Download Transportation of Energy in Organisms

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Transportation of Energy in Organisms
Bioenergetics
Autotrophs vs. Heterotrophs
Two (2) types of autotrophs
 Organisms that get energy from the sun – the best-known autotroph that harness solar energy
through the process of photosynthesis.
Through photosynthesis, these autotrophs use light energy to power chemical reactions that convert
carbon dioxide and water into oxygen and energy-rich carbohydrates such as sugars and starches.

Organisms that use energy from chemicals – these autotrophs produce energy without light. They
rely on energy within the chemical bonds of inorganic molecules such as hydrogen sulfide.
Chemosynthesis is the process where organisms use chemical energy to produce carbohydrates. This
process is performed by several types of bacteria. Some chemosynthetic bacteria live in very remote
places on Earth, such as volcanic vents on the deep ocean floor and hot springs. Others live in more
common places, such as tidal marshes along the coast.

There are many organisms such as animals, fungi, and many bacteria, cannot harness energy directly
from the physical environment as autotrophs do. These organisms rely on other organisms for their
energy and food supply. They are called heterotrophs or consumers.
Types of Heterotrophs
 Herbivores – eat only plants. Examples are cows, caterpillars, and deer.
 Carnivores - eat animals. Examples are snakes, owls, and dogs.
 Omnivores – eat both plants and animals. Examples are bears, crows, and humans.
 Detritivores – feed on plant and animal remains and other dead matter. Examples are mites,
earthworms, snails, and crabs.
 Decomposers – breaks down organic matter. Examples are bacteria and fungi.
Chloroplasts and Photosynthesis
Chloroplasts are organelles found in plant cells and some other eukaryotic organisms. Aside from
conducting photosynthesis, they also carry out almost all fatty acid synthesis in plants, and are involved
in a plant's immune response. A chloroplast is a type of plastid that specializes in photosynthesis.
The chloroplasts contain saclike photosynthetic membranes called thylakoids. Thylakoids are arranged
in stacks called grana (singular: granum). Thylakoids contain clusters of chlorophyll and other pigments
and protein called photosystems that are able to capture the energy from the sunlight.
Photosynthesis
Photosynthesis is one (1) of the most vital biochemical processes since almost all the living organisms
depend on it for nutrition directly or indirectly. It is the process by which several living organisms utilize
solar energy (that is, sunlight) for growth and metabolism. By definition, photosynthesis is described as
the process of converting light energy into chemical energy by living organisms.
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The process of photosynthesis uses raw materials like carbon dioxide, water, and solar energy to produce
oxygen and carbohydrates. Higher plants, phytoplankton, algae, as well as some bacteria carry out the
process of photosynthesis.
Because photosynthesis usually produces 6-carbon sugars (C6H12O6) as its final products, the overall
equation for photosynthesis can be shown as follows:
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To understand photosynthesis, scientists break the reaction into two (2) stages: the light-dependent
reactions and the light-independent reactions, or Calvin cycle. Before going to details of the stages of
photosynthesis, discuss electron carriers:
NADP+ and NADPH
When sunlight excites electron in chlorophyll, the electrons gain a great deal of energy. These highenergy electrons require a special carrier. Think of a high-energy electron as being similar to a red-hot
coal from a fireplace or campfire. If you wanted to move the coal from one (1) place to another, you
wouldn’t want to pick it up with your own hands. You would use a pan or bucket, a carrier, to transport
it. Cells treat high-energy electrons the same way. Cells use electron carriers to transfer high-energy
electrons to other molecules.
One (1) of these carrier molecules is a compound known as NADP+ (nicotinamide adenine dinucleotide
phosphate). NADP+ accepts and holds two (2) high energy electrons along with the hydrogen ion (H+).
This converts the NADP+ to NADPH. The conversion of NADP+ into NADPH is one way in which
some of the energy from the sunlight can be trapped in chemical form.
The NADPH can carry high-energy electrons produced by light absorption in chlorophyll to chemical
reactions elsewhere in the cell. The high-energy electrons are used to build variety of molecules the cell
needs, including carbohydrates like glucose.
Two (2) Stages of Photosynthesis:
I. Light-dependent Reactions
The light-dependent reactions use energy from the sunlight to produce oxygen gas and convert ADP
and NADP+ into the energy carriers ATP and NADPH. The light-dependent reactions take place
within the thylakoid membranes of the chloroplasts.
Steps in Light-dependent Reactions:
a) Photosystem II (The first photosystem in the light-dependent reaction is called photosystem II
because it was discovered after photosystem I) - Light is absorbed by chlorophyll or other
pigments in photosystem II. The energy from this light is transferred to electrons, which are then
passed on to the electron transport chain. Separately, enzymes break up water molecules into
electrons, hydrogen ions (H+), and oxygen.
b) Electron Transport Chain – High energy electrons from photosystem II move through the
electron transport chain to photosystem I. The molecules in the electron transport chain use
energy from electrons to transport hydrogen ions from the stroma into the inner thylakoid.
c) Photosystem I – As in photosystem II, pigments add energy from light to the electrons. The
high-energy electrons are then picked up by NADP+ to form NADPH.
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d) Hydrogen Ion Movement – As a result of the H+ ions released during water-splitting and
electron transport, the inside of the thylakoid membranes becomes positively charged and the
outside of becomes negatively charged. The difference in the charges across the membrane
provide energy to make ATP.
e) ATP Formation – Hydrogen ions will pass through ATP synthase. ATP synthase binds ADP
and converts it to ATP.
Photosystem II
Electron
Transport
Chain
Photosystem
I
Hydrogen
Ion
Movement
ATP
Formation
II. Light-independent Reactions or Calvin Cycle
The ATP and NADPH formed by light-dependent reactions are not stable enough to store energy for
more than a few minutes. The Calvin cycle uses ATP and NADPH from the light reactions to form
high-energy sugars that can be stored for a long time. The Calvin cycle occurs in the stroma. This
cycle is named after the American scientist Melvin Calvin, who worked out the details of this
remarkable cycle. Because the Calvin cycle does not require light, this is also called the lightindependent reactions.
Steps in Calvin cycle:
a) CO2 Enters the Cycle – Six (6) carbon dioxide molecules enter the cycle from the atmosphere.
The carbon dioxide molecules combine with six 5-carbon molecules. The result is twelve 3-carbon
molecules.
b) Energy Input – The twelve 3-carbon molecules are then converted into higher energy forms. The
energy for this conversion comes from ATP and high-energy electrons from NADPH.
c) 6-Carbon Sugar Produced – Two (2) of the twelve 3-carbon molecules are converted into two
(2) similar 3-carbon molecules. These 3-carbon molecules are used to form various 6-carbon
sugars and other compounds
d) 5-Carbon Molecules Regenerated – The remaining ten 3-carbon molecules are converted back
into the 5-carbon molecules to begin the next cycle.
CO2 enters the
Cycle
Energy
Input
6-Carbon
Sugar
Produced
5-Carbon
Molecules
Regenerated
The Calvin cycle uses six (6) molecules of carbon dioxide to produce a single 6-carbon sugar
molecule. As photosynthesis proceeds, the Calvin cycle works steadily, turning out energy-rich sugars
and removing carbon dioxide from the atmosphere. The plant uses sugars for energy and to build more
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complex carbohydrates such as starches and cellulose, which is important form plant growth and
development. When other organisms eat plants, they can also use the energy stored in carbohydrates.
Cellular Respiration
All organisms need energy to function and we get this energy from the food we eat. The most efficient
way for cells to harvest energy stored in food is through cellular respiration. Cellular respiration is the
process that releases energy by breaking down food molecules in the presence of oxygen.
The Equation for cellular respiration is:
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Three (3) main stages of cellular respiration
I. Glycolysis
Literally means “splitting sugars”. Glucose, a six-carbon sugar, is split into two (2) molecules of a
three-carbon sugar. In the process, two (2) molecules of ATP, two (2) molecules of pyruvic acid,
and two (2) “high energy” electron carrying molecules of NADH are produced. Glycolysis can occur
with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration.
Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called
fermentation.

