Survival of an organism greatly depends on the ability of that organism to adjust to the changes in its environment. Acclimatization and adaptation are two ways by which an organism survives in the changing environment. Acclimatization takes place in a short period of time and causes temporary changes in the body which ensures survival. On the other hand, adaptation results in the development of new characters over a long period of time that ensures the survival of organism. Adaptation is a part of evolution. Furyther, in this piece of writing we will discuss on acclimatization.

What is Acclimatization?

Acclimatization is a physiological process that occurs naturally in organisms exposed to new environmental conditions like pH, salinity, light, pressure, chemicals, altitude, and temperature. These changes help the organisms survive in a wide range of varying environmental conditions.

Difference between Acclimatization and Adaptation

Acclimatization and adaption can be differentiated as follows −.

Acclimatization Adaptation
Short and temporary change Long-term and permanent change
Seen in a short span of time Takes a long time to appear
Physical change occurs Physical and chemical changes occur
Changes can be reversed once previous conditions return Changes are irreversible
Evolutionary process is unaffected Changes lead to evolution
Seen during the life-span of the organism Seen over multiple generations
Eg- Heavy coat during winter Eg- Sharp beaks in birds

Acclimatization in Humans

Human body, like other organisms, acclimatises to sudden change in environment. This allowed long survival of human race and spread of human species to various regions of the world having different environment conditions. For example, when a human moves to a significantly hot climate, his body starts reducing the loss of salt through sweat however, sweating increases to keep the body cool. Apart from this, our ability to climb up high mountains and dive deep down into the sea can be credited to the ability of our body to acclimatize. Lets understand the mechanism of acclimatization at high altitude in details.

Consequences of High Altitude

Areas located above 2,400 meters above sea level are considered to be situated at higher altitudes. These areas experience a colder climate as compared to the areas near sea level. The air pressure decreases with increasing altitude. The amount of oxygen available in the atmosphere is also reduced. The Himalayan mountain ranges are an example of a high altitude area.


In human beings, on exposure to changing environmental conditions with increasing altitude can result in changes in cognitive skills and personality. Water is lost from the body through urination, perspiration, and breathing. This can lead to dehydration. Other symptoms associated with increased altitude are mountain sickness, edema in pulmonary and cerebral areas, weight gain due to fluid retention, increased ventilation, insomnia, vomiting, dizziness, and fatigue.

The above-mentioned consequences of high altitude occurs if humans ascend at a faster pace. If enough time is given to the body to adapt to the changing conditions, the body gets temporarily adapted to the changing conditions. It takes around 1 to 3 days for the body to get acclimatized to the conditions.

A lack of oxygen in the air inhaled triggers the carotid bodies. These arterial chemoreceptors increase the rate and depth of breathing. The kidneys in response to low pressure of oxygen in arteries release erythropoietin. This induces the production of red blood cells from the bone marrow.

This process occurs over a period of a few weeks. Changes in oxidative enzyme composition reduction in the distance between capillaries, and changes in the affinity of haemoglobin towards oxygen are a few changes seen in people subjected to an increase in altitude. Due to an increase in the heart rate, the stroke volume decreases thereby reducing other non-essential body functions like digestion.

A few notable chemical changes in the body includes respiratory alkalosis, reduction in lactate production, and an increase in 2,3-bisphosphoglycerate. In pregnant women, such environmental conditions can restrict intrauterine growth, reduce placental blood flow, and thereby reduce the height of such children born.

Oxygen-dissociation Curves

Oxygen being almost insoluble in water is mostly carried by the hemoglobin present in the red blood cell and not by the blood plasma. One hemoglobin molecule can bind maximum four oxygen molecule to form oxyhemoglobin. This is a reversible reaction. The binding of oxygen to the hemoglobin is directly proportional to the partial pressure of oxygen. This relation of oxygen saturation to the partial pressure of oxygen is represented by a sigmoidal curve called the oxygen dissociation curve.

A normal oxygen dissociation curve shows that the initial binding of hemoglobin to oxygen is difficult and the binding affinity increases with each binding i.e. the binding of first oxygen molecule to a deoxyhemoglobin is difficult than the the binding of second one which is again difficult than the binding of the third one and so on.

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Various factors affect the binding of oxygen molecules to the haemoglobin. Temperature, pH, carbon dioxide, carbon monoxide, and 2,3- BPG influence the binding of oxygen to the haemoglobin in the blood. The curve in the graph can show a shift towards either the right or left side.

A shift towards the right side

This is seen under the following conditions −.

  • The partial pressure of oxygen decreases.

  • The partial pressure of carbon dioxide increases.

  • Hydrogen ion concentration increases.

  • pH or acidity decreases.

  • Body temperature increases.

  • 2,3- Diphosphoglycerate, a by-product from glycolysis is produced in excess.

A shift towards the left side

  • The partial pressure of carbon dioxide decreases.

  • The hydrogen ion concentration decreases.

  • pH or alkalinity increases.

  • Fetal haemoglobin has an increased affinity for oxygen compared to adult haemoglobin.

Oxygen dissociation curve : Fetus vs Adult

Due to a slightly different composition of fetal haemoglobin, it shows an increase in its affinity towards oxygen molecules. It is able to load oxygen in the placenta where the maternal haemoglobin undergoes unloading. It takes about 6 months post-birth for adult haemoglobin to be completely replaced with adult .

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In skeletal muscles, specialized molecules for binding to oxygen are present. These single polypeptide chains are called myoglobin. They can bind to one oxygen molecule at a time as they consist of one heme molecule. Its graph shows a logarithmic pattern as opposed to the sigmoidal curve seen in haemoglobin molecules. Myoglobin shows a high affinity to oxygen and exhibits a delayed release during intense activities.


Q1. Give examples of any two medications to be carried while climbing the Himalayas

Ans. Dexamethasone and mannitol are examples of medications to be carried while climbing the Himalayas. They help in relieving cerebral edema.

Q2. Name the substances that help certain organisms acclimatize to changing temperatures.

Ans. Cryoprotectants and heat-shock proteins are substances produced in response to changing temperatures. Cryoprotectants prevent the formation of ice crystals in cells thus surviving subzero temperatures. Heat-shock proteins prevent protein denaturation when the cells experience an increase in temperatures.

Q3. How is hibernation different from acclimatization?

Ans. Hibernation is a long-term reversible adaptation to overcome the scarcity of food and cold conditions. Generally, the metabolism decreases thereby helping the organism survive on low resources for a prolonged period.

Q4. Name the respiratory pigment found in other animals.

Ans. Haemocyanin is a respiratory pigment found in molluscs and arthropods. It comprises a copper component which binds to oxygen thereby giving blood a bluish-coloured appearance.

Q5. Name the location where the loading and unloading of oxygen take place

Ans. The loading of oxygen takes place in the lungs whereas the unloading of oxygen takes place in the tissues.


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