Energy Flow

1
Energy Flow

• in the Life of a Cell

2
W O R K T O G E T H E R

• Which of these supplies our cells with energy for
  cell metabolism?
• caffeine
• sugar
• oxygen
• water
• carbon dioxide
• other (explain)

3
W O R K T O G E T H E R

• Which of these supplies plant cells with energy
  for cell metabolism?
• sugar
• sunlight
• water
• oxygen
• carbon dioxide
• other (explain)

4
Our cells get energy from

1. Caffeine
2. Sugar
3. Oxygen
4. Water
5. Carbon dioxide

5
Plant cells run their metabolism using which of
the following?

1. Sunlight
2. Sugar
3. Water
4. Oxygen
5. Carbon dioxide

6
Energy

• Energy is the ability to do work, such as
  causing motion, or interaction between molecules.
  This is the idea of energy used in your
  textbook.
• Energy is used in an everyday sense to mean
  alertness, strength, or vitality.

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• Energy is a not a material. It is best
  described as a phenomenon.
• Energy can be measured a number of ways
  including
• calories (food energy)
• degrees (heat energy)
• voltage (electrical potential)

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Potential vs. Kinetic Energy
Potential
Kinetic
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Potential energy is stored energy.
Kinetic energy is energy released to do work.
Examples coiled spring, energy in chemical bonds.
Examples car in motion, heat, light, electrical
current.
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When we consume food as an energy source, the
energy in the food is

1. Potential energy
2. Kinetic energy

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Energy Conversions
Combustion by engine.
gas
100 units chemical energy (concentrated)
75 units heat energy
25 units kinetic energy (motion)

All energy conversions involve a loss of energy,
often as heat energy.
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heat
HEAT
energy stored in chemical bonds
producer
primary consumer
secondary consumer
detritus feeders and decomposers
In living systems, too, energy conversions
involve a loss of energy, about 90 at each level.
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tertiary consumer (1 calorie)
secondary consumer (10 calories)
primary consumer (100 calories)
producer (1000 calories)
Top-level predators need huge territories. Use
what you have just learned about energy
conversion to explain this.
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W O R K T O G E T H E R

• Why is only about 10 of energy passed from one
  organism to another in the food chain?
• If it takes about 30 acres of land to raise
  enough cattle to feed a family of five for a
  year, how much land would the family need if they
  went vegetarian?

15
Which of these is true about photosynthesis?

1. Photosynthesis makes energy.
2. Photosynthesis consumes energy.

16
Which of these is true about cellular respiration?

1. Cellular respiration creates energy.
2. Cellular respiration releases energy.
3. Cellular respiration consumes energy.

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Endergonic reactions
energy used
products
reactants
Endergonic reactions consume (and may store)
energy.
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Endergonic Reaction
Ammonium thiocyanate Barium hydroxide
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Photosynthesis is an example of an endergonic
reaction. Explain why.
Energy is captured from sunlight.
Oxygen is released.
Sugar is synthesized and used in plant tissues.
Carbon dioxide is absorbed from the air.
plant tissues, growth
photosynthesis
Water is absorbed from soil, used
in photosynthesis, and stored in cells.
Inorganic mineral nutrients (nitrate, phosphate)
are absorbed from soil and used in plant tissues.
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energy input
C6H12O6 (glucose)
O2 (oxygen)

6 CO2 (carbon dioxide)
6 H2O (water)

Producers (such as plants) take in light energy
and use it to bind carbon, hydrogen, and oxygen
into carbon-based compounds such as sugar.
Sugar is stored (potential) energy used by
Eukaryotes to make ATP for their cells.
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Exergonic Reactions
energy released
reactants
products
Exergonic reactions release energy.
22
Exergonic Reaction
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TERTIARY CONSUMER (4th trophic level)
PRIMARY CONSUMER (2nd trophic level)
SECONDARY CONSUMER (3rd trophic level)
PRODUCER (1st trophic level)
Metabolizing food (cellular respiration) is an
example of an exergonic reaction. Explain why.
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energy released
C6H12O6 (glucose)
O2 (oxygen)

6 CO2 (carbon dioxide)
6 H2O (water)

Both producers and consumers break down sugars
and other carbon compounds to get usable energy
for their cells.
All Eukaryotes use the process of cellular
respiration to break down sugar in order to make
ATP.
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Burning glucose (sugar) an exergonic reaction
high
activation energy needed to ignite glucose
glucose O2
energy content of molecules
energy released by burning glucose
CO2 H2O
low
progress of reaction
Getting energy out of sugar by burning requires a
high input of energy. What kind of molecule do
cells use to lower the activation energy in order
to use sugar?
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ATP
(a) Adenosine diphosphate (ADP)
(b) Adenosine triphosphate (ATP)
adenine
"high-energy" bond
"high-energy" bond
ribose
phosphate groups
phosphate groups
Shorthand representations
or
or
Energy content
low
high
What class of molecule is ATP?
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energy
phosphate
ATP
ADP
Which is exergonic and which is endergonic?
energy
ATP
phosphate
ADP
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Coupled reaction glucose breakdown and protein
synthesis
glucose
exergonic (glucose breakdown)
protein
endergonic (ATP synthesis)
exergonic (ATP breakdown)
endergonic (protein synthesis)
CO2 H2O heat
ADP heat
amino acids
net exergonic downhill reaction
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Which process makes ATP for a plant cell to use?

1. Photosynthesis
2. Cellular respiration
3. Both
4. Neither

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When do plants carry out photosynthesis?

1. Day only
2. Night only
3. Both day and night

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When do plants carry out cellular respiration?

1. Day only
2. Night only
3. Day and night
4. Never. Plants only carry out photosynthesis.

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When does a plant do photosynthesis (synthesizing
organic, energy-rich molecules)?
Photosynthesis
Day
Night
When does a plant do cellular respiration
(breaking down organic molecules to release
energy)?
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Remember...

• Photosynthesis does not give a plant energy or
  make energy.
• Photosynthesis uses energy to make organic
  molecules.
• Cellular respiration releases energy to the cells
  by breaking down organic molecules.

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Energy drinks
W O R K T O G E T H E R
In a scientific sense, what is the source of real
energy in these drinks?
Why does a 0-calorie energy drink make no sense
in science?
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Recap

• Photosynthesis is an endergonic
  (energy-consuming) process.
• Cellular respiration is an exergonic
  (energy-releasing) process.
• Which process must ALL Eukaryotic organisms
  (including plants) do to make ATP?