Download Chapter 9 - Holden R-III School District

Chapter 9
Energy in a Cell
9.1 Energy for Organisms

All organisms require energy
– The energy source for everything on earth is
the sun
 Producers obtain energy directly from the sun
through photosynthesis
 Consumers obtain energy by consuming it from
producers, either directly (herbivores) or indirectly
(carnivores)
9.1 Energy molecules

The primary energy molecule in organisms
is ATP, or adenosine triphosphate
– ATP is made up of an adenosine molecule
with 3 phosphate groups
 ADP is similar to ATP, but with only 2 phosphate
molecules
 As the ATP molecule breaks down, it releases
energy (and a phosphate group) to the cell and
turns into ADP
9.1 ATP Binds to proteins

The energy from ATP is released by
binding to an active site on a protein
– The site on the protein is a specific shape that
fits with the ATP molecule
– When the energy and phosphate group is
released to produce ADP, the shape of ADP no
longer fits on the site and is released from the
protein, allowing another ATP molecule to
bind
9.1 Cell Uses of Energy

Cells use energy for a variety of processes,
including:
– Metabolism
– Making new molecules
– Building membranes and organelles
– Maintaining homeostasis
9.2 Photosynthesis

Photosynthesis is the process that uses the sun’s
energy to make simple sugars
6CO2 + 6H2O  C6H12O6 + 6O2
– These simple sugars are converted into
carbohydrates, which are energy storage molecules
– Photosynthesis occurs in 2 stages
 The light dependent reactions convert light energy into
chemical energy (produce ATP)
 The light independent reactions convert the ATP into simple
sugars
9.2 Plant Pigments

Photosynthesis occurs in the plant
organelles called the chloroplasts
– Chloroplasts contain thylakoid disks containing
pigments
 The specific pigment leading to the green color is
chlorophyll, which absorbs every wavelength of
light except green
– The color change of leaves in the fall occurs because the
leaves stop producing chlorophyll and the other pigments
become visible
9.2 Light Dependent Reactions

The first phase of photosynthesis requires
sunlight
– The sunlight strikes the chlorophyll molecules and
release electrons
– The electrons go into a series of 2 electron transport
chains, releasing small amounts of energy as they
travel
– The energy released helps to form ATP from ADP
– The energy remaining goes into NADP+ to form
NADPH, which is used in the light independent
reactions
9.2 Light Independent Reactions

The second phase of photosynthesis does
not need light and is commonly referred to
as the Calvin Cycle
– The Calvin cycle uses carbon dioxide to form
sugars
– It takes place inside the chloroplasts in a
section called the stroma
9.2 The Calvin Cycle
http://edu.tebyan.net/biology/Cells/images/calvin_cycle.gif
9.3 Cellular Respiration

Cellular respiration is the process by which
mitochondria break down food molecules
to produce ATP
– It has 3 stages:
 Glycolysis
 Citric acid cycle
 Electron transport chain
– Glycolysis is anaerobic (needing no oxygen)
– Citric acid cycle and electron transport chain are aerobic
(requiring oxygen)
9.3 Glycolysis

Glycolysis is a series of chemical reactions
in the cytoplasm that break down glucose
into pyruvic acid
– Glucose has 6 carbons and pyruvic acid has 3,
so each glucose makes 2 pyruvic acid
 Glycolysis requires 2 ATP molecules to start and
ends with 4 ATP molecules, so 2 new molecules of
ATP are produced
 2 molecules of PGAL are also produced
9.3 Citric Acid Cycle

In the citric acid cycle, one molecule of
ATP and 2 molecules of CO2 are produced
for each molecule of acetyl-CoA broken
down
– It is also called the Kreb’s Cycle
9.3 Citric Acid Cycle Diagram
9.3 Electron Transport Chain

The electron transport chain in cellular
respiration is similar to the one in
photosynthesis
– It passes electrons along using NADH and
FADH2 losing small amounts of energy along
the way
 The lost energy goes to form ATP or to move
hydrogen ions into the mitochondria
 At the end of the chain, the remaining energy goes
into oxygen and produces 2 molecules of water
9.3 Fermentation

There are 2 types of fermentation, both of
which occur when there is no oxygen
available for ATP production
– Lactic acid fermentation reverses the pyruvic
acid production and releases lactic acid which
builds up in muscles and causes fatigue
– Alcoholic fermentation is used by yeast and
some bacterial cells to produce CO2 and ethyl
alcohol.
 The CO2 bubbles are what causes bread to rise
and the ethyl alcohol cooks off when it is baked
9.3 Comparing Photosynthesis &
Cellular Respiration
Photosynthesis
Respiration
Food synthesized
Food broken down
Energy from the sun stored
in glucose
Energy in glucose released
Carbon dioxide taken in
Carbon dioxide given off
Oxygen given off
Oxygen taken in
Produces sugars from PGAL
Produces CO2 and H2O
Requires light
Does not require light
Occurs only in the presence
of chlorophyll
Occurs in all living cells