Respiration is the process by which cells convert biochemical energy from nutrients into ATP through a series of metabolic reactions involving the oxidation of molecules and reduction of others. Aerobic respiration uses oxygen as the final electron acceptor, while anaerobic respiration uses other molecules like sulfate, nitrate or sulfur. The energy from respiration is used to synthesize ATP, which cells use to power processes like biosynthesis, locomotion and transport.

1. Respiration
 Respiration is the process by which
animals take in oxygen necessary for
cellular metabolism and release the
carbon dioxide that accumulates in their
bodies as a result of the expenditure of
energy. When an animal breathes, air or
water is moved across such respiratory
surfaces as the lung or gill in order to help
with the process of respiration. Oxygen
must be continuously supplied to the
animal and carbon dioxide, the waste
product, must be continuously removed
for cellular metabolism to function
properly. For example, if this does not
happen and carbon dioxide levels increase
in the body, pH levels decrease and the
animals may eventually die (see Question:
Why is the regulation of body pH
important?).

2. Cellular respiration
 Cellular respiration (also known as 'oxidative
metabolism') is the set of the metabolic reactions and
processes that take place in organisms' cells to convert
biochemical energy from nutrients into
adenosine triphosphate (ATP), and then release waste
products. The reactions ducoda fields involved in
respiration are catabolic reactions that involve the
oxidation of one molecule and the reduction of another.
Respiration is one of the key ways a cell gains useful
energy to fuel cellular reformations.
 Nutrients commonly used by animal and plant cells in
respiration include glucose, amino acids and fatty acids,
and a common oxidizing agent (electron acceptor) is
molecular oxygen (O2). Bacteria and archaea can also
be lithotrophs and these organisms may respire using a
broad range of inorganic molecules as electron donors
and acceptors, such as sulfur, metal ions, methane or
hydrogen. Organisms that use oxygen as a final electron
acceptor in respiration are described as aerobic, while
those that do not are referred to as anaerobic[1].
 The energy released in respiration is used to synthesize
ATP to store this energy. The energy stored in ATP can
then be used to drive processes requiring energy,
including biosynthesis, locomotion or transportation of
molecules across cell membranes

3. Anaerobic respiration
 biology, anaerobic respiration is a way for an
organism to produce usable energy, in the form of
adenosine triphosphate, or ATP, without the involvement
of oxygen; it is respiration without oxygen. This process
is mainly used by prokaryotic organisms (bacteria) that
live in environments devoid of oxygen. Although oxygen
is not used, the process is still called respiration because
the first step of respiration is used, glycolysis. In order
for the electron transport chain to function, an
exogenous final electron acceptor must be present to
take the electron away from the system after it is used.
In aerobic organisms, this final electron acceptor is
oxygen. Oxygen is a highly electronegative atom and
therefore is an excellent candidate for the job. In
anaerobes, the chain still functions, but oxygen is not
used as the final electron acceptor. Other less
electronegative substances such as sulfate (SO4), nitrate
(NO3), and sulfur (S) are used. Oftentimes, anaerobic
organisms are obligate anaerobes, meaning they can only
respire using anaerobic compounds and can actually die
in the presence of oxygen
 Anaerobic respiration is not the same as fermentation,
which does not use either the citric acid cycle or the
respiratory chain (electron transport chain). In
anaerobic respiration, microorganisms are donating
electrons to a final electron acceptor, while in
fermentation they are essentially creating their own
electron acceptor to which they can dump electrons
with the purpose of regenerating their NAD+ pool. .

4. Respiratory system
 In humans and other animals, for example,
the anatomical features of the
respiratory system include airways,
lungs, and the respiratory muscles.
Molecules of oxygen and carbon dioxide
are passively exchanged, by diffusion,
between the gaseous external
environment and the blood. This exchange
process occurs in the alveolar region of
the lungs. [1]
 Other animals, such as insects, have
respiratory systems with very simple
anatomical features, and in amphibians
even the skin plays a vital role in
gas exchange. Plants also have respiratory
systems but the directionality of gas
exchange can be opposite to that in
animals. The respiratory system in plants
also includes anatomical features such as
holes on the undersides of leaves known
as stomata.

