biology EXAM #3 pt.4

Question 1

Photosynthesis is the process that

Photosynthesis converts

It happens in the

Plants and other

Plants use the energy of …….. = _________

Answer 1

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

Question 2

Photosynthesis occurs in

Answer 2

plants, algae, certain other protists, and some prokaryotes

Question 3

Chemosynthesis

Organisms (bacteria) in hydrothermal vents use

Produce energy (food) mediated by

Bacteria use

Answer 3

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

Question 4

Heterotrophs:
-Obtain their organic material from :
-Are the…
-Some _____________________; others, called ______________, __________________

-Almost all heterotrophs, including humans, depend on:

Answer 4

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

Question 5

Earth’s supply of fossil fuels was formed from

Fossil fuels are

Researchers are exploring methods of

Answer 5

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

Question 6

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 _______

Answer 6

locations of photosynthesis in plants

cells of the mesophyll, the interior tissue of the leaf

30–40

stomata

Question 7

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 ______________

Answer 7

two membranes surrounding a dense fluid called the stroma in mitochondria = matrix

Thylakoids
grana

thylakoid membranes

Question 8

Photosynthesis is summarized as
(formula)

Chloroplasts split water into _____________, incorporating the :

Answer 8

6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2 O

hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules

Question 9

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:

Answer 9

water is oxidized, carbon dioxide is reduced

endergonic; light

The light reactions
The Calvin cycle or C3

Question 10

The light reactions occur :
Splits:

The Calvin cycle
Occurs in the:
Forms :

Answer 10

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

Question 11

The light reactions convert

Light - Is a form of ______________, also called:

Electromagnetic energy travels

Wavelength is

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Pigments are

Different pigments absorb

Wavelengths that are not absorbed are

Leaves appear green because

Answer 13

substances that absorb visible light

different wavelengths

reflected or transmitted

chlorophyll reflects and transmits green light

Question 14

The spectrophotometer is a

An absorption spectrum is a

Answer 14

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

Question 15

The absorption spectrum of chlorophyll a suggests that

An action spectrum profiles the

Answer 15

violet-blue and red light work best for photosynthesis

relative effectiveness of different wavelengths of radiation in driving a process

Question 16

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

Answer 16

broader than the absorption spectrum of chlorophyll

spectrum used for photosynthesis

slight structural difference between the pigment molecules

Question 17

Chlorophyll a is the

Chlorophyll b is an

Other accessory pigments absorb

Other pigment is

Answer 17

main photosynthetic pigment

accessory pigment

different wavelengths of light and pass the energy to chlorophyll a

carrotenoid

Question 18

In the last decade, two other forms of chlorophyll were discovered—______________________—that absorb:

The cyanobacterium, Chroococcidiopsis thermalis, uses

Answer 18

chlorophyll d and chlorophyll f; higher wavelengths of light

chlorophyll f in place of chlorophyll a in shaded conditions

Question 19

When a pigment absorbs light, it goes from a

When excited electrons fall back to the

In isolation, some pigments also

Answer 19

ground state to an excited state, which is unstable

ground state, excess energy is released as heat

emit light, an afterglow called fluorescence

Question 20

A photosystem is composed of a

The reaction-center complex is an

Answer 20

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

Question 21

The light-harvesting complexes consist of

Funnel the energy of

These chlorophyll a molecules can

Answer 21

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

Question 22

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, …..

Answer 22

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

Question 23

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

Answer 23

two types of photosystems, I and II

first

Question 24

Noncyclic electron flow is the

Answer 24

primary pathway of energy transformation in the light reactions

Question 25

During the light reactions, there are two possible routes for electron flow:

Answer 25

cyclic and linear

Question 26

Linear electron flow, the _______ pathway, involves :

Produces :

Answer 26

primary pathway, both photosystems

NADPH, ATP, and oxygen

Question 27

eight steps in linear electron flow:

Answer 27

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

Question 28

The energy changes of electrons during linear flow through the light reactions can be shown in a

Answer 28

mechanical analogy

Question 29

Under certain conditions, photoexcited electrons take

In cyclic electron flow, only

electrons cycle back from

Cyclic electron flow uses only

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Cyclic electron flow is probably, in part an

Cyclic electron flow may have some _____________ _______; plants that do not have it:

Answer 31

“evolutionary leftover” in organisms with both photosystems

photoprotective capability; grow well in low light, but cannot grow well in intense light

Question 32

Chloroplasts and mitochondria generate ATP by

Mitochondria transfer ……….; chloroplasts transform………

Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities

Answer 32

chemiosmosis, but use different sources of energy

chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP

Question 33

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:

Answer 33

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

Question 34

The light reactions and chemiosmosis:

______________ are produced on the side facing the _______, where the ________ ________ takes place

In summary, light reactions generate ____ and increase: by …..

Answer 34

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

Question 35

The Calvin cycle, like the citric acid cycle regenerates

The Calvin cycle is _________; it builds

It occurs in the ____

Answer 35

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

Question 36

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:

Answer 36

CO2; leaves as a sugar named G3P

three times, fixing three molecules of CO2

Carbon fixation
Reduction
Regeneration of the CO2 acceptor

Question 37

Phase 1: Carbon fixation

The binding of CO2 to a ………. is catalyzed by ………

The six-carbon intermediate molecule is immediately split into :

Answer 37

five-carbon sugar named (RuBP) is catalyzed by RuBP, or rubisco

two molecules of 3-phosphoglycerate

Question 38

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

Answer 38

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

Question 39

Phase 3: Regeneration of the CO2 acceptor (RuBP)

The remaining five molecules of G3P are

Three additional molecules of ATP are

Answer 39

rearranged in a complex series of reactions yielding three molecules of RuBP

used to facilitate the regeneration of RuBP

Question 40

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

Answer 40

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

Question 41

In most plants (_____ plants), 
(3-phosphoglycerate)

In photorespiration, rubisco adds

Photorespiration consumes

Answer 41

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

Question 42

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

Answer 42

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

Question 43

___ plants minimize the :
by incorporating …..

There are two distinct types of cells in the leaves of C4 plants:

Answer 43

C4 plants minimize the cost of photorespiration

by incorporating CO2 into four carbon compounds in mesophyll cells or oxaloacetate.

Bundle-sheath cells

Mesophyll cells

Question 44

Bundle-sheath cells are

Mesophyll cells are

In hot, dry weather, C4 plants partially close their _______, conserving ……

C4 has evolved :

Important agricultural examples include:

Answer 44

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

Question 45

Sugar production in C4 plants occurs in a three-step process:

Answer 45

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

Question 46

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

Answer 46

relative abundance of these species

Question 47

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

Answer 47

decreasing; because of climate change but demand for food is rising

C4 less water than C3

Question 48

Some plants, including succulents, use

CAM plants :

During the day, the stomata

Answer 48

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

Question 49

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

Answer 49

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

Question 50

The energy entering chloroplasts as sunlight gets stored as

Sugar made in the chloroplasts supplies

Plants store excess sugar as

Answer 50

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

Question 51

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

Answer 51

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