How nutrients are used to create energy for Organisms
Nutrients are chemical substances found in every living thing on Earth. They
are necessary to the lives of people, plants, animals, and all other organisms. Nutrients help
break down food to give organisms energy. They are used in every process of an organism’s
body. Some of the processes are growth (building cells), repair (healing a wound), and
maintaining life (breathing).
Plants and other autotrophs absorb nutrients
from soil and water. Autotrophs are organisms that can
make their own food. The most important nutrients they
need are carbon, hydrogen, and oxygen. Other nutrients
needed by plants are nitrogen,
phosphorous, potassium, calcium, magnesium, and sulfur.
From these basic nutrients, plants and other autotrophs
synthesize, or create, their own nutrients, such as sugars.
The human body can also synthesize some nutrients, such
as amino acids. However, most organisms need nutrients
created by autotrophs. People and animals get most of their nutrients from food.
Essential nutrients are nutrients that the
human body is unable to synthesize. They
must be obtained from food or water.
Essential nutrients
include carbohydrates, proteins,
fats, vitamins, and minerals.
Carbohydrates, proteins, and fats are all
part of a group of essential nutrients called
macronutrients. “Macro-” means large, and
these are the nutrients humans need in the
largest amounts. Foods that are high in
macronutrients include potatoes, which are high in carbohydrates; nuts, which are high in
proteins; and avocados, which are high in fats.
Each macronutrient supplies a specific amount of energy. We know how much energy is in a
kind of food by how many calories it has. A calorie is a unit of energy. Think of calories like
gallons of fuel in a tank: If your car can go 20 kilometers by using one gallon of fuel and you
are taking a 40-kilometer trip, you know that you need two gallons of fuel. Calories are fuel
in the human body.
Vitamins and minerals are part of a group of essential nutrients called micronutrients.
“Micro-” means small; humans need micronutrients in small amounts. Vitamins have names
like vitamin A, vitamin C, and vitamin D. Vitamins contain the element carbon, which means
they are organic compounds. Minerals, such as calcium and iron, come from the earth or
environment. Minerals do not contain carbon, meaning they are inorganic compounds.
Nutrients in the Environment
Nutrients accumulate, or build up, in the environment. Nutrient-rich soil or water contains
large amounts of nitrogen, carbon, phosphorus, sulfur, and potassium. These nutrients can
come from natural sources, like plant and animal remains. As plants and animals die, they
decompose. Decomposition releases nutrients into the environment.
Human activity also adds nutrients to soil and water. Many factories use nutrients to help
preserve their products. Nutrients are either released as gas into the atmosphere, or
as liquid. Either way, the nutrients enter the water cycle.
Sewage and wastewater are also full of nutrients such as carbon. Wastewater is often used
on golf courses, where it enters local creeks as runoff. Treated wastewater is sometimes
released directly into the environment.
Fertilizers, used in agriculture, are rich in carbon, nitrogen, and phosphorus. Farmers use
fertilizers on crops such as grains, fruits, and vegetables. Phosphorus-based fertilizers are
also used on golf courses, parks, and even neighborhood lawns.
Fertilizer not absorbed by plants accumulates in the soil. Nutrients from fertilizer can
also leech into groundwater or runoff. Nutrient-rich runoff flows into creeks, rivers, and
bays. Ponds, lakes, and even the ocean can absorb huge amounts of nutrients, especially
nitrogen and phosphorus.
Balance of Nutrients
Nutrients such as carbon, oxygen, and nitrogen make all life possible. Nutrient-poor areas
cannot support much biodiversity. Bogs, for instance, are nutrient-poor wetlands found in
cool climates. The soil of bogs is much more acidic than fertile, or nutrient-rich, soil. Few
species of plants can grow in the nutrient-poor soil of bogs. With fewer species of plants
available, the ecosystem is unable to support a large variety of other organisms, such as
animals and fungi.
The introduction of nutrients into an environment can make the ecosystem healthy and
fertile. Upwelling is the natural process of cold, nutrient-rich water being pushed to the
upper layers of the ocean. Upwelling brings a huge supply of nutrients to fish, seaweeds,