ATP production – to get glycolysis going, the cell uses energy in the form of two (2) ATP
molecules. When glycolysis is complete, four (4) ATP molecules are produced. This gives the
cell a net gain of two (2) ATP molecules.

NADH production – one (1) of the reactions in glycolysis removes four (4) high-energy
electrons and passes them to an electron carrier called NAD+ (nicotinamide adenine
dinucleotide). Like NADP+ in photosynthesis, each NAD+ accepts a pair of high energy
electrons. This molecule, known as NADH, holds the electrons until they can be transferred to
other molecules.

Pyruvic acid production – during glycolysis, glucose is broken down into two (2) molecules of
pyruvic acid.

Fermentation – when oxygen is not present, glycolysis is followed by a different pathway. The
combined process of this pathway and glycolysis is called fermentation. Because fermentation
does not require oxygen, it is also referred to as anaerobic respiration. The term anaerobic means
“not in air”. The two (2) main types of fermentation are the following:

Alcoholic Fermentation – used by yeast and a few other microorganisms that forms ethyl
alcohol and carbon dioxides as wastes. When yeast in dough runs out of oxygen, it begins to
ferment, giving off bubbles of carbon dioxide, which form the air spaces in a slice of bread.
The small amount of alcohol produced in dough evaporates when the bread is baked.

Lactic Acid Fermentation – pyruvic acid that accumulates as a result of glycolysis are
converted to lactic acid. Lactic acid is produced in your muscles during rapid exercise when
your body cannot supply enough oxygen to the tissues. Your muscles rapidly begin to
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produce ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning
sensation. This is why your muscles may feel sore after only a few seconds of intense activity.
II. Citric Acid Cycle
The Citric Cycle, also referred as Krebs cycle, is named after Hans Krebs, the British biochemist
who demonstrated its existence in 1937. In the presence of oxygen, pyruvic acid produced in
glycolysis passes through the Krebs cycle. During the cycle, pyruvic acid is broken down into carbon
dioxide in a series of energy extracting reactions. The first compound formed in this series of
reactions is citric acid, thus the term citric acid cycle.