5. Ecosystem respiration
 Ecosystem respiration is the sum
of all respiration occurring by the
living organisms in a specific
ecosystem.
 Ecosystem respiration is typically
measured in the natural environment,
such as a forest or grassland field,
rather than in the laboratory.
Ecosystem respiration is the
production portion of carbon dioxide
in an ecosystem's carbon flux, while
photosynthesis typically accounts for
the majority of the ecosystem's
carbon consumption.


6. Plant Respiration
 Respiration in plants, as in all living organisms, is
essential to provide metabolic energy and carbon
skeletons for growth and maintenance. As such,
respiration is an essential component of a plant's carbon
budget. Depending on species and environmental
conditions, it consumes 25-75% of all the carbohydrates
produced in photosynthesis - even more at extremely
slow growth rates. Respiration in plants can also
proceed in a manner that produces neither metabolic
energy nor carbon skeletons, but heat. This type of
respiration involves the cyanide-resistant, alternative
oxidase; it is unique to plants, and resides in the
mitochondria. The activity of this alternative pathway
can be measured based on a difference in fractionation
of oxygen isotopes between the cytochrome and the
alternative oxidase. Heat production is important in
some flowers to attract pollinators; however, the
alternative oxidase also plays a major role in leaves and
roots of most plants. A common thread throughout this
volume is to link respiration, including alternative
oxidase activity, to plant functioning in different
environments.

7. Animals Respiration
 In complex animals, where the cells of internal
organs are distant from the external
environment, respiratory systems facilitate the
passage of gases to and from internal tissues. In
such systems, when there is a difference in
pressure of a particular gas on opposite sides of
a membrane, the gas diffuses from the side of
greater pressure to the side of lesser pressure,
and each gas is transported independently of
other gases. For example, in tissues where
carbon dioxide concentration is high and
oxygen concentration is low as a result of active
metabolism, oxygen diffuses into the tissue and
carbon dioxide diffuses out.
Read more:
respiration: Animal Respiration — Infoplease.com
http://www.infoplease.com/ce6/sci/A0860708.html#ixzz18BtNM9KO

8. Aerobic Respiration
 Aerobic respiration is the release of
energy from glucose or another
organic substrate in the presence of
Oxygen. Strictly speaking aerobic
means in air, but it is the Oxygen in
the air which is necessary for aerobic
respiration. Anaerobic respiration is
in the absence of air.
 Here is a molecular model of a
glucose molecule. You do not need to
memorise the diagram for you GCSE
exam, but it should help you to
understand that a molecule of
glucose contains six atoms of Carbon
(shown in blue), twelve atoms of
Hydrogen (shown in green), and six
atoms of Oxygen (shown in red).

9. Glycolysis
 Glycolysis (from glycose, an older term[1]
for glucose + -lysis degradation) is the
metabolic pathway that converts glucose
C6H12O6, into pyruvate, CH3COCOO−
+ H+. The free energy released in this
process is used to form the high-energy
compounds ATP (adenosine triphosphate)
and NADH (
reduced nicotinamide adenine dinucleotide
). Glycolysis is a definite sequence of ten
reactions involving ten intermediate
compounds (one of the steps involves two
intermediates). The intermediates provide
entry points to glycolysis. For example,
most monosaccharides, such as fructose,
glucose, and galactose, can be converted
to one of these intermediates

10. Photosynthesis
 Photosynthesis (from the Greek φώτο- [photo-],
"light," and σύνθεσις [synthesis], "putting together",
"composition") is a process that converts
carbon dioxide into organic compounds, especially
sugars, using the energy from sunlight.[1] Photosynthesis
occurs in plants, algae, and many species of bacteria, but
not in archaea. Photosynthetic organisms are called
photoautotrophs, since they can create their own food. In
plants, algae, and cyanobacteria, photosynthesis uses
carbon dioxide and water, releasing oxygen as a waste
product. Photosynthesis is vital for all aerobic
life on Earth. As well as maintaining the normal level of
oxygen in the atmosphere, nearly all life either depends
on it directly as a source of energy, or indirectly as the
ultimate source of the energy in their food[2] (the
exceptions are chemoautotrophs that live in rocks or
around deep sea hydrothermal vents). The rate of
energy capture by photosynthesis is immense,
approximately 100 terawatts,[3] which is about six times
larger than the power consumption of human
civilization.[4] As well as energy, photosynthesis is also
the source of the carbon in all the organic compounds
within organisms' bodies. In all, photosynthetic
organisms convert around 100–115 teragrams of
carbon into biomass per year.

11. RESPIRATION
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