and marine mammals. Economic activity also depends on upwelling. The fisheries off the
western coast of South America, for instance, depend on the annual upwelling of the Pacific
Ocean to bring nutrients to fish and shellfish stocks.
Excess Nutrients
Although life depends on nutrients, too many nutrients can have a negative impact on an
ecosystem. Algal blooms, for instance, are caused by excess nutrients. They can
actually prevent the natural nutrient flow in an aquatic ecosystem.
Algal blooms form as excess nutrients, from natural and manmade sources, accumulate in a
body of water. When the conditions are just right, algae, bacteria, and other microbes
bloom, or multiply quickly. The rapid reproduction uses almost all the nutrients in the water.
The bloom forms a thin mat near the surface of the water, preventing light from reaching
below.
The organisms in many algal blooms are not eaten by other organisms, so they are not part of
the food web. An algal bloom uses up important nutrients—including oxygen—without
contributing to the aquatic environment. Some algal blooms even contain toxic microbes. This
type of algal bloom is called a harmful algal bloom (HAB). Without light and oxygen, plants
die quickly. An algal bloom uses up nutrients and prevents the development of plants that
fish and other living things depend on for survival.
Algal blooms can die off as quickly as they form. The dead algae and other microbes sink to
the bottom of the body of water. Sunlight and nutrients can once again enter the ecosystem.
However, bacteria that help decay the algal bloom now absorb most of these nutrients. It
can take weeks or even months for an ecosystem to recover from an algal bloom.
Algal blooms can reduce nutrients in an area to such a degree that the area is known as
a dead zone. This means that few organisms can survive in the environment. Dead zones do
not have enough nutrients to support a food web.
Energy from Nutrients
Energy from nutrients comes in the way of calories. A Calories is defined as the energy
needed to raise the temperature of 1 kilogram of water through 1 °C, and often used to
measure the energy value of foods. The energy needed to raise the temperature of water
comes from the chemical bonds in food, such as the bonds between carbon, oxygen, and
hydrogen. The breaking of chemical bonds absorbs energy because it takes energy to pull the
atoms apart. The forming of chemical bonds releases energy as the atoms come together
because they are attracted to each other. In order for animals to be able to hunt for food
they need more energy input than output.
Cellular Respiration
 Cellular respiration involves various metabolic pathways that break down
carbohydrates and other metabolites with the concomitant buildup of ATP.
 Cellular respiration consumes oxygen and produces CO2; because oxygen is required,
cellular respiration is aerobic.
 Cellular respiration usually involves the complete breakdown of carbohydrates into CO 2
and H2O.
The net equation for carbohydrates breakdown is: C6H12O6 + 6 O2 = 6 CO2 + 6 H2O +
energy
 Carbohydrates is a high-energy molecule; CO2 and H2O are low-energy molecules;
cellular respiration releases energy.
 The reactions of cellular respiration allow energy in carbohydrates to be released
slowly; therefore ATP is produced gradually.
 In contrast, if carbohydrates were broken down rapidly, most of its energy would be
lost as non-usable heat.
 This is relatively efficient compared to, for example, the 25% efficiency of a car
burning gasoline.
Fermentation and Decomposition
 Fermentation is an anaerobic (i.e., occurs in
the absence of oxygen) process which
consists of microorganisms such as bacteria
or yeast that breakdown the chemical bonds
in carbohydrates to either lactate or to
alcohol and CO2 (depending on the organism).
 Decomposition is when a plant, animal, or
insect dies, that plant, animal, or insect is
broken into tiny pieces and those pieces
become part of the soil. Bacteria, fungi, and some worms are what break down dead
plants, animals, and insects. The bacteria, fungi, and worms are called decomposers.
Decomposers need to eat some of the dead things so they can live and grow. The tiny
pieces left over after decomposers eat become part of the soil. Living plants take
what they need from these pieces so they can grow. The parts of these pieces that
living plants take to grow are called nutrients. So, living plants make their own food,
but they also need to get nutrients from the soil. Decomposers help provide these
nutrients.

