Have you ever visited a hill station? If you have then you must have noticed that the higher we go up the hilly terrain, the more difficult it is to breathe. In fact, we also feel a little light-headed and dizzy as we go to higher altitudes. This happens because air pressure and amount of oxygen in air decreases with height. But what happens in the case of the inhabitants of the hilly regions? Do they feel the same? No, they are quite acclimated to the conditions of high altitude. But how? We will find the answer to this question in this article.
Do you think you can survive for more than 2-3 days in the hot summers of the deserts? But the camel can, that is because it is adapted to the hot desert climate. But, if you put a camel in the North Pole, will it survive? Or will a polar bear survive in the tropical forests? They won’t because the camel does not have adaptations to survive in such a cold climate and the polar bear is not adapted to the hot and humid climate of the tropical forests. So what do we mean when we speak about adaptations?
Morphological, physiological, behavioural attributes of an organism that increase its chances of survival and reproductive fitness (ability to give birth to healthy and fertile offspring) is known as adaptation. Both plants and animals develop adaptations during their course of evolution to survive in a particular environment. Adaptations can be passed on as traits. In fact, the ability to regulate the homeostasis of the body under changing conditions of environmental factors, or conform to the changes or deal with the changes by migrating or suspending growth, are different adaptations to one’s environment. Let’s discuss more about such adaptations.
Physiological adaptations: Tiny kangaroo rats are adapted to survive in the hot and dry/arid climate of the deserts of North America (Southwest USA) with scanty rains and almost no water source. To overcome this water scarcity, the kangaroo rat has adapted by generating water by fat oxidation. Oxidising fats produces metabolic water which is enough for the survival of this rat. Kangaroo rats also excrete concentrated urine with uric acid as nitrogenous waste to reduce water loss.
Fig: North American desert and Kangaroo rat
Even the camel shows some physiological adaptations to survive in the desert. It does not sweat till the body temperature goes above 50oC. It generates water by oxidation of fats in the hump and can lose up to 25% of its body weight by releasing water from the tissues. When water is available, it can drink up to 80 litres of water and it excretes very concentrated urine and very dry faeces to conserve body water.
Desert lizards lack the ability to develop physiological adaptations to combat the hot desert climate so they have developed behavioural adaptations to maintain a constant body temperature throughout the day. They come out in the morning to warm up in the sun when their body temperature starts falling beneath their comfort level but when the surrounding temperatures become too high, they move under shades. Some other desert species often hide in burrows when the temperature above ground becomes too high due to heating of the sand.
Fig: Behavioural adaptations of desert lizard
The camel has a number of structural adaptations to survive in the hot and arid climate of the desert. It has heavy eyelashes to cover the eyes from the blowing sand.
Fig: Heavy eyelashes in camels
Nostrils are reduced in size and the nasal countercurrent system reduces the loss of moisture during exhalation. They have broad padded feet to walk comfortably in the sand without sinking.
Fig: Feet of camels
The hump in camels stores fats which can be oxidised to release metabolic water for the survival of the camel.
What about plants in deserts? Plants have morphological, anatomical and physiological adaptations to prevent water loss.
Transpiration is one of the major reasons for loss of water from the plant body. Thick layer of cuticle and stomata sunk deeper into the epidermal layer are some of the adaptations to minimise water loss through transpiration.
Fig: Sunken stomata to reduce transpiration
Some desert plants like Cactus/Opuntia have modified flat stems called phylloclade to carry out photosynthesis. Their leaves are reduced into spines to prevent water loss by transpiration.
Fig: Morphological adaptations in desert plants to prevent water loss
The xerophytic plants undergo CAM (Crassulacean Acid Metabolism) pathway, for the light-independent phase of photosynthesis, to avoid water loss. This allows the plants to fix carbon dioxide at night and use it for photosynthesis during the daytime and the stomata can remain closed during the daytime when the temperature is high. This temporal separation ensures optimum photosynthesis and low transpiration.
Fig: Physiological adaptations in plants to reduce water loss
Adaptations in animals: To adapt to the cold, mammals in Arctic regions have smaller ears and shorter limbs to reduce the amount of exposed surface area for heat loss. This is an adaptation to keep extremities closer to the core and thus keeping the body warm
An eco-geographical rule was formulated by Joel Asaph Allen in 1877, which is known as the Allen’s rule. Allen's rule broadly states that animals adapted to cold climates have shorter limbs and bodily appendages than animals adapted to warm climates. Or specifically, it states that the body surface-area-to-volume ratio for homeothermic animals is lower in cold and higher in hot region.
