Chapter Eight- Photosynthesis

8-1 Energy and Life
Copyright Pearson Prentice Hall

Living things need energy to survive.
This energy comes from food. The energy
in most food comes from the sun.

Plants are able to use light
energy from the sun to
produce food.

autotrophs –Organisms that make their
own food, such as plants.
heterotrophs must get energy from the
foods they consume. Ex. Animals
I can
make my
own
food!!
I will
eat
you!!

Chemical Energy and ATP
Energy comes in many forms including light,
heat, and electricity.
Energy can be stored in chemical
compounds, too.

An important chemical compound that cells use to
store and release energy is adenosine
triphosphate, abbreviated ATP.
Adenosine triphosphate or ATP is
used by all types of cells as their
basic energy source.
ATP
Movie

ATP consists of:
•adenine
•ribose (a 5-carbon sugar)
•3 phosphate groups
Adenine
ATP
Ribose 3 Phosphate groups

The three phosphate groups are the key to
ATP's ability to store and release energy.

Storing Energy
ADP has two phosphate groups
instead of three.
A cell can store small amounts of energy by
adding a phosphate group to ADP.
ADP ATP
Energy
Energy
Partially
charged
battery
Fully
charged
battery
+
Adenosine Diphosphate
(ADP) + Phosphate
Adenosine Triphosphate (ATP)

Releasing Energy
Energy stored in ATP is released
by breaking off the third
phosphate.
P
ADP
2 Phosphate groups

The energy from ATP is needed for many
cellular activities, including active transport
across cell membranes, protein synthesis
and muscle contraction.
ATP’s characteristics make it
exceptionally useful as the basic
energy source of all cells.

Using Biochemical Energy
Using Biochemical Energy
Most cells have only a small amount of ATP,
because it is not a good way to store large
amounts of energy.
Cells can regenerate ATP from ADP as
needed by using the energy in foods like
glucose.

8-1
Organisms that make their own food are called
a. autotrophs.
b. heterotrophs.
c. decomposers.
d. consumers.

8-1
Most autotrophs obtain their energy from
a. chemicals in the environment.
b. sunlight.
c. carbon dioxide in the air.
d. other producers.

8-1
How is energy released from ATP?
a. A phosphate is added.
b. An adenine is added.
c. A phosphate is removed.
d. A ribose is removed.

8-1
How is it possible for most cells to function
with only a small amount of ATP?
a. Cells do not require ATP for
energy.
b. ATP can be quickly regenerated from
ADP and P.
c. Cells use very small amounts of
energy.
d. ATP stores large amounts of energy.

8-1
Compared to the energy stored in a molecule of
glucose, ATP stores
a. much more energy.
b. much less energy.
c. about the same amount of energy.
d. more energy sometimes and less at
others.

8-2 Photosynthesis: An
Overview

Photosy
nthesis:
An
Overvie
w
The key cellular process identified with energy
production is photosynthesis.
Photosynthesis is the process
in which green plants use the
energy of sunlight to convert
water and carbon dioxide
into sugar and oxygen.

Investigating Photosynthesis
Research into photosynthesis began centuries ago.
Van Helmont’s Experiment
a. In the 1600s, Jan van Helmont wanted to find out
if plants grew by taking material out of the soil.
b. He determined the mass of a pot of dry soil and
a small seedling, planted the seedling in the pot,
and watered it regularly.
c. After five years, the seedling was a small tree
and had gained 75 kg, but the soil’s mass was
almost unchanged.

igatin
g
Photo
synth
a.Van Helmont concluded that
the gain in a plants’ mass
comes from water because water
was the only thing he had added.
b. His experiment accounts for the “hydrate,” or
water, portion of the carbohydrate produced
by photosynthesis.

igatin
g
Photo
synth a. Although van Helmont did not realize it,
carbon dioxide in the air also made a
major contribution to the mass of his
tree.
b. In photosynthesis, the carbon in carbon
dioxide is used to make sugars and
other carbohydrates.
c. Van Helmont had only part of the story,
but he had made a major contribution
to science.