Citric acid production – As pyruvic acid enters the mitochondrion, a carbon is removed,
forming CO2, and electrons are removed, changing NAD+ to NADH. Coenzyme A joins the 2carbon molecule, forming acetyl-CoA. Acetyl-CoA then adds the two (2) carbon acetyl group to
a 4-carbon compound, forming citric acid.

Energy extraction – Citric acid is broken down into a 5-carbon compound, then into a 4-carbon
compound. Along the way, two (2) more molecules of CO2 are released, and electrons join
NAD+ and FAD (flavine adenine dinucleotide), forming NADH and FADH2. In addition, one
(1) molecule of ATP is generated. The energy tally from one (1) molecule of pyruvic acid is four
(4) NADH, one (1) FADH2, and one (1) molecule of ATP.
The Krebs cycle spins round and round, generating high energy electrons that are passed to
NADH and FADH2.
III. Electron Transport
The electron transport chain uses high energy electrons from the Krebs cycle to convert ADP into
ATP.
 High energy electrons from NADH and FADH2 are passed into and along the electron transport
chain. In eukaryotes, the electron transport chain is composed of a series of carrier proteins
located in the inner membrane of the mitochondrion. In prokaryotes, the same chain is in the cell
membrane. High energy electrons are passed from one carrier protein to the next. At the end of
the electron transport chain is an enzyme that combines electrons from the electron chain with
hydrogen ions and oxygen to form water. Oxygen serves as the final electron acceptor of the
electron transport chain. It is essential for getting rid of low-energy electrons and hydrogen ions,
the wastes of cellular respiration.
 Every time two (2) high energy electrons transport down the electron transport chain, their
energy is used to transport hydrogen ions (H+) across the membrane. During electron transport,
H+ ions build up in the intermembrane space, making it positively charged. The other side of the
membrane, from which those H+ ions have been taken, is now negatively charged.
 The inner membranes of the mitochondria contain protein spheres called ATP synthases. As H+
ions escape through channels into these proteins, the ATP synthases spin. Each time it rotates,
the enzyme grabs a low-energy ADP and attaches a phosphate, forming high energy ATP. On
an average, each pair of high-energy electrons that moves down the electron transport chain
provides enough energy to convert 3 ADP molecules into 3 ATP molecules.
In the presence of oxygen, the Krebs cycle and electron transport enable the cell to produce 34 more
ATP molecules per glucose molecule in addition to the two (2) ATP molecules obtained from
glycolysis.
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The 36 ATP molecules the cell makes per glucose represent 38% of the total energy of glucose. The
62% is released as heat, which is one (1) of the reasons your body feels warmer during vigorous
exercise.
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Function
Location
Reactants
Products
Equation
Photosynthesis
Energy Storage
Chloroplasts
CO2 and H2O
C6H12O6 and O2
6CO2 + 6H2O
C6H12O6 + 6O2
Cellular Respiration
Energy Release
Mitochondria
C6H12O6 and O2
CO2 and H2O
6O2 + C6H12O6
6CO2 + 6H2O
Photosynthesis and cellular respiration are almost opposite processes:
 Photosynthesis stores energy and cellular respiration withdraws energy.
 The equations of photosynthesis and cellular respiration are the reverse of each other.
 Photosynthesis removes carbon dioxide from the environment and cellular respiration puts it back.
 Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to
release energy from food.
 Products of photosynthesis are similar to the reactants of cellular respiration and vice versa.
 Cellular respiration takes place in all eukaryotes and some prokaryotes while photosynthesis only
occurs in plants, algae and some bacteria.
The Energy Flow
Feeding Relationships:

Food Chain – illustrates that energy stored by producers can be passed through an ecosystem. This
is a series of steps in which organisms transfer energy by eating and being eaten.
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http://zarkanderson.com

Food Webs – show feeding relationships among various organisms in an ecosystem form a network
of interactions. A food web links together all the food chains in an ecosystem.

Trophic Level – refers to each step in a food chain or food web. Producers make up the first level.
Consumers make up the second. Each consumer depends on the trophic level below it for energy.
Only about 10% of the energy available within a trophic level is transferred to organisms at the next
trophic level.
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For instance, 1/10 of the solar energy captured by grasses ends up stored in tissues of cows and
other grazers. Only 1/10 of that energy or 1% in total is transferred to humans when they eat
cows. Thus, the more levels that exist between a producer and a top-level consumer in an
ecosystem, the less energy that remains from the original amount.
References:
Bioenergetics. (n.d.). Retrieved July 28, 2014 from: http://www.merriamwebster.com/dictionary/bioenergetics
Cellular Respiration. (n.d.). Retrieved July 30, 2014 from:
http://biology.about.com/od/cellularprocesses/a/cellrespiration.htm
Miller, K & Levine, J. (2002). Biology. Upper Saddle River, NJ: Pearson Education, Inc.
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