Fig: Animals in cold climate have shorter limbs and smaller ears
Aquatic mammals like seals, walrus, whales, etc have a thick layer of fat under skin called blubber for insulation against the loss of body heat.
Fig: Adaptations in seals to conserve body heat
In the polar region all the water bodies are frozen. So how do aquatic organisms like fishes survive? We are aware that water expands anomalously as it cools down from 4oC to 0oC. This is one of the reasons why ice is less dense than water and floats on it. So when the water in the water bodies of the polar regions freeze to ice, the ice moves up and floats on the surface and forms an insulating layer which makes sure that the water beneath remains at a temperature above 0oC and does not freeze. This protects the aquatic organisms from freezing to death. This is not an adaptation in the organisms but an environmental phenomenon.
Fig: Anomalous expansion of water
The vegetation in the temperate coniferous forests (Taiga) includes coniferous trees which have thick cuticle, sunken stomata and needle-like leaves to reduce transpiration. The sloping branches prevent the accumulation of snow on the plant surfaces. These trees are also evergreen which is why they can prepare food throughout the year and have better chances at survival.
Fig: Adaptations in coniferous trees
Ever thought about the pressure under the sea? Can we survive in the deep sea, without the help of an oxygen tank? Never !! We cannot survive at higher pressures because the pressure doesn't allow our lungs to expand. But how do the fishes survive? As fishes do not have lungs, they have no problem breathing at higher pressure. Some fishes and invertebrates have also evolved to survive at pressures more than 100 times the atmospheric pressure.
Even some microbes such as archaebacteria are adapted to survive under high pressure at the sea beds.
Fig: Fishes and invertebrates under deep sea
As we go higher and higher above the sea level, the air get’s thinner or less dense and the oxygen saturation decreases, which means you are not getting enough oxygen with each breath. This is known as altitude sickness. But do not fear, this sickness does not last long because soon you will adapt or acclimatise to this condition too.
Fig: Comparison of density of air at sea level and mountain top
There are two types of adaptations to higher altitude. They are short term adaptation and long term adaptation.
Fig: Types of biological adaptations at higher altitudes
What helps us to immediately recover from breathlessness can be considered as short term adaptation in which the breathing rate increases and forces us to inhale more air in a minute. Thus, the oxygen intake increases.
GIF: Increased breathing rate
Another short-term response is that the affinity of haemoglobin for oxygen is decreased which allows easy dissociation of oxygen near the tissues.
Fig: Oxygenated haemoglobin
Long term adaptations are seen in individuals who are inhabitants of areas at high altitudes. The kidney of such individuals releases a hormone called erythropoietin in response to the decreased oxygen. Erythropoietin signals bone marrow to produce more RBCs. More RBCs means more haemoglobin (Hb). If there is more Hb, our blood can carry more oxygen.
Fig: Release of erythropoietin increases the production of RBCs
Hence, people dwelling near the Himalayas have a higher RBC count. Many tribes living in the high altitude of Himalayas have evolved over the years to battle altitude sickness by increasing breathing rate, dilation of capillaries and increased Hb content.
Some archaebacteria can flourish in hot springs and deep-sea hydrothermal vents where temperatures exceed 1000C. How is it possible? This is possible because they have special heat tolerant enzymes, for example, Taq polymerase in Thermus aquaticus, which do not denature at high temperatures and can maintain their functional activity. These bacteria can also withstand the high pressure of these hydrothermal vents
Fig: Adaptations of bacteria to survive in deep hydrothermal vents
Q1. Assertion : Seals are well adapted to live in polar regions.
Reason : Seals have shorter extremities and blubber under their skin.
A. Both assertion and reason are true and the reason is the correct explanation for the assertion
B. Both assertion and reason are true but the reason is not the correct explanation for the assertion
C. Assertion is true. But reason is false
D. Both assertion and reason are false
Solution: Animals surviving polar regions require special adaptations to survive in the extreme cold conditions. Seals are warm-blooded animals or homeotherms that can maintain a constant body temperature, irrespective of the changes in the environmental temperature. This is achieved due to the presence of the fatty blubber that acts as an insulator and prevents the loss of body heat to the external environment.