Joseph Priestley discovered oxygen
and that plants release it.
More than 100 years after van Helmont’s
experiment--
a. Priestley took a candle, placed a glass jar over
it, and watched as the flame gradually died
out.
b. He reasoned that the flame needed something
in the air to keep burning and when it was
used up, the flame went out. That substance
was oxygen.

a. Priestley then placed a live sprig of mint
under the jar and allowed a few days to pass.
b. He found that the candle could be relighted
and would remain lighted for a while.
c. The mint plant had produced the substance
required for burning. In other words, it had
released oxygen.

Jan Ingenhousz
a.Later, Jan Ingenhousz
showed that the effect observed by
Priestley occurred only when the plant
was exposed to light.
b. The results of both Priestley’s and
Ingenhousz’s experiments showed that
light is necessary for plants
to produce oxygen.

igatin
g
Photo
synth
The experiments performed by van
Helmont, Priestley, and Ingenhousz led to
work by other scientists who finally
discovered that, in the presence of light,
plants transform carbon dioxide and water
into carbohydrates, and they also release
oxygen.

The equation for photosynthesis is
6CO2 + 6H2O Light
C6H12O6 + 6O2
carbon water sugars oxygen
dioxide
Photosynthesis uses the energy of sunlight
to convert water and carbon dioxide into
high-energy sugars and oxygen.
Photosynthesis
activity

Light energy
O2
CO2
+
H20
ADP
NADP+
Sugar
Light-
Dependent
Reactions
(thylakoids)
H2O
ATP
NADPH
Calvin
Cycle
(stroma)

Light
and
Pigme
nts
In addition to water and carbon
dioxide, photosynthesis
requires light and chlorophyll.

Plants gather the sun's energy
with light-absorbing molecules
called pigments.
The main light-absorbing pigment
in plants is chlorophyll.
There are two main types of chlorophyll:
chlorophyll a
chlorophyll b

Chlorophyll absorbs light well in the blue-violet
and red regions of the visible spectrum.
Wavelength (nm)
100
80
60
40
20
0
400 450 500 550 600 650 700 750
Wavelength (nm)
Estimated Absorption (%)

Chlorophyll does not absorb light well in the green
region of the spectrum. Green light is reflected
by leaves, which is why plants look green.
Wavelength (nm)
100
80
60
40
20
0
400 450 500 550 600 650 700 750
Wavelength (nm)
Estimated Absorption (%)

Light is a form of energy, so any compound
that absorbs light also absorbs energy from
that light.
When chlorophyll absorbs light, much of the
energy is transferred directly to electrons in
the chlorophyll molecule, raising the energy
levels of these electrons.
These high-energy electrons are what make
photosynthesis work.

8-2
In van Helmont's experiment, most of the added
mass of the tree came from
a. soil and carbon dioxide.
b. water and carbon dioxide.
c. oxygen and carbon dioxide.
d. soil and oxygen.

8-2
Plants use the sugars produced in
photosynthesis to make
a. oxygen.
b. starches.
c. carbon dioxide.
d. protein.

8-2
The raw materials required for plants to carry out
photosynthesis are
a. carbon dioxide and oxygen.
b. oxygen and sugars.
c. carbon dioxide and water.
d. oxygen and water.

8-2
The principal pigment in plants is
a. chloroplast.
b. chlorophyll.
c. carotene.
d. carbohydrate.

8-2
The colors of light that are absorbed by
chlorophylls are
a. green and yellow.
b. green, blue, and violet.
c. blue, violet, and red.
d. red and yellow.

