Download Chapter 8 PPT Photosynthesis

Chapter 8
-Energy
and Life
Living things need energy to survive.
This energy comes from food. The
energy in most food comes from the
sun.
Where do plants get the energy they
need to produce food?
Autotrophs and Heterotrophs
Plants and some other types of
organisms are able to use light energy
from the sun to produce food.
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.
ATP is used by all types of cells as their basic
energy source.
ATP consists of:
• adenine
• ribose (a 5-carbon sugar)
• 3 phosphate groups
Adenine
ATP
Ribose
3 Phosphate groups
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.
ATP
ADP
+
Adenosine Diphosphate
(ADP) + Phosphate
Partially
charged
battery
Energy
Energy
Fully
charged
battery
Adenosine Triphosphate (ATP)
Releasing Energy
Energy stored in ATP is released by breaking the
chemical bond between the second and third
phosphates.
2 Phosphate groups
P
ADP
What is the role of ATP
in cellular activities?
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
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.
Quiz 8-1
Organisms that make their own food are called
a. autotrophs.
b. heterotrophs.
c. decomposers.
d. consumers.
Most autotrophs obtain their energy from
a. chemicals in the environment.
b. sunlight.
c. carbon dioxide in the air.
d. other producers.
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.
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.
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.
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 high-energy carbohydrates
and oxygen.
What is the overall equation for
photosynthesis?
The Photosynthesis Equation
The equation for photosynthesis is:
6CO2 + 6H2O
Light
carbon dioxide + water
C6H12O6 + 6O2
Light
sugars + oxygen
Photosynthesis uses the energy of sunlight
to convert water and carbon dioxide into
high-energy sugars and oxygen.
Light energy
H2O
Light-Dependent
Reactions
(thylakoids)
ADP
+
NADP
Sugar
O2
ATP
NADPH
Calvin Cycle
(stroma)
CO2
+
H20
What is the role of light and
chlorophyll in photosynthesis?
Light and Pigments
How do plants capture the energy of sunlight?
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 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.
Chlorophyll does not absorb light in the green
region of the spectrum. Green light is reflected by
leaves, which is why plants look green.
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.
Photosynthesis Video
Quiz 8-2
Most of the added mass of a tree comes from
a. soil and carbon dioxide.
b. water and carbon dioxide.
c. oxygen and carbon dioxide.
d. soil and oxygen.
Plants use the sugars produced in
photosynthesis to make
a. oxygen.
b. starches.
c. carbon dioxide.
d. protein.
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.
The principal pigment in plants is
a. chloroplast.
b. chlorophyll.
c. carotene.
d. carbohydrate.
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.
Inside a Chloroplast
In plants, photosynthesis takes place inside
chloroplasts.
Plant
Chloroplast
Plant cells
Chloroplasts contain thylakoids—saclike
photosynthetic membranes.
Single
thylakoid
Thylakoids are arranged in stacks known as
grana. A singular stack is called a granum.
Granum
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
H2O
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
Calvin
Calvin
cycle
Cycle
Chloroplast
O2
Sugars
Electron Carriers
When electrons in chlorophyll absorb sunlight, the
electrons gain a great deal of energy.
Cells use electron carriers to transport these highenergy electrons from chlorophyll to other
molecules.
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.
Light-Dependent Reactions
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.
Photosynthesis begins when pigments in
photosystem II absorb light, increasing their
energy level.
Photosystem II
These high-energy electrons are passed on to the
electron transport chain.
Photosystem II
High-energy
electron
Electron
carriers
Enzymes on the thylakoid membrane break water
molecules into:
Photosystem II
2H2O
High-energy
electron
Electron
carriers
– hydrogen ions
– oxygen atoms
– energized electrons
Photosystem II
+
O2
2H2O
High-energy
electron
Electron
carriers
The energized electrons from water replace the
high-energy electrons that chlorophyll lost to the
electron transport chain.
Photosystem II
+
2H2O
High-energy
electron
O2
As plants remove electrons from water, oxygen is
left behind and is released into the air.
Photosystem II
+
2H2O
High-energy
electron
O2
The hydrogen ions left behind when water is
broken apart are released inside the thylakoid
membrane.
Photosystem II
+
2H2O
High-energy
electron
O2
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
+
O2
2H2O
Photosystem I
Pigments in photosystem I use energy from
light to re-energize the electrons.
+
O2
2H2O
Photosystem I
NADP+ then picks up these high-energy
electrons, along with H+ ions, and becomes
NADPH.
+
O2
2H2O
2 NADP+
2
2
NADPH
As electrons are passed from chlorophyll to
NADP+, more H+ ions are pumped across the
membrane.
+
O2
2H2O
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.
+
O2
2H2O
2 NADP+
2
2
NADPH
The difference in charges across the membrane
provides the energy to make ATP
+
O2
2H2O
2 NADP+
2
2
NADPH
H+ ions cannot cross the membrane directly.
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
The cell membrane contains a protein called ATP
synthase that allows H+ ions to pass through it
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
As H+ ions pass through ATP synthase, the
protein rotates.
ATP synthase
+
O2
2H2O
2 NADP+
2
2
NADPH
As it rotates, ATP synthase binds ADP and a
phosphate group together to produce ATP.
ATP synthase
+
O2
2H2O
ADP
2 NADP+
2
2
NADPH
Because of this system, light-dependent electron
transport produces not only high-energy electrons
but ATP as well.
ATP synthase
+
O2
2H2O
ADP
2 NADP+
2
2
NADPH
What is the Calvin cycle?
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.
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 molecules are used to produce sugars, lipids,
amino acids and other compounds.
12
12 ADP
12 NADPH
12 NADP+
6-Carbon sugar
produced
Sugars and other compounds
The 10 remaining 3-carbon molecules are
converted back into six 5-carbon molecules,
which are used to begin the next cycle.
12
12 ADP
6 ADP
12 NADPH
6
12 NADP+
5-Carbon Molecules
Regenerated
Sugars and other compounds
The two sets of photosynthetic reactions work
together.
– The light-dependent reactions trap sunlight energy in
chemical form.
– The Calvin Cycle uses that chemical energy to
produce stable, high-energy sugars from carbon
dioxide and water.
Quiz 8-3
In plants, photosynthesis takes place inside the
a. thylakoids.
b. chloroplasts.
c. photosystems.
d. chlorophyll.
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.
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.
What is another name for the Calvin cycle?
a. light-dependent reactions
b. light-independent reactions
c. electron transport chain
d. photosynthesis
Which of the following factors does NOT directly
affect photosynthesis?
a. wind
b. water supply
c. temperature
d. light intensity