The shorter limbs and ears also help to reduce the exposed surface area that can be vulnerable to heat loss.
Hence the correct option is a.
Q2. Xerophytic plants prefer the CAM pathway for photosynthesis because
A. it does not need water for carrying out photosynthesis
B. it allows the stomata to be closed during the day
C. it does not need carbon dioxide for carrying out photosynthesis
D. it does not need energy for the fixation of carbon dioxide
Solution: The stomata in most xerophytic plants remain closed during the day to prevent transpiration. As a result, these plants follow a specialised photosynthetic pathway known as the Crassulacean acid metabolism (CAM) pathway in which they fix carbon dioxide at night and use it for photosynthesis during daytime. This allows the stomata to be closed during the day.
Hence the correct option is b.
Q3. Match column A with column B and select the correct option.
1. Behavioural adaptation
A. Production of concentrated urine in camels
2. Anatomical adaptation
B. Hiding in burrows by some desert animals
3. Physiological adaptation
C. Sunken stomata in xerophytic plants
A. 1 - A, 2 - C, 3 - B
B. 1 - A, 2 - B, 3 - C
C. 1 - B, 2 - C, 3 - A
D. 1 - B, 2 - A, 3 - C
Solution: When an organism uses behavioural strategies to adapt to its environment, it is known as behavioural adaptations. One such example is the tendency of some desert animals to hide inside burrows during extremely hot days. Specialised internal structures that help in adapting to the environment are referred to as anatomical adaptations. Desert plants or xerophytic plants have the presence of sunken stomata, buried in pits, that help to prevent the loss of water via transpiration. Production of thick and concentrated urine by the kidneys of camels to conserve water is a physiological adaptation to survive in hot and arid desert climates.
Hence the option is c.
Q4. By which of the following mechanisms, the human body adapts to the less availability of oxygen at higher altitudes?
1. Increasing the number of red blood cells.
2. Increasing the oxygen affinity of haemoglobin.
3. Decreasing breathing rate.
A. I and III
B. II and III
C. I and II
D. Only I
Solution: People, moving to places at higher altitudes initially experience altitude sickness, difficulty in breathing, dizziness, etc. This feeling however passes with time and an individual gets adapted to the atmospheric conditions of higher altitudes. This is due to some short term and long term physiological adaptations in the body such as the increased breathing rate to inhale more oxygen per minute and reduced affinity of haemoglobin towards oxygen to allow ready dissociation of oxyhaemoglobin in the tissues. Long term adaptation includes the increase in the number of red blood cells to increase the transport of available oxygen to the tissues.
Hence the correct option is d.
Question 1. Is Allen's rule valid for humans?
Answer: Sweating is the most common way for humans to lose heat. As sweat evaporates from the skin, it takes away body heat and cools the body. Humans sweat a lot of heat from their palm and feet. At low ambient temperatures, these are the regions most vulnerable to loss of body heat, as you must have experienced that our palms and feet hardly warm up during the winters. This is only effective when the relative humidity is low.
In many human populations that have acclimated to heat or cold, Allen's rule applies to relative limb lengths and people living at colder regions have shorter limbs than the ones living in warmer regions.
Question 2. What is parallel adaptation?
Answer: Parallel evolution occurs when two or more independent species present in the same ecospace at the same time, evolve together to develop similar characteristics. Parallel adaptation occurs as a result of parallel evolution between two or more different species that develop similar adaptations against a particular evolution pressure for surviving in the same environment.
Question 3. What adaptations do plants make in the rainforest?
Answer: Trees in the rainforests have tall and thin trunks to raise their heads above the vast tree canopy to obtain sunlight. As it rains frequently, the leaves of the plants have pointy tips which allow the water to run off quickly without damaging the leaves. The larger trees have buttress roots with ridges which create a large surface area for greater support. Many plants which grow on the branches of other trees, that lie high up on the canopy, have epiphytic or hygroscopic roots that cant absorb water from the air.
Question 4. Why do humans become ill after being exposed to the cold?
Answer: Low temperatures are ideal for the replication and spread of viruses which cause cold and flu and as we breathe in cold air, the temperature of the nasal tract falls and it becomes the breeding ground for these viruses. Thus we are more vulnerable to catching an infection and falling sick when exposed to cold.
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