Slide 1

- Chapter 8
As the alcohol travels up
the filter paper it carries
leaf pigments.
The small pigments
travel farthest and
The largest pigments
travel slow and stay
close to the start.
Carotene 
Xanthophyll 
Chlorophyll a 
Chlorophyll b 
8-1 Energy and Life
• Energy is the ability to do work
• Living things depend on energy to maintain
• Without the ability to obtain and use energy,
life would cease to exist
• Where does this energy come from?
Chemical Energy and ATP
• Energy comes in many forms
Exs. – light, heat and electricity
• ATP and ADP
– Cell activities are powered by chemical
– One of the principal chemical compounds
that living things use to store and release
energy is ATP (adenosine triphosphate)
• An ATP molecule consists of a
nitrogen-containing compound called
adenine, a 5-carbon sugar called
ribose, and three phosphate groups
Fig. 8-2 ATP is used by all types of cells as their basic energy
source. For example, the energy needed by the cells of a soccer
player comes from ATP.
pg. 202
• ADP (adenosine diphosphate) has a
structure that is similar to ATP
• There is one important difference: ADP
has two phosphate groups instead of
• This is the key to the way in which
cells store energy
• A cell can store small amounts of
energy by adding a phosphate group
to ADP molecules, producing ATP
• ATP is like a fully charged battery,
ready to power the machinery of the
pg. 203
Releasing Energy From ATP
• Energy stored in ATP is released when
ATP is converted into ADP and a
phosphate group
• Cells can add and subtract a third
phosphate group giving it a way of
storing and releasing energy as
• Most cells have only a small amount of
ATP, enough to last for only a few
seconds of activity
• ATP is a great molecule for
transferring energy.
• It is not good for long term energy
The ATP Cycle
Using Biochemical Energy
• ATP carries just enough energy to
power a variety of cellular activities
– Exs.:
• Active Transport (Protein Pumps)
• Movement (cilia, flagella, muscles)
• Light (Fireflies)
• The characteristics of ATP make it an
exceptionally useful molecule that is
used by all types of cells as their basic
energy source
Autotrophs and Heterotrophs
• Originally, nearly all energy in food
comes from the Sun.
• The energy that living things need
comes from food
• Autotrophs are organisms such as
plants, which make their own food
• Heterotrophs obtain energy from the
foods they consume
– Ex.: Impalas, leopards, & mushrooms
Fig. 8-1 Autotrophs vs. Heterotrophs Autotrophs use light energy from
the sun to produce food. These impalas get their energy by eating grass. A
leopard, in contrast, gets its energy by eating impalas and other animals.
Impalas and leopards are both heterotrophs.
pg. 201
8–2 Photosynthesis: An Overview
• Photosynthesis is a process in which
plants use the energy of sunlight to
convert water and carbon dioxide into
oxygen and high-energy
carbohydrates (sugars and starches)
that can be used as food.
An Overview of
An Overview of Photosynthesis
• The overall equation for photosynthesis
can be shown as follows:
6CO2 + 6H2O
C6H12O6 + 6O2
carbon dioxide +
Chlorophyll and Chloroplasts
• Energy from the Sun travels to Earth
as light.
• Our eyes perceive this as “white light”
which is actually mixture of different
• We see these wavelengths as:
Red, Orange, Yellow, Green, Blue,
Indigo and Violet.
• In addition to water and carbon dioxide,
photosynthesis requires light and
chlorophyll, a molecule in chloroplasts
• Plants gather the sun’s energy with lightabsorbing molecules called pigments
• The plants’ principal pigment is chlorophyll
• There are two main types of chlorophyll:
– chlorophyll a
– chlorophyll b
• Chlorophyll absorbs the blue and red
regions of the visible spectrum
• Chlorophyll does not absorb light well in the
green region of the spectrum
• This is why plants are green
• Plants also contain red and orange
pigments that absorb light in other regions
of the spectrum
– Ex.: carotene
pg. 207
Fig. 8-5 Photosynthesis requires light and chlorophyll, which absorbs
light energy. In the graph, notice how chlorophyll a absorbs light in the violet and
red regions of the visible spectrum, while chlorophyll b absorbs light in the blue
and red regions of the visible spectrum.
• Inside a Chloroplast
– Photosynthesis takes place inside
– Chloroplasts contain saclike
photosynthetic membranes called
• Thylakoids:
– Are arranged in stacks known as grana
(singular: granum)
– The fluid portion of the chloroplast outside
the thylakoids is known as the stroma.
– Contain clusters of chlorophyll and other
pigments and photosystems (proteins that
are able to capture the energy of sunlight.
High-Energy Electrons
• Sunlight excites electrons in
chlorophyll and the electrons gain a
great deal of energy
• These high-energy electrons require a
special carrier
• One of these carrier molecules is a
compound known as NADP+
• The conversion of NADP+ into NADPH
is one way in which some of the
energy of sunlight can be trapped in
chemical form.
Fig. 8-4 Photosynthesis is a series of reactions that uses
energy from the sun to convert water and carbon dioxide
into sugars and oxygen. Photosynthesis takes place in a plant
organelle called the chloroplast.
pg. 206
• The photosynthesis reaction has two
– The Light-Dependent reactions
• take place within the thylakoid membranes
– The Light-Independent reactions (Calvin
• The Calvin Cycle takes place in the stroma,
the region outside the thylakoid membranes.
The Process of Photosynthesis
Light & H2O
pg. 209
8–3 The Process of
Light-Dependent Reactions
• Require light
• Why plants need light to grow
• Use energy from light to produce
oxygen gas, ATP and NADPH
Light-Independent Reactions
• The light-independent (dark) reactions use
ATP and NADPH from the light-dependent
reactions to produce high-energy sugars
• These reactions are also called the
Calvin Cycle
• The Calvin Cycle does not require light
pg. 212
Factors Affecting Photosynthesis
• Many factors affect the rate at which
photosynthesis occurs
• Temperature:
– Temperatures above or below 0°C and
35°C may slow down the rate of
– At very low temperatures, photosynthesis
may stop entirely
– Plants at these temperatures can carry
out photosynthesis only on sunny days
• Intensity of Light
– Affects the rate at which photosynthesis
– Increasing light intensity increases the
rate of photosynthesis
– At a certain level, the plant reaches its
maximum rate of photosynthesis
– This level varies from plant to plant.
• Water:
– A shortage of water can slow or even
stop photosynthesis
– Plants that live in dry conditions (desert
plants and conifers) have a waxy coating
on their leaves that reduces water loss
Photosynthesis Under
Extreme Conditions
• Plants have small openings (stomata) in
their leaves that admit CO2 for
• To prevent the plant from drying out, these
openings must close to conserve water.
• This may slow down or stop the process of
C4 and CAM Photosynthesis
• Some plants have adapted to extremely
bright, hot conditions
• There are two major groups of these
specialized plants:
– C4 plants
– CAM plants
• These processes minimize water loss while
still allowing photosynthesis in intense
• C4 plants have an added step during the
carbon-fixing stage to preserve moisture in
hotter climates.
C4 plants capture CO2 so that plants can
keep working under intense light and high
• C4 Plants:
Soy Beans
Sugar Cane
• CAM plants take in CO2 only at night,
trapping carbon in the leaves.
• During the day, when the openings in
the leaves are tightly closed, the CO2
is released allowing photosynthesis to
take place.
• CAM Plants:
– Pineapple
– Cactus

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