8-3 The Reactions of
Photosynthesis

Inside a Chloroplast
In plants, photosynthesis takes
place inside chloroplasts.
Plant
Plant cells
Chloroplast
Chloroplast
movie

Chloroplasts contain thylakoids—
saclike photosynthetic membranes.
Chloroplast
Single
thylakoid

Inside
a
Chlor
opTlahstylakoids are arranged in stacks known as
grana. A singular stack is called a granum.
Granum
Chloroplast

Proteins in the thylakoid membrane organize
chlorophyll and other pigments into
clusters called photosystems, which are
the light-collecting units of the chloroplast.
Chloroplast
Photosystems

The long chain of photosynthesis reactions is
divided into two parts
The light-dependent reactions take
place within the thylakoid
membranes.
The Calvin cycle takes
place in the stroma,
which is the region outside the
thylakoid membranes.

Light
Chloroplast
H2O
O2
Copyright PHOTOSYNTHESIS Pearson Prentice Hall
CO2
Sugars
NADP+
ADP + P
Light-dependent
reactions
Calvin
cycle

Electr
on
Carrie
rs
When electrons in chlorophyll absorb sunlight,
the electrons gain a great deal of energy.
Cells use electron carriers to transport these
high-energy electrons from chlorophyll to
other molecules.

Electr
on
Carrie
rs
One carrier molecule is NADP+.
Electron carriers, such as NADP+,
transport electrons.
NADP+ accepts and holds 2 high-energy
electrons along with a hydrogen ion (H
+). This converts the NADP+ into
NADPH.

Electr
on
Carrie
rs
The conversion of NADP+ into NADPH is one
way some of the energy of sunlight can be
trapped in chemical form.
The NADPH carries high-energy electrons to
chemical reactions elsewhere in the cell.
These high-energy electrons are used to help
build a variety of molecules the cell needs,
including carbohydrates like glucose.

The light-dependent reactions require light.
The light-dependent reactions
produce oxygen gas and
convert ADP and NADP+
into the energy carriers
ATP and NADPH.
Light-dependent
movie

Depen
dent
Reacti
ons
Photosystems I and II carry out the
light-dependent reactions and are
in the thylakoid membrane.

Depen
dent
Reacti
ons Photosynthesis begins when pigments in
Photosystem
II
photosystem II absorb light, increasing
their energy level.

These high-energy electrons are passed
on to the electron transport chain.
Photosystem
II
Electron
carriers
High-energy
electron

Enzymes on the thylakoid membrane
break water molecules into:
Photosystem
II
2H2O
Electron
carriers
High-energy
electron

hydrogen ions
oxygen atoms
energized electrons
Photosystem
II
2H2O
+ O2
Electron
carriers
High-energy
electron

The energized electrons from water replace
the high-energy electrons that chlorophyll
lost to the electron transport chain.
Photosystem
II
2H2O
+ O2
High-energy
electron

As plants remove electrons from water, oxygen
is left behind and is released into the air.
Photosystem
II
2H2O
+ O2
High-energy
electron

The hydrogen ions left behind when water is
broken apart are released inside the
thylakoid membrane.
Photosystem
II
2H2O
+ O2
High-energy
electron

Energy from the electrons is used to
transport H+ ions from the stroma into the
inner thylakoid space.
Photosystem
II
2H2O
+ O2

High-energy electrons move through the
electron transport chain from photosystem II
to photosystem I.
Photosystem
II
2H2O
+ O2
Photosystem I

Pigments in photosystem I use energy
from light to re-energize the electrons.
2H2O
+ O2
Photosystem I

NADP+ then picks up these high-energy
electrons, along with H+ ions, and becomes
NADPH.
2H2O
+ O2
2 NADP+
2
2 NADPH

As electrons are passed from chlorophyll
to NADP+, more H+ ions are pumped
across the membrane.
2H2O
+ O2
2 NADP+
2
2 NADPH

Soon, the inside of the membrane fills up
with positively charged hydrogen ions,
which makes the outside of the membrane
negatively charged.
2H2O
+ O2
2 NADP+
2
2 NADPH

