How Do Biological
Organisms Use Energy?
The importance of ATP
F
F
F
All organisms use a two-step process to
provide the energy needed for most of their
biological activities:
First, chemical energy from organic
molecules like glucose is used to make
ATP. This process is called cellular
respiration.
Then, ATP provides the energy for most
biological processes.
F
Two steps: First, energy from cellular
respiration is used to make ATP (adenosine
triphosphate, with 3 phosphates) from ADP
(adenosine diphosphate, with 2 phosphates)
plus a phosphate.
F
The reverse reaction (breakdown of ATP to
ADP and a phosphate) releases energy
which is used for many different cellular
processes.
The Importance of ATP
Our cells are constantly using energy from
organic molecules like glucose to make ATP
and using the ATP molecules to provide the
energy for biological processes such as
muscle contraction, synthesizing molecules,
and pumping ions and molecules into and
out of cells. On average, each ATP
molecule in our body is used and resynthesized more than 30 times per minute
when we are at rest and more than 500
times per minute during strenuous exercise.
What Is ATP?
Energy used by all Cells
Adenosine Triphosphate
Organic molecule containing highenergy Phosphate bonds
Copyright Cmassengale
Chemical Structure of ATP
Adenine Base
3 Phosphates
Ribose Sugar
Copyright Cmassengale
What Does ATP Do for
You?
It supplies YOU with ENERGY!
Copyright Cmassengale
How Do We Get Energy From
ATP?
By breaking
the highenergy
bonds
between the
last two
phosphates
in ATP
Copyright Cmassengale
What is the Process Called?
HYDROLYSIS (Adding H2O)
H 2O
Copyright Cmassengale
How Does That Happen?
An Enzyme!
Copyright Cmassengale
How is ATP Re-Made?
The reverse of the previous
process occurs.
Another Enzyme is
used!
ATP Synthetase
Copyright Cmassengale
The ADP-ATP Cycle
ATP
Synthetase
ATP-ase
Copyright Cmassengale
When is ATP Made in the
Body?
During a
Process called
Cellular
Respiration
that takes
place in both
Plants &
Animals
Copyright Cmassengale
ATP  ADP
The energy that was held in that bond (now broken) is able to
fuel a cellular reaction.
The remaining molecule now has only two phosphate groups
and is called ADP (adenosine diphosphate). This reaction is
sped up by the enzyme ATPase.
... and in reverse
Free energy obtained from an
exergonic reaction can also be
used to add a phosphate group
to ADP, converting it to ATP.
The ATP-ADP cycle is the
cells way of shuttling energy
between reactions.
The addition of a phosphate
group to an organic molecule
of any sort is called
phosphorylation.
Important Coenzymes
ABBREVIATION
COENZYME
Loaded
form
Unloaded
form
FUNCTION
Adenosine triphosphate
ATP
ADP
Energy transfer
Nicotine adenine
dinucleotide
NADH
NAD+
Transfer of electrons and
protons
NADPH
NADP+
Transfer of electrons and
protons
FADH2
FAD
Transfer of electrons and
protons
(based on the vitamin niacin)
Nicotine adenine
dinucleotide phosphate
(based on the vitamin niacin)
Flavine adenine
dinucleotide
(based on the vitamin B12)
PHOTOSYNTHESIS
Harnessing Energy
Heterotrophs and Autotrophs
All living organisms require
organic compounds and
energy for their cells.
Depending on how
organisms obtain these
compounds and energy, we
classify them as being:
Heterotrophs: consumersmust consume organic
molecules as they cannot
produce them, themselves .Eg.
Animals.
or autotrophs: Producersthey can produce organic
molecules. Eg plants.
Photosynthesis
Organisms such as plants, algae and some protists (such as
phytoplankton) are able to trap light energy and make organic
compounds, such as sugars, from simple compounds such as
carbon dioxide and water.
Photosynthesis is the process in which light energy is
transformed into chemical energy stored in sugars.
Organisms with this ability are termed producers.
Other organisms, such as animals and fungi, that depend,
directly or indirectly, on the organic compounds produced by
producers, are called consumers.
