(1A)
Metabolism and introduction to respiration and its
significance
Reminder: Metabolism is the scientific term used for
all the chemical reactions that go on inside an organism's body.
Metabolic reactions synthesise molecules of all shapes and size for
specific uses in an organism. Metabolic reactions break down larger
molecules down into smaller ones (e.g. in digestions). Metabolic
reactions supply the energy needs for the chemistry of every cell
from respiration in the mitochondria.
DO NOT CONFUSE BREATHING and
RESPIRATION
The
human respiratory system
The diagram on the right shows the connection between
the mouth, windpipe (trachea), bronchus, bronchiole, lungs with their
alveolus and alveoli sub-structures.
It is important to excrete carbon dioxide from
the lungs because a build-up of the gas can have toxic effects in high
concentration in the lungs or the bloodstream.
See separate page for
Mechanism
of breathing and gas exchanges
Respiration is the process of releasing
energy in the mitochondria from digested food- therefore respiration is an exothermic process. Respiration transfers energy that
cell needs to fully function. 'Aerobic' means 'with oxygen'
(usually in reference to respiration). 'Anaerobic' means 'without oxygen'
(usually refers to respiration).
Know and understand that respiration in cells can take place aerobically or anaerobically
depending on conditions and whether the cell is in an animal, plant, fungi or
bacteria. Know and understand that the energy
released in respiration is used in a variety of ways.
Know that the human body needs to react to the increased demand for energy during
exercise. You should be able to use your
skills, knowledge and understanding to interpret the data relating to the effects of exercise
on the human body. Know how to do a simple calorimetry experiment to measure the
energy content of a food.
Do NOT think respiration is breathing in
and out.
Respiration is the process of transferring
chemical energy to power the chemistry of ALL cells by breaking down sugars like
glucose - aerobically with oxygen or anaerobically without oxygen and overall
the process is exothermic - energy releasing.
Anaerobic or anaerobic respiration is
sometimes referred to as cellular respiration.
Respiration powers all the metabolic
biochemistry of all living organisms.
Respiration chemistry is very complex
involving many reactions and takes place mainly in the mitochondria.
Mitochondria are known as the
powerhouses of the cell.
They are organelles that act like
a digestive system in the sense they take in nutrients, break them down, and
creates energy rich molecules for the cell that can react with
oxygen.
Respiration occurs in both plants
animals and must be continuously happening to keep the organism alive!
Glucose, under the right conditions, can
be completely oxidised to carbon dioxide and water.
This is analogous to burning a fuel
in a combustion reaction - but a lot slower and no flame!
This is an exothermic reaction and
forming H2O and CO2 releases the maximum amount of
chemical energy.
The overall very complex
biochemistry of aerobic respiration can be summarised as:
glucose + oxygen ===> carbon dioxide
+ water + energy
C6H12O6(aq)
+ 6O2(g) ===> 6CO2(g) + 6H2O(l)
+ energy
Organisms cannot survive without the
energy from respiration and this process must go on continuously in every
cell in any living organism.
An organism's cells cannot use the energy
directly, but a molecule called ATP (adenosine triphosphate) is made
and acts as a secondary chemical potential energy store.
The ATP molecule can then power all
the essential chemistry e.g. breaking down or synthesising molecules in
an organism's metabolism (*), facilitating active transport, organ function
including the working of the muscles.
(*
Metabolism is all the
chemical reactions in an organism that keep it alive)
Overall cellular respiration
must be exothermic, otherwise there would be no net energy
release! So, eventually, there is a net transfer of energy to the
environment.
A typical person might average a
power output of over 50 J/s, about the same as a 50 W light bulb!
All the chemistry of respiration is
catalysed by the specific enzymes in cells.
The rate of respiration is
affected by the ambient temperature, pH of the cell fluids
and transport systems and the concentration of e.g.
sugars and oxygen.
Note that these are the three
factors which affect the efficiency of enzyme controlled reactions
including respiration.
The substrate molecules required for
respiration are usually sugars like glucose, but the products of respiration
depend on conditions e.g. oxygenated environment or lack of oxygen and whether
the cells are animal, plant, fungi or bacteria.
Apart from glucose, other carbohydrates -
sugars, proteins and fatty acids from lipids can be consumed in respiration.
This page
compares the processes of aerobic respiration and anaerobic respiration
- in plants/fungi and animals and considers the different conditions, substrates, products and
relative yields of ATP for the different respiration situations.
You should understand that respiration in cells can take place
all the time aerobically or anaerobically.
What does the energy from
respiration do?
Well it powers the vast majority of chemistry of all
cells of all organisms!
You should know and understand that
the energy
released in respiration is used in a variety of ways to maintain the life of
any organism e.g.