The difference in charges across the
membrane provides the energy to make ATP
2H2O
+ O2
2 NADP+
2
2 NADPH

H+ ions cannot cross the membrane directly.
2H2O
+ O2
ATP synthase
2 NADP+
2
2 NADPH

The cell membrane contains a protein called
ATP synthase that allows H+ ions to pass
through it
2H2O
+ O2
ATP synthase
2 NADP+
2
2 NADPH

As H+ ions pass through ATP synthase, the
protein rotates.
2H2O
+ O2
ATP synthase
2 NADP+
2
2 NADPH

As it rotates, ATP synthase binds ADP and a
phosphate group together to produce ATP.
2H2O
+ O2
2 NADP+
2
ATP synthase
ADP
2 NADPH

Because of this system, light-dependent
electron transport produces not only high-energy
2H2O
electrons but ATP as well.
+ O2
ATP synthase
2 NADP+ ADP
2
2 NADPH

The light-dependent reactions use water,
ADP, and NADP+.
The light-dependent reactions produce
oxygen, ATP, and NADPH.
These compounds provide the energy to
build energy-containing sugars from low-energy
compounds.

The Calvin Cycle
ATP and NADPH formed by the light-dependent
reactions contain an abundance
of chemical energy, but they are not stable
enough to store that energy for more than a
few minutes.
During the Calvin cycle plants use the energy
that ATP and NADPH contain to build high-energy
compounds that can be stored for a
long time.

The Calvin cycle uses ATP and
NADPH from the light-dependent
reactions to
produce high-energy sugars.
Because the Calvin cycle does not require
light, these reactions are also called
the light-independent
reactions.
Calvin Cycle
Movie

Six carbon dioxide molecules enter the cycle from
the atmosphere and combine with six 5-carbon
molecules.
CO2 Enters
the Cycle

The result is twelve 3-carbon molecules, which
are then converted into higher-energy forms.

The energy for this conversion comes from
ATP and high-energy electrons from NADPH.
Energy Input
12
12 ADP
12 NADPH
12 NADP+

Two of twelve 3-carbon molecules are
removed from the cycle.
Energy Input
12
12 ADP
12 NADPH
12 NADP+

The Calvin Cycle
The molecules are used to produce sugars,
lipids, amino acids and other compounds.
12
12 ADP
6-Carbon sugar
produced
Sugars and other compounds
12 NADPH
12 NADP+

The 10 remaining 3-carbon molecules are
converted back into six 5-carbon molecules,
which are used to begin the next cycle.
6 ADP
5-Carbon Molecules
Regenerated
12
12 ADP
Sugars and other compounds
6
12 NADPH
12 NADP+

The two sets of photosynthetic reactions
work together.
The light-dependent reactions trap
sunlight energy in chemical form.
The light-independent reactions use that
chemical energy to produce
stable, high-energy sugars from
carbon dioxide and water.

Many factors affect the rate of
photosynthesis, including:
• Water
• Temperature
• Intensity of light
Photosynthesis
overview movie

8-3
In plants, photosynthesis takes place inside the
a. thylakoids.
b. chloroplasts.
c. photosystems.
d. chlorophyll.

8-3
Energy to make ATP in the chloroplast comes
most directly from
a. hydrogen ions flowing through an enzyme in
the thylakoid membrane.
b. transfer of a phosphate from ADP.
c. electrons moving through the electron
transport chain.
d. electrons transferred directly from
NADPH.

8-3
NADPH is produced in light-dependent reactions
and carries energy in the form of
a. ATP.
b. high-energy electrons.
c. low-energy electrons.
d. ADP.

8-3
What is another name for the Calvin cycle?
a. light-dependent reactions
b. light-independent reactions
c. electron transport chain
d. photosynthesis

8-3
Which of the following factors does NOT directly
affect photosynthesis?
a. wind
b. water supply
c. temperature
d. light intensity

Chapter Eight- Photosynthesis

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Chapter Eight- Photosynthesis