Energy Flowin the Life of a Cell

• Which of these supplies our cells with energy for cell metabolism?

• caffeine

• sugar

• oxygen

• water

• carbon dioxide

• other (explain)

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• Which of these supplies plant cells with energy for cell metabolism?

• sugar

• sunlight

• water

• oxygen

• carbon dioxide

• other (explain)

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Our cells get energy from:

1 2 3 4 5

0%

80%

0%0%

20%

1. Caffeine

2. Sugar

3. Oxygen

4. Water

5. Carbon dioxide

Plant cells run their metabolism using which of

the following?

1 2 3 4 5

40%

60%

0%0%0%

1. Sunlight

2. Sugar

3. Water

4. Oxygen

5. Carbon dioxide

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.”

• “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)

Potential vs. Kinetic Energy

Potential

Kinetic

Potential energy is stored energy.

Examples: coiled spring, energy in chemical

bonds.

Kinetic energy is energy released to do work.

Examples: car in motion, heat, light, electrical

current.

When we consume food as an energy source, the energy in the food is:

1 2

0%

100%1. Potential energy

2. Kinetic energy

Energy Conversions

gas

Combustionby engine.

100 unitschemical energy(concentrated)

75 unitsheat

energy

25 unitskinetic energy

(motion)

+

All energy conversions involve a loss of energy, often as heat energy.

In living systems, too, energy conversions involve a loss of energy, about 90% at each

level.

energystored inchemicalbonds

producer primary consumer secondary consumer

detritus feeders and decomposers

heatHEAT

tertiary consumer(1 calorie)

producer(1000 calories)

primary consumer(100 calories)

secondary consumer(10 calories)

Top-level predators need huge territories. Use what you have just learned about energy

conversion to explain this.

• 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?

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Which of these is true about photosynthesis?

1 2

100%

0%

1. Photosynthesis makes energy.

2. Photosynthesis consumes energy.

Which of these is true about cellular respiration?

1 2 3

0%

20%

80%1. Cellular respiration

creates energy.

2. Cellular respiration releases energy.

3. Cellular respiration consumes energy.

Endergonic reactions

energyused

products

reactants

Endergonic reactions consume (and may store) energy.

Endergonic Reaction

Ammonium thiocyanate + Barium hydroxide

Inorganic mineral nutrients(nitrate, phosphate) areabsorbed from soil andused in plant tissues.

Energy iscapturedfromsunlight.

Oxygen isreleased.

Sugar issynthesizedand used inplant tissues.

planttissues,growth

Carbon dioxideis absorbedfrom the air.

Water is absorbedfrom soil, used inphotosynthesis, andstored in cells.

photosynthesisphotosynthesis

Photosynthesis is an example of an

endergonic reaction. Explain why.

energyinput

C6H12O6

(glucose) O2

(oxygen)6 CO2

(carbondioxide)

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.

Exergonic Reactions

energyreleased

products

reactants

Exergonic reactions release energy.

Exergonic Reaction

TERTIARY CONSUMER(4th trophic level)

PRODUCER(1st trophic level)

PRIMARY CONSUMER(2nd trophic level)

SECONDARY CONSUMER(3rd trophic level)

Metabolizing food (cellular respiration) is an example of an exergonic reaction. Explain why.

energyreleased

C6H12O6

(glucose) O2

(oxygen)6 CO2

(carbondioxide)

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.

progress of reaction

energy releasedby burning glucose

activation energy neededto ignite glucose

CO2 + H2O

Burning glucose (sugar) : an exergonic reaction

high

low

energycontent

ofmolecules

glucose + O2

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?

ATP(a) Adenosine diphosphate (ADP)

ribose

Energycontent

Shorthandrepresentations

or

"high-energy"bond

adenine

phosphate groups

low

"high-energy"bond

phosphate groups

or

high

(b) Adenosine triphosphate (ATP)

What class of molecule is ATP?

ADP

energy

phosphateATP

ATP

energy

phosphateADP

Which is exergonic and which is endergonic?

net exergonic“downhill” reaction

glucose

protein

aminoacids

CO2 + H2O + heat

ADP + heat

Coupled reaction: glucose breakdown and protein synthesis

endergonic(ATP synthesis)

exergonic(ATP breakdown)

exergonic(glucose breakdown)

endergonic(protein synthesis)

What does this mean? (Think back to the first slides.)

Which process makes ATP for a plant cell to use?

1 2 3 4

40%

0%0%

60%

1. Photosynthesis

2. Cellular respiration

3. Both

4. Neither

When do plants carry out photosynthesis?

1 2 3

80%

20%

0%

1. Day only

2. Night only

3. Both day and night

When do plants carry out cellular respiration?

1 2 3 4

0%

20%

80%

0%

1. Day only

2. Night only

3. Day and night

4. Never. Plants only carry out photosynthesis.

Day

Night

When does a plant do photosynthesis (synthesizing organic, energy-rich molecules)?

When does a plant do cellular respiration (breaking down organic molecules to release

energy)?

Photosynthesis

Cellular Respiration

Cellular Respiration

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.

“Energy drinks”

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?