light reactions of photosynthesis occur in the __________.
G3P production
Which of the following processes occurs during the second phase, the reduction phase, of the Calvin cycle?
use chemiosmosis to produce ATP
Both mitochondria and chloroplasts __________.
The Calvin cycle requires products only produced when the photosystems are illuminated
The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night. Why?
their electrons become excited
When chloroplast pigments absorb light, __________.
Carbon dioxide and oxygen enter and exit a leaf by diffusion. Which structure(s) on a leaf allow(s) this process to happen?
carbon dioxide
In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.
-Chlorophyll molecules
-Primary electron acceptor
-Reaction-center complex
-Light-harvesting complexes
A photosystem consists of which of the following structures?
The most important role of pigments in photosynthesis is to __________.
Water is oxidized and carbon dioxide is reduced.
Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?
The first product of carbon fixation in C4 plants is a four-carbon compound instead of a three-carbon compound.
Which of the following statements correctly describes the difference in carbon fixation between C3 and C4 plants?
The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from __________.
-Production of cell walls in growing plants
-Production of starch
-Production of glucose
-Production of cellulose
-Production of sucrose
G3P is used in which of the following processes?
Where do the electrons entering photosystem II come from?

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