Common decomposers in an ecosystem are: bacteria, fungus and
earthworm

The Energy Organelles Revisited
 Chloroplasts and mitochondria may be related based on their likeness, yet they carry
out opposite processes.
o The inner membrane of the chloroplasts forms the thylakoids of the grana. The
inner membrane of the mitochondrion forms the convoluted cristae.
o In chloroplasts the electrons passed down the ETC have been energized by the
sun. In mitochondria the electrons passed down the ETC have been removed
from glucose products.
o In chloroplasts the stroma contains the enzymes of the Calvin cycle. In the
mitochondria the matrix contains the enzymes of the citric acid cycle.
 Flow Of Energy
o Energy flows through organisms. For example, the sun is the energy source for
producing carbohydrates in chloroplasts. In the mitochondria, the carbohydrate
energy is converted into ATP molecules during cellular respiration.
o Chemicals cycle throughout cells. Mitochondria use carbohydrates and oxygen
produced in chloroplasts, and chloroplasts use carbon dioxide and water
produced in the mitochondria.
Evidence that chloroplasts split water molecules enabled researchers to track atoms
through photosynthesis.

Powered by light, the green parts of plants produce organic compounds and O 2 from
CO2 and H2O.

The equation describing the process of photosynthesis is:

6CO2 + 12H2O + light energy  C6H12O6 + 6O2+ 6H2O

C6H12O6 is glucose.

Water appears on both sides of the equation because 12 molecules of water are
consumed, and 6 molecules are newly formed during photosynthesis.

We can simplify the equation by showing only the net consumption of water:

6CO2 + 6H2O + light energy  C6H12O6 + 6O2

The overall chemical change during photosynthesis is the reverse of cellular
respiration.

In its simplest possible form: CO2 + H2O + light energy  [CH2O] + O2

[CH2O] represents the general formula for a sugar.

One of the first clues to the mechanism of photosynthesis came from the discovery
that the O2 given off by plants comes from H2O, not CO2.

Before the 1930s, the prevailing hypothesis was that photosynthesis split carbon
dioxide and then added water to the carbon:

Step 1: CO2  C + O2

Step 2: C + H2O  CH2O

C. B. van Niel challenged this hypothesis.

In the bacteria that he was studying, hydrogen sulfide (H 2S), not water, is used in
photosynthesis.

These bacteria produce yellow globules of sulfur as a waste, rather than oxygen.

Van Niel proposed this chemical equation for photosynthesis in sulfur bacteria:

CO2 + 2H2S  [CH2O] + H2O + 2S

He generalized this idea and applied it to plants, proposing this reaction for their
photosynthesis:

CO2 + 2H2O  [CH2O] + H2O + O2

Thus, van Niel hypothesized that plants split water as a source of electrons from
hydrogen atoms, releasing oxygen as a byproduct.

Other scientists confirmed van Niel’s hypothesis twenty years later.

They used 18O, a heavy isotope, as a tracer.

They could label either C18O2 or H218O.

They found that the 18O label only appeared in the oxygen produced in photosynthesis
when water was the source of the tracer.

Hydrogen extracted from water is incorporated into sugar, and oxygen is released to
the atmosphere (where it can be used in respiration).

Photosynthesis is a redox reaction.

It reverses the direction of electron flow in respiration.

Water is split and electrons transferred with H + from water to CO2, reducing it to
sugar.

Because the electrons increase in potential energy as they move from water to sugar,
the process requires energy.

