Photosynthesis:
Trapping the Sun's Energy
) Before You Read
c.atte,g photoslmttresis' is
This section teils how plants trap sunlight to make."".Ig-y. The proceT,
key terms rrr the Read to Learn section'
one of the key ,"r*, fo, thls ,".aiorr. #ghligh_t each of the
Then use a different color to highlight the definition of each key tenn'
) Read to Learn
Trapping EnergY from Sunlight
STUIIY GOAGH
Make Flash Cards For each
paragraph, think of a question that might be on a test.
Write the question on one
side of a flash card. Write the
answer on the other side.
Quiz yourself until You know
all the answers.
1. What are the
two Parts
of photosynthesis?
Chapter 9
plents and other green organisms must trap light energy from
the sun to be able ,J or. it. ihe energy must then be stored in a
form that can be used by cells. That form is AIP. The process
plants use ro trap and make energy from suniigtrt is called photosynthesis. During photosynthesis, plants use the sunt energy to
*rk simple togrii These sllgars are then made into complex
carbohydrates, such as starch. These starches store energ'y'
Theie are rwo parts to photosynthesis: light-dependent redctions and light-independent reactions. Tlre light'dependent
reactions .irrrg" light energy into chemical energy' This results
in the splitting if *rt.t and the release of o4ygen' The lightindependent reactions produce simple sugars' d
Where does photosynthesis take place?
The chloroplast is the part of the plant's leaf where phgtosilnthesis takes place. The chloroplast conrains pigments, wtrich are
molecules that take in specificwavelengths of sunlight' Wavelengths of sunlight tt"t tf.t energy. The most common pigment
in the chloroplast is chlorophyll.
Chlorophyll is a plant pig*".rt tlat absorbs most_wavelengths
of sunlighi .*."pt green. B".rot. it cannot take in the green
*rrr"l.rigth, it rlflJ.ts the green. This is what makes leaves look
green. Ii A" fall, leaves stop producing chloroph,ii, so other pigir.r,.r, become visible. This-gives leaves a wide variety of colors.
READING ESSENTIALS
Photosynthesis: Trapping the Sun's Energy,
Lig
continued
ht-Dependent Reactions
2. What happens during the
The first phase of photospthesis needs sunlight. The sunJight
Calvin cycle?
in
the
plant's
chlorophyll
leaves
and
the
energy
from
strikes the
the sunlight is tansferred to electons in the chlorophyll. The
elecffons move from the chlorophyll to an electron transport
chain. An electron transport chain is a line of proteins embedded in a membrane along which the electrons are passed down.
Each protein in the line passes the electron to the next protein.
fu the electrons pass along this line, they lose
some of their energy. If you filled a bucket with
Light-Dependent Reactions
water and passed it along a line of people very
ri ;
" tl€3*
._a{o$.lss*
quickliz, some of the water would spill out. This is
*isun*ffi
*&'is''
similar to how the electons lose their energy.
.:
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Light energy
What happens to the lost energy?
,!}i
q
I
tran sfers to, chl or o oh vll.
The energy the electrons lose can be
used to form ATP from ADP, which you learned
about in the last section. Energy that is not used
to form AIP can be stored for use in the lightindependent reactions. The energy is stored in an
electron carrier called NADPH, shown at the
right. NADPH carries the energy to the tight-
rs&
fr
ffi
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Ch I orophyll
independent reactions.
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Light-lndependent Reactions
The second phase of photosynthesis does not
need sunlight. It takes place in the chloroplast and
is called the Calvin cycle. The Calvin cycle uses
carbon dioxide to form sugars. The sugars then
become stored energ'y. It is a large task for a cell
to make sugars from carb-on dioxide. The AIP
and NADPH produced in the light-dependent
reactions are used. The chloroplast breaks down
this large task into very smail steps. The end result
is energy that is stored in the plant as sugars.
Organisms that eat plants use t}ese sugars to
give them energy. The energy is used in cellular
respiration, which you will learn about in the
next section. d
pa
sses en
ergy
down through the
eledrontransportchain.
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Energized eledrons provide
energy that
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oonas
-(
"L'roo* \.ffi3;l
+
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toaor
forming
ATP
NADPH
{or use in the
I i g ht- i ndepend e nt re adi ons.
ro
READING ESSENTIALS
Chapter
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Name
Photosynthesisl Trapping the Sun's Energy'
continued
) After You Read
Mini Glossary
Calvin cycle: series of reactions durinE the lightindlpendent phase-of photosynthesis in
whic'h sugars are for'rned from carbon dioxide using ATP and NADPH from the lightdependent reactions
chlorophyll: Iight-absorbing pigment in plants
to*" other green organisms that is
"na
required for photosynthesis; absorbs most
wavelengths of light except for green
electron transport chain: series of proteins
embedded in a membrane along which
energized electrons are transported; as electroniare passed from molecule to molecule,
energy is released
light-dependent reactions: phase of photosyntheiis where light energy is converted to
chemical energy in the form of ATP; results
in the splitting of water and the release
light-independent reactions: phase of photosynthesii where energy from light-dependent
reactions is used to produce sugar and additional ATP molecules
by which plants and
photosynthesis:
' other green process
organisms trap energy from
sunlight with chlorophyll and use this
energy to convert carbon dioxide and water
into simPle sugars
pigments: molecules that absorb specific wavelengths of sunlight
one of the key
1. Read the key terms and their definitions in the Mini Glossary above. Circle
terms and, in the space provided, define it in your own words.
il
f,il
the question in the
2. select one of the question headings in the Read to Learn section. W'rite
that follow.
space below. Then write your ans\trer to that question on the lines
Question:
f,1
Answer:
f,
F
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Chapter 9
READING ESSENTIALS
i
Photosynthesis: Trapping the Sun's Energy,
cantinued
3. Complete the concept diagram below using the following terms: AIP, Calvin cycle,
chlorophyll, electron transport chain, light-dependent reactions, Iight-independent
reactions, and NADPH.
Phases
Light energy transfers to
of Photosynthesis
Use carbon dioxide to
form sugars that are stored
as energy in the
which passes the energy
through the
Lost energy is
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used too form
form
stored as
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Visit the Glencoe Science Web site at science.gtencoe.com to find
your biology book and learn more about photosynthesis.
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READING ESSENTIALS
Chapter 9
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