Download Section 8

Section 8-1 Notes
Energy and Life
 Energy is the ability to do work.
 Living things depend on energy.
 Without the ability to obtain and use
energy, life would cease to exist.
 Where does the energy that living things
need come from?
Autotrophs and Heterotrophs
 Plants and some other types of organisms
are able to use light energy from the sun
to produce food.
 Autotrophs are organisms that make their
own food. EX: plants
 Heterotrophs obtain energy from the
foods they consume because they cannot
use the sun’s energy directly.
Chemical Energy
 All organisms must release the energy in
sugars and other compounds.
 Energy comes in many forms:
 Light
 Heat
 Electricity
Chemical Energy
 Living things use chemical fuels as well.
 One of the principal chemical compounds
that cells use to store and release energy
is adenosine triphosphate (ATP).
 ATP consists of adenine, a 5-carbon sugar
called ribose, and three phosphate groups.
Adenine
Ribose
3 Phosphate groups
Storing & Releasing Energy
 Adenosine diphosphate (ADP) is a
compound that looks almost like ATP,
except there is only 2 phosphate groups.
 This difference is the key to the way in
which living things store energy.
 Simply by breaking the bond between the
second and third phosphate, energy is
released.
ADP
ATP
Using Biochemical Energy
 Cells use the energy provided by ATP to
carryout these cellular activities:
 Active transport
 Synthesis of proteins
 Synthesis of nucleic acids
 Responses to chemical signals
 Producing light (fireflies)
Using Biochemical Energy
 Cells have only a small amount of ATP to
last them for a few seconds of activity.
 Cells can regenerate ATP from ADP as
needed by using energy in foods like
glucose.
Section 8-2 Notes
Photosynthesis
The key cellular process identified
with energy production is
photosynthesis
Several scientists investigated the
process
Van Helmont’s Experiment
1643 – He concluded that trees gain
most of their mass form water
Photosynthesis
 Priestley’s Experiment
 1771 – Finds that plants release oxygen
 Jan Ingenhousz
 1779 – He finds that aquatic plants produce
oxygen bubbles in the light but not in dark
 Concludes that plants need sunlight to produce
oxygen
Photosynthesis Equation
Light
 6CO2 + 6H2O  C6H12O6 + 6O2
 Photosynthesis uses the energy of sunlight
to convert water and carbon dioxide into
high energy sugars and oxygen
 Plants get CO2 from the air or water
 Plants use the sugars to make complex
carbohydrates such as starches
Plants also need a source of sunlight
and chlorophyll (found in
chloroplasts)
Plants use molecules called
pigments to absorb the light.
Main pigment is chlorophyll
Two types
Chlorophyll a
Chlorophyll b
 When chlorophyll absorbs light, the
energy is sent to the electrons in the
chlorophyll molecules
 This raises the energy levels of the
electrons
 These high energy electrons make
photosynthesis work
 Chlorophyll absorbs blue-violet and red
light from the visible light spectrum (fig.85)
 Chlorophyll does not absorb light in the
green region well.
 Plants look green because the leaves
reflect the green light.
Section 8-3 Notes
Inside a Chloroplast
 Photosynthesis takes place inside
chloroplasts.
 Chloroplasts contain saclike membranes
called thylakoids.
 Thylakoids are arranged in stacks known
as grana.
 Proteins organize chlorophyll and other
pigments into clusters known as
photosystems.
Inside a Chloroplast
 The reactions of photosynthesis are in two
parts:
 1.) Light dependent reactions-take place within
the thylakoid membrane.
 2.) Light independent reactions (Calvin cycle)take place in the stroma, the region outside the
membrane.
Light
Water
O2
CO2
Sugars
Electron Carriers
 Cells use electron carriers to transport
high-energy electrons from chlorophyll to
other molecules.
 This process is called electron transport.
 One of these carrier molecules is a
compound known as NADP+.
Electron Carriers
 NADP+ accepts and holds 2 high-energy
electrons along with a hydrogen ion (H+).
 This converts the NADP+ into NADPH and
energy can be trapped in chemical form.
 The NADPH can then carry high-energy
electrons to chemical reactions elsewhere
in the cell.
Light-Dependent Reactions
There are five steps:
A) Photo system II- Light absorbed is
used to break up water molecules into
energized electrons, hydrogen and
oxygen.
B) Electron Transport Chain- High
energy electrons from A move through
the electron transport chain to
photosystem I.
Light-Dependent Reactions
C) Photo system I- Electrons released
by A are energized again here.
Enzymes in the membrane use the
electrons to form NADPH. NADPH is
used to make sugar in the Calvin cycle.
D) Hydrogen Ion Movement- The inside
to the membrane fills up with positively
charged hydrogen ions.
 E) ATP Formation- As hydrogen ions pass
through ATP synthase, their energy is used
to covert ADP into ATP.
Light – Independent Reactions
There are four steps:
A) CO2 Enters the Cycle- six carbon
dioxide molecules are combined with
six 5-carbon molecules to produce
twelve 3-carbon molecules.
B) Energy Input- Energy from ATP and
high-energy electrons from NADPH are
used to convert the twelve 3-carbon
molecules into higher-energy forms.
C) 6-Carbon Sugar Produced- Two 3carbon molecules are removed from the
cycle to produce sugars, lipids, amino
acids, and other compounds.
D) 5-Carbon Molecules RegeneratedThe 10 remaining 3-carbon molecules
are converted back in to six 5-carbon
molecules, which are used in the next
cycle.
Factors Affecting Photosynthesis
A shortage of water can stop or slow
the process.
Temperature of the enzymes needs
to be between 0oC and 35oC.
The intensity of light.