The energy boost is provided by light.
The Carbon Cycle
The time it takes carbon to move through the fast carbon cycle is measured in a lifespan.
The fast carbon cycle is largely the movement of carbon through life forms on Earth, or the
biosphere. Between 1015 and 1017 grams (1,000 to 100,000 million metric tons) of carbon move
through the fast carbon cycle every year.
Carbon plays an essential role in biology because of its ability to form many bonds—up to
four per atom—in a seemingly endless variety of complex organic molecules. Many organic
molecules contain carbon atoms that have formed strong bonds to other carbon atoms,
combining into long chains and rings. Such
carbon chains and rings are the basis of living
cells. For instance, DNA is made of two
intertwined molecules built around a carbon
chain.
The bonds in the long carbon chains contain a
lot of energy. When the chains break apart,
During photosynthesis, plants absorb carbon dioxide and sunlight
to create fuel—glucose and other sugars—for building plant
structures. This process forms the foundation of the fast
(biological) carbon cycle. (Illustration adapted from P.J. Sellers et
al., 1992.)
the stored energy is released. This energy makes carbon molecules an excellent source of
fuel for all living things.
Plants and phytoplankton are the main components of the fast carbon cycle. Phytoplankton
(microscopic organisms in the ocean) and plants take carbon dioxide from the atmosphere by
absorbing it into their cells. Using energy from the Sun, both plants and plankton combine
carbon dioxide (CO2) and water to form sugar (CH2O) and oxygen. The chemical reaction
looks like this:
CO2 + H2O + energy = CH2O + O2
Four things can happen to move carbon from a plant and return it to the atmosphere, but all
involve the same chemical reaction. Plants break down the sugar to get the energy they need
to grow. Animals (including people) eat the plants or plankton, and break down the plant sugar
to get energy. Plants and plankton die and decay (are eaten by bacteria) at the end of the
growing season. Or fire consumes plants. In each case, oxygen combines with sugar to
release water, carbon dioxide, and energy. The basic chemical reaction looks like this:
CH2O + O2 = CO2 + H2O + energy
Figure 1. Box and arrow
In all four processes, the carbon dioxide released in the
diagram of the terrestrial
reaction usually ends up in the atmosphere. The fast carbon
carbon cycle.
cycle is so tightly tied to plant life that the growing season can
be seen by the way carbon dioxide fluctuates in the atmosphere. In the Northern
Hemisphere winter, when few land plants are growing and many are decaying, atmospheric
carbon dioxide concentrations climb. During the spring, when plants begin growing again,
concentrations drop. It is as if the Earth is breathing.
Decomposition and Respiration
Decomposition in soils is a key ecosystem function that in part determines the productivity
and health of the plants growing there. Decomposers feed on dead organic matter in the
presence of oxygen and in the process break it down into its simplest components: carbon
dioxide, water and nutrients (organic matter consists of
material or molecules produced by living organisms). The
process of decomposition releases large quantities of
essential nutrients to the soil solution, thereby making them
available to plant roots. In northern hardwood forests, for
example, about 85% of a tree’s nitrogen comes from
decomposition (Bormann and Likens 1979). Thus, if
decomposition of a forest is impaired by drought, acid rain
or some other stress, the vegetation may experience
nutrient deficiencies. In addition, if the soil receives too
much water or is impacted, then the soil cannot get oxygen
and become anaerobic. This causes death to the soil of the forest ecosystem.
Decomposition is also important because it is part of the global carbon cycle. The carbon
cycle is the cyclical movement of carbon atoms from the atmosphere to the
biosphere/lithosphere and back to the atmosphere (Figure 1). In the atmosphere, carbon is
in the form of carbon dioxide gas. Through the process of photosynthesis, some of that
carbon is converted into organic carbon which makes up organic matter or biomass. Plants
and animals perform cellular respiration and convert a small percentage of that organic
carbon back to CO2.
A larger portion of that organic carbon in plants is transferred to the soil when plants shed
their leaves or when they die. Decomposers then begin their work of breaking down the
organic matter. Some of the organic carbon in the organic matter is converted into
CO2 which is released into the soil pore spaces leading to relatively high concentrations of
CO2 compared to the atmosphere. This difference in concentration causes CO 2to diffuse
from the soil to the atmosphere. This movement or flux of CO2 is known
as CO2 emission (Figure 1).
Decomposition is not the only source of CO2 in soil. In a forest or grassland ecosystem, plant
roots are abundant in the soil and root cells perform cellular respiration, metabolizing
carbohydrates that are sent down from the leaves. This CO 2 is released to the soil and can
be responsible for anywhere between 0 and 60% of a soil’s CO 2 emission. Note that
CO2 emission is the movement of CO2 from soil to the atmosphere, whereas decomposition
and root respiration are processes that produce CO 2 in the soil.