Energy for Life

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Photosynthesis is an important part of the carbon cycle.
The processes of photosynthesis and cellular respiration are complementary processes, meaning they work together to benefit living organisms.

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Autotrophs, such as plants, produce glucose using the carbon in carbon dioxide.
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Both autotrophs and heterotrophs, such as grasshoppers that eat plants, use those carbohydrates in cellular respiration.
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Respiration, in turn, produces carbon dioxide.

6 CO
2
+ 6 H
2
O light
C
6
H
12
O
6
+ 6O
2

Photosynthesis combines water, carbon dioxide and sunlight to produce glucose and oxygen, converting light energy into chemical energy.

6O
2
+ C
6
H
12
O
6
6CO
2
+ H
2
O + Energy

Respiration breaks down glucose and other food molecules in the presence of oxygen.

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
Energy captured from sunlight by photosynthetic organisms is used and released in the cellular respiration of living things.
The energy that living things use, must continually be renewed through photosynthesis.

Where does photosynthesis occur?
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In plants and other photosynthetic eukaryotes, photosynthesis takes place inside chloroplasts.
The chloroplasts contain saclike membranes called thylakoids.
Thylakoids are arranged in stacks known as grana.

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Proteins in the thylakoid organize chlorophyll and other pigments into light-collecting units called photosystems.

What are the reactions of photosynthesis?
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
Scientists divide the reactions of photosystems into two parts: Light-dependent reactions and light-independent reactions or the Calvin cycle.
The light-dependent reactions take place within the thylakoid membranes.

They use energy from light to produce ATP and
NADPH, which are energy carriers.

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Photosystem II absorbs light and breaks water molecules into energized electrons, hydrogen ions (H+) and oxygen.
High-energy electrons move through the electron transport chain from photosystem II to photosystem I.
As electrons pass from chlorophyll to NADP+, more hydrogen ions are pumped across the membrane.
ATP synthase in the membrane allows H+ ions to pass through it. The enzyme binds ADP and a phosphate group to produce ATP.


The light-independent reactions of the Calvin
Cycle take place in the stroma outside of the thylakoid membranes.

The Calvin Cycle uses ATP and NADPH from the light-dependent reactions to produce highenergy sugars.

What is the visible spectrum of light and why is it important?

The visible spectrum of light is the set of varying wavelengths of light that are visible to our eyes as different colors.

Sunlight is a mixture of different wavelengths of light, even though it appears as “white light” to your eyes.

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In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a pigment molecule within chloroplasts.
The two main types of chlorophyll are chlorophyll a and chlorophyll b.
Chlorophyll absorbs blueviolet and red light very well.
Green light is reflected by plant leaves, which is what gives them their green color.

Light absorption powers photosynthesis
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
Chlorophyll absorbs blue-violet and red light very well. Green light is reflected by plant leaves, which is what gives them their green color.
The high-energy electrons produced when chlorophyll absorbs light make photosynthesis work.

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Our bodies have a lot of work to do every day…
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Moving muscles,
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Building essential molecules, and
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Transporting substances across cell membranes.

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Food provides the energy living things need to grow and reproduce.

Food is the source of the material our cells use to build new molecules.

How much energy is present in food?
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
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Quite a lot!
One gram of the sugar glucose (C
6
H
12
O
6
) when burned in the presence of oxygen, releases 3,811 calories of heat energy.
A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree
Celsius.

What is cellular respiration?

Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
6O
2
+ C
6
H
12
O
6 oxygen + glucose
6CO
2
+ 6H
2
O + Energy carbon dioxide + water + energy

Where does cellular respiration take place?
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The beginning pathway of cellular respiration,
glycolysis, takes place in the cell cytoplasm.
The two remaining pathways—the Krebs
Cycle and electron
transport—take place inside the mitochondria of the cell.

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Glycolysis: a glucose molecule is split to produce two molecules of pyruvic acid.
Krebs Cycle: pyruvic acid is used to produce carbon dioxide, NADH, ATP and
FADH
2
. Sometimes called the citric acid cycle because citric acid is first formed.
Electron Transport Chain: uses high-energy electrons from the Krebs Cycle to convert ADP to ATP.

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What happens if oxygen is not available?
Glycolysis is then followed by a different pathway.
The combined process of this pathway and glycolysis is called fermentation.
Fermentation releases energy from food molecules by producing
ATP in the absence of oxygen.