Respiration
Respiration: The process by which a living being utilises the food to get
energy, is called respiration. Respiration is an oxidation reaction in which
carbohydrate is oxidized to produce energy. Mitochondria is the site of
respiration, and the energy released is stored in the form of ATP (adenosine
triphosphate). ATP is stored in mitochondria and is released as per need.
Steps of respiration:
• Breaking down of glucose into pyruvate: This step happens in the
cytoplasm. Glucose molecule is broken down into pyruvic acid. Glucose
molecule is composed of 6 carbon atoms, while pyruvic acid is composed
of 3 carbon atoms.
• Fate of Pyruvic Acid: Further breaking down of pyruvic acid takes place
in mitochondria and the molecules formed depend on the type of
respiration in a particular organism.
Respiration involves
• Gaseous exchange: Intake of oxygen from the atmosphere and
release of CO2 → Breathing.
• Breakdown of simple food in order to release energy inside the cell
→ Cellular respiration
Types of Respiration
• Aerobic respiration: This type of respiration happens in the presence of
oxygen. Pyruvic acid is converted into carbon dioxide. Energy is released
and water molecule is also formed at the end of this process.
• Anaerobic respiration: This type of respiration happens in the absence
of oxygen. Pyruvic acid is either converted into ethyl alcohol or lactic
acid. Ethyl alcohol is usually formed in case of anaerobic respiration in
microbes, like yeast or bacteria. Lactic acid is formed in some microbes
as well as in the muscle cells.
Glucose 6 carbon molecule → Pyruvate (3
carbon molecules) + Energy
Pyruvate (In yeast, lack of O2) Ethyl alcohol + Carbon dioxide +
Energy
Pyruvate (In muscles, lack of O2) Lactic Acid + Energy
Pyruvate (In mitochondria; the Carbon dioxide + Water + Energy
presence of O2)
Pain in leg muscles while running:
• When someone runs too fast, he may experience throbbing pain in the leg
muscles. This happens because of anaerobic respiration taking place in
the muscles.
• During running, the energy demand from the muscle cells increases. This
is compensated by anaerobic respiration and lactic acid is formed in the
process.
• The deposition of lactic acid causes pain in the leg muscles. The pain
subsides after taking rest for some time.
Exchange of gases:
• For aerobic respiration, organisms need a continuous supply of oxygen,
and carbon dioxide produced during the process needs to be removed
from the body.
• Different organisms use different methods for the intake of oxygen and
expulsion of carbon dioxide.
• Diffusion is the method which is utilized by unicellular and some simple
organisms for this purpose.
• In plants also, diffusion is utilized for exchange of gases.
• In complex animals, respiratory system does the job of exchange of
gases.
• Gills are the respiratory organs for fishes. Fishes take in oxygen which is
dissolved in water through gills.
• Since, availability of oxygen is less in the aquatic environment, so the
breathing rate of aquatic organisms is faster.
• Insects have a system of spiracles and trachease which is used for taking
in oxygen.
• Terrestrial organisms have developed lungs for exchange of gases.
• Availability of oxygen is not a problem in the terrestrial environment so
breathing rate is slower as compared to what it is in fishes.
Terrestrial organisms: Use atmospheric oxygen for respiration.
Aquatic organisms: Use dissolve oxygen for respiration.
Human respiratory system
The human respiratory system is composed of a pair of lungs. These are
attached to a system of tubes which open on the outside through the nostrils.
Following are the main structures in the human respiratory system:
1. Nostrils: There are two nostrils which converge to form a nasal passage.
The inner lining of the nostrils is lined by hair and remains wet due to
mucus secretion. The mucus and the hair help in filtering the dust
particles out from inhaled air. Further, air is warmed up when it enters the
nasal passage.
2. Pharynx: It is a tube-like structure which continues after the nasal
passage.
3. Larynx: This part comes after the pharynx. This is also called voice box.
4. Trachea: This is composed of rings of cartilage. Cartilaginous rings
prevent the collapse of trachea in the absence of air.
5. Bronchi: A pair of bronchi comes out from the trachea, with one bronchus
going to each lung.
6. Bronchioles: A bronchus divides into branches and sub-branches inside
the lung.
7. Alveoli: These are air sacs at the end of bronchioles. The alveolus is
composed of a very thin membrane and is the place where blood
capillaries open. This is alveolus, where the oxygen mixes with the blood
and carbon dioxide exits from the blood. The exchange of gases, in
alveoli, takes place due to the pressure differential.
Passage of air through the respiratory system in human beings:
Breathing Mechanism
• The breathing mechanism of lungs is controlled by the diaphragm and the
intercostal muscles.
• The diaphragm is a membrane which separates the thoracic chamber from
the abdominal cavity.
• When the diaphragm moves down, the lungs expand, and the air is
inhaled.
• When the diaphragm moves up, the lungs contract and air are exhaled.
Do not include the activities in the notebook
Activity 5.4: Lime Water Test for Carbon Dioxide
• Take freshly prepared lime water in a test tube.
• Blow air through it and note the time taken for it to turn milky.
• In another test tube, use a syringe or pichkari to pass air and observe the
time taken for the lime water to turn milky.
• Conclusion: Exhaled air contains more carbon dioxide (CO₂) than
normal air.
Activity 5.5: Fermentation and Lime Water Test
• Mix fruit juice or sugar solution with yeast in a test tube and seal with a
cork.
• Attach a bent glass tube leading into another test tube containing lime
water.
• Observe how long it takes for the lime water to turn milky.
• Conclusion: Fermentation produces CO₂, which turns lime water milky.
Activity 5.6: Breathing in Fish vs. Humans
• Observe a fish in an aquarium and count the number of times it opens its
mouth.
• Compare this with human breathing rate.
• Conclusion: Aquatic organisms have a higher breathing rate due to
lower oxygen levels in water.
