Respiration:

• Respiration is the biochemical process in which the cells of living organisms obtain energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and ATP.

C₆H₁₂O₆ + 6O₂  → 6CO₂ + 6H₂O + ATP

• Diverse organisms use oxygen to break-down glucose completely into carbon dioxide and water.
• The oxidation of glucose provides energy required for all cellular activities.
• In the absence of glucose, the cells break down proteins and fats to produce glucose. Further oxidation of this glucose fulfil the respiratory needs of the cell.
• At first, the six carbon glucose is broken down into two molecules of three carbon pyruvate (C₃H₄O₃). This process takes place in the cytoplasm.
• Cellular respiration takes place in mitochondria. That’s why mitochondria are also known as the powerhouse of the cell.

Difference between breathing and respiration:

Types of respiration:

Different living organisms respire in different ways. Based on their respiration process either in presence or absence of oxygen there are two types of respiration:

Anaerobic respiration:

• The respiration which takes place in absence of oxygen is called anaerobic respiration.
• Also, we can say it is the process of producing cellular energy without oxygen.
• There is no release of water in this process.
• Anaerobic respiration is a relatively fast reaction and produces 2 ATP, which is much less than aerobic process.
• Some examples include alcohol fermentation, lactic acid fermentation and in the decomposition of organic matter.

Glucose + Enzymes = Carbon Dioxide + Ethanol / Lactic acid

Aerobic respiration:

• Aerobic respiration is the breakdown of glucose in the presence of oxygen.
• This type has end products carbon dioxide, water and energy.
• The amount of energy released in aerobic respiration is very high i.e. 686 kcal or 38 ATP of chemical energy and 420 kcal of heat energy.
• Aerobic respiration is carried out in two stages that are: Glycolysis and Krebs cycle.
• It is mainly seen in multicellular organisms such as animals, plants, humans, several bacteria, fungi etc.

Difference between aerobic and anaerobic respiration:

Respiration in plants:

• Every part of a plant carries respiration process.
• Stems, leaves and roots respire at very lower rate as compared to animals.
• The leaves of plants have tiny pores on their surface which are called stomata. Plants exchange gases by diffusion through the stomata during respiration.
• Oxygen from the air diffuses into a leaf and reaches all the cells.
• During respiration carbon dioxide produced is released into the air through the stomata.
• Plants respire during the day as well as during the night.
• During the day, plants respire the same oxygen produced during photosynthesis and the extra amount of oxygen is released through the stomata.
• The air present in the soil is taken up from roots.
• In stems, from either stomata or lenticels, the exchange of gases takes place.

Respiration in animals:

• In simple unicellular animals like Amoeba, respiration takes place by the simple diffusion of gases through the cell membrane.
• Earthworms use their skin to absorb oxygen from air and release carbon dioxide. So, skin is the respiratory organ in the earthworm.
• Fish, prawns and mussels are the aquatic animals which have gills as the respiratory organs. Gills absorbs oxygen dissolved in water and releases carbon dioxide out of the body.
• In the insects like grasshopper, cockroach, housefly and a mosquito, the tiny holes called spiracles on their body and the air tubes called tracheae are the respiratory organs.
• The land animals such as man (humans), birds, lizard, dog and frog etc. respire through the lungs. However, Frogs breathe both by lungs and skin.

Human Respiratory System:

The respiratory system in human beings consists of the nose, pharynx, larynx, trachea, bronchi, alveoli and pair of lungs.

• Air enters the body through nostrils.
• The air passing through the nostrils is filtered by fine hairs present inside the nostrils.
• Nostrils are also lined with mucus which prevents dust particles to enter inside.
• From here, it goes to pharynx which is a common passage for both the respiratory and digestive system. After that, it moves into the larynx (voice box).
• In the throat (trachea, which also known as wind-pipe and is 10-12 cm long tube with a diameter of 2-3 cm) there are rings of cartilage which ensures that the air-passage does not collapse.
• From here, the air passes through the throat and into the lungs.
• The lungs, which are a pair of spongy and elastic respiratory organs protected by a bony rib-cage.
• Inside lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures called alveoli.
• The role of alveoli is to provide a surface where the exchange of gases can take place.
• The surface of the alveoli is reached with the extensive network of blood vessels.
• As air enters the lungs through nostrils, alveoli gets filled with air.
• The blood vessels present in alveoli absorbs all the oxygen.
• Haemoglobin (Present in RBC) present in blood has a great affinity towards oxygen.
• From here oxygen is transported to all the cells in the body.
• The blood brings carbon dioxide from the rest of the body cells and releases it into the alveoli.
• When there is breathing process, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.
• As we know that carbon dioxide is more soluble in water than oxygen and hence is mostly transported in the dissolved form in our blood.