- to
build larger molecules from smaller ones e.g .proteins from amino acids
(plants and animals), starch from glucose (plants), cellulose from
glucose (plants),
- plants use sugars, nitrates and other
nutrients to make their own amino acids are then built up into proteins,
- animals can't
do this, e.g. we need to take in protein, break it down to small amino acids and rebuild to our
required proteins and all of these processes need chemical energy,
- in animals excess protein is
broken down to urea, a waste product excreted in urine.
- fats in plants and animals are made
from glycerol and three long chain fatty acid molecules - these
become energy stores or structural parts of certain tissues,
- organisms require energy from
respiration for cell division
- the central nervous system,
including the brain, and the peripheral nervous system, all require
inputs of energy, the electrical nerve signals to the brain won't go
on their own without some sort of 'battery help'!
- animals require energy to enable
muscles to
contract and relax eg to move limbs and move around - that's why muscle
cells have lots of mitochondria to power the movement and
work done by muscles,
- in mammals and birds, any excess thermal energy is used to
maintain a steady warm body temperature in
colder surroundings (thermoregulation), we slowly cease to function if we get too hot or too
cold,
- also appreciate that the human body needs to react to any increased demand for energy
e.g. during vigorous exercise - so more glucose will be
broken down in respiration,
- energy from respiration is
needed to help maintain a constant environment in the organism
e.g. water levels (osmoregulation), oxygen levels, removing
waste products and not just temperature,
- energy is needed for transport
of
materials (nutrients or waste products) around a multicellular plant
or animal organism - particularly with active transport where extra
energy is needed to move molecules against the natural diffusion
gradient e.g. powering and using protein carrier molecules.,
- plants need to move
nutrients like mineral ions from the soli into the roots and up
the rest of the plant, they also need energy for other functions
like opening and closing the stomata in the leaves.
All of these examples are
part of the metabolism chemistry of an organism.
See
Enzymes - structure and functions notes
for examples of metabolic chemistry
Sources of substrate molecules for
respiration
Plants are producers and make
their own glucose for respiration from
photosynthesis.
Animals are consumers and have to
produce glucose by breaking down the biomass of the organisms-food
that they eat e.g. breaking down carbohydrates like starch.
There are two types of respiration -
aerobic (with plenty of oxygen) and anaerobic (with little,
if any, oxygen)
(1B) Respiration is a continuous process in all organisms to
release chemical energy from food - a chemical energy store:
Aerobic respiration in
animals
Aerobic respiration needs the sugar from
digesting carbohydrates and oxygen via air breathed in/absorbed by the organism, and from the lungs
carried round the body by specialised red blood cells in the case of many
animals.
Aerobic respiration using oxygen
takes place in animal and plant cells and many microorganisms too.
You need plenty of oxygen for
aerobic respiration - oxygenated conditions from free dissolved oxygen gas.
Most of the reactions of aerobic respiration
in eukaryotes (plant or animal)
take place inside the sub-cellular structures called the mitochondria of cells.
Mitochondria contain all the enzymes needed for respiration.
In microorganisms like bacteria, prokaryotic cells, the aerobic respiration chemistry occurs in the
cytoplasm.
The starting 'fuel' molecule for
respiration is often the sugar type molecule called glucose.
The glucose is made by breaking down
food e.g. carbohydrates like starch from or from stores of glycogen
molecules in animals. Plants can use glucose directly from
photosynthesis.
The overall very complex
biochemistry of aerobic respiration can be summarised as:
glucose + oxygen ===> carbon dioxide
+ water + energy
C6H12O6(aq)
+ 6O2(g) ===> 6CO2(g) + 6H2O(l)
+ energy
Energy is released at each
stage of the process of respiration.
The complete oxidation of glucose in aerobic
respiration releases the most chemical potential energy and is
much more efficient than anaerobic respiration.
The initial steps of
respiration occur in the cytoplasm of cells, but most of the
chemical energy transfers happen in the mitochondria - the
chemical 'factory' organelles.
(Note that aerobic
respiration is the opposite of photosynthesis)
The glucose is eventually completely
oxidised to the waste products - carbon dioxide and water - but via lots
of complicated chemical reactions and producing 32 molecules of ATP per
molecule of glucose!
Most of the time, you are using this type of aerobic respiration and the
simple experiment (illustrated on the right) shows a simple limewater
test for the presence of carbon dioxide in the air you breathe out -
the presence of carbon dioxide is shown by the appearance of a white
precipitate ('milkyness').
The actual energy release from respiration takes place through
a very complex biochemistry cycle involving ADP (adenosine diphosphate) and its
conversion to ATP (adenosine triphosphate) which is the molecule that actually
supplies the chemical energy to power most of the chemistry of any cell. The more ATP
that is made, the greater the supply of energy available.
Aerobic respiration can make over 32
molecules of ATP per molecules of glucose.
Know and understand the chemical
reactions inside cells are controlled by enzymes.