Photosynthesis
carbon dioxide + water ---------------------------> glucose + water+
oxygen
6CO2 + 12H2O -------------------------> C6H12O + 6H2O + 6O2
light
chlorophyll
light
chlorophyll
Where does photosynthesis occur?
In a terrestrial flowering plant, only some cells are able to carry out
photo synthesis and these are principally located in green leaves.
The shape and structure of leaves equips them to carry out
photosynthesis.
is the semi-liquid
interior of the
chloroplast , in
which the light
independent
phase takes place.
are membrane stacks
that form the grana.
They contain
chlorophyll and are the
site of light dependent
phase.
Why are leaves so special?
Their flat shape provides a large surface area exposed to
sunlight.
The presence of many stomata (pores) on one or both leaf
surfaces provides access into the leaf for carbon dioxide.
The thinness and the presence of internal air spaces in the
leaves enables the ready diffusion of carbon dioxide to
photosynthetic cells in the leaf tissue.
The network of xylem vessels in the vascular tissue
transports water to the photosynthetic cells.
Each photosynthetic cell possesses many chloroplasts
enabling it to trap the energy of sunlight.
Chloroplasts
Present in some cells of plants and algae.
The boundary of each chloroplast is a double membrane (inner and
outer).
The inner membrane extends to form a system of membranous sacs
called lamella or thylakoids.
When several of these stack together they form grana.
Chlorophyll is located in the grana.
The semi-fluid substance between the grana is called the stroma.
Chlorophyll
Chlorophyll is pigment that absorbs or traps light.
There are three types of chlorophyll – a, b and c.
Chlorophyll a is the major photosynthetic pigment and is found
in all photosynthetic plants, protists, and cyanobacteria.
Chlorophyll molecules are embedded in the membrane
structure of grana.
Chlorophylls absorb wavelengths of violet-to-blue and red
light. They reflect green which is why leaves appear green.
Stages of Photosynthesis
Photosynthesis from:
“photo” – light
“synthesis” – put together
The name reflects the two-stage nature of the
process.
Light-dependent stage involving trapping of light energy
Light-independent stage in which energy trapped in the
first stage is used to make organic compounds from carbon
dioxide and water.
...now for the Chemical Reactions of photosynthesis
Photosynthesis involves two stages;
Light dependent reactions in which light
energy trapped by chlorophyll in the
chloroplast (grana) is used to produce ATP
and split water into H+ and oxygen gas.
The light independent reactions, which
use ATP to combine carbon dioxide and H+ to
form glucose and water in the stroma.
Light-dependent Reaction
Also known as the light reaction.
Occur within the grana of the chloroplasts
Requires the input of water as well as light energy.
Can be summarised by the reaction below:
Steps in light-dependent reaction
Sunlight is trapped by chlorophyll a (or other pigments) and light
energy is converted to chemical energy.
Absorbed energy is used to produce ATP and split water
molecules to form H+ ions and oxygen (waste product). This involves
the electron transport chain.
H+ ions are gathered by a carrier molecule or acceptor molecule
(NADP in this case).
NADP becomes NADPH and transports H+ ions from the grana to
the stroma.
H+ ions and ATP produced in light-dependent reaction are utilised in
light-independent reaction.
Light dependent reaction
Light-independent Reaction
Also known as dark reaction or Calvin cycle.
Occurs in the stroma and involves the reduction of carbon.
Does not directly depend on light involvement but does
dependent on previous stage occurring.
Can be summarised by the reaction below:
Steps in light-independent reaction
Carbon reduction (from CO2 to a sugar [C(H2O)]n) requires a supply
of carbon dioxide and hydrogen ions, and an input of energy.
Carbon dioxide can come from the air surrounding the leaf or from
cellular respiration reactions.
Energy required to drive these reactions comes from ATP and
‘loaded’ carriers (NADPH molecules) produced during the lightdependent stage.
H+ is the reducing agent and ATP is the source of energy for reducing
carbon dioxide to organic compounds such as glucose and other
sugars.
Plants do not build sugars simply by joining CO2 molecules together.
Sugar formation involves a cyclic set of reactions in which
intermediate substances are formed.
Light independent reaction
The Calvin Cycle
Each time the cycle proceeds, one carbon one carbon dioxide
molecule enters the cycle and is fixed and reduced.
To produce a 6-carbon compound that is released from the
cycle, six turns of the cycle must take place.
At the completion of each turn of the cycle, the starting
compound is regenerated and so the cycle can proceed
provided that CO2, ATP and NADPH are also available.
The Calvin Cycle
The importance of sugars
All cells can use sugars as a starting point for the
manufacture of other carbohydrates and lipids.
They can react sugars with with nitrogen to form nonessential amino acids and nitrogenous bases that are
found in nucleic acids.
The chemical energy is starch is used directly or
indirectly by consumers in cellular respiration to
produce ATP for their energy requirements.
Factors that influence
photosynthesis
Light intensity
Carbon dioxide availability
Temperature
Indirect factors
Light intensity
The rate of photosynthesis
usually increases with light
intensity until there is another
limiting factor, such as the
saturation of chloroplasts.
About 20% of light that hits the leaf
is reflected.
Only about 1% of light absorbed by
the leaf is converted to chemical
energy.
Carbon dioxide
For most plants, carbon dioxide from air dissolves in extracellular fluid
before entering photosynthetic cells.
There are local variations in carbon dioxide levels in air, in different
habitats and at different times of the day.
Aquatic plants can also use hydrogen carbonate (carbonic acid), which
forms when carbon dioxide dissolves in water.
CO2 released as a product of cellular respiration can also be used for
photosynthesis, but usually only provides a small amount of the total
carbon dioxide requirements.
The degree to which the level of carbon dioxide affects the rate of
photosynthesis is different for C3, C4 and CAM plants.
C4 and CAM plants are more efficient than C3 plants at trapping
carbon dioxide when it is warm.
Compensation point
At low levels of light intensity,
the rate of photosynthesis is
less than the rate of cellular
respiration, so there is net
output of carbon dioxide by
plants.
The light intensity at which the
rate of carbon dioxide produced
by cellular respiration equals the
rate of carbon dioxide used in
photosynthesis is known as the
light compensation point.
Temperature
Photosynthesis increases with
increasing temperature until
around 20-40oC, depending on
plant species, then it declines
again.
Plants that live in hotter climates
are at higher end of the range.
In C3 plants, oxygen displaces
trapped carbon dioxide more
rapidly as temperature
increases (enzyme binds
oxygen instead of carbon
dioxide).
Indirect factors
Water
Required in photosynthesis
Only 1% of water passing up the xylem is used in photosynthesis. The
rest is used in other chemical reactions, to hydrate cells or is lost in
transpiration.
If there is not enough water to hydrate the cells and keep them turgid,
the stomata close. This prevents carbon dioxide entering the leaves,
therefore photosynthesis decreases.
Level of chlorophyll
Limits photosynthesis
Yellow leaves will have a lower rate of photosynthesis.
Nitrogen and Magnesium
Chlorophyll contains the elements nitrogen and magnesium.
If the soil is deficient in one or both these elements, the plants cannot
make sufficient chlorophyll.
Rate of photosynthesis
Any of the factors that influence photosynthesis may limit the rate
of photosynthesis.
Photosynthesis will be limited by
only one factor at a time, but if
conditions in an individual
chloroplast change, the
particular factor that is
limiting may also change.
For example, carbon dioxide
levels that are adequate (not
limiting) in conditions of low light
may become limiting if light
intensity increases.
Chemosynthesis
Chemosynthetic organisms use the chemical energy within inorganic
molecules.
This energy comes from oxidising reactions.
These reactions involve the addition of oxygen to (or the removal of
electrons from) a substance.
Examples include bacteria who obtain energy by converting:
Ammonium ions (NH4+) to nitrite ions (NO2-)
Nitrite (NO2-) ions to nitrate (NO3-)
Sulfide ions (S2-) to sulfate ions (SO42-)
Whole communities of heterotrophic organisms live around volcanic
vents on the deep ocean floors where light does not penetrate. They
rely directly or indirectly on chemosynthetic bacteria for their food
supply in much the same way as terrestrial communities depend on
plants to trap energy.