Your body, hence your enzyme
systems, will respond to its needs e.g. when you use muscles in doing
physical work or exercise.
Know and understand during aerobic respiration
(respiration that uses oxygen) chemical reactions occur that produce useful energy is released to
'power' the cell chemistry.
Know and understand that aerobic respiration
takes place continuously in both plants and animals.
Know and understand that energy that is released
during respiration is used by the organism.
Know that the energy may be used
in cells:
to
build larger molecules from smaller ones eg proteins from amino acids,
in animals, to enable muscles to
contract and relax eg to move limbs and move around,
in mammals and birds, to maintain a steady body temperature in
colder surroundings, we slowly cease to function if we get to hot or too
cold.
in plants, to build up from sugars, nitrates and other
nutrients, amino acids which are then built up into proteins - animals can't
do this, we need to take in protein, break it down and build it up to our
required proteins.
Know and understand that during exercise a number of
changes take place in your body:
the more you use your muscles,
the more oxygen you need for respiration
the heart rate increases, the
more so, the more vigorous the exercise, and even more oxygen and glucose
are needed
the rate and depth of
breathing increases, to increase oxygen intake.
Know and understand that these changes increase
the blood flow to the muscles and so increase the supply of sugar and oxygen
for energy from respiration and also increase the rate of removal of carbon dioxide
- the waste product.
Know and understand that muscles store glucose
as glycogen, which can then be converted back to glucose for use during
exercise.
Glycogen is produced, stored and
then released for conversion to glucose on a supply and demand basis.
If there is surplus glucose and
physical activity is low, more glycogen is produced.
The more you physically
exercise, the greater the glucose demand, if this exceeds what is available
in the blood stream, then the glycogen reserves are called upon to fill the
energy gap.
Summary of important points on aerobic respiration
Be able to explain
why heart rate and breathing rate increase with exercise.
All chemical reactions inside
cells are controlled by enzymes.
Your body, hence your enzyme
systems, will respond to its needs e.g. when you use muscles in doing
physical work or exercise.
As stated, during aerobic respiration
(respiration that uses oxygen) chemical reactions occur that use
glucose (a sugar) and oxygen
The sugar is from digesting
carbohydrates and oxygen in via air breathed in, and from the lungs
carried round the body by specialised red blood cells,
Respiration produces useful energy is released to
'power' the cell chemistry.
During exercise a number of
changes take place in your body.
The more you use your muscles,
the more oxygen you need for respiration
The heart rate increases, the
more so, the more vigorous the exercise, and even more oxygen and glucose
are need, so the rate and depth of
breathing increases, to increase oxygen intake.
(1C)
Experiments - measuring your pulse rate - a
simple measure of your rate of respiration
You can measure your pulse rate
quite easily e.g. put two fingers on the back of your wrist and time
the number of pulses in a minute e.g. with a digital stopwatch or
your iphone app etc.
You can do this as a simple homework
exercise!
OR as a class exercise on a fine day, or any day in the gym, and average the class
results giving a wider range of people and more accurate data
set.
Wear appropriate footwear and
make sure all the class do the same exercise!
Record your pulse rate after do
the following sorts of exercise for 5 minutes at a time:
1. sitting quietly; 2.
walking at your normal pace; 3. slow jogging; 4.
running
For greater statistical
accuracy ('best value') you should repeat the experiment several
times to get four average pulse rates.
You could also analyse the
average for the class.
You can present the results
as a simple bar chart - average pulse from 1. to 4.
After allowing extra rest
time between each activity, you should find your pulse rate
increases from 1. to 4. because your rate of respiration is
increasing and you need an increase in the rate of transfer of
oxygen to your cells and simultaneously remove waste carbon dioxide
too.
More vigorous the exercise changes increases
your heart rate, hence the blood flow to the muscles and to increase the supply of sugar and oxygen
for energy from respiration and also increase the rate of removal of carbon dioxide
- the waste product.
Your breathing (ventilation) rate increases to meet the
increased demands of the aerobic respiration rate.
Aerobic respiration
takes place continuously in both plants and animals and most of the reactions in
aerobic respiration take place inside the mitochondria of cells.
Regular aerobic exercise can reduce
your risk from some non-communicable diseases.
See the
Keeping healthy - diet and exercise
and also
Keeping healthy - non-communicable diseases
- risk factors for e.g. cancers
Regular aerobic exercise can reduce your
risk from some non-communicable diseases.
Keywords, phrases and learning objectives for this part on ?
In the context of an organisms metabolism understand
the importance of the process of aerobic respiration in releasing
energy from chemical reactions in the mitochondria of the cells.
Be able to describe what the energy is used for and
the importance of increasing your metabolic rate of respiration when
you are doing more physically demanding work e.g. heavy manual work
or vigorous